Effect of structural vacancies in interstitial phases on their sintering shrinkage

Андриевский, Р. А.; Клименко, В. В.; Mitrofanov, V. I.; Poltoratskii, N. I.

doi:10.1007/bf00790792

Cited by 6 publications

(5 citation statements)

References 4 publications

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“…The melting points of the mixed-metal carbides outperform those of the pure-metal carbides, as well. For example, 8TaC-ZrC and 4TaC-HfC exhibit melting points of 3890 • C and 3990 • C, respectively, somewhat higher than those of the pure-metal carbides (measured at 3470, 3750, and 3840 • C for ZrC, HfC and TaC, respectively) [42].…”

Section: Mixed-metal Carbidesmentioning

confidence: 90%

Novel Processing of Unique Ceramic-Based Nuclear Materials and Fuels

Zhang¹,

Singh²

2008

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Advances in nuclear reactor technology and the use of gas-cooled fast reactors require the development of new materials that can operate at the higher temperatures expected in these systems. These include refractory alloys based on Nb, Zr, Ta, Mo, W, and Re; ceramics and composites such as those based on silicon carbide (SiC f -SiC); carbon-carbon composites; and advanced coatings. Besides the ability to handle higher expected temperatures, effective heat transfer between reactor components is necessary for improved efficiency. Improving thermal conductivity of the materials used in nuclear fuels and other temperature critical components can lower the center-line fuel temperature and thereby enhance durability and reduce the risk of premature failure.Silicon carbide (SiC) is an important ceramic, most commonly used because of its excellent properties such as high strength, high modulus, excellent creep resistance and its high temperature stability. Moreover, crystalline silicon carbide is attracting wide attention as a promising candidate for several applications in nuclear reactors owing to its high thermal conductivity, high melting temperature, good chemical stability, and resistance to swelling under heavy ion bombardment. There have been many efforts to develop SiC based composites in various forms for use in advanced energy systems. However, fabricating SiC based composites by traditional powder processing route generally requires very high temperatures for pressureless sintering. In recent years, with the development of high yield preceramic precursors, the polymer infiltration and pyrolysis (PIP) method has aroused interest for the fabrication of ceramic based materials. Polymer derived ceramic materials offer unique advantages such as ability to fabricate net shaped components, incorporate reinforcements, along with lower processing temperatures, and perhaps most importantly relatively easy control over the microstructure. The raw materials are element-organic polymers whose composition and architecture can be tailored and varied.The primary focus of this work is to use a pyrolysis-based process to fabricate a host of novel silicon carbide-metal carbide/oxide composites, and to synthesize new materials based on mixed-metal (metal/silicon) carbides that cannot be processed using conventional techniques. These mixedcarbide material systems are expected to offer improved material properties for higher-temperature applications. Our fabrication technique resulted in both amorphous and nano-grained SiC matrix composites by controlled pyrolysis of allylhydridopolycarbosilane (AHPCS), the precursor for SiC for our study, under inert argon atmosphere.Cylindrical pellets, φ25 × 25 mm, were fabricated for bulk scale characterization. These samples were analyzed in terms of density and porosity, thermal conductivity, and flexural strength under multiaxial loading conditions. The final composition in the fabricated composite was studied use Xray diffraction (XRD). This was useful in understanding the relative stabil...

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Section: Mixed-metal Carbidesmentioning

confidence: 90%

Novel Processing of Unique Ceramic-Based Nuclear Materials and Fuels

Zhang¹,

Singh²

2008

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“…(4) does not hold for this case. The sintering of nonstoichiometric zirconium carbides was examined in detail to reveal three dependences ΔV/V = = f(C/Me): shrinkage increases with deviation from stoichiometry at T < 2300°C, does not depend on structural vacancies at T = 2300°C, and decreases with increase in structural vacancies at T > 2300°C [57]. The last dependence was attributed to the substantial grain growth in sintered samples.…”

Section: Diffusion Phenomenamentioning

confidence: 99%

Research into sintering and related phenomena: personal experience

Андриевский

2011

Powder Metall Met Ceram

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The studies on deformation and diffusion processes during sintering are analyzed. Attention is paid to the effect of compressive and tensile stresses on shrinkage of silver, copper, and nickel powders. Superplastic deformation and displacement of particles as a whole are observed during shrinkage. Self-diffusion in transition metal carbides as well as their creep and neck growth during sintering are widely studied. The theory of effective diffusion coefficient is developed to be applied to diffusion-controlled processes in interstitial phases. The proposed relationships are shown to be applicable to creep and neck growth during sintering. Areas of further nanoscale studies are discussed.

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“…(A) Young's modulus as calculated 42,62,105 and measured experimentally, 102,103,106–111 (B) bulk modulus as calculated 16,42,62,105 and measured experimentally, 102,103,107,108,112 (C) shear modulus as calculated 16,42,62,105 and measured experimentally, 102,103,112–114 (D) Pugh's ratio as calculated 16,42,62,105 and measured experimentally, 103,112 and (E) hardness as calculated 16,42,62,105 and measured experimentally 87,97,111–113,115–125 …”

Section: Property Variation With Vacancy Concentration and Orderingmentioning

confidence: 99%

Vacancy ordering in substoichiometric zirconium carbide: A review

Davey

Chen

2022

Int J Ceramic Engine & Sci

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Zirconium carbide has a wide range of substoichiometry facilitated by varying numbers of carbon vacancies. Most experimental studies consider a solid solution of carbon and vacancies without long-range ordering of vacancies. However, theoretical studies predict several superstructural long-range ordered phases to be stable at low temperatures, and these predictions have been validated by experimental fabrication in some cases. The thermophysical properties of zirconium carbide are, therefore, affected not only by the number of carbon vacancies, but their arrangement, which increases the potential of its use as a tuneable ceramic in various applications in aerospace and nuclear industries. This review summarizes the experimental and theoretical studies exploring the longrange ordered zirconium carbides including the known crystal structures, the mechanism for vacancy ordering, and the presently available information on the thermophysical properties. Explanations for the infrequent experimental observations of ordered zirconium carbides are also discussed considering fabrication temperatures, vacancy diffusion, and the effects of impurities, which may be helpful for future synthesis. While our understanding of vacancy ordering in zirconium carbide has vastly improved in recent years, there remain significant knowledge gaps. Areas where more experimental and theoretical studies are needed for further understanding are highlighted.

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Effect of structural vacancies in interstitial phases on their sintering shrinkage

Cited by 6 publications

References 4 publications

Novel Processing of Unique Ceramic-Based Nuclear Materials and Fuels

Novel Processing of Unique Ceramic-Based Nuclear Materials and Fuels

Research into sintering and related phenomena: personal experience

Vacancy ordering in substoichiometric zirconium carbide: A review

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