Polyselenides formation

The potentiometric titration data (295 K , pH-buffer scale) were all collected at an analytical composition of the solution very close to HSe, which make them highly vulnerable to experimental errors. The evaluated value of pA a2, 11.7, is also claimed to be much too low because of the formation of polyselenide ions . 

GLA/DUB] Gladyshev, V. P., Dubinina, L. K., The free energy of formation of polyselenide anions in aqueous solutions, Russ. J. Phys. Chem., 56, (1982), 259-260. Cited on page 154. 

White, fine, hygroscopic crystals rapidly turns red in moist air because of Se separation and formation of polyselenides. 

Cadmium Selenide. This compound, or the polyselenide, is responsible for the colour in selenium ruby glass. With some CdS in solid solution it forms the basis of Cd-Se red ceramic (especially vitreous enamel) colours the firing temperature must not exceed about 850°C. The presence of up to 3% V2O5 is claimed to stabilize the colour, blackening in the presence of a glaze or flux containing Pb is caused by the formation of PbSe. Cadmium Silicate. CdSi03, sp. gr. 4.9 m.p. 1240°C. 

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