MCG2361W02-1slides(1) - 1 MCG 2361 Engineering Materials II Week 8 Ceramics introduction structure(2\/2 Ceramics review Ceramics are generally

MCG2361W02-1slides(1) - 1 MCG 2361 Engineering Materials II...

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1 Week 8: Ceramics: introduction & structure (2/2) MCG 2361 Engineering Materials II
2 Ceramics: review
3 Ceramics: review Ceramics are generally crystalline structures. Ionic bond… The ionic bond is not oriented , so in a stable structure each type A atom (say a metal) can only have type B atoms (say a non metal) as immediate neighbours, in all directions. Attraction energies associates to this type Of bond are very high, which explains some physical properties of ceramics such as their high melting temperatures
4 Ceramics: review Ceramics are generally crystalline structures. Ionic bond… The ionic bond is not oriented , so in a stable structure each type A atom (say a metal) can only have type B atoms (say a non metal) as immediate neighbours, in all directions. Electrons are strongly associated with the atoms that they link, not free to move/flow. Attracted to non-metals to complete their energy levels. Stuck in bonds. Thermal and electrical conductivity values for ceramics are therefore generally very low.
5 Ceramics: review Ceramics are generally crystalline structures. Ionic bond… The ionic bond is not oriented , so in a stable structure each type A atom (say a metal) can only have type B atoms (say a non metal) as immediate neighbours, in all directions. Stable electron configuration: full/empty valence shells (2, 8, 8, 18, etc) Example of industrial ceramic material where bonds are ionic: MgO Magnesium oxide
6 Ceramics: review Ceramics are generally crystalline structures. Chemical bonds that unit the atoms in such materials sometimes have a covalent character. Covalent bond: bond between two atoms that have partly complete valences; by sharing free electrons on these valences and by sharing them between the two atoms , a complete configuration is obtained. The covalent bond is oriented and defined between specific atoms (a specific orientation in space between bonded atoms). Ex.: SiC silicon carbide GaAs gallium arsenide
7 ionic covalent metallic sharing... loss or gain loss (free)... ... of valence electrons Ceramics: review
8 Ceramics: review . ,

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