Diffusion of ZrCl4 is very important for the production of nuclear grade metallic Zr in the magnesiothermic reduction process, i.e., Kroll's process. The diffusion coefficient of ZrCl4 was investigated by thermogravimetric analysis (TGA). Binary diffusion coefficients of ZrCl4 in an Ar atmosphere were 0.130, 0.187, 0.257, 0.270, and 0.426 cm(2)/s at 603, 623, 673, 723, and 773 K, respectively. The diffusion coefficient of ZrCl4 in an Ar atmosphere is proportional to T-1.75 and is given by D-ZrCl4,D-Ar = 2.89(+/- 0.33) x 10(-6)T(1.75). (C) 2015 Elsevier B.V. All rights reserved.