CH 12 - Structures & Properties of Ceramics Flashcards Preview

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Flashcards in CH 12 - Structures & Properties of Ceramics Deck (18):

What is the bonding found in ceramics?

-can be ionic and/or covalent
-% ionic character increases with difference in electronegativity of atoms
-degree of ionic character may be large or small


Describe oxide structures

-oxygen anions larger than metal cations
-close packed oxygen in a lattice (usually FCC)
-cations fit into interstitial sites among oxygen ions


What are factors that determine the crystal structure of ceramics?

-relative size of ions; formation of stable structures maximizes the # of oppositely charge ion neighbors
-maintenance of charge neutrality


What is the tetrahedral position? (ceramics)

-type of interstitial site
-four atoms surround it
-three in one plane, single atom in the adjacent plane
-lines drawn from the centers of the surrounding spheres form a four sided tetrahedron


What is the octahedral position? (ceramics)

-type of interstitial site
-six ion spheres
-three in each plane
-octahedron forms when lines are drawn connecting all six atoms


How are silicates formed?

bonding of adjacent SiO4(4-) accomplished by the sharing of common corners, edges or faces


Describe the glass structure

-basic unit: SiO4(4-)
-fused silica to which no impurities have been added


What are layered silicates?

-SiO4 tetrahedra connected to form a 2D plane
-net negative charge associated with each (Si2O5)2- unit
-neg charge balanced by adjacent plane rich in cations


Describe kaolinite clay

-alternating layers of (Si2O5)2- with Al2(OH)4(2+)
-adjacent sheets are loosely bound by van der Waal's forces


What are the properties of diamond?

-tetrahedral bonding of carbon
-hardest material known
-very high thermal conductivity
-large single crystals = gemstones
-small crystals used to grind/cut other materials
-diamond thin films used as surface coatings for cutting tools & medical devices


What are the properties of graphite?

-layered structure
-parallel hexagonal arrays of carbon atoms
-weak van der Waal's forces between layers
-planes slide easily over one another
-good lubricant


What are fullerenes?

-spherical cluster of 60 carbon atoms
-shaped like soccer ball


What are carbon nanotubes?

-sheet of graphite rolled into a tube
-ends capped with fullerene hemispheres


What are the types of point defects in ceramics?

vacancies & interstitials


What is a Frenkel defect?

cation vacancy, cation interstitial pair


What is a Shottky defect?

paired set of cation and anion vacancies


What does annealing do to glass?

removes internal stresses caused by uneven cooling


How is glass tempered?

-puts surface of glass into compression
-suppresses growth of cracks from surface scratches