材料学基础10.ppt

1、材料科学基础Fundamental of Materials,Prof: Tian Min Bo Tel: 62795426 ，62772851 E-mail: Department of Material Science and Engineering Tsinghua University. Beijing 100084,Lesson ten,3.6 Intermetallic Compounds (Intermetallic Phases),. Future 1. The structure of AmBn differs from those of either A or B 2. I

2、ts composition is variable to more or less extension 3. Mixed bonding 4. Intermediate properties,. Formation AB The property of AmBn is between that of A and B.,. Factor governing the structure of “compounds”. 1) Electrochemical factor (X) 2) Electron concentration (e/a) 3) Size factor Metal Nonmeta

3、l Metalloid,3.7 Normal Valence Compounds,. Definition: If the number of valence electrons of the cation is sufficient to complete octahedron of the anion, the compound is called the normal valence compounds. Example: CmAn meCn(8eA) sometimes: m(eCeCC)n(8eAeAA),. Classification according to structure

4、 1. NaCl and CaF2 types NaCl: (Mg Ca Sr Ba)(Se Te) (Mn Pb Sn)(Se Te) CaF2: PtSn2 PtIn2 Pt2P Anti-CaF2: Mg2(Si Ge Sn Pb) Cu2Se Li3AlN2 LiMg(N As Sb Bi) AgMgAs,2. Diamond, Zinc blende, Wurtzite types Zinc blende: (Be Zn Ca Hg)(S Se Te) (Al Ga In)(P As Sb) Wurtzite: (Zn Cd Mn)S (Cd Mn)Se,3. NiAs struct

5、ure Example: (Cr Fe Co Ni)(S Se Sb) (Fe Co)Te (Mn Fe Ni Pt Cn)Sn Ni(As Sb Bi),Structure,Normal state Ni : As = 1 : 1,When Ni does not full fill octahedral interspaces Ni : As 1 : 1,Extreme state： Ni occupy trigonal interspaces Ni : As 1 : 1,4. Electron Phase (Electron compounds) For Alloys of IB or

6、transition metals, and B group metals phases with sane or similar structure occur at approximately some electron concentration(e/a) these alloys are therefore called as electron compounds,3.8 Electron Phases (Hume-Rothery phases),Feature: Identical on similar structure occur at approximately the sam

7、e electron concentration, e/a.,For example: CuZn : Cu5Zn8 : CuZn3 : (HCP) : (2+1)/2 = 21/14 : 21/13 : 21/12, Components IB or transition metalmetals in B group Composition range is related to e/a Metallic character,3.9 Size Factor Compounds,. Interstitial phases (Interstitial compounds) Condition A

8、B B: H (0.46), B (0.97), C (0.77), N (0.71) 1. Simple interstitial compound structure,A: Transition metals B: Interstitial elements (H, B, C, N),2. Complex structure,M3C , (Fe3C) , M23C6 , M6C properties of interstitial compounds Some metallic properties Hard and brittle For size factor compounds,. Three principles for the structure 1. space-filling principle: Atoms tend to fill the space as closely as possible 2. Symmetry principle: Atoms tend to build a configuration of high symmetry 3. Principle of multi-dimensional connection,. Intermetallic compounds Examples: 1. Laves phas