课程名称︰材料科学 课程性质︰必带 课程教师︰宋家骥 开课学院：工学院 开课系所︰工程科学与海洋工程学系 考试日期（年月日）︰2008/4/16 考试时限（分钟）：180 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : Midterm-exam 1.(a)briefly cite the main differences between ionic, covalent, and metallic bonding. (b)state the pauli exclusion principle.(8pt) 2.what type of bonding predominates in (a) metals (b) ceramics (c) polymers? (5pt) 3.iron titanate, FeTiO3, forms in the ilmenite crystal structure which consists of an HCP arrangement of O-2 ions. If the ionic radius of Fe2+, Ti4+,O2- is 0.077, 0.061, and 0.140nm respectively. (a)which type of interstitial site will the Fe2+ ions occupy? why?(4pt) (b) which type of interstitial site will the Ti4+ ions occupy? why?(4pt) (c) what fraction of the total tetrahedral sites will be occupied?(1pt) (d) what fraction of the total octahedral sites will be occupied?(1pt) 4.a sheet of BCC iron 1mm thick was exposed to a carburizing gas atmosphere on the other side at 725度C. after having reached steady state, the iron was quickly cooled to room temperature. the carbon constrations at the two surfaces of the sheet were determined to be 0.012 and 0.0075wt%. (a) iron has an atomic radius of 0.124nm, and an atomic weight of 55.85 g/mol. compute its density.(10pt) (b)compute the diffusion coefficient if the diffusion flux is 1.4*10^-8 kg/m^2*s. the density of carbon is 2.25g/cm^3.(6pt) 5.polymers for engineering use can be classified as: (a)thermoplastic,(b)thermosetting, and(c)elastomeric. Fill in the type ID for each polymer listed in the following table. Answer example:I-a,II-b (5pt) name of polymer type ID natural rubber I polyethylene(PE) II polyester(PET) III phenol-formaldehyde(bakelite) IV polyvinyl chloride(PVC) V 6.for both FCC and BCC crstal structures, there are two different types of interstitial sites. in each case, one site is larger than the other, which site is normally occupied by impurity atoms. for both FCC and BCC crystal strcutures, compute the radius r of an impurity atom that will just fit nto one of these sites in terms of the atomic radius R of the host atom. (10pt) 7.For a bronze alloy, the stress at which plastic deformation begins is 275 Mpa, and the modulus of wlasticity is 115Gpa. (a) what is the maximum load that may be applied to a specimen with a cross-sectional area of 325mm^2 without plastic deformation? (b)If the original specimen length is 115mm, what is the maximum length to which it may be strentched without causeing plastic deformation?(10pt) 8.matching (a)isotactic,(b)syndiotactic,(c)atactic,(d)cis-,(e)trans- (5pt) ANS Figure I H H H H H R H H c c c c c c c c H R H R H H H R II HHHHHHHH CCCCCCCC HRHRHRHR III HHHRHHHR CCCCCCCC HRHHHRHH IV CH3 CH2- C===C -CH2 H V CH3 H C===C -CH2 CH2- ANSWER example:I-a II-b... the molecular structures above can be classified in to two schemes of isomerism.fill in the corresponding molecular structures.(5pt) Geometrical isomer:VI________ Stereo isomers: VII_________ 9.determine the composition, in atom percent, of an alloy that consists of 97wt% aluminum and 3wt% copper. (the atomic weight of copper and aluminum is 63.55 and 26.98 respectively)(10pt) 10.for some applications, it is necessary to harden the surface of a steel (or iron-carbon alloy) above that of its interior. One way this may be accomplished is by increasing the surface concentration of carbon in a process termed carburizing; the steel piece is exposed, at an elevated temperature, to an atmophere rich in a hydrocarban gas,such as methane (CH4).consider one such alloy that initially has a uniform carbon concentration of 0.25wt% and is to be treated at 950度C. if the concentration of carbon at the surface is suddenly brought to and maintained at 1.20wt%, how long will it take to achieve a carbon content of 0.80wt% at a position 0.5mm below the surface? the diffusion coefficient for carban in iron at his temperature is 1.6*10^-11 m^2/s; assume that the steel piece is semi-infinite.(10pt) --

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