UNIVERSITEIT VAN PRETORIA DEPARTEMENT MATERIAALKUNDE EN METALLURGIESE INGENIEURSWESE

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1 UNIVERSITEIT VAN PRETORIA DEPARTEMENT MATERIAALKUNDE EN METALLURGIESE INGENIEURSWESE MATERIAALKUNDE NMC 122 MATERIALS SCIENCE SEMESTERTO ETS 1 SEMESTER TEST 16 AUG TYD/TIME: 1½ HOURS/ UUR INSTRUKSIES Beantwoord alle vrae in die spasies wat voorsien word. Vrae wat in potlood beantwoord is, sal nie nagesien word nie. Tippex of n soortgelyke produk, mag nie gebruik word nie. Rofwerk mag op die blanko bladsy gedoen word, maar sal nie gemerk word nie. Nie-progammeerbare sakrekenaars mag gebruik word. Geen vrae mag gedurende die toets gevra word nie. Maak aannames waar nodig en stel dit as sodanig. Die vraestel bevat 8 bladsye. INLIGTING WAT VIR DIE BEANTWOORDING VAN SOMMIGE VRAE BENODIG MAG WORD, KAN VAN DIE BYLAAG OP BLADSY 7 VERKRY WORD. DEEL A (34 PUNTE) INSTRUCTIONS Answer all the questions in the spaces provided. Questions answered in pencil, will not be marked. Tippex or a similar product may not be used. Rough work may be done on the blank pages, but will not be marked. Non-programmable calculators may be used. No questions may be asked during the test. Make assumptions where required and state it as such. The paper contains 8 pages. INFORMATION REQUIRED FOR ANSWERING SOME OF THE QUESTIONS, CAN BE OBTAINED FROM THE APPENDIX ON PAGE 7. PART A (34 MARKS) Elke vraag tel twee punte / Each question counts two marks Toon dmv 'n kruisie in die toepaslike blokkie, die korrekte antwoord op elk van onderstaande vrae. Elke vraag het slegs een korrekte antwoord. Dus mag slegs een blokkie per vraag gemerk word. Indicate with a cross in the appropriate block, the correct answer to each of the questions below. Each question has only one correct answer. Therefore, only one block may be marked per question. 1. Die besluit om n spesifieke material in n komponent te gebruik, hoort tot die studieveld van: The decision to use a specific material in a component, belongs to the field of study of: Materiaal-ingenieurswese Materials engineering Materiaalkunde Materials science Metallurgiese ingenieurswese Metallurgical engineering Metallografie Metallography 2. Deur die struktuur van n material te verander, verander die: The following will be changed by changing the structure of a material: afmetings van die materiaal dimensions of the material interatomiese binding van die materiaal inter-atomic bonding of the material eienskappe van die materiaal properties of the material prosessering van die materiaal processing of the material 1

2 3. Die volgende is n materiaal met oorwegend kovalente karakter: The following is a material with a predominantly covalent character: LiCl Co GaAs BaO 4. Die volgende material is oorwegend nie-kristallyn: / The following material is predominantly non-crystalline: Grafiet Sink Sout Graphite Zinc Salt Diamant Geelkoper Polietileen Diamond Brass Polyethylene 5. Die eenheidsel afmeting a is n afmeting waar: / The unit cell dimension a is a dimension where: die kristalstruktuur elektries neutral is the crystal structure is electrically neutral die kristalstruktuur die digste gepak is the crystal structure has the densest packing die potensiële energie tussen atome of ione n minimum is the potential energy between atoms or ions is a minimum die potensiële energie tussen atome of ione nul is the potential energy between atoms or ions is zero 6. Die verskil tussen n KVG en n HDG kristalstruktuur is nl. dat: The difference between a FCC and a HCP crystal structure is as a result of: hulle APF verskil a difference in APF hulle koördinasiegetalle verskil a difference in coordination number die planêre digthede van die diggepakste vlakke verskil a difference in the planer density of close packed planes die pakkingsvolgorde van die diggepakste vlakke verskil a difference in packing sequence of close packed planes 7. Die volgende is nie waar vir die vlakke (110) en (011) nie: The following is not true for the planes (110) and (011): die vlakke is beide deel van die {110} familie van vlakke the planes are both members of the {110} family of planes die vlakke sny mekaar the planes intercept each other die planêre atomiese digtheid vir albei vlakke is dieselfde vir die kubiese eenheidselle the planer atomic density for both planes for a cubic unit cell are the same die vlakke is die diggepakste vlakke in KVG materiale the planes are the closest packed planes in FCC material 8. Allotropie (polimorfisme) is die verskynsel dat: / Allotropy (polymorfism) is the phenomena that: n material verskillende chemiese samestellings by verskillende temperature het a material has different chemical compositions at different temperatures n materiaal geen kristalstruktuur bevat nie a material has no crystal structure n element in die vaste fase toestand verskillende kristalstrukture kan hê an element in the solid phase can have different crystal structures 2

3 n materiaal ondergaan n omkeerbare faseverandering met verandering in temperatuur en druk a material shows a reversible phase change with change in temperature and pressure 9. n Interstisiële vaste oplossing sal vorm indien: / An interstitial solid solution will form if: die radius verskil groter as + 15% is the radius difference larger is than + 15% n moedermataalatoom uit die rooster verplaas word an atom is displaced from the lattice of the parent metal koue verwerking die aantal leë ruimtes verhoog cold working increases the number of vacancies n nie-metaal van periode 2 van die periodieke table in die metal oplos a non-metal from period 2 of the periodic table dissolves in the metal 10. Die eenheidsel hieronder toon die kristalstruktuur van Ge / The unit cell shown below is that of Ge. a = 0.56 nm R = nm 10.1 Die koördinasiegetal vir die Ge is: / The coordination number for Ge is: Die posisie-koordinate vir die atoom wat met n pyl aangedui word is: The position coordinates for the atom indicated by the arrow is: ( ¼ ¼ ¼ ) (¼, ¼, ¼) (¾ ¼ ¼) (¾, ¼, ¼) 10.3 Die Millerindekse vir die getoonde vlak in bostaande eenheidsel is: The Miller indices for the plane shown in the unit cell above is: (012) (0, 2,1) (021) (114) 10.4 Die planêre digtheid van die getoonde vlak vir Ge is: / The planar density of the shown plane for Ge is 1/ 2 a 2 3/ 5 a 2 1/ 1¼ a 2 1/ 5 a 2 atm/nm 2 atm/nm 2 atm/nm 2 atm/nm Die ekwivalente aantal atome per eenheidsel is: / The equivalent number of atoms per unit cell is:

4 10.6 Trek die [0 1 1] rigting in die eenheidsel in / Draw the [0 1 1] direction in the unit cell. 11. Die waarde van die diffusiwiteit D vir diffusie van Cu in Ni sal vergroot indien: The value of the diffusivity D for diffusion of Cu in Ni will increase if: die temperatuur verlaag word the temperature is increased die atm% Cu verhoog word the atm.% Cu is increased die ASTM korrelgrootte-getal n vergroot word the ASTM grain size number n is increased die aantal kantontwrigtings verminder word the number of edge dislocations are decreased 12. Die volgende mikro-defek kom voor in n Si-enkelkristal: The following micro defect occurs in a Si single crystal: korrelgrens grain boundaries pore pores inklusies inclusions leë ruimtes vacancies DEEL B (36 PUNTE) PART B (36 MARKS) 1. Bereken die volume digtheid van Ge. / Calculate the volume density of Ge. (5) n Materiaal het 2400 korrels / mm 2 by 1X vergroting. Bereken die ASTM korrelgrootte getal. Toon u berekeninge. A material has 2400 grains / mm 2 at 1X magnification Calculate the the ASTM grain size number. Show your calculations (5) By watter temperatuur sal die diffusiwiteit (D) van Cu in Al 3X groter wees as die diffusiwiteit by 300 o C. At what temperature will the diffusivity (D) of Cu in Al be 3X larger than at 300 o C. (5) 4

5 4. Beskou elemente A en B. Hoe groot moet die verskil in elektronegatiwiteite tussen die elemente wees om n binding met 30% ioniese karakter te verkry. Consider elements A and B. What must the differnece in electronegativity between the elements be to obtain a bond with 30 % Ionic character. (4) 3. Watter van die elemente Cu of Mg sal die hoogste oplosbaarheid in Al hê. Motiveer u antwoord met die nodige berekeninge en vergelyking van toepaslike data. Which of the elements Cu or Mg will have the highest solubility in Al. Motivate your answer with the required calculations and reference to applicable data. (5) Tabel met bruikbare data. / Table with usable data: Eienskap / Property Al Cu Mg Kristalstruktuur Crystal structure FCC FCC HCP Atoomgetal Atomic number Digtheid Density 2,71 8,94 1,74 Valansie Valance Elektronegatiwiteit Electronegativity 1,5 1,9 1,2 Smeltpunt Melting point Atoomradius Atomic radius 0,143 0,128 0,160 5

6 6. Beskou ongestadigde diffusie / Consider non-steady state diffusion. 6.1 Trek konsentrasie profiele vir vraag 6.2 op n benoemde assestelsel vir Al diffusie in Si op verskillende tye t o, t 1 en t 2 Draw concentration profiles for question 6.2 on labelled axis for Al diffusion in Si at different times t o, t 1 and t 2. (3) 6.2 n Suiwer silikonskyf word doteer met aluminium by 1100 o C vir 8 uur. Wat is die diepte onder die oppervlakte in µm, waar die Al-konsentrasie atome/m 3 sal wees, indien die oppervlakkonsentrasie van die Al atome/m 3 is? D = 2 x cm 2 /s vir diffusie van Al in Si by 1100 o C. A pure silicon wafer is doped with aluminum at 1100 o C for 8 hours. What is the depth below the surface in µm, at which the Al concentration is atoms/m 3, if its surface concentration is atoms/m 3. D = 2x10-12 cm 2 /s for Al diffusion in Si at 1100 o C. (6) 6

7 7. Noem drie maniere of metodes hoe kantdefekte of ontwrigtings in n metaal kan ontstaan. Name three methods or ways by which edge dislocations can form in a metal. (3) BYLAAG / APPENDIX N = 2 n 1 ρ v = M/V ρ p = eq. no. atom./ area ρ l = eq. no. atm. dia / length ρ v = ekw. aantal atoom / oppv. ρ l = ekw. atm. dia / lengte D = D o e - Q/RT N A = 6,023 x R = 8,314 Atm.mass. Ge = a Ge = 0.56 nm (Cs Cx) / (Cs Co)= erf (x / 2 Dt) % IC = [ 1 e ¼ ( Xa Xb) ] x 100 = % Ioniese karakter Area circle =π.r 2 Vol. sphere = 4/3.π.r 3 Area sirkel =π.r 2 Vol. sfeer = 4/3.π.r 3 Tabel met elektronegatiwiteite / Table of electronegativities. 8. Die diffusiemeganisme van Co in Fe is: / The diffusion mechanism of Co in Fe is: self-diffusie self diffusion substitisionele diffusie substitutional diffusion ring-diffusie ring diffusion interstisionele diffusie interstitional diffusion 1s 2s 2p 1s 2s 2p 1s 2s 2p 1s 2s 2p 7