【2017年整理】Unit 6 Metals.docVIP

Metals金属 About three-quarters of the elements available can be classified as metals, and about half of these are of at least some industrial or commercial importance. Although the word metal, by strict definition, is limited to the pure metal elements, common usage gives it wider scope to include metal alloys. While pure metallic elements have a broad range of properties, they are quite limited in commercial use. Metal alloys, which are combinations of two or more elements, are far more versatile and for this reason are the form in which most metals are used by industry. 大约现有元素中的四分之三可归类为金属；而大约一半金属元素都有一定的工业或商业上的重要性。尽管严格定义的金属只局限于纯金属，但是普遍的用法是把它扩展到更广范围的金属合金。尽管纯金属有很多特性，他们在商业中的应用也很局限。金属合金由两种或两种以上的元素组成，用途非常广泛，正是由于这种结构上的原因，很多金属被用于工业上。 Metallic materials are crystalline solids. Individual crystals are composed of unit cells repeated in a regular pattern to form a three-dimensional crystal-lattice structure. A piece of metal is an aggregate of many thousands of interlocking crystals (grains) immersed in a cloud of negative valence electrons detached from the crystals’ atoms. These loose electrons serve to hold the crystal structures together because of their electrostatic attraction to the positively charged metal atoms (ions). The bonding forces, being large because of the close-packed nature of metallic crystal structures, account for the generally good mechanical properties of metals. Also, the electron cloud makes most metals good conductors of heat and electricity. 金属材料是晶状固体。单个晶体是由单元晶粒按有规则模式重复而形成的三维晶格。一块金属则是成千上万相联晶体的集合体，而这些晶粒都沉浸在从晶体原子中脱离出来的带负电的价电子云中。由于这些自由电子对带正电的金属原子或离子有静电吸引力，因此可以将晶体结构紧凑的结合在一起。而由于金属结晶结构致密本质导致的这种很大的结合力是造成金属一般都具有良好机械性质的原因。同样，电子云使大多数金属有很好的导电性和导热性。 Metals are often identified by the method used to produce the forms in which they are used. When a metal has been formed or shaped in the solid, plastic state, it is referred to as a wrought metal. Metal shapes that have been produced by pouring liquid metal into a mold are referred to as cast metals.