Abstract
Glass fibres drawn from a glass of molecular percentage composition 25 Li 2O 74 SiO 2 1 P 2O 5 were subjected to two stage heat treatments to bring about crystallization. The tensile strength was found to decrease with crystallization time for any given crystallization temperature and this strength decrease is shown to correlate with the increase in thickness of a surface layer of lithium disilicate. It is suggested that the strength controlling flaws in the fibre are caused by grain boundary cracks in this surface layer and it is argued that if this be so the fibre tensile strength σ should be inversely proportional to the square root of the crystallization time t. Curve fitting procedures are employed to establish this relationship with the data available and a good correlation is found in this case. Other evidence obtained by electron microscopy and X-ray diffraction tends to strengthen the above argument.
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