M6.2

• Ceramics

  Compounds of metallic and non-metallic elements, generally oxides, nitrides, and carbides
• Ceramics

  • Clay
  • Cement
  • Glass
• Ceramics

  • Insulative to electricity and heat
  • Very resistant to high temperatures and harsh environments than metals and polymers
  • Very hard but brittle
• Ceramic applications

  • Porcelain ("China")
  • Wine glass
  • Ceramic cutting blades
  • Insulating tiles on the Space Shuttle
• Ceramic materials

  • Al2O3, SiO2
  • Silicon Carbide (SiC)
• Ceramic applications

  • Refractories for containing molten metals
  • Cutting tools
• Ceramic materials

  • High temperature resistance
  • Hardness, temperature resistance
• Classification of ceramic materials

  • Refractories
  • Glasses
  • Clay products
  • Abrasives
  • Cements
  • Advanced ceramics

  
• Glasses

  Noncrystalline silicates containing other oxides, notably CaO, Na2O, K2O, and Al2O3, which influence the glass properties
• Soda-lime glass

  Approximately 70 wt% SiO2, the balance being mainly Na2O (soda) and CaO (lime)
• Glasses

  • Optical transparency
  • Relative ease of fabrication
• Glass ceramics

  Fine-grained polycrystalline material which is a product of crystallization

  
  

  Crystallization

  • inorganic glasses can be made to transform from a noncrystalline state to one that is crystalline by the proper high-temperature heat treatment
• Glass ceramics

  • Relatively high mechanical strengths
  • Low coefficients of thermal expansion (to avoid thermal shock)
  • Relatively high temperature capabilities
  • Good dielectric properties (for electronic packaging applications)
  • Good biological compatibility
• Compositions and characteristics of common commercial glasses

  • Soda-lime glass
  • Borosilicate glass
  • Lead glass
  • Aluminosilicate glass
  • Fused silica

  
• Clay products

  • One of the most widely used ceramic raw materials.
  • Inexpensive ingredient and found naturally in great abundance
  • Ease in forming its products
  • Clay and water form a plastic mass that is very amenable to shaping
  • Dried to remove some moisture
  • Fired at an elevated temperature to improve its mechanical strength
• Clay products

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

  • Capacity to withstand high temperatures without melting or decomposing
  • Capacity to remain unreactive and inert when exposed to severe environments
  • Ability to provide thermal insulation
  • Bricks
• Refractory applications

  • Furnace linings for metal refining
  • Glass manufacturing
  • Metallurgical heat treatment
  • Power generation
• Refractory porosity

  • One microstructural variable that must be controlled to produce a suitable refractory brick.
  • Strength, load-bearing capacity, and resistance to attack by corrosive materials increase with porosity reduction
  • Thermal insulation characteristics and resistance to thermal shock are diminished with reduced porosity
• Fireclay refractories

  • Primary ingredients are high-purity fireclays, alumina and silica mixtures usually containing between 25 and 45 wt% alumina
  • Used principally in furnace construction to confine hot atmospheres and to thermally insulate structural members from excessive temperatures
• Silica (acid) refractories

  • Primary ingredient is silica
  • Well known for their high-temperature load-bearing capacity
  • Resistant to slags that are rich in silica (acid slags)
  • Readily attacked by slags composed of high proportion of CaO and/or MgO (basic slags)
• Basic refractories

  • Rich in periclase, or magnesia (MgO)
  • May also contain calcium, chromium, and iron compounds
  • The presence of silica can cause harm to their high-temperature performance
  • Resistant to attack by slags containing high concentrations of MgO and CaO
  • Use in some steel-making open hearth furnaces.
• Special refractories

  • Relatively high-purity oxide materials, many of which may be produced with very little porosity
  • Included are alumina, silica, magnesia, beryllia (BeO), zirconia (ZrO2), and mullite (3Al2O3–2SiO2)
  • Silicon carbide (SiC) used for electrical resistance heating elements, as a crucible material, and internal furnace components, very expensive
• Most common ceramic abrasives includes

  • Silicon carbide
  • Tungsten Carbide (WC)
  • Aluminum Oxide (corundum)
  • Silica sand
• Abrasives

  • Used to wear, grind, or cut away other material, which necessarily is softer
  • Prime requisite is hardness or wear resistance
  • High degree of toughness is essential to ensure that the abrasive particles do not easily fracture
  • diamond
• Forms of abrasives

  • Bonded - Abrasive particles are bonded to a wheel by means of a glassy ceramic or an organic resin.
  • Coated - those in which an abrasive powder is coated on some type of paper or cloth material (Sandpaper)
  • Loose grains - Grinding, lapping, and polishing wheels often employ loose abrasive grains that are delivered in some type of oil - or water-based vehicle.
• Cements

  • Characteristic feature is that when mixed with water, they form a paste that subsequently sets and hardens
  • Portland cement is produced by grinding and intimately mixing clay and lime-bearing minerals in the proper proportions, and then heating the mixture to about in a rotary kiln, process is calcination
• Portland cement

  Termed a hydraulic cement because its hardness develops by chemical reactions with water
• Advanced ceramics

  • Microelectromechanical Systems (MEMS) - Miniature "smart" systems consisting of a multitude of mechanical devices that are integrated with large numbers of electrical elements on a substrate of silicon
  • Optical Fibers - Made of extremely high-purity silica, which must be free of even minute levels of contaminants and other defects that absorb, scatter, and attenuate a light beam
• Ceramic ball bearings


  • A bearing consists of balls and races that are in contact with and rub against one another when in use
  • In most instances races are still made of steel, because its tensile strength is superior to that of silicon nitride. This combination of ceramic balls and steel races is termed a hybrid bearing