The Bursting Phenomena of the Chrome Bearing Refractories (1)

Abstract

The bursting expansion is one of the important disintegrations of the chrome bearing refractories and has been studied by synthetic spinels, chrome ores and chrome spinel grains separated from chrome ores.
The mechanism of the bursting expansion is related to formation of solid solution and is one of the phenomena of the Kirkendall effect. (a) Formation of solid solution among spinel group minerals, (b) unequal diffusion coefficients of ions in the phases, (c) movement of Pt-mark in the sample, (d) displacement of Pt-mark during heating, inversely proportional to square root of diffusion time, (e) occurrence of pores in the refractories, and (f) expansion after heat treatment and/or reaction are evidences for the fact that the bursting expansion is the Kirkendall effect. By adopting the Kirkendall effect ast he mechanism of the bursting, it is able to explain of pores and expansion after heat treatment.
The bursting expansions of synthetic spinel mixtures by a dilatometric method are divided into 3 types namely type E, type S and type L. Samples of the type E showed the bursting expansion, samples of the type S did not show the bursting expansion but showed shrinkage and samples of the type L showed a linear expansion up to 1600°C.
In the case of the chrome spinel grains, there are 2 types of E and S for the bursting. The type E of the chrome spinel grains for the bursting belongs to the type C and A of TGA curves and the type S for the bursting showed TGA curve of the type B. The type C showed the largest bursting expansion among 3 types of A, B and C and the second expansion was shown by the type A. The type B did not show the bursting.
Chrome spinel grains of No. 5 Inazumi, No. 2 Imobara, No. 12 Hinokami No. 18 Cuba and No. 19 Masinloc belonged to the type B, No. 1 and No. 6 Wakamatsu belonged to the type A and No. 3 Hatta, No. 4 Tomioto Shizunai, No. 7 Akaishi, No. 8 Philippine, No. 9 Philippine, No, 10 Hatta Main Mixture, No. 11 Tomimoto Nukahira, No. 13 Nitto, No. 14 Tsuchiya Horokanai, No. 15 Hatta Yawata, No. 16 Hatta Main, and No. 17 Nitto Washing belonged to the type C.
The bursting expansions of the 15 chrome ores by means of a bottom method were in the following order from large to small: No. 17 Nitto Washing, No. 13 Nitto, No. 10 Hatta Main Mixture, No. 9 Philippine, No. 1 Hirose, No. 6 Wakamatsu, No. 8 Philippine, No. 16 Hatta Main, No. 3 Hatta, No. 14 Tsuchiya Horokanai, No. 2 Imobara, No. 5 Inazumi, No. 7 Akaishi and the smallest No. 4 Tomimoto Shizunai.
Diffusion coefficients of ⁵⁹Fe at 1200°C and 1400°C in the system MgO⋅Cr₂O₃-iron oxide were D₁₂₀₀=2.89×10^-11cm²/sec and D₁₄₀₀=3.69×10^-10cm²/sec, respectively.
We have to consider the following points as counterplans for the bursting expansion: (a) selection of chrome spinel grains from chrome ores, (b) content of chrome spinel grains in the refractory, (c) grain size, (d) calcination of chrome ore, (e) dense structure of the refractory, (f) porous structure and (g) others.