Structure, Mechanical properties and its applications.

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Presentation transcript:

Structure, Mechanical properties and its applications.

Ceramic bonds are mixed, ionic and covalent, with a proportion that depends on the particular ceramics The ionic character is given by the difference of electronegativity between the cations (+) and anions (- ). Covalent bonds involve sharing of valence electrons.

AX-type crystal structure Rock salt structure Sodium chloride (NaCl) is the most common Rc/Ra = CN=6 for both cations and anions Unit cell: FCC arrangement of anions with one cation at center of each of 12 cube edges Two interpenetrating FCC lattices

Cesium chloride structure  CN=8, 8 anions at cube corners and 1 cation at center of cube,  simple cubic (not BCC) Zinc Blende structure  CN=4, FCC structure of S with Zn at interior tetrahedral positions

Rc/Ra=0.8, CNCa=8, CNF=4 Ca atoms at center of cubes with F atoms at cube corners, similar to CsCl, but only 1/2 of sites are filled with Ca atoms Unit cell consists of 8 cubes A unit cell of CaF2 (AX2) The AmBnXp type crystal structures Ba at cubic corner, O at center of 6 faces, Ti at body center CNO=12, CNBa=6, and CN Ti=6 Large A cation and oxygen form an FCC lattice Cubic--tetragonal at 1300C (Curie points) Cubic -- orthrhombic and rhombohedral at low T

 Ceramics are brittle. For brittle fracture stress concentrators are very important.  Fracture strength of ceramic may be greatly enhanced by creating compressive stresses at Surface.  The compressive strength is typically ten times the tensile strength. This makes ceramics good structural materials under compression.

 Alumina99  Excellent mechanical strength, thermal conductivity, electrical insulation, high- frequency loss, abrasion resistance, good chemical resistance and other properties.  Used for piston pump, electromagnetic pump, thin film circuit substrates and other special purpose

 Alumina95  Can be used in thick film circuit substrates,and applications where the mechanical strength is required.

 Steatite  Good electrical and mechanical properties. Widely used in lamps and various electrical appliances

 Cordierite  Resistance to thermal shock, high temperature,  Widely used in water heater, hairdryer and other electric heater.