GB1250190A - - Google Patents

Abstract

1,250,190. Refractory magnesia and compositions. BRITISH PERICLASE CO. Ltd. 7 Nov., 1968 [7 Nov., 1967], No. 52891/68. Addition to 1,115,386. Headings C1A and C1J. A dead-burnt refractory magnesia comprises MgO, CaO, SiO 2 , Fe 2 O 3 , Al 2 O 3 , B 2 O 3 and an oxide selected from Na 2 O, K 2 O, and Li 2 O, these constituents being in the following proportions by weight:-MgO, between 90% and 99%; CaO + SiO 2 -up to 5%, the weight ratio CaO/ SiO 2 being between 1À5: 1 and 2À2: 1; Fe 2 O 3 + Al 2 O 3 -a total amount up to one quarter of that of CaO+SiO 4 ; B 2 O 3 up to 0À1% ; and Na 2 O, K 2 O or Li 2 O-an amount at least equal to that of B 2 O 3 and up to a maximum of 0À25%, and when this refractory is made into bricks using conventional techniques, after firing the resultant bricks have moduli of rupture of at least 1500 lbs./inch<SP>2</SP> at 1260‹ C., at least 1000 lbs./inch<SP>2</SP> at 1400‹ C. and at least 800 lbs./inch<SP>2</SP> at 1500‹ C. In a preferred magnesia the CaO/ SiO 2 ratio is between 1À7:1 1 and 2À0: 1 and the B 2 O 3 content has a maximum of 0À05% by weight. If desired Cr 2 O 3 in an amount up to 0À5% by weight may be incorporated into the magnesia. The bulk density of the modified magnesia is 3À2 g./c.c. The magnesia may be prepared by dead burning a synthetic magnesia of known composition to which has been added if necessary sufficient CaO or SiO 2 to bring the CaO/SiO 2 ratio from 1À0 1 to 4À0 :1 1 and adding Na 2 O, K 2 O or Li 2 O or a material which gives these oxides on dead burning, the composition of the starting mixture being such as to give a product having the parameters listed above. In a preferred mixture the CaO/SiO 2 ratio is 1À5 : 1 to 2À7 : 1 and the Na 2 O, K 2 O or Li 2 O content is 0À5% to 1À0% by weight. The sodium, potassium or lithium may be added as the carbonate, hydroxide sulphate or chromate, and the composition may contain up to 0À5% by weight of chromium oxide.