Minor mullite

Although fly ash is largely non-crystalline glass, the major and minor elements in fly ash (O, Si, Al, Fe, Ca, Mg, and S) foim several different phases that have been characterized by XRD in many research projects (Diamond 1984 McCarthy 1988 Bergeson etal. 1988 Thedchanamoorthy McCarthy 1989 Ainsworth et al. 1993). The phases of major elemental constituents that have been commonly identified in fly ash include quartz mullite, Al6Si20 3 tricalcium aluminate, Ca3Al206... 

As with pfa low in CaO, fine, spherical particles consisting largely of glass predominate, but the glasses are higher in CaO and the assemblages of crystalline phases are different. In a study of 26 ashes from the western USA. McCarthy el al. (M84) found that quartz, lime, periclase, anhydrite and a ferrite spinel were ubiquitous or nearly so. Other crystalline phases present in some cases or in minor amounts included C3A, merwinite, alkali sulphates, melilites, mullite, sodalite and possibly others. Due to the presence of... 

The work by Boyer [50] was concerned with mullite refractories utilized in blast-furnace applications. The major reaction appeared to be K2C03 fluxing of the mullite-glass samples to form minor kaliophilite. Boyer described the reaction as a soft black hygroscopic crust confined to the... 

Structural Organization and Rearrangement—II50°C up—Exotherm —Minor (Variable). This represents the formation of mullite and cristobalite. The intensity varies with impurities or additives as well as particle size. 

Other minor crystals present mullite (3AI2O3 2Si02) Tough, machinable (with conventional metalworking tools) House of cards structure, only local mechanical damage Apphcations precision dielectric components, electrical insulators, high-vacuum components, other electronic and mechanical parts Example Macor (Corning code 9658)... 

AI2O3 or kyanite Phases on phase diagram Major phase—mullite and minor phase—glass (can contain free Si02 ) clay since clays do not contain sufficient AI2O3 Made from 60% alumina minerals and contain some fireclay. Can be made with bauxite and clay Can be used in excess of 1700°C... 

AI2O3 Phases on phase diagram The major phase is corundum, with a minor quantity of mullite and glass Usually used in aluminum contact refractories... 

AI2O3 Alumina Phases on phase diagram The major phase is corundum, with a substantially minor quantity of mullite and glass. Brick for molten iron contact usually contain fused AI2O3 for enhanced abrasion resistance Made from tabular and/or fused S3mthetic (Bayer process) alumina aggregates Can be used in excess of 1800°C... 

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