Sodium Lanthanum Selenates

The anhydrous double selenate is formed by dehydration of NaLa(8e04)2 2.5H20 at 140 to 200°C (TG) or 222 to 240°C (DTA), lonashiro, Giolito [3]. Behavior on further heating see below. 

The compound is prepared like and has properties corresponding to LiLa(8e04)2 6H20, see p. 504. The pycnometrically determined density at 25°C is 3.01 g/cm, Gomez Madrazo et al. [4]. 

Preparation and investigations on thermal decomposition are like LiLa(8e04)2 4H20, see p. 505. Decomposition may be represented by the following reaction scheme  

NaLa(8e04)2 2.5H20 NaLa(8e04)2 + 2.5H20 140 to 200 220, 240 

Above 900°C, partial reduction of Na2Se04 to Na2Se03 occurs. This mixture undergoes decomposition and evaporation. Thus, the residue contains La203 and 30% of the theoretical amount of Na20 [3]. 

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