for a given electron as T for a given mechanism j. Use the information to deduce Matthiessen's rule, which expresses the total electrical resistivity in terms of the resistivity due to thermal effects, pt(scattering from phonons)and the resistivity due to solutes, pi Questions No 9 Nearly pure liquid copper contains 1X10 weight H and 8X10 wt %O. Initially the solidification is dendritic with the H and o rejected to interdendritic spaces (a) At what fraction of solid will pores begin to form? (b) What will be the final volume fraction of voids present in this casting? (c) What gas or gases will comprise the voids? Assume compete diffusion of H and o in the liquid and solid over distances of the dendrite spacing. The ratio of solid solubility of H to that of the liquid is 1: 3. The o negligible solid solubility. Neglect effects of surface energy and metallo-static head. The casting solidifies at ambient pressure. The melting point of copper is 1083C Solubility data are H2=2H1 logK'=-4620/T-322 logK=7030-2.84 H20=2HL+O2 logK=-10640/-3.09 Question No. 10 An austenitic stainless steel pump was severely corroded by concentrated sulfuric acid containing solids in suspension. a study was made in which a disc specimen was rotated at different velocities in the above environment. Under static conditions the potential of the specimen was found to be +200 mV positive to a solid calomel reference electrode. The electrode potential became more positive as the specimen was rotated at a peripheral velocity from 0 to 8 ft/sec. Negligible corrosion was observed in this range of velocities. When the velocity was increased from 8 to 12 ft/sec the potential changed to -200 mV and the rate of metal loss increased gradually to a ratio of several thousand mils per year. Upon reducing the velocity to 8 ft per second the potential of the stainless again returned to 200 mV. Describe in detail the causes of the shifts in electrode potential and metal removal as a function of velocity over the entire velocity range from zero to 12 fu/sec Question No. 1l Open-circuit galvanic cell measurements are made for the following cell at 1000C Pt, Cr +Cr,O3 ZrO+ Cao Cr, (Cr, Al)O3, Pt Where(Cr, Al)O3 is an oxide solid solution and Zro Cao is an exclusive oxide electrolyte (a) Write the half-cell reactions for this cell (b) Interpret the cell emf in term of the thermodynamic properties of the phases involved (c) If the cell voltage is measured over a range of temperature. What is the interpretation of the temperature dependence of the cell voltage? (d) Suppoes the electrolyte exhibite some(non-negligible) electronic conduction. How will the cell voltage be affected ( i) For reversible electrodes? (ii For non-reversible electrodes?for a given electron as Tj for a given mechanism j. Use the information to deduce Matthiessen’s rule, which expresses the total electrical resistivity in terms of the resistivity due to thermal effects, ρ t (scattering from phonons) and the resistivity due to solutes, ρ i. Questions No. 9 Nearly pure liquid copper contains 1×10-4 weight % H and 8×10-4 wt % O. Initially the solidification is dendritic with the H and O rejected to interdendritic spaces. (a) At what fraction of solid will pores begin to form? (b) What will be the final volume fraction of voids present in this casting? (c) What gas or gases will comprise the voids? Assume compete diffusion of H and O in the liquid and solid over distances of the dendrite spacing. The ratio of solid solubility of H to that of the liquid is 1:3. The O negligible solid solubility. Neglect effects of surface energy and metallo-static head. The casting solidifies at ambient pressure. The melting point of copper is 1083C. Solubility data are: H2=2HL log K’ = -4620/T - 3.22 1/2O2=OL log K’ = 7030/T - 2.84 H2O=2HL+O2 log K’ = -10640/T - 3.09 Question No. 10 An austenitic stainless steel pump was severely corroded by concentrated sulfuric acid containing solids in suspension. A study was made in which a disc specimen was rotated at different velocities in the above environment. Under static conditions the potential of the specimen was found to be +200 mV positive to a solid calomel reference electrode. The electrode potential became more positive as the specimen was rotated at a peripheral velocity from 0 to 8 ft/sec. Negligible corrosion was observed in this range of velocities. When the velocity was increased from 8 to 12 ft/sec the potential changed to -200 mV and the rate of metal loss increased gradually to a ratio of several thousand mils per year. Upon reducing the velocity to 8 ft per second the potential of the stainless again returned to 200 mV. Describe in detail the causes of the shifts in electrode potential and metal removal as a function of velocity over the entire velocity range from zero to 12 ft/sec. Question No. 11 Open-circuit galvanic cell measurements are made for the following cell at 1000C: Pt, Cr + Cr2O3 ZrO2 + CaO Cr, (Cr, Al)2O3, Pt Where (Cr, Al)2O3 is an oxide solid solution and ZrO2 + CaO is an exclusive oxide ion conducting electrolyte. (a) Write the half-cell reactions for this cell. (b) Interpret the cell emf in term of the thermodynamic properties of the phases involved. (c) If the cell voltage is measured over a range of temperature. What is the interpretation of the temperature dependence of the cell voltage? (d) Suppoes the electrolyte exhibite some (non-negligible) electronic conduction. How will the cell voltage be affected: (i) For reversible electrodes? (ii) For non-reversible electrodes?