Lecture14

Lecture14 - ENGR 2220 Structure & Properties of Materials...

Info iconThis preview shows pages 1–13. Sign up to view the full content.

View Full Document Right Arrow Icon
ENGR 2220 ENGR 2220 – Structure & Properties of Materials Lecture 14 Structures & Properties of Ceramics Chapter 12, 13
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Coordination # and Ionic Radii Coordination # increases with r cation r anion Issue: How many anions can you r cation Coord ZnS incblende) arrange around a cation? 2 r anion # < 0.155 linear Adapted from Fig. 12.4, Callister 7e. (zincblende) 0.155 - 0.225 0.225 - 0.414 3 4 triangular T D Adapted from Fig. NaCl (sodium chloride) 0.414 - 0.732 6 O H 12.2, Callister 7e. CsCl (cesium hloride) Adapted from Table 12.2, Callister 7e. 0.732 - 1.0 8 cubic Adapted from Fig. 12.3, Callister 7e. chloride)
Background image of page 2
Example: Predicting Structure of FeO On the basis of ionic radii, what crystal structure would you predict for FeO? Answer: 077 0 cation . r Ionic radius (nm) 0.053 Cation Al 3+ 550 0 140 0 anion . . r = = 0.077 0.069 Fe 2+ Fe 3+ + based on this ratio, --coord # = 6 0.100 nion Ca 2+ --structure = NaCl 0.140 181 Anion O 2- l - Data from Table 12.3, Callister 7e. 0.181 0.133 Cl F -
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Silicates – Combine SiO 4 4- tetrahedra by having them share corners, edges, or faces Adapted from Fig. 2 12 allister 7e – Cations such as Ca 2+ , Mg 2+ , & Al 3+ act to Mg 2 SiO 4 Ca 2 MgSi 2 O 7 12.12, Callister 7e. neutralize & provide ionic bonding
Background image of page 4
+ Layered Silicates Kaolinite clay alternates (Si 2 O 5 ) 2- layer with Al 2 (OH) 4 2+ layer Adapted from Fig. 12.14, Callister 7e. Note: these sheets loosely bound by van der Waal’s forces
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Features of Layered Silicates Clay is inexpensive • Adding water to clay Shear Adding water to clay -- allows material to shear easily along weak van der Waals bonds -- enables extrusion charge neutral -- enables slip casting weak van Structure of aolinite Clay: der Waals bonding + Kaolinite Clay: Adapted from Fig. 12.14, Callister 7e . (Fig. 12.14 is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American charge neutral Si 4 Al 3+ - OH - Ceramic Society Bulletin , Vol. 30 (4), 1951, p. 140.) O 2 Shear
Background image of page 6
Type of Defects
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Defects in Ceramic Structures Frenkel Defect -- a cation is out of place. Shottky Defect -- a paired set of cation and anion vacancies. Adapted from Fig. 12.21, Callister 7e. (Fig. 12.21 is from W.G. Moffatt, G.W. Pearsall, and J. Wulff, The Structure and Shottky Defect: , Properties of Materials , Vol. 1, Structure , John Wiley and Sons, Inc., p. 78.) Frenkel efect Equilibrium concentration of defects kT / Q D e ~ Defect
Background image of page 8
Charge Balance Maintain electro-neutrality One Fe 2+ for every 2Fe 3+ ions
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Vacancy Defects: Impurity
Background image of page 10
Impurities Impurities must also satisfy charge balance = Electroneutrality x: NaCl a + l - Ex: NaCl Substitutional cation impurity Na Cl Ca 2+ cation vacancy Na + Na + a 2+ initial geometry Ca 2+ impurity resulting geometry Ca Substitutional anion impurity anion vacancy O 2- initial geometry O 2- impurity Cl - Cl - resulting geometry
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Diffusion in Ceramics Complicated: 2 type ions; opposite charges ain mechanism is Vacancies Main mechanism is Vacancies Ionic vacancies occur in pairs orm in non toichiometric compounds Form in non-stoichiometric compounds Created by different charge state of Substitutional impurity compared to host py p Diffusion of an ion is accompanied by motion of an opposite charge: rate determined by slower one: vacancy, impurity, hole or free electron
Background image of page 12
Image of page 13
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/29/2008 for the course ENGR 2220 taught by Professor Rizvi during the Fall '08 term at UOIT.

Page1 / 46

Lecture14 - ENGR 2220 Structure & Properties of Materials...

This preview shows document pages 1 - 13. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online