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 m) 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.
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Document Type: Research Article
Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409
Institute of Bioengineering and Information Technology Materials, Tongji University, Shanghai, 200092, China
Publication date: 2008-07-01