2011 APS104-MSE-Chapter03-NPK-L23[1].pdf

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Published on 15 Apr 2013
School
UTSG
Department
Chemical Engineering and Applied Chemistry
Course
APS104H1
Professor
Chapter 3 - 1
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Chapter 3 -
Ceramic Crystal Structures
Lattice and basis
How do you estimate the crystal structure
for a ceramic?
What are the common crystal structures for
ceramics?
Reading pp. 45 -53 (sections 3.6, 3.7)
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Chapter 3 -
Metals vs. Ceramics
Structural Characteristics
Component
Metal: 1 element
Ceramic: at least 2 elements
Bonding
Metal: metallic
Ceramic: ionic to covalent
To calculate the percent Ionic Character
100e1 4)(
2
BA
×
XX
Electronegativities of the
elements A and B
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Document Summary

Lattice and basis: how do you estimate the crystal structure for a ceramic, what are the common crystal structures for ceramics, reading pp. Component: metal: 1 element, ceramic: at least 2 elements. Bonding: metal: metallic, ceramic: ionic to covalent. - can be ionic and/or covalent in character. - % ionic character increases with difference in electronegativity of atoms (see table 3. 2 next slide: degree of ionic character may be large or small: 2. 7 is adapted from linus pauling, the nature of the. Chemical bond, 3rd edition, copyright 1939 and 1940, 3rd edition. Bond hybridization is possible when there is significant covalent bonding. For example for sic hybrid electron orbitals form. Xsi = 1. 8 and xc = 2. 5 ionic% character. 511: ~ 89% covalent bonding, both si and c prefer sp3 hybridization, therefore, for sic, si atoms occupy tetrahedral sites. Ceramics with ionic character: cations metal ions (+, anions nonmetallic ions (-, factors influencing the structure of ceramics.

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