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• Commercial glass-ceramic trade names

  • Pyroceram
  • CorningWare
  • Cercor
  • Vision
• Clay


  An inexpensive, naturally abundant ceramic raw material that is easily formed when mixed with water
• Types of clay products

  • Structural clay products (building bricks, tiles, sewer pipes)
  • Whitewares (porcelain, pottery, tableware, china, plumbing fixtures)
• Refractories


  Ceramics that can withstand high temperatures without melting or decomposing, and remain unreactive and inert when exposed to severe environments
• Refractory ceramics


  • Have the capacity to provide thermal insulation and support mechanical loads
  • Have resistance to thermal shock (fracture caused by rapid temperature changes)
• Common refractory oxide raw materials

  • SiO2
  • Al2O3
  • MgO
  • CaO
  • Cr2O3
  • ZrO2
• Types of clay refractories

  • Fireclay (25-45 wt% Al2O3)
  • High-alumina (50-87.5 wt% Al2O3)
• Types of nonclay refractories

  • Silica
  • Periclase
  • Extra-high alumina
  • Zircon
  • Silicon carbide
• Silica refractories


  Well known for their high-temperature load-bearing capacity, used in furnace roofs at temperatures up to 1650°C, with some liquid phase present
• Even small amounts of alumina have an adverse influence on the performance of silica refractories, lowering the liquidus temperature significantly
• Temperatures as high as 1650°C (3000°F) may be realized. Under these conditions, some small portion of the brick actually exists as a liquid
• The presence of even small concentrations of alumina has an adverse influence on the performance of these refractories, which may be explained by the silica–alumina phase diagram, Figure 12.25
• Because the eutectic composition (7.7 wt% Al2O3) is very near the silica extremity of the phase diagram, even small additions of Al2O3 lower the liquidus temperature significantly, which means that substantial amounts of liquid may be present at temperatures in excess of 1600°C (2910°F)
• The alumina content should be held to a minimum, normally to between 0.2 and 1.0 wt%
• These refractory materials are also resistant to slags that are rich in silica (called acid slags) and are often used as containment vessels for them
• They are readily attacked by slags composed of high proportions of CaO and/or MgO (basic slags), and contact with these oxide materials should be avoided
• Compositions of Seven Ceramic Refractory Materials

  • Fireclay
  • High-alumina fireclay
  • Silica
  • Periclase
  • Extra-high alumina
  • Zircon
  • Silicon carbide
• Refractories that are rich in periclase (the mineral form of magnesia, MgO), chrome ore, and mixtures of these two minerals are termed basic; they may also contain calcium and iron compounds
• The presence of silica is deleterious to their high-temperature performance
• Basic refractories are especially resistant to attack by slags containing high concentrations of MgO; these materials find extensive use in the steel-making basic oxygen process (BOP) and electric arc furnaces
• The extra-high alumina refractories have high concentrations of alumina—between 87.5 and 99+ wt%
• These materials can be exposed to temperatures in excess of 1800°C without experiencing the formation of a liquid phase; in addition, they are highly resistant to thermal shock
• Common applications include use in glass furnaces, ferrous foundries, waste incinerators, and ceramic kiln linings
• Zircon's most outstanding refractory characteristic is its resistance to corrosion by molten glasses at high temperatures
• Zircon has a relatively high mechanical strength and is resistant to thermal shock and creep
• Its most common application is in the construction of glass-melting furnaces
• Silicon carbide (SiC), another refractory ceramic, is produced by a process called reaction bonding—reacting sand and coke in an electric furnace at an elevated temperature (between 2200°C and 2480°C)
• The high-temperature load-bearing characteristics of SiC are excellent, it has an exceptionally high thermal conductivity, and it is very resistant to thermal shock that can result from rapid temperature changes
• The primary use of SiC is for kiln furniture to support and separate ceramic pieces that are being fired
• Carbon and graphite are very refractory, but find limited application because they are susceptible to oxidation at temperatures in excess of about 800°C (1470°F)
• Refractory ceramics are available in precast shapes, which are easily installed and economical to use
• Precast products include bricks, crucibles, and furnace structural parts
• The monolithic refractories are typically marketed as powders or plastic masses that are installed (cast, poured, pumped, sprayed, vibrated) on site
• Types of monolithic refractories

  • Mortars
  • Plastics
  • Castable
  • Ramming
  • Patching
• Abrasive ceramics (in particulate form) are used to wear, grind, or cut away other material, which necessarily is softer
• The abrasive action occurs by rubbing action of the abrasive, under pressure, against the surface to be abraded, which surface is worn away
• The prime requisite for this group of materials is hardness or wear resistance; most abrasive materials have a Mohs hardness of at least 7
• In addition, a high degree of toughness is essential to ensure that the abrasive particles do not easily fracture
• Furthermore, high temperatures may be produced from abrasive frictional forces, so some refractoriness is also desirable
• Common applications for abrasives include grinding, polishing, lapping, drilling, cutting, sharpening, buffing, and sanding