INTRODUCTION TO CERAMICS (Engineering C1B)

Steve Roberts

Synopsis

• Introduction to the class of ceramic materials: traditional ceramics, engineeringceramics, glasses and ceramic composites.

• Interatomic bonding and crystal structures found in ceramics.

• Structure of glasses - random network model.

• Classes of oxides in glassy networks: network formers, network modifiers,

intermediates.

• Brittle nature of ceramics.

• Fabrication of ceramics: powder synthesis, powder processing, sintering and reactionsintering.

• Fabrication of glasses and glass ceramics.

• Microstructures, mechanical properties and applications of: traditional triaxial porcelains, alumina, zirconia, silicon nitride, silicon carbide.

Reading List

• “Engineering Materials 2”, M.F. Ashby and D.r.H. Jones, Chapters 15-20.

• “Introduction to Ceramics”, W.D. Kingery, H.K. Bowen and D.R. Uhlmann.

• “Ceramic Science for Materials Technologists”, I.J. McColm.

• “Ceramic Microstructures”, W.E. Lee and W.M. Rainforth

• “Materials Science and Technology – volume 11 - Structure and Properties ofCeramics”, edited by M.V. Swain

• “Mechanical Behaviour of Ceramics”, R.W. Davidge

• "An Introduction to the Mechanical Properties of Ceramics", D.J. Green

 

 

INTRODUCTION TO CERAMICS (Engineering C1B)

Steve RobertsHilary 2000

Questions

1) Explain why the yield strength of a ceramic can approach of a crystal, wheras the yield

strengths of engineering alloys are much lower than the ideal strength. How would youattempt to measure the yield strength of a ceramic, given that the fracture strengths of

ceramics in tension are usually much lower than the yield strengths?

2) Why are ceramics usually much stronger in compression than in tension?An Al2O3 material has a fracture toughness K Ic of about 3 MPam

1/2 and a hardness of

13 GPa. A batch of samples of this material is found to contain surface flaws about 30µm

deep. Estimate: (a) the tensile strength and (b) the compressive strength of this batch ofthe alumina ceramic.

3) Describe the random network model of glass structure explaining the role of networkforming, modifying and intermediate oxides.

4) Describe the main mechanisms of mass redistribution which can occur during

sintering. Explain which mechanisms lead to an increase in component density.

5) A ceramic material is sintered in a nitrogen atmosphere (at normal atmospheric

 pressure). In the sintering process, pores become isolated at a diameter of 5 µm. Theceramic has a surface energy of 0.28 Jm

-2. What will be the equilibrium pore size (when

the gas pressure just balances the closure pressure due to surface tension)? If the original

 pores are in a material with 15% porosity by volume, what will be the linear shrinkage ofthe material from pore closure to when the pores reach equilibrium?

6) Sketch the microstructures you would expect to see in the following materials (indicate

the principal components and the scale of the microstructure). Explain in each case the processing routes used to achieve these microstructures and components.

a) A porcelain used for fine tableware.

 b) A high-toughness partially stabilised zirconia piston crown.c) A reaction bonded SiC heat exchanger.

 Numerical Answers:

2) 309 MPa tension, 4250 MPa compression.

4) Final pore diameter 3.34 µm, linear shrinkage 3.64%.