INCREASING STRENGTH OF GLASS BY ETCHING AND ION-EXCHANGE

The tensile strength of ordinary soda-lime glass can be increased by an order of magnitude to 3×105 psi* by etching with hydrofluoric acid, but this high strength is catastrophically reduced by surface damage and by heating. But for the loss in strength on heating it would be possible to protect the etched surface from damage in handling by ion-exchange with the salt of a cation larger than sodium, which produces a compressive stress in the surface. This investigation showed that a major factor responsible for heat-damage in etched glass is water adsorbed on the surface, and that glass that has either been dehydrated after etching, or etched in an anhydrous reagent, retains a high proportion of its strength on heating. This result has made it possible to protect the surface of etched glass against abrasive damage by ion-exchange in molten potassium and silver nitrates. In this way, tensile strengths of the order of 105 psi have been obtained in glass with a deliberately abraded surface. © 1969 Chapman and Hall.