magnetic separator machine

PTMS magnetic separation

what is magnetic separation method ？

The spherical silicon micropowder is purified by ultra-fine pulverization of natural quartz stone, and through a certain high temperature field, its phase, crystal form and shape change instantaneously, from solid to molten state and then to solid state, from crystalline state to crystalline state. A powder obtained by changing irregular angular particles into regular spherical particles. The preparation methods thereof are generally as follows.

1. High temperature plasma melting method

The high-temperature plasma melting method uses a high-temperature gas generated by an alternating current or a direct current arc plasma as a heat source, and sprays the quartz powder into a plasma flame. The powder is melted by heat and instantly vaporized, and then quenched, collected by a cyclone and a bag. A spherical silicon micropowder is obtained.

It is characterized by high heating temperature, which can obtain a temperature (3000K or more) higher than chemical combustion, and the high temperature and high heat and high active atmosphere make the chemical reaction proceed very rapidly; when the reaction material leaves the plasma, it is rapidly cooled and the particles are cooled. No longer grow up; plasma states of different atmospheres can be formed according to different needs, and the reactant selection range is wide. However, plasma technology is very difficult, making the product spheroidization rate difficult to control and difficult to form scale production.

2, high temperature melt injection method

The high-temperature melt-spray method is to place the material in a high-temperature field to melt it into a melt. At the moment of the melt flowing out, the high-pressure air is sprayed through the ejector, and the melt is dispersed into a mist by a high-speed air flow. The small droplets are then rapidly cooled, and the small droplets quickly and naturally shrink into spherical particles with smooth surface when they are cold.

The high temperature melt injection method is the most easy method to ensure the spheroidization and amorphous rate. However, a series of key technologies such as furnace high temperature materials, viscous quartz melt atomization and prevention of secondary pollution have not broken through, and it is very difficult to manufacture high purity spherical quartz powder.

3. Gas combustion flame method

The gas combustion flame method uses a fuel gas such as acetylene gas, hydrogen gas or natural gas as a raw material, and uses oxygen or air as a combustion gas to generate a clean flame through a closed furnace. At the same time, the angular quartz powder is delivered to the flame with the gas stream. When the angular powder passes through the high temperature flame field, it is first melted into amorphous particles, and when it is rapidly cooled away from the high temperature field, it is immediately shrunk into spherical particles, and then collected by cyclone to obtain a finished product.

Compared with plasma high-temperature flame, this method firstly has a relatively low temperature field, followed by fewer influencing factors, simpler equipment manufacturing, easy industrialization, and better development prospects.

4. Chemical synthesis

There are significant differences between the chemical synthesis method and other preparation methods, mainly by using a sol-gel technique to prepare spherical quartz powder in the presence of a dispersant and a spherical catalyst. The spherical quartz powder produced by the chemical method has a sphericity, a spheroidization rate, and an amorphous rate of 100%, and can achieve a very low radioactivity index, but has a low bulk density and a large specific surface area. The oil absorption rate is high. When the spherical powder is completely made of epoxy resin molding compound, the compacting performance and strength of the molding compound are reduced. The linear expansion ratio becomes large, which affects the packaging performance of the molding compound, so the maximum addition amount of the spherical quartz powder is limited in practical use.

5, explosion method

The production of spherical silicon micropowder by the explosion method is a technology developed in Japan and is mainly used to produce ultrafine spherical quartz powder. The blasting method is a method of producing spherical oxide particles by utilizing the explosion process of metal powder. The single crystal or polycrystalline silicon powder is sprayed in an oxygen stream to ignite, and the generated silica becomes a vapor or a liquid at a high temperature, and after cooling, spherical silica particles are formed, and the reaction heat generated by the combustion is used to ignite the continuous addition. Silicon powder.

The blasting method has many advantages, which simplifies the process, saves energy, and does not produce harmful by-products. The key to this method is the control of the reaction process, which can explode if the reaction is too intense. In addition, since the ultrafine powder has a large specific surface area and is easily agglomerated, how to disperse the product is also a problem.

6, gas phase method

The gas phase method SiO2 (commonly known as gas phase white carbon black) is a fine and special amorphous powder material prepared by hydrolyzing silicon halide at high temperature.

The gas phase SiO2 product has high purity, average primary particle size of 7-40 nm, specific surface area of ​​50-380 m2/g, and SiO2 mass fraction of not less than 99.8%, but it is difficult to disperse in organic matter.

7. Precipitation method

The precipitation method uses water glass and an acidifying agent as raw materials, and a surfactant is added at a proper time to control the reaction temperature. When the pH of the precipitation solution is 8, a stabilizer is added, and the obtained precipitate is washed, dried, and calcined to form a silicon fine powder.

The SiO2 produced by the precipitation method has uniform particle size and low cost, and the process is easy to control, which is favorable for industrial production, but there is a certain agglomeration phenomenon.

8, microemulsion method

The microemulsion method uses two immiscible solvents to form a uniform emulsion under the action of a surfactant, so that the processes of nucleation, production, coalescence, agglomeration and the like are confined in a tiny spherical droplet from the emulsion. The solid phase is precipitated to form spherical particles, which avoids further agglomeration between the particles. Most of the SiO2 prepared by the microemulsion method uses tetraethyl orthosilicate as the silicon source, and the SiO2 is obtained by the molecular diffusion of tetraethyl orthosilicate through the reverse micelle interface membrane and then into the water core, followed by hydrolysis and condensation reaction. The product prepared by the method has the advantages of narrow particle size distribution, controllable particle size and good dispersibility.

9, hydrothermal synthesis

Hydrothermal synthesis is a common method for preparing nanoparticles in liquid phase. Generally, inorganic and organic compounds are combined with water at a temperature of 100-350 ° C and high pressure, and improved by controlling the accelerated dialysis reaction and physical processes. The inorganic matter is filtered, washed, and dried to obtain high-purity, ultra-fine particles.

The hydrothermal method has the advantage that the oxide can be directly formed, and the step of converting the calcination into an oxide by the general liquid phase synthesis method is avoided, thereby reducing the formation probability of hard agglomeration. Compared with the sol-gel method, this method not only can increase the reaction rate, eliminate the local concentration unevenness, but also has a destructive effect on the agglomerated powder particles.

10, spray method

The spray method is a chemical and physical method in which a solution is atomized by various physical means to obtain ultrafine particles. Its basic processes are solution preparation, spraying, drying, collection and heat treatment. The method is characterized by relatively uniform particle distribution, but the particle size is submicron to 10 μm, which is a new method for synthesizing particle size controllable nanoparticle oxide.

11. Self-propagating low-temperature combustion method

The process includes the steps of preparing sodium silicate, preparing silicate sol, preparing mixed combustion liquid, burning reaction, annealing carbon removal, washing treatment and the like. Although the technology has some obvious advantages such as: wide raw materials, simple process, and favorable preparation of high-purity silicon micropowder, the method is still only in the experimental stage, and can not be mass-produced very well.

12, high temperature calcination spheroidization

The process is as follows: coarse selection of natural powder quartz ore powder, after the coarse selection of high-quality natural powder quartz ore powder is washed, adding an aging agent to make the powder quartz ore powder aged under alkaline conditions, aged After filtration, the filtrate is dehydrated and dried, dispersed into powder or added into a binder to form a block, and then the powdery or massive quartz ore powder is kept in a high temperature furnace at 1280-1680 ° C for 1-10 hours. After firing, cooling, and then spheroidizing, magnetic separation and air separation are carried out to obtain high-purity ultra-fine spherical silicon micropowder. The technology is currently in the experimental stage.