Abstract

The use of CsCl as a matrix for the preparation of disks for infrared spectra of sodium salts was investigated. During the grinding of the disks, sodium salts form a substitutional solid solution of hydrated Na⁺ in a CsCl lattice. The IR spectrum of the substitutional hydrated solid solution has four characteristic HOH absorption bands which are very sharp, whereas in general, the spectra of hygroscopic salts have broad HOH absorption bands. The spectra of sodium salts in a CsCl matrix were compared to those of (1) potassium halides and LiCl in KBr, CsCl, and CsI matrices; (2) various cesium salts in NaCl and NaBr matrices; (3) various sodium salts in a CsI matrix. From the various spectra it was concluded that the formation of the substitutional solid solution of hydrated Na⁺ in CsCl crystals is a mechanochemical process. In the first step, NaCl is formed because of a double decomposition reaction between the sodium salt and CsCl. In the second step, a solid solution of NaCl in CsCl crystals is obtained because of a mechanochemical process in which planes of NaCl crystals and atmospheric water combine with planes or fractures of CsCl crystals due to sliding of crystal planes under the effect of shearing. Substitutional solid solutions of hydrated Na⁺ in CsBr and CsI are obtained when NaBr or NaI is ground with CsBr or CsI.

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