Method of making lithium containing glass with high oxidized iron content using oxidizer consisting essentially of cerium oxide and/or manganese oxide
A low infrared absorbing lithium glass includes FeO in the range of 0.0005-0.015 wt %, more preferably 0.001-0.010 wt %, and a redox ratio in the range of 0.005-0.15, more preferably in the range of 0.005-010. The glass can be chemically tempered and used to provide a ballistic viewing cover for night vision goggles or scope. A method is provided to change a glass making process from making a high infrared absorbing lithium glass having FeO in the range of 0.02 to 0.04 wt % and a redox ratio in the range of 0.2 to 0.4 to the low infrared absorbing lithium glass by adding additional oxidizers to the batch materials. A second method is provided to change a glass making process from making a low infrared absorbing lithium glass to the high infrared absorbing lithium glass by adding additional reducers to the batch material. In one embodiment of the invention the oxidizer is CeO 2 . An embodiment of the invention covers a glass made according to the method.
1. A method of changing molten glass in a furnace from a molten high infrared absorbing lithium glass composition having FeO in the range of 0.02 to 0.04 wt % and a redox ratio in the range of 0.2 to 0.4 to a molten low infrared absorbing lithium glass composition having FeO in the range of 0.0005 to 0.015 wt %, a redox ratio in the range of 0.005 to 0.10, comprising:
feeding high infrared absorbing lithium glass batch material and a predetermined amount of a first oxidizer to oxidize the FeO to provide the molten low infrared absorbing lithium glass composition, wherein the first oxidizer consists essentially of CeO 2 , MnO 2 , or mixtures thereof; and
ceasing the practice of the preceding step after a predetermined period of time.
2. The method according to claim 1 , wherein after the step of feeding the glass batch material the method further comprises,
adding a second oxidizer to the high infrared absorbing lithium glass batch material in an amount in the range of one to two times the amount of the first oxidizer for a predetermined period of time to oxidize the FeO in the molten glass in the furnace, wherein the second oxidizer consists essentially of CeO 2 , MnO 2 , or mixtures thereof.
3. The method of claim 2 , wherein the first and the second oxidizers are each CeO 2 .
4. The method of claim 2 , wherein the first and the second oxidizers are each MnO 2 .