The initial strength of the Al₂O₃ sample is relatively high at t=0, but it drops rapidly as the temperature difference approaches the critical threshold. In contrast, the initial strength of the zirconia-added samples is lower, yet the critical temperature difference increases with higher zirconia content. This leads to a significant reduction in the rate of thermal shock intensity loss. The thermal shock curves of both Ze and Al₂O₃ samples exhibit similar shapes, but the strength of the Ze sample declines sharply after exceeding 200°C. Meanwhile, the strength of the Zw samples decreases as zirconia content increases, but both the critical temperature difference and the drop in strength are notably improved. For instance, the Zw15 sample maintains almost constant strength between 0–900°C, indicating exceptional thermal stability.
These experimental observations can be explained by the way zirconia particles agglomerate, which is influenced by the cleaning medium used. When cleaned in water, zirconia particles tend to form an oxygen-linked structure during drying, resulting in hard agglomeration. However, when washed in alcohol, the hydroxyl groups on the surface of hydrated zirconia gel interact through hydrogen bonding, reducing surface energy and creating steric hindrance. After sintering, the phase transformation stress and residual stress between zirconia and alumina contribute to the formation of micro-cracks, which enhance toughness but may also lead to strength loss if cracks become interconnected.
Agglomerated zirconia helps increase crack propagation length, raise the critical temperature difference, and reduce the loss of residual strength. To better quantify the thermal shock behavior of aluminum-zirconium materials, a multi-phase thermal shock model was developed using functional construction methods, along with universal equations, surface fitting, and isoline distribution. The strength curves for Ze-based materials show dense clustering between 100–300°C, suggesting rapid strength decay. In contrast, Zw-based materials display a ring-shaped, stepped surface, indicating that the critical temperature difference increases significantly with higher zirconia content. Once zirconia exceeds 10%, the material's strength remains largely unaffected within 0–900°C.
By analyzing the relationship between crack propagation length and temperature difference, the critical temperature difference can be theoretically calculated from measured crack lengths. However, this is challenging in practice. Instead, the tC value can be estimated through data fitting and thermal shock surface analysis. Crack length is determined using the thermal shock damage factor Rd. Results show that Rd values increase with zirconia content, and tC rises proportionally. Water washing has a more pronounced effect on Rd, highlighting the dominant role of thermal shock damage mechanisms. The water-based cleaning process enhances the thermal shock performance of zirconia-alumina refractories. At 15% zirconia content, the material retains nearly constant strength across 0–900°C.
Introducing agglomerated zirconia instead of micropores in traditional alumina significantly improves the thermal shock resistance of corundum materials. Through the development of refractory interface models, the thermal shock behavior of the material can be quantitatively analyzed, and the critical temperature difference can be accurately measured. Moreover, the critical temperature difference is directly linked to Rd, reinforcing the idea that the thermal shock damage mechanism governs the material’s response.
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