Patent ID: 8309482

Claim:
A fused and cast refractory product comprising, on oxides basis in percent by weight and for a total of 100%: ZrO 2 +HfO 2 : complement to 100% SiO 2 : 3.5% to 6.0% Al 2 O 3 : 0.7% to 1.5% Na 2 O+K 2 O: 0.10% to 0.43% B 2 O 3 : 0.05% to 0.80% CaO+SrO+MgO+ZnO: <0.4% P 2 O 5 : <0.05% Fe 2 O 3 +TiO 2 : <0.55% other species: <1.5%, a ratio of percentages by weight of Al 2 O 3 /(Na 2 O+K 2 O) being greater than or equal to 3.5 and a ratio of percentages by weight of B 2 O 3 /(Na 2 O+K 2 O) being between 0.3 and 2.5.