  We study the vanishing viscosity limit of a nonlinear diffusion equation
describing chemical reaction interface or the spatial segregation interface of
competing species, where the diffusion rate for the negative part of the
solution converges to zero. As in the standard one phase Stefan problem, we
prove that the positive part of the solution converges uniformly to the
solution of a generalized one phase Stefan problem. This information is then
employed to determine the limiting equation for the negative part, which is an
ordinary differential equation.
