Mechanism of Thermal Shock
During calcination, when the temperature rises or drops sharply, different parts of the material heat up or cool down at different rates, creating temperature gradients. Because the expansion or contraction of different parts is constrained by each other, thermal stresses develop internally. When the thermal stress exceeds the tensile strength (or fracture strength) of the material, cracks initiate — this is the phenomenon known as “thermal shock.” Its essence lies in the combined effect of the thermal expansion coefficient, elastic modulus, and rate of temperature change: the larger the thermal expansion coefficient, the higher the elastic modulus, and the faster the temperature change, the greater the thermal stress generated, and the more prone the material is to thermal shock. In addition, if phase transformations exist within the material (such as the α-β transition of quartz at 573°C) or thermal expansion mismatch occurs at multiphase interfaces, additional volumetric effects are produced, further intensifying the thermal stress.
Hazards of Thermal Shock
First, instantaneous fracture (thermal impact fracture): When the temperature difference exceeds the critical limit, the material cracks or even shatters directly. Large equipment such as rotary kilns may experience kiln shell vibration, loss of contact between the tyre and supporting rollers, and synchronous vibration of drive gears. If not addressed promptly, this can lead to fatigue fracture of the kiln shell.
Second, cumulative damage (thermal shock damage): Under repeated thermal shock cycles, cracks initiate, propagate, and spread, causing surface spalling, continuous strength loss, and eventual complete fragmentation. This is especially lethal for refractory lining bricks — once through-cracks form in the masonry structure, sealing and erosion resistance deteriorate sharply, drastically shortening kiln service life.
Third, impact on product quality: For example, when alumina-based clinker or ternary cathode materials encounter thermal shock during calcination, micro-cracks form on particle surfaces. The strength loss rate increases with the number of thermal shock cycles, directly affecting subsequent performance and electrochemical behavior.
Brief Evaluation Criterion: The thermal shock resistance coefficient of a material is R = σ_f(1−μ) / (αE), where σ_f is the strength, μ is Poisson’s ratio, α is the thermal expansion coefficient, and E is the elastic modulus. The larger the R value, the stronger the thermal shock resistance. Therefore, reducing the thermal expansion coefficient, increasing thermal conductivity and strength, and lowering the elastic modulus are the core directions for improving thermal shock resistance.
Post time: Jun-08-2026