The diffusion of C from CH4 gas and into coarse powder was studied at room temperature by means of the magneto-optical polar Kerr effect. It was found that diffusion initially occurred along preferential paths, and then through the bulk. The results indicated the existence of smooth, bathtub-like, C concentration profiles. The diffusivity of C at 450C was estimated to be 2.5 x 10-16m2/s.

J.Zawadzki, P.A.P.Wendhausen, B.Gebel, A.Handstein, D.Eckert, K.H.Müller: Journal of Applied Physics, 1994, 76[10], 6717-9