High Total Transmittance Alumina Discharge Vessels Having Submicron Grain Size

Abstract

The present invention uses a post-sinter-HIP anneal to increase the total transmittance of ceramic discharge vessels comprised of a submicron-grained alumina doped with MgO. After the anneal, the submicron-grained alumina discharge vessels have high values of both total and in-line transmittance, and are thus suitable for use in focused-beam, short-arc lamps. In particular, the total transmittance of the discharge vessel is increased to greater than 92% in the wavelength range from about 400 nm to about 700 nm.

1 . A method of making a ceramic discharge vessel comprising: 
 (a) forming the discharge vessel with a submicron-grained alumina powder doped with MgO;    (b) sinter-HIPing the discharge vessel; and    (c) annealing the discharge vessel to increase the total transmittance of the discharge vessel to >92% in a wavelength range from about 400 nm to about 700 nm.    
     
     
         2 . The method of  claim 1  wherein the discharge vessel is annealed at about 1000° C. to about 1150° C.  
     
     
         3 . The method of  claim 2  where the discharge vessel is annealed for about 1 hour to about 20 hours.  
     
     
         4 . The method of  claim 1  wherein the discharge vessel is annealed at about 1100° C. for about 2 hours.  
     
     
         5 . The method of  claim 1  wherein the discharge vessel is annealed in an atmosphere containing a partial pressure of oxygen of about 1×10 −3  atm to about 1×10 −9  atm.  
     
     
         6 . The method of  claim 5  wherein the partial pressure of oxygen is about 1×10 −5  atm to about 1×10 −7  atm.  
     
     
         7 . The method of  claim 5  wherein the discharge vessel is annealed at about 1000° C. to about 1150° C.  
     
     
         8 . The method of  claim 7  where the discharge vessel is annealed for about 1 hour to about 20 hours.  
     
     
         9 . The method of  claim 1  wherein the discharge vessel is formed with a submicron-grained alumina powder doped with about 200 ppm to about 800 ppm MgO.  
     
     
         10 . The method of  claim 8  wherein the discharge vessel is formed with a submicron-grained alumina powder doped with about 200 ppm to about 800 ppm MgO.  
     
     
         11 . The method of  claim 9  wherein the submicron-grained alumina powder has a mean particle size of about 150 nm.  
     
     
         12 . The method of  claim 5  wherein the annealing atmosphere is comprised of nitrogen or argon.  
     
     
         13 . The method of  claim 10  wherein the annealing atmosphere is comprised of nitrogen or argon.  
     
     
         14 . A ceramic discharge vessel comprising: a ceramic body comprised of a submicron-grained alumina doped with MgO, the discharge vessel having a total transmittance of greater than 92% in a wavelength range from about 400 nm to about 700 nm.  
     
     
         15 . The discharge vessel of  claim 14  wherein the total transmittance is greater than 95%.  
     
     
         16 . The discharge vessel of  claim 14  wherein the ceramic body contains about 200 ppm to about 800 ppm MgO.  
     
     
         17 . The discharge vessel of  claim 14  wherein the ceramic body has a discharge cavity with a wall thickness of about 0.8 mm.  
     
     
         18 . The discharge vessel of  claim 14  wherein submicron-grained alumina has an average grain size of about 0.5 microns.