材料科学与工程导论课件:Chapter-02.ppt
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- 材料科学 工程 导论 课件 Chapter 02
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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
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