1、原子尺度的结构原子尺度的结构James P. SchafferJames P. SchafferThe Science and Design of Engineering The Science and Design of Engineering MaterialsMaterials(Second Edition)(Second Edition)D. R. Askeland and P. P. PhuleD. R. Askeland and P. P. Phule The Science and Engineering of Materials The Science and Engineer
2、ing of Materials (Fourth Edition)(Fourth Edition) 20092009年材料科学与工程讲义年材料科学与工程讲义2This moment will nap, you will have a dream; but this moment study, you will interpret a dream.20092009年材料科学与工程讲义年材料科学与工程讲义3Level of Structure Example of Technologies1.Atomic Structure Diamond edge of cutting toolsAtomic
3、Arrangements: Lead-zirconium-titanate Long-Range Order Pb(Zrx Ti1-x )O3 or PZT(LRO) gas ignitersAtomic Arrangements: Amorphous silica - fiberShort-Range Order optical communications(SRO) industryLevels of StructureLevels of Structure不同层次的结构不同层次的结构20092009年材料科学与工程讲义年材料科学与工程讲义4Level of Structure Examp
4、le of Technologies2.Nanostructure Nano-sized particles of(1-100nm) iron oxide ferrofluids3.Microstructure Mechanical strength of(10-1000nm) metals and alloys4.Macrostructure Paints for automobiles(1000nm) for corrosion resistance20092009年材料科学与工程讲义年材料科学与工程讲义52.12.1原子尺度的结构原子尺度的结构原子尺度的结构包括原子尺度的结构包括: :
5、原子的类型原子的类型 原子键的类型原子键的类型 原子的堆垛方式原子的堆垛方式材料的性能取决于各种尺度的结构形式材料的性能取决于各种尺度的结构形式, ,但是也有仅决定于原但是也有仅决定于原子尺度的结构子尺度的结构20092009年材料科学与工程讲义年材料科学与工程讲义6Scientists are considering using nano-particles of such magnetic materials as iron-platinum (Fe-Pt) as a medium for ultrahigh density data storage. Arrays of such par
6、ticles potentially can lead to storage of trillions of bits of data per square incha capacity that will be 10 to 100 times higher than any other devices such as computer hard disks. If these scientists considered iron (Fe) particles that are 3 nm in diameter, what will be the number of atoms in one
7、such particle?例题例题 Fe-PtFe-Pt纳米颗粒用于信息存储纳米颗粒用于信息存储20092009年材料科学与工程讲义年材料科学与工程讲义7The radius of a particle is 1.5 nm.Volume of each iron magnetic nano-particle = (4/3) (1.5 10-7 cm)3= 1.4137 10-20 cm3Density of iron = 7.8 g/cm3. Atomic mass of iron is 56g/mol.Mass of each iron nano-particle = 7.8 g/cm3
8、1.4137 10-20 cm3= 1.102 10-19 g.One mole or 56 g of Fe contains 6.023 1023 atoms, therefore, the number of atoms in one Fe nano-particle will be 1186.SOLUTION20092009年材料科学与工程讲义年材料科学与工程讲义8例题例题 单晶硅中的掺杂浓度单晶硅中的掺杂浓度 Dopant Concentration In Silicon Crystals Silicon single crystals are used extensively to
9、make computer chips. Calculate the concentration of silicon atoms in silicon, or the number of silicon atoms per unit volume of silicon. During the growth of silicon single crystals it is often desirable to deliberately introduce atoms of other elements (known as dopants) to control and change the e
10、lectrical conductivity and other electrical properties of silicon. Phosphorus (P) is one such dopant that is added to make silicon crystals n-type semiconductors. Assume that the concentration of P atoms required in a silicon crystal is 1017 atoms/cm3.Compare the concentrations of atoms in silicon a
11、nd the concentration of P atoms. What is the significance of these numbers from a technological viewpoint? Assume that density of silicon is 2.33 g/cm3.20092009年材料科学与工程讲义年材料科学与工程讲义9Atomic mass of silicon = 28.09 g/mol. So, 28.09 g of silicon contain 6.023 1023 atoms.Therefore, 2.33 g of silicon will
12、 contain (2.33 6.023 1023/28.09) atoms = 4.99 1022 atoms. Mass of one cm3 of Si is 2.33 g. Therefore, the concentration of silicon atoms in pure silicon is 5 1022 atoms/cm3.SOLUTION20092009年材料科学与工程讲义年材料科学与工程讲义10Significance of comparing dopant and Si atom concentrations: If we were to add phosphorus
13、 (P) into this crystal, such that the concentration of P is 1017 atoms/cm3, the ratio of concentration of atoms in silicon to that of P will be (5 1022)/(1017)= 5 105. This says that only 1 out of 500,000 atoms of the doped crystal will be that of phosphorus (P)! This is equivalent to one apple in 5
14、00,000 oranges! This explains why the single crystals of silicon must have exceptional purity and at the same time very small and uniform levels of dopants.20092009年材料科学与工程讲义年材料科学与工程讲义112.22.2键的类型键的类型 一次键一次键(Primary bonding):(Primary bonding):都涉及到电子从一个原子向另外都涉及到电子从一个原子向另外一个原子转移，或者电子在原子间的共用一个原子转移，或者电子
15、在原子间的共用 离子键离子键 共价键共价键 金属键金属键二次键二次键(Secondary bonding):(Secondary bonding):不涉及电子的转移和共用不涉及电子的转移和共用20092009年材料科学与工程讲义年材料科学与工程讲义12 2003 Brooks/Cole Publishing / Thomson LearningThe metallic bond forms when atoms give up their valence electrons, which then form an electron sea. The positively charged ato
16、m cores are bonded by mutual attraction to the negatively charged electrons.金属键金属键20092009年材料科学与工程讲义年材料科学与工程讲义13 2003 Brooks/Cole Publishing / Thomson LearningCovalent bonding requires that electrons be shared between atoms in such a way that each atom has its outer sp orbital filled. In silicon, wi
17、th a valence of four, four covalent bonds must be formed. 共价键共价键20092009年材料科学与工程讲义年材料科学与工程讲义14 2003 Brooks/Cole Publishing / Thomson LearningCovalent bonds are directional. In silicon, a tetrahedral structure is formed, with angles of 109.5 required between each covalent bond20092009年材料科学与工程讲义年材料科学与
18、工程讲义15 2003 Brooks/Cole Publishing / Thomson Learning An ionic bond is created between two unlike atoms with different electronegativities. When sodium donates its valence electron to chlorine, each becomes an ion; attraction occurs, and the ionic bond is formed.离子键离子键20092009年材料科学与工程讲义年材料科学与工程讲义162
19、.32.3键的类型对材料性能的影响键的类型对材料性能的影响（1 1）键的类型对力学性能的影响）键的类型对力学性能的影响 塑性塑性 脆性脆性（2 2）键的类型对电学性质的影响）键的类型对电学性质的影响 导电性导电性20092009年材料科学与工程讲义年材料科学与工程讲义17 金属和离子固体对外应力作出的原子尺度响应的差异对比金属和离子固体对外应力作出的原子尺度响应的差异对比（a）外应力作用前，离子固体中每个离子都是由带相反电荷的离子所包围，（b）在外力作用下，离子试图相互滑过时产生强的排斥力，导致断裂，（c）相反在金属中电子云将带正电荷的原子核相互屏蔽开来，因此不产生排斥力20092009年材料
20、科学与工程讲义年材料科学与工程讲义18材料的电导率取决于三个因素：材料的电导率取决于三个因素： 载流子的类型载流子的类型 载流子的密度载流子的密度 载流子的迁移率载流子的迁移率金属金属 载流子的高迁移率，高浓度载流子的高迁移率，高浓度导电性好导电性好离子固体离子固体 载流子的低迁移率，低浓度载流子的低迁移率，低浓度绝缘性好绝缘性好20092009年材料科学与工程讲义年材料科学与工程讲义19 2003 Brooks/Cole Publishing / Thomson LearningWhen voltage is applied to a metal, the electrons in the
21、electron sea can easily move and carry a current.20092009年材料科学与工程讲义年材料科学与工程讲义20 2003 Brooks/Cole Publishing / Thomson Learning When voltage is applied to an ionic material, entire ions must move to cause a current to flow. Ion movement is slow and the electrical conductivity is poor.20092009年材料科学与工程
22、讲义年材料科学与工程讲义21例题例题 热敏电阻的设计热敏电阻的设计 Design of a ThermistorA thermistor is a device used to measure temperature by taking advantage of the change in electrical conductivity when the temperature changes. Select a material that might serve as a thermistor in the 500 to 1000oC temperature range.Photograph
23、 of a commercially available thermistor. (Courtesy of Vishay Intertechnology, Inc.)20092009年材料科学与工程讲义年材料科学与工程讲义22热敏电阻包括：热敏电阻包括：正温度系数热敏电阻（正温度系数热敏电阻（ positive temperature coefficient of resistance， PTC）负温度系数热敏电阻负温度系数热敏电阻（ negative temperature coefficient of resistance， NTC）临界温度热敏电阻临界温度热敏电阻（Critical Te
24、mperature Resistor ，CTR）负电阻突负电阻突变特性变特性 Two design requirements must be satisfied. First, a material with a high melting point must be selected. Second, the electrical conductivity of the material must show a systematic and reproducible change as a function of temperature. SOLUTION20092009年材料科学与工程讲义年
25、材料科学与工程讲义23Covalently bonded materials might be suitable. They often have high melting temperatures, and, as more covalent bonds are broken when the temperature increases, increasing numbers of electrons become available to transfer electrical charge. 半导体半导体SiSi是可行的是可行的 The semiconductor silicon is
26、one choice: Silicon melts at 1410oC and is covalently bonded. A number of ceramic materials also have high melting points and behave as semiconducting materials. Silicon will have to be protected against oxidation. 20092009年材料科学与工程讲义年材料科学与工程讲义24We will have to make sure the changes in conductivity i
27、n the temperature range are actually acceptable. Some thermistors that show a predictable decrease in the resistance with increasing temperature are made from semiconducting materials.聚合物不可行聚合物不可行 Polymers would not be suitable, even though the major bonding is covalent, because of their relatively
28、low melting, or decomposition, temperatures.20092009年材料科学与工程讲义年材料科学与工程讲义25Many thermistors that can be used for switching applications make use of barium titanate (BaTiO3) based formulations. Many useful NTC materials are based on Fe3O4-ZnCr2O4, Fe3O4-MgCr2O4, or Mn3O4, doped with Ni, Co, or Cu.在性能满
29、足的前提下，当然我们还要考虑原材料的费用、加工制在性能满足的前提下，当然我们还要考虑原材料的费用、加工制造成本、寿命、对环境的影响等等。造成本、寿命、对环境的影响等等。20092009年材料科学与工程讲义年材料科学与工程讲义262.42.4键键力曲线与键力曲线与键能曲线能曲线 键能曲线上的最小值对应于平衡间距 从键能曲线上能够直接获取一些重要的宏观材料性质： 键能 平均键长 弹性模量 热膨胀系数20092009年材料科学与工程讲义年材料科学与工程讲义27键能曲线的应用 （1）原子系统对外载荷的响应 键能曲线在平衡位置的曲率正比于弹性模量，（曲率半径越小，弹性模量越大） 物理解释：能量势阱的两壁
30、越陡，将原子从其平衡位置移动所需的能量越大。ExFxU2220092009年材料科学与工程讲义年材料科学与工程讲义28 （2）原子系统对温度的响应 )(000TTxxxthe键能曲线不对称性增加，热膨胀系数增加键能曲线不对称性增加，热膨胀系数增加高键能的材料会具有低的热膨胀系数高键能的材料会具有低的热膨胀系数20092009年材料科学与工程讲义年材料科学与工程讲义292.52.5原子的堆垛和配位数原子的堆垛和配位数 诸如密度一类的性质主要取决于原子在固体中的排列。诸如密度一类的性质主要取决于原子在固体中的排列。 配位数配位数: : 固体中每个原子周围的最近邻的原子数目固体中每个原子周围的最近邻
31、的原子数目20092009年材料科学与工程讲义年材料科学与工程讲义302.6 2.6 二次键二次键（1 1）暂时电偶极子）暂时电偶极子 不断运动的电子临时排列形成非对称电荷分布不断运动的电子临时排列形成非对称电荷分布 范德华键范德华键 也存在于也存在于CHCH4 4，CClCCl4 4这样的对称分子这样的对称分子 随分子量增大而增大随分子量增大而增大 键能（键能（10KJ/mol10KJ/mol）20092009年材料科学与工程讲义年材料科学与工程讲义3120092009年材料科学与工程讲义年材料科学与工程讲义32（2 2）永久偶极子）永久偶极子 正电荷的中心始终与负电荷的中心不同正电荷的中心
32、始终与负电荷的中心不同 实例：实例：H H2 2O O，H H2 2S S，NHNH3 3 氢键是最强的二次键（氢键是最强的二次键（51KJ/mol51KJ/mol） 纸张纸张20092009年材料科学与工程讲义年材料科学与工程讲义332.7 2.7 混合键混合键（1 1）许多陶瓷包含混合离子）许多陶瓷包含混合离子/ /共价特性的一次键共价特性的一次键 组成元素的电负性差别越大，化合物离子键占的份额越大。共价键占的组成元素的电负性差别越大，化合物离子键占的份额越大。共价键占的份额可用下列经验公式计算份额可用下列经验公式计算 )25. 0exp(2Ef例如：例如：SiO2 f = exp-0.2
33、5(3.5 - 1.8)2= exp(-0.72) = 0.486SiOSiO2 2 用途：玻璃、光纤、制造高纯用途：玻璃、光纤、制造高纯SiSi、纳米、纳米SiOSiO2 2作为添加物增强橡胶作为添加物增强橡胶的强度的强度20092009年材料科学与工程讲义年材料科学与工程讲义34三种有代表性的电负性计算方法（补充）电负性的计算方法有多种，每一种方法的电负性数值都不同，比电负性的计算方法有多种，每一种方法的电负性数值都不同，比较有代表性：较有代表性：（1 1）L.C.L.C.鲍林提出的标度。根据热化学数据和分子的键能，指定鲍林提出的标度。根据热化学数据和分子的键能，指定氟的电负性为氟的电负性
34、为3.983.98，计算其他元素的相对电负性。，计算其他元素的相对电负性。（2 2）R.S.R.S.密立根从电离势和电子亲合能计算的密立根从电离势和电子亲合能计算的绝对电负性绝对电负性。（3 3）A.L.A.L.阿莱提出的建立在核和成键原子的电子静电作用基础上阿莱提出的建立在核和成键原子的电子静电作用基础上的电负性。的电负性。利用电负性值时，必须是同一套数值进行比较。利用电负性值时，必须是同一套数值进行比较。20092009年材料科学与工程讲义年材料科学与工程讲义35（2 2）金属）金属 过渡族元素的原子中会出现一些共价键，熔点高过渡族元素的原子中会出现一些共价键，熔点高 金属间化合物金属间化
35、合物 如如NiNi3 3AlAl，TiTi3 3AlAl（3 3）一次键和二次键混合）一次键和二次键混合 气体分子以共价键结合，气体分子以共价键结合， 分子凝聚依靠范德华键分子凝聚依靠范德华键 聚合物长链内部共价键结合，链与链之间可以以范德华键聚合物长链内部共价键结合，链与链之间可以以范德华键 和氢键结合和氢键结合 层状石墨层状石墨 （其中单层石墨其中单层石墨 GrapheneGraphene是目前的研究热点！是目前的研究热点！）20092009年材料科学与工程讲义年材料科学与工程讲义36Graphene2004年年 曼彻斯特大学研究员曼彻斯特大学研究员Andre Geim小组发现小组发现 该
36、图系单层(石墨烯)AFM 图象.箭头处的台阶高度为0.8nm. 20092009年材料科学与工程讲义年材料科学与工程讲义37SiO2可用于制造光纤。面临两个问题：可用于制造光纤。面临两个问题：1. 1. 由于由于Si-OSi-O是离子是离子/ /共价共价混合键，强度很高（很脆）；混合键，强度很高（很脆）；2. 2. 其表面容易与水蒸汽反应产生裂其表面容易与水蒸汽反应产生裂纹。如何设计制造弯曲性能较好的光纤？纹。如何设计制造弯曲性能较好的光纤？Silica is used for making long lengths of optical fibers. Being a covalently
37、and ionically bonded material, the strength of Si-O bonds is expected to be high. Other factors such as susceptibility of silica surfaces to react with water vapor in atmosphere have a deleterious effect on the strength of silica fibers. Given this, what design strategies can you think of such that
38、silica fibers could still be bent to a considerable degree without breaking?例题例题 SiO2光纤的设计策略光纤的设计策略 Design Strategies for Silica Optical Fibers20092009年材料科学与工程讲义年材料科学与工程讲义38（1 1）由于）由于Si-OSi-O是离子是离子/ /共价混合键，强度很高（很脆）；增加其延展性很难共价混合键，强度很高（很脆）；增加其延展性很难Based on the mixed ionic and covalent bonding in silic
39、a we know that the Si-O bonds are very strong. We also know that covalent bonds will be directional and hence we can anticipate silica to exhibit limited ductility. Therefore, our choices to enhance ductility of optical fibers are rather limited since the composition is essentially fixed. Most other
40、 glasses are also brittle. （2 2）升高温度可以提高延展性，在实际应用并不可取）升高温度可以提高延展性，在实际应用并不可取We can make an argument that silica fibers will exhibit better ductility at higher temperatures. However, we have to use them for making long lengths of optical fibers (most of which are to be buried underground or under the
41、sea) and hence keeping them at an elevated temperature is not a practical option.SOLUTION20092009年材料科学与工程讲义年材料科学与工程讲义39Therefore, we need to understand, beyond what the nature of bonding consideration can offer us, why glass fibers exhibit limited ductility. Is this a property that is intrinsic to t
42、he glass or are there external variables that are causing a change in the chemistry and structure of the glass? （3 3）表面容易与水蒸汽反应产生裂纹，也是其延展性差的原因）表面容易与水蒸汽反应产生裂纹，也是其延展性差的原因Materials scientists and engineers have recognized that the lack of ductility in optical glass fibers is linked to the ability of th
43、e silica surface to react with water vapor in the atmosphere. They have found that water vapor in the atmosphere reacts with the surface of silica leading to micro-cracks on the surface.20092009年材料科学与工程讲义年材料科学与工程讲义40When subjected to stress these cracks grow rapidly and the fibers break quite easily
44、! They have also tested silica fibers in a vacuum and found that the levels to which one can bend fibers are much higher.So what about protecting the surface of silica fibers, just like we paint cars and bridges to prevent them from rusting? This is what is done by manufacturers of optical fibers su
45、ch as Corning and Lucent. （4 4）具体的解决方案）具体的解决方案 镀一层高分子薄膜，再用金属外壳加以保护镀一层高分子薄膜，再用金属外壳加以保护When the optical fibers are manufactured, they are immediately coated with a polymeric film. Later, bundles of such fibers are encased in metallic cables and used in the fiber optics network.20092009年材料科学与工程讲义年材料科学与
46、工程讲义412.82.8聚合物分子的结构聚合物分子的结构20092009年材料科学与工程讲义年材料科学与工程讲义42 2003 Brooks/Cole Publishing / Thomson Learning 聚氯乙烯的结构聚氯乙烯的结构In polyvinyl chloride (PVC), the chlorine atoms attached to the polymer chain have a negative charge and the hydrogen atoms are positively charged. The chains are weakly bonded by
47、van der Waals bonds. This additional bonding makes PVC stiffer, (b) When a force is applied to the polymer, the van der Waals bonds are broken and the chains slide past one another20092009年材料科学与工程讲义年材料科学与工程讲义4320092009年材料科学与工程讲义年材料科学与工程讲义44热塑性（热塑性（thermoplasticthermoplastic） 共价键聚合链间具有弱的二次键共价键聚合链间具有弱
48、的二次键热固性（热固性（thermosetthermoset） 三维的一次键网络三维的一次键网络20092009年材料科学与工程讲义年材料科学与工程讲义45例题例题 宇宙飞行器的机械手材料设计宇宙飞行器的机械手材料设计 Design of a Space Shuttle ArmNASAs space shuttles have a long manipulator robot arm, also known as the Shuttle Remote Manipulator System or SRMS , that permits astronauts to launch and retri
49、eve satellites. It is also used to view and monitor the outside of the space shuttle using a mounted video camera. Select a suitable material for this device.NASAs Shuttle Remote Manipulator System: SRMS Courtesy of Getty Images)20092009年材料科学与工程讲义年材料科学与工程讲义46Lets look at two of the many material cho
50、ices.1 1 所选的材料必须具有高强度高弹性模量所选的材料必须具有高强度高弹性模量First, the material should be stiff so that little bending occurs when a load is applied; this feature helps the operator maneuver the manipulator arm precisely. Generally, materials with strong bonding and high melting points also have a high modulus of el
