Strengthening of Glass by an Electroionic Technique.
NAVAL ORDNANCE LAB WHITE OAK MD
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An electroionic strengthening process for glass which produces a relatively deep surface compressive layer to preserve this strength has been examined. The process consists of using an electric field to drive large alkali ions from a molten salt bath into the glass to replace the small resident alkali ions. This exchange of ions, carried out at temperatures below the strain point of the glass, produces a compression stress on the glass surface and hence strengthens the glass. Alkali-aluminosilicate glass hemispheres 7.6 an OD, 0.4 cm. thick and cylinders 4.7 cm diameter, 4.4 cm long were strengthened using postassium ions from a molten potassium nitrate bath. Maximum compressive stresses on the order of 1,000,000 psi and treatment depths of 0.65 mm were obtained for the cylindrical specimens. Although high strengths were also obtained for the hemispherical specimens there was a large variation in the measured strengths in addition to a very high incidence of specimen there was a large variation in the measured strengths in addition to a very high incidence of specimen breakage during treatment. Oxygen and hydroxyl ion attack accelerated the growth of cracks. Author Modified Abstract
- Physical Chemistry
- Ceramics, Refractories and Glass