Carbide heat capacity

WES/FEI2] Westrum, Jr., E. F., Feick, G., Zirconium carbide Heat capacity and thermodynamic properties from 5 to 350 K, J. Chem. Eng. Data, 8, (1963), 176-178. Cited on pages 209, 210. 

The Group 4—6 carbides are thermodynamically very stable, exhibiting high heats of formation, great hardness, elevated melting points, and resistance to hydrolysis by weak acids. At the same time, these compounds have values of electrical conductivity. Hall coefficients, magnetic susceptibiUty, and heat capacity in the range of metals (7). 

H. Krlkorian, "Estimation of High-Temperature Heat Capacities of Carbides," University of California, UCRL 6785,... 

Table 5. The Heat Capacity of Ordered VCy Carbides with Different Carbon Contents...

A determination of AH29s by combustion calorimetry gave —43.9 0.4kcal/mole for a composition near TiC, 0 (Humphrey, 1951). The carbide was TiCo.996 (total carbon) with 0.60% impurities and was the same material used by Naylor (1946) for his heat capacity measurement. This becomes — 44.1 kcal/mole when a more recent value for the heat of formation of TiOj is used (Mah et al, 1957). The heat produced by the direct reaction between the elements above 1320° has been used to calculate a standard heat of formation of —45.5 + 4.6 kcal/mole for an unstated composition (Lowell and Williams, 1961). 

The measurements of Volkova et al. (1965) also are high and the resulting heat capacity of > 16 cal/mole-deg would be greater than other transition metal carbides. In addition, there is some doubt concerning the purity of the sample used. 

In the absence of measurements, a number of estimations of the heat capacity have fluorished. Two of the more widely used attempts are compared to several direct measurements and the results of the present treatment in Fig. 62. Note that this system, like many of the other carbides, has an increasingly larger Cp as the melting point is approached. Also, like the other carbides, one would expect to find an important change in these... 

As a result of this treatment, a number of the carbides were also found to have an increasing Cp value near their melting temperatures. When an explanation is attempted, it should be borne in mind that many of the carbides, TiC for example, precipitate carbon from the stoichiometric composition upon cooling. The heat thus generated would add to the heat content and increase the heat capacity at high temperatures. On the other hand, some carbides precipitate carbon upon heating. As a result, the measured sample would consist of a mixture of graphite and a carbide of a reduced stoichiometry. 

Heat of Formation, Heat Capacity, and Entropy at 298.I5°K for the Transition and Actinide Carbides... 

Schick s work includes the study of borides, carbides, nitrides, and oxides of some elements in Groups IIA, IIIB, IVA, IVB, VB, VIIB, and VIII as well as selected rare earths and actinides. As far as possible, the tables have been made compatible with the JANAF tables. Among the subjects treated are phase diagrams, heat capacities, enthalpies, entropies, enthalpies of phase transformation, formation, and reaction, melting temperatures, triple points, free energies of formation, vapour pressures, compositions of vapour species, ionization and appearance potentials, e.m.f. of cells, and enthalpies of solution and dilution. Volume 1 summarizes the techniques used to analyse data and cites the data analysed, and Volume 2 gives tables of values produced by this study. 

AA Rempel, A1 Gusev. Heat capacity of niobium carbide in different structural states. Phys Status Solid (a) 113 353, 1989. 

AI Gusev, AA Rempel, VN Lipatnikov. Heat capacity of niobium and tantalum carbides NbC, and TaCj, in disordered and ordered states below 300 K. Phys Status Solid (b) 194 467, 1996. 

Heat capacities of titanium carbides and nitrides as a function of temperature. (From Ref. 

Reference Material—Glass beads, alumina powder, silicon carbide, or any material known to be unaffected by repeated heating and cooling and free from interfering transitions. The specific heat capacity of the reference should be as close as possible to that of the test material. 

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