Ceramic Engineering 103 Final Exam (5/17/01)

Transcription

1 Test5_ (1) Name Ceramic Engineering 103 Final Exam (5/17/01) 1) Arrange each set of oxides in order from most basic to most acidic then write out the name of the resulting glass. (Example: a glass with Na 2 O, CaO, Al 2 O 3 and SiO 2 is a sodium calcium aluminosilicate.) (4 points each): a) K 2 O, P 2 O 5, B 2 O 3 b) CaO, GeO 2, Na 2 O c) SiO 2, B 2 O 3, BaO d) SiO 2, ZnO, Fe 2 O 3 2) Using Zachariasen s Rules, explain why silica is a glass-forming oxide. (6 points each)

2 Test5_ (2) 3) Sketch a TTT curve for a system containing 100 ppm of crystalline material. Add a second curve for 10 ppm crystallinity. Label both curves and label each axis. Identify on one axis the crystal melting temperature and the glass transition temperature. (10) 4) On the plot above, place an X to indicate a heat treatment time and temperature that will produce a material with 50 ppm crystallinity. (4 points) 5) The nose of a TTT curve occurs at 20 minutes and 700ºC for a composition whose crystallization temperature is 900ºC and glass transition temperature is 500ºC. What is the critical cooling rate for glass formation for this material? Show your work (8) Critical Cooling Rate:

3 Test5_ (3) 6) A glass is prepared from a batch that consists of 25 grams of K 2 CO 3, 10 grams of Al 2 O 3, and 40 grams of H 3 BO 3. What is the final composition (in mole%) of the glass? What is the final weight of your sample? Show your work. (12) Molecular weights: K 2 O = 94.2 g/mole B 2 O 3 = 69.6 g/mole Al 2 O 3 = g/mole K 2 CO 3 = g/mole H 3 BO 3 = 61.8 g/mole Mole% K 2 O: Mole% Al 2 O 3 : Mole% B 2 O 3 : 7) Vycor possesses what phase-separated morphology? (2) Pyrex possesses what phase-separated morphology? (2) The composition of Pyrex is near ( the edge or the center ) of the immiscibility dome for the Na 2 O-B 2 O 3 -SiO 2 system. Circle one. (2)

4 Test5_ (4) 8) A glass has the composition 25K 2 O 10Al 2 O 3 65SiO 2 (mole%). a. If all nonbridging oxygens are associated with Si-tetrahedra, what fraction of silica tetrahedra will have one NBO? Show your work. (8 points) f(q 3 ) 9) What will happen to the strength of a soda-containing glass that is ion-exchanged in a lithium salt bath at a temperature below T g? Explain your answer (8 points) 10) Estimate the viscosities for glass melts described in the following situations and describe a method to measure that viscosity (6 points each) a) Stresses in the glass relax in several minutes. b) The glass flows under it s own weight.

5 Test5_ (5) 11) List three oxides that, if added to a soda-lime silicate glass, will increase it s refractive index without changing its color. (2 points each) 12) List three oxides that, if added to soda lime silicate glass, will change it s color. (2 points each) 13) Draw curves for the nucleation and crystal growth rates as a function of temperature for a material with a maximum in nucleation rate at 600 C and in crystallization rate at 800 C. The metastable zone is 100K wide. The melting point of this material is 1100 C. The glass transformation temperature is 500 C. Be sure to indicate which curve is which. (10) Rate Temperature ( C)

6 Test5_ (6) 14) Circle the correct choice (2 points each) a) The chemical formula for soda ash is (NaHCO 3, Na 2 CO 3, Na 2 O). b) Of these three, the smallest ion is (Sr 2+, Mg 2+, Ca 2+ ). c) The glass forming oxide with the highest processing temperature: (B 2 O 3, SiO 2, P 2 O 5 ). d) Nucleation/crystallization is more likely to occur in (high viscosity, low viscosity) melts. e) An oxide added to glass batches as a fining agent: (Al 2 O 3, As 2 O 5, BaO). f) Network connectivity (increases, decreases) when Al 2 O 3 replaces Na 2 O in a sodium aluminosilicate glass. g) Assuming the simplest structural model, the network of a 20Na 2 O 80SiO 2 glass consists of (Q 3 +Q 4, Q 2 +Q 3, Q 2 +Q 4 ) tetrahedra. h) Glass with larger fraction of nonbridging oxygens: 20Na 2 O 80SiO 2, 20Na 2 O 80B 2 O 3 i) Higher annealing temperature: 15Na 2 O 10CaO 75SiO 2 or 25Na 2 O 75SiO 2 j) Glass with the lowest thermal expansion coefficient: SLS glass, Pyrex, silica k) Adding K 2 O to a soda silicate glass (increases, decreases) ionic conductivity. l) You ll have to wait longest for flow to occur at the (working point, softening point) m) Glasses with large elastic moduli exhibit (large, small) strains under an applied stress. n) Phase separation occurs (above, below) the consolute temperature.

7 Test5_ (7) o) Taking a glass from the freezer to the oven initially puts the surface in (compression, tension) p) (Noble metal, Actinide, Lanthanide) ions are typically the optically active species in glass lasers. q) The CTE of soda lime silicate glass is near (5x10-7 /ºC, 50x10-7 /ºC, 100x10-7 /ºC) r) Circle the refractive index that will be lowest in a glass (n D, n F, n C ). s) The ion that absorbs at the longer wavelength: (Fe 2+, Fe 3+ ). Bonus 1: Give the names and chemical formulae for up to five raw materials listed in Shelby s Table 3.1 for adding CaO to a glass melt (2 points each, 10 points maximum). Bonus 2: You make a new glass and after annealing, discover that it has turned milky white. What could have happened? What experiment(s) can you do to test your hypothesis? (5 points) Bonus 3: (5 points, if it makes a difference): I deserve a for my grade in this course because: