Method of manufacturing a high-pressure discharge lamp with end seal evaporation barrier

A method of manufacturing a high-pressure discharge lamp comprising a tubular shaped envelope enclosing a discharge space and consisting of translucent densely sintered aluminum oxide, a ceramic end plug in a sunken position in regard to an end of said envelope and sintered to the inner surface of said envelope said end plug being provided with an aperture through which a tubular current lead-in member extends into said discharge space, said method comprising:

• a) positioning a ceramic end plug provided with an aperture for said tubular current member in said end of said envelope, said aperture being dimensioned so as to provide only a capillary space between said current lead-in member and said plug,
• b) sintering said end plug to said end of said envelope and positioning said current lead-in member so as to extend through said end-plug into said discharge space,
• c) providing a thin disc-shaped sealing member formed of a magnesium oxide containing glass frit, and provided with an aperture for said current lead-in member on the outer surface of said end plug,
• d) positioning a thin disc-shaped barrier member of a high temperature material, provided with an aperture for said current lead-in member, on the outer surface of said sealing member, said barrier member being dimensioned so as to extend over the outer surface of said sealing member and
• e) heating the resultant assembly to a temperature sufficient to melt said sealing member and said barrier member to thereby cause said sealing member to melt and form a magnesium oxide containing glass seal between said current lead-in member and said plug and cause said barrier member to melt and bond to the outer surface of said glass seal.