Patent ID: 8183168

Claim:
A glass ceramic composition, comprising a fired mixture of a powder of a lead-free glass and a powder of titanium oxide, wherein the lead-free glass comprises, as represented by mass % based on the following oxides and relative to the total mass of the lead-free glass, from 30 to 50% of B 2 O 3 , from 21 to 25% of SiO 2 , from 10 to 23% of ZnO, from 9 to 19% in total of K 2 O and at least one of Li 2 O and Na 2 O, from 0 to 10% of Al 2 O 3 , and from 0 to 5% of ZrO 2 and optionally at least one component selected from the group consisting of MgO, CaO, SrO and BaO, the total content thereof is at most 5%, with the molar fractions of Li 2 O, Na 2 O and K 2 O represented by l, n and k, respectively, l is at most 0.025, and l+n+k is from 0.08 to 0.17, the powder of lead-free glass is present in the fired mixture in an amount of from 90 to 99.9 mass %, relative to the total mass of the fired mixture, the powder of titanium oxide is present in the fired mixture in an amount of from 0.1 to 10 mass %, relative to the total mass of the fired mixture, and the lead-free glass has a calculated strength index value of at least 1.7.