Lattice Energies of Apatites and the Estimation of ΔHf°(PO43-, g)

• DOI: 10.1021/ic030255o
• Publication Date: 2004-03-29T05:24:45Z
• Authors: Natalie J. Flora; Claude H. Yoder; H. Donald Brooke ...
• Keywords: Lattice (music)

Experimentally based lattice energies are calculated for the apatite family of double salts M5(PO4)3X, where M is a divalent metal cation (Ca, Sr, Ba) and X hydroxide or halide. These values also shown to be estimable, generally within 4%, using recently derived Glasser−Jenkins equation, UPOT = AI(2I/Vm)1/3, A 121.39 kJ mol-1. The apatites exhibiting greater covalent character (e.g., Pb, Cd, etc.) less well reproduced but 8% experimentally value. energy ionic (having identical strengths, I) takes particularly simple form UPOT/kJ mol-1 26680/(Vm/nm3)1/3, reproducing cycle when Vm estimated by ion volume summation employing PO43- (not previously quantified with an associated error) 0.063 ± 0.003 nm3. value enthalpy formation gaseous phosphate ion, ΔHf °(PO43-, g), absent from current thermochemical tabulations. Examination solution solid state cycles apatites, however, leads us remarkably consistent 321.8 1.2 Experimental were used along other thermodynamic data determine enthalpies, entropies, free dissolution uncertain stabilities. compared corresponding stable rationalize relative instability certain derivatives.