Patent ID: 7285506

Claim:
A process for making heat-resistant glass-ceramic lamp reflector substrates, comprising the following steps: (i) mixing raw materials in amounts such that upon melting thereof a glass is produced of a composition by weight of the total glass composition, comprising 56-67% SiO 2 ; 19-22% Al 2 O 3 ; 3.4-3.8% Li 2 O; 1.8-2.6% ZnO; 1.5-2.5% MgO; 3.3-5% TiO 2 ; 0-2.5% ZrO 2 ; 1.5-3% B 2 O 3 ; 0-6% P 2 O 5 ; 0-0.6% F; less than 500 ppm Fe 2 O 3 ; and refining-effective amounts of refining agents, wherein iron oxide contamination is minimized; (ii) melting the raw material mixture of step (i) at a temperature up to 1550° C. into melted glass followed by refining and homogenization thereof; (iii) forming the melted glass of step (ii) into glass moldings of lamp reflector substrates having a reflecting surface with an average surface roughness Ra of less than 75 nm; (iv) annealing and cooling said glass reflector moldings; (v) raising the temperature of the glass reflector substrate moldings to a nucleating temperature T n between 600 and 750° C. and maintaining the moldings in this temperature range for at least 15 minutes; (vi) raising the temperature of the glass reflector substrate moldings to a ceramming temperature T c between 700 and 850° C.; (vii) maintaining the temperature of the reflector substrates at the ceramming temperature for a period of time over 30 minutes to complete crystallization into β-quartz solid solution; and (viii) cooling the reflector substrates to room temperature; whereby heat resistant glass-ceramic lamp reflector substrates having β-quartz solid solution as the predominant crystalline phase and a reflective surface having an average roughness of less than 75 nm are produced.