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  • Articles  (33)
  • Wiley  (33)
  • Copernicus
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (33)
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  • Articles  (33)
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  • 1
    Publication Date: 2013-09-19
    Description: The implementation of Ceramic Matrix Composites necessitates the understanding of stress-dependent damage evolution. Toward this goal, two liquid silicon infiltrated SiCf reinforced SiC composites were tensile tested with electrical resistance (ER) monitoring as well as acoustic emission to quantify matrix cracking. ER was modeled using a combination of resistors in series and parallel to model transverse matrix cracks and fiber/matrix segments between matrix cracks. It is shown that resistance change is sensitive to transverse matrix crack formation and stress-dependent debonding length. The model appears to be accurate up to the stress for matrix crack saturation.
    Print ISSN: 1546-542X
    Electronic ISSN: 1744-7402
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
    Publication Date: 2013-04-11
    Description: Structural and dielectric properties of (1− x ) BaTiO 3 – x Bi ( Mg 1/2 Ti 1/2 ) O 3 ( x  = 0.1–0.5) were investigated to understand the binary system and utilize it for high-voltage, high energy density capacitors. The solubility limit for Bi ( Mg 1/2 Ti 1/2 ) O 3 in a BaTiO 3 perovskite was between x  = 0.4 and x  = 0.5. A phase with pseudocubic symmetry was formed for x  = 0.1–0.4; a secondary phase developed at x  = 0.5. Dielectric measurements showed highly diffusive and dispersive relaxor-like characteristics from 10 to 40 mol% of Bi ( Mg 1/2 Ti 1/2 ) O 3 . These compositions also showed high relative permittivity with low-temperature coefficients of permittivity over a wide range of temperatures −100°C–600°C. Relaxation behavior was quantitatively investigated using the Vogel–Fulcher model, which revealed the activation energy of 0.17–0.22 eV. Prototyped multilayer capacitors of 18 mm × 17 mm × 4 mm dimensions with a capacitance of 12.5 nF at 1 kHz were successfully constructed and demonstrated multiple charge–discharge characteristics up to 10 kV.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
    Publication Date: 2018
    Description: Abstract The electrical behavior of iron‐doped strontium titanate (Fe:SrTiO3) single crystals equilibrated at 900°C and quenched below 400°C at various oxygen partial pressures () was investigated via impedance spectroscopy and compared to defect chemistry models. Fe:SrTiO3 annealed and quenched between 1.2 × 10−14 and 2.0 × 10−4 Pa exhibits a conduction activation energy (EA) around 0.6 eV, consistent with ionic conduction of oxygen vacancies. However, sudden changes in EA are found to either side of this range; a transition from 0.6 to 1 eV is found in more oxidizing conditions, while a sudden transition to 1.1 and then 0.23 eV is found in reducing These transitions, not described by the widely used canonical model, are consistent with predictions of transitions from ionic to electronic conductivity, based on first principles point defect chemistry simulations. These models demonstrate that activation energies in mixed conductors may not correlate to specific conduction mechanisms, but are determined by the cumulative response of all operative conduction processes and are very sensitive to impurities. A comparison to electrically degraded Fe:SrTiO3 provides insight into the origins of the conductivity activation energies observed in those samples.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 4
    Publication Date: 2016-08-30
    Description: Conventional thermal sintering of ceramics is generally accomplished at high temperatures in kilns or furnaces. We have recently developed a procedure where the sintering of a ceramic can take place at temperatures below 200°C, using aqueous solutions as transient solvents to control dissolution and precipitation and enable densification (i.e., sintering). We have named this approach as the “Cold Sintering Process” because of the drastic reduction in sintering temperature and time relative to the conventional thermal process. In this study, we fabricate basic monolithic capacitor array structures using a ceramic paste that is printed on nickel foils and polymer sheets, with silver electrodes. The sintered capacitors, using a dielectric Lithium Molybdenum Oxide ceramic, were then cold sintered and tested for capacitance, loss, and microstructural development. Simple structures demonstrate that this approach could provide a cost-effective strategy to print and densify different materials such as ceramics, polymers, and metals on the same substrate to obtain functional circuitry.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
    Publication Date: 2011-04-01
    Description: We have synthesized high-purity Yb 3+ -doped Lu 2 O 3 powder by the coprecipitation method. We have demonstrated that the recrystallization of the metal nitrates greatly improve the chemical purity of the resulting oxides. From thermogravimetry and differential thermal analysis study, we have calculated the approximate formula of the oxinitrate precipitate precursor as Lu 1.8 Yb 0.2 (OH) 5.44 (NO 3 ) 0.56 ·0.58H 2 O. Fine and soft agglomerate powders were obtained after calcinations. We have shown that the powder is mainly in the form of polycrystalline soft agglomerates composed with 15–20 nm size crystals. The resulting ceramic showed higher transparency (close to theoretical limit) compared with the ones fabricated with commercial powders.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
    Publication Date: 2016-10-25
    Description: We recently developed a novel technique of cold sintering process (CSP) to obtain dense ceramics at extraordinarily low temperatures. In this communication, we demonstrate the feasibility of applying CSP to zirconia-based ceramics. As exemplified by 3Y-TZP ceramics, a significantly enhanced densification evolution is observed. Water is simply utilized as a sintering aid to assist the ceramic densification under an applied external pressure. The low-temperature advantage of CSP outstands in contrast to the densification curves compiled from other sintering techniques. A gradual monoclinic-to-tetragonal phase transformation is revealed in correspondence to the densification development, as well as contributes to the mechanical hardness evolution. A Vickers Hardness reaches ~10.5 GPa after annealing the cold-sintered ceramics at 1100°C, which is comparable to those values reported in the previous studies at higher sintering temperatures. Such a sintering methodology is of significant importance as it provides a roadmap for cost-effective processing of zirconia-based ceramics and composites that enable broad practical applications.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
    Publication Date: 2016-10-28
    Description: Cold sintering process (CSP) is an extremely low-temperature sintering process (room temperature to ~200°C) that uses aqueous-based solutions as transient solvents to aid densification by a nonequilibrium dissolution–precipitation process. In this work, CSP is introduced to fabricate microwave and packaging dielectric substrates, including ceramics (bulk monolithic substrates and multilayers) and ceramic–polymer composites. Some dielectric materials, namely Li 2 MoO 4 , Na 2 Mo 2 O 7 , K 2 Mo 2 O 7 , and (LiBi) 0.5 MoO 4 ceramics, and also (1− x )Li 2 MoO 4 − x PTFE and (1− x )(LiBi) 0.5 MoO 4 − x PTFE composites, are selected to demonstrate the feasibility of CSP in microwave and packaging substrate applications. Selected dielectric ceramics and composites with high densities (88%–95%) and good microwave dielectric properties (permittivity, 5.6–37.1; Q × f , 1700–30 500 GHz) were obtained by CSP at 120°C. CSP can be also used to potentially develop a new co-fired ceramic technology, namely CSCC. Li 2 MoO 4 −Ag multilayer co-fired ceramic structures were successfully fabricated without obvious delamination, warping, or interdiffusion. Numerous materials with different dielectric properties can be densified by CSP, indicating that CSP provides a simple, effective, and energy-saving strategy for the ceramic packaging and microwave device development.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 8
    Publication Date: 2016-10-28
    Description: With the cold sintering process (CSP), it was found that adding acetic acid to an aqueous solution dramatically changed both the densities and the grain microstructures of the ZnO ceramics. Bulk densities 〉90% theoretical were realized below 100°C, and the average conductivity of CSP samples at around 300°C was similar to samples conventionally sintered at 1400°C. Frequently, ZnO is also used as a model ceramic system for fundamental studies for sintering. By the same procedure as the grain growth of the conventional sintering, the kinetic grain growth exponent of the CSP samples was determined as N = 3, and the calculated activated energy of grain growth was 43 kJ/mol, which is much lower than that reported using conventional sintering. The evidence for grain growth under the CSP is important as it indicates that there is a genuine sintering process being activated at these low temperatures and it is beyond a pressurized densification process.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 9
    Publication Date: 2017-04-22
    Description: Cold-sintered ZnO and Ca 3 Co 4 O 9 polycrystalline materials were shown to have thermoelectric properties comparable to those of conventionally sintered ceramics. Extending these processing conditions into a cold sintering co-fired ceramic (CSCC) technology, we integrated n -type and p -type thermoelectric oxides and a separating insulating layer to demonstrate functional multilayer thermoelectric generator devices. A co-fired structure with an insulating 8 mol% yttria-stabilized zirconia (8YSZ) layer enabled multilayer thermoelectric generators (TEG) to be fabricated with a 5 n-p junction device (20 layers). A transmission electron microscopy analysis of the interfaces between the various materials under the co-firing cold sintering showed some interdiffusion of chemical constitutes in a 2.0 μm interface region between the respective ceramic phases. The co-firing of multilayer ceramic and polymer structures were also shown to be possible using insulation layers of polytetrafluoroethylene (PTFE) thermoplastic layers. This demonstrated the feasibility of a single-step process for new structures with both ceramics and polymers, opening up new directions for many new device designs.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
    Publication Date: 2016-10-14
    Description: Research on sintering of dense ceramic materials has been very active in the past decades and still keeps gaining in popularity. Although a number of new techniques have been developed, the sintering process is still performed at high temperatures. Very recently we established a novel protocol, the “Cold Sintering Process (CSP)”, to achieve dense ceramic solids at extraordinarily low temperatures of 〈300°C. A wide variety of chemistries and composites were successfully densified using this technique. In this article, a comprehensive CSP tutorial will be delivered by employing three classic ferroelectric materials (KH 2 PO 4 , NaNO 2 , and BaTiO 3 ) as examples. Together with detailed experimental demonstrations, fundamental mechanisms, as well as the underlying physics from a thermodynamics perspective, are collaboratively outlined. Such an impactful technique opens up a new way for cost-effective and energy-saving ceramic processing. We hope that this article will provide a promising route to guide future studies on ultralow temperature ceramic sintering or ceramic materials related integration.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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