Ceramic envelope for high intensity discharge lamp and method for producing a polycrystalline transparent sintered alumina body

摘要

The invention provides a method for producing a polycrystalline transparent sintered alumina body suitable for use in a ceramic envelope for a high intensity discharge lamp, with optimized kinds and amounts of sintering aids. First, adding and mixing, to alumina of a purity of 99.9 % or higher, MgO within a range from 0.002 to 0.010 wt.% and La2O3 within a range from 0.005 to 0.020 wt.%, in such a manner that a sum of MgO and La2O3 is 0.030 wt.% or less and that a ratio thereof satisfies a relation 0.2≤MgO/La2O3≤0.5. Next, firing a mixture at 900 to 1200°C and cast molding the fired alumina. Then, after a chelating treatment, sintering the molded alumina for at least 1 hour at 1650 to 1900°C in a reducing atmosphere under a normal pressure.