Yuan Lei's Little Knowledge | Preparation and Application of Wollastonite Powder
Wollastonite (CaSiO3) is a white calcium-containing metasilicate crystalline mineral, natural production of wollastonite is usually flaky, needle-like, radial or fibrous aggregates. It has a series of excellent properties such as high whiteness, brightness, high aspect ratio and low water absorption and oil absorption.
With the development of powder technology, synthesis technology and surface modification technology, the application field of wollastonite powder is constantly expanding and deepening, mainly used in plastics, rubber, polymers, coatings, dyes, ceramics, metallurgy, building materials, environmental protection and asbestos substitutes. China's wollastonite plays an important role in the world market and has occupied 2/3 of the European foundry powder market, but the preparation technology of high aspect ratio of wollastonite needle-like ultrafine powder lags behind developed countries.
Preparation Technology of Wollastonite Powder
Natural wollastonite products according to particle size can be divided into block particles, ordinary powder, fine powder, ultra-fine powder and needle powder five categories, powder preparation method according to the principle can be divided into physical preparation and chemical preparation, in which physical preparation to mechanical preparation, chemical preparation to sintering and melting method.
Mechanical crushing can be divided into dry and wet methods according to different environmental media. Wet microwave crushing is better for protecting fiber length-diameter ratio, single fiber fineness and one-time slack. Dry method has higher energy consumption but powder agglomeration problem is not prominent in wet method, so it is also an effective way.
chemical precipitation method
The preparation of wollastonite by chemical precipitation method is a method of using soluble salts containing silicon and calcium, dissolving them in water, and generating calcium silicate through chemical reaction.
Advantages:The process is simple, easy to operate, wide source of raw materials, low energy consumption, and does not require expensive equipment.
Disadvantages:The particle size of the synthetic product is difficult to control.
The sol-gel method uses an inorganic salt or a metal alkoxide as a precursor. The precursor is dissolved in a solvent to form a uniform solution, and the solute reacts with the solvent to hydrolyze or alcoholysis to form a sol; the sol is transformed into a gel after aging, evaporation and drying. The nanoparticles are dispersed in the network structure of the gel, and the nanoparticles can be obtained by thermal post-treatment of the gel.
Advantages:The equipment required is simple and less energy consumption, which is an effective means to prepare high-quality inorganic ultrafine powder.
Disadvantages:Heat treatment must be carried out, otherwise it is easy to produce hard agglomeration and the growth of ultra-fine particles.
Hydrothermal method refers to a method of synthesizing coal in a closed container with water or other solvents as dissolved coal at a certain temperature and pressure. Hydrothermal synthesis is an important method for the preparation of special structural and functional materials.
Advantages:High activity powder can be obtained, and hydrothermal is at low temperature, pressure, liquid phase reaction conditions, is conducive to the regular orientation of the crystal, easy to control the particle size of the product.
Disadvantages:The precursor of this method is expensive and is not conducive to large-scale industrial production.
solid phase sintering method
The preparation principle of solid-phase sintering method is to use CaO, SiO2Mineral raw materials or industrial waste are prepared by dry mixing, crushing and sintering directly under high temperature conditions. This method is currently the main synthetic method for the artificial preparation of wollastonite.
Advantages:Wide application, simple process.
Disadvantages:The purity of the product is low, the energy consumption is high, the equipment investment is large, and the performance and use of the product are greatly affected by the variety of raw materials and the origin.
Application of wollastonite powder
Role in the plastics industry
Wollastonite powder deep processing products are widely used in plastics. As a plastic filler, it is mainly used to improve tensile strength and flexural strength and reduce costs.
Role in the rubber industry
Natural wollastonite powder has a special needle-like structure, white, non-toxic, after ultra-fine grinding, surface modification is the ideal filler of rubber, not only can reduce the production cost of rubber products, but also can improve the mechanical properties of rubber, giving the rubber itself does not have a special function.
Role in the coatings industry
Wollastonite powder as a filler for paints and coatings can improve the physical and chemical properties of products, durability and weather resistance, reduce the gloss of the paint, enhance the expansion ability of the paint, reduce cracks, and also reduce oil absorption and enhance corrosion resistance.
Role in the paper industry
Wollastonite powder can be used as a filler and plant fiber composite paper composite fiber to replace part of the plant fiber. Reduce the amount of wood pulp, reduce costs, improve the performance of paper products, improve the smoothness of paper products, opacity, improve the uniformity of paper products, eliminate static electricity of paper, paper products have less shrinkage, good printability, and can reduce pollution emissions in the pulping process of plant fiber.
Kaolin is a non-metallic mineral, which is a kind of clay and clay rock mainly composed of kaolinite clay minerals. Because it is white and delicate, also known as white earth. It is named after Gaoling Village, Jingdezhen, Jiangxi Province.
Barium sulfate is based on barite as the main raw material, through beneficiation, ore washing, crushing and other processes. Barium sulfate has a hardness of 3~3.5 (Mohs) and a specific gravity of 4.3~4.7. It has the characteristics of high specific gravity, low hardness and brittleness. Barite is almost insoluble in water, ethanol and acid, soluble in hot concentrated sulfuric acid. With the development of some high-performance barium sulfate products, the application field of barium sulfate is constantly expanding.