Application of an adiabatic calomimeter to the determination of the heats of fusion and heats of formation of several metallic compounds
High temperature thermodynamic properties of metal alloys and refractory materials are important in both research and engineering. Reliable and precise measurements are difficult to make and require rather elaborate equipment. In recent years a commercial adiabatic calorimeter has been made available by the Rigaku Denki Company, Ltd., of Tokyo, Japan. The general operating principles of this apparatus are summarized; its application to the measurement of heats of fusion and transformation of materials, and heats of formation of intermetallic phases is described. The results of the heat of formation experiments are: MgZn2 @863° K, -4. 30 kcal/ g-atom; CaMg2 @532° K, -3. 12 kcal/ g-atom; and CeZn @623° K, -10. 6 kcal/ g-atom. The results of the heat of fusion of the materials are: MgZn2, 9. 687 kcal/mole; CaMg2, 11. 744 kcal/mole; CeZn, 7. 826 kcal/mole. The average values for the heats of fusion are accurate to ±2 pct. Disciplines Ceramic Materials | Metallurgy This report is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ameslab_isreports/99
Metal hydride reactions: II. Reaction of hydrogen with CaMG2 and CaCU5 and thermodynamic properties of the compounds☆
Abstract The equilibrium hydrogen pressure for the reaction CaMg2 + H2aiCaH2 + 2Mg was measured in the temperature range 450°–637°C. The data below 517°C can be represented by log PH 2 ( atm ) = −6919 T + 5.95 and that above 517°C by log PH 2 ( atm ) = −6666 T + 5.56 The change in slope at 517°C is to be expected on the basis of a eutectic horizontal at this temperature. The data in the temperature range 450°–517°C were combined with known thermodynamic data for calcium hydride to give the relations ΔFoCaMg2 = −10,624 + 4.28 T (440°–517°C) and ΔFoCaMg2 = −9,735 − 2.46 T + 1.93 T log T (25°–440°C) The equilibrium hydrogen pressure for the reaction CaCu5 + H2aiCaH2 + 5Cu was measured for the temperature range 492°–648°C. The data can be represented by log PH 2 ( atm ) = −6700 T + 7.11 These data were combined with thermodynamic data for calcium hydride to obtain the relations ΔFoCaCu5 = −11,600 − 1,0 T (440°–780°C) and ΔFoCaCu5 = −10,740 − 7.70 T + 1.93 T log T (25°–440°C)
Metal hydride reactions: I. Reaction of hydrogen with solutes in liquid metal solvents
Abstract The precipitation of various solutes as hydrides from liquid metal solutions with hydrogen at one atmosphere pressure was investigated. The solutes considered were calcium, yttrium, lanthanum, cerium and thorium and the solvents were magnesium, Mg-55 wt.% Zn, Mg-30 wt.% Al, and zinc. The residual concentrations of the above solutes in atom percent in magnesium at 650°C were found to be 5.6, 0.034, 2.9. 3-3 and 0.67 respectively. The residual concentration increases rapidly with an increase in temperature as expected from the free-energy data for the hydrides. The addition of a more electronegative component, such as zinc, to the magnesium also increases the residual concentration. The solubilities at various temperatures, under an inert gas, for yttrium in zinc, zirconium in aluminium, thorium in Mg-30 wt.% Al and in Mg-55 wt.% Zn were measured. Hydrogen at one atmosphere pressure was found to have no detectable effect on the solubility of yttrium in zinc, or the solubility of zirconium in aluminum. The activity coefficients of the solutes in magnesium were calculated from the data obtained.