1) Design a spherical tank, with a wall thickness of 2 cm that will assure that no more than 50 kg of hydrogen will be lost per year. The tank, which will operate at 500 C, can be made of nickel, aluminum, copper, or iron. The diffusion coefficient of hydrogen and the cost per kg for each available material is listed here. Diffusion Data Material Do (cm/s) Q (cal/mol) Cost ($/kg) Nickel 0.0055 8,900 9.0 Aluminium 0.16 10,340 1.32 Copper 0.011 9,380 2.43 Iron (BCC) 0.0012 3,600 0.33 2) Decarburization of a steel occurs when carbon diffuses from the steel to the surface and enters the atmosphere. How long will it take for a 0.6% C steel surface to decarburize below 0.1 % C for a depth of 2 mm if the FCC steel is held at 1250 C in an atmosphere containing zero carbon? 3) A nitriding heat treatment of a BCC steel normally requires 2 h at 600 C. What temperature would be required to reduce the heat treatment time to 1 h? (Q-76570 J/mol, Do =0.0047x10-4 m/s)