High Temperature Measurement of the Effective Diffusivity of Gas through Coke and Graphite by the WICKE-KALLENBACH Method

Abstract

The WICKE-KALLENBACH method had not been applied to the high temperature measurement due to the difficulty of preventing gas leakage from the portion between the diffusion cell and a sample. However, this problem was overcome by devising the Na₂O-SiO₂ cement containing liquid phase at elevated temperatures.
This technique made it possible to evaluate the effective diffusivity of Ar-He system through coke and graphite in a wide temperature range from 20 to 1300°C. The effective diffusivity for CO-CO₂ up to 300°C and permeant fluxes for Ar and He up to 1000°C were also measured.
From these measurements, molecular, KNUDSEN and surface diffusion through pores could be evaluated distinctively, the results of which showed the temperature dependence of molecular diffusivity as T^1·66T^1·69in coincidence with the theoretical value by CHAPMAN-ENSKOG.
The technique proposed in the present work was also applied to the in situ measurement of effective diffusivity of Ar-He through coke in the course of oxidation with CO₂ at 900°C.
The variation of diffusivity with the increase in degree of reaction was found to be several times larger than that expected by the "Parallel pore" model.