skja_11 The Structures of Alloys 材料科学基础（英文课件）.pptVIP

材料科学基础Fundamental of Materials §3.10 Silicates Ⅰ.Introduction Silicates are compounds that mainly composed of [SiO4]. It is the essential components of most rock and soil, such as quartz, feldspar, mica etc. Ⅱ.Features 1. Basic sell: [SiO4] rsi/rO＝0.40/1.35＝0.300.414 Si4+ is the cation that have small radii and large electrovalence. 2. The bonds of Si-O-Si is not beeline but zigzag line. The angle of oxygen point is 145o in silicate. 3. For every oxygen, there is at most two SiO4 tetrahedrons can share it. 4. The SiO4 tetrahedrons can exist isolated or connect each other at common point. 5. In silicate structure: So, the CN of aluminum could be 4 or 6 6. The chemic expression or mineral. molecular formula : Al2O3·2SiO2·H2O ; ZrO2·SiO2 structural formula : Al2[Si2O5](OH)4 ; Zr[SiO4] Ⅲ.Classification island chain (single, double) sheet (single, double) frame 1. Island silicates characteristic single: molecular formula: M4+[SiO4]、 M22+[SiO4] typical minerals olivine, zircon, garnet 2. Chain silicates typical minerals tremolite ; (OH)6Mg6(Si4O11)·H2O 3. Sheet silicates typical minerals 4. Frame silicates typical minerals cristobalite（silica SiO2）, feldspar §3.11 Summary Ⅰ.Terminology: components , composition and its description , phase , structure Ⅱ.Classification: Ⅲ.Features Examples and Discussions Exercise * * Prof: Tian Min Bo Tel: E-mail: tmb@mail.tsinghua.edu.cn Department of Material Science and Engineering Tsinghua University. Beijing 100084 Lesson eleven [SiO4]4- 4－ SiO4 tetrahedron The distance between Si and O: Si－O : 1.6 ? (practical) 1.75 ? (theoretic) (0.40+1.35) aluminum + oxygen aluminum-oxygen tetrahedrons replace SiO4 tetrahedrons aluminum-silicate aluminum-oxygen octahedron Si:O=1