Preparation of Inorganic Compounds at Near Room Temperature by the Direct Conversion of Borate Glass in Solutions of the Corresponding Anions

The preparation of alkaline-earth chromate, selenite, and stannate compounds at near room temperature by the direct conversion of borate glass in aqueous solutions of the corresponding anions was investigated. Borate glass particles (150–300 μm) with the composition 20Na₂O·20CaO·60B₂O₃ or 20Na₂O·20BaO·60B₂O₃ (mol%) were prepared by conventional methods and immersed in dilute solutions of K₂CrO₄, K₂SeO₃, or K₂SnO₃ at 37°C. The conversion of the glasses was monitored using weight loss and pH measurements, while X-ray diffraction (XRD), X-ray fluorescence, and scanning electron microscopy were used to characterize the structure and composition of the products. After a reaction for 140–320 h, porous crystalline products identified by XRD as CaSeO₃.H₂O, CaSnO₃.3H₂O, BaCrO₄, and BaSeO₃ were obtained. The conversion of fibers (0.5–1.0 mm in diameter) of the Na₂O–BaO–B₂O₃ glass in K₂CrO₄ solution was pseudomorphic. The kinetics and mechanisms of the conversion process, as well as the structure of the products, are discussed.