Papers by Keyword: Transition Metal Carbide

Abstract: In the present study, seven refractory compounds - TiC, NbC, TaC, WC, Ti (C,N), (Ti,Nb)(C,N) and TiN - have been produced by plasma-chemical synthesis and carbothermal reduction process of a precursor prepared by sol-gel method. The phase composition, crystallite size, morphology and specific surface area of the synthesized powders are investigated by XRD, TEM, SEM and BET respectively. Spark plasma sintering (SPS) method (up to 1850 °C, heating rate of 100 °C/min and dwelling time of 5 min.) are used for investigation of compacting of these compounds. Characteristics of the obtained ceramic materials are provided.

Abstract: The earlier studies showed that addition of different chromium carbides to nonstoichiometric fine titanium carbide improve sintering in the similar way. The phase, structural and microstructural changes for addition of various chromium carbides were also similar. In the present work the composite materials were made of various carbon quantity saturated titanium carbide (as matrix) and commercial chromium carbide Cr3C2 (as additive). The titanium carbide powders with variable content of carbon in structure were synthesized by the SHS method. The chromium carbide in quantity of 7.5 % by volume was added to the initial mixture. The influence of various stoichiometry of titanium carbide on onset temperature of sintering was examined by use of high temperature dilatometer. The phase and structural changes of examined materials during sintering were made using XRD and Rietveld method. The evolution of microstructure, versus of different stoichiometry titanium carbides, was observed by use of scanning electron microscopy.

Abstract: An ab initio study was carried out on interface energies at coherent interfaces between bcc Fe and MXs (NaCl structure, M = Ti, Zr, Hf, V, Nb, Ta, X=C, N). The interface energies have positive values for carbides and nitrides of group IVB metals (Ti, Zr, Hf), while they have negative values for carbides and nitrides of group VB metals (V, Nb, Ta). Influence of bond energy was estimated using the discrete lattice plane/nearest neighbor broken bond (DLP/NNBB) model. It was found that the dependence of interface energy on the type of carbides and nitrides was closely related to changes of the bond energies between Fe, M and X(=C, N) atoms before and after formation of the interfaces Fe/MX.

Abstract: In the frame of the development of new nuclear reactors (Gen-IV project), materials able to withstand very high temperatures are required. Among the components of the cores, the transition metal carbides could be favourably considered as fission products barriers or inert matrix for the fuel. They are highly refractory, have good neutron properties and fission products retention. Unfortunately, first they are brittle and second the elaboration process of bulk materials requires drastical conditions (temperature, pressure). We have then undertaken the comparison of different materials to investigate the potentialities of nano-sized microstructures for the improvement of the mechanical properties and to determine the impact of different elaboration routes to obtain high density articles. The elaboration process of the nano-sized powders is presented elsewhere [M. Dollé et al., this meeting]. Here, we compare different sintering processes (uniaxial hot-pressing, spark plasma sintering) and we present a new process able to produce high density zirconium carbide articles with soft conditions. We show that the sintering of co-ground zirconium and graphite powders lead to high density, homogeneous, low grain-size materials at temperatures as low as 1500°C. At the contrary, the nano-powders appear to be more difficult to densify that classical micro-sized powders.