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Vacuum Preparation of High Purity Glass

IP.com Disclosure Number: IPCOM000096789D
Original Publication Date: 1963-Nov-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Narken, B: AUTHOR [+2]

Abstract

Powdered spectoscopic grade starting materials are ground and mixed well in an agate mortar and then are transferred to platinum crucible 10. This is then covered. Then the materials are mixed vigorously. Next, crucible 10 and its contents are placed in vacuum chamber 11. Here they are heated by induction heater 12. For maximum stirring action and mixing of the glass to be formed in crucible 10, the initial heating of materials 13 in it is first performed at atmospheric pressure. In this initial heating, considerable outgassing occurs. Such is caused by water vapor and certain of the materials then in crucible 10, which are not in the oxide form but are present as acids or carbonates. These must dissociate before reacting to form glass.

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Vacuum Preparation of High Purity Glass

Powdered spectoscopic grade starting materials are ground and mixed well in an agate mortar and then are transferred to platinum crucible 10. This is then covered. Then the materials are mixed vigorously. Next, crucible 10 and its contents are placed in vacuum chamber 11. Here they are heated by induction heater 12. For maximum stirring action and mixing of the glass to be formed in crucible 10, the initial heating of materials 13 in it is first performed at atmospheric pressure. In this initial heating, considerable outgassing occurs. Such is caused by water vapor and certain of the materials then in crucible 10, which are not in the oxide form but are present as acids or carbonates. These must dissociate before reacting to form glass.

After the mixture in crucible 10 becomes completely molten, chamber 11 is evacuated. Evacuation, when the mixture of materials 13 is still in a powder form, is undesirable because it leaves very little gas in the mixture when it becomes molten. The formation of gas bubbles in the molten mixture is most advantageous, since violent outgassing provides an additional mixing of various ingredients. Bubbling causes the melt to form a froth which collapses either when vacuum is removed or when the melt is completely outgassed. Rather than outgassing the melt in one vacuum application, repeated evacuations are more desirable. Air or nitrogen is introduced between successive evacuations to form a fro...