ALBERT

Description: Over 10 μm-thick ( K , N a) N b O 3 KNN -based films doped with complex-perovskite-materials (CPs) were deposited on platinized sapphire substrates by aerosol deposition (AD). Three CPs were selected: B a( C u 1/3 N b 2/3 ) O 3 ( BCN ), C u( C u 1/3 N b 2/3 ) O 3 ( CCN ), and S r( C u 1/3 N b 2/3 ) O 3 ( SCN ). The films of 0.985( N a 0.5 K 0.5 ) N b O 3 -0.015CPs ( KNN -CPs) were post annealed at 1050°C for 1 h in air without any serious phase decomposition. The microstructure showed abnormal grain growth due to C u-rich liquid phase. The KNN – BCN film had the largest abnormal grain size of over 10 μm, whereas the KNN – SCN film had the smallest grain size and also the smallest frequency of abnormal grains. All the films exhibited typical characteristics of ferroelectric hysteresis similar to those of the bulk materials without any leakage. The KNN – BCN films possessing the biggest abnormal grains also exhibited the highest density, piezoelectric constant, and piezoelectric voltage constant of 110 pC/N and 15.45 × 10 −3  Vm/N, respectively, which are the highest values reported so far for KNN -based films. This indicated that KNN -CPs lead-free films are suitable candidates for sensor applications.

Description: The oxide inclusion and porosity defect structures in a tantalum carbide specimen fabricated from vacuum plasma spraying with postspraying sintering and hot-isostatic pressing has been characterized. The tantalum carbide powders were obtained using a carbothermal reduction process of tantalum oxide precursors. During its fabrication, oxide-based inclusions formed from intrinsic impurities in the powder. Using serial sectioning and three-dimensional reconstruction techniques, interconnected globular oxide inclusions were revealed to be within the matrix phase and in the grain boundaries. The oxide phase was identified to be z -Ta 2 O 5 through selected area electron diffraction. The two- and three-dimensional porosity size distribution was compared and accounted for ~2% of the volume.

Description: In this study, multi-phase borosilicate-based glass-ceramics were investigated as an alternative waste form for immobilizing non-fissionable products from used nuclear fuel. Currently, borosilicate glass is the waste form selected for immobilization of this waste stream, however, the low thermal stability and solubility of MoO 3 in borosilicate glass translates into a maximum waste loading in the range 15–20 mass%. Glass-ceramics provide the opportunity to target chemically durable crystalline phases, e.g., powellite, oxyapatite, celsian, and pollucite that will incorporate MoO 3 as well as other waste components such as lanthanides, alkalis, and alkaline earths at levels twice the solubility limits of a single-phase glass. In addition a glass-ceramic could provide higher thermal stability, depending upon the properties of the crystalline and amorphous phases. Here, glass-ceramics were synthesized at waste loadings of 42, 45, and 50 mass% with the following glass additives: B 2 O 3 , Al 2 O 3 , CaO , and SiO 2 by slow-cooling from a glass melt. Glass-ceramics were characterized in terms of phase assemblage, morphology, and thermal stability. Only two of the targeted phases, powellite and oxyapatite, were observed, along with lanthanide-borosilicate and cerianite. Results of this initial investigation show promise of glass-ceramics as a potential waste form to replace single-phase borosilicate glass.

Description: The dielectric properties of a new, cubic, pyrochlore-type solid solution B i (1.6−1.08 x ) N d x T i 2 O (6.4−0.11 x ) have been studied across the compositional range 0.35 〈  x  〈 0.86. The dielectric constant (ε) of the ceramics based on the pyrochlore-type solid solution within the experimental compositional range varied from 104 to 76 at 1 MHz, whereas the dielectric losses were well below tan δ = 8 × 10 −3 . The temperature coefficient of the dielectric constant τ k for single-phase pyrochlore samples was found to be in the range between −20 and −40 ppm/K. Below room temperature dielectric relaxation phenomena were observed for all the compositions.

Description: The mechanism of core/shell formation during sintering in B a T i O 3 -based systems was studied in ( M g, Y )-doped B a T i O 3 . The effect of ball milling time on core size and shell thickness was first observed. The core size was similar irrespective of ball milling time whereas the shell thickness increased with increasing ball milling time. The measured powder size after ball milling suggested that the cores were from the larger B a T i O 3 particles and the shells formed via dissolution of smaller particles and precipitation of dissolved material, in contrast with the interpretation of the results of a previous investigation. To identify the core/shell formation mechanism, bi-layer samples with different chemical compositions, 94 B a T i O 3 –2 Y 2 O 3 –2 M g O –2 S i O 2 (mol%) ( BT – YMS ) and 98 B a T i O 3 –2 S i O 2 (mol%) ( BT – S ), and different grain sizes were prepared. The morphology of the newly formed shell layer and the shape of an {111} twin across the interface between a core and a shell confirmed that the formation mechanism of the core/shell structure during sintering is the dissolution and precipitation of material rather than solid-state diffusion of solutes into B a T i O 3 .

Description: B i 2 (( Z n 1/3 N b 2/3 ) 1− x T i x ) 2 O 7 ceramics with 0 ≤  x  ≤ 0.4 were synthesized using solid-state reaction method. The crystal structure is pure zirconolite type for the compositions with 0 ≤  x  ≤ 0.15, single weberite type for the compositions with 0.3 ≤  x  ≤ 0.4, and mixture of zirconolite and weberite for the compositions with 0.15 〈  x  〈 0.3. The weberite ceramics with only B i as the A-site cation are first reported. A possible correlation between the crystal structure transformation and T i content in system of B i 2 (( Z n 1/3 N b 2/3 ) 1− x T i x ) 2 O 7 with 0 ≤  x  ≤ 0.4 was suggested. Dielectric constant (ε), dielectric loss (tan δ) and temperature coefficient of capacitance (TCC) are ~85, ~0.001, and ~200 ppm/°C for the zirconolite solid solutions, ~140, 0.004, and between −120 and −200 ppm/°C for the weberite solid solutions, respectively, at 1 MHz. Ceramics with a near zero TCC consisting of the zirconolite and weberite phases were obtained. High ε, low tanδ, and low sintering temperatures (~950°C) make the novel ceramic system of B i 2 (( Z n 1/3 N b 2/3 ) 1− x T i x ) 2 O 7 potential dielectrics for applications in low-temperature co-fired ceramic and multiplayer ceramic capacitors.

Description: LaNbO 4 / La 3 NbO 7 and LaNbO 4 / LaNb 3 O 9 cer-cer composites were prepared by impregnating Ca -doped LaNbO 4 powder, synthesized by spray pyrolysis, with La - or Nb -precursor solutions. The sintering of the calcined powders was investigated by dilatometry, and dense composites were prepared by conventional sintering, hot pressing, and spark plasma sintering. The particle size of the starting powders was about 50 nm, and the average grain size of the dense materials ranged from 100 nm and upwards, depending on the sintering temperature, sintering procedure, and the phase composition. The unit cell parameters of LaNbO 4 showed a finite size effect and approached the cell parameters of tetragonal LaNbO 4 with decreasing crystallite size, both for the single-phase material and the composites. The minority phase ( La 3 NbO 7 or LaNb 3 O 9 ) were observed as isolated grains and accumulated at triple points and not along the grain boundaries, pointing to a large dihedral angle between the phases. The calcium-solubility in the minority phases was larger than in LaNbO 4 , which corresponds well with previous reports. The electrical conductivity of the hetero-doped materials was similar to, or lower than, that for Ca -doped LaNbO 4 .

Description: We studied the nucleation and growth of nano-sized crystals on two glass-ceramic systems: a conventional lithium-aluminosilicate (LAS) and a ( M g, Z n) spinel. We combined several techniques: in situ Small Angle Neutron Scattering (SANS), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), and laboratory X-ray diffraction (XRD). We observed by SANS, and confirmed by DSC, that during a temperature ramp, transient phenomena occur between the regions of nucleation and growth in the LAS, which do not follow classic kinetic theories. In contrast, the spinel material shows a smooth transition during the temperature ramp between the nucleation and the growth stages, and follows a more conventional growth pattern. In the spinel system the initial phase separation plays a very important role in determining the crystalline phase distribution in the glassy matrix, as crystallites are confined only in one phase.

Description: A key requirement for the use of bio scaffold is that its degradation rate matches the growth rate of target tissue. Therefore, the degradation of recently developed tailored amorphous multiporous (TAMP) scaffold of 70 SiO 2 ·30 CaO (mol%) in simulated body fluid (SBF) was studied under both static and quasi-dynamic conditions. The degradation was assessed through the dissolution of silica from the glass into SBF, while the in-vitro bioactivity was characterized by precipitation of calcium phosphate ( CaP ) on and inside the scaffold. Under static conditions, the degradation stopped due to the saturation of solution with silica in 3 days, whereas the precipitation of CaP continued. Rapid degradation and better in-vitro bioactivity was found under quasi-dynamic conditions, where the concentration gradient across the sample was maintained. The degradation followed exponential dependence on time with a half-life of 15.4 days and initial degradation rate 4.5% day −1 . The remaining samples maintained their integrity and pore structure during degradation. The degradation occurred in three distinct stages: (a) wetting stage, (b) initial degradation stage when CaP precipitation dominates, and (c) intensive degradation stage when the nanopores rupture and network dissolves. By varying the sintering parameters the nanopore structure, and hence the degradation rate, can be tailored to suit the anticipated tissue regeneration rate. With demonstrated rapid and controllable degradation and good in-vitro bioactivity, the TAMP scaffold shows promise as candidate for bone regeneration application under various conditions in the body.

Description: Traditionally, the nuclear and aerospace industries have been the main drivers behind the development of high-temperature materials. These applications demand a high degree of reliability and extensive characterization of every new material. There is a lack of experimental thermodynamic data above 1500°C even for HfO 2 , ZrO 2 , La 2 O 3 , Y 2 O 3 , and other constituents of widely used ceramic systems. Such data, as are available, were often obtained half a century ago using custom-built instruments. We review classic experimental approaches for the measurement of formation enthalpies, high-temperature enthalpy increments by the drop method, and also discuss more recent developments which include mass spectrometric measurements of vapor pressures, pulsed laser relaxation methods for heat capacity, and melting temperature determination and high-temperature oxide melt solution calorimetry in application to refractory compounds. Approaches to the experimental determination of phase diagrams at high temperature are introduced using studies of liquid immiscibility in the Zr(O) –UO 2 system as an example. Thermal analysis above 2000°C is now possible with commercially available instruments, as shown by the first experimental measurements of the phase transition and fusion enthalpies of La 2 O 3 . New results on a premelting phase transition in Y 2 O 3 in oxygen are reported from in situ synchrotron X-ray diffraction study on levitated samples.

Description: Nano-hafnium diboride powder was synthesized by boro/carborthermal reduction process of HfO 2 using a spark plasma sintering (SPS) apparatus. The agglomerated product was found to be 1–2 μm in size, which was composed with small primary particles of 100–200 nm in size. The particle size of HfO 2 played an important role to produce the nano-boride powder. In addition, the grain growth of HfB 2 could be effectively suppressed by using SPS due to the fast heating rate. The synthesized powder had a low oxygen content (~0.66 wt%). Excessive B 4 C and C were necessary during the boro/carborthermal reduction in HfO 2 process because of the volatilization of boron as a form of B 2 O 3 and the reduction in residual HfO 2 .

Description: 0.65 Pb ( Mg 1/3 Nb 2/3 ) O 3 –0.35 PbTiO 3 powder was prepared by a single-step, solid-state synthesis at 850°C. This was enabled by the controlled agglomeration of precursor particles by the change of pH in water suspensions. With the design of the contacts between the particles in the agglomerates, a phase-pure perovskite powder was synthesized from a suspension with a pH = 12.5. At the inherent pH = 11.4, the agglomerates that promote the pyrochlore formation were formed, resulting in a mixture of perovskite and pyrochlore phases after the calcination. The ceramics prepared from the suspension with pH = 12.5 were sintered to 96% of theoretical density at only 950°C, and exhibited electrical properties comparable to ceramics prepared by the columbite method, sintered at much higher temperatures. In contrast, the properties of the ceramics from the pH = 11.4 suspension were heavily deteriorated due to the presence of the pyrochlore phase and the high degree of porosity.

Description: The properties that determine the thermal shock resistance in materials are reported for porous cordierite, a leading candidate material for the fabrication of diesel particulate filters. Fracture toughness and slow crack growth tests were performed on test specimens obtained from the walls of diesel particulate filter monolithic substrates using the double-torsion test method at temperatures between 20°C and 900°C. The thermal expansion and elastic properties were characterized between 20°C and 1000°C. The role of the microstructure of porous cordierite in determining its unusual thermal expansion and elevated temperature Young's modulus and fracture toughness are discussed.

Description: Reaction-bonded silicon carbide ceramics fabricated from tape casting and Si infiltration have been reported in previous studies. To reduce the residual Si content in the sintered bodies, impregnation of phenol–formaldehyde resin (PF) into the porous green preforms before Si infiltration was proposed and studied in this work. The impregnation of PF solution not only helped to reduce the porosity and increase the carbon content of the green preforms, but also improved their strength. As a result, the flexural strength of the RBSC increased a lot and reached 856 ± 161MPa, whereas the residual Si content was reduced to 10 vol%.

Description: A T300 carbon fiber and a SiC -coated C/SiC composite made from the same fiber were studied in atomic oxygen environment. The carbon fiber shows significant degradation while the erosion rate of SiC -coating of C/SiC is about 50 times lower. Evidence shows that Si is preferentially etched from the SiC surface. And XPS information showed that amorphous carbon and diamond-like carbonare periodically generated on the tested composite surface. Statistical analysis shows that the C/SiC specimens have no significant change in flexural properties after 1-year fluence AO treatment.

Description: Chitosan/Boron nitride ( BN ) composites were prepared by solution method using CuSO 4 /glycine chelate complex as the catalysis with variable percentage of boron nitride loading. The dispersion of BN with the chitosan polymer was achieved with sonication at power of 120 W and frequency of 80 kHz. The chemical interactions of chitosan and BN were studied by Fourier transform infrared spectroscopy. The structure of chitosan and BN composites were investigated by XRD and TEM. It was observed that the BN were dispersed with chitosan matrix through intercalation. The quantitative identification of composites was investigated by Energy Dispersive X-ray Spectroscopy and Selected Area Electron Diffraction. Thermal stabilities of chitosan/ BN composites were studied by thermogravimetric analysis. It was found that, the thermal stability of the chitosan/ BN composites was increased compare with virgin chitosan. The oxygen barrier properties of chitosan/ BN composites were measured using gas permeameter. A substantial reduction in oxygen permeability was observed increasing boron nitride concentrations by which the synthesized composite materials may applicable in packaging industry.

Description: Two different commercial refractory castables based on mullite or magnesia aggregates have been improved through addition of 0–25 wt.% nano-magnesium aluminate spinel (MA) powder. Physico-mechanical and refractory properties were tested at different firing temperatures. The phase composition, thermal analysis, and microstructure of these refractory castables were detected using X-ray diffraction (XRD), differential thermal analysis (DTA), as well as scanning electron microscope (SEM) attached with energy dispersive X-ray unit, respectively. The castable sample mix containing 10 wt.% nano-MA spinel powder was chosen as an optimum composition according to its good sintering, mechanical as well as refractory properties.

Description: Using three different sintering methods: spark plasma sintering, two-step sintering, and normal sintering ( Ba 0.85 Ca 0.15 )( Zr 0.1 Ti 0.9 ) O 3 ( BCZT ) lead-free piezoelectric ceramics with grain sizes in the range of 0.4–32.2 μm were prepared. The effects of grain size on the electrical properties and temperature stability of BCZT ceramics were systematically investigated. Results showed that reducing grain size shifted both the T c and T T-R to higher temperatures, and tended to enhance the relaxor behavior. A strong dependence of piezoelectric properties on the grain size was observed, and ~10 μm was a critical point for fabricating high-performance BCZT ceramics. For samples with grain sizes 〉10 μm, excellent piezoelectric properties of k p  〉 0.48, k t  〉 0.46, d 33  〉 470 pC/N and d 33 * 〉 950 pm/V were obtained. Moreover, no evident relationship between the grain size and temperature stability existed in this material, and all samples exhibited thermal instability below the Curie temperature. However, increasing grain size was helpful for improving the resistance to thermal depoling. The depolarization was assisted by internal mechanical stresses and the movement of 180° and 90° domain walls, which explained the increased resistance to thermal depoling in coarse-grained samples.

Description: ( Ca , Dy ) co-stabilized α-Sialon with elongated grains was prepared from SiO 2 – AlN – CaF 2 – Dy 2 O 3 powders by carbothermal reduction-nitridation (CRN) at 1700°C. Detailed investigations on the formation process of ( Ca , Dy )-α-Sialon elongated grains performed under various firing conditions revealed that the big quartz particles were initially reduced and decomposed gradually by carbon, and a large number of ball-shaped particles consisting of amorphous ( Si , Al , Ca , Dy ) x ( O , N ) y were formed. With increasing temperature, nitrogen continuously diffused into the liquid to form nitrogen-rich solid balls. Further increasing the temperature to 1700°C and held for 2 h, hollow α-Sialon spheres with nanometric particles were obtained from nitrogen-rich solid balls. Subsequently, the framework structure of hollow spheres was destroyed at 1700°C for 3 h, and ( Ca , Dy )-α-Sialon grains grew up continuously by consuming nanometric particles in the rough interface via Ostwald ripening and growth stages moving on the smooth interface. Finally, ( Ca , Dy )-α-Sialon developed well-defined crystalline elongated grains because the growth rate of rough surfaces is more rapid than that of smooth surfaces.

Description: A new temperature stable, low-loss, low sintering temperature microwave dielectric material Mg 0.5 Zn 0.5 TiNb 2 O 8 was investigated for the first time. Single phase Mg 0.5 Zn 0.5 TiNb 2 O 8 was obtained, and it showed Columbite structure which was tri-ixiolite structure. The variation trend of dielectric constant was in accordance with variation trend of relative density. When the sintering temperature was lower than 1120°C, the Qf value increased with the increasing of relative density. When the sintering temperature was higher than 1120°C, the Qf value decreased with the increasing of the unit cell volume. With the decrease of bond strength, the τ f increased. The typical values of ε = 30.74, Qf  = 66 900 GHz, τ f  = −4.01 × 10 −6 /°C were obtained for Mg 0.5 Zn 0.5 TiNb 2 O 8 sintered at 1120°C for 6 h.

Description: Oxide ion transport in Pb ( Zr x Ti 1– x ) O 3 ( PZT ) was investigated using 18 O tracer diffusion and time-of-flight secondary ion mass spectrometry analysis. Particularly diffusion in the near-surface regions (a few 100 nm in depth) is discussed and strong evidence for a space charge layer near the surface is provided. In this layer, an enrichment of oxygen vacancies is found at temperatures up to 600°C, resulting in box-shaped tracer diffusion profiles. At 650°C, however, the profile shape is modified and reveals a depletion of oxygen vacancies close to the surface. Accordingly, a change in the polarity of the surface charge takes place between 600°C and 650°C. The tracer diffusion profiles are very sensitive to surface modification, caused by etching or annealing at higher temperature, and also depend on the sintering procedure. Moreover, application of an external field during the tracer experiments affected the tracer diffusion at the cathode, while leaving the profile at the anode unperturbed. Quantitative analysis of the profiles was performed by means of numerical calculations based on Gouy-Chapman or Mott-Schottky space charge models. Estimates of the oxygen vacancy concentration and ionic transference number of donor-doped PZT are provided.

Description: Nanocrystalline tetragonal ZrO 2 polycrystals ( TZP ) have been fabricated by the pressureless sintering of recently developed tetragonal ZrO 2 powder containing 5.69 mol% YO 1.5 and 0.60 mol% AlO 1.5 . The average grain sizes were 160 nm in the TZP sintered at 1150°C for 10 h and 150 nm in the 0.25 mol% GeO 2 -doped TZP sintered at 1100°C for 100 h. The TZP and Ge 4+ -doped TZP-sintered bodies were essentially single-phase materials, and neither the amorphous layer nor the second-phase particle was observed along the grain boundary faces. High-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and nanoprobe energy-dispersive X-ray spectrometer (EDS) measurements revealed that the Y 3+ , Al 3+ and Ge 4+ cations tend to segregate in the vicinity of the grain boundaries in the TZP -sintered bodies. The TZP and Ge 4+ -doped TZP exhibited an elongation to failure of more than 100% in the temperature range of 1150°C–1300°C and initial strain rate range of 1.4 × 10 −5  s −1 to 1.0 × 10 −2  s −1 . For instance, an elongation to failure in the Ge -doped TZP reached about 200% at 1150°C and 1.4 × 10 −5  s −1 . The nanocrystallization reduced the lower limit of the superplastic temperature of conventional, submicron-grain TZP materials by 150°C. The improved ductility of the TZP at low temperatures was essentially attributed to the reduced grain size.

Description: This paper presents the results of preparing and investigating the solid solution of lead barium zirconate titanate stannate (Pb 1− x Ba x )[(Zr 1− y Ti y ) 1− z Sn z ]O 3 with x  =   0.25, y  =   0.35 and z  =   0.00, 0.02, 0.04, 0.08, 0.10. Ceramic samples were obtained from oxides and carbonates using conventional ceramic technology and pressureless sintering. The results of Energy-dispersive X-ray spectroscopy (EDS) investigations, XRD studies, as well as dielectric measurements and electromechanical investigations are presented. It was stated that at the room temperature, the structure of the investigated samples is pseudo-cubic, typical for relaxors. Maximal value of elementary cell parameter is observed for z  =   0.02, and for higher values of z, we observe almost linear decrease with increasing z . It was found that with increasing content of the Sn, the temperature T m at which dielectric permittivity reaches its maximum decreases. Analyzing P-E hysteresis loops it was stated that the phase transition in the investigated samples takes place at temperatures approximately 100°C lower than the temperature of the dielectric permittivity maximum. The temperature of phase transition was calculated also from hysteresis loops and compared with that obtained from measurements of dielectric permittivity.

Description: In this work atmospheric plasma spraying of SiC and Si 3 N 4 was investigated. Plasma spraying of these ceramics raises several problems since they would tend to decompose instead of melting at elevated temperatures during the process. To circumvent this problem the nonoxide ceramics were deposited as a composite powder mixed with nonoxide ceramic particles resulting in a ceramic/ceramic composite structure. Our findings were that using such a composite feedstock powder both oxidation and decomposition of the nonoxide particles could be avoided. A vitrified phase was also developed in the coating.

Description: A facile synthetic strategy was implemented to obtain nanosized barium titanate ( BaTiO 3 ) powders with tetragonal structure. The nanoparticles were synthesized using solvothermal process employing diethanolamine and triethanolamine to suppress the particle growth and the as-prepared nanopowders were characterized using X-ray diffraction, scanning electron microscopy, and high-resolution dispersive Raman spectroscopy. It was found that the particle size can be easily tuned by adjusting the experimental parameters while retaining the tetragonality. The average diameters of the particles prepared with and without the organic amines were found to be 80 and 100 nm, respectively. All the synthesized BaTiO 3 nanopowders exhibit a narrow size distribution with a uniform morphology. Rietveld refinement of the XRD patterns and Raman spectra revealed that the synthesized BaTiO 3 nanopowders have tetragonal asymmetry dominant structures. A slight decrease in the tetragonality of the prepared powders with decrease in particle size is attributed to the presence of cubic shell layer and inner defects. The tetragonal-dominant structure was also confirmed by normalizing the peak area of the Raman spectra.

Description: To improve the microwave dielectric properties, CuO was doped into composite ceramics BaTi 4 O 9 – BaZn 2 Ti 4 O 11 by the solid-state reaction. CuO worked as flux former and caused the liquid-phase sintering mechanism, which effectively improved the densification process and lowered the sintering temperature by nearly 100°C. Moreover, Cu 2+ substituted for Zn 2+ sites in BaZn 2 Ti 4 O 11 phase, which led to the increase of BaZn 2 Ti 4 O 11 phase and the reduction of lattice parameters of BaZn 2 Ti 4 O 11 phase, and both these two results had the positive effect on the dielectric properties, especially the Q  ×  f value. As increasing CuO content from 0.0 to 3.0 wt%, the dielectric constant ( ε r ) increased from 35.5 to 36.5, the Q  ×  f value increased first from 49 100 GHz to the peak value 62 600 GHz (1.0 wt% CuO ) and thereafter decreased to 31 900 GHz, and the temperature coefficient of resonant frequency ( τ f ) kept in a low value as 〈2.0 wt% CuO was added. At last, 0.85 BaTi 4 O 9 –0.15 BaZn 2 Ti 4 O 11 ceramics with 1.0 wt% CuO sintered at 1150°C for 3 h showed excellent microwave dielectric properties: the high ε r  = 36.4, the high Q  ×  f = 62 600 GHz and the near-zero τ f  = +0.2 ppm/°C.

Description: A piezoelectric system of (1− x ) Bi ( Ni 1/2 Ti 1/2 ) O 3 – x ( Pb (1− y ) Sr y TiO 3 ) ( BNT–PST ) is developed to have good high temperature piezoelectric properties with much improved resistivity. The crystal structure shows that the phase transformation from tetragonal phase to rhombohedral one is gradually shifted to the composition with high content of PT by the substitution of strontium. The problem of leakage current for the Bi ( Ni , Ti ) O 3 – PbTiO 3 can be well resolved by introducing the dopant of strontium. Both dielectric loss and DC resistivity can be much reduced not only at room temperature but also high temperature. An optimum composition of 0.53 Bi ( Ni 1/2 Ti 1/2 ) O 3 –0.47( Pb 0.95 Sr 0.05 ) TiO 3 is obtained to have a good potential application of high temperature piezoelectric ( d 33  = 205 pC/N, E C  = 3.32 kV/mm, P r  = 41.2 μC/cm 2 ). Strontium could be a useful dopant for the studies on the high temperature piezoelectric ceramics in future.

Description: The results of an experimental investigation on epoxy-joined silicon carbide tested in shear mode by four different configurations of torsion test are presented and compared to results obtained by asymmetric four-point bending and four different lap tests in compression. All samples have been joined by an epoxy adhesive (Araldite AV119) which is to be considered as a model brittle joining material chosen to obtain several joined samples in a reasonable time. Advantages and disadvantages of each configuration are discussed and compared to results previously obtained with epoxy-joined Carbon/Carbon composites and ceramics tested with the same methods.

Description: The detection of bridging tetrahedra, or Q 2 (L), in the silica chains constituting C – S – H gels is controversial. While some authors maintain that 29 Si MAS - NMR can be used to distinguish between Q 1 and Q 2 units but not between the silicon environments associated with Q 2 (intermediate position) and Q 2 (L) (intermediate and bridging position) units, others claim the contrary. The present article addresses this issue with a report on 29 Si MAS - NMR studies of a number of calcium silicate hydrate gels. The findings showed that nuclear magnetic resonance can differentiate between Q 2 and Q 2 (L) units in highly polymerized C – S – H gels with mean chain lengths (MCL) of over 12 and Ca / Si ratios of 〈1. At higher Ca / Si ratios, however, the MCL declined, with the concomitant rise in Q 1 units. Under these conditions, in which it was practically impossible to distinguish between Q 2 and Q 2 (L), the presence of a single signal for all Q 2 units was assumed.

Description: Yttria partially stabilized zirconia (YSZ) coatings are widely used for thermal barrier coatings (TBCs) to increase operating temperature of gas turbines. In the wavelength range where most of the radiation by walls and combustion gas is emitted within the gas turbine YSZ is semitransparent leading to increasing radiation heat flows into the components at increasing service temperatures. The objective of this work is to optimize the diffuse reflectance of plasma-sprayed TBCs by improving the coating microstructure such that the reflectance of radiation is increased. As a result, a more efficient thermal screening of the underlying metallic substrate is achieved. In this work, air plasma-sprayed and suspension plasma-sprayed (SPS) coatings of 7% YSZ using powder of different grain size distributions and different spray parameters were deposited. The reflectance and transmittance has been investigated in the wavelength range from 0.3 to 2.5 μm. The SPS-coatings showed the highest reflectance up to 94% at 1.5 μm wavelength. In addition, the scattering and absorption coefficients of the sprayed TBCs calculated with the Kubelka–Munk two flux model showed strong correlation with the measured porosity. By improving the microstructure, we were able to reduce thermal conductivity while increasing scattering of radiation, resulting in lower heat flow and lower temperature at the metallic substrate. These results are strengthened by numerical calculations.

Description: The non-isothermal crystallization kinetics of the strontium zinc silicate (SZS) glasses, having composition 51 SrO -9 ZnO -40 SiO 2 (wt%), was studied using the differential thermal analysis (DTA). Glasses prepared by quenching the melt in air, were subjected to different heat treatments for studying the crystallization behavior. Formation of crystalline phases and microstructure were studied by using powder X-ray diffraction and scanning electron microscopy. The activation energy and mechanism of crystallization were determined according to Kissinger, Ozawa and Matusita-Sakka equations. The DTA exotherm observed at around 920°C consists of two overlapping crystallization peaks corresponding to two different crystalline phases. Strontium silicate ( Sr 3 Si 3 O 9 ) and SZS ( Sr 2 ZnSi 2 O 7 ) phases crystallize almost simultaneously as major phases. The activation energies for the these crystallization peaks are 700 kJ/mol and 704 kJ/mol. Higher activation energies indicate that the kinetics are more thermally activated making the control of crystallization more difficult. The values of growth morphology parameters n (Avarami parameter) and m (dimensionality of crystal growth) suggest a diffusion controlled bulk crystallization with three- and two-dimensional growth. This is also confirmed by an interconnected growth of stubby granular/prismatic shaped crystals in the glass-ceramic. The microstructural evolution of the glass upon heating suggests the occurrence of phase separation with an apparently spinodal decomposition mechanism prior to the crystallization.

Description: A facile starch-assisted sol–gel method combined with freeze-drying technique has been developed to synthesize K -doped Li 2 ZrO 3 sorbents. SEM, TEM, and XRD techniques have been applied to characterize the morphology and structure of the synthesized K -doped Li 2 ZrO 3 samples. The CO 2 capture-regeneration properties of the prepared K -doped Li 2 ZrO 3 sample were investigated using thermogravimetric analysis at different CO 2 partial pressures. The K -doped Li 2 ZrO 3 synthesized using the starch-assisted sol–gel method combined with the freeze-drying technique shows excellent CO 2 capture properties. At 823 K and a CO 2 partial pressure of 0.25 bar, the uptake of CO 2 reaches 22 wt% within 20 min, which is approximately 87% of the stoichiometric sorption capacity (25.3 wt%) of CO 2 in the K -doped Li 2 ZrO 3 with a K : Li : Zr composition of 0.2:1.6:1 in molar ratio. Furthermore, the sorbent shows a good stability, confirmed using capture-regeneration cycles.

Description: Fully dense nanocrystalline MgO -based ceramics were consolidated by field and pressure assisted sintering (also known as Spark Plasma Sintering) using anhydrous nanosized powders (~5 nm) prepared by laser ablation and handled in a controlled, water-free environment prior to sintering. The high reactivity of the powders promoted excellent sinterability at relatively low temperatures. Highly transparent specimens were produced by sintering at 0.23–0.28 T m (650°C–800°C) for 15–30 min with good control over the final nanometric grain size. To preserve the nanocrystalline nature of the samples, the high temperature exposure time during sintering was reduced by the application of 300 MPa uniaxial pressure; higher pressure or two-step procedures did not provide extra benefits to densification or microstructural control.

Description: Two innovative glass compositions based on the commonly used 45S5 Bioglass ® were developed by increasing the calcium quantity and replacing the sodium oxide with a specific content of potassium oxide. The new glasses, named BG_ Ca / K and BG _ Ca /Mix, can be prepared using a conventional melting process and show a very low tendency to crystallize. Thanks to this peculiarity, BG_ Ca / K and BG_ Ca /Mix powders can be sintered at a relatively low temperature (800°C) to obtain samples of high compactness and bioactivity, since their amorphous nature is preserved. Consequently, the proposed glasses are perfect for making specific products such as scaffolds or hydroxyapatite-based composites. Furthermore, the relatively low alkali amount in the new compositions gives rise to a slow ion leaching in simulated body fluid, thus avoiding abrupt changes in pH that can damage osteoblasts or negatively affect their behavior.

Description: Solid solution effects on thermal conductivity within the MgO – Al 2 O 3 – Ga 2 O 3 system were studied. Samples with systematically varied additions of MgGa 2 O 4 – MgAl 2 O 4 were prepared and the laser flash technique was used to determine thermal diffusivity at temperatures between 200°C and 1300°C. Heat capacity as a function of temperature from room temperature to 800°C was also determined using differential scanning calorimetry (DSC). Solid solution in the MgAl 2 O 4 – MgGa 2 O 4 system decreases the thermal conductivity up to 1000°C. At 200°C thermal conductivity decreased 24% with a 5 mol% addition of MgGa 2 O 4 to the system. At 1000°C, the thermal conductivity decreased 13% with a 5 mol% addition. Steady-state calculations showed a 12.5% decrease in heat flux with 5 mol% MgGa 2 O 4 considered across a 12 inch thickness.

Description: The presence of leachable alkali ions, or their hydrated sites in the glass, is believed to be a determining factor for the interfacial water structure at the glass surface, influencing the surface properties of glass. The interfacial water structure on soda-lime silicate glass in humid ambience at room temperature was analyzed with sum-frequency-generation (SFG) vibration spectroscopy, which can probe the interfacial water layer without spectral interferences from the gas phase water. The soda-lime glass surface exposed to water vapor shows three sharp SFG peaks at 3200, 3430, and 3670 cm −1 in SFG, which is drastically different from the SFG spectra of the water layers on the fused quartz glass surface and the liquid water/air interface. The sharp peak at 3200 cm −1 is believed to be associated with the hydronium ions in the Na + -leached silicate glass surface. The 3200 cm −1 peak intensity varies with the relative humidity, indicating its equilibrium with the gas phase water. It is proposed that the hydronium ions in the Na + -leached sites produce compressive stress in the silicate glass surface; thus the growth of hydronium ions with increasing humidity might be responsible for the increased wear resistance of soda-lime glass surfaces in near-saturation humidity conditions.

Description: We introduce a novel method to produce macroporous ceramics by capillary suspensions. Adding a small amount (~1 vol%) of an immiscible secondary phase to a low concentration (~20 vol%) suspension can increase the yield stress by several orders of magnitude. This drastic change in flow behavior is induced by the creation of a sample-spanning particle network in the suspension controlled by capillary forces. This strong network may persist even if the primary bulk phase is removed. Accordingly, capillary suspensions can be used as a precursor for manufacturing porous materials. Here, we focus on the specific features of this universal, low-cost processing route for porous ceramics. An Al 2 O 3 model system is used to demonstrate how to adjust porosity and pore size. With this system, we were able to achieve open porosities higher than 60% with an average pore size below 10 μm.

Description: Binary metal oxides occur in different polymorphic states under applied pressure and temperature. Structural changes occur due to polymorphic transitions in binary metal oxides. It is essential to theoretically predict the conditions of polymorphic transitions so that materials can be effectively used in engineering applications. Temperature and pressure are the two main factors affecting the bulk state phase transformation of materials. For nanomaterials, it has been observed that particle size and temperature are the main factors affecting the phase transformation, e.g., γ- Fe 2 O 3 to α- Fe 2 O 3 , monoclinic to orthorhombic transformation in MoO 3 , anatase to rutile transformation in Titania, γ to α Alumina transformation. We compile from literature the main factors which affect the phase stability of a nanocrystalline binary metal oxide. A heuristic approach to formulate particle size is put forth. Factors like surface energy, surface tension, and particle shape are considered, and a value for critical particle size is formulated. The model fits well with the experimental results for nanocrystalline alumina, titania, zirconia, and Fe 2 O 3 . Such an approach can be applied to predict the particle size-dependent stability of a phase at known temperature range.

Description: This work revealed that the solid solution compounds of Sr 2 − x Ba x Nb 2 O 7 are promising lead-free materials for high-temperature piezoelectric sensor application. These compounds were confirmed as ferroelectric materials with high Curie points ( 〉 900°C) by their piezoelectric activity after poling, ferroelectric domain switching in their P – E hysteresis loops and thermal depoling behavior. The effect of Ba substitution on the structure and properties of Sr 2 − x Ba x Nb 2 O 7 ( x  〈  1.0) was investigated. The solid solution limit of Sr 2 − x Ba x Nb 2 O 7 was determined by XRD as x  〈 0.6. The a -, b -, c - axes, and cell volume increase with Ba addition. The textured ceramics of Sr 2 − x Ba x Nb 2 O 7 were prepared for the first time. The highest d 33 was measured as 3.6  ±  0.1 pC/N for Sr 1.8 Ba 0.2 Nb 2 O 7 .

Description: Containerless levitation technique, where the undercooling can be treated as one of the major thermodynamic parameters, was used to study the influence of oxygen partial pressure ( ) on the microstructure and physical properties of rare-earth orthoferrites RFeO 3 (where R = Rare-earth element) in the ranges from 10 5 to 10 −1  Pa. The microstructure of the as-solidified samples changed into orthorhombic RFeO 3 ( o - RFeO 3 ), metastable hexagonal RFeO 3 ( h - RFeO 3 ), and Fe 2+ -containing RFe 2 O 4 and a new metastable R 3 Fe 2 O 7 phases with decreasing . The effect of on the magnetic properties was indicated as that the saturation magnetization gradually increased for R = La to Yb and decreased for R = Lu with decreasing due to the formation of metastable and magnetic phases such as Fe 3 O 4 and Fe .

Description: The rapid densification behavior of 8 mol% Y 2 O 3 -stabilized ZrO 2 polycrystalline (8 Y -SZP) powder compacts at the initial stage of pressure sintering (relative density ( ) below 0.92) has been investigated using an electric current-activated/assisted sintering (ECAS) system. Data points corresponding to a fixed heating rate were extracted from the densification rate ( ) versus ρ and versus temperature ( T ) curves. These curves were obtained experimentally by consolidation at a fixed current. Under fixed current ECAS, the heating rate ( ) decreases continuously over sintering time. Using a quasi- constant heating rate (CHR) method, data points were extracted to plot vs. ρ, vs. T , and ρ vs. T curves at a fixed . The stress exponent ( n ), estimated from a log-log plot of grain size ( d )-corrected /ρ and effective stress (σ eff ) at 1300–1400 K, shows an almost constant value of 1. In addition, the activation energy ( Q ) for rapid densification, estimated from an Arrhenius plot of d -corrected /ρ also shows an almost constant value of 350 kJ/mol, which is considerably lower than the previously reported value of the activation energy for Zr 4+ lattice diffusion of about 440 kJ/mol. These results suggest that rapid densification of 8 Y -SZP by ECAS seems to proceed by diffusional creep controlled by grain-boundary diffusion of Zr 4+ ions.

Description: The various applications of transparent conducting oxides (TCO), e.g., as electrodes in flat panel displays and solar cells or as low-emissivity coatings have stimulated extensive research on their fabrication and properties. Recent experimental and theoretical studies of defect properties have considerably improved the understanding of the limitations of the electrical conductivity of both n - and p -type transparent conductors and of the structural and electronic surface properties of the most important TCO materials. Development of emerging and future applications in the area of transparent thin film electronics with oxide semiconductors as well as the improvement of existing applications require a detailed control of the Fermi level position in the bulk and at surfaces and interfaces of polycrystalline and amorphous TCO materials. This feature article describes how the important parameters for such control can be identified using photoelectron spectroscopy with in situ sample preparation. The parameters influencing doping, work functions, ionization potentials, and surface band bending as well as energy band alignment at interfaces are described and discussed providing a fundamental understanding of important material properties for tailoring TCOs in electronic devices.

Description: Highly orientated Co -doped Zn ( Mg , Cd ) O thin films have been prepared on Si (001) substrate using pulsed laser deposition (PLD). Our results indicate that Mg and Cd -doping can tune the bandgap of ZnO thin film. Apparent room-temperature ferromagnetism is observed in these films, which can be modified by the bandgap of ZnO . A narrow bandgap enhances the ferromagnetism of the films through the Cd -doping, and wide bandgap does the opposite through the Mg-doping, which may be ascribed to the ferromagnetic (FM) exchange interaction between the 3 d states of magnetic Co ions and the impurity band. These experimental results provide some new evidence that the ferromagnetism in Co : ZnO is closely related to crystal defects and improve our knowledge about ferromagnetism in dilute magnetic oxides.

Description: Nanocrystalline TiO 2 and Ti 1− x V x O 2 ( x  = 0.01) powders have been prepared by thermal decomposition, in air, of amorphous precursors resulting from the freeze-drying of appropriate solutions. In addition, TiO 2− x N y (anatase and rutile) and Ti O x N y (rock-salt) have been prepared by thermal treatment in ammonia of a crystalline precursor ( TiO 2 obtained at 673 K). TEM and SEM images, as well as the analysis of the X-ray diffraction (XRD) patterns, show the nanoparticulated character of those solids obtained at low temperatures, with typical particle sizes in the 10–20 nm range when prepared at 673 K. The UV–Vis results indicate both the insertion of V in the anatase lattice and the feasibility of nitridation at low temperatures. The photocatalytic properties of these materials (as prepared and after their incorporation to mortar samples) in the degradation of nitrogen oxides have been preliminary evaluated. Although N-doping enhances the photocatalytic activity of the TiO 2 matrix, V-doping worsens it.

Description: Two processing methods were successfully combined to obtain Ag-modified calcium phosphate scaffolds with antibacterial properties: (i) hydrothermal conversion of macroporous biogenic carbonates and (ii) vapor transport sintering. Hydrothermal conversion of two precursor materials, i.e., coral skeletons and sea urchin spines, resulted in the pseudomorphic replacement of highly porous calcium carbonates by calcium phosphate scaffolds. Vapor transport sintering of these scaffolds within a reactive AgCl atmosphere facilitated near net-shape processing accompanied by the condensation of finely dispersed Ag -bearing particles over the scaffold's surface. Chemical and phase compositions were analyzed using WDXRF, XRD, and DRIFTS (FTIR), and the microstructure development was characterized by SEM and TEM imaging. The dissolution kinetics of Ag + ions in aqueous solution was determined and growth inhibition experiments with Gram-positive and Gram-negative bacteria were performed to assess the antibacterial properties of Ag -modified ceramics.

Description: Electric field-induced magnetization characteristics are demonstrated in (100− x ) NaNbO 3 – x NiFe 2 O 4 ( x  = 15, 25, 35, 45), synthesized by the solid-state sintering method. The composites show well-defined ferroelectric behaviors and magnetic characteristics. The CME effect characteristics with driving frequency in a range 10 k – 15 kHz were investigated at room temperature. The CME couplings increase initially with increasing the driving frequencies and then decrease with the further increase in the frequency. Large CME coefficients are obtained at electromechanical resonance frequency of 12.8 kHz. These lead-free multiferroic composites exhibiting electrostatically induced ME resonance provide great opportunities for electric field-tunable microwave devices.

Description: A sucrose-mediated aqueous sol–gel procedure was developed to synthesize MgO – Y 2 O 3 nanocomposite ceramics for potential optical applications. The synthesis involves the generation of a precursor foam containing Mg 2+ and Y 3+ cations via the chemical and thermal degradation of sucrose molecules in aqueous solution. Subsequent calcination and crushing of the foam gave MgO – Y 2 O 3 nanocomposites in the form of thin mesoporous flake-like powder particles with uniform composition and surface areas of 27–85 m 2  g − 1 , depending on calcination conditions. The flakes exhibited a homogeneous microstructure comprising intimately mixed nanoscale grains of the cubic MgO and Y 2 O 3 phases. This microstructure was resistant to grain coarsening with average grain sizes of less than 100 nm for calcination temperatures of up to 1200°C. The results indicate that the sucrose-mediated sol–gel process is a simple effective method for making nanoscale mixed oxides.

Description: Multilayered composites consisting of silica, carbon nanotubes (CNTs), and continuous carbon fibers (C f ) were prepared by hot-pressing technique. Microstructures of different layer presented few pores of the composites. The thermal stability of the composites was analyzed by TG/DTA measurement. After being heat treated at 400°C for 10 h, the composites retained the equivalent shielding property compared to room temperature, and the impedance matching property at material/wave interface was improved slightly. The multilayer CNTs/C f /silica composites have not only the excellent absorbing properties but also the outstanding thermal stability, and it can be a promising candidate for high-temperature electromagnetic interference shielding applications.

Description: In industrial high-intensity discharge lamps, cracks and delaminations occasionally develop at the interface between SiO 2 and the Mo foil in the seal. Here, functionally graded SiO 2 -Mo materials for use in these lamps were fabricated by uniaxial compression casting and pressureless sintering. Consequently, vertical cracks developed across the sintered body layers, and interfacial cracks developed between the 100 wt% SiO 2 and 90 wt% SiO 2 -Mo layers. Therefore, the effects of residual stress, difference in the coefficient of thermal expansion (CTE), and difference in the volume shrinkage on these cracks were investigated. Vertical cracks were suppressed when residual stress was relaxed by annealing near the annealing point of silica glass during the cooling step in the sintering process. Interfacial cracks were suppressed when the difference in the CTE of the interface between the 100 wt% SiO 2 and 90 wt% SiO 2 -Mo layers was relaxed by inserting layers of 95 wt% SiO 2 -Mo between them. Furthermore, the suppression effect became stronger when the difference in the volume shrinkage of the layers was relaxed by sintering to join the separately sintered monolayers. Thus, the development of these cracks was influenced by the residual stress, CTE, and volume shrinkage. Therefore, these cracks can be prevented by optimizing these factors.

Description: As research continues, the control on the polymorph and morphology of calcium carbonate ( CaCO 3 ) becomes a hot topic because its application is limited by these parameters. The polymorph and morphology control of CaCO 3 was successfully achieved via temperature and PEG ( M w  = 6000) during the decomposition of Ca ( HCO 3 ) 2 , which has rarely been employed to prepare precipitated CaCO 3 . As-prepared CaCO 3 was characterized using XRD and SEM. In the case of no PEG, rhombohedra calcite, lamellar vaterite, rod- and needlelike aragonite are observed, and calcite is the major phase at all samples and it increases with temperature, whereas vaterite and aragonite decrease with temperature. The addition of PEG restrains the formation of vaterite and promotes the emergence of needlelike aragonite particles at 70°C, and prevents the generation of calcite and encourages the production of rodlike aragonite particles at 80°C and 90°C. This work not only provides a new way on the preparation of CaCO 3 powder but also presents the feasible control method in this route.

Description: We have synthesized a partially nitridated Ca 13.7 Eu 0.3 Mg 2 Si 8 O 32 (CMSN: Eu 2+ ) using Si 3 N 4 with a conventional solid-state reaction and successfully determined the structural parameters by a combined Rietveld refinement method. The partial nitridation of Ca 13.7 Eu 0.3 Mg 2 Si 8 O 32 (CMS: Eu 2+ ) led to a large enhancement in the luminescence intensity, as much as 148%. From the Rietveld refinement results, the anisotropic changes of the lattice parameters were observed for the partially nitridated samples. By incorporating this phosphor + red phosphor with an encapsulant on an InGaN light-emitting diode (LED) (λ max  = 395 nm), white light with a color rendering index of 92 and a color temperature of 5320 K under 20 mA was obtained.

Description: In March 2012, a group of researchers met to discuss emerging topics in ceramic science and to identify grand challenges in the field. By the end of the workshop, the group reached a consensus on eight challenges for the future:—understanding rare events in ceramic microstructures, understanding the phase-like behavior of interfaces, predicting and controlling heterogeneous microstructures with unprecedented functionalities, controlling the properties of oxide electronics, understanding defects in the vicinity of interfaces, controlling ceramics far from equilibrium, accelerating the development of new ceramic materials, and harnessing order within disorder in glasses. This paper reports the outcomes of the workshop and provides descriptions of these challenges.

Description: The BiOCl / Ag 3 PO 4 composites have been prepared via a facile and reproducible route. In the composite, Ag 3 PO 4 particles are deposited on the surface of plates of BiOCl . Among the as-prepared samples, the ultraviolet (UV) and visible light photocatalytic reaction rates of BiOCl / Ag 3 PO 4 composite with the ratio of 1:0.1 are about 4.4 times and 4.5 times than that of pure BiOCl , respectively. Overall, the BiOCl / Ag 3 PO 4 composites not only show highly enhanced visible light photocatalytic activity but also exhibit highly improved UV photocatalytic activity, which could find enormous potential application in addressing environmental protection issues utilizing solar energy effectively.

Description: Porous yttria-stabilized zirconia (YSZ) ceramics were fabricated using tert-butyl alcohol (TBA)-based gelcasting with monodisperse polymethylmethacrylate (PMMA) microspheres as both pore-forming agent and lubricant agent. The TBA-based slurry of 50 vol% solid loading with excellent rheological properties appropriate for casting was successfully prepared by using a commercial polymer dispersant DISPERBYK-163 as both dispersant and stabilizer. The distribution of the spherical pores made from PMMA microspheres was very homogeneous. Their average diameter decreased from 16.9 to 15.7 μm when the sintering temperature was increased from 1350°C to 1550°C. The compressive strength increased from 14.57 to 142.29 MPa and the thermal conductivity changed from 0.17 to 0.65 W/m·K when the porosity decreased from 71.6% to 45.1%. The results show that this preparation technology can make all the main factors controllable, such as the porosity, the size and shape of pores, the distribution of pores, and the thickness and density of pore walls. This is significant for fabricating porous ceramics with both high compressive strength and low thermal conductivity.

Description: Improving the high-temperature strength and stiffness of Ti 3 SiC 2 is the task of many investigations. However, methods for high-temperature strengthening have not been established although various ways are applicable to enhance the room-temperature mechanical properties of Ti 3 SiC 2 . In this work, we report that significant strengthening was realized at both room and high temperatures by incorporating a small amount of W into Ti 3 ( Si , Al ) C 2 . The onsite temperature for the rapid degradation of stiffness and strength moved more than 150°C upward to over 1200°C. The flexural strength of 5 at.% W -doped Ti 3 ( Si , Al ) C 2 is 632.9 MPa at RT and 285 MPa at 1200°C, being 176% and 170% of those for baseline material, respectively.

Description: Lanthanum zirconate has been prepared via a new chemical synthesis method by combining sol–gel processing and complex precipitation. The synthesis was carried out in aqueous solution under ambient conditions. The synthesized powder possessed the pyrochlore superstructure upon calcination above 1200°C. A suite of characterization techniques, including FTIR, Raman, X-ray and electron diffraction, TEM, SEM, and nitrogen sorption were employed to investigate the microstructural evolution and bulk properties. Dense ceramics (〉90% relative density) were obtained after sintering at 1400°C, without need for additional processing (i.e., hot or cold isostatic pressing) or any milling steps. A mechanism has been proposed that elucidates molecular assembly of this chemical synthesis method.

Description: The diffusion couples of lanthanum-based barium borosilicate glass with high- and low-temperature electrolytes have been heat-treated at 850°C and 800°C, respectively, for 5, 100 and 750 h. These prepared diffusion couples have been characterized using various techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray dot mapping, and electron probe microanalysis (EPMA). The thermodynamic parameters like frequency factor, crystallization constants, free volume, and bulk thermal expansion coefficients have been calculated to understand the behavior of glass. Interestingly, glass revealed self-healing tendency with heat treatment duration.

Description: Direct synthesis of silicon carbide ( SiC ) nanopowders (size 50–200 nm, BET ~20 m 2 /g) in Si – C system is conducted in an inert atmosphere (argon) using a self-propagating high-temperature synthesis (SHS) approach. A preliminary short-term (e.g., minutes) high-energy ball milling (HEBM) of the initial mixture, which involves pure Si and C powders, is used to enhance system reactivity. Two conditions of HEBM with different force fields (17G and 90G) are applied and the results are compared. The influence of HEBM's conditions on the microstructure of mechanically treated mixtures and combustion products is also investigated and discussed. Obtained results suggest that by changing the intensity of mechanical treatment one may prepare a completely amorphous reactive mixture containing carbon and silicon, or gradually change the ratio of ( Si / C )– SiC phases and finally produce pure silicon carbide powder during the milling process. The influence of HEBM on the combustibility of the Si / C mixture possesses a critical character: the self-sustained reaction becomes feasible only after a critical time of ball milling (i.e., 10 min for 90G; 30 min for 17G). Comparison of the microstructures for as-milled and as-synthesized powders reveals that for all investigated conditions the morphologies of the as-milled reactive Si / C media are essentially the same as that for SiC combustion products. The mechanism for direct synthesis of SiC by combustion reaction is also proposed.

Description: One of the most serious causes of degradation of concrete is the alkali–silica reaction. Amorphous silicates present in certain aggregates react with the alkaline pore solution of the concrete to form a gel, which absorbs water and swells, leading to the expansion of the concrete. It is known that the deleterious effects of ASR can be suppressed by the incorporation of supplementary cementitious materials in the concrete, but the mechanisms operating are not clear. In this article, we study a model system of amorphous silica plates in simulated pore solutions by X-ray photoelectron spectroscopy (XPS), to demonstrate that aluminum in solution can directly suppress the dissolution of amorphous silica under the highly alkaline conditions found in concrete. XPS shows that aluminum species are incorporated into the framework of the silica structure. Scanning electron microscope (SEM) and atomic force microscope (AFM) images confirmed the reduction in dissolution of silica in solutions containing aluminum.

Description: Single crystal titanium nitride powder was used to fabricate titanium nitride films using a vacuum kinetic spray (VKS) process. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (FETEM) were used to investigate the microstructure of the as-fabricated films under different process conditions. Plastic deformation features (i.e., amorphization, rotated grain, slip bands, and distorted lattices in the transition structure) revealed an elastic-to-inelastic transition of titanium nitride particles at high strain rate and high pressure induced by hypervelocity impact, which was considered vital for grain refinement and film growth during the process.

Description: We report the diffusion and stress coupling effect during oxidation. An analytical model is developed for the stress and diffusion coupling effect based on equilibrium relationship and diffusion equation considering for the stress effect. Compressive stress will generate during the oxidation due to the growth strain. This growth stress can modify the diffusion coefficient; therefore, the oxidation kinetics is also affected. The coupling effect reduces both the oxidation rate and the stress. The proposed model is applied to predict the oxidation evolution for SiC and its consistence with the experimental data demonstrates the theoretical analysis.

Description: Composites of ZrC – SiC with relative densities in excess of 98% were prepared by reactive hot pressing of ZrC and Si at temperature as low as 1600°C. The reaction between ZrC and Si resulted in the formation of ZrC 1− x , SiC , and ZrSi . Low-temperature densification of ZrC − SiC ceramics is attributed to the formed nonstoichiometric ZrC 1− x and Zr – Si liquid phase. Adding 5 wt% Si to ZrC , the three-point bending strength of formed ZrC 0.8 –13.4 vol% SiC ceramics reached 819 ± 102 MPa with hardness and toughness being 20.5 GPa and 3.3 MPa·m 1/2 , respectively.

Description: Oxidation of SiC can occur in a passive mode, where a protective film is generated, or in an active mode, where a volatile suboxide is generated. The transitions from active-to-passive and passive-to-active are particularly important to understand as they occur via different mechanisms. In Part II of this article, the passive-to-active transition is explored. Three different types of SiC are examined— Si -rich SiC , stoichiometric SiC , and C-rich SiC . In addition to an in situ transition from passive-to-active, the effect of a preformed film on all three types of SiC is explored. It appears that the passive-to-active transition occurs when the SiO 2 scale begins to react with the SiC substrate. This reaction generates SiO (g) and CO (g), which build pressure beneath the SiO 2 scale, eventually causing the oxide to rupture. In addition, the SiO (g) can oxidize a distance away from the surface leading to the formation of SiO 2 needles and further promoting this SiO 2 / SiC reaction. Thermodynamic and kinetic data are used to predict transition pressures of oxygen, which show reasonable agreement with those measured.

Description: Camber evolution and stress development during co-firing of asymmetric bilayer laminates, consisting of porous Ce 0.9 Gd 0.1 O 1.95 gadolinium-doped cerium oxide (CGO) and La 0.85 Sr 0.15 MnO 3 lanthanum strontium manganate (LSM)-CGO were investigated. Individual layer shrinkage was measured by optical dilatometer, and the uniaxial viscosities were determined as a function of layer density using a vertical sintering approach. The camber evolution in the bilayer laminates was recorded in situ during co-firing and it was found to correspond well with the one predicted by the theoretical model. The estimated sintering mismatch stress in co-fired CGO-LSM/CGO bilayer laminates was significantly lower than general sintering stresses expected for free sintering conditions. As a result, no co-firing defects were observed in the bilayer laminates, illustrating an acceptable sintering compatibility of the ceramic layers.

Description: Erbium Er 3+ and ytterbium Yb 3+ codoped fluoro-phosphate glasses belonging to the system NaPO 3 –YF 3 – BaF 2 – CaF 2 have been prepared by the classical melt-quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry (DSC) and UV–visible and near-infrared spectroscopy. Transparent and homogeneous glass–ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X-ray diffractometry (XRD) and scanning electron microscopy (SEM) have evidenced the formation of fluorite-type cubic crystals based during the devitrification process. Finally, infrared to visible up-conversion emission upon excitation at 975 nm has been studied on the Er 3+ and Yb 3+ codoped glass–ceramics as a function of thermal treatment time. A large enhancement of intensity of the up-conversion emissions–about 150 times- has been observed in the glass–ceramics if compared to the parent glass one, suggesting an incorporation of the rare-earth ions (REI) into the crystalline phase.

Description: In this work, we present a systematic study on the effect of monovalent and divalent cation inclusion on the magnetic properties of the manganites series La 0.80 ( Ag 1− x Sr x ) 0.20 MnO 3 ( x  = 0.0–1.0) synthesized by the solid-state reaction method. The decreasing Sr : Ag proportion across the compositional series was verified by X-ray photoelectron spectroscopy. Concerning magnetic properties, the hysteresis curves manifested an initial paramagnetic response at x  = 0.0, followed by a progressive ferromagnetic behavior with an optimum Ag : Sr ratio at x  = 0.75, for which an enhanced saturation magnetization of 51 Am 2 /kg and a Curie temperature of 336 K were recorded. Results are explained on the basis of the effect of the increasing unit cell volume on the double exchange interaction between magnetic Mn 3+ – Mn 4+ atoms.

Description: A simple solvothermal low-temperature synthesis process of TiO 2 nanoparticles was investigated in different solvents [Octanol ( Oc ), Ethanolamine ( Am ) and Terathane ( Tr )] with titanium (IV) chloride ( TiCl 4 ) as precursor. The samples were characterized by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). XRD showed the crystallite size ranging from 4 to 12 nm, which were calculated using Debye–Scherrer's equation. The existence of poor or high crystalline anatase phases and high crystalline anatase/rutile mixture was also shown. TEM images displayed variations in the morphological behavior depending on the synthesis condition. Particles of irregular morphology with high irregular agglomeration up to well-defined particles can be observed, which are self-assembled by oriented attachment (OA). This self-assembly led to TiO 2 microparticles with 3-D Wulff shape for anatase and 1-D shape for rutile. The results showed that the TiO 2 nanopowder could be easily engineered and adapted by the solvent type, the TiCl 4 concentration and the synthesis time.

Description: x Nd ( Zn 1/2 Ti 1/2 ) O 3 –(1− x ) Ba 0.6 Sr 0.4 TiO 3 ( x NZT–BST) thin films were fabricated on Pt / Ti / SiO 2 / Si substrates by sol–gel method with x  =   0, 3%, 6%, and 10%. The structures, surface morphology, dielectric and ferroelectric properties, and thermal stability of x NZT–BST thin films were investigated as a function of NZT content. It was observed that the introduction of NZT into BST decreased grain size, dielectric constant, ferroelectricity, tunability, and significantly improved dielectric loss and dielectric thermal stability. The corresponding reasons were discussed. The 10%NZT–BST thin film exhibited the least dielectric loss of 0.005 and the lowest temperature coefficient of permittivity (TCP) of 3.2 × 10 −3 /°C. In addition, the figure of merit (FOM) of x NZT–BST ( x  = 3%, 6%, and 10%) films was higher than that of pure BST film. Our results showed that the introduction of appropriate NZT into BST could modify the dielectric quality of BST thin films with good thermal stability. Especially for the 3%NZT–BST thin film, it showed the highest FOM of 33.58 for its appropriate tunability of 32.87% and low dielectric loss of 0.0098.

Description: The influence of the addition of 1 mol% Tm 2 O 3 on the nanocrystallization of LaF 3 in a glass of composition 55 SiO 2 –20 Al 2 O 3 –15 Na 2 O –10 LaF 3 (mol%) has been studied. Tm 2 O 3 affects the phase separation in the glass and delays the onset of crystallization with respect to the undoped glass. Additionally, the maximum LaF 3 crystal size is slightly greater than that in the undoped glass–ceramics. The microstructural and compositional changes in the glass matrix have been studied using several techniques, including viscosity, dilatometry, X-ray and neutron diffraction (XRD, ND), quantitative Rietveld refinement, transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and Raman spectroscopy. Photoluminescence measurements indicate that the Tm 3+ ions are distributed between the glassy matrix and LaF 3 crystals. Eu 2 O 3 has been used as structure probe and part of the Eu 3+ ions are reduced to Eu 2+ when incorporated in the LaF 3 nano-crystals. Up-conversion spectra under IR-excitation show a higher intensity of the blue emission in the Tm -doped glass–ceramic compared with that in the glass.

Description: Multiferroic ( Bi 0.95 La 0.05 )( Fe 0.97 Mn 0.03 ) O 3 / CoFe 2 O 4 and CoFe 2 O 4 /( Bi 0.95 La 0.05 )( Fe 0.97 Mn 0.03 ) O 3 double-layered thin films were prepared on Pt (111)/ Ti / SiO 2 / Si (100) substrates via a chemical solution deposition method. In both the thin films, superior multiferroic properties were observed at room temperature. However, substantial enhancements in magnetic properties, such as saturated ferromagnetic hysteresis loop with large 2 M r (68.8 emu/cm 3 ) and 2 H c (11.7 kOe), as well as moderate ferroelectric properties, such as 2 P r (58 μC/cm 2 ) with low leakage current density (4 × 10 −9  A/cm 2 at 100 kV/cm), were observed in the ( Bi 0.95 La 0.05 )( Fe 0.97 Mn 0.03 ) O 3 / CoFe 2 O 4 at room temperature. Structural distortion, deformation of [( Fe , Mn ) O 6 ] oxygen octahedra, and superexchange interaction in the ( Bi 0.95 La 0.05 )( Fe 0.97 Mn 0.03 ) O 3 are attributed to the enhanced properties.

Description: In this paper the dielectric properties of crack-free, Bi 12 Si O 20 thin films were investigated. The films were prepared on Pt / TiO 2 / SiO 2 / Si and corundum substrates using the sol–gel method. The formation of a pure Bi 12 SiO 20 phase was observed at a temperature of 700°C. The Bi 12 SiO 20 thin films, heat treated at 700°C for 1 h, had a dense microstructure with an average roughness ( R a ) of 50 nm. The dielectric properties of the film were characterized by using both low- and microwave-frequency measurement techniques. The low-frequency measurements were conducted with a parallel capacitor configuration. The dielectric constant and dielectric losses were 44 and 7.5 × 10 −3 , respectively. The thin-film dielectric properties at the microwave frequency were measured using the split-post, dielectric resonator method (15 GHz) and the planar capacitor configuration (1–5 GHz). The dielectric constant and the dielectric losses measured at 15 GHz were 40 and 17 × 10 −3 , respectively, while the dielectric constant and the dielectric losses measured with the planar capacitor configuration were 39 and 65 × 10 −3 , respectively.

Description: Nanocrystalline Ni 1− x Zn x Fe 2 O 4 (0 ≤  x  ≤ 1.0) powder with grain size of 30 nm was prepared using the spraying-coprecipitation method. The obtained nanocrystalline Ni 1− x Zn x Fe 2 O 4 powder was sintered using conventional and microwave sintering techniques. The results show that the microstructure and magnetic properties of the sintered samples are obviously improved by microwave sintering of nanocrystalline Ni 1− x Zn x Fe 2 O 4 ferrite powder. The initial permeability of Ni 1− x Zn x Fe 2 O 4 ferrite increases with the increase in zinc concentration, although its resonance frequencies shift from high frequency to low frequency. The maximum initial permeability for microwave-sintered Ni 0.4 Zn 0.6 Fe 2 O 4 ceramic obtained at the temperature of 1170°C for 30 min reaches up to 360.9, and its resonance frequency is ~10 MHz. It may be attributed to the nanocrystalline Ni 1− x Zn x Fe 2 O 4 raw powder as well as the microwave sintering process, which results in a synergistic effect on improvement of the microstructure and magnetic properties.

Description: Uniform alumina microfibers precursor (ammonium aluminum carbonate hydroxide, AACH) were successfully synthesized using the microwave hydrothermal method, with average length of 5–10 μm and the diameter around 300–500 nm. FT-IR spectra indicated AACH was composed of NH 4 [ Al ( OOH ) HCO 3 ]· H 2 O . The thermal behaviors of the as-prepared AACH were investigated using differential scanning calorimeter and thermogravimetric analysis (DSC-TG), XRD, and SEM. The results showed that the thermal decomposition of the AACH microfibers occurred via three steps, which were respectively divided into adsorption of physical water, dehydration of crystalline water, and decomposition of AACH. The activation energies for the above three steps were calculated using Coats-Redfern method. The phase transformation sequence was found to be AACH→ amorphous Al 2 O 3 → γ- and θ- Al 2 O 3 → α- Al 2 O 3 . It was also observed that the thermal treatment had little influence on fiber morphology of the products. The fibers morphology with high thermal stability will endow to prepare alumina microfibers with novel application potentials.

Description: The effect of B 2 O 3 addition on the microwave dielectric properties and microstructure of Li 2 ZnTi 3 O 8 ceramics prepared using conventional solid-state reaction was investigated for low-temperature co-fired ceramic (LTCC) applications. X-ray diffraction and scanning electron microscopy were used to investigate the effect of B 2 O 3 addition on the sintering process. The Li 2 ZnTi 3 O 8 ceramic sintered at 875°C with 0.5 wt% B 2 O 3 for 4 h showed good microwave dielectric properties including ε r  = 25, Q  ×  f  = 50,917 GHz, and τ f  = −17.8 ppm/°C. Silver was found to be unreactive toward the 0.5 wt% B 2 O 3 doped Li 2 ZnTi 3 O 8 ceramic under the above sintering conditions.

Description: This contribution describes the development of tape casting for solid oxide fuel cells (SOFCs) anode supports starting with the characterization of the powders and ending with manufacturing of cells for stack testing. After casting the support, full cells were prepared by screen printing and sintering of the functional layers. The results of single-cell and stack tests of the novel SOFC will be discussed. The new cell showed excellent electrochemical performance in single-cell tests with more than 1.5 A/cm 2 (800°C, 0.7 V). Furthermore, stack tests showed no significant difference from earlier standard cells when operated at 800°C with a current density of 0.5 A/cm 2 .

Description: In the present study, we examined how the active aluminum nano-oxide in the gamma form used as a neutral carrier for the nanoparticles of various metals (as Ag , Pr ) affected their toxic behavior. Our experiments have shown that exposure to metal nanoparticles can be reduced by binding the nanoparticles to alumina nanoparticles and the aluminum nano-oxide is suitable to function as the nano-stabilizer for the Ag and Pr nanoparticles. We have managed to manufacture new alumina-stabilized silver and praseodymium nanoparticles using dry sol-gel method that are not phyto- and eco-toxic.

Description: This work presents the ultraviolet–visible spectroscopic properties of Ba 3 Y 2 ( BO 3 ) 4 : Ce 3+ , Tb 3+ phosphors prepared by a high-temperature solid-state reaction. Under ultraviolet light excitation, tunable emission from the blue to yellowish-green region was obtained by changing the doping concentration of Tb 3+ when the content of Ce 3+ is fixed. The efficient energy transfer process between Ce 3+ and Tb 3+ ions was observed and confirmed in terms of corresponding excitation and emission spectra. In addition, the energy transfer mechanism between Ce 3+ and Tb 3+ was proved to be dipole–dipole interaction in Ba 3 Y 2 ( BO 3 ) 4 : Ce 3+ , Tb 3+ phosphor. By utilizing the principle of energy transfer and appropriate tuning of Ce 3+ / Tb 3+ contents, Ba 3 Y ( BO 3 ) 4 : Ce 3+ , Tb 3+ phosphors can have potential application as an UV-convertible phosphor for near-UV excited white light-emitting diodes.

Description: The microstructural properties and the chemical compositions of a 0.65 Pb ( Zr 0.42 Ti 0.58 ) O 3 -0.35 Pb ( Ni 1/3 Nb 2/3 ) O 3 (0.65PZT58-0.35PNN) ceramic system sintered at 900°C for 4 h with 10 mol% CuO additives were studied using transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS). CuO pockets were found as new microstructural constituents. The liquid phase has formed by the partial melting of CuO additives at the sintering temperature by reacting with Pb element in the matrix. The reaction started at the interfaces and then proceeded into the pocket through the diffusion of the Pb element. The presence of the Pb -rich precipitates during cooling was confirmed by EDS analyses. Cu -rich crystals in the pocket were observed near the boundaries between the matrix grain and the pocket. Rather smaller Pb - Cu - O -contained particle segments were detected around the center of the pocket, demonstrating that the reaction of melting of CuO has occurred with the Pb element which was diffused from the matrix. Due to the existence of the liquid phase, a dense microstructure was achieved during the sintering process and abnormal grain growth occurred in the process.

Description: “Self-sensitized” TiO 2 photocatalysts sensitized by TiO 2 nanocrystals with quantum structures were successfully prepared via a solvothermal process and a facile subsequent treatment process. We calculated an optimized structure by using a pseudopotential Hartree–Fock method and investigated the structure using X-ray diffraction, scanning, and transmission electron microscopy, and UV–Vis spectrophotometer. The self-sensitized products exhibit an extremely high photocatalytic activity due to their unique optical properties. To discuss the optical properties of the 3-D nanoparticles sensitized by the TiO 2 nanocrystals, we proposed a model of the electron band structure of the as-prepared products to give a reasonable explanation for such a high photocatalytic activity.

Description: High power characteristics of lead-free ( Bi , Na ) Ti O 3 (BNT) and Ba Ti O 3 (BT)-based piezoceramics were investigated and compared to commercial “hard” Pb ( Zr , Ti ) O 3 PZT materials. Acceptor-modified BNT and BT-based ceramics showed typical “hardening” characteristics, exhibiting high mechanical quality factor Q m  〉 800 and low dielectric loss, 〈0.01, comparable to “hard” PZT ceramics. Of particular significance is that BNT-based ceramics were found to exhibit minimal variation of resonance frequency shift and high Q m under high level vibration velocity, being ~0.6% and ~800 at 0.25 m/s, respectively, due to the high domain stability associated with their high coercive fields, being on the order of 35 kV/cm.

Description: Bioactive glass 45S5 foams were produced using a powder technology process developed by The National Research Council Canada–Industrial Materials Institute. NRC–IMI's proprietary process, combining powder technology and polymer foam technique, allows the production of materials having different structures and properties. It can be used to produce components into various forms, such as fully porous bodies or coatings on solid structures. During foaming, the foaming agent is decomposed and expands the binder-bioactive glass suspension. Then, the binder is burnt out by heating the sample at 500°C and finally the bioactive glass particle network is sintered to consolidate the material. Foams sintered at various temperatures were characterized from a microstructural and mechanical point of view. The foam structure and properties are affected by the sintering temperature when it is varied between 950°C and 1025°C. Foams exhibited open porosity (64%–79%) and pore size (335–530 μm) optimal for bone ingrowth. In all cases, the glass crystallized during sintering and the material was mostly composed of Na 6 Ca 3 Si 6 O 18 and Na 2 Ca 4 ( PO 4 ) 2 SiO 4 phases. The mechanical strength increased from 1.7 to 5.5 MPa while the density of the material increased from 0.56 to 0.97 g/cm 3 .

Description: Single crystals of Na 2 Ba 9 Si 20 O 50 were obtained from solid state reactions performed along the join Na 2 Si 2 O 5 - BaSi 2 O 5 . The crystal structure has been determined from a data set collected at ambient temperatures and subsequently refined to a residual of R (|F|) = 0.0328 for 2211 independent reflections. The compound belongs to the group of phyllosilicates and adopts the monoclinic space group C 2/ m with the following lattice parameters: a  =   39.111(3) Å, b  =   7.6566(6) Å, c  =   8.2055(6) Å, β = 97.319(6)°, V  = 2437.2(3) Å 3 , Z  = 2. Furthermore, weak one-dimensional diffuse streaks running parallel to a * as well as a very small number of low intensity reflections at b */3, indicating the presence of a superstructure, were observed. Basic buiding units are silicate layers parallel to (40-1) which can be obtained from the condensation of single chains with a periodicity of four running along [010]. The sheets can be partitioned into two kinds of consecutive strips containing (i) a sequence of four- and eight-membered rings and (ii) a four-ring wide “zig-zag shaped” unit consisting of exclusively six-membered rings. The sodium and barium cations—distributed among six crystallographically independent positions—are sandwiched between subsequent layers and are linked to seven to nine nearest oxygen neighbors. The structure of Na 2 Ba 9 Si 20 O 50 is closely related to that of K 2 Ba 5 Si 12 O 30 and K 2 Ba 7 Si 16 O 40 , respectively. There are strong arguments that the previously claimed phase Na 4 Ba 8 Si 20 O 50 is actually misinterpreted Na 2 Ba 9 Si 20 O 50 and that the composition of the intermediate phase along the join Na 2 Si 2 O 5 – Ba Si 2 O 5 is slightly different from that described in the literature.

Description: This study focuses on constrained sintering of Ba La 4 Ti 4 O 15 (BLT) thick films on Pt foils and BLT rigid substrates. The densification of BLT films is only retarded in comparison with their bulk counterpart, but, and in opposition to other constrained systems investigated until now, grain growth is favored in constrained BLT films. An additional degree of constraint is provided by using a rigid BLT substrate instead of a compliant platinum foil, which induces even larger coarsening. These observations point to the possible effect of mechanical stress developing during constrained sintering on the microstructure development.

Description: Flower-like hydroxyapatite (HA) was prepared by a solvothermal method using calcined eggshells as calcium source and hydrogen peroxide/ N , N -dimethylformamide (DMF) as solvent. The products are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM). All the above-mentioned instrumental analysis such as XRD and FT-IR showed the purity of HA. The SEM indicates that the as-obtained flower-like HA are composed of microsheets. These nanosheets interleaved each other to form the uniform flower-like morphology. The influence of precipitation temperature and ratio of hydrogen peroxide to DMF were systematically investigated by SEM analysis.

Description: Zirconium carbide ( ZrC ) was synthesized by solution-based processing using versatile starting reagents including zirconium oxychloride octahydrate ( Zr O Cl 2 ·8 H 2 O , ZOC), acetylacetone (Hacac), and phenolic resin. Polyzirconoxane (PZO), obtained by chelation of Hacac to zirconium, was used to combine with phenolic resin to form a precursor for ZrC . It generated ZrC at a relatively low temperature (1550°C) and in a low C / Zr molar ratio of 2 assuming that phenolic resin was the only carbon source. As a comparison, synthesis of ZrC only using ZOC and phenolic resin was also conducted. Besides, the pyrolysis of PZO was carried out and the transformation mechanism during the pyrolysis was studied, during which ZrC was obtained at 1550°C in flowing argon. The conversions from as-synthesized preceramic precursors to ceramics were studied by means of FTIR, DSC-TG, SEM, EDS, and XRD.

Description: Phase evolution accompanying the isothermal aging of free-standing air-plasma sprayed (APS) 7–8 wt% yttria-stabilized zirconia (8YSZ) thermal barrier coatings (TBCs) is described. Aging was carried out at temperatures ranging from 982°C to 1482°C in air. The high-temperature kinetics of the phase evolution from the metastable t′ phase into a mixture of transformable Y-rich (cubic) and Y-lean (tetragonal) phases are documented through ambient temperature X-ray diffraction (XRD) characterization. A Hollomon–Jaffe parameter (HJP), T [27 + ln( t )], was used to satisfactorily normalize the extent of phase decomposition over the full range of times and temperatures. Comparison to vapor deposited TBCs reveal potential differences in the destabilization mechanism in APS coatings. Furthermore, the lattice parameters extracted from Rietveld refinement of the XRD patterns were used to deduce the stabilizer concentrations of the respective phases, which suggest a retrograde tetragonal solvus over the temperature range studied. In concert with a complementary microstructural study presented in Part II, this effort offers new insights into the mechanisms governing the phase evolution and raises implications for the high-temperature use of 8YSZ ceramics.

Description: Enhanced Eu 3+ luminescence by three Ag species in transparent Ag – Eu 3+ co-doped oxyfluoride glasses was investigated systematically. Under 464 nm excitation, enhancement of Eu 3+ luminescence (four times) is attributed to local-field surface plasmon resonance (SPR) effect of Ag nanoparticles (NPs). Under 350 nm excitation, significant enhancement of Eu 3+ emission (540 times) is assigned to energy transfer (ET) from very small molecule-like, nonplasmonic Ag particles (ML- Ag ) to Eu 3+ . Under 270 nm excitation, big enhancement of Eu 3+ luminescence (75 times) is ascribed to ET from isolated Ag + to Eu 3+ . Our research may extend the understanding of interactions between Ag species and Eu 3+ .

Description: Use of high alumina cement (HAC) as low cement castables (LCC) and ultra-cement castables (ULCC) has increased for refractories applications over the last few years. HAC is being prepared commercially, by fusing or sintering a mixture of argillaceous and calcareous materials above 1500°C and subsequent grinding to obtain a fine powder. Powders produced by this method have low specific surface area. Therefore, the present work was aimed to prepare nano structured HAC powders at lower temperatures than the conventional one. The powder process adopted here was modified gel-trapped precipitation method as described earlier. Two compositions of calcium aluminate powders containing 70 and 80 wt% Al 2 O 3 , respectively, were selected. The remaining material was Ca O in both mixtures. The gel powders obtained by the abovementioned process were calcined at different temperatures with varying soaking periods. The prepared cements were characterized for structural, mechanical, and cementing properties. Finally, the calcination temperature and time were optimized to obtain the desired phases in HAC. The prime cementing phases observed were CA , CA 2 , CA 6 , C 3 A 5 , and C 4 A 3 SO 4 . These cements were then used with bauxite of different grain sizes to prepare LCC and then their physical properties were studied. The XRD patterns of the bauxite-based castables indicated the formation of the corundum phase along with a mullite phase in all samples. Castable containing HAC and 10 wt% zirconia substituted for bauxite improved physico-mechanical and refractory properties. Mullite formed at high temperature acts as a bonding phase and is accounted for high CCS values. These excellent properties of such castables may enable their use in various applications such as refractory lining for fabrication of steel, aluminum, copper, glass, cement, chemicals, and ceramics.

Description: The correlation between microstructural and phase evolution in aged, yttria-partially-stabilized zirconia, air plasma-sprayed coatings is discussed. Freestanding coatings with the dense, vertically cracked structure were isothermally aged at 1482°C (2700°F) in air. Characterization of the resulting microstructures was conducted using transmission electron microscopy, then compared with a parallel analysis of the phase evolution via synchrotron X-ray diffraction (XRD) described in Part I. Additional context was provided by related studies on vapor-deposited coatings. Several salient points can be extracted from these assessments. XRD was further validated as a practical method for studying phase stability after clarification of how the possible phases are defined, including the following: (i) the nature of the t′ phase observed in XRD after phase decomposition has begun and (ii) the relationship between the Y-rich tetragonal ( t″ ) and Y-rich cubic ( c ) phases reported to coexist via XRD. A strong relationship between the initial microstructure and the subsequent phase destabilization is also reported. As a result, phase evolution is proposed to proceed via two competing routes. The interplay between these mechanisms dictates the incubation time for monoclinic formation within a given coating.

Description: Lead-free ( Na 0.53 K 0.45 Li 0.02 )( Nb 0.8 Ta 0.2 ) O 3 (NKLNT) was prepared using a conventional cold-pressing method. A commercial piezoresponse force microscope (PFM) was applied to observe the domain structures of NKLNT ceramics. The typical configuration of the ferroelectric domain was analyzed in abnormal grains with grain sizes that exceeded 40 μm, where tetragonal 90° domains are predominant. The local piezoresponse hysteresis loops were characterized and studied as a function of the domain width ( dw ) in the range 300–1000 nm. It was found that the amplitude signals increased and the coercive field reduced significantly with a decrease in the domain size. Finally, the local longitudinal piezoelectric coefficient ( d 33 ) increased as the domain size decreased.

Description: A phase diagram of Ta 2 O 5 – SnO 2 system was modeled thermodynamically with experimental data available in the literatures. The excess Gibbs energies of the solution phases were described on the basis of the Redlich-Kister solution models. A consistent set of optimized interaction parameters was derived for describing the Gibbs energy of each phase in this system leading to a good fit between calculation and experimental data. The liquidus, solidus, and solvus were calculated and also the lattice stabilities of the components were estimated. In addition, tentative activity diagram and the metastable miscibility gaps in the liquid, α-tantala, and cassiterite phases were calculated from the present thermodynamic modeling.

Description: A new thermally stable microwave dielectric ceramic with low-firing temperature in (1− x ) Li 3 Bi 2 P 3 O 12 – x TiO 2 [(1− x ) LBP – x T , 0 ≤  x  ≤ 0.6] ceramics system was obtained using conventional solid-state reaction method. The phase transformation, microstructure, and microwave dielectric properties of materials were investigated using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) , and a network analyzer. The LBP ceramic ( x  =   0) sintered at 725°C has optimum microwave dielectric properties with relative permittivity (ε r ) of 15.8, Q  ×  f of 26 600 GHz and temperature coefficients of resonant frequency (τ f ) of −130 ppm/°C. The ε r and τ f of (1− x )LBP– x T ceramics were tailored with increasing x values. At x  =   0.55, the ceramic exhibits improved microwave dielectric properties with ε r  = 22.1, Q  ×  f  = 14 900 GHz and τ f  = −2.6 ppm/°C.

Description: The internal reduction of Ni 2+ ions dissolved in 10YSZ (10 percent by mole Y 2 O 3 - stabilized ZrO 2 ) was studied using magnetometry. Chemical methods were used to produce specimens with varying amounts of NiO (0.01–11.8% by mol), below and above the solubility limit of NiO in 10YSZ. The solubility limit was determined using x-ray diffraction measurements in which the change in lattice parameter was correlated to the amount of Ni 2+ ions in solution. Vibrating sample magnetometry (VSM) was used to unequivocally establish that NiO does not exist as a second phase for specimen compositions less than or equal to 0.5 m/o NiO . Specimens with compositions 0.5, 0.1, and 0.01 m/o NiO in YSZ were then prepared and heat treated in Ar – 2% H 2 at 1273 K for times ranging from 1 to 20 h. The ferromagnetic response of the reduced specimens was measured using SQUID magnetometry at 100 K to quantify the amount of Ni metal formed as a function of time. SQUID magnetometry measurements of the same specimens were performed at 5 K where the paramagnetic response may be used to quantify the decrease of Ni 2+ ions during reduction. The two SQUID measurements agree well and revealed parabolic growth law kinetics. Transmission electron microscopy revealed that internal reduction in these specimens proceeds by the formation of Ni 0 along the YSZ grain boundaries. The results indicate that there are two stages of internal reduction in polycrystalline NiO -containing YSZ. For short times, precipitation of Ni occurs at grain-boundary regions, and for longer times, it occurs inside the grains.

Description: A low sintering temperature microwave dielectric material ZnZrNb 2 O 8 was reported. It exhibits a monoclinic structure, belongs to the space group P 2/ c ( C 2 h 4 ), and Z  = 1. The dielectric constant increased with increasing relative density. The Qf value increased with increasing packing fraction. The τ f increased with increasing dielectric constant. The typical values of ZnZrNb 2 O 8 were ε  = 30, Qf  =   61 000 GHz, τ f =−52 × 10 −6  °C −1 , sintered at 950°C.

Description: The mullite ceramic/fiber brick system was bonded by two kinds of phosphate adhesives. The specimens were treated from 200 to 1400°C. The mechanical properties were tested at room temperature and at high temperature, and the relevant bonding mechanism was also discussed. The results show that the addition of silicon can greatly improve the adhesive's mechanical properties. The room-temperature shear strength of the component bonded by adhesive with the silicon calcined at 800°C can reach 6.58 MPa. The shear strength of the adhesive with silicon tested at 800°C can reach 0.42 MPa.

Description: A diagram representing the phase relationships in the Ca 3 ( PO 4 ) 2 – CePO 4 phosphate system has been developed on the basis of results obtained using thermal analysis (DTA/DSC/TG), X-ray diffraction (XRD), and scanning electron microscopy (SEM/EDS) methods. One intermediate compound with formula Ca 3 Ce ( PO 4 ) 3 occurs in the Ca 3 ( PO 4 ) 2 – CePO 4 system at temperature exceeding 1275°C. The compound melts at 1833°C and has one structural form. In the system a solid solution, having the structure of low-temperature form of calcium phosphate Ca 3−3 x Ce x ( PO 4 ) 2− x (where x is a molar fraction of CePO 4 ), exists. The temperature and concentration range of the solid solution has been determined. It has been shown that the Ca 9 Ce ( PO 4 ) 7 phase should be understood as a limited solid solution with x  = 0.25.

Description: The phase-pure AgNbO 3 has been prepared through the hydrothermal reactions of NH 4 HF 2 , Ag 2 O , and Nb 2 O 5 . The room-temperature powder X-ray diffraction analysis reveals that it crystallizes in orthorhombic perovskite lattice with a space group of Pmc 2 1 and cell parameters a  = 15.6999(9), b  = 5.5521(1), and c  = 5.5830(1) Å. The temperatures, pH values, and times play crucial roles in obtaining phase-pure silver niobate. The structural phase transitions were observed at 813 K from cubic to tetrahedral phase and to final orthorhombic phase at 718 K, confirmed by TGA-DTA.

Description: A novel borophosphate glass doped with Ho 2 O 3 and Bi 2 O 3 has been investigated. The efficient energy transfer process between Ho 3+ and bismuth ions is observed and the energy transfer efficiency is 47.8%. The enhanced broadband 2.0 μm emission with a full width at half maximum of 180 nm of Ho 3+ : 5 I 7 → 5 I 8 is obtained by codoping Bi 2 O 3 excited by a 445 nm laser diode. The emission properties and energy transfer mechanism of Ho 3+ sensitized by bismuth ions are discussed. The results indicate that this glass is a promising candidate for 2.0 μm laser material.

Description: A new calorimetry-based method for calculating the activation energy of cement hydration is described. The method requires a scanning calorimeter that can change the sample temperature relatively quickly and has a stable baseline, but the technique is straightforward to perform. Activation energy values can be calculated at multiple hydration times from a single specimen, allowing any changes with time to be assessed. With this method, the measured activation energy at a given time does not depend on the previous microstructural development, as is the case with traditional methods of calculating the activation energy from parallel specimens hydrated isothermally at different temperatures. For tricalcium silicate ( C 3 S ) hydrated in pure water or in a calcium chloride solution, the activation energy remains statistically constant from the earliest times until the degree of hydration exceeds 0.65, with an overall average value of (51.1 ± 1.8) kJ/mol. For cement hydration, the activation energy is also constant until well past the main hydration peak, with slightly lower average values. These results suggest that the rate-controlling step in the hydration process does not change during the early hydration period (the first few days after mixing), as different reaction steps tend to have different activation energies.

Description: This paper reports on the structure, mechanical, and photocatalytic properties of titanium dioxide (TiO 2 ) and tungsten oxide (WO 3 ) films on a brass substrate. TiO 2 and WO 3 films have been successfully deposited on brass by a simple sol-gel dip-coating method and it has been shown that, while both films possess photocatalytic properties, WO 3 films were superior to TiO 2 . Higher surface area and rod-like morphology of WO 3 films might have contributed to their higher photocatalytic activity. Nanoindentation results have shown that both films attach well to the substrate and possess good mechanical properties.