| abstract |
This invention relates to a chemical method of strengthening glass articles subjected to abrasion resistance treatment, which comprises (1) a first step of applying a metal oxide-forming compound to the surface of a heated glass article to form the corresponding metal oxide coating having a thickness of 50 to 130 Angstrom on the surface of the glass article, (2) a second step of causing to adhere, to the outer and inner surfaces of the glass article, a mixed solution of potassium chloride and potassium nitrate, having a potassium chloride to potassium nitrate ratio by weight of 85 to 45:15 to 55, or a mixed solution of potassium sulfate and potassium nitrate, having a potassium sulfate to potassium nitrate ratio by weight of 30 to 100:70 to 0, (3) a third step of holding the glass article at an elevated temperature below the strain point of the glass but as near the strain point as possible for a period of time sufficient to obtain a compressive stress layer having a depth of at least 10 microns and a compressive stress of at least 700 kg/cm2 and (4) a fourth step of cooling the glass article to room temperature and then washing the glass article to remove the mixture of the potassium salts remaining on the outer surface and inner surface of the glass article. |