Question

An undesirable consequence of welding steel by acetylene torch is the rise in hydrogen concentration in the metal. That hydrogen contamination embrittles the steel. The metal is typically subjected to a vacuum heat treatment to restore ductility. A steel part is placed in a vacuum furnace at 600∘C for one hour. The H concentration (initially uniform in the weld) falls to 1/2 its initial value at a depth of 500μm from the surface: It is known that the diffusivity of H in the steel at 600∘ C is 3.091×10−4 cm2/sec. An identical part is heat treated at 700∘ C. Under these conditions the H concentration falls to 1/2 its initial value at a depth of 500μm in 50 minutes. What is the diffusivity of H in steel at 700∘ C?

Give your answer in units of cm2/s, in scientific notation up to two decimal places