School of Chemistry UNIVERSITY OF KWAZULU-NATAL JUNE 2008 EXAMINATION APCH312W1: MATERIALS CHEMISTRY DURATION: 3 HOURS TOTAL MARKS: 100

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1 School of Chemistry UNIVERSITY OF KWAZULU-NATAL JUNE 2008 EXAMINATION APCH312W1: MATERIALS CHEMISTRY DURATION: 3 HOURS TOTAL MARKS: 100 External Examiner: Internal Examiner: Dr M Fernandes University of the Witwatersrand Dr M Bala IMPORTANT: COMPLETE THIS SECTION IMMEDIATELY SURNAME AND INITIALS (Optional): SIGNATURE: Student Number. Seat No. Notes: This paper consists of 17 pages, including a periodic table and a data sheet. Please ensure that you have them all. The use of non-programmable electronic calculators is permitted. STUDENTS ARE REQUESTED, IN THEIR OWN INTERESTS, TO WRITE LEGIBLY.

2 Page 2 QUESTION 1 a) Give the typical composition, one important property and principal application of the following types of glass: (4) i) soda glass borosilicate glass b) State the advantages of annealing and tempering of glass products. (3) c) What type of crystal defect will result when CaO is introduced as an impurity in NaCl? Explain your choice of answer. (2)

3 Page 3 QUESTION 2 a) Describe the steps involved in the following ceramic processing techniques: (4) i) blowing of glass bottles. particulate forming. b) Drying & firing are important steps in ceramic processing. Discuss. (4)

4 Page 4 QUESTION 2 continue c) Given a cation and an anion radii and nm respectively, determine the coordination number and hence predict the geometry around the Ca 2+ ion in a crystal of CaCl 2. (2) QUESTION 3 a) Advanced ceramics such as Si 3 N 4, SiC & ZrO 2 may be used in engineering applications such as in engine block, piston coatings and jet engines. Give three points for and against the use of advanced ceramics in heat engines. (6)

5 Page 5 QUESTION 3 continue b) Give the chemical formulae (not cement abbreviation) and main functions of the following constituents of cement? (3) i) alite. belite. c) What is the effect of adding citrate salts to gypsum cement? (1)

6 Page 6 QUESTION 3 continue d) Give an example of a superplasticizer and state its use in concrete manufacture. (2) QUESTION 4 a) For a benzoyl peroxide initiated radical polymerization of ethylene write down the chemical equations that represent the initiation, propagation and termination by disproportionation steps. (6)

7 Page 7 QUESTION 4 continue b) (6) i) What is polymer tacticity? Using a chain of sufficient length show how polyvinyl chloride(pvc) with the following tacticities differ: i syndiotactic;

8 Page 8 QUESTION 4 continue iv) isotactic QUESTION 5 a) Polyethylene terephthalate (PETE) is a typical polyester used in the manufacture of wash and wear fabrics. (4) i) Write a chemical equation for the polymerization of PETE from its monomers. Give the chemical names of the monomers used in (i).

9 Page 9 QUESTION 5 continue b) An unknown polymer sample has a degree of polymerization of 1136; given the following data: (6) Molecular weight range x i w i (g/mol) 8,000-20, ,000-32, ,000-44, ,000-56, ,000-68, ,000-80, ,000-92, Calculate: i) the number-average molecular weight. the weight average molecular weight. i determine which one of poly(vinylchloride), polypropylene and polyethylene is the unknown polymer.

10 Page 10 QUESTION 6 a) Composite materials are composed of a matrix phase and a dispersed phase. Compare and contrast the two phases. (4) b) Using the Cu-Ni system as an example explain with the aid of well labeled diagrams the effect of alloying on tensile strength and ductility. (4)

11 Page 11 QUESTION 6 continue c) The microstructure of steel is affected by composition and thermal history. On this basis briefly write on the following types of steel: (6) i) Martensite Austenite i Bainite d) With the aid of appropriate examples from the iron carbide system distinguish between a eutectic and a peritectic phase change. (4)

12 Page 12 QUESTION 7 The following is a typical steel phase diagram. Refer to the diagram and answer the questions that follow: 1600 T ( C) δ 1400 A 1200 B D 1148 C α 600 C 727 C (Fe) wt% C i) Identify the phases marked A and B on the diagram. (2) What is point C called? Write an equation for the change that happens at this point as temperature drops. (2)

13 Page 13 QUESTION 7 continue i On the diagram mark a point D to represent 1200 C and 3 wt% C. What phase(s) are present at D? (1) iv) What is the composition of the phases present at point D in wt% C? (2) v) What is the relative amount of each phase present at point D? (3)

14 Page 14 QUESTION 8 a) For the following pairs of metal/alloys that are coupled in seawater, predict the possibility of corrosion; if corrosion is probable, note which metal/alloy will corrode. (3) i) Aluminum and cast iron Cadmium and zinc i Brass and titanium b) Briefly describe the two techniques that are used for galvanic protection. (4)

15 Page 15 QUESTION 8 continue c) Cite the differences between hard and soft magnetic materials in terms of both hysteresis behaviour and typical applications. (4) QUESTION 9 a) An external magnetic field is applied to a paramagnetic and a diamagnetic material. How will each material respond?. (2) b) Citing appropriate examples, write briefly on ferroelectric and piezoelectric materials. (4) c) Briefly describe the Meissner effect. (2)