Faraday rotation glasses - US Patent 3,935,020
Glasses Patent Claim
We claim:
1. A Faraday rotation glass exhibiting a high Verdet constant and low susceptibility toward devitrification consisting essentially of the following constituents as expressed in weight percent:
where the alkaline earth oxide is selected from the group consisting of CaO, BaO, ZnO, and combinations thereof, the rare earth oxide is selected from the group consisting of Tb.sub.4 O.sub.7, and the combination of Tb.sub.4 O.sub.7 and La.sub.2 O.sub.3, the Tb.sub.4 O.sub.7 being present in an amount of 20-45 weight percent, and the alkali metal oxide being selected from the group consisting of Na.sub.2 O, K.sub.2 O, and combinations thereof.
2. A Faraday rotation glass according to claim 1 wherein the constituents are present according to the following ranges as expressed in weight percent:
3. A Faraday rotation glass according to claim 2 wherein the constituents are present as follows as expressed in weight percent:
4. A Faraday rotation glass according to claim 2 wherein the constituents are present as follows as expressed in weight percent:
5. A Faraday rotation glass exhibiting a high Verdet constant and low susceptibility toward devitrification consisting essentially of the following constituents as expressed in weight percent:
where the alkaline earth oxide is selected from the group consisting of CaO; the combination of CaO and BaO; the combination of CaO and ZnO; the combination of CaO, BaO and ZnO; and ZnO which when present alone is in an amount of at least 10 weight percent, the rare earth oxide is selected from the group consisting of Tb.sub.4 O.sub.7 and the combination of Tb.sub.4 O.sub.7 and La.sub.2 O.sub.3, the Tb.sub.4 O.sub.7 being present in an amount in the range of 20 to 45 weight percent, the alkali metal oxide is selected from the group consisting of Na.sub.2 O and the combination of Na.sub.2 O and K.sub.2 O, the fining agent is selected from the group consisting of As.sub.2 O.sub.3, Sb.sub.2 O.sub.3, and combinations thereof, when the amount of CaO present is less than 3 weight percent, WO.sub.3 is required to be present, and the total amount of Al.sub.2 O.sub.3 and ZrO.sub.2 is at least 3 weight percent.