Ceramics

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Ceramics

• Mixture of metallic and non-metallic elements
  (clay products).
• Traditional whiteware, tiles, brick, sewer pipe,
  pottery, and abrasive wheels.
• Industrial (fine ceramics) turbine, automotive,
  aerospace components, heat exchangers,
  semiconductors, seals, cutting tools.

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Ceramic Applications

• Electronic insulators
• Engine components
• Machining tools
• Porcelain
• Bioceramics for prosthetics

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Structure of Ceramics

• The structure of ceramic crystals is among the
  most complex of all materials.
• Contain various elements.
• Covalent bonding (electron sharing), stronger
  than metals.
• Hardness, thermal, and electrical resistance
  higher than metals.
• Finer the grain size, higher strength and
  toughness.

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Ceramic Materials

• Clay (kaolin) silicate of aluminum.
• Flint fine-grained silica.
• Feldspar aluminum silicates, potassium,
  calcium/sodium.

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General Properties of Ceramics

• Mechanical Properties
• Much stronger in compression vs. tension (one
  magnitude difference)
• Sensitive to cracks, impurities, porosity
• Lack toughness, ductility, are brittle and strong
• static fatigue failure (load over a period of
  time)- similar to stress-corrosion cracking.
• pre-stressing (compressing) increases resistance
  to breakdown from tensile stress.

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General Properties of Ceramics

• Physical Properties
• low specific gravity/density.
• low thermal conductivity (porosity air is poor
  conductor).
• low thermal expansion.
• resistance to wear.
• Alloying With metallic elements can cause
  ceramics to conduct

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Types of Ceramics

• Oxide Ceramics
• Alumina
• most widely used
• high temperature applications
• Electrical, thermal insulation, cutting tools
• Zirconia
• high toughness/strength
• resistance to thermal shock, wear, and corrosion.
• low thermal conductivity, friction coefficient.
• Engine components

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Ceramic Knife (Zirconia)
(global.kyocera.com)
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Other Types of Ceramics

• Carbides
• tungsten, titanium, and silicon carbide.
• Silicon is an abrasive
• Grinding wheels, cutting tools
• Nitrides
• cubic boron nitride, titanium nitride, and
  silicon nitride.
• Grinding and cutting tools, turbine engines,
  bearings, sand-blast nozzles

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Other Types of Ceramics (Cont.)

• Sialon
• silicon nitride and aluminum oxide, yttrium
  oxide, titanium carbide.
• Higher strength and thermal-shock resistance than
  silicon nitride
• Cutting tools
• Cermets
• ceramics bonded with metallic elements.
• cutting tools/high temperature applications.

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Silica

• Polymorphic material (different crystal
  structures)
• Quartz
• Most glasses are 50 silica
• Silicates- reaction of silica and oxides of al,
  mg, fe, etc. (clay, asbestos, mica, and silicate
  glasses)

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Glasses

• Amorphous solid (structure of a liquid)
• No specific freezing or melting point
• Cooled at a rate too high for crystals to form
  (supercooled).
• All glasses contain at least 50 silica.

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Glass Applications

• Containers
• Windows
• Cookware
• Fiber Optics
• Monitors
• Lighting

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Glass Properties

• Brittle, hard
• Resistant to chemicals and corrosion
• Low thermal conductivity and expansion.
• Dielectric properties.
• Reflection, refraction, absorption.
• Static Fatigue

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Glass Ceramics

• High crystalline structure
• Stronger than glass
• Shaped first and heat treated
• devitrification or recrystallization of glass.

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Graphite

• Crystalline form of carbon, having a layered
  structure.
• solid lubricant, low friction properties.
• brittle in nature.
• strength and stiffness increases with temperature.

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Diamond

• Hardest substance known
• Synthetic (or industrial)
• lacks impurities which natural diamonds might
  have.
• electrical conductivity is 50 times higher than
  natural diamonds (heat sinks)

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Topic Support

• Kyocera- http//americas.kyocera.com/kicc/index.cf
  m
• http//kyoceraadvancedceramics.com/index.html
• http//www.ceramics.org/