Ceramic materials are ceramic materials that are designed to withstand high temperatures without melting, softening, breaking down chemically or losing other essential properties required for the process such as strength and thermal shock resistance. They are commonly used in applications where very high temperatures are generated such as furnaces, incinerators, kilns and steam boilers.
Properties and Classification of Ceramic materials
Ceramic materials are classified based on their chemical composition and physical properties. The main classifications are:
- Acidic Ceramic materials: These are made primarily from alumina, alumina-silica or similar materials and are suited for environments with lower pH levels. Refractories have good corrosion resistance against slags containing basic oxides.
- Basic Ceramic materials: Containing a higher proportion of alkaline earth oxides like magnesia, doloma and chromite, basic Ceramic materials are better suited for applications with high pH levels and resist corrosion from acidic slags.
- Neutral Ceramic materials: Containing oxide mixtures like Al2O3-SiO2-MgO, these exhibit balanced basic and acidic properties making them useful in applications with varying pH conditions.
- Zirconia and graphite Refractories: Materials like zirconia resist thermal shock well due to low thermal expansion while graphite types have high thermal conductivity and are used in applications where heat transfer is important.
Refractory Materials
Common raw materials used in the production of Ceramic materials include:
- Bauxite: High in alumina content, it is the primary source material for acidic Ceramic materials. Calcined bauxite aggregates are also used.
- Silicon carbide: Known for its excellent thermal shock resistance and strength retention at high temperatures. Used as aggregates in special refractory mixes.
- Chromite: Supplies alumina and magnesia required for basic Ceramic materials and has good slag corrosion resistance.
- Fireclay: Containing alumina and silica, it is formed due to weathering of feldspathic rocks. Used in basic, neutral and acidic monolithic mixes.
- Magnesite: Used as a fluxing agent to control corrosion by slags. Granted magnesium oxide content makes it suitable for basic refractory shapes.
- Andalusite: Aluminum silicate mineral with low thermal expansion. Used in insulating firebrick where thermal shock resistance is important.
Shaping and Installation of Refractories
After raw materials processing and quality checks, Ceramic materials are shaped using different forming techniques:
- Dry pressing: Pre-mixed raw materials are compacted in steel dies with pressure to form bricks, shapes and blocks.
- Vibration: To improve density and minimize air pockets, pressed greenware undergoes vibro-compaction before firing.
- Fired or sintered: Formed pieces are fired in kilns anywhere between 1000°C - 1600°C for bonding and maturation depending on composition.
- Gunning/ramming: A wet, creamy mix is machine fed into place and packed where monolithic linings are required like furnace channels.
- Castables: Pre-mixed dry aggregate and refractory cement are blended with water on site and poured into formwork to setup.
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