The effect addition of Na2O on the solubility properties of phosphate glass of the composition, 45P2O5-18CaO-xNa2O-(34-x)K2O-6Al2O3, where x = 0,5,10,15 and 20 wt. %. has been studied. Glass transition temperature (Tg) of glass samples, weight loss and pH of the immersion solution were measured. The Tg value of the phosphate glass also decreased with the incorporation of Na2O up to 10 wt. % and increased with the incorporation of 15 and 20 wt. %. These results indicates that the solubility and Tg value of phosphate glass were highly influence by the glass composition. The substitution of Na2O to the phosphate glass system with the present of K2O has decrease the solubility of phosphate glass. The released of phosphate and calcium ion seem to decrease with the increasing of Na2O content in the glass composition.
Currently, the solubility of phosphate glasses has been extensively studied for potential glass fertilizer. This work presents the study of 45P2O5-20CaO-xK2O-(29-x)Na2O-6Al2O3 glass, where x equals to 5, 10, 15 and 20 wt. % of K2O. Free bubble glasses were obtained at melting temperature of 1300 °C. Solubility study of phosphate glass indicates that the glass containing 15 wt. % of K2O released the highest amounts of PO43- ion and K+ ion and it exhibits the lowest pH value compare to other glasses. Spectroscopy analysis revealed the addition of K2O to the glass system contributed to the formation of metaphosphate and phyrophosphate units around 919 cm-1 and 1119 cm-1. The morphology analysis indicates the formation of pores on the glass surface was associated with the corrosion of the glass samples due to the immersion. The addition of K2O to the glass system has increased the glass solubility due to the breakup of the glass structure.
Currently, phosphate-based glasses have been extensively studied for their special characteristic of being soluble in aqueous medium and capable of releasing ions. This paper presents the relationship between the solubility properties and ion released of phosphate glasses having a composition of 6Al2O3-15K2O-14Na2O-(20-x)CaO-xFe2O3-45P2O5, where x = 2, 4, 6 and 8 wt.%. Clear and free bubbles of dark green glasses were obtained from the used of conventional melting technique at 1300 oC. The ion released and weight loss studies were determined from the immersion of the glass samples in deionised water for about 16 weeks under static condition. IR spectra revealed the formation of phosphate units such as metaphosphate and orthophosphate unit around 1097 cm-1 and 1107 cm-1 with the presence of Fe2O3 in the glass system. SEM image of the phosphate glass structure before and after immersion seems to be associated with the solubility of these glasses. From the study, the concentration of Na+ and K+ release decreased when more Fe2O3 contents were added to the system. Fe2O3 stabilize the network structure via the formation of P-O-Fe bond which more hydration resistant towards water penetrating molecules.
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