Conversion of Tetranary Borate Glasses to Phosphate Compounds in Aqueous Phosphate Solution
Abstract:In our earlier work, it was found that particles of a ternary alkali-borate glass, containing either CaO or BaO, converted completely to a crystalline phosphate of calcium or barium when reacted in an aqueous phosphate solution at 37°C. The present work is an extension of our earlier work to investigate the conversion of tetranary borate glass with the composition 10Li2O·10CaO·10(AeO or T2O3)·60B2O3 (weight percent), where Ae is the alkai-earth metal Mg or Ba, and T is the transition metal La, Sm, or Dy. In the experiments, particles of each glass (150–300 m) were reacted in 0.25M K2HPO4 solution with a starting pH of ∼9.0 at 37°C. Weight loss and pH measurements indicated that the reaction was complete after 30–50 h, yielding an amorphous product. X-ray fluorescence showed that the as-formed product consisted of a calcium phosphate phase that contained the alkali-earth metal or transition metal present in the starting glass. Heating the as-formed material for 8 h at 600°–700°C produced a mixture of two crystalline phosphates: calcium phosphate and an alkali-earth or transition metal phosphate. The kinetics and mechanism of converting tetranary borate glass to phosphate materials are discussed and compared with data from earlier work for the conversion of ternary borate glass.
Document Type: Research Article
Affiliations: 1: Graduate Center for Materials Research, University of Missouri-Rolla, Rolla, Missouri 65409 2: Department of Materials Science and Engineering, University of Missouri-Rolla, Rolla, Missouri 65409
Publication date: 2008-06-01