Third Law Entropy of Barium Molybdate

Abstract

The isobaric heat capacities, C p;m , for BaMoO 4 at 2300 K were measured by the relaxation method. The third law entropy, S m , was determined via the Debye-Einstein function into which the Debye temperature, # D , as physico-chemical constant and a thermal expansion term were incorporated. # D was determined from C p;m at very low temperatures. The obtained thermodynamic properties were: S m (BaMoO 4 (cr), 298.15 K)/J K ¹1 mol ¹1 = 152.69 « 1.53; # D (BaMoO 4 (cr))/K = 295 « 3. The phase stability of BaMoO 4 was discussed on the basis of its standard Gibbs energy of formation, Á f G m . It was derived by combining S m determined in this study with the reference data of the standard enthalpy of formation, Á f H m . The thermodynamic properties obtained in the present study can be used for evaluating the hierarchy for formation of the yellow phase related-substances in nuclear waste glasses.

Third Law Entropy of Silver Molybdate

“…• and K for precipitation of transition metal molybdates such as NiMoO 4 22) and Zr 2 MoO 8 [23][24][25] evaluated in our former study 5) • and K data for the end members of the yellow phases of BaMoO 4 5) were listed in Table 5. BaMoO 4 5) is the most stable among such molybdates, meaning that depressing crystallization of the yellow phases is serious problem in the safety nuclear waste management.…”

“…The U r (C [29][30][31][32][33][34] : a semi-empirical power law function composed of the electronic and lattice vibration terms at very low temperatures; an empirical power law temperature function at mediate low temperatures; the Debye-Einstein (DE) at high temperature range, expressed as 5,7,9,11 …”

“…The heat capacities, C • p,m , for Ag 2 MoO 4 were measured in the temperature range 2-300 K by using a relaxation method instrument (model PPMS, Quantum Design, San Diego, CA) 26,27) as in the way of our previous studies 2,5,22) . Two samples (≅ 2.5 × 2.5 × 1 t mm) were prepared by polishing the sintered bodies.…”

“…In our laboratory, thermodynamic investigations for molybdenum related-substances have been carried out [2][3][4][5] as a part of the OECD/NEA TDB Mo Project. Molybdenum is generated as ssion product from uranium in the operating nuclear reactor.…”

Thermodynamic Properties for Nd₂(MoO₄)₃ Formed in the Nuclear Fuel Waste Glasses

“…The unknown standard Gibbs energies of solution, Δ sln G  , at 298. [11][12][13][14][15][16][17] において，OECD/NEA-TDB プロジェク…”