Heat capacity and thermodynamic properties of ditungsten carbide, W2C1-x, from 10 to 1000 K

Thermodynamic properties of tungsten carbide, W2C0.833, have been derived from heat capacities measured by adiabatic calorimetry in the range 10-1000 K on a sample rich in this phase. The standard entropy of W2C0.833 was found to be 75.80 J K-1 mol-1 at 298.15 K and 159.8 J K-1 mol-1 at 1000 K. Thermodynamic formation values for W2C0.833 were deduced from the reported coexistence of this phase with tungsten and tungsten monocarbide at about 1550 K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27259/1/0000268.pd

Heat capacity of MnAs0.88P0.12 from 10 to 500 K: Thermodynamic properties and transitions

The heat capacity of MnAs0.88P0.12 has been measured by adiabatic shield calorimetry from 10 to 500 K. It is shown that very small energy changes are connected with two magnetic order-order transitions, indicating that these can be regarded as mainly "noncoupled" magnetic transitions. At higher temperatures contributions to the excess heat capacity arises from a magnetic order-disorder transition, a conversion from low- to high-spin state for manganese, and a MnP- to NiAs-type structural transition. The observed heat capacity is resolved into contributions from the different physical phenomena, and the character of the transitions is discussed. In particular it is substantiated that the dilational contribution, which includes magnetoelastic and magnetovolume terms as well as normal anharmonicity terms, plays a major role in MnAs0.88P0.12. The entropy of the magnetic order-disorder transition is smaller than should be expected from a complete randomization of the spins, assuming a purely magnetic transition. Thermodynamic functions have been evaluated and the respective values of Cp, {SOm(T) - SOm(0)}, and -{GOm(T) - HOm(0)}/T at 298.15 K are 68.74, 72.09, and 32.30 J K-1 mole-1, and at 500 K 56.05, 108.12, and 56.64 J K-1 mole-1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26552/1/0000091.pd

Thermodynamics of iron sulfides I. Heat capacity and thermodynamic properties of Fe9S10 at temperatures from 5 K to 740 K

Measurements of the heat capacity of Fe9S10 over the temperature range 5 K to 740 K reveal a first-order structural transition at 495 K and two higher-order transitions with maxima at 534 K and 591 K. The last two are of coupled magnetic and structural origin. The structural changes giving rise to the heat-capacity effects are identified, and the magnetic properties are interpreted in terms of these. The standard entropy at 298.15 K of (1/19)Fe9S10 is compared with those of (1/2)FeS and (1/15)Fe7S8. The origin of the higher molar entropy for the first compound is found to reside mainly in the higher electronic heat-capacity contribution. The thermodynamic properties for (1/10)Fe9S10 have been evaluated and the values of Cp, m ΔT0Sm, and ΔT0Hom are 6.171 · R, 7.598 · R and 1147.3 · R · K at 298.15 K and are 6.944 · R, 14.524 · R, and 4572.4 · R · K at 740 K. (R = 8.31441 J · K-1 · mol-1).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29435/1/0000516.pd

Thermodynamics of thallium alkanoates VI. Thallium(I) n-heptanoate revisited

The heat capacity of thallium(I) n-heptanoate has been remeasured on a new sample on which the preparative procedures were modified to eliminate the 1-1 (salt+acid) complex (soap) in a previously studied sample. The sub-ambient heat capacity of a new highly pure thallium(I) n-heptanoate is characterized by one set of transitions between 262 and 272 K and another transition at 301 K. The lowest transition temperature at 262.1 K has a maximum of Cp, m [approximate] 559R. Next, a bifurcated pair (at 268.6 and 271.4K) have Cp, m [approximate] 300R, and the highest transition (at 301.0 K) has a maximum Cp, m [approximate] 1697R. The corresponding values of [Delta]trsSmo for the two sets are about 2.24R and 1.10R. At 298.15 K the values of [Delta]0TSmo, [Delta]0THmo, and [Phi]mo(T) are 39.79R, 5979R[middle dot]K, and 19.74R. Smoothed thermodynamic functions at selected temperatures are tabulated through melting.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28189/1/0000641.pd