第一章固体材料的结构.docVIP

第一章 固体材料的结构 Chapter 1. The Structure of Materials 本章要讨论的主要问题是： (1) 为什么原子能结合成固体？(2) 材料中存在哪几种键合方式？(3) 决定键合方式的主要因素有哪些？(4) 材料的哪些性能和其键合方式有密切的关系？ (5) 如何描述晶体中原子的排列？ (6) 金属晶体有哪些常见的晶体结构？ Questions for Chapter 1 What is crystal structure? What is crystal lattice? How many types of bonding between atoms? What are the most important factors in determining the types of bonds? What is the relationship between bonds and properties of materials? How to describe the atom arrangement in crystalline? What are the most metal’s crystal structures? 1-1 几何晶体学的基本知识 Sec.1.1 The Fundamentals of Geometric Crystallology The most important aspect of any engineering material is its structure, because its properties are closely related to this feature. To be successful, a materials engineer must have a good understanding of this relationship between structure and properties. 1、原子之间的键合 The types of bonds Atomic scale structure: By atomic structure we mean (1) The types of atoms present; (2) The types of bonding between the atoms; (3) The way the atoms are packed together. The two major classes of atomic bonds are primary and secondary bonds. Primary bonds are generally one or more orders of magnitude stronger than secondary bonds. The three major types of primary bonds are ionic, covalent and metallic bonds. All primary bonds involve either the transfer of electrons from one atom to another or the sharing of electrons between atoms. One of the important factors in determining the type of band that an atom will form is its electronegativity. 离子键与离子晶体 Ionic bonding The most common type of bond in a compound containing both electropositive and electronegative elements is the Ionic bonds. This bond involves electron transfer from the electropositive atom to the electronegative atom. 原子结合：电子转移，结合力大，无方向性和饱和性； 离子晶体：硬度高，脆性大，熔点高、导电性差。如氧化物陶瓷。 共价键与原子晶体 covalent bonding Covalent bonds form in compounds composed of electronegative elements, especially those with four or more valence electrons. Since