In the production process of calcined zinc oxide, although the cooling link is at the end of the process, it has a crucial impact on the activity of the product. Different cooling methods will change the microstructure, crystal morphology and surface properties of zinc oxide, which will determine its reactivity in subsequent applications and profoundly affect the quality and performance of the product.
Rapid cooling methods, such as air cooling or water cooling technology, can quickly cool down zinc oxide after high-temperature calcination in a short time. At high temperatures, zinc oxide molecules have high activity and the grains are in a rapid growth stage. When rapid cooling intervenes, heat is quickly taken away, molecular thermal motion slows down sharply, and the grain growth process is forcibly interrupted. In this case, the grains formed by zinc oxide are small and evenly distributed, and the specific surface area is significantly increased. Since the active sites are directly related to the specific surface area, more surface atoms are exposed, so that zinc oxide can be more fully in contact with the reactants when participating in chemical reactions, thereby effectively improving the activity of the product. For example, zinc oxide produced by rapid cooling in the rubber industry can more efficiently promote rubber vulcanization reactions, improve vulcanization speed and product quality.
In contrast to rapid cooling, during slow cooling, calcined zinc oxide stays in the high temperature range for a long time, providing sufficient time and space for grain growth. As the temperature slowly drops, smaller grains gradually aggregate and fuse to form larger grains. Grain coarsening reduces the specific surface area of zinc oxide, and the number of surface active sites decreases accordingly. When used in fields that require high activity, such as catalysis, the slowly cooled zinc oxide has insufficient activity and significantly reduces its catalytic efficiency. Taking the use in the desulfurization process as an example, when coarse-grained zinc oxide reacts with sulfides, the contact area is limited, resulting in a significant reduction in the desulfurization effect, which cannot meet the high efficiency requirements of industrial production.
The vacuum cooling method creates a low-pressure cooling environment by reducing the ambient pressure. Under vacuum conditions, adsorbed impurities and gas molecules on the surface of zinc oxide are more easily desorbed, effectively purifying the surface of zinc oxide. The pure surface reduces the coverage and interference of impurities on the active sites, allowing the intrinsic activity of zinc oxide to be fully exerted. At the same time, the vacuum environment helps to inhibit the oxidation reaction of zinc oxide during the cooling process and avoid the formation of an oxide layer on the surface that is not conducive to activity. The zinc oxide produced by this cooling method can show better electrical properties and stability when used in fields such as electronic ceramics that require extremely high purity and activity, greatly improving the added value and application value of the product.
Protective gas cooling, such as using inert gases such as nitrogen and argon as cooling media, can form an isolation layer on the surface of calcined zinc oxide, effectively preventing oxygen from contacting zinc oxide and preventing it from oxidizing during the cooling process. Oxidation may change the valence and crystal structure of zinc oxide, thereby reducing its activity. Through protective gas cooling, the chemical composition and crystal structure of zinc oxide are stably maintained, and the active sites are not destroyed. When preparing high-performance zinc oxide varistors, the use of zinc oxide raw materials cooled by protective gas can ensure that the resistor has stable and excellent performance in applications such as overvoltage protection, maintaining the high activity and reliability of the product.
The segmented cooling strategy is to divide the cooling process into multiple stages, each stage using different cooling rates and environmental conditions. This method can accurately control the microstructural evolution of zinc oxide. For example, a faster cooling rate is used in the high temperature stage to inhibit excessive growth of grains; in the stage close to room temperature, the cooling rate is appropriately slowed down to fully release the internal stress and avoid crystal defects caused by internal stress generated by rapid cooling. Through segmented cooling, zinc oxide products with suitable grain size, low internal stress and good crystal integrity can be obtained, and the activity of the product can be precisely controlled to meet the diverse needs of zinc oxide activity in different application scenarios.
The circulating cooling system maintains the stability and continuity of the cooling process by continuously circulating the cooling medium. Stable cooling conditions can reduce the impact of cooling environment fluctuations on the activity of zinc oxide and ensure that the activity of each batch of products has good consistency. In large-scale industrial production, the circulating cooling system is particularly important. It can ensure the stability of product quality and reduce production risks and cost losses caused by product activity fluctuations. For example, when paint manufacturers use zinc oxide produced by circulating cooling as a pigment additive, they can ensure the consistency of color stability and hiding power between paint batches, thereby enhancing the market competitiveness of the company.
Different cooling methods affect the product activity of calcined zinc oxide from multiple dimensions. Rapid cooling, vacuum cooling and protective gas cooling can improve activity by inhibiting grain growth, improving surface properties and preventing oxidation, while slow cooling may reduce activity due to grain coarsening. Segmented cooling and cycle cooling, as optimization and guarantee means, play a role in microstructure regulation and production stability respectively. In actual production, enterprises need to scientifically and rationally select cooling methods according to product application requirements in order to produce high-activity zinc oxide products that meet the requirements of different fields.
