Diffusion coatings formed in molten calcium systems IV. Intrinsic diffusivities of iron and chromium and diffusivity calculations

• Published in: Journal of the less-common metals 1974, Vol.37 (2), p.189-198
• Main Author: Carter, Giles F.
• Format: Article
• Language: English
• ISSN: 0022-5088
• DOI: 10.1016/0022-5088(74)90034-4

The Matano-Boltzmann method has been used to calculate interdiffusion coefficients as a function of chromium concentration in a chromium-iron diffusion coating on iron. These interdiffusion coefficients agreed well with calculations made by a new, modified Grube method, using the concentration gradient for the diffusion coating. At N Cr = 0.48 and 1180 °C the intrinsic diffusivity of chromium, D Cr , equals 2.3 × 10 −9 cm 2/ s, and D Fe = 0.66 × 10 −9 cm 2/ s.The diffusion coating was prepared by treating iron in liquid calcium containing finely-divided chromium powder. The specimen lost iron to the liquid whilst it gained chromium; the calculated chromium-gained/iron-lost ratio equals D cr × at. wt. Cr D Fe × at. wt. Fe , or 3.2, which agrees with experimental results. A simplified experimental method involving diffusion couples in which one half of the couple is a liquid or gaseous phase is presented for calculating intrinsic diffusivities. The concept of bulk diffusivity is defined and discussed.