KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY, KUMASI COLLEGE OF ENGINEERING B.Sc. (Engineering) Second Semester Examinations Third Year MSE 354 CERAMIC ENGINEERING II April 2015 Duration: 3 Hours Attempt all Questions. Answer questions in the spaces provided. 1. What is a glass? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 2. What are the two prime assets of glasses? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 3. Draw a volume diagram showing the behaviour of melts which cools to form (a) glass and (b) crystals. Label each section of this diagram. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. ...................................................................................................................................................................... .................................................................................................................................................................... 4. Define the role of each of the following in a glass batch. Give two examples of each. a) Glass forming oxides: ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………………. b) Modifier oxides: ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………………. c) Intermediate oxides Page 1 of 10 ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………………. 5. Differentiate between glass formability and glass stability. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 6. Explain why the energy requirements of glass manufacturing process could be reduced by use of cullets. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 7. Construct a TTT curve for a glass melt containing 1 ppm of crystalline material. Add a curve for 1% crystallinity. Label each axis. Draw curves for constant cooling rates which are greater than, exactly equal to, and less than the critical cooling rate for the 1 ppm crystalline sample. Also write and equation for the critical cooling rate of such a system. Discuss HOW one might determine the critical cooling rate for a given glass. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 8. The nose of a TTT curve occurs 100 K below Tm, at a time of 1000 seconds. What is the critical cooling rate for this melt? What is the critical cooling rate if the nose occurs at 10,000 seconds? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… Page 2 of 10 …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 9. Briefly explain the statement “Glass formation is a kinetic transition”. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 10. Vitreous silica has a viscosity of about 106 Poise at Tm. The viscosity increases slowly with temperature as the melt is cooled below Tm. Discuss why this should lead to good glass formation. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 11. Fluoride glasses have very high values of dη/dT, but the viscosity of the melt at Tm is only about 1 Poise. Explain how these properties can also lead to good glass formation. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… Page 3 of 10 …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 12. State the six (6) basic steps involved in any glass manufacturing process. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… In the melting of glasses, release of gases is beneficial as these gases produces stirring and homogenization of the melt. Use this information to answer questions 13 and 14. 13. By appropriate equation, show how such gases are generated. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 14. Outline two side effects of the release of such gases in the processing of glasses? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 15. In glass technology, what is “batch-free time”? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… Page 4 of 10 …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. ...................................................................................................................................................................... ...................................................................................................................................................................... ...................................................................................................................................................................... 16. Why is grinding of raw materials necessary in glass manufacturing process? What precautionary measure must be taken during grinding? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 17. A large number of the components of glasses such as Na2O and K2O are quite volatile at elevated temperatures. Loss of these components can significantly alter the composition of the glass and hence affects its properties. As a process engineer in a glass manufacturing company, how would you reduce the loss of such components? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… Page 5 of 10 18. With appropriate equations, discuss the use of As2O5, as a fining agent. The discussion should include how this oxide serves to both increase the rate of bubble rise and increase dissolution of gases from bubbles. Indicate also the conditions under which each process occurs. Due to the toxic nature, recommend an alternative fining agent that can be used in place of As2O5. Write a balanced equation for its reaction. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 19. Differentiate between the following: (a) long and short glasses ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… (b) hard and soft glasses ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… Page 6 of 10 ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… 20. Glasses can be strengthened via heat treatment and chemical processes. With appropriate diagrams, describe the principles underlying both strengthening mechanisms. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 21. Discuss the effect of impurities in the mixing water for concrete. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… Page 7 of 10 The table below shows the chemical composition (wt%) of clinker. Use this information to answer questions 22 to 24. SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O SO3 LOI 21.5 5.2 2.8 66.6 1.0 0.6 0.2 1.0 1.5 Free lime = 1.0% 22. Determine the Bogue composition of the cement given that 𝐶3 𝑆 = 4.07𝐶 − 7.60𝑆 − 6.72𝐴 − 1.43𝐹 − 2.85𝑆̅ 𝐶2 𝑆 = 2.87𝑆 − 0.75𝐶3 𝑆 𝐶3 𝐴 = 2.65𝐴 − 1.69𝐹 𝐶4 𝐴𝐹 = 30.4𝐹 …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 23. Mention any two (2) assumptions made in the calculation of Bogue composition. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 24. What is the significance of the various phases calculated? Hence sketch a graph of compressive strength (in MPa) against time (in days) for C3S and C2S. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… Page 8 of 10 …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. 25. Calculate the batch weights of each component needed to yield 50 grams of 20Na2O-5Al2O3-75SiO2 glass composition. The raw materials to be used are albite feldspar (Na2O-Al2O3-6SiO2) as source of alumina and Na2CO3 as the source of the additional soda. Indicate the weight of each component (Na2CO3, albite and sand) and the total batch weight of the glass. [Molecular weights (g/mol): Na2O=61.98; Al2O3=101.96; SiO2=60.09; Na2CO3=106.00] …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… Page 9 of 10 …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………….. A. Andrews Page 10 of 10
