Performance changes of refractory castables at different temperatures

The performance changes of refractory castables at different temperatures are significantly affected by material composition, binder type, and heat treatment conditions. The following is a systematic analysis based on the comprehensive search results:

1、 Low temperature stage (room temperature~500 ℃)

Changes in volume and strength

Shrinkage and strength fluctuation: At low temperatures (such as 5-10 ℃), the hydration of aluminate cement is incomplete, resulting in low demolding strength (24-hour flexural strength is only 30%~50% of room temperature), and significant strength loss after drying. If not baked properly, the casting material may experience linear shrinkage, leading to cracks.

Decreased fluidity: At low temperatures (5 ℃), the viscosity of the slurry increases, and the bond between the aggregate and mortar is fragile, resulting in a rapid decrease in fluidity (no flow value after 60 minutes).

countermeasures

Add hardening agents (such as metal silicon powder) or cover insulation materials to accelerate hydration and reduce shrinkage.

2、 Medium temperature stage (500~1100 ℃)

Structural transformation and strength trough

Dehydration and phase transition: At around 350 ℃, the dehydration of cement hydrates leads to a loose structure, a decrease in bulk density followed by stability, and a decrease in strength to a low point (a decrease of up to 40%).

Fluctuations in linear rate of change: When the temperature is between 700 and 900 ℃, the linear shrinkage rate increases (such as -0.4%), and then the shrinkage slows down due to the transformation of mullite crystal structure.

Performance recovery

After the temperature rises to 1100 ℃, the cement paste is sintered and generates mullite crystals, and the strength gradually recovers.

3、 High temperature stage (1100~1500 ℃)

High temperature strengthening and wear resistance improvement

Ceramic sintering: above 1300 ℃, the matrix glass phase liquefies to form a ceramic like structure, significantly improving strength (such as a compressive strength of 60MPa at 1300 ℃).

Reduced wear: After heat treatment at 1500 ℃, the wear amount (2.43) decreased by 63% compared to 1300 ℃ (6.66) due to high temperature densification.

Difference in erosion resistance

High alumina castable: Its resistance to melting loss is better than that of clay at 1200 ℃, but silicon carbide is better above 1250 ℃.

Alkali resistant castables: A glaze layer is formed on the surface at 1100 ℃, which can resist alkali vapor erosion (such as reduced formation of KAlSiO ₄ expanding minerals).

4、 The impact of extreme temperature fluctuations

Thermal shock stability

The thermal shock resistance of mullite castable under 1100 ℃ water cooling cycle is ≥ 30 times, thanks to its low thermal expansion coefficient.

Kilns that frequently start and stop (such as cement kiln burners) need to use steel fiber reinforced castables to resist thermal stress.

Environmental synergy

High temperature (40 ℃) and low humidity (humidity<30%) accelerate water evaporation, leading to plastic shrinkage cracks.

5、 Material optimization direction

Application of Nanotechnology

Nano ZrO ₂ coating can enhance surface density and reduce slag penetration.

Composite aggregate design

The porosity of corundum silicon carbide composite aggregate is less than 20%, and the high-temperature wear resistance is doubled.

Summary: The performance of refractory castables varies nonlinearly with temperature, and it is necessary to select materials according to the working conditions (such as 1400 ℃ at the front of the cement kiln or 5 ℃ during winter construction), and optimize the curing system (such as gradient baking) and additives (such as silica micro powder) to balance strength, thermal shock resistance, and corrosion resistance.