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Publication of GB931023ApublicationCriticalpatent/GB931023A/en
931,023. Alumina. GENERAL ELECTRIC CO. June 29, 1959, No. 22226/59. Class 1(2) [Also in Group XXIII] Transparent bodies of alumina containing an aluminium-magnesium spinel, are prepared by mixing up to 0À5% by weight of magnesia powder with alumina powder, compacting the mixture and firing the compact at above 1700‹C. in a vacuum or in hydrogen. The compact may be prefired at 1000‹ to 1200‹C. in an oxygencontaining atmosphere for at least an hour before the firing at above 1700‹C. In examples magnesia is mixed with alumina, the mixture compressed into disc shapes, prefired in air and fired in hydrogen, and the faces polished for optical measurements.