材料科学与工程专业英语05—unit07.pptVIP

Physical properties Metals in general have high electrical conductivity, high thermal conductivity, and high density.They typically are deformable under stress without cleaving.通常地，金属具有良好的导电性和导热性，具有金属光泽，密度较大，并且具有在压力下变形而不会断裂的能力。 Some metals that have low density, low hardness, and low melting points, these (the alkali and alkaline earth metals). In terms of optical properties, metals are opaque, shiny, and lustrous. The majority of metals have higher densities than the majority of nonmetals. Nonetheless, there is wide variation in the densities of metals. Lithium is the least dense solid element and osmium is the densest. The metals of groups I A and II A are referred to as the light metals because they are exceptions to this generalization. The high density of most metals is due to the tightly packed crystal lattice of the metallic structure. The strength of metallic bonds for different metals reaches a maximum around the center of the transition metal series, as those elements have large amounts of delocalized electrons in tight binding type metallic bonds. However, other factors (such as atomic radius, nuclear charge, number of bonding orbitals, overlap of orbital energies, and crystal form) are involved as well. The nondirectional nature of matallic bonding is thought to be the primary reason for the malleability of metal .金属键没有方向性被认为是金属有延展性的原因 Crystals with covalent bond can only be deformed by breaking the bonds between atoms，thereby resulting in fragmentation of the crystal。只有破坏原子之间的共价键，共价键晶体才会变形，从而导致晶体破碎 Malleability：可锻性，延展性，韧性的 Cleavage：裂缝 Covalent bond：共价键 Originate from:源于 Heat capacity：热容 Electric charge：电荷 Potential：电位 Brillouin zone? ：布里渊区，在数学和固体物理学中，第一布里渊区是动量空间中晶体倒易点阵的原胞 Alloy 合金 Solid solution:固溶体 Questions What is an alloy? Give some examples. Discussion What physical and chemical properties do metals have? Physical properties: Chemical properties: * * 材料科学与工程专业英语Special English for Materials Science and Engineering Unit 7 Introduction to meta