Correlation of pore structure and alkali vapor attack resistance of bauxite–SiC composite refractories

Alkali attack resistance of cement kiln refractories has become one of the key factors affecting their performance life. In this paper, the correlation between mean pore size, pore size distribution of bauxite–SiC composite refractories and their alkali attack resistance was investigated by means of mercury intrusion porosimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Also, the percolation theory, as well as modeling prediction, was applied associated with thermodynamic calculations. The results showed that quartz phase was generated from the oxidation process of silicon filling in part of pores, which resulted in a significant decrease in both the mean pore size and permeability of the samples. The proposed alkali attack mechanism indicated that K2CO3 was firstly reduced to K vapor and then infiltrated into the sample through the open pores. Consequently, the KAlSiO4 phase was formed in the edge part of the samples. When the K vapor permeated into the center of the sample, the KAlSi2O6 phase was first generated. Afterwards, the decomposition of KAlSi2O6 in the K-rich atmosphere gave rise to the formation of quartz and KAlSiO4. The decrease of mean pore size and apparent porosity, especially the reduction of the proportion of large pores, helped to prevent the alkali vapor from infiltrating into the samples, bringing about a superior vapor attack resistance at high temperature.