Scandium selenites

Scandium selenite hydrates have been prepared, usually by reaction of scandium compounds like Sc(OH)3 or SCCI3 with H2Se03 or with alkali selenites in aqueous systems. The anhydrous selenites have been obtained by dehydration of the corresponding hydrates. 

Precipitation from Aqueous Scandium Selenite Systems 

The amorphous compound is prepared from aqueous solutions of 8CCI3 and Na28e03, Maier et al. [7]. The heat of formation is AH =-1326.5 kcal/mol, Wagman et al. [9]. A decahydrate was not found by Znamenskaya, Komissarova [3] in aqueous solutions of 8c(OH)3 and H28e03. 

The pycnometrically measured density is 2.80 g/cm at 20°C. Intensities and d values of the X-ray diffraction diagram are given in the paper [3]. 

The thermal decomposition processes on heating from 20 to lOOO C at a heating rate of 8 to 10 K/min in air or N2 are similar but in the latter case the temperatures of the endothermic effects are increased by 30 K. DTA and TG curves are given. Dehydration occurs in a single stage at 120 to 160°C. The decomposition can be represented schematically as follows  

In view of the disagreement between the primary and the reported experimental data and the scatter amongst the derived values of Af//° (802(8003)3-IOH2O, am, 298.15 K), no value of the enthalpy of formation of scandium selenite will be selected. 

No other thermodynamic data have been found for scandium selenites. 

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The scandium selenite formed in the reaction between an aqueous solution of ScCls and Na2Se03(cr) was amorphous and contained 10 molecules of water. The enthalpy of formation of Sc2(SeO3)3-10H2O(am) is evaluated in Table A-61 both with the reported enthalpy changes and those calculated by the review from the primary data. 

Normal and acid scandium selenites have been prepared from aqueous solutions and their solubilities in H2O and HgSeOs determined. The thermal decomposition of 802(8003)3,5H2O may be represented by the sequence ... 

Precipitation from Aqueous Scandium Selenite Systems... 

Alkali Scandium Selenites Anhydrous Alkali Scandium Selenites... 

Infrared absorption frequencies (cm ) of scandium selenites. The assignments are based on the and Cj, symmetries of the selenite and... 

MAI/SUP] Maier, A. I., Suponitskii, Y. L., Karapet yants, M. K., Enthalpy of formation of scandium and yttrium selenites, Izv. Akad. Nauk SSSR, Neorg. Mater., 4, (1968), 921-924, in Russian, English translation in [68MAI/SUP2]. Cited on pages 354, 356, 498, 522, 528. 

Ternary rare earth selenites are also known, although the number of studies on them is still very limited. Giesbrecht and Giolito (1967) reported the precipitation of amorphous sodium yttrium selenite NaY(SeOj)2-3H20 by mixing yttrium chloride and sodium selenite solutions. A systematic study of the formation of the sodium, potassium, and ammonium compounds was carried out by Erametsa et al. (1973). Besides the composition of the MR(Se03)2 H20 (M = Na, K, or NH4 n = 2 or 2 ) phases they recorded the X-ray powder diffraction patterns for the different structural types and studied the compounds by IR spectroscopic and thermoanalytical techniques. A detailed study on the formation of scandium... 

The presence of an additional cation also makes the thermogram more complex, as seen for the alkali rare earth selenites (Erametsa et al., 1973) and the corresponding scandium compounds, which also contain variable amounts of hydrogen (Znamenskaya et al., 1978). Below 1000°C the end products contain the alkali ion. The extra cation is volatilized at relatively low temperatures or below 600°C only in the case of ammonium compounds (Erametsa et al., 1973). 

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