In sanitary ceramics manufacturing, kaolin is far more than a filler—it is the builder of structure, the determinant of performance, and the enabler of process. From providing the plasticity required for forming to creating a robust mullite skeleton after firing; from determining the final whiteness and appearance of the product to controlling shrinkage behavior throughout the drying and firing processes—the quality and characteristics of kaolin directly dictate the forming yield rate, final strength, dimensional accuracy, surface quality, and overall performance of sanitaryware products.
Providing Excellent Plasticity and Binding Properties to Ensure Forming Processes
| Kaolin has been used extensively in the ceramic industry for a long time, typically accounting for 20–30% of formulations. Kaolin increases the Al₂O₃ content in ceramics, facilitating the formation of mullite. This enhances the sintering strength and stability of ceramics. During firing, the decomposition of kaolin into mullite forms the body framework. This process prevents deformation of the ceramic body, broadens the firing temperature range, and improves the whiteness of the ceramic. Additionally, kaolin's inherent plasticity, binding properties, suspension stability, and cohesiveness improve the formability of porcelain slips and glazes, facilitating processes like wheel-throwing, slip casting, and ceramic forming. Its binding properties ensure sufficient dry strength when combined with non-plastic raw materials (such as quartz and feldspar), enabling large, structurally complex sanitaryware bodies (like toilets and sinks) to maintain dimensional stability during forming and drying, minimizing cracking or deformation. |  |
Influences body whiteness and color, determining product appearance quality
| Sanitaryware demands exceptionally high whiteness and visual cleanliness. High-purity kaolin is white, and its calcination whiteness directly determines the whiteness of sanitaryware green bodies. Impurities (especially iron Fe₂O₃ and titanium TiO₂ compounds) reduce whiteness and cause defects like color spots and melt scars, necessitating strict control of harmful impurities in kaolin. Kaolin brightness also affects the final product's visual texture, with high brightness enhancing perceived premium quality. |  |
Controlling Drying and Firing Shrinkage to Reduce Product Defects
| Generally, finer-grained kaolin with better plasticity exhibits greater drying shrinkage. Sanitaryware bodies, characterized by large volumes and thick walls, are prone to deformation and cracking due to excessive drying shrinkage. Therefore, drying sensitivity must be managed by controlling kaolin fineness and water content. During high-temperature firing, kaolinite undergoes decomposition and mullitization while generating liquid phases, causing further body shrinkage. A stable and appropriate firing shrinkage rate is crucial for ensuring dimensional accuracy and preventing cracking. The sintering temperature and sintering range of kaolinite are key parameters for establishing the firing schedule. |
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| Forming the Body Skeleton to Ensure Mechanical Strength and Thermal Stability During firing, kaolinite decomposition ultimately generates needle-like mullite crystals. These crystals interlock to form a robust network skeleton, significantly enhancing sanitaryware's flexural strength and thermal stability. This enables the product to withstand mechanical stresses and thermal shocks during use. Kaolin imparts excellent resistance to acid, alkali, and salt corrosion to ceramic bodies, which is crucial for maintaining product durability in humid bathroom environments where cleaning agents are frequently used. | Provides excellent suspension properties, optimizing slip casting processes Slip casting is widely used in sanitaryware production. Kaolin's superior suspension and dispersion properties ensure the slip remains stable and uniform for extended periods without settling, which is vital for forming dense, consistent bodies. Controlling particle size distribution and adding electrolytes can further optimize slip performance. | Possesses ion exchange capacity, facilitating formulation control Kaolinite's mild cation adsorption and exchange capacity enables viscosity and thixotropy adjustment through electrolyte addition, accommodating diverse forming process requirements. |
As a critical foundational material in sanitaryware production, kaolinite serves multifaceted and indispensable functions. Therefore, meticulous selection and strict control of kaolinite raw materials constitute the primary step in manufacturing high-quality sanitaryware.
