Abstract: During the production of magnesium calcium bricks，due to lax quality control of raw materials，there may be defects such as air voids left on the surfaces of calcined bricks， causing great products losses and resource waste. In this paper, by means of conducting microscopic detections such as component analysis, XRD phase analysis，and SEM scanning electron microscopy to the air voids in the magnesium calcium bricks，it is found that the excessive content of SiO2 and Al2O3 impurities in the magnesium calcium sand causes the conversion of C2S（dicalcium silicate）and C3S （tricalcium silicate）and the formation of manganolite with low melting point and low melting mineral phase with high aluminum at the enrichment of silicon and aluminum.

Key words: Magnesium calcium bricks, Air voids, Manganolite