Powder Drying Technology

       

There are many preparation methods of ceramic powder. According to the state of raw materials, ceramic powder can be divided into three types: liquid phase preparation, solid phase preparation and gas phase preparation. Each type contains several different production methods. Liquid phase synthetic powder is a type widely used in laboratory and industry. The preparation of powder in liquid phase can be divided into melt method and solution method, in which the solution method is the more common method. The powder prepared by solution method must be dried, that is, the water contained in the powder must be separated from the powder in gaseous form. When preparing ceramic powder from solution, the general method is to directly generate composite metal salt or calcine it into oxide powder through drying treatment.

      There are many kinds of powder drying technology. This series mainly introduces four methods: hot air drying, infrared drying, spray drying and freeze-drying.

Hot air drying method: the treatment method of hot air drying is hot air drying, which uses hot air as the drying medium to dry the powder, which needs to be carried out in a specific dryer. According to the different temperature and humidity of hot air, there are three main drying process systems.

        Low humidity and high temperature drying this method uses dry and hot air with low humidity as the medium to keep the powder in a dry environment with low humidity and high temperature throughout the drying process. Due to the low humidity and high temperature of the hot air, the water on the powder surface evaporates quickly during the drying process, so there is less heat transferred to the interior of the powder. In this way, it is easy to form an internal low and external high temperature gradient, causing the direction of heat diffusion to go inward and hindering the smooth progress of internal diffusion. When the powder layer is thick, this effect becomes more prominent, so that the internal diffusion speed can not catch up with the demand of external diffusion for water evaporation, resulting in the phenomenon of "dry surface" of powder. Therefore, this method is only suitable for the heating and drying of thin powder layer.

        This method is to keep the hot air at low humidity and gradually increase its temperature during the drying process. The purpose is to gradually increase the drying speed of the powder from small to large, so as to reduce the internal and external temperature difference and internal diffusion resistance of the powder, so as to ensure the mutual adaptation of the internal and external diffusion speed of the powder and avoid the phenomenon of "dry surface" of the powder. This method is mostly used for heating and drying thick powder layer. However, the drying time is long and the drying efficiency is low.

        This method has reasonable system and is suitable for drying with large amount and thick powder layer, but it needs drying equipment that can regulate the humidity and temperature of drying medium. The advantages and disadvantages of hot air drying method are: when drying powder with hot air drying method, it is fast and can dry a large amount continuously. The disadvantages are: when drying powder with hot air drying method, it needs to be crushed, and the drying effect of block is not ideal.

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