Kinetics of NiCr2O4 Formation and Diffusion of Cr3+ Ions in NiO

Abstract

The reaction kinetics for NiCr2O4 formation and the diffusion of Cr3+ ions into single‐crystal NiO were studied between 1300° and 1600°C in air. The experimental activation energy for NiCr2O4 formation was about 83 kcal/mol. After incubation, NiCr2O4 formed by a diffusion‐controlled process. The origin of pores at the NiO/NiCr2O4 interface is discussed. The concentration profiles of Cr3+ in NiO were linear because the interdiffusion coefficient was directly proportional to the mol fraction Cr3+. Theoretical considerations indicate that the interdiffusion coefficient equals 3/2 the self‐diffusion coefficient of Cr3+, which is rate‐determining. The interdiffusion coefficient at 1 mol% Cr2O3 can be expressed as D̄=4×10−3 exp (−55,000/RT) cm2 s−1. Copyright © 1970, Wiley Blackwell. All rights reserved