ALBERT

Description: Gd2O2S:Tb nanophosphor with favorable dispersion and high chemical/phase purity was obtained via a low temperature precipitation approach. Abstract Titrating the aqueous solution of equimolar RE(NO3)3 and (NH4)2SO4 with NH4OH to pH~9 at ~4°C produced an amorphous precursor that yielded phase‐pure and well‐dispersed RE2O2S nanopowder (RE = Gd0.99Tb0.01; GOS:Tb) via a RE2O2SO4 intermediate upon annealing in H2. The powders calcined at the typical temperatures of 700/1200°C exhibited unimodal size distributions and have the average crystallize sizes of ~17/55 nm, average particle sizes of ~284/420 nm, and specific surface areas of ~14.62/4.53 m2/g (equivalent particle sizes: ~56/180 nm). The 1200°C product exhibited sharp green luminescence at ~544 nm (FWHM = 2.3 nm; λex = 275 nm), with an absolute quantum yield of ~24.8% and a fluorescence lifetime of ~1.34 ms at room temperature. It was also shown that the powder possesses favorable thermal stability (the activation energy for thermal quenching of luminescence ~0.305 eV) and is stable under electron beam irradiation up to 7 kV and 50 μA. The synthetic technique has the advantages of scalability and favorable dispersion and high chemical/phase purity for GOS powder, which may allow the sintering of scintillation ceramics at lower temperatures.

Description: Abstract Up until now, many previous works have indicated us that the photoluminescence (PL) properties of phosphors sometimes can be changed with the change in the external temperature, resulting in the anomalous PL phenomena and correlated new applications that are difficult to achieve at room temperature. In this work, we report the temperature‐dependent Bi3+‐related PL properties in the YVO4:Bi3+ phosphor. Our findings show that increasing the temperature from 10 to 300 K enables manipulating the energy interaction from groups to Bi3+, thereby leading to the temperature‐induced color tuning from blue (0.183, 0.212) to yellow (0.418, 0.490). Upon this heating process, we further reveal that the dynamic Bi3+ luminescence has experienced a regular transition from double‐exponential to single‐exponential decay, which results in the decrease in the average Bi3+ lifetime from 122.606 to 0.376 μs. Discussions on the PL results imply that the tunable PL observations are due to the interplay of temperature‐dependent energy transfer from groups to Bi3+ and redistribution of the excited 3P0 and 3P1 states of Bi3+ upon the thermal stimulation. This work not only presents the temperature‐triggered Bi3+ tunable properties in the well‐studied YVO4 host lattice but also can provide new insights into revealing Bi3+‐related PL mechanism in other Bi3+‐doped photonic materials in the future and, in the meanwhile, gives some directive ideas for us to explore previously unnoticed applications for rare‐earth (RE; eg, Eu3+, Pr3+, Tb3+, Eu2+, Er3+, etc) and other non‐RE (eg, Bi3+, Mn4+, Mn2+, Cr3+, etc) doped phosphors.

Description: Broad phase boundary with successive R‐O and O‐T to optimize the piezoelectric/strain properties and enhance the temperature stability in lead‐free barium titanate ceramics. Abstract A new piezoelectric system of (1−x−y)BaTiO3‐yCaZrO3‐xBaSnO3 (BT‐yCZ‐xBS) was designed to achieve enhanced piezoelectric/strain properties and temperature stability. First, the relationships between composition, phase, and electrical properties are systematically investigated. The broad phase boundary with successive rhombohedral‐orthorhombic (R‐O) and orthorhombic‐tetragonal (O‐T) was obtained in 0.04 ≤ x ≤ 0.05 and 0.04 ≤ y ≤ 0.07 by tailoring the relationship of composition and phase structure, confirmed by X‐ray diffraction, temperature‐dependent dielectric constants, and Raman spectra. The optimized piezoelectric coefficient of d33 = 560 pC/N, high strain of 〉0.20%, and large converse piezoelectric coefficient of d33* = 1170 pm/V were realized. Second, the optimized piezoelectricity both demonstrate a stable performance with fluctuation 〈8% for d33* and 20% for d33 between 22 and 60°C since the broad phase boundary is exhibited in this temperature range. We believe that this work is a successful example to optimize piezoelectric properties and enhance the stability for piezoceramics.

Description: ABSTRACT The effective medium theory based on the Hertz–Mindlin contact law is the most popular theory to relate dynamic elastic moduli (or elastic velocities) and confining pressure in dry granular media. However, many experimental results proved that the effective medium theory predicts pressure trends lower than experimental ones and over‐predicts the shear modulus. To mitigate these mispredictions, several evolutions of the effective medium theory have been presented in the literature. Among these, the model named modified grain contact theory is an empirical approach in which three parametric curves are included in the effective medium theory model. Fitting the parameters of these curves permits to adjust the pressure trends of the Poisson ratio and the bulk modulus. In this paper, we present two variations of the modified grain contact theory model. First, we propose a minor modification in the fitting function for the porosity dependence of the calibration parameters that accounts for non‐linearity in the vicinity of the critical porosity. Second, we propose a major modification that reduces the three‐step modified grain contact theory model to a two‐step model, by skipping the calibration parameter–porosity fit in the model and directly modelling the calibration parameter–pressure relation. In addition to an increased simplicity (the fitting parameters are reduced from 10 to 6), avoiding the porosity fit permits us to apply the model to laboratory data that are not provided with accurate porosity measurements. For this second model, we also estimate the uncertainty of the fitting parameters and the elastic velocities. We tested this model on dry core measurements from literature and we verified that it returns elastic velocity trends as good as the original modified grain contact theory model with a reduced number of fitting parameters. Possible developments of the new model to add predictive power are also discussed.

Description: ABSTRACT We built a five‐component (5C) land seismic sensor that measures both the three‐component (3C) particle acceleration and two vertical gradients of the horizontal wavefield through a pair of 3C microelectromechanical accelerometers. The sensor is a small cylindrical device planted vertically just below the earth's surface. We show that seismic acquisition and processing 5C sensor data has the potential to replace conventional seismic acquisition with analogue geophone groups by single 5C sensors placed at the same station interval when combined with a suitable aliased ground roll attenuation algorithm. The 5C sensor, therefore, allows for sparser, more efficient, data acquisition. The accuracy of the 5C sensor wavefield gradients depends on the 3C accelerometers, their sensitivity, self‐noise and their separation. These sensor component specifications are derived from various modelling studies. The design principles of the 5C sensor are validated using test data from purpose‐built prototypes. The final prototype was constructed with a pair of 3C accelerometers separated by 20 cm and with a self‐noise of 35 ng Hz−1/2. Results from a two‐dimensional seismic line show that the seismic image of 5C sensor data with ground roll attenuated using 5C sensor gradient data was comparable to simulated analogue group data as is the standard in the industry. This field example shows that up to three times aliased ground roll was attenuated. The 5C sensor also allows for correcting vertical component accelerometer data for sensor tilt. It is shown that a vertical component sensor that is misaligned with the vertical direction by 10° introduces an error in the seismic data of around –20 dB with respect to the seismic signal, which can be fully corrected. Advances in sensor specifications and processing algorithms are expected to lead to even more effective ground roll attenuation, enabling a reduction in the receiver density resulting in a smaller number of sensors that must be deployed and, therefore, improving the operational efficiency while maintaining image quality.

Description: 〈b〉Global sounding of 〈i〉F〈/i〉 region irregularities by COSMIC during a geomagnetic storm〈/b〉〈br〉 Klemens Hocke, Huixin Liu, Nicholas Pedatella, and Guanyi Ma〈br〉 Ann. Geophys. Discuss., https//doi.org/10.5194/angeo-2018-117,2018〈br〉 〈b〉Manuscript under review for ANGEO〈/b〉 (discussion: open, 0 comments)〈br〉 The GPS radio occultation data of the COSMIC-FORMOSAT-3 mission are used to visualize the global distribution of ionospheric irregularities in the F2 region during a geomagnetic storm, at solar minimum, and at solar maximum.

Description: 〈b〉The computation of bending eigenfrequencies of single-walled carbon nanotubes based on the nonlocal theory〈/b〉〈br〉 Jozef Bocko, Pavol Lengvarský, Róbert Huňady, and Juraj Šarloši〈br〉 Mech. Sci., 9, 349-358, https://doi.org/10.5194/ms-9-349-2018, 2018〈br〉 The paper is concerned to the computation of eigenfrequencies of single-walled carbon nanotubes (SWCNTs). Classical treatment, where the nanotube is approximated by beam theory, is replaced by the nonlocal theory of beam bending. The eigenfrequencies are computed by combination of analytical, as well as numerical methods for four types of boundary conditions. The results can be used for determination of Young’s modulus of homogenized SWCNTs from experimental measurements.

Description: Abstract Dense Bi(Ni2/3Ta1/3)O3‐PbTiO3 (BNT‐PT) ceramics were prepared by solid‐state reaction method. Morphotropic phase boundary between tetragonal and rhombohedral phase was observed around the composition 0.38BNT‐0.62PT, at which large photovoltages of 13.2V were obtained under 405 nm laser illumination with power density of 200 mW/cm2. By B‐site Ni2+ ions doping, the bandgap values of BNT‐PT solid solutions were reduced to 2.25~1.85 eV, and the anomalous photovoltaic response was extended from the ultraviolet region to a wavelength of 550 nm at the visible light region.

Description: Abstract This contribution couples (a) Small angle X‐ray scattering (SAXS) experiments of a high‐performance concrete (HPC) at the millimetric scale, and (b) Focused ion beam/scanning electron microscopy (FIB/SEM) of the cement paste of the HPC, with 10‐20 nm voxel size. The aim is to improve the understanding of the 3D pore network of the HPC at the mesoscale (tens of nm), which is relevant for fluid transport. The mature HPC is an industrial concrete, based on pure Portland CEMI cement, and planned for use as structural elements for deep underground nuclear waste storage. Small angle X‐ray scattering patterns are computed from the 3D pore images given by FIB/SEM (volumes of 61‐118 μm3). They are positively correlated with SAXS measurements (volumes of 5 mm3). Aside from correlations with FIB/SEM data, experimental SAXS allows to investigate a wider range of effects on the pore structure. These are mainly the HPC drying state, the presence of aggregates (by analyzing data on cement paste alone), and the use of Poly Methyl MethAcrylate resin impregnation.

Description: Abstract A series of (Pr, Ce)‐ZrSiO4 ceramic pigments were synthesized and characterized using XRD, SEM, EDS, XPS, XRF, colorimeter, and a UV‐VIS‐NIR spectrometer. The prepared pigments were mainly composed of the zircon phase and were well crystallized. Only a specific amount of Pr was incorporated into the ZrSiO4 lattice. Compared with Pr, Ce was almost completely incorporated into the ZrSiO4 lattice and was homogeneously distributed within the pigment particles. The dopant Ce reduced the amount of Pr dissolved in the ZrSiO4 lattice and thus caused the b* values of the samples to decrease slightly. Meanwhile, the presence of Ce induced an apparent increase in red tone in the samples. The enhanced red tone resulted primarily from an increase in the absorption of light with wavelengths between 500 and 565 nm. High‐temperature stability analysis demonstrated that it is feasible to improve the tone of Pr‐ZrSiO4 pigment by doping with Ce.

Description: Abstract In this work, we investigated a procedure which exploits microwave ovens to produce SiC‐ based components by reactive melt infiltration of silicon into graphite preforms. The employed oven is designed to grant optical access to the sample surface, which allows to measure its temperature evolution though a noncontact pyrometer. This signal was used as a feedback to control the power provided to the preform and as an experimental output whose analysis provides insight into the reaction mechanism. Specifically, it is found that complete infiltration is achieved much before the end of the reaction. The latter is not fully self‐sustained as the global reaction rate continuously decreases with time until it is no more able to keep the temperature above the silicon solidification value. At that point, the reaction stops. The analysis of the processed samples proved that this procedure allows producing fully infiltrated samples without material failure by adjusting the heat provided during the infiltration stage rather than by tuning the preform structure and composition, which is the usual approach. The proposed method is less time and energy consuming than the standard one.

Description: Intrinsic pores orient, preferentially, parallel to the applied compressive stress during sinter‐forging. Abstract There is significant interest in the design and processing of porous ceramics due to their use in a variety of applications including energy storage, catalysis, adsorption, separation, and life science applications. For many of these applications, it is desirable to have a hierarchical porous structure in which there is a distinct difference between sizes of pores. Our previous study has shown that microstructure and properties of porous materials become anisotropic after sinter‐forging. In particular, the small interparticle pores (intrinsic pores) orient parallel to the applied compressive stress, in contrast to large pores from pore formers (extrinsic), which orient perpendicular to the applied stress. However, the pore size, for transition from extrinsic to intrinsic behavior, (transient pore size) has not been quantified. In this study, we report on the effect of applied stresses during sinter‐forging on the morphology (shape and size) of pores of different size. Based on these results, we propose a two‐step approach to predict transient pore size for hierarchically porous ceramics. We use this approach to quantify the effect of applied stresses on the transient pore size. Finally, we postulate that the stress dependence of the transient pore size may be related to sintering stress—a fundamental quantity in continuum models of sintering. In addition, it can be used to calculate the effective surface energy of complex sintering systems.

Description: Abstract Nickel Sulfide (NiS) inclusions can provoke the rupture of thermally treated glass due to a phase transformation with volume increase that stresses the surrounding glass. Starting from a Pareto statistics for the population of inclusion sizes, from an assumed kinetics of the phase transformation, a micro‐mechanically motivated model provides the statistical characterization of the probability of spontaneous failure of glass during lifetime. A distinction based upon the composition of NiS is used to discuss the effects of the heat soak test (HST), where glass remains at high temperature for a certain time to speed‐up the phase transformation and destroy those elements with critical inclusions. Three functions à la Weibull for the probability of spontaneous rupture during lifetime are theoretically derived for the case of no HST, short HST, and long HST. In particular, the probability of collapse for long HSTs depends upon the holding time in the oven. An explanatory example shows the potentiality of the model for optimizing the HST parameters toward a target probability of failure, but experimental campaigns are needed for a proper calibration.

Description: Abstract The pyrochlore‐type rare‐earth oxides attract considerable attentions due to their outstanding properties and extensive applications. In this work, contour maps of mechanical/thermal properties as a function of A and B cation radii across a wide variety of A2B2O7 (A = La‐Lu and Y; B = Ti, Sn, Hf, Zr, Pr and Ce) pyrochlore oxides are studied using the first‐principles calculations. The mechanical/thermal properties vary dramatically with increasing of the B cation sizes but do not show a strong systematic dependence on the A cation sizes. Furthermore, the machine learning algorithm is performed for the large family of pyrochlores and the parameters playing key role on mechanical/thermal properties are clarified. Besides, the expressions of focused mechanical and thermal properties are constructed. These results are expected to guide the future material design through composition tailoring.

Description: Abstract ZnS has been found superiority in photoelectrochemistry for the fast response of photo‐inducing and its high conductor band position (~0.8 eV) results in strong reduction ability for hydrogen production. However, the solar absorbance of ZnS is much low for the wide band gap (~3.2 eV) and the carriers’ migration efficiency also need to be improved. Here, nano‐ZnS were coupled with ultrathin SnS2 nanosheets as heterojunction composites. This heterojunction composite demonstrated largely increase in specific surface area (from 4 to 12‐25 m2/g), obvious improvement of UV‐vis absorbance and narrower band gap. Furthermore, the carriers’ migration efficiency of ZnS/SnS2 heterojunction has been confirmed to be much higher by photocurrent response and electrochemical impedance spectroscopy. Due to the improvement in structure, compared with pristine ZnS, this ZnS/SnS2 heterojunction exhibited vast enhancement in photoelectrochemical performance. The composite with best activity exhibited 12.8 times enhancement in photocurrent density. The conduction band and valence band of ZnS are both more negative than those of SnS2, the photo‐induced electrons at the conduction band of ZnS will transfer into the conduction band of SnS2 while the photo‐induced holes at the valence band of SnS2 will transfer into the valence band of ZnS. In this way, the photo‐produced carriers will flow into different semiconductors and the carriers’ migration efficiency is enhanced. The work improves a new structure to develop the heterojunction property for photoelectrochemical application.

Description: Lead‐free piezoelectric performance; relationship among sintering temperature, piezoelectric coefficient, and Curie temperature. Abstract Through modification of the heat‐treatment process using a higher heating rate and a lower binder burnout temperature, the piezoelectric performance of water‐quenched 0.67Bi1.05FeO3‐0.33BaTiO3 (BF33BT) lead‐free piezoelectric ceramics was improved. The observed physical properties of BF33BT ceramics were very sensitive to the process temperatures. The sintering temperature (TS) was changed within a narrow temperature range, and its effects were investigated. The largest rhombohedral distortion (90°‐αR = 0.14°) and tetragonality (cT/aT = 1.022) were observed for the ceramic sintered at 980°C, and its Curie temperature was 476°C. This ceramic showed good piezoelectric properties and large grains; the piezoelectric sensor charge coefficient (d33) was 352 pC/N, and the piezoelectric actuator charge coefficient () was 270 pm/V. The high piezoelectric performance and low TS of BF33BT ceramics indicate their potential as new low‐cost eco‐friendly lead‐free piezoceramics.

Description: Abstract The knowledge of the aqueous phase composition during the hydration of tricalcium silicate (C3S) is a key issue for the understanding of cement hydration. A new in situ method of computing calcium ion concentration from the measurement of the electrical conductivity on paste was coupled to isothermal calorimetry and BET measurements to get new insights on the early hydration of C3S. Ion concentrations of the aqueous phase are mainly dependent on the degree of hydration and the water to C3S ratio. In the case of C3S paste, the calcium and silicon concentrations determined at low degrees of hydration can be related to the equilibrium curve of C‐S‐H having C/S = 1.27 and named C1.27SHy. It is expected that C1.27SHy thermodynamically controls the aqueous phase composition at this early stage. Indeed, the formation of C1.27SHy is quasi‐immediate when C3S is in contact with water inducing a very rapid increase of the specific surface area that remains constant during the induction period. At higher degrees of hydration, the aqueous phase composition departs from the C1.27SHy equilibrium curve. C1.27SHy appears to be a metastable C‐S‐H that could be related to an intermediate phase previously reported. The quasi‐immediate precipitation of C1.27SHy on C3S surface explains why calcium and silicon concentrations remain low during early hydration even though C3S is strongly undersaturated. This also agrees with the control of the end of the induction period by the nucleation and growth of more stable C‐S‐H.

Description: Abstract We firstly reported the electrocaloric properties in relaxor (1−x−y)NaNbO3–yBaTiO3–xCaZrO3 ceramics, and high electrocaloric effect (∆T ~0.451 K and∣∆T/∆E∣~0.282 Km/MV) can be realized in the ceramics (x = 0.04 and y = 0.10) under low temperature and low electric field. Relaxor behavior of NaNbO3 ceramics can be found by doping both BaTiO3 and CaZrO3. In addition, optimized piezoelectric effects (d33 ~235 pC/N and d33* ~230 pm/V) can be observed in the ceramics (x = 0.04 and y = 0.10) due to the involved morphotropic phase boundary (MPB). Excellent piezoelectric effect (ie, d33~330 pm/V at 41°C, and d33*~332 pm/V at 60°C) can be found because of the characteristics of MPB. Good temperature reliability of piezoelectric effect can be shown because of both MPB and relaxor behavior. We believe that the ceramics with high electrocaloric effect and good piezoelectric effect can be considered as one of the most promising lead‐free materials for piezoelectric devices.

Description: Abstract A single‐phase full‐color emitting phosphor Na3Sc2(PO4)3:Eu2+/Tb3+/Mn2+ has been synthesized by high‐temperature solid‐state method. The crystal structure is measured by X‐ray diffraction. The emission can be tuned from blue to green/red/white through reasonable adjustment of doping ratio among Eu2+/Tb3+/Mn2+ ions. The photoluminescence, energy‐transfer efficiency and concentration quenching mechanisms in Eu2+‐Tb3+/Eu2+‐Mn2+ co‐doped samples were studied in detail. All as‐obtained samples show high quantum yield and robust resistance to thermal quenching at evaluated temperature from 30 to 200°C. Notably, the wide‐gamut emission covering the full visible range of Na3Sc2(PO4)3:Eu2+/Tb3+/Mn2+ gives an outstanding thermal quenching behavior near‐zero thermal quenching at 150°C/less than 20% emission intensity loss at 200°C, and high quantum yield‐66.0% at 150°C/56.9% at 200°C. Moreover, the chromaticity coordinates of Na3Sc2(PO4)3:Eu2+/Tb3+/Mn2+ keep stable through the whole evaluated temperature range. Finally, near‐UV w‐LED devices were fabricated, the white LED device (CCT = 4740.4 K, Ra = 80.9) indicates that Na3Sc2(PO4)3:Eu2+/Tb3+/Mn2+ may be a promising candidate for phosphor‐converted near‐UV w‐LEDs.

Description: Journal of the American Ceramic Society, Volume 101, Issue 12, Page 5289-5292, December 2018. 〈br/〉

Description: Cover Photograph: Top‐left: SEM‐EDS analysis in line‐scan mode across the cross section at BZCY‐containing anode|GDC electrolyte interface. Top‐middle: Schematic diagram of the metal ion diffusion mechanism at BZCY‐containing anode|GDC electrolyte interface. Top‐right: OCV values of some typical DCO‐based SOFCs with or without electron‐blocking layers. Bottom‐left: TEM image of the grain from NiO‐BZCY|GDC foam|NiO‐BZCY. Bottom‐middle: EDS results in line‐scan mode of the grain from NiO‐BZCY|GDC foam|NiO‐BZCY. Bottom‐right: HRTEM image of the grain obtained from NiO‐BZCY|GDC foam|NiO‐BZCY.

Description: Abstract In this work, a new manufacturing process of CMC by liquid molding was studied. An instrumented device has been developed to characterize the through‐thickness impregnation of ceramic fibers by a slurry charged with submicron ceramic particles. This instrument was used to characterize the permeability of the fibrous reinforcement and the formation of the ceramic cake by filtration of a ceramic particle suspension. Slurries containing different concentrations (10, 25, 33, and 40 vol%) of mono‐dispersed alumina particles were filtered under different pressure conditions (345, 415, 485 kPa) to optimize the cake formation and filling of fibrous reinforcements while controlling the porosity level. Ceramic cakes exhibited an average permeability of 1.0 × 10−17 m2 while the manufactured all‐oxide composites resulted in a permeability of 0.6 × 10−17 m2. Furthermore, a mathematical model based on Darcy's law was developed in this study to predict the rate of filtering and cake formation during injection using the permeability and filtration data measured with the experimental device. This mathematical model allows to determine the filtration time to produce a dense ceramic composite with an accuracy of ±15%, which corresponds to an error of less than 0.1 mm on the thickness of formed CMC.

Description: Abstract Luminomagnetic nanostructured Nd3+ doped fluorapatite (FAP) coated Fe3O4 nanoparticles were produced by hydrothermal method. X‐ray diffraction analysis indicates that the prepared nanoparticles contain both FAP and Fe3O4 phases. Electron microscope analysis shows the formation of nanoparticles of Fe3O4 encased in rod shaped FAP nanoparticles of average length 40 nm. Magnetic measurements confirm the room temperature superparamagnetic nature of the nanoparticles with saturation magnetization value up to 7.8 emu/g. The prepared nanoparticles display strong near infrared (NIR) emission at 1060 nm under 800 nm excitation. Cell viability studies for 72 hour demonstrate the survival rate of over 84% with 500 μg/mL concentration indicating the good cytocompatibility of the prepared materials. The present Nd3+ doped FAP coated Fe3O4 nanostructure provides an excellent multifunctional platform for diagnostics and therapeutic applications.

Description: Abstract In this paper, the effect of water immersion and humid weathering on the near‐surface mechanical properties of phosphate laser (PL) glass was investigated using nanoindentation. The results indicate that, in the water immersion condition, the reduced modulus and nano‐hardness of PL glass decrease first, then increase and finally keeps unchanged with the increase in immersion duration; however, in the humid weathering condition, they decrease monotonously. The reaction mechanism occurring between water molecules and the glass network, especially during the later stage of the reaction process, determines the near‐surface mechanical properties and their differences when exposed to water and/or humid air. The results in this paper provide additional insight into the nano‐mechanics of glass surfaces, which also help understand the surface alteration process of phosphate laser glass during machining, storage, and serving in wet environments.

Description: Abstract During the sintering of powder metallurgy steels the full removal of the iron oxide layer is required in order to develop strong inter‐particle necks. Although this iron oxide layer has low thermodynamic stability, its removal from the powder compact is a very complex process that is determined by a number of parameters such as temperature profile, sintering atmosphere, compact properties, powder properties, and additives. This paper summarizes these sintering parameters in correlation with the powder properties through the use of thermogravimetry analysis. In this work, hydrogen additions were identified as the most effective agent for the removal of the surface iron oxide during the early stages of sintering (at temperature range between ~300 and 600°C). The process depends on the heating rate and a rather low activation energy of 48 kJ/mol was determined for this reaction. Carbothermal reduction plays the largest role in the oxide reduction at high temperatures where two main reactions can be distinguished. The first was the reduction of the surface oxide residue and particulates, which occurred at temperatures between 950 and 1150°C. This reaction is characterized by an activation energy of 253 kJ/mol. Second was believed to be associated with the reduction of the internal oxides, occurred at temperatures above 1150°C. This reaction is characterized by rather high activation energy of 422 kJ/mol.

Description: Abstract The multi‐component glass fibers have demonstrated their unique advantages in the application of single‐frequency lasers due to their higher solubility of rare‐earth ions and thus a higher gain per unit length in a compact fiber laser cavity. In this study, multi‐component yttrium aluminosilicate (YAS) fiber with high doping concentration of Yb3+ was prepared by the “melt‐in‐tube” (MIT) method. A unit‐length gain of 3 dB/cm was obtained in a 4.4 cm‐long YAS fiber, the laser output slope efficiency reached 23.8% in a 10 cm‐long Yb:YAS fiber. Single‐frequency laser operation was achieved in a 1.7‐cm‐long Yb:YAS active fiber. To the best of our knowledge, this is the first demonstration of single‐frequency laser with this YAS glass fiber as gain medium. The novel multi‐component YAS fiber can be applied as a new gain material to realize single‐frequency fiber laser.

Description: Ammonolysis changes the white color of amorphous titania‐silica to greenish brown to bluish color depending the preparation condition. Abstract Coloration of amorphous silica powder containing titania was investigated by nitridation in an ammonia flow. The oxide precursors were obtained by the hydrolysis of a mixture of tetraethyl orthosilicate (TEOS) and tetrabutoxy titanium (TBT). The color changed with the amount of TBT in the mixture, the hydrolysis pH and the ammonolysis temperature. The original white color of the 8 mol% TBT powder hydrolyzed under basic pH conditions changed to pale goldenrod at 700°C, then to dark olive green at 800°C, and further darkened with increasing ammonolysis temperature. A steel‐blue color appeared at 900°C for the powder obtained with 3 mol% TBT, and increased in darkness at 1000°C. A similar bluish color was observed for powders obtained by acidic hydrolysis after ammonolysis above 900°C, and this was independent of the amount of titania, although the chroma decreased with increasing firing temperature for the powder with 3 mol% TBT. The ammonolysis powder products were characterized using X‐ray diffraction (XRD), electron probe micro analysis (EPMA), transmission electron microscopy‐electron energy‐loss spectroscopy (TEM‐EELS), scanning transmission electron microscopy‐high‐angle annular dark‐field imaging (STEM‐HAADF) and Ti–K edge X‐ray absorption fine structure (XAFS). The color change was related to both precipitated TiN nanocrystals and residual titanium in the amorphous silica matrix. The TiN exhibited a goldish reflection and also plasmonic absorption from light blue to gray depending on the TiN crystallite size. The plasmonic absorption and resonance of nanocrystalline TiN will be useful similarly to that of gold in nanotechnology for various kinds of energy application.

Description: Abstract Electrostatic potential barriers at doped ZnO‐ZnO interfaces can be modified by stress‐induced polarization charges. This concept was enhanced by preparing ZnO‐based single crystal‐polycrystal‐single crystal structures by diffusion bonding. Increasing time for epitaxial solid‐state transformation results in structures with a decreasing thickness of residual polycrystalline material in between two well‐oriented single crystals. Microstructural and electrical analysis quantifies the influence of high‐temperature treatment during epitaxial growth on the stress sensitivity of the prepared structures. The orientation of the single crystals is defined to maximize the interaction between stress‐induced polarization charges and the potential barriers at doped ZnO‐ZnO interfaces. With decreasing thickness of residual polycrystalline material, the percentage of grain boundaries with favorably aligned polarization vectors is increased resulting in a higher stress sensitivity. This effect is compensated by an adverse effect of the high‐temperature treatment on the initial potential barrier height. Hence, a maximum in stress sensitivity can be observed for intermediate times of epitaxial growth. The prepared structures close the gap between the varistor piezotronics based on bulk ceramics with random orientation of the polarization vector and the bicrystal piezotronics with perfect orientation of the polarization vector, demonstrating the capability of microstructural engineering for varistor‐based piezotronic devices.

Description: Abstract Bismuth (Bi)‐doped glasses and fibers are of current interest as promising active media for new fiber lasers and amplifiers due to their 800‐1700 nm near‐infrared (NIR) emission. However, the optically active Bi centers in silica are easily volatilized during high‐temperature fiber drawing, which results in low Bi doping concentration and low gain NIR luminescence. Here, we explored the glass‐forming region in a model glass system of sodium tantalum silicate (Na2O‐Ta2O5‐SiO2) glass and attained suitable glass host for enhancing Bi NIR emission, right followed by detailed analysis on optical and structural characterization. Glass‐forming region roughly lies in where Ta2O5 ≤ 30 mol%, SiO2 ≥ 40 mol%, and Na2O ≤ 40 mol%. Not only is glass‐forming ability improved but also Bi NIR emission is enhanced (~60 times) by the introduction of Ta into glass network. Dissociated Na cations are restricted beside Ta, the high‐field‐strength element, so that the negative impacts of Na cations on glass formation and Bi NIR emission are weakened, which is responsible for the highly enhanced Bi NIR emission. This work helps us understand the glass‐forming of tantalum silicate glass systems and luminescent behaviors of Bi. Hopefully, it could contribute to designing the Bi‐doped laser glasses and high gain fibers with stable luminescent properties in future.

Description: Abstract Flash spark plasma sintering (FSPS) offers extremely high heating rates to consolidate ceramics at a short time. However, significant grain growth sometimes occurs accompanied by rapid densification. In this work, a FSPS apparatus available for applying pressure was used to sinter TaC ceramics from powder compacts without preheating. It is found that the use of a higher pressure can efficiently promote densification and retard significant grain growth. Dense bulk TaC ceramics (95.18%) with average grain size of 4.09 μm were obtained in 90 seconds under 80 MPa. Such a process should facilitate the fast preparation of refractory ceramics with fine‐grained microstructure.

Description: Abstract Field‐assisted processing techniques can enhance the kinetics of powder synthesis, accelerate sintering processes, and drive phase transformations at significantly lower temperatures compared to conventional methods. However, the exact nature of this nonthermal interaction between field and matter remains vastly speculative. A 2‐day workshop on “Electromagnetic Effects in Materials Synthesis” was organized at Carnegie Mellon University (Pittsburgh, USA) in June 2017, jointly sponsored by the U.S. National Science Foundation and the U.S. Office of Naval Research. This workshop gathered the scientific community working on field‐assisted techniques of materials processing. Inspired by the discussions held at the workshop, this paper summarizes the advancements to date and opens scientific questions and research opportunities in the three major field‐assisted sintering techniques (laser, microwave, and flash sintering). Significant challenges remain in (a) experimental design, measurements, and computational simulations to distinguish the nonthermal effects of the externally applied fields from conventional thermal phenomena; and (b) identifying fundamental mechanisms behind low temperature, nonthermal effects that produce phase transitions and microstructural evolution in materials under externally applied fields. We also present the recent developments in multiscale characterization techniques and the theory and modeling efforts, which aim to tackle the aforementioned grand multidisciplinary challenges facing researchers.

Description: Abstract The synthesis of TiB2 nanopowders arouses considerable interests due to its importance for implementing the extensive applications of TiB2 ceramic. Herein, the high‐purity ultrafine TiB2 nanopowders were successfully synthesized via a molten salt assisted borothermal reduction technique at a relatively low temperature of 1173 K using TiO2 and B powders as precursors within a KCl/NaCl salt. The results showed that the as‐obtained TiB2 nanopowders possessed a polycrystallinity structure, and their specific surface area and equivalent average particle size were 33.18 m2/g and 40 nm, respectively. This study provides a new low temperature synthesis technique of TiB2 nanopowders.

Description: Journal of the American Ceramic Society, Volume 101, Issue 12, Page 5870-5870, December 2018. 〈br/〉

Description: Abstract The usual way to prepare TaC‐TaB2 ceramics by adding B4C to TaC leads to formation of residual C, which degrades samples’ mechanical properties. To eliminate the residual C, we suggest incorporating Si together with B4C into TaC ceramics, resulting in new ultrahigh‐temperature ceramics (TaC‐TaB2‐SiC). Dense ceramics (〉99%) with SiC volume fraction ranging from 15.86% to 41.04% were fabricated by reactive spark plasma sintering at 1900°C for 5 minutes. The formation of SiO2‐based transient liquid phase was evidenced by the “film” in intermediate products, which can promote densification. The fine‐grained microstructure in final products was found to be associated with the in situ formed SiC, which impeded TaC and TaB2 grains from coarsening by the pinning effect. Besides, ultrafine TaB2 grains (~100 nm) produced during the reaction and then rearranged in liquid also contributed to grain refinement. Compared to TaC‐TaB2(‐C) ceramics prepared from TaC and B4C, the acquired composites exhibit better mechanical properties, due to their fine‐grained microstructures and the elimination of residual C.

Description: Abstract Polycrystalline bilayer thin film of multiferroic [Ba(Zr0.2Ti0.8)O3‐0.5(Ba0.7Ca0.3)TiO3]/CoFe2O4([BZT‐0.5BCT]/CFO) has been deposited on Pt/Si (100) substrate using a pulsed laser deposition technique. The dielectric analysis reveals a significant change in the dielectric constant (~39% at a typical frequency of 100 Hz) at room temperature when a magnetic field is applied, in addition to a substantial improvement in the saturation polarization. A low leakage current density (~ 5 × 10−7 A/cm2) and a high magnetoelectric coupling coefficient (αE) both in the transverse (~2.085 V/Oe cm) as well as in the longitudinal (~0.708 V/cm Oe) directions, indicate in‐principle usability of this system for multifunctional device applications in thin film form.

Description: Abstract Silicon oxycarbide (SiOC) ceramics with highly adjustable properties and microstructures have many promising applications in batteries, catalysis, gas separation, and supercapacitors. In this study, additive structures on the nucleation and growth of SiO2 within SiOC ceramics are investigated by adding cyclic tetramethyl‐tetravinylcyclotetrasiloxane (TMTVS) or caged octavinyl‐polyhedral oligomeric silsesquioxane (POSS) to a base polysiloxane (PSO) precursor. The effects of the 2 additives on the polymer‐to‐ceramic transformation and the phase formation within the SiOC are discussed. POSS encourages SiO2 nucleation and leads to more SiO2 formation with significantly increased ceramic yield, which subsequently leads to higher specific surface of 1557 m2/g with a larger pore size of ∼1.8 nm for the porous SiOC. High TMTVS content decreases both the specific surface area and pore volume of the resulting porous SiOCs. This study demonstrates a new approach of using Si‐rich additive POSS to increase the SiOC yield while maintaining or even increasing the specific surface area.

Description: Abstract A thermally activated crack‐velocity formulation that includes a threshold at thermodynamic equilibrium is used in the prediction of long‐term time‐to‐failure for brittle materials. A new closed‐form time‐to‐failure solution is derived for straight cracks propagating under the influence of constant stress. Explicit connections are made between the macroscopic crack‐velocity parameters and the underlying bond‐rupture parameters. A feature of the solution is the divergence of time‐to‐failure for applied loading approaching the thermodynamic threshold. A new reliability framework is developed and long‐term reliability and hazard predictions made using the time‐to‐failure solution. A bathtub hazard curve is shown to be generated by a single crack‐velocity failure mechanism.

Description: Abstract The fictive temperature of glass is a consequence of its thermal history (cooling rate, primarily) and has a direct effect on physical and chemical properties of the glass. But, it is not easy to measure. The ability to nondestructively and spectroscopically measure it at room temperature would be of great benefit. Although empirical correlations have been established between fictive temperature and selected absorption peaks in the infrared spectra of silica glass, the fundamental understanding for this correlation has not been reported. Here, we use molecular dynamics simulations to show that the blue shift in the Si–O–Si asymmetric stretching peak of pure silica glass, which is known to correlate with a decrease in fictive temperature, can be attributed to a decrease in the average length of the Si–O bond in the silica network, not changes in the density or the Si–O–Si bond angle. The decrease in density at higher fictive temperatures of silica is associated with a decreased population of 5‐ and 6‐membered rings and broadening of the ring‐size distribution, and an increase in the average Si–O–Si bond angle.

Description: Abstract In this study, first‐principles calculations were performed to study the stability, mechanical property, electronic structure and lattice dynamics of β‐Si3(Cx,N1−x)4 silicon carbonitride. The solubility of carbon in β‐Si3(Cx,N1−x)4 having a stable structure is shown to be about 15 at.%. Within the limit of solubility, an increase in carbon concentration in β‐Si3(Cx,N1−x)4 will lead to a decrease in the Young's modulus and density and an increase in the Poisson's ratio. The study of deformation behavior shows that the most likely slip system of is on prismatic plane rather than on basal plane. This feature of β‐Si3(Cx,N1−x)4 is similar to WC. In addition, the ductility and fracture toughness of β‐Si3(Cx,N1−x)4 can be optimized by controlling the carbon concentration. The improvement in ductility and fracture toughness can be attributed to the formation of metallic bonds by the incorporation of carbon atoms. The lattice dynamics study shows that the structural stability of β‐Si3(Cx,N1−x)4 is controlled by energy stability criteria under stress‐free condition. In the stressed state, the structural stability of β‐Si3(Cx,N1−x)4 is controlled by the elastic stability criteria. Subsequently, the β‐Si3(Cx,N1−x)4 solid solution was prepared by self‐propagating high‐temperature synthesis (SHS), and the carbon‐concentration‐dependent mechanical properties were consistent with the first‐principles calculations. The maximum fracture toughness of 10.4 MPa·m0.5 was obtained in β‐Si3(Cx,N1−x)4 at carbon concentration of 5 wt%, which means that the solid solution toughening can be used as a supplement to crack bridging toughening and phase transition toughening for ceramic toughening. The results obtained in this study reveal that the β‐Si3(Cx,N1−x)4 solid solution is a promising candidate for high‐speed ceramic bearings.

Description: Abstract Large‐scale, uniform, monodisperse LaCO3OH cherry‐blossom‐like nanogears and/or nanocubes have been synthesized under hydrothermal reaction conditions. Upon the addition of only 5 mol% Ca2+ ions into a La nitrate salts solution with pH 8.5, LaCO3OH crystals with novel cubic or nanogear structures are formed in the hexagonal phase. The hydrothermal reactions were carried out without the addition of a template or catalysts. Both 24 hour and 48 hour hydrothermal reactions yield 100% pure LaCO3OH with no irregular particles. We examined the photoluminescence properties of the as‐synthesized powders of the pure LaCO3OH nanogears and found one broad emission band centered at 394 nm after excitation at λ  =  280 nm. The NO reduction activity was also examined over highly dispersed CaO‐containing La2O3 obtained after calcination the LaCO3OH at 800○C for 2 hours. The CaO‐containing La2O3 catalysts showed good stability for NO reduction with CH4 in the presence of O2 and H2O vapor.

Description: Abstract Polycrystalline Ni(Cr1−xMnx)2O4 (0.1 ≤ x ≤ 0.325) ceramic samples were studied through different protocols of dc magnetization measurements. The samples exhibit 2 kinds of magnetic compensation effects below the ferrimagnetic transition temperature TC. Remarkable magnetization reversal is observed between the 2 compensation temperatures Tcomp1 and Tcomp2, which is regarded as arising from the negative exchange coupling between the 2 magnetic sublattices at different crystallographic sites. The magnetization is reversed at TSR due to spin‐reorientation caused by magnetostructural coupling. The spin‐reorientation is supported by Mn substitution and TSR is increased to 96 K when x reaches 0.325. However, it is suppressed due to the strong ionic site preference and thus the magnetization is slightly increased in the negative direction of the magnetic field. Near the 2 compensation temperatures, tunable magnetic switching effects can be obtained just by changing the magnitude of the applied magnetic field. Moreover, both normal and inverse magnetocaloric effects were also demonstrated.

Description: Abstract A new type of (0.7−x)Bi0.5Na0.5TiO3‐0.3Sr0.7Bi0.2TiO3‐xLaTi0.5Mg0.5O3 (LTM1000x, x = 0.0, 0.005, 0.01, 0.03, 0.05 wt%) lead‐free energy storage ceramic material was prepared by a combining ternary perovskite compounds, and the phase transition, dielectric, and energy storage characteristics were analyzed. It was found that the ceramic materials can achieve a stable dielectric property with a large dielectric constant in a wide temperature range with proper doping. The dielectric constant was stable at 2170 ± 15% in the temperature range of 35‐363°C at LTM05. In addition, the storage energy density was greatly improved to 1.32 J/cm3 with a high‐energy storage efficiency of 75% at the composition. More importantly, the energy storage density exhibited good temperature stability in the measurement range, which was maintained within 5% in the temperature range of 30‐110°C. Particularly, LTM05 show excellent fatigue resistance within 106 fatigue cycles. The results show that the ceramic material is a promising material for temperature‐stable energy storage.

Description: Abstract Tin fluorophosphate (TFP) glass, which can be used to manufacture a phosphor‐in‐glass (PiG) for achieving high‐power white light‐emitting diodes (w‐LEDs), has attracted a great deal of attention because of its low‐melting point. Mn2+‐doped ultralow glass transition temperature (~122°C) Sn–F–P–O glasses were prepared to achieve broadband visible light emission from 390 to 720 nm. By controlling the concentration of MnO, the emission color of the TFP glass can be adjusted from blue/cool white to warm white/red. In particular, 0.2 mol% MnO‐doped TFP glass, which yields bright and warm white light and has ultralow glass transition temperature and thermal stability, has a promising application prospect in the field of high‐power w‐LEDs.

Description: Abstract The BaO–Sm2O3 system is of interest for the optimization of synthesis of electroceramics. The only systematic experimental study of phase equilibria in the system was performed more than 40 years ago. The reported experimental values of the enthalpy of formation of BaSm2O4 are in conflict, and the reported compound Ba3Sm4O9 has never been confirmed. In this work we synthesized BaSm2O4 by solid‐state reaction and determined its heat capacity, enthalpy of formation, and phase transitions by differential scanning calorimetry, high‐temperature oxide melt solution calorimetry and ultra‐high‐temperature differential thermal analysis, respectively. We confirmed the existence of Ba3Sm4O9 and its apparent stability from 1873 to 2273 K by X‐ray diffraction on quenched laser‐melted samples but were not able to obtain single‐phase material for calorimetric measurements. The CALPHAD method was used to assess phase equilibria in the BaO–Sm2O3 system, using both available literature data and our new measurements. A self‐consistent thermodynamic database and the calculated phase diagram of the BaO–Sm2O3 system are provided. This work can be used to model and thus to understand the relationships among composition, temperature, and microstructure for multicomponent systems with BaO and Sm2O3.

Description: Abstract With the aim to design a particular material for low and high frequency cooperative electromagnetic absorption at high temperature, a multiscale design is proposed by combining the microstructure and meta‐structure in one material. The SiCf/Si3N4 composite is prepared via the chemical vapor infiltration technique with SiCf as the EM wave absorbing phase and Si3N4 as the wave‐transparent ceramic matrix. The crossing grooved meta‐structure is designed and fabricated to further improve its absorbing properties and to guarantee its absorbing capacity stability at high temperature. A minimum reflection loss of −15.3 dB and −14.8 dB can be reached at 8 and 18 GHz with a total thickness of 5 mm. The temperature‐dependent reflection loss of the designed meta‐structure keeps relative reliable high temperature absorbing performances from room temperature to 500°C. This effective enhanced EM wave absorbing property is believed to be a consequence of multiscale effect induced by combining the traditional EM absorbing materials with metamaterial structure.

Description: Abstract A facile solvothermal synthetic route has been developed to prepare CuInTe2 nanowires with the template aiding of anodic aluminum oxide. Microstructure analysis reveals that the as‐prepared single crystalline CuInTe2 nanowires have a [112] direction preferential growth. Oriented attachment mechanism has been proposed to explain the anisotropic growth of CuInTe2 nanowires during a polycrystalline‐to‐single‐crystalline transformation process. CuInTe2 nanowires have strong absorption in the visible region based on UV‐Vis absorption spectra measurement, confirming its suitability as a light absorbing material in solar cells.

Description: Abstract The oxidation behavior of Sylramic SiC fibers without a boron nitride surface layer was compared to Sylramic iBN SiC fibers with a boron nitride surface layer by conducting thermogravimetric analysis in dry O2 at temperatures ranging from 800 to 1300°C for times up to 100 hours. Sylramic fibers followed the Deal and Grove oxidation kinetic model. A transient period of accelerated oxidation kinetics was observed with Sylramic iBN fibers. Raman spectroscopic analysis of oxidized fibers provided evidence for a borosilicate glass structure. The boron concentrations in the oxides, quantified by inductively coupled plasma‐optical emission spectrometry, were correlated with the weight change behavior, oxide thickness, and fiber recession of the oxidized fibers. Oxides formed from Sylramic iBN fibers were typically higher in boron concentration, which led to initial rapid oxidation rates that were 3‐10 times faster than observed for pure SiC. Slower oxidation rates followed as the oxide surface became increasingly enriched with SiO2 due to boria volatilization, thus limiting boria effects on SiC fiber oxidation kinetics. The accelerated high‐temperature oxidation of SiC fibers due to the presence of BN are discussed in terms of the borosilicate glass structure and composition.

Description: Abstract We report a comprehensive investigation of fabricating nanostructured anodic aluminum oxide (AAO) cladding on optical fiber. We show that the pore size and interpore distance in the AAO cladding with pore channels vertically aligned to fiber surface can be readily controlled by applied voltage, the type, and concentration of electrolytic acid during anodization of aluminum‐coated optical fiber. The structural characteristics of the AAO cladding were examined by scanning electron microscopy (SEM) and analyzed using ImageJ software. Processing maps correlating AAO growth and anodization parameters were established. Compared to planar AAO growth on aluminum foil, higher growth rate as well as larger pore diameter and interpore distance were observed for AAO cladding formation on optical fiber under identical anodization conditions due to circumferential tensile stress in the AAO growth front at the convex AAO/aluminum interface. This tensile stress also contributed to radial cracking of the AAO cladding upon exceeding some threshold thickness.

Description: Abstract For the first time, potassium sodium niobate (KNN)‐based lead‐free piezoelectric ceramic coating with strong piezoelectric response was fabricated on stainless steel substrates by thermal spray process, after introducing NiCrAlY and yttria‐stabilized zirconia (YSZ) intermediate layers. A large effective piezoelectric coefficient (d33) of 125 pm/V was obtained with the thermal‐sprayed KNN‐based ceramic coating on the steel substrates. The mechanisms of improving the structure and enhancing the properties of the KNN‐based piezoelectric ceramic coatings by introducing the intermediate layers were analyzed. Ultrasonic transducers were designed and fabricated from the KNN‐based coatings directly formed on a steel plate structure, and the feasibility for generation and detection of ultrasonic waves for structural health monitoring using the thermal‐sprayed lead‐free piezoelectric ceramic coating was demonstrated.

Description: Abstract Partial reduction of bulk CuAlO2 results in hierarchical structures wherein there are copper‐alumina regions with widely differing morphologies and scale. At the finest level, the distribution of the 2 phases is at the nanoscale. By means of atomic resolution STEM and electron diffraction, the nanocomposite regions were shown to consist of a dense array of metallic copper platelets dispersed in a matrix of θ‐Al2O3. The copper nanoplatelets were single crystal, and they all exhibited the same orientation relationship with the matrix, namely [110]Cu//[010]θ‐Al2O3, (111)Cu//()θ‐Al2O3. It was shown that the 2‐phase regions where the copper exhibited a significantly coarser, globular morphology, resulted from discontinuous coarsening. Interestingly, a change in the matrix phase from θ‐ to δ‐alumina was also observed as a result of the coarsening reaction. It is believed that in the nanocomposite regions, the θ‐alumina phase was stabilized by the lower interfacial energy between the copper (110) platelets and the matrix.

Description: Abstract In this study, β‐tricalcium phosphate/phosphate‐based glass (β‐TCP/PG) composite spheres were prepared by an extrusion‐spheronization method featuring high production and fine control of sphere size. Subsequently, fully interconnected β‐TCP composite ceramic sphere‐based (TCCS) scaffolds were fabricated by sintering the randomly packed β‐TCP/PG composite spheres. The results manifested that at least 20% microcrystalline cellulose (MCC) was required to obtain β‐TCP/PG composite spheres in good spherical shape. The prepared TCCS scaffolds showed hierarchical pore architecture, which consisted of interconnected macropores among the spheres, a hollow core in the sphere, plentiful medium‐sized pores in the sphere shell and micropores among the grains. The pore architecture and mechanical strength of the TCCS scaffolds could be tailored by adjusting the sintering temperature, sphere size, and amounts of PG and MCC in the β‐TCP/PG composite spheres. This work is believed to open up new paths for the design and fabrication of interconnected bioceramic scaffolds for application in bone regeneration.

Description: Abstract The molecular structures of CaO–FeOx–SiO2 slags and their inorganic polymer counterparts were determined using neutron and X‐ray scattering with subsequent pair distribution function (PDF) analysis. The slags were synthesized with approximate molar compositions: 0.17CaO–0.83FeO–SiO2 and 0.33CaO–0.67FeO–SiO2 (referred to as low‐Ca and high‐Ca, respectively). The PDF data on the slags reasserted the predominantly glassy nature of this iron‐rich industrial byproduct. The dominant metal‐metal correlation was Fe–Si (3.20‐3.25 Å), with smaller contributions from Fe–Ca (3.45‐3.50 Å) and Fe–Fe (2.95‐3.00 Å). After inorganic polymer synthesis, a rise in the amount of Fe3+ was observed via the shift of the Fe–O bond length to shorter distances. This shortening of the Fe–O distance in the binder is also evidenced by the apparent rise of the Fe–Fe correlation at 2.95‐3.00 Å, although this feature may also suggest a potential aggregation of FeOx clusters. In general, the atomic arrangements of the reaction product was shown to be very similar to the precursor structure and the dominance of the Fe–Si correlation suggests the participation of Fe in the silicate network. The binder was shown to be glassy, as no distinct atom‐atom correlations were observed beyond 8 Å.

Description: Abstract We show, by means of ab initio calculations, that amorphous zirconia progressively transforms to a high‐density amorphous phase with the application of pressure. The average coordination number of Zr and O atoms under pressure rises gradually to 8 and 4, respectively. The main building unit of the dense noncrystalline state is the eightfold‐coordinated Zr atoms (62.5%). When the coordinated modification of Zr atoms in the zirconia crystal at high pressure and temperature conditions is considered, it can be perceived that amorphous zirconia follows a transformation mechanism similar to the one observed at high temperature but different than the one detected at high pressure. The dense disordered phase is indeed found to be locally comparable with the high‐temperature tetragonal crystal. Upon decompression, some high‐pressure arrangements are persevered in the model and a transformation into another amorphous state whose structure is intermediate between uncompressed and dense amorphous phases is observed in the simulations. The high‐pressure amorphous structures are found to be semiconductors with a band gap smaller than that of the original model.

Description: Abstract In this work, we report a lead‐free piezoelectric ceramic of (0.9‐x)NaNbO3‐0.1BaTiO3‐xBaZrO3, and the effects of BaZrO3 on the phase structure, microstructure, electrical properties and temperature stability are investigated. A morphotropic phase boundary‐like region consisting of rhombohedral (R) and tetragonal (T) phases is constructed in the compositions with x = 0.035‐0.04. More importantly, in situ temperature independence of the piezoelectric effect {piezoelectric constant (d33) and strain} can be achieved below the Curie temperature (Tc). Intriguingly, the electric field‐induced strain is still observed at T ≥ Tc due to the combined actions of the electrostrictive effect and the electric field‐induced phase transition. We believe that NaNbO3‐based ceramics of this type have potential for applications in actuators and sensors.

Description: Abstract The Dy‐ and Eu‐activated Ca3B2O6 phosphors were synthesized by a high‐temperature solid‐state reaction technique and their structural and luminescent properties were investigated. The phosphors are characterized by X‐ray diffraction, photoluminescence spectra, and Commission International de I'Eclairage (CIE) chromaticity coordinates. It is found that the charge compensator Na+ plays an important role in modifying the emission spectral profiles of Dy and Eu ions in the phosphors. The ratio of the emission located at the yellow wavelength portion to that located at the blue wavelength region of the Dy3+ ions can be apparently tuned by changing the Na+ content. The luminescence intensity of the phosphors can be enhanced with introducing Na+ ions as well. The emission colors of Dy/Eu codoped phosphors change from blue to white and successfully acquire the superior white light emission (x = 0.330, y = 0.329) by appropriately tuning the Na+/Dy3+ content and the excitation wavelength. The energy transfer process from Eu2+ to Dy3+ and Eu3+ occurs in the Dy/Eu codoped phosphors, providing a further approach to modify the emission spectral profile of the examined phosphors. The phosphors presented here have promising applications in the fields of light‐emitting diodes.

Description: Abstract A series of high‐quality Cu‐doped Zn–In–S nanocrystals (d‐NCs) were prepared by a conventional hot injection process. The full‐visible spectrum emission from 480 to 648 nm can be easily achieved by adjusting the Cu doping concentration in the Zn–In–S system, but not by varying the ratio of In/Zn in the alloyed host material. After wrapping the ZnS shell around the Zn–In–S:Cu d‐NCs core, the resultant Zn–In–S:Cu/ZnS core/shell d‐NCs not only exhibited an enhanced prominent photoluminescent quantum yield (PLQY) up to 65% but also possessed the excellent thermal, photochemical stability, and longer PL lifetime. Furthermore, high color rendition white light was generated from a single color converter Zn–In–S:Cu/ZnS core/shell NCs‐assisted white light‐emitting diodes (LEDs). Under operation of 38 mA forward bias current, the fabricated white LEDs emitted bright natural white light with a luminous efficiency of 62 lm/W, and the correlated color temperature of 5658 K. Simultaneously, the good color stability was accompanied by the CIE color coordinates of (0.3287, 0.3527) under different forward bias currents.

Description: Abstract Compatibility of Bi‐based piezoelectric ceramic and copper electrodes is demonstrated by co‐firing 0.88Bi1/2Na1/2TiO3–0.08Bi1/2K1/2TiO3–0.04BaTiO3 (BNKBT88) with copper. A combination of Bi2O3, CuO, ZnO, Li2CO3, and B2O3 are used as additives to reduce firing temperature to 900°C with minimal effect on the electromechanical properties compared to sintering at 1150°C without additives. Co‐firing with copper electrodes requires controlled oxygen sintering at low temperature. The atmosphere is controlled using carbon dioxide and hydrogen gas to maintain an oxygen partial pressure of 6.1 × 10−8 atm, which is necessary for the coexistence of Cu metal and Bi2O3. The thermodynamic activity of bismuth oxide in BNKBT88 is calculated to be 0.38. BNKBT88 ceramics were successfully co‐fired with internal as well as surface Cu metal electrodes. The copper co‐fired ceramics were successfully polarized and the dielectric and piezoelectric properties are evaluated.

Description: Abstract To simulate interfacial reactions process and deformation in γ‐TiAl and glass‐ceramic coating system at high temperature, we developed a coupled chemomechanical model with chemical reactions, diffusion, and mechanical deformation incorporated. Tensile radial and circumferential stresses develop in interfacial zone and coatings as the interfacial reactions occur. Tensile radial stress could tear coatings off alloys while the tensile circumferential stress could result in crack initiation and propagation, even spalling of coatings. The bulk radial stress can be markedly reduced by taking the surface effect into account. Consequently, tensile radial stress vanishes in alloy‐coating system on nano scale.

Description: ABSTRACT In the Russian school, the total normalized gradient method belongs to the most wide‐spread of direct interpretation methods for potential field data. This method was also used and partly developed by many experts from abroad. The main advantage of the total normalized gradient method is its relative independence of parameters such as the expected differential density of interpreted structures. The method is built from a construction of a specially transformed field (total normalized gradient) on a section crossing the potential field sources. The special properties of this transformed field allow it to be used to detect the source positions. From the 1960s, the mathematical basis of the method underwent enormous development and several modifications of the method have been elaborated. The total normalized gradient operator itself represents a relatively complicated, non‐linear band‐pass filter in the spectral domain. The properties of this operator can be handled by means of several parameters that act to separate the information about field sources at different depth levels. In this contribution, we describe the development of the method from its very beginning (based mostly on qualitative interpretation of simple total normalized gradient sections) through to more recent numerical improvements to the method. These improvements include the quasi‐singular points method, which refines the filter properties of the total normalized gradient operator and defines an objective criteria (so called criterion ‘α’ and ‘Г') for the definition of source depths in the section. We end by describing possibilities for further development of the method in the future.

Description: ABSTRACT Up–down wavefield decomposition is effectuated by a scaled addition or subtraction of the pressure and vertical particle velocity, generally on horizontal or vertical surfaces, and works well for data given on such surfaces. The method, however, is not applicable to decomposing a wavefield when it is given at one instance in time, i.e. on snapshots. Such situations occur when a wavefield is modelled with methods like finite‐difference techniques, for the purpose of, for example, reverse time migration, where the entire wavefield is determined per time instance. We present an alternative decomposition method that is exact when working on snapshots of an acoustic wavefield in a homogeneous medium, but can easily be approximated to heterogeneous media, and allows the wavefield to be decomposed in arbitrary directions. Such a directional snapshot wavefield decomposition is achieved by recasting the acoustic system in terms of the time derivative of the pressure and the vertical particle velocity, as opposed to the vertical derivative in up–down decomposition for data given on a horizontal surface. As in up–down decomposition of data given at a horizontal surface, the system can be eigenvalue decomposed and the inverse of the eigenvector matrix decomposes the wavefield snapshot into fields of opposite directions, including up–down decomposition. As the vertical particle velocity can be rotated at will, this allows for decomposition of the wavefield into any spatial direction; even spatially varying directions are possible. We show the power and effectiveness of the method by synthetic examples and models of increasing complexity.

Description: ABSTRACT The application of blended acquisition has drawn considerable attention owing to its ability to improve the operational efficiency as well as the data quality and health, safety and environment performance. Furthermore, the acquisition of less data contributes to the business aspect, while the desired data density is still realizable via subsequent data reconstruction. The use of fewer detectors and sources also minimizes operational risks in the field. Therefore, a combined implementation of these technologies potentially enhances the value of a seismic survey further. One way to encourage this is to minimize any imperfection in deblending and data reconstruction during processing. In addition, one may derive survey parameters that enable a further improvement in these processes as introduced in this study. The proposed survey design workflow iteratively performs the following steps to derive the survey parameters responsible for source blending as well as the spatial sampling of detectors and sources. The first step is the application of blending and sampling operators to unblended and well‐sampled data. We then apply closed‐loop deblending and data reconstruction. The residue for a given design from this step is evaluated and subsequently used by genetic algorithms to simultaneously update the survey parameters related to both blending and spatial sampling. The updated parameters are fed into the next iteration until they satisfy the given termination criteria. We also propose a repeated encoding sequence to form a parameter sequence in genetic algorithms, making the size of problem space manageable. The results of the proposed workflow are outlined using blended dispersed source array data incorporating different scenarios that represent acquisition in marine, transition zone and land environments. Clear differences attributed solely to the parameter design are easily recognizable. Additionally, a comparison among different optimization schemes illustrates the ability of genetic algorithms along with a repeated encoding sequence to find better solutions within a computationally affordable time. The optimized parameters yield a notable enhancement in the deblending and data reconstruction quality and consequently provide optimal acquisition scenarios.

Description: ABSTRACT Synthetic rock samples can offer advantages over natural rock samples when used for laboratory rock physical properties studies, provided their success as natural analogues is well understood. The ability of synthetic rocks to mimic the natural stress dependency of elastic wave, electrical and fluid transport properties is of primary interest. Hence, we compare a consistent set of laboratory multi‐physics measurements obtained on four quartz sandstone samples (porosity range 20–25%) comprising two synthetic and two natural (Berea and Corvio) samples, the latter used extensively as standards in rock physics research. We measured simultaneously ultrasonic (P‐ and S‐wave) velocity and attenuation, electrical resistivity, permeability and axial and radial strains over a wide range of differential pressure (confining stress 15–50 MPa; pore pressure 5–10 MPa) on the four brine saturated samples. Despite some obvious physical discrepancies caused by the synthetic manufacturing process, such as silica cementation and anisotropy, the results show only small differences in stress dependency between the synthetic and natural sandstones for all measured parameters. Stress dependency analysis of the dry samples using an isotropic effective medium model of spheroidal pores and penny‐shaped cracks, together with a granular cohesion model, provide evidence of crack closure mechanisms in the natural sandstones, seen to a much lesser extent in the synthetic sandstones. The smaller grain size, greater cement content, and cementation under oedometric conditions particularly affect the fluid transport properties of the synthetic sandstones, resulting in lower permeability and higher electrical resistivity for a similar porosity. The effective stress coefficients, determined for each parameter, are in agreement with data reported in the literature. Our results for the particular synthetic materials that were tested suggest that synthetic sandstones can serve as good proxies for natural sandstones for studies of elastic and mechanical properties, but should be used with care for transport properties studies.

Description: ABSTRACT P‐wave and S‐wave velocities are vital parameters for the processing of seismic data and may be useful for geotechnical studies used in mine planning if such data were collected more often. Seismic velocity data from boreholes increase the robustness and accuracy of the images obtained by relatively costly seismic surface reflection surveys. However, sonic logs are rarely acquired in boreholes in‐and‐near base metal and precious metal mineral deposits until a seismic survey is planned, and only a few new holes are typically logged because the many hundreds of holes previously drilled are no longer accessible. If there are any pre‐existing petrophysical log data, then the data are likely to consist of density, magnetic susceptibility, resistivity and natural gamma logs. Thus, it would be of great benefit to be able to predict the velocities from other data that is more readily available. In this work, we utilize fuzzy c‐means clustering to build a “fuzzy” relationship between sonic velocities and other petrophysical borehole data to predict P‐wave and S‐wave velocity. If boreholes with sonic data intersect most of the important geological units in the area of interest, then the cluster model developed may be applied to other boreholes that do not have sonic data, but do have other petrophysical data to be used for predicting the sonic logs. These predicted sonic logs may then be used to create a three‐dimensional volume of velocity with greater detail than would otherwise be created by the interpolation of measured sonic data from sparsely located holes. Our methodology was tested on a dataset from the Kevitsa Ni‐Cu‐PGE deposit in northern Finland. The dataset includes five boreholes with wireline logs of P‐wave velocity, S‐wave velocity, density, natural gamma, magnetic susceptibility and resistivity that were used for cluster analysis. The best combination of input data for the training section was chosen by trial and error, but differences in the misfit between the various training datasets were not particularly significant. Our results show that the fuzzy c‐means method can predict sonic velocities from other borehole data very well, and the fuzzy c‐means method works better than using multiple linear‐regression fitting. The predicted P‐wave velocity data are of sufficient quality to robustly add low‐frequency information for seismic impedance inversion and should provide better velocity models for accurate depth conversion of seismic reflection data.

Description: ABSTRACT This paper reviews the impacts of new satellite altimeter data sets and new technology on the production of satellite gravity. It considers the contribution of the increased data volume, the application of new altimeter acquisition technology and the potential for future developments. Satellite altimeter derived gravity has provided gravity maps of the world's seas since the 1980s, but, from 1995 to 2010, virtually all improvements were in the processing as there were no new satellite data with closely spaced tracks. In recent years, new data from CryoSat‐2 (launched in 2010) and the geodetic mission of Jason‐1 (2012–2013) have provided a wealth of additional coverage and new technology allows further improvements. The synthetic aperture radar mode of CryoSat‐2 uses a scanning approach to limit the size of the altimeter sea surface footprint in the along‐track direction. Tests indicate that this allows reliable data to be acquired closer to coastlines. The synthetic aperture radar interferometric mode of CryoSat‐2 uses two altimeters to locate sea‐surface reflection points laterally away from the satellite track. In a study to generate gravity for freshwater lakes, this mode is found to be valuable in extending the available satellite coverage. The AltiKa altimeter uses higher frequency radar to provide less noisy sea‐surface signals and its new orbit mode gives potential for further improvements in satellite gravity. Future developments include the potential for swath mapping to provide further gravity improvements.

Description: ABSTRACT Deghosting of pressure‐only data has become a routine in marine seismic processing. Most existing techniques suffer from noise susceptibility or excessive simplification of the used ghost model, which leads to difficulties in removing the ghost waves. The algorithm presented in this paper is based on the wavefield extrapolation theory, and is capable of taking into account arbitrary streamer shapes and rough sea surfaces. The computations are performed in the frequency domain and come down to solving systems of linear equations. Regularization and data‐adaptive statistical optimization of the parameters prevent noise amplification. We describe the theory of the method and test it against synthetic and field datasets with different streamer shapes for both rough and flat sea surfaces.

Description: ABSTRACT Part one of this paper reported results from experimental compaction measurements of unconsolidated natural sand samples with different mineralogical compositions and textures. The experimental setup was designed with several cycles of stress loading and unloading applied to the samples. The setup was aimed to simulate a stress condition where sediments underwent episodes of compaction, uplift and erosion. P‐wave and S‐wave velocities and corresponding petrophysical (porosity and density) properties were reported. In this second part of the paper, rock physics modelling utilizing existing rock physics models to evaluate the model validity for measured data from part one were presented. The results show that a friable sand model, which was established for normally compacted sediments is also capable of describing overconsolidated sediments. The velocity–porosity data plotted along the friable sand lines not only describe sorting deterioration, as has been traditionally explained by other studies, but also variations in pre‐consolidation stress or degree of stress release. The deviation of the overconsolidated sands away from the normal compaction trend on the VP/VS and acoustic impedance space shows that various stress paths can be predicted on this domain when utilizing rock physics templates. Fluid saturation sensitivity is found to be lower in overconsolidated sands compared to normally consolidated sands. The sensitivity decreases with increasing pre‐consolidation stress. This means detectability for four‐dimensional fluid saturation changes can be affected if sediments were pre‐stressed and unloaded. Well log data from the Barents Sea show similar patterns to the experimental sand data. The findings allow the development of better rock physics diagnostics of unloaded sediments, and the understanding of expected 4D seismic response during time‐lapse seismic monitoring of uplifted basins. The studied outcomes also reveal an insight into the friable sand model that its diagnostic value is not only for describing sorting microtextures, but also pre‐consolidation stress history. The outcome extends the model application for pre‐consolidation stress estimation, for any unconsolidated sands experiencing similar unloading stress conditions to this study.

Description: ABSTRACT If there are some erratic data (e.g. outliers), which may arise from measurement error, or other reasons, in seismic data, the seismic deconvolution and inversion need to be implemented in a way that minimizes their effects. However, the deconvolution and inversion methods based on L2‐norm misfit function are highly sensitive to these erratic seismic observations. As an alternative, L1‐norm misfit functions are more robust and erratic‐resistant. In order to find the solution of the inverse problem constrained by an L1‐norm misfit function, an iteratively re‐weighted least squares algorithm is used frequently. However, it is relatively time consuming. In this paper, we propose a new method based on the sparse signal representation theory. The overcomplete dictionary used for the sparse representation of seismic data with erratic data is composed of two bases: a wavelet basis used for representing the seismic data to implement deconvolution and a Dirac basis used for representing the erratic data. In addition, at the stage of seismic inversion after deconvolution, total variation and a priori model are used as the regularization constraint terms to estimate inversion results with a blocky and laterally continuous structure. The new method is successfully tested on the noisy synthetic seismic data with erratic data. Finally, the proposed method is performed on a real seismic data section, and the inversion results are reasonable, i.e. consistent with the geologic structure of the original seismic data. Compared to the conventional sparse deconvolution and inversion method, the proposed method not only eliminates the effect of outliers, but also has highly improved computational efficiency.

Description: ABSTRACT Nowadays, full‐waveform inversion, based on fitting the measured surface data with modelled data, has become the preferred approach to recover detailed physical parameters from the subsurface. However, its application is computationally expensive for large inversion domains. Furthermore, when the subsurface has a complex geological setting, the inversion process requires an appropriate pre‐conditioning scheme to retrieve the medium parameters for the desired target area in a reliable manner. One way of dealing with both aspects is by waveform inversion schemes in a target‐oriented fashion. Therefore, we propose a prospective application of the convolution‐type representation for the acoustic wavefield in the frequency–space domain formulated as a target‐oriented waveform inversion method. Our approach aims at matching the observed and modelled upgoing wavefields at a target depth level in the subsurface, where the seismic wavefields, generated by sources distributed above this level, are available. The forward modelling is performed by combining the convolution‐type representation for the acoustic wavefield with solving the two‐way acoustic wave‐equation in the frequency–space domain for the target area. We evaluate the effectiveness of our inversion method by comparing it with the full‐domain full‐waveform inversion process through some numerical examples using synthetic data from a horizontal well acquisition geometry, where the sources are located at the surface and the receivers are located along a horizontal well at the target level. Our proposed inversion method requires less computational effort and, for this particular acquisition, it has proven to provide more accurate estimates of the target zone below a complex overburden compared to both full‐domain full‐waveform inversion process and local full‐waveform inversion after applying interferometry by multidimensional deconvolution to get local‐impulse responses.

Description: ABSTRACT This paper aims at analysing the application of the gravimetric method in the search for copper ore in the Valley of Curaçá River in northern Bahia, Brazil. The area where this study was carried out is known as Angico Farm, one of the claims of Caraíba S.A., a copper producer in the northern Bahia, Brazil. There are 18 drill holes at the Angico Farm target, drilled in order to investigate the mineralizations in depth. We have obtained information such as geographic coordinates and chemical results from the company in order to test the geophysical response and the correlation with geology. A 3D inverse gravimetric model was generated in order to verify the validity of the method in exploring for copper ore associated with hydrothermally altered mafic and ultramafic. Both mafic/ultramafic rocks and copper ore present high density, therefore the gravity method may not be effective for identification. We have shown, however, that copper ore from the Curaçá Valley presents a fairly good gravity response, and 3D inverse mathematical model pointed out a well‐delimited copper orebody in the regions where drill holes intersect the ore and coincide with the positive gravity anomaly. The ore contents were overlapped on cross‐sections of density extracted from the inverse model and such information helped us to check out the consistency of the gravimetric method in mapping and modelling mineralized bodies associated with mineral occurrence. Additionally, magnetic susceptibility and gammaspectrometric data were acquired along 18 drillcores to investigate their possible correlation with orebodies.

Description: ABSTRACT Electrical anisotropy in earth media increases the complexity of magnetotelluric responses. Magnetotelluric models based on anisotropic media must be developed to fully understand observed data. This paper presents a three‐dimensional algorithm for calculating magnetotelluric responses of arbitrary anisotropic media in the frequency domain. Using a staggered‐grid finite difference method, the model space is discretized into rectangular blocks with electric fields on the edges of each block and the magnetic fields normal to the faces of each block. The electric field Helmholtz vector equation that considers a full 3 × 3 conductivity tensor is calculated numerically under two orthogonal polarizations. In calculating the boundary values on the four sides of the three‐dimensional anisotropic model, we adopt different procedures for calculating the two‐dimensional responses on the sides in the x and y directions. The responses for a layered anisotropic model and a three‐dimensional isotropic model calculated with this algorithm are compared with the corresponding analytical and numerical solutions, respectively. The comparisons show that the algorithm's approximations are highly precise for a wide frequency band. A typical two‐dimensional anisotropic model and a general three‐dimensional anisotropic model were also constructed, and their responses were calculated. These anisotropic models have ordinary structures but can produce phase rolling out of quadrant magnetotelluric responses, which indicates that considering electrical anisotropy may improve our interpretation of observed data. Using this algorithm, we can model the observed data from the northern Qaidam Basin in northern Tibet, where ultrahigh‐pressure metamorphic rocks are exposed along an old suture, and seismic anisotropy was indicated in neighbouring areas. The phase tensors of the magnetotelluric sites at this location show large skew angles, and the corresponding phase splits are distinct in the off‐diagonal impedance elements. Although the isotropic three‐dimensional electrical structure can model the profile data well, the structure shows a sequence of conductive and resistive bodies in the mid‐lower crust of the north Qaidam Basin, which is very spatially inhomogeneous, and a simple intrinsic anisotropic body can also produce similar surficial responses. Using the three‐dimensional anisotropic algorithm, we found an equivalent anisotropic replacement for this area. The results of the three‐dimensional anisotropy modelling of the magnetotelluric data from the northern Tibetan Plateau show the valuable applicability of the three‐dimensional anisotropic algorithm in testing the qualitative presumption of electrical anisotropy.

Description: ABSTRACT Pore structure heterogeneity is a critical parameter controlling mechanical, electrical and flow transport behaviour of rock. Multi‐fractal analysis method was used for a heterogeneity comparison of three‐dimensional rock samples with different lithology. Six real digital samples, containing three sandstones and three carbonates, were used. Based on the mercury injection capillary pressure test on these samples, we found that the carbonate samples are more heterogeneous than sandstones, but primary results of multi‐fractal behaviours for all samples were similar. We show that if multi‐fractal is used to evaluate and compare heterogeneity of different samples, one needs to follow some considerations such as (1) all samples must have the same size in pixel, (2) samples volume must be bigger than representative volume element, (3) multi‐fractal dimensions should be firstly normalized to a determined porosity value and (4) multi‐fractal results should be interpreted based on resolution of the imaging tool (effects of fine scale sub‐resolution pores are missed). Results revealed that using normalized fractal dimensions, the real samples were divided to less and high heterogeneous groups. Moreover, the study of scale effect also showed that porous structures of these samples are scale invariant in a wide range of scales (from one to eight times bigger).

Description: ABSTRACT Machine learning methods including support‐vector‐machine and deep learning are applied to facies classification problems using elastic impedances acquired from a Paleocene oil discovery in the UK Central North Sea. Both of the supervised learning approaches showed similar accuracy when predicting facies after the optimization of hyperparameters derived from well data. However, the results obtained by deep learning provided better correlation with available wells and more precise decision boundaries in cross‐plot space when compared to the support‐vector‐machine approach. Results from the support‐vector‐machine and deep learning classifications are compared against a simplified linear projection based classification and a Bayes‐based approach. Differences between the various facies classification methods are connected by not only their methodological differences but also human interactions connected to the selection of machine learning parameters. Despite the observed differences, machine learning applications, such as deep learning, have the potential to become standardized in the industry for the interpretation of amplitude versus offset cross‐plot problems, thus providing an automated facies classification approach.

Description: ABSTRACT CO2 saturations are estimated at Sleipner using a two‐step imaging workflow. The workflow combines seismic tomography (full‐waveform inversion) and rock physics inversion and is applied to a two‐dimensional seismic line located near the injection point at Sleipner. We use baseline data (1994 vintage, before CO2 injection) and monitor data that was acquired after 12 years of CO2 injection (2008 vintage). P‐wave velocity models are generated using the Full waveform inversion technology and then, we invert selected rock physics parameters using an rock physics inversion methodology. Full waveform inversion provides high‐resolution P‐wave velocity models both for baseline and monitor data. The physical relations between rock physics properties and acoustic wave velocities in the Utsira unconsolidated sandstone (reservoir formation) are defined using a dynamic rock physics model based on well‐known Biot–Gassmann theories. For data prior to injection, rock frame properties (porosity, bulk and shear dry moduli) are estimated using rock physics inversion that allows deriving physically consistent properties with related uncertainty. We show that the uncertainty related to limited input data (only P‐wave velocity) is not an issue because the mean values of parameters are correct. These rock frame properties are then used as a priori constraint in the monitor case. For monitor data, the Full waveform inversion results show nicely resolved thin layers of CO2–brine saturated sandstones under intra‐reservoir shale layers. The CO2 saturation estimation is carried out by plugging an effective fluid phase in the rock physics model. Calculating the effective fluid bulk modulus of the brine–CO2 mixture (using Brie equation in our study) is shown to be the key factor to link P‐wave velocity to CO2 saturation. The inversion tests are done with several values of Brie/patchiness exponent and show that the CO2 saturation estimates are varying between 0.30 and 0.90 depending on the rock physics model and the location in the reservoir. The uncertainty in CO2 saturation estimation is usually lower than 0.20. When the patchiness exponent is considered as unknown, the inversion is less constrained and we end up with values of exponent varying between 5 and 20 and up to 33 in specific reservoir areas. These estimations tend to show that the CO2–brine mixing is between uniform and patchy mixing and variable throughout the reservoir.

Description: ABSTRACT Kirchhoff prestack time migration, which works trace‐by‐trace, remains appealing to academia and industry due to its robustness and efficiency. However, like the other prestack migration methods, Kirchhoff prestack time migration also suffers from the angle‐dependent stretching effect, which narrows the amplitude spectra of seismic data. This effect gets more severe as the incident angle increases. In this paper, we propose a novel approach, which attaches a prediction shaping filter to the Kirchhoff prestack time migration, to mitigate the stretching effect. Our approach takes advantage on the trace‐by‐trace implementation of the prestack time migration algorithm, without the output of the angle‐domain common‐imaging gather. Also, our method can cascade with Q‐compensation in prestack time migration. We demonstrate our method with both a numerical example and a field data example.

Description: ABSTRACT Fluid conductivity and elastic properties in fractures depend on the aperture geometry – in particular, the roughness of fracture surfaces. In this study, we have characterized the surface roughness with a log‐normal distribution and investigated the transport and flow behaviour of the fractures with varying roughness characteristics. Numerical flow and transport simulations have been performed on a single two‐dimensional fracture surface, whose aperture geometry changes with different variances and correlation lengths in each realization. We have found that conventional measurement of hydraulic conductivity alone is insufficient to determine these two parameters. Transient transport measurements, such as the particle breakthrough time, provide additional constraints to the aperture distribution. Nonetheless, a unique solution to the fracture aperture distribution is still under‐determined with both hydraulic conductivity and transport measurements. From numerical simulations at different compression states, we have found that the flow and transport measurements exhibit different rates of changes with respect to changes in compression. Therefore, the fracture aperture distribution could be further constrained by considering the flow and transport properties under various compression states.

Description: ABSTRACT Obtaining an accurate image of the subsurface still remains a great challenge for the seismic method. Migration algorithms aim mainly on positioning seismic events in complex geological contexts. Multiple reflections are typically not accounted for in this process, which can lead to the emergence of artefacts. In Marchenko imaging, we retrieve the complete up‐ and downgoing wavefields in the subsurface to construct an image without such artefacts. The quality of this image depends on the type of imaging condition that is applied. In this paper, we propose an imaging condition that is based on stabilized unidimensional deconvolution. This condition is computationally much cheaper than multidimensional deconvolution, which has been proposed for Marchenko imaging earlier. Two specific approaches are considered. In the first approach, we use the full up‐ and downgoing wavefields for deconvolution. Although this leads to balanced and relatively accurate amplitudes, the crosstalk is not completely removed. The second approach is to incorporate the initial focussing function in the deconvolution process, in such a way that the retrieval of crosstalk is avoided. We compare images with the results of the classical cross‐correlation imaging condition, which we apply to reverse‐time migrated wavefields and to the up‐ and downgoing wavefields that are retrieved by the Marchenko method.

Description: ABSTRACT Random noise attenuation, preserving the events and weak features by improving signal‐to‐noise ratio and resolution of seismic data are the most important issues in geophysics. To achieve this objective, we proposed a novel seismic random noise attenuation method by building a compound algorithm. The proposed method combines sparsity prior regularization based on shearlet transform and anisotropic variational regularization. The anisotropic variational regularization which is based on the linear combination of weighted anisotropic total variation and anisotropic second‐order total variation attenuates noises while preserving the events of seismic data and it effectively avoids the fine‐scale artefacts due to shearlets from the restored seismic data. The proposed method is formulated as a convex optimization problem and the split Bregman iteration is applied to solve the optimization problem. To verify the effectiveness of the proposed method, we test it on several synthetic seismic datasets and real datasets. Compared with three methods (the linear combination of weighted anisotropic total variation and anisotropic second‐order total variation, shearlets and shearlet‐based weighted anisotropic total variation), the numerical experiments indicate that the proposed method attenuates random noises while alleviating artefact and preserving events and features of seismic data. The obtained result also confirms that the proposed method improves the signal‐to‐noise ratio.

Description: ABSTRACT Understanding how physical properties and seismic signatures of present day rocks are related to ancient geological processes is important for enhanced reservoir characterization. In this paper, we have studied this relationship for the Kobbe Formation sandstone in the Barents Sea. These rocks show anomalous low shear velocities and high VP/VS ratios, which does not agree well with conventional rock physics models for moderately to well consolidated sandstones. These sandstones have been buried relatively deeply and subsequently uplifted 1–2 km. We compared well log data of the Kobbe sandstone with velocity–depth trends modelled by integrating basin modelling principles and rock physics. We found that more accurate velocity predictions were obtained when first honouring mechanical and chemical compaction during burial, followed by generation of micro‐cracks during uplift. We suspect that these micro‐cracks are formed as overburden is eroded, leading to changes in the subsurface stress‐field. Moreover, the Kobbe Formation is typically heterogeneous and characterized by structural clays and mica that can reduce the rigidity of grain contacts. By accounting for depositional and burial history, our velocity predictions become more consistent with geophysical observables. Our approach yields more robust velocity predictions, which are important in prospect risking and net erosion estimates.

Description: Geophysical Prospecting, Volume 66, Issue 8, Page 1439-1440, October 2018. 〈br/〉

Description: ABSTRACT Knowledge of hydraulic parameters (hydraulic conductivity and transmissivity) is essential for the delineation of groundwater potential zones. Conventionally, these parameters are measured using pumping tests carried out on boreholes. However, pumping tests are costly, labour intensive and require a considerable amount of equipment. The integration of geophysical methods with pumping tests provides efficient and cost‐effective alternative to calculate hydraulic parameters. Fifty electrical resistivity soundings were carried out in the study area using Schlumberger inter‐electrode configuration to obtain hydraulic characteristics that are estimated through the pumping tests. To apply this approach successfully, sufficient number of boreholes are used. Part of the boreholes, in which pumping tests were carried out, is used for both to constrain resistivity inversions and to establish the empirical relationship between the interpreted geophysical and hydraulic parameters. The rest of the boreholes without pumping tests are still used for constraining the inversions. Initially, aquifer parameters were measured using pumping tests at 12 water wells. Afterwards, transmissivity (T) and hydraulic conductivity (K) were correlated with transverse resistance (Tr) and the bulk resistivity (ρo) of the aquifer at other sites where pumping tests had not been conducted. In this way, the entire study area was covered to assess the groundwater reserves. The hydraulic properties obtained by the geophysical method fit pretty well to both the pumping and physicochemical data of the investigated area. The integrated study reveals five layers (i.e. topsoil, clay, clay sand, sand and gravel sand) and three potential zones (i.e. high, medium and low potential aquifer zones) with specific ranges of T, K, Tr and ρo. The results suggest that, in case of sparse well data, the aquifer parameters can be estimated using the relations depending on the specifications of the area.

Description: ABSTRACT A review and analysis of post‐stack time‐lapse time‐shifts has been carried out that covers published literature supplemented by in‐house datasets available to the authors. Time‐shift data are classified into those originating from geomechanical effects and those due to fluid saturation changes. From these data, conclusions are drawn regarding the effectiveness of post‐stack time‐shifts for overburden and reservoir monitoring purposes. A variety of field examples are shown that display the range and magnitude of variation for each class of application. The underlying physical mechanisms creating these time‐shifts are then described, and linked to a series of generic and field‐specific rock physics calculations that predict their magnitudes. These calculations serve as a guide for practitioners wishing to utilize this information on their own datasets. Conclusions are drawn regarding the reliability of this attribute for monitoring purposes, and the extent to which further development is required and how it should be reported by authors.

Description: ABSTRACT This paper presents, in a tutorial form, some analytical inversion techniques for the Goupillaud‐layered earth model. Finding the reflection coefficients from the reflection seismogram is the inverse problem for the model. For this reason we present a thorough description of the inverse problem for the Goupillaud model, two solutions to solve the inverse scattering problem using linear discrete equations and the solution obtained using the classic dynamic deconvolution method. The inversion is achieved using Robinson's polynomials Pk(z), Qk(z), Ak(z) and their reverse polynomials, as well as some properties of the model (the Lorentz transformation and the Einstein subtraction formula). The method of dynamic deconvolution, which makes the inversion of the model very simple computationally, is based on the physical structure of the reflection seismogram. We present the classic dynamic deconvolution algorithm for the non‐free‐surface Goupillaud model to show that the dynamic deconvolution method can provide efficient discrete procedures for the inversion. For this reason, though the inverse dynamic deconvolution procedures are old algorithms, they could be useful today for solving inverse scattering problems arising in exploration geophysics and various fields.

Description: ABSTRACT Quantifying the effects of pore‐filling materials on elastic properties of porous rocks is of considerable interest in geophysical practice. For rocks saturated with fluids, the Gassmann equation is proved effective in estimating the exact change in seismic velocity or rock moduli upon the changes in properties of pore infill. For solid substance or viscoelastic materials, however, the Gassmann theory is not applicable as the rigidity of the pore fill (either elastic or viscoelastic) prevents pressure communication in the pore space, which is a key assumption of the Gassmann equation. In this paper, we explored the elastic properties of a sandstone sample saturated with fluid and solid substance under different confining pressures. This sandstone sample is saturated with octadecane, which is a hydrocarbon with a melting point of 28°C, making it convenient to use in the lab in both solid and fluid forms. Ultrasonically measured velocities of the dry rock exhibit strong pressure dependency, which is largely reduced for the filling of solid octadecane. Predictions by the Gassmann theory for the elastic moduli of the sandstone saturated with liquid octadecane are consistent with ultrasonic measurements, but underestimate the elastic moduli of the sandstone saturated with solid octadecane. Our analysis shows that the difference between the elastic moduli of the dry and solid‐octadecane‐saturated sandstone is controlled by the squirt flow between stiff, compliant, and the so‐called intermediate pores (with an aspect ratio larger than that of compliant pore but much less than that of stiff pores). Therefore, we developed a triple porosity model to quantify the combined squirt flow effects of compliant and intermediate pores saturated with solid or viscoelastic infill. Full saturation of remaining stiff pores with solid or viscoelastic materials is then considered by the lower embedded bound theory. The proposed model gave a reasonable fit to the ultrasonic measurements of the elastic moduli of the sandstone saturated with liquid or solid octadecane. Comparison of the predictions by the new model to other solid substitution schemes implied that accounting for the combined effects of compliant and intermediate pores is necessary to explain the solid squirt effects.

Description: ABSTRACT The Sierra Grande region in northern Patagonia is considered the largest iron ore reserve in Argentina; however, the extension of the non‐outcropping deposits as well as the depth of the basins that contain them remains unknown. Utilizing 3D litho‐constrained inversion of gravity and magnetic data, we delimited an area with good prospects for iron ore deposits. In this region, high‐resolution magnetic and self‐potential profiles were acquired over the most important anomalies. Correlating both methodologies, it was possible to specify the possible existence of iron oxides (martite–hematite) in the form of 2D inclined sheets.

Description: ABSTRACT In reverse time migration, we can produce angle‐domain common‐imaging gathers in either the scattering‐angle domain or the dip‐angle domain. The latter, although not used as widely as the former, still provides a unique view to look into seismic imaging. The reverse time migration dip‐angle angle‐domain common‐image gather can be computed via the subsurface offset extension, which is a bit costly in storage. We here obtain dip‐angle angle‐domain common‐imaging gathers efficiently in acoustic reverse time migration by using the normalized Poynting vectors. Poynting vector, an indicator of the directional energy flux, is easy to compute during wavefield propagation. Similar to the subsurface‐offset method, our method also has dip‐angle angle‐domain common‐imaging gathers of blocky horizontal coherence. In the theory of local semblance analysis, the signal with better horizontal coherence has a higher semblance score, and vice versa. Based on the estimated semblance scores, we can thus design a specularity filter to preserve valid signals and suppress noises. We validate our method with two data sets. Both the Marmousi data and the real data show that our method works effectively in eliminating noises and enhancing resolution in the acoustic reverse time migration imaging.

Description: ABSTRACT Shales play an important role in many engineering applications such as nuclear waste, CO2 storage and oil or gas production. Shales are often utilized as an impermeable seal or an unconventional reservoir. For both situations, shales are often studied using seismic waves. Elastic properties of shales strongly depend on their hydration, which can lead to substantial structural changes. Thus, in order to explore shaly formations with seismic methods, it is necessary to understand the dependency of shale elastic properties on variations in hydration. In this work, we investigate structural changes in Opalinus shale at different hydration states using laboratory measurements and X‐ray micro‐computed tomography. We show that the shale swells with hydration and shrinks with drying with no visible damage. The pore space of the shale deforms, exhibiting a reduction in the total porosity with drying and an increase in the total porosity with hydration. We study the elastic properties of the shale at different hydration states using ultrasonic velocities measurements. The elastic moduli of the shale show substantial changes with variations in hydration, which cannot be explained with a single driving mechanism. We suggest that changes of the elastic moduli with variations in hydration are driven by multiple competing factors: (1) variations in total porosity, (2) substitution of pore‐filling fluid, (3) change in stiffness of contacts between clay particles and (4) chemical hardening/softening of clay particles. We qualitatively and quantitatively analyse and discuss the influence of each of these factors on the elastic moduli. We conclude that depending on the microstructure and composition of a particular shale, some of the factors dominate over the others, resulting in different dependencies of the elastic moduli on hydration.

Description: ABSTRACT Seismic time‐lapse surveys are susceptible to repeatability errors due to varying environmental conditions. To mitigate this problem, we propose the use of interferometric least‐squares migration to estimate the migration images for the baseline and monitor surveys. Here, a known reflector is used as the reference reflector for interferometric least‐squares migration, and the data are approximately redatumed to this reference reflector before imaging. This virtual redatuming mitigates the repeatability errors in the time‐lapse migration image. Results with synthetic and field data show that interferometric least‐squares migration can sometimes reduce or eliminate artifacts caused by non‐repeatability in time‐lapse surveys and provide a high‐resolution estimate of the time‐lapse change in the reservoir.

Description: ABSTRACT Seismic attenuation mechanisms receive increasing attention for the characterization of fractured formations because of their inherent sensitivity to the hydraulic and elastic properties of the probed media. Attenuation has been successfully inferred from seismic data in the past, but linking these estimates to intrinsic rock physical properties remains challenging. A reason for these difficulties in fluid‐saturated fractured porous media is that several mechanisms can cause attenuation and may interfere with each other. These mechanisms notably comprise pressure diffusion phenomena and dynamic effects, such as scattering, as well as Biot's so‐called intrinsic attenuation mechanism. Understanding the interplay between these mechanisms is therefore an essential step for estimating fracture properties from seismic measurements. In order to do this, we perform a comparative study involving wave propagation modelling in a transmission set‐up based on Biot's low‐frequency dynamic equations and numerical upscaling based on Biot's consolidation equations. The former captures all aforementioned attenuation mechanisms and their interference, whereas the latter only accounts for pressure diffusion phenomena. A comparison of the results from both methods therefore allows to distinguish between dynamic and pressure diffusion phenomena and to shed light on their interference. To this end, we consider a range of canonical models with randomly distributed vertical and/or horizontal fractures. We observe that scattering attenuation strongly interferes with pressure diffusion phenomena, since the latter affect the elastic contrasts between fractures and their embedding background. Our results also demonstrate that it is essential to account for amplitude reductions due to transmission losses to allow for an adequate estimation of the intrinsic attenuation of fractured media. The effects of Biot's intrinsic mechanism are rather small for the models considered in this study.

Description: ABSTRACT A constrained 3D density model of the upper crust along a part of the Deccan Syneclise is carried out based on the complete Bouguer anomaly data. Spectral analysis of the complete Bouguer gravity anomaly map of the study region suggests two major sources: short wavelength anomalies (〈100 km) caused primarily due to the density inhomogeneities at shallow crustal level and long wavelength anomalies (〉100 km) produced due to the sources deeper than the upper crust. A residual map of the short wavelength anomalies is prepared from the complete Bouguer anomaly using Butterworth high‐pass filter (100 km cut‐off wavelength). Utilizing the constraints from deep resistivity sounding, magnetotellurics and deep seismic sounding studies, 2.5D density models have been generated along 39 profiles of this region. The mismatch between the calculated response of the a priori 2.5D model with the residual (short wavelength) gravity anomalies is minimized by introducing high‐density intrusive bodies (≥2.81 g/cm3) in the basement. With these 2.5D density models, the initial geometry of our 3D density model, which includes alluvium, Deccan trap, Mesozoic sediment and high‐density intrusive bodies in the basement up to a depth of 7 km (upper crust), is generated. In the final 3D model, Deccan trap extends from 200 m to nearly 1700 m below the 90–150 m thick Quaternary sediment. Further down, the sub‐trappean Mesozoic sediment is present at a depth range of 600–3000 m followed by the basement. The derived 3D density model also indicates six intrusive bodies of density 2.83 g/cm3 in the basement at an average depth of about 4–7 km that best fits the residual gravity anomaly of the study area.

Description: ABSTRACT Selecting a seismic time‐to‐depth conversion method can be a subjective choice that is made by geophysicists, and is particularly difficult if the accuracy of these methods is unknown. This study presents an automated statistical approach for assessing seismic time‐to‐depth conversion accuracy by integrating the cross‐validation method with four commonly used seismic time‐to‐depth conversion methods. To showcase this automated approach, we use a regional dataset from the Cooper and Eromanga basins, Australia, consisting of 13 three‐dimensional (3D) seismic surveys, 73 two‐way‐time surface grids and 729 wells. Approximately 10,000 error values (predicted depth vs. measured well depth) and associated variables were calculated. The average velocity method was the most accurate overall (7.6 m mean error); however, the most accurate method and the expected error changed by several metres depending on the combination and value of the most significant variables. Cluster analysis tested the significance of the associated variables to find that the seismic survey location (potentially related to local geology (i.e. sedimentology, structural geology, cementation, pore pressure, etc.), processing workflow, or seismic vintage), formation (potentially associated with reduced signal‐to‐noise with increasing depth or the changes in lithology), distance to the nearest well control, and the spatial location of the predicted well relative to the existing well data envelope had the largest impact on accuracy. Importantly, the effect of these significant variables on accuracy were found to be more important than choosing between the four methods, highlighting the importance of better understanding seismic time‐to‐depth conversions, which can be achieved by applying this automated cross‐validation method.

Description: ABSTRACT The Tobago Basin, which is located offshore northern Venezuela with a southern margin close to Trinidad and Tobago, has an area of approximately 59,600 km2. The Tobago Basin has relatively favourable hydrocarbon prospects, and to date, exploration work has mainly concentrated on small areas of the southwestern portion of the basin. To conduct a comprehensive study of the structural framework of the basin and the characteristics of the basement in order to identify prospective zones for hydrocarbon exploration, shipborne‐measured and satellite‐measured gravity data, shipborne‐measured magnetic data, and aeromagnetic survey data were analysed. A regularisation filtering method was used to separate and obtain regional and residual gravity and magnetic anomalies. Directional gradients of gravity and magnetic anomalies and the total horizontal gradient and vertical second derivative of gravity anomalies were employed to extract information about fault structures. Regression analysis methods were used to determine the basement depth. The geological significance of the gravity and magnetic fields was examined, the structural framework of the basin was assessed, the basement depth was estimated, and favourable hydrocarbon exploration prospects within the basin were identified. The results show that the Tobago Basin contains complex structures consisting mainly of two groups of faults trending in northeasterly and northwesterly directions and that the major northeasterly trending faults control the main structural configuration and depositional system within the basin. The basement of the Tobago Basin has deep rises and falls. It can be divided into the following four secondary tectonic units: the western sub‐basin, the central uplift area, the southern sub‐basin, and the northeastern sub‐basin. The central uplift area and northeastern sub‐basin are most likely to have developed hydrocarbon accumulations and should be targeted for further exploration.

Description: ABSTRACT Although narrow‐azimuth towed‐streamer data provide good image quality for structural interpretation, it is generally accepted that for wide‐azimuth marine surveys seabed receivers deliver superior seismic reflection measurements and seismically derived reservoir attributes. However, seabed surveys are not widely used due to the higher acquisition costs when compared to streamer acquisition. In recent years, there have been significant engineering efforts to automate receiver deployment and retrieval in order to minimize the cost differential and conduct cost‐efficient seabed receiver seismic surveys. These engineering efforts include industrially engineered nodes, nodes on a rope deployment schemes and even robotic nodes, which swim to and from the deployment location. This move to automation is inevitable, leading to robotization of seismic data acquisition for exploration and development activities in the oil and gas industry. We are developing a robotic‐based technology, which utilizes autonomous underwater vehicles as seismic sensors without the need of using a remotely operated vehicle for deployment and retrieval. In this paper, we describe the autonomous underwater vehicle evolution throughout the project years from initial heavy and bulky nodes to fully autonomous light and flexible underwater receivers. Results obtained from two field pilot tests using different generations of autonomous underwater vehicles indicate that the seismic coupling, and navigation based on underwater acoustics are very reliable and robust.

Description: ABSTRACT Eikonal solvers often have stability problems if the velocity model is mildly heterogeneous. We derive a stable and compact form of the eikonal equation for P‐wave propagation in vertical transverse isotropic media. The obtained formulation is more compact than other formulations and therefore computationally attractive. We implemented ray shooting for this new equation through a Hamiltonian formalism. Ray tracing based on this new equation is tested on both simple as well as more realistic mildly heterogeneous velocity models. We show through examples that the new equation gives travel times that coincide with the travel time picks from wave equation modelling for anisotropic wave propagation.

Description: ABSTRACT The injection of CO2 at the Ketzin pilot site commenced in June 2008 and was terminated in August 2013 after 67 kT had been injected into a saline formation at a depth of 630–650 m. As part of the site monitoring program, four 3D surface seismic surveys have been acquired to date, one baseline and three repeats, of which two were conducted during the injection period, and one during the post‐injection phase. The surveys have provided the most comprehensive images of the spreading CO2 plume within the reservoir layer. Both petrophysical experiments on core samples from the Ketzin reservoir and spectral decomposition of the 3D time‐lapse seismic data show that the reservoir pore pressure change due to CO2 injection has a rather minor impact on the seismic amplitudes. Therefore, the observed amplitude anomaly is interpreted to be mainly due to CO2 saturation. In this study, amplitude versus offset analysis has been applied to investigate the amplitude versus offset response from the top of the sandstone reservoir during the injection and post‐injection phases, and utilize it to obtain a more quantitative assessment of the CO2 gaseous saturation changes. Based on the amplitude versus offset modelling, a prominent decrease in the intercept values imaged at the top of the reservoir around the injection well is indeed associated solely with the CO2 saturation increase. Any change in the gradient values, which would, in case it was positive, be the only signature induced by the reservoir pressure variations, has not been observed. The amplitude versus offset intercept change is, therefore, entirely ascribed to CO2 saturation and used for its quantitative assessment. The estimated CO2 saturation values around the injection area in the range of 40%–60% are similar to those obtained earlier from pulsed neutron‐gamma logging. The highest values of 80% are found in the second seismic repeat in close vicinity to the injection and observation wells.

Description: ABSTRACT Since its introduction in the late 1950s, hydraulic vibrators have become the dominant source for land seismic surveys. The hydraulic vibrators typically used for commercial land seismic acquisition, however, are large, costly to operate and expensive to purchase. This inhibits their use for small‐scale and short‐duration surveys as well as Vibroseis research. In this paper we describe, in detail, the construction of a portable vibrator from commercially available components for a cost of less than $US2,000. Data shows that the vibrator is able to successfully transmit sweeps from 15 to 180 Hz with different spectral contents. The vibrator produces a stronger signal than a sledgehammer and we estimate its output to be around 1 kN. The frequency content of the data was concentrated at lower frequencies (〈100 Hz) and the ground‐roll was far more energetic than that produced using a sledgehammer.

Description: ABSTRACT Porosity measurement is an important step for petrophysical characterization of reservoir rocks, as porosity is essential for analysing elastic properties and estimating the capacity of rocks to hold hydrocarbon resources. Commonly used porosity measurement methods fail to work on heavy oil sands, because of the loose fragile sand frame and solid‐like irreducible heavy oil. We develop three methods to measure the porosity of heavy oil sands, which are feasible and affordable in most laboratories. Method 1 involves calculating the bulk volume of the sample by measuring its physical dimensions directly. Method 2 uses calibrated sample weight and volume (after removing the protecting foil cover and metal clips). Method 3 first applies pressurizing on samples and then measures the weight and volume of the bare samples. The measurement results of the three methods are then compared and method 3 is determined as the most reliable, which is also verified by the porosity log. Finally, an analysis of the potential sources of errors associated with method 3 is performed.

Description: ABSTRACT The measured geophysical response of sand–shale sequences is an average over multiple layers when the tool resolution (seismic or well log) is coarser than the scale of sand–shale mixing. Shale can be found within sand–shale sequences as laminations, dispersed in sand pores, as well as load bearing clasts. We present a rock physics framework to model seismic/sonic properties of sub‐resolution interbedded shaly sands using the so‐called solid and mineral substitution models. This modelling approach stays consistent with the conceptual model of the Thomas–Stieber approach for estimating volumetric properties of shaly sands; thus, this work connects established well log data‐based petrophysical workflows with quantitative interpretation of seismic data for modelling hydrocarbon signature in sand–shale sequences. We present applications of the new model to infer thickness of sand–shale lamination (i.e., net to gross) and other volumetric properties using seismic data. Another application of the new approach is fluid substitution in sub‐resolution interbedded sand–shale sequences that operate directly at the measurement scale without the need to downscale; such a procedure has many practical advantages over the approach of “first‐downscale‐and‐then‐upscale” as it is not very sensitive to errors in estimated sand fraction and end member sand/shale properties and remains stable at small sand/shale fractions.

Description: ABSTRACT Elastic properties of an unconsolidated sand are largely dependent on the elastic properties of its constituent grain and the microstructure that defines how the grains are arranged within themselves. Coordination number, i.e. the average number of contacts a grain has with its neighbours, and contact surface area are the two parameters closely related to the microstructure. Moreover, grain shapes and sorting also have substantial influence on these parameters. To calculate these parameters and find any potential relationships with the shape factors, we acquire high resolution micro‐CT images of four mechanically compacted unconsolidated dry sand samples which are of different shape factors and sorting indices. After a comprehensive voxel based data processing, we calculate shape factors such as sphericity and roundness of each grain in all samples. Using own algorithm, we then calculate the coordination number and contact surface area. Results show that samples of well sorted and higher spherical and rounded grains have higher coordination number and contact surface area than the samples of poorly sorted and lower spherical and rounded grains. Among the poorly sorted samples, coordination number is largely dependent on the fraction of larger grain sizes present in the sample. Inside any given sample, grains of lower sphericity tend to have higher coordination numbers. Moreover, more spherical and rounded grains have greater contact surface area with their neighbors. We use the results from these four samples in our next study at Part‐2 (submitted to this issue), where our objective is to find the elastic parameters of the constituent grains after inverting ultrasonic velocity data measured through those samples following a contact based model derived using effective medium theory. This article is protected by copyright. All rights reserved

Description: ABSTRACT Time‐domain marine controlled source electromagnetic methods have been used successfully for the detection of resistive targets such as hydrocarbons, gas hydrate, or marine groundwater aquifers. As the application of time‐domain marine controlled source electromagnetic methods increases, surveys in areas with a strong seabed topography are inevitable. In these cases, an important question is whether bathymetry information should be included in the interpretation of the measured electromagnetic field or not. Since multi‐dimensional inversion is still not common in time‐domain marine controlled source electromagnetic methods, bathymetry effects on the 1D inversion of single‐offset and multi‐offset joint inversions of time‐domain controlled source electromagnetic methods data are investigated. We firstly used an adaptive finite element algorithm to calculate the time‐domain controlled source electromagnetic methods responses of 2D resistivity models with seafloor topography. Then, 1D inversions are applied on the synthetic data derived from marine resistivity models, including the topography in order to study the possible topography effects on the 1D interpretation. To evaluate the effects of topography with various steepness, the slope angle of the seabed topography is varied in the synthetic modelling studies for deep water (air interaction is absent or very weak) and shallow water (air interaction is dominant), respectively. Several different patterns of measuring configurations are considered, such as the systems adopting nodal receivers and the bottom‐towed system. According to the modelling results for deep water when air interaction is absent, the 2D topography can distort the measured electric field. The distortion of the data increases gradually with the enlarging of the topography's slope angle. In our test, depending on the configuration, the seabed topography does not affect the 1D interpretation significantly if the slope angle is less or around 10°. However, if the slope angle increases to 30° or more, it is possible that significant artificial layers occur in inversion results and lead to a wrong interpretation. In a shallow water environment with seabed topography, where the air interaction dominates, it is possible to uncover the true subsurface resistivity structure if the water depth for the 1D inversion is properly chosen. In our synthetic modelling, this scheme can always present a satisfactory data fit in the 1D inversion if only one offset is used in the inversion process. However, the determination of the optimal water depth for a multi‐offset joint inversion is challenging due to the various air interaction for different offsets.

Description: Layer double hydroxide (LDH) structure (left) and formation enthalpies vs various compositions (right). Abstract Layered aluminum double hydroxide chloride sorbents, LiCl∙Al2(OH)6.nH2O, Li‐LDH, have shown promising application in selective Li extraction from geothermal brines. Maintaining LiCl uptake capacity and retaining a long cycle life are critical to widespread application of sorbent materials. To elucidate the energetics of Li capture, enthalpies of LDH with different Li content have been measured by acid solution calorimetry. The formation enthalpies generally become less exothermic as the Li content increases, which indicates that Li intercalation destabilizes the structure, and the enthalpies seem to approach a limit after the Li content x = 2Li/Al exceeds 1. To improve stability, metal doping of the aluminum LDH structure with iron was performed. Introduction of a metal with greater electron density but a similar ionic radius was postulated to improve the stability of the LDH crystal structure. The calorimetric results from Fe‐doped LDH samples corroborate this as they are more exothermic than LDH‐lacking Fe. This suggests that Fe doping is an effective way to stabilize the LDH phase.