Neodymium selenites

Aleksandrovich and Serebrennikov [62ALE/SER] measured the solubility of Nd2(Se03)3(s) at (298.15 + 0.05) K in HCI, HNO3, and H2SO4 of unspecified concentration. The experiments and the evaluation of the solubility product of the reaction  

Suponitskii, and Karapet yants [71MA1/SUP] prepared crystalline Nd2(Se03)3 and subjected it to calorimetric measurements, see Appendix A. The reevaluated data resulted in the value Aj//° (Nd2(Se03)3, cr, 298.15 K) = - (2848.2 5.8) kJ-mol. Oppermann et al. obtained for this quantity the value -(2833.8 + 5.4) kJ mol from calorimetric measurements in [2002ZHA/OPP] and -(2846 41) kJ-mol from measurements of equilibria at high temperatures in [20020PP/ZHA]. 

The calorimetric results should be the most accurate but they are significantly different. The review adopts their mean value with suitable error bars  

Since the calculation of the enthalpy of formation from the experimental results involved non-TDB auxiliary data, it is included in Appendix E. 

The anhydrous selenite forms on heating NdH(Se03)2 1.5H20 at 535°C. For its further decomposition, see p. 449, Savchenko etal. [1]. 

The refractive indices are n =. 660, n = 1.720. On heating to 300, 400, 600, and 850°C the molar ratio Se.Nd is 1.43,1.38,1.00, and 0.72, respectively. Thus, it differs from the weight loss of NdH(Se03)2 1.5H20 until 850°C is reached where in both cases oxide selenites of the composition Nd202Se03 are formed, Savchenko etal. [1]. 

A fine-grained precipitate of Nd(HSe03)3 1.5H20 is formed in the system Nd203-Se02-H20, see p. 448, at 25 C. Its refractive indices are nx=1.700 and nz=1.767. For the thermal decomposition the following scheme is postulated  

Nd2(Se03)3 0.5 Se02- Nd202Se03- 2 Nd203 A thermogravigram is given, Savchenko et al. [1]. 

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Maier, Suponitskii, and Karapet yants prepared anhydrous crystalline lanthanum, praseodymium, and neodymium selenite by keeping the amorphous salts at an elevated temperature in a sealed tube. The salts are denoted by M2(Se03)3. The standard enthalpies of formation of the compounds have been calculated from the experimental results and auxiliary data in Table A-87. The solvent (sin) employed in the calorimetric dissolution experiments was HCI(aq, 1 18.5). Dissolution was made to the appropriate concentrations and the composition of the solutions will be denoted simply as dilute (dil). 

The authors measured the enthalpy change of the reaction between aqueous solutions of the chlorides of Lu, Yb, Er, Ho, Dy, Tb, Gd, and Nd (Ln) and Ma2Se03(cr). No experimental details of the calorimetric measurements are presented. From other sources it is concluded that the selenites formed were amorphous. The chemical formulas of the se-lenites are written with 8 molecules of water except for neodymium selenite, which is written with 4 molecules of water. No analytical results are, however, provided in the paper. 

The authors reacted a solution of cerium(lll) or neodymium chloride with Na2Se03(cr) in an electrically calibrated calorimeter. The selenites precipitated were amorphous and contained 10 and 8 molecules of water, respectively, when dried at 298 K. These numbers have been used in the re-evaluation of the measurements. The recalculation used the values of the standard enthalpies of formation of Ce (aq) and Nd (aq) proposed in the critical evaluation by Cordfunke and Konings [2001COR/KON], see Appendix E, and of Cl (aq) in [89COX/WAG]. A correction for the enthalpy of dilution from (aq 1 1500) to the aqueous standard state of- (3.5 1.0) kJ-mol was applied. 

Maier, Suponitski, and Karapet yants [67MA1/SUP] studied the same reaction for neodymium and state that the amorphous selenite formed contained 8 molecules of water. The enthalpy change of the reaction found by the two groups is the same. Neo-... 

K2Se04 evaporates without intermediate formation of selenite, Giolito, lonashiro [7]. Potassium Neodymium Selenates... 

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