Common knowledge of refractory bricks

Clay bricks refer to clay products made of aluminum silicate materials with an Al2O3 content of 30% to 40%. Clay bricks are made of 50% soft clay and 50% hard clay clinker, mixed according to certain particle size requirements, formed, dried, and fired at high temperatures of 1300-1400 ℃. The mineral composition of clay bricks is mainly kaolinite (Al2O3 · 2SiO2 · 2H2O) and 6% to 7% impurities (oxides of potassium, sodium, calcium, titanium, and iron). The firing process of clay bricks mainly involves the continuous dehydration and decomposition of kaolinite to form mullite (3Al2O3 · 2SiO2) crystals. SiO2 and Al2O3 in clay bricks form eutectic low melting point silicates with impurities during the firing process, surrounding the mullite crystals.

Within the temperature range of 0-1000 ℃, the volume of clay bricks expands uniformly with increasing temperature, and the linear expansion curve approximates a straight line, with a linear expansion rate of 0.6% to 0.7%, which is only about half of that of silica bricks. When the temperature reaches 1200 ℃ and continues to rise, its volume will start to shrink from the maximum expansion value. The residual shrinkage of clay bricks leads to loose cracks in the mortar joints of the masonry, which is a major drawback of clay bricks. When the temperature exceeds 1200 ℃, the low melting point substances in the clay brick gradually melt, and the particles are tightly pressed against each other due to surface tension, resulting in volume shrinkage.