Alumina

Alumina and Fireclay
refractories
-Raw materials
-Brick Properties

Raw Materials
• Silica Sand
– Chemical composition
• > 95% SiO2

– Mineralogical composition
• α-Quartz

– Advantages• Abundant
• Inexpensive processing and mining

– Disadvantages
• Huge expansion at 1063ºF – cracking!

Raw Materials
• Quartzite
– Chemical composition
• > 97% SiO2

– Mineralogicalcomposition
• α-Quartz

– Advantages
• High purity

– Disadvantages
• Huge expansion at 1063ºF – cracking!
• Processing leads to silica dust generation –
silicosis!

Raw Materials
• Fusedsilica
– Chemical composition
• > 99,5% SiO2

– Mineralogical composition
• Vitreous

– Advantages
• High purity
• Low expansion coefficient – volumetric stability

– Disadvantages
• Veryexpensive
• Short market availability

Raw Materials
• Clays
– Clay is a term which designates
aluminosilicates of lamelar structure with or
without ionic changes in the lamelae
– Mineralogicalcomposition
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•
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Al2O3.2SiO2.2H2O – Kaolinite
Al2O3.2SiO2.2H2O - Halloysite
Al2O3.2SiO2.4H2O – Pyrophillite
K2O.3Al2O3.6SiO2.2H2O – Muscovite

Raw Materials
• Clays used inrefractory processing
• Ball Clays – with high kaolinite content and a certain content
of muscovite and illite type minerals, these clays are very
plastic and present suitable refractoriness
• Kaolins –with high kaolinite content and limited amount of
impurities, these clays are fairly plastic and highly refractory
and stable under firing
• Flint Clays – with high kaolinite and halloysite contentsand
limited amount of impurities, are only suitable to chamotte
manufacturing, due to low plasticity
• Pyrophillite – generally, these clays present muscovite and
micaceous minerals as majorimpurities, which lead to higher
alkali contents. Due to large expansion at low temperatures
during firing, this mineral generally is used in monolithics,
when expansion is needed to compensate...