Discharge lamps with coated ceramic arc tubes and fabrication thereof
AssigneeGTE Laboratories Incorporated
InventorsCarmine Persiani, Alfred E. Feuersanger, Frank C. Palilla
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Abstract
A high pressure sodium lamp brightness was increased 8.9%, its relative voltage stability was improved by a factor of 4, and its relative maintenance was improved by a factor of 3 over a 24,000 hour lifetest. These improvements were accomplished by the application of a fine grained alumina protctive coating on the surface of the polycrystalline alumina arc tube. The process for applying the protective coating comprises the deposition of Al(NO.sub.3).sub.3 from solution on the surface of the arc tube followed by the thermal decomposition of the Al(NO.sub.3).sub.3 to form an alumina coating on the surface of the alumina arc tube.
Claims7
A high pressure sodium arc tube comprising
- a polycrystalline ceramic arc tube envelope, end closures, electrodes, electrical connectors and an arc tube fill;
- said polycrystalline ceramic arc tube envelope having a surface, a wall, and grain boundaries on said surface;
- said polycrystalline ceramic arc tube envelope having a protective oxide coating concentrated at said grain boundaries on said surface of said arc tube envelope to retard sodium migration through said arc tube envelope wall.
A method of applying a protective oxide coating on a polycrystalline ceramic arc tube envelope having a surface, a wall, and grain boundaries on said surface to retard sodium migration through the wall of the arc tube envelope comprising the following steps:
- Step 1--applying an aqueous nitrate solution of a metal corresponding to the cation of the polycrystalline ceramic arc tube envelope to the surface of the envelope to form a polycrystalline arc tube envelope coated with said aqueous nitrate solution;
- Step 2--drying the product from step 1 to form an nitrate coating on said surface of said polycrystalline ceramic arc tube envelope;
- and
- Step 3--converting said nitrate coating on said surface to an oxide to form a protective oxide coating concentrated at the grain boundaries of said surface of said envelope.
Dependencies are inferred from the claim text.