How does calcined zinc oxide improve the thermal stability of ceramic wall and floor tiles by reducing the coefficient of thermal expansion in glazes?
Publish Time: 2025-11-19
In the building ceramics industry, wall and floor tiles are frequently used products exposed to temperature variations over extended periods. Their thermal stability directly impacts their lifespan and safety. Defects such as glaze cracking, peeling, or pinholes often stem from internal stress caused by the mismatch in the coefficients of thermal expansion between the glaze layer and the ceramic body during thermal expansion and contraction. Calcined zinc oxide, as a highly efficient ceramic flux, plays a crucial role in optimizing glaze formulations, reducing the coefficient of thermal expansion, and improving thermal stability due to its unique physicochemical properties.
1. Calcination Process Endows Zinc Oxide with Superior Physicochemical Properties
Ordinary zinc oxide is easily volatile at high temperatures and has excessively high reactivity, easily leading to violent glaze reactions and uncontrolled shrinkage. However, heavy calcined zinc oxide, obtained by calcination at approximately 1975℃, has a denser crystal structure, higher specific gravity, better fluidity, and significantly reduced volatility. Its light yellow appearance indicates low impurity content, high purity, and more stable chemical properties. This "pre-curing" treatment not only reduces volume changes during firing but also makes the energy release of zinc oxide more gradual during the glaze melting stage, effectively suppressing the formation of pinholes, bubbles, and cracks on the glaze surface, laying the foundation for subsequent control of expansion behavior.
2. Reducing the coefficient of thermal expansion of the glaze and achieving stress balance between the body and glaze
The coefficient of thermal expansion of the glaze is mainly determined by the ratio of its network forging body to its network modifiers. Zn²⁺ ions in calcined zinc oxide have strong polarization capabilities and can partially enter the silicon-oxygen tetrahedral network, enhancing the network connection strength and thus suppressing excessive expansion of the glaze at high temperatures. Simultaneously, ZnO exhibits a "two-way regulatory" characteristic in the glaze: promoting the formation of the glassy phase and expanding the firing range during the high-temperature melting stage; and significantly reducing the coefficient of thermal expansion of the glaze layer by strengthening the network structure during the cooling stage. When the coefficient of thermal expansion of the glaze is slightly lower than that of the body, the glaze surface will bear slight compressive stress after cooling. This state is most conducive to resisting external thermal shock and avoiding cracking.
3. Enhanced Overall Glaze Performance, Balancing Aesthetics and Durability
In addition to improving thermal stability, calcined zinc oxide simultaneously optimizes multiple glaze properties. Its dynamic melting action maintains good fluidity of the glaze over a wide temperature range, promotes bubble removal, and increases glaze density; it also enhances light scattering and reflection, significantly improving whiteness and gloss. Furthermore, ZnO improves the elastic modulus of the glaze layer, giving the glaze a certain deformation buffering capacity under stress, further enhancing thermal shock resistance. These synergistic improvements make wall and floor tiles not only visually appealing but also able to withstand the challenges of low winter temperatures, summer sun exposure, and frequent changes in indoor and outdoor temperature differences.
4. Widely Compatible with Various Ceramic Systems, Broad Application Prospects
Calcined zinc oxide is particularly suitable for medium- and low-temperature glaze systems in architectural ceramic wall and floor tiles, and is also widely used in artistic porcelain, daily-use porcelain, and ceramic pigments. Its high purity and low shrinkage characteristics make it perform exceptionally well in high-end products such as large-format thin tiles, antique tiles, and glazed tiles. By precisely controlling the addition ratio, an optimal balance between thermal stability, gloss, and process tolerance can be achieved without sacrificing the glaze texture.
Calcined zinc oxide, through high-temperature pretreatment to achieve a stable structure, plays multiple roles in the glaze, including reducing the coefficient of expansion, enhancing network connectivity, and optimizing melting behavior, fundamentally improving the thermal stability of architectural ceramic wall and floor tiles. It is not only a key raw material for technological upgrades but also a crucial support for achieving the product goals of "high aesthetics + high durability." In today's world of increasing demand for green manufacturing and high-performance building materials, the value of calcined zinc oxide will continue to be demonstrated, injecting solid momentum into the high-quality development of the ceramic industry.
