Mechanical properties of phosphate glasses

The effect of different cations (Fe+3/+2, Na, Ca, Al, U, Mg, Mn+4/+3, Zn) on the tensile strength, Young’s modulus and chemical durability of binary and complex phosphate glasses was investigated. The tensile strength and Young’s modulus of the glass fibers were measured. Mossbauer spectroscopy was used to determine the concentration and the coordination number of Fe+3 and Fe+2 in the binary iron phosphate glasses. The length of phosphate chain was resolved using high performance liquid chromatography on phosphate glasses with high iron content. Tensile strength and Young’s modulus as well as chemical durability was found to be dependent on the structure of phosphate glasses, which in turn was influenced by the nature of modifier or intermediate cations. Addition of intermediates, such as Fe2O3 and Al2O3 improved tensile strength due to formation of cross-linked structure. The highest tensile strength and Young’s modulus was found for glass with 40 mol% of Fe2O3 and 60 mol% of P2O5. The structure of this glass was observed to be similar to structure of crystalline Fe3(P2O7)2, and exhibited cross-linked pyrophosphate network with high bond density. Among all studied zinc containing phosphate glasses, the glass with highest tensile strength had the composition of 10ZnO·20Al2O3·70P2O5, mol%, where cross-link density was also very high. Although, addition of modifiers e.g. Na, Ca, U, Mg, Mn+4/+3 normally breaks the structural of network due to the big size of cations, which eventually leads to the diminution of tensile strength. Decrease of tensile strength of glass fibers exposed to ambient atmosphere for 10 days at room temperature was attributed to corrosion products on the surface of glass fibers. The corrosion products occurred due to reactions on the glass surface with moisture in the air, which in turn created flaws and caused the reduction in tensile strength --Abstract, page iv