.png?x-oss-process=image/resize,h_100,m_lfit/format,webp)
.png?x-oss-process=image/resize,h_100,m_lfit/format,webp)
.png?x-oss-process=image/resize,h_100,m_lfit/format,webp)
In industrial settings where furnaces undergo frequent start-stop cycles, selecting refractory materials with exceptional thermal shock resistance is vital for ensuring equipment longevity and operational stability. This article delves into the fundamental physical mechanisms underlying thermal shock resistance, comparing the microstructural and thermal properties of corundum bricks and high alumina bricks. Focusing particularly on annealing furnaces characterized by intermittent operation, the analysis reveals why high alumina insulating bricks, reinforced by their mullite/corundum and glass phase composite structure, stand out as an energy-efficient and durable solution.
Thermal shock resistance defines a material’s ability to withstand rapid temperature changes without undergoing structural damage. When a refractory material experiences a sudden temperature gradient, internal stresses arise due to constrained thermal expansion differences. Specifically, the outer surface expands or contracts faster than the cooler inner regions, generating tensile stresses that can exceed the material's fracture strength, thereby causing cracking or spalling.
Quantitatively, the thermal stress σ is given by:
σ = E · α · ΔT / (1 - ν)
where E is Young’s modulus, α is the coefficient of thermal expansion, ΔT is the temperature difference, and ν is Poisson’s ratio.
The thermal shock resistance of refractory bricks depends strongly on a balanced combination of low thermal expansion (α), high fracture toughness, and the ability to dissipate stress via micro-cracking or phase transformations.
Corundum bricks chiefly consist of alpha-alumina (Al₂O₃) crystals exhibiting high mechanical strength and high melting points (> 2050°C). Their dense crystal lattice contributes to robust wear resistance but results in a relatively high thermal expansion coefficient (~8.0–8.5 ×10⁻⁶ /°C), which amplifies thermal stresses during rapid temperature shifts.
Conversely, high alumina bricks incorporate a composite matrix of mullite (3Al₂O₃·2SiO₂), corundum, and glassy phases. Mullite's interlocking needle-like crystals introduce intrinsic crack deflection mechanisms that enhance fracture toughness significantly (by up to 30%), while the glass phase imparts stress relaxation capacity. The overall thermal expansion coefficient varies between 5.5–7.5 ×10⁻⁶ /°C, lower than that of pure corundum bricks, which dramatically improves resistance against thermal shock. Furthermore, their insulating properties reduce heat loss, contributing to energy savings.
| Property | Corundum Brick | High Alumina Brick |
|---|---|---|
| Primary Phase Composition | Alpha-Al₂O₃ (Corundum) | Mullite, Corundum + Glass Phase |
| Thermal Expansion Coefficient (×10⁻⁶ /°C) | 8.0 – 8.5 | 5.5 – 7.5 |
| Fracture Toughness (MPa·m^0.5) | 1.5 – 2.0 | 2.0 – 2.6 |
| Thermal Conductivity (W/m·K at 1000°C) | 4.0 – 5.0 | 2.0 – 3.0 |
In steel, ceramics, and petrochemical industries, furnaces like electric arc and annealing units frequently undergo rapid cycling between ambient and operating temperatures. Such intermittent operation imposes severe thermal shock demands on linings.
Field data from a steel manufacturer operating a batch annealing furnace demonstrated that high alumina insulating bricks achieved a lining life extension of up to 25% compared to corundum bricks under identical cycling frequency (~6 cycles/day). This improvement correlates with a 15% decrease in refractory repair downtime, contributing to increased production continuity and cost savings.
Similarly, petrochemical plants employing high alumina bricks in their intermittent-fired regenerator furnaces have observed not only reduced thermal spalling but also significant energy efficiency gains due to lower thermal conductivity, reducing heat loss by approximately 10%.
Key parameters influencing the suitability of refractory bricks for intermittent furnace applications include:
High alumina insulating bricks combine these features effectively through their composite microstructure. This synergy supports long-term stable operation, especially in annealing furnaces and other high-frequency start-stop applications. Their slightly lower mechanical strength verses pure corundum bricks is offset by superior crack tolerance and energy-saving benefits.
.jpg)
Leveraging advanced manufacturing techniques, our company produces high alumina insulating bricks with optimized mullite-to-corundum ratios and controlled glass phase distribution. These bricks deliver:
