Solubilities and Some Physical Properties of Alkaline Earth Phosphate Glasses

Abstract

Solubilities and physical properties of phosphate glasses in the systems, alkaline earth oxides-phosphorous pentoxide, were measured. Glass systems concerned in the present study are CaO-P2O5, MgO-P2O5, SrO-P2O5, BaO-P2O5, CaO-MgO-P2O5 and CaO-MgO-SrO-BaO-P2O5. The composition of the glass specimens covered from 0.7 to 1.7 in mole ratio RO/P2O5. The subjects tested in this paper are solubility of P2O5 component in various solvents, chain-length distribution of phosphate ions, mineral composition of the devitrified specimens obtained by heat-treatment, density and refractive index. As the solvents for the solubility test, N/2 hydrochloric acid, 2% citric acid, 10% neutral sodium citrate, 10% sodium hydroxide and 10% ammonium hydroxide etc. were used.The solubility of P2O5 in the acid solvents increased with the increase of mole ratio RO/P2O5, whereas the reverse change was observed in the case of the basic solvents. It was recognized that the solubility by using the neutral solvents gave a maximum value at a composition of RO/P2O5=1. For the sodium hydroxide solvent, MgO-P2O5 glass resulted in a considerably high solubility comparing with the other glasses.The anomalies of some physical properties and solubility in a system MgO-P2O5 glass disappeared by adding other alkaline earth oxide to a original system. For instance CaO-MgO-P2O5 and CaO-MgO-SrO-PaO-P2O5 glasses had no anomalies concerning density and refractive index curves. When the system contained the mixed alkaline earth oxides, glass formation was observed even in high alkaline earth oxide region. The inclusion of RO in the melt of a sample up to 1.7 in mole ratio RO/P2O5 gave the vitrifaction of the specimen. In these mixed alkaline earth glasses, only two kinds of phosphate ions with short size, i.e. ortho and pyro, were detected by paper chromatographic test and their acid solubilities were higher than those of the other phosphate glasses.No change in the size-distribution of the phosphate ions was seen in the process of dissolution of the glasses in the various solvents except for the acid solvents in which the hydrolysis of phosphate ions occured considerably and rapidly. It seems that when these glasses are heat-treated and then devitrified no reaction among the phosphate ions arises and the phosphate ions with the various size in the original glass make the correspondingly crystalline phosphates.