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Title: The compatability relationships of periclase in basic refractories at high temperatures with special reference to the effects of the solid solubility of Al2O3, Cr2O3 and iron oxides in magnesia
Author: Goncalves, Geraldo Edwardo
ISNI:       0000 0004 2741 1651
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 1973
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The objective of the investigation was to establish melting relationships in certain phase diagrams of importance to the technology of basic refractories, with special reference to the effects of the solid solubility of Al203, Cr203 and iron oxide in magnesia at high temperatures. Because of this solubility, the freezing paths of mixtures lying in the primary phase volumes of periclase in the systems caO-MgO-Al203-Si02, CaOMgO- Fe203-Si02 and CaO-MgO-Cr203-Si02 do not radiate from the MgO corner of the composition tetrahedron. Bence projections of the boundary surface of the primary phase volume of periclase, through the MgO corner onto the opposite face of the tetrahedron, do not describe the freezing behaviour of such mixtures accurately. The first investigation was of the phase changes occurring in mixtures containing 80 Wt.% MgO in the system CaO-MgO-Al203-Si02. conventional techniques involving firing and microscopic examination, after water quenching were used to establish the identity and crystallization temperatures of the secondary phases and the results were plotted on a composition triangle in terms of the cao, A1203 and Si02 contents of the mixtures recalculated to 100 wt.%. comparison of this diagram with the published diagram of the boundary surface shows that displacement of the boundary lines due to solid solution of AlaO, becomes appreciable at temperatures over lSOOoC, where the solid solubility of this oxide becomes appreciable. COmparison with similar diagrams established in the Department for the systems CaO-MgO-FeaO,-SiOa and CaO-MgO-cra03-SiOa has further shown that, at comparable MgO contents the range of Ra03/(CaO + SiOa) ratios over which spinel is the secondary phase decreases in the order AlaO, > Cra03 » FeaO, which is the order of increasing solid solubility of the sesquioxide in periclase at high temperatures. An explanation for this effect has been advanced and a graphical method of predicting the displacement of the spinel-silicate boundary with varying MgO content has been described.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available