International Business Machines Corporation

Hitachi Global Storage Technologies Netherlands B.v.

Terry Lee Jensen

Rick Allan Sprague

John William Marier

Douglas Howard Piltingsrud

Nathan Ellis Jacobson

A salt mixture used for chemical strengthening of data recording disks is subjected to sub-micron filtration prior to use to remove certain impurities. Preferably, glass disks are chemically strengthened by ion exchange in a bath of molten sodium nitrate and potassium nitrate. A salt fresh mixture is prepared by starting with high-grade bulk salt in the intended proportions, melting the salt, and filtering the salt in a stainless steel filter, which is preferably approximately 2 micron or smaller. Filtration removes trace amounts of certain contaminants. The salt mixture thus prepared is then used for chemical strengthening of disks in the conventional manner.

Chemical strengthening process for disks used in disk drive data storage devices

A method of adjusting the pH of a strengthening melt to provide an adjusted melt for use in microetching glass substrates, such as glass disk substrates for use in data storage devices. A base is added to the strengthening melt to raise its pH. A desired degree of microetch is provided on an aluminosilicate glass disk substrate, for example, by immersion for 2-4 hours at 360&#xb0; C. in a melt adjusted to have a pH of 10. This single operation both strengthens and microetches the glass substrate. A slight etching of the surface of a glass substrate, i.e., microetching, improves the performance and durability of a data storage disk made from the substrate. To avoid an overly aggressive etch that can create undesirable damage to the substrate surface, an acid may be added to the melt if the pH is subsequently determined to have shifted to above an upper limit.

pH adjustment of a melt for use in microetching glass substrates

A method of adjusting the pH of a strengthening melt for use in strengthening glass substrates, e.g., glass disk substrates for use in data storage devices. A non-particle-forming acid is added to the strengthening melt to lower the pH of the strengthening melt to &lE;8. The acid is added while the strengthening melt is in a molten state and selected to avoid particle formation. Nitric acid, for example, is non-particle-forming with respect to nitrate based strengthening melts such as potassium nitrate and/or sodium nitrate. A base, e.g., sodium hydroxide, may be added if the pH of the strengthening melt falls below 5. Strengthening melts are subject to pH shift that can cause glass substrates strengthened therein to etch, creating pits on the substrate surface. Glass disk substrates treated in the pH adjusted strengthening melt are essentially free from such pits, as well as contamination caused by particle formation.

Growing community of inventors

Rochester, MN, United States of America

Terry Lee Jensen