Consider an A-B alloy with 2 wt% B and a phase diagram shown on the right with Tm(A) = 1000 C, T(eutectic) = 600C, Xmax = 5 wt% B, and X(eutectic) = 10 wt% B. Assume that the solidus and liquidus lines are linear. Diffusion coefficient of the liquid is D = 4E(-7) cm2/s and the planar solid/liquid interface moves with a rate of 10 um/s. What is the critical temperature gradient required to maintain a planar interface