Can we consistently improve glass strength?

Russell J Hand, University of Sheffield

There is currently great interest in consistently improving the practical strength of glass to increase its commercial competitiveness. It has been known since the 1920s that the practical strength of glass is determined by the presence of small surface defects that arise either during processing or subsequently in service. Compositional modifications, residual stresses and coatings have all been suggested as ways in which these defects can be overcome or, possibly, prevented. Our work on relating mechanical properties and glass composition indicate that compositional gains are likely to be limited and that surface hydration leads to at least a local degradation of glass properties. Meanwhile our work on thin soft epoxy based coatings shows that damage can be overcome and strengths returned to values similar to those arising from initial production. Significant increases in the practical strength of glass articles must do more than this and must also be maintained with time whilst retaining other desirable properties. This presentation will review our compositions and coating related work with the aim of identifying realistic approaches to improving practical glass strength.