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,...

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. (Assume that the tank capacity is 15 kg)

Diffusion Data

Material    Do (cm2/s)     Q (cal/mol)   Cost ($/kg)
Nickel          0.0055              8900               9.0
Aluminium   0.16                10340              1.32
Copper         0.011               9380               2.43
Iron (BCC)     0.0012             3600               0.33