Rubidium Lanthanum Selenates

The compound is prepared like and its properties correspond to LiLa(Se04)2 6H20, see p. 504. The pycnometrically determined density is Dexp = 3.13 g/cm at 25°C. The monohydrate RbLa(Se04)2 H20 is obtained on heating at 110°C and RbLa(Se04)2 at 150°C [4]. 

The preparation is analogous to the lithium double selenate, see p. 505, and thermal decomposition was studied by TG (5.2 K/min) and DTA (9 K/min, diluted to 20% in a-Al203) in static air atmosphere at ambient pressure. The reactions are represented by the following scheme  

During the last step, Rb2Se04 is evaporated and the final residue consists almost entirely of La203. The formation of La2(Se03)3 could not be detected by TG, probably because of the almost simultaneous formation of La202Se03 [3]. 

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