The strength changes of refractory fire clay brick SK-34 and SK-36 high alumina bricks at different temperatures are as follows:
Low to Medium Temperature Stage (from Room Temperature to around 700°C)
- At room temperature, the cold compressive strength of SK-34 is ≥30MPa, and that of SK-36 is ≥45MPa, showing relatively high strength and being able to withstand certain mechanical pressure.
- As the temperature gradually rises to around 700°C, its strength remains basically stable with little change. This is because within this temperature range, the mineral structure and chemical bonds inside the brick body do not change significantly, and the crystal structure is relatively stable, thus still maintaining good mechanical properties.
Medium Temperature Stage (700°C – 1350°C)
- When the temperature is between 700°C and 900°C, the high alumina brick is generally within the elastic range, and its strength begins to decline to a certain extent. This is because as the temperature rises, the thermal stress inside the brick body gradually increases, and at the same time, some minor changes in the crystal structure, such as intensified lattice vibration, occur, resulting in a slight decrease in strength.
- In the range of 900°C to 1350°C, the mullite and corundum phases in SK-34 and SK-36 high alumina bricks gradually play a better role in high-temperature stability, and the decreasing trend of strength gradually slows down or may even show a short stable stage. At this time, some adjustments begin to occur in the crystal structure inside the brick body, and the content and distribution of mullite and corundum phases play a key role in maintaining strength.
High Temperature Stage (above 1350°C)
- When the temperature exceeds 1350°C, the strength of SK-34 and SK-36 high alumina bricks changes significantly again. Around 1350°C to 1500°C, with the further increase of temperature, the amount of liquid phase inside the brick body gradually increases, and the viscous flow of the glass phase strengthens, which may lead to a certain degree of softening of the brick body and a rapid decrease in strength.
- When the temperature approaches or exceeds its refractoriness, for example, the refractoriness of SK-34 is ≥1750°C, and that of SK-36 is ≥1790°C, the crystal structure inside the brick body may change greatly, and the stability of the mullite and corundum phases is also affected, resulting in a sharp decrease in strength until it loses its bearing capacity.