(e) Derive an expression for the Po2- dependence of n-type electronic conduction in the ZrO2-CaO solid electrolyte Question No. 12 (a)Present on the same graph plots of velocity of sustained crack growth for a sharp tipped crack as a function of applied mode I stress intensity for steel specimens failing (i) Intergranular cleavage (ii) Ductile rupture by hole growth (b) Can the above cracking processes be described in terms of the J-integral? (c)Describe the mode of crack initiation and the fraction of life spent in crack initiation for the high-cycle-fatigue failure in (1) Pure, Single-crystal copper igh-strength alloy steel Question No. 13 Briefly discuss the following terms which are frequently encountered in corrosion science: (i) active dissolution, (ii) passivity,(iii) transpassive dissolution, and (iv)cathodic polarizatio Illustrate your answer by reference to the schematic polarization curve for a metal or alloy which exhibits the above phenomenon, and indicate briefly the mechanisms involved in these processes (a) In an oil refinery the metal cap at the top of a "flare " can corrode rapidly at 600C although the hotter portions of the pipe are less attacked.(A flare"is a small chimney uded for burning waste process gases.) How can you explain this higher corrosion rate at lower temperatures? (b)A"heat wheel"for the recovery of waste heat is a paddle-type wheel which rotates slowly with one half heated by exiting hot waste combustion product gases while the other half (previously heated) is being cooled by heating cool incoming air. The worst corrosion occurs where the wheel is coolest(about 70C)and in contact with the humid waste gases Explain the corrosive stack and recommend corrective action (c) At very high temperatures, platinum evaporates in air as P+ O2 (vapor). Deposition of a porous ceramic coating on the metal reduces drastically the rate of oxidation-evaporation Explain this result. ( d)A common laboratory test for the tendency of a high-temperature Fe-Ni-Cr-Si alloy to suffer carburization in highly reduced gases with unit carbon activity is to pack the alloy in an enclosure with carbon and argon But this test provides much too severe carburization attack compared to service in a process gas of CO/CO2/H2/H2)with unit carbon activity Explain these results Question No 15 Your employer(a petrochemical company) has a large steel pressure vessel (wall 0.3 m thick) which has contained high pressure hydrogen at temperatures of 400C for a year. Your problem is to calculate the time the vessel should be held at temperature with, the hydrogen pressure removed So that 90% of the hydrogen can diffuse out. (The aim is to avoid hydrogen cracking on cooling.(e) Derive an expression for the PO2 – dependence of n-type electronic conduction in the ZrO2-CaO solid electrolyte. Question No. 12 (a) Present on the same graph plots of velocity of sustained crack growth for a sharp tipped crack as a function of applied mode I stress intensity for steel specimens failing. (i) Intergranular cleavage (ii) Ductile rupture by hole growth (b) Can the above cracking processes be described in terms of the J-integral? (c) Describe the mode of crack initiation and the fraction of life spent in crack initiation for the high-cycle-fatigue failure in (i) Pure, Single-crystal copper (ii) High-strength alloy steel Question No. 13 Briefly discuss the following terms which are frequently encountered in corrosion science: (i) active dissolution, (ii) passivity, (iii) transpassive dissolution, and (iv) cathodic polarization. Illustrate your answer by reference to the schematic polarization curve for a metal or alloy which exhibits the above phenomenon, and indicate briefly the mechanisms involved in these processes. Question No. 14 (a) In an oil refinery the metal cap at the top of a “flare” can corrode rapidly at 600C although the hotter portions of the pipe are less attacked. (A “flare” is a small chimney uded for burning waste process gases.) How can you explain this higher corrosion rate at lower temperatures? (b) A “heat wheel” for the recovery of waste heat is a paddle-type wheel which rotates slowly with one half heated by exiting hot waste combustion product gases while the other half (previously heated) is being cooled by heating cool incoming air. The worst corrosion occurs where the wheel is coolest (about 70C) and in contact with the humid waste gases. Explain the corrosive stack and recommend corrective action. (c) At very high temperatures, platinum evaporates in air as P + O2(vapor). Deposition of a porous ceramic coating on the metal reduces drastically the rate of oxidation-evaporation. Explain this result. (d) A common laboratory test for the tendency of a high-temperature Fe-Ni-Cr-Si alloy to suffer carburization in highly reduced gases with unit carbon activity is to pack the alloy in an enclosure with carbon and argon. But this test provides much too severe carburization attack compared to service in a process gas of CO/CO2/H2/H2) with unit carbon activity. Explain these results. Question No. 15 Your employer (a petrochemical company) has a large steel pressure vessel (wall 0.3 m thick) which has contained high pressure hydrogen at temperatures of 400C for a year. Your problem is to calculate the time the vessel should be held at temperature with, the hydrogen pressure removed. So that 90% of the hydrogen can diffuse out. (The aim is to avoid hydrogen cracking on cooling.)