As a key additive in ceramic glazes, the optimization of calcined zinc oxide's chemical properties and physical morphology plays a decisive role in improving the gloss and whiteness of the glaze surface. This process involves crystal structure reorganization induced by high-temperature calcination, enhanced surface activity, and synergistic reactions with glaze components, ultimately achieving macroscopic performance improvements through microstructural adjustments.
From a crystal structure perspective, the calcination process causes a crystal transformation in zinc oxide particles through high-temperature treatment. Uncalcined zinc oxide has a loose crystal structure, low surface energy, and weak interaction with other components in the glaze. However, after calcination at around 1200℃, the internal atomic arrangement of the zinc oxide particles becomes more compact, forming a stable hexagonal crystal structure. This structural reorganization not only improves the chemical stability of zinc oxide but also significantly increases its surface active sites, providing more contact points for subsequent reactions with silicates, aluminosilicates, and other components in the glaze, thereby promoting glaze densification.
Regarding enhanced surface activity, the particle morphology of calcined zinc oxide undergoes significant changes. High-temperature calcination creates a microporous structure on the surface of the zinc oxide particles, which greatly increases the specific surface area. When calcined zinc oxide is added to glaze, its microporous structure adsorbs tiny bubbles and impurities, reducing surface defects. Simultaneously, the increased number of surface active sites makes it easier for zinc oxide to react with coloring oxides in the glaze, inhibiting the formation of unwanted hues and thus improving glaze whiteness. For example, in glazes with high iron content, calcined zinc oxide can adsorb iron ions, reducing yellowing caused by iron ion coloring.
The synergistic reaction with glaze components is the core mechanism by which calcined zinc oxide enhances glaze performance. During glaze melting, calcined zinc oxide acts as a flux, lowering the melting temperature and promoting uniform mixing of components. When the glaze reaches a molten state, zinc oxide forms a eutectic mixture with silicates, aluminosilicates, and other components. This mixture forms a fine crystalline structure during cooling. The denser arrangement of these fine crystals reduces light scattering on the glaze surface, resulting in a higher gloss. Simultaneously, zinc oxide reacts with aluminum oxide to form zinc spinel crystals. These crystals have a high refractive index, enhancing the translucency of the glaze and further improving its whiteness.
The adjustment of the glaze's microstructure by calcined zinc oxide also reduces glaze defects. Uncalcined zinc oxide particles are relatively large and easily form agglomerates in the glaze, leading to defects such as pinholes and bubbles. Calcined zinc oxide particles are fine and uniform, dispersing better in the glaze and reducing agglomeration. Furthermore, the addition of calcined zinc oxide can adjust the viscosity of the glaze, making it easier to form a uniform glaze layer during application and avoiding gloss differences caused by uneven glaze thickness.
In colored glaze systems, the role of calcined zinc oxide is more complex. For chromium-containing black or green glazes, zinc oxide should be used with caution, as it may react with chromium ions, affecting the color rendering effect. However, in most colored glazes, calcined zinc oxide can stabilize the color by adjusting the glaze's melting properties and crystal structure. For example, in cobalt blue glaze, zinc oxide, acting as a mineralizer, lowers the color development temperature, allowing the glaze to exhibit a vibrant blue color at lower temperatures while maintaining its gloss and whiteness.
The improved wear resistance and stain resistance of calcined zinc oxide indirectly affects the durability of gloss and whiteness. By promoting the formation of wear-resistant phases such as anorthite, calcined zinc oxide enhances the mechanical strength of the glaze, reducing gloss loss due to wear during use. Simultaneously, its photocatalytic effect generates active oxygen, inhibiting bacterial growth, reducing stain adhesion, and maintaining long-term cleanliness and whiteness.
Calcined zinc oxide significantly improves the gloss and whiteness of the glaze through multiple mechanisms, including crystal structure restructuring, enhanced surface activity, synergistic reactions with glaze components, and microstructure adjustment. Its effect extends beyond the physicochemical changes during glaze melting to the performance maintenance during use, providing crucial support for the high-quality presentation of ceramic products.
