The production process of ultrafine powder - Impact pulverization
It is a method that has been widely used since ancient times to mechanically pulverize bulk materials into powder. At present, bulk ultrafine powder still mainly relies on mechanical crushing. Commonly used ultrafine crushing equipment includes: autogenous mill, jet mill, high-speed mechanical impact mill, vibration mill, stirring mill (including various sand mills, tower mills, etc.), Colloid mill (including homogenizer, etc.), ball mill, Raymond mill, etc.
Mechanical pulverization is generally used to produce powders larger than 1 μm. A small number of equipment, such as jet jet mill, can be used to produce materials smaller than 1 μm, which can crush materials to sub-micron level, that is, 0.1+0.5 μm. Its structure is that the compressed air produced by the air compressor is sprayed out from the nozzle, and the powder collides with each other in the jet flow and is crushed.
Raw materials are fed from the hopper, accelerated to supersonic speed by the Venturi nozzle, and introduced into the pulverizer; in the pulverization zone formed by the fluid ejected from the grinding nozzle inside the pulverizer, the material particles collide with each other, rub and pulverize into fine powder. Among them, those who lose centrifugal force and are introduced into the center of the pulverizer are superfine powders; coarse powders do not lose centrifugal force, and continue to be pulverized in the crushing belt.
The jet mill developed in Germany suspends and collides the powder smaller than 0.088mm into superfine powder, so it can produce products of various grades not larger than 44μm, and the average particle size can reach 1, 2, 3, 4μm. This kind of jet mill has high production efficiency, does not pollute the environment, and the product has high purity, fine particles, and no agglomeration. It is an ideal ultrafine grinding equipment. The technical development trend of the mechanical pulverization method is to improve the process technology on the existing basis, develop high-efficiency and low-consumption ultra-fine pulverization equipment, fine classification equipment and supporting auxiliary process equipment, and expand the particle size limit of mechanical pulverization, while improving the processing capacity , forming economies of scale.
In the ultra-fine crushing process, fine grading equipment is also required to separate qualified fine powder materials in a timely manner, improve the efficiency of crushing operations, and control the particle size distribution of products. At present, there are two types of commonly used classification equipment: one is dry classification, generally centrifugal or turbine wind classifier; the other is wet classification equipment, generally using horizontal spiral centrifugal classifier, small diameter and small Cone angle hydrocyclone, and hydrocyclone etc.
Generally, hydraulic classification is used, and the commonly used methods are sedimentation method, overflow method, cyclone method and centrifugation method. The sedimentation method uses the mechanism of different sedimentation speeds in water for different particle sizes to classify; the mechanism of the overflow method is similar to the sedimentation method, the difference is that the water flow speed is greater than the particle sedimentation speed, thereby bringing out the fine powder; the cyclone method The slurry rotates at high speed in the cyclone to generate centrifugal force, and the particle size is different, the centrifugal force is also different, so that the large and small particles can be separated; the centrifugal method is that the slurry rotates at high speed in the centrifuge, and the centrifugal force generated by particles of different sizes is also different.
After classification, the obtained products of various particle sizes are dehydrated and then dried.
In ultrafine grinding, the particle size of the powder is fine, and its specific surface area and surface energy are both large. The finer the particle size, the higher the mechanical strength of the material. Therefore, the energy consumption of ultra-fine pulverization is high, and the powder is easy to agglomerate under repeated mechanical force. In order to improve the crushing efficiency, in addition to strengthening the classification, grinding aids and additives are sometimes added.
The production process of the mechanical pulverization method is simpler than that of the chemical synthesis method, the output is large, the cost is low, and the produced micropowder has no agglomeration. However, it is unavoidable to mix impurities in the crushing process, and the particle shape of the crushed product is generally irregular, and it is difficult to obtain fine particles smaller than 1 μm.
4 major application fields of silica powder
Due to its advantages of acid and alkali corrosion resistance, high temperature resistance, low linear expansion coefficient and high thermal conductivity, microsilica powder is widely used in copper clad laminates, epoxy molding compounds and other fields to improve the performance of related products.
1. Copper clad laminate
Adding silicon micropowder to the copper clad laminate can improve the physical properties such as the linear expansion coefficient and thermal conductivity of the printed circuit board, thereby effectively improving the reliability and heat dissipation of electronic products.
At present, there are five types of silica powder used in copper clad laminates: crystalline silica powder, molten (amorphous) silica powder, spherical silica powder, composite silica powder, and active silica powder.
Spherical microsilica powder is mainly used in high-filling, high-reliability high-performance copper clad laminates due to its unique characteristics of high filling, good fluidity, and excellent dielectric properties. The main indicators of spherical silica powder for copper clad laminates are: particle size distribution, sphericity, purity (conductivity, magnetic substances and black spots). At present, spherical silicon micropowder is mainly used in rigid copper clad laminates, and the proportion of mixed casting in copper clad laminates is generally 20% to 30%; the usage of flexible copper clad laminates and paper-based copper clad laminates is relatively small.
2. Epoxy molding compound
Filling silicon micropowder into epoxy molding compound can significantly increase the hardness of epoxy resin, increase the thermal conductivity, reduce the exothermic peak temperature of the reaction of cured epoxy resin, reduce the linear expansion coefficient and curing shrinkage rate, reduce internal stress, and improve The mechanical strength of epoxy molding compound can reduce the cracking phenomenon of epoxy molding compound, thereby effectively preventing external harmful gas, moisture and dust from entering electronic components or integrated circuits, slowing down vibration, preventing external force damage and stabilizing component parameters.
Common epoxy molding compounds are mainly composed of 60-90% filler, less than 18% epoxy resin, less than 9% curing agent, and about 3% additives. The currently used inorganic fillers are basically microsilica powder, with a content of up to 90.5%. Silica powder for epoxy molding compound mainly focuses on the following indicators:
(1) Purity. High purity is the most basic requirement of electronic products for materials, and the requirements are more stringent in VLSI. In addition to the low content of conventional impurity elements, it is also required that the content of radioactive elements be as low as possible or not. With the advancement of the manufacturing process, the electronics industry has higher and higher requirements for the purity of silicon micropowder.
(2) Particle size and uniformity. VLSI packaging materials require fine silicon powder particle size, narrow distribution range, and good uniformity.
(3) Spheroidization rate. High spheroidization rate is the prerequisite to ensure high fluidity and high dispersibility of fillers. High spheroidization rate and good sphericity of silicon micropowder have better fluidity and dispersion performance, and can be more fully dispersed in epoxy molding compounds to ensure The best filling effect.
3. Electrical insulation materials
Microsilica powder is used as epoxy resin insulating packing material for electrical insulation products, which can effectively reduce the linear expansion coefficient of the cured product and the shrinkage rate during the curing process, reduce internal stress, and improve the mechanical strength of the insulating material, thereby effectively improving and enhancing the insulating material. mechanical and electrical properties.
4. Adhesive
As an inorganic functional filler, silica powder can effectively reduce the linear expansion coefficient of the cured product and the shrinkage rate during curing when filled in the adhesive resin, improve the mechanical strength of the adhesive, improve heat resistance, permeability and heat dissipation performance, thereby improving the viscosity. Knot and seal effect.
The particle size distribution of microsilica powder will affect the viscosity and sedimentation of the adhesive, thereby affecting the manufacturability of the adhesive and the linear expansion coefficient after curing. Therefore, the field of adhesives pays attention to the function of microsilica powder in reducing the linear expansion coefficient and improving mechanical strength. The requirements for appearance and particle size distribution are relatively high, and products of different particle sizes with an average particle size between 0.1 microns and 30 microns are usually used for compound use.
Process properties and application of kaolin
According to the quality, plasticity and sandy content of kaolin ore itself, it can be divided into three types: hard, soft and sandy kaolin. Hard kaolin has a hard texture and no plasticity, but it has a certain plasticity after crushing and grinding; soft kaolin has a softer texture and better plasticity, and the amount of sand contained in it is less than 50%; The sandy kaolin has a looser texture and poor plasticity. It is better after sand removal, and the amount of sand contained in it generally exceeds 50%.
Pure kaolin has high whiteness, soft quality, easy to disperse and suspend in water, good plasticity and high viscosity, excellent electrical insulation properties; has good acid solubility, low cation exchange capacity, good Physical and chemical properties such as fire resistance.
Application of kaolin
1. Application of kaolin in cement-based materials
Kaolin becomes metakaolin due to dehydration. Cement can usually be prepared by alkali activation, or used as an additive to concrete materials. Kaolin can improve the strength, workability and durability of concrete, and at the same time resist the autogenous shrinkage of concrete. Kaolin cement-based materials have excellent performance and a wide range of applications, and their development prospects are worthy of attention.
2. Application of kaolin in ceramic industry
In the ceramic industry, the application of kaolin is earlier than other industries, and the dosage is also very large, usually accounting for about 20% to 30% of the formula. Kaolin can increase the content of A1203 in ceramics, and the formation process of mullite is easier, thus improving the stability and sintering strength of ceramics.
3. Application of kaolin in refractory industry
Because of its high refractoriness, kaolin is usually used in the production and processing of refractory products. Refractory materials are mainly divided into two types: refractory bricks and silicon-aluminum wool, which have the characteristics of high temperature resistance and small deformation under pressure. A series of high temperature resistant clays including kaolin, bauxite, bentonite, etc. are collectively called refractory clay.
4. Application of modified kaolin in coatings
Kaolin has been used as a filler for coatings and paints for a long time because of its white color, low price, good fluidity, stable chemical properties, and large cation exchange capacity on the surface. Kaolin used in coatings generally includes washed superfine kaolin and calcined superfine kaolin.
5. Application of kaolin in paint industry
TiO2, CaC03, talc, and kaolin are the main mineral raw materials used in the paint industry. Among them, kaolin has requirements for its dispersibility, particle size, and content of colored oxides. Because of its white color, low cost, good fluidity and suspension, chemical inertness, strong covering power and other properties, kaolin mainly plays the role of filler and pigment substitute in paints, and can reduce the need for expensive dyes quantity.
6. Kaolin is used in plastic industry
As a filler, kaolin is generally used in an amount of 15% to 60% in plastics. Its function is to make the appearance of plastic products smooth, accurate in size, resist chemical corrosion, reduce thermal shrinkage and thermal fission, and facilitate the polishing process. In the production process of polyvinyl chloride, kaolin is usually used as a strengthening agent to improve the abrasion resistance and durability of plastic products.
7. Kaolin is used to make glass fiber in pond kiln
Kaolin, which is low in iron, is used in fiberglass manufacturing primarily as a source of aluminum and silicon, as well as to dull its luster. The technical content of glass fiber drawing in the pool kiln is relatively high, and for glass fiber forming, it is required to reach the quasi-optical level. The quality and stability of kaolinite homogenized micropowder are the primary factors affecting the kiln glass fiber drawing process, and the alkali-free kiln glass fiber has strict quality requirements for kaolinite homogenized micropowder.
8. Application of kaolin in paper industry
In the paper industry, the international market of kaolin is relatively prosperous, and its sales volume exceeds that of ceramics, rubber, paint, plastics, refractory materials and other industries. In pulp, kaolin usually does not react with its ingredients, has strong stability, and is well retained in paper fibers.
9. Application of kaolin in rubber industry
Kaolin, which is used in the rubber industry, is filled into the colloidal mixture, which can enhance the wear resistance, chemical stability and mechanical strength of the rubber, prolong its hardening time, and can also adjust the mixing, rheological and vulcanization properties of the rubber, and improve the durability of the rubber.
7 advantages of air classifier
The classifier, cyclone separator, dust collector and induced draft fan form a classifying system. Under the action of fan suction, the material moves to the classification area at high speed from the inlet at the lower end of the classifier along with the updraft, and the coarse and fine materials are separated under the strong centrifugal force generated by the high-speed rotating classifying turbine.
The fine particles that meet the particle size requirements enter the cyclone separator or dust collector through the gap between the blades of the classifying wheel to collect. The coarse particles entrain some fine particles and the speed disappears after hitting the wall, and drop down to the secondary air outlet along the cylinder wall. The washing effect separates the coarse and fine particles, the fine particles rise to the classification area for secondary classification, and the coarse particles descend to the discharge port for discharge.
The air classifier, cyclone separator, dust collector and induced draft fan form a complete crushing system. After the compressed air is filtered and dried, it is sprayed into the crushing chamber through the Laval nozzle at high speed, at the intersection of multiple high-pressure airflows.
The materials are repeatedly collided, rubbed, sheared and crushed. The crushed materials are moved to the classification area with the upward airflow under the action of the fan suction. Under the strong centrifugal force generated by the high-speed rotating classification turbine, the coarse and fine materials are separated to meet the particle size The required fine particles enter the cyclone separator and dust collector through the classification wheel to collect, and the coarse particles descend to the crushing area to continue crushing.
The seven advantages of the air classifier are as follows:
●Airflow classifier is suitable for dry crushing of various materials with Mohs hardness below 9, especially for high hardness, high purity and high value-added materials.
●The airflow classifier contains a horizontal classifying device, the top cutting is accurate, the product particle size D97: 2-45 microns is adjustable, the particle shape is good, and the particle size distribution is narrow.
●Low temperature and medium-free crushing, especially suitable for crushing heat-sensitive, low-melting, sugar-containing and volatile materials.
●The crushing process is mainly completed by the collision between the materials themselves, which is different from mechanical crushing which relies on the impact crushing of the materials by blades or hammers, so the equipment is wear-resistant and the product purity is high.
●The equipment is easy to disassemble and clean, and the inner wall is smooth without dead ends.
●The whole system is sealed and crushed, with less dust and low noise, and the production process is clean and environmentally friendly.
●The control system of the air classifier adopts program control, which is easy to operate.
The advantages of metal silicon powder as a refractory material
Features of metal silicon powder:
1. High temperature resistance
Metal silicon powder has strong high temperature resistance, so adding an appropriate amount of metal silicon powder many times in the production of refractories and powder metallurgy can greatly improve the high temperature resistance.
2. Wear resistance
Usually we add metal silicon powder in the production of some wear-resistant castings to improve the wear-resistant performance of the castings.
3. Deoxygenation
Metal silicon powder, as the name suggests, contains a certain amount of silicon, which can have an affinity with oxygen to form silicon dioxide, which reduces the melting reactivity during deoxidation and ensures the safety of deoxidation!
In addition, metal silicon powder has also been widely used in the metallurgical foundry industry. In steelmaking, metal silicon powder can be used as deoxidizer, alloy additive, etc., and the effect is very obvious.
Silicon fume and metal silicon fume are two completely different products. In practice, these two products are often confused because they are inextricably linked.
The silica fume we usually say is also called silica fume and micro silica fume. It is the soot recovered from the production process of metal silicon or ferroalloy. Due to its high content of silica, extremely fine particles and high activity, it can be used in concrete, refractory materials, rubber, paint, etc. There are a wide range of applications in industries such as.
The main component of metal silicon powder is crystalline silicon (Si). Its initial form is lumpy, and it becomes powder after being crushed or ground, which is used in industries such as refractory materials.
The reason why metal silicon powder is turned into powder is because it is physically ground, and silicon powder is naturally formed during the production process.
The chemical composition varies greatly. Silicon powder is mainly silicon dioxide, and the main content of metal silicon is SI element.
Metallic silica fume is generally inert, while silica fume is a pozzolan. The color of metallic silicon powder is usually relatively stable, while the color of silicon powder varies greatly from white to black. Silica fume is widely used. The price of metal silica fume is very high, several times that of micro silica fume
The Progress of Superfine Pulverization Technology in Modern Food Processing
Superfine Grinding (SG) technology, as a new technology developed rapidly in the past 20 years, is a deep processing technology that combines mechanical mechanics and fluid mechanics, overcomes the internal cohesion of objects, and crushes materials into micron or even nanometer powders. Ultrafine pulverization treatment can make the material particle size reach 10 μm or even nanometer level. Since the powder structure and specific surface area are greatly changed compared with ordinary particles, the ultrafine pulverization particles have special properties that ordinary particles do not have, and with the modern equipment With the development of science, superfine pulverization technology has made major breakthroughs in many fields such as food and pharmaceuticals, especially in the extraction of Chinese herbal medicines, the development of functional foods, and the utilization of waste resources.
According to the particle size of processed finished powder, ultrafine pulverization technology can be mainly divided into: micron pulverization (1 μm ~ 100 μm), submicron pulverization (0.1 μm ~ 1.0 μm) and nano pulverization (1 nm ~ 100 μm). The preparation of micron powder generally adopts physical pulverization method; the preparation of submicron and below particle size powder adopts chemical synthesis method. The chemical synthesis method has the disadvantages of low output and high operation requirements, which makes the physical pulverization method more popular in the modern processing industry.
1. Extraction of natural active ingredients of precious Chinese herbal medicine
The demand for precious medicinal materials is high due to their remarkable medicinal effects, and wild resources are almost exhausted. Now they rely on artificial planting for supply, but the market is still in short supply, resulting in high prices. Therefore, it is necessary to make full use of precious Chinese herbal medicines and improve their processing technology.
Researchers generally use methods such as microscopic identification and physical property testing to perform characterization and physical property testing of ordinary Chinese herbal medicine powder and ultrafine powder. It was found that the ultrafine pulverization technology can effectively destroy the cell walls of a large number of cells in medicinal materials, increasing cell fragments, and its water solubility, swelling power, and bulk density are also improved to varying degrees compared with ordinary powder. At the same time, the dissolution rate of active ingredients in the ultrafine pulverization process is improved.
2. Reuse of food and drug processing waste resources
Food and drug processing waste usually still contains certain natural active ingredients, and discarding them will not only cause a lot of waste but also pollute the environment. The emergence of ultrafine pulverization technology provides more possibilities for the reuse of food and drug processing waste resources. In recent years, researchers' research on ultrafine pulverization technology has mostly focused on the reuse of food and drug processing waste resources, usually combined with enzymatic hydrolysis technology. For example, the reutilization of potato pomace, linseed husk, grape seed, coffee peel, etc., mostly focuses on the influence of different particle sizes on the physical and chemical properties and functional properties of ultrafine powders, as well as its influence on the relevant characteristics of food matrices.
3. Development and utilization of functional food processing
Because the cell structure of some raw materials rich in natural active ingredients is tough and not easy to be destroyed, the release rate of the nutrients and functional ingredients contained in them is usually at a low level, which cannot be fully developed and used. Ultrafine pulverization technology brings the possibility to destroy the cell structure and improve its nutrient release efficiency. Studies have shown that proper ultrafine pulverization can improve the hydration properties of raw materials, while excessive pulverization will reduce the hydration properties; at the same time, within an appropriate range, the dissolution rate of active ingredients will gradually increase with the decrease of particle size.
4. Other aspects
Research on ultrafine pulverization technology also focuses on the flavor components of spices, usually using low-temperature ultrafine pulverization technology. At present, some researchers have pretreated rattan pepper, dried pepper, and ginger through ultrafine pulverization technology, and studied their flavor. The research results show that the appropriate particle size will enhance the aroma of raw materials, and the aroma will not be lost in the later storage process; too small particle size will cause the aroma to lose faster with the prolongation of storage time.
Application of jet pulverization equipment in the production of titanium dioxide
1. Titanium dioxide requirements for crushing
Titanium dioxide used as a pigment has excellent optical properties and stable chemical properties. Titanium dioxide has very high requirements on particle size, particle size distribution and purity. Generally, the particle size of titanium dioxide is based on the wavelength range of visible light, that is, 0.15m ~ 0.35m. And as a white basic pigment, it is very sensitive to the increase of impurities, especially iron impurities, and the increase is required to be less than 5 ppm when pulverized. In addition, titanium dioxide is also required to have good dispersibility in different coating systems. Therefore, the general mechanical crushing equipment is difficult to meet the requirements, so the final crushing of titanium dioxide (finished product crushing), at present, jet mills are used at home and abroad.
2. The choice of jet mill for titanium dioxide production
According to the crushing requirements of titanium dioxide: narrow particle size distribution, less increase in inclusions, good dispersibility, etc., and the material characteristics of titanium dioxide: high viscosity, poor fluidity, fine particle size and easy wall attachment, etc. The flat type (also known as horizontal disc type) jet mill with high-level function is used as the final crushing equipment for titanium dioxide;
And use superheated steam as the crushing medium. Because the steam is easy to get and cheap, the pressure of the steam working medium is much higher than that of the compressed air and it is also easy to increase, so the kinetic energy of the steam is larger than that of the compressed air. At the same time, the cleanliness of superheated steam is higher than that of compressed air, with low viscosity and no static electricity. Moreover, while crushing, it can eliminate the static electricity generated by material collision and friction, and reduce the secondary cohesion of powdered materials. In addition, crushing at high temperature can improve the application dispersibility of titanium dioxide and increase the fluidity of titanium dioxide. The energy consumption of superheated steam is low, which is only 30% to 65% of that of compressed air.
In addition, using a flat jet mill, organic additives can be added while pulverizing to organically modify the surface of titanium dioxide to increase the dispersibility of titanium dioxide in different application systems.
3. Factors affecting jet milling equipment
(1) Jet mill: As the most important equipment for jet milling, the quality of the jet mill directly determines the quality of the product. The gas powder machine is required to be reasonably designed, well-made, with high impact kinetic energy, good classification effect, wear resistance and high temperature resistance. Therefore, it is very important to choose a gas powder machine.
(2) Steam quality: The crushing medium of jet milling is superheated steam. If the steam quality does not meet the crushing requirements, it will seriously affect the quality of gas powder. Generally, the requirements for the steam of the gas powder machine are: the pressure is 1.6-2.0 MPa, and the temperature is between 290 ° C and 310 ° C. If the temperature and pressure are lower than the requirements, the impact kinetic energy will be low, the crushing force will be reduced, the heat of the system will not be enough, the material will be easily affected by moisture and many other unfavorable factors, which will affect the crushing effect, block the system, and make it unable to operate normally; if the temperature and pressure are too high, it will damage the damage to equipment within the system.
(3) Process control: Jet milling requires stable and continuous operation, and the fluctuation of steam and feed amount should be controlled within a certain range. The adjustment must be adjusted slowly, and it is strictly forbidden to be suddenly large or small. In addition, once the air-powder system is normal, it should keep running continuously, and avoid frequent driving and parking. Furthermore, the operating procedures should be strictly followed when driving and parking.
(4) System monitoring: In order to ensure the normal operation of the system, necessary monitoring equipment must be installed in a reasonable position of the system, so that timely adjustments can be made according to changes in the situation.
Application of Superfine Talc Powder in Coatings and Paints
The nature of ultrafine talc powder is a natural hydrous magnesium silicate mineral. It is inert to most chemical reagents and does not decompose when in contact with acids. It is a poor conductor of electricity, low thermal conductivity and high thermal shock resistance. It does not decompose at a high temperature of 900°C. These excellent properties of talc make it a good filler, which can be used to fill plastics or be used as an excellent filler in paints and paints.
1. Talc powder and industrial coatings
The main advantages of coating talcum powder in coating applications are: high natural whiteness, generally do not need chemicals for bleaching, can improve whiteness, softness, smoothness, gloss, and can prepare high-solid content coatings.
Talc can be used in many industrial coatings, especially primers. Talc powder can be used in whole or in part for the steel structure primer, which can improve the precipitation of the paint, the mechanical force of the coating film and the recoatability. Talc is preferred for many manufactured and flash primers and vehicle paints. Sheet magnesium silicates, including talc, are suitable for use in metallic primers because of their ability to improve sanding and water resistance, which may arise from the fact that the flake particles extend the path of moisture through the film.
Because talc has excellent physical and chemical properties such as lubricity, anti-adhesion, flow aid, fire resistance, acid resistance, insulation, high melting point, chemical inactivity, good hiding power, softness, good gloss, and strong adsorption, it is widely used in The application in coatings is mainly reflected in: in coatings, talc powder is used as a filler, which can play a skeleton role, reduce manufacturing costs and improve the film hardness of coatings. It can mainly increase the stability of the product shape, increase the tensile strength, shear strength, bending strength, pressure strength, reduce deformation, elongation, thermal expansion coefficient, high whiteness, uniform particle size and strong dispersion.
As a filler of polyurethane waterproof coatings, talc powder can not only reduce the volume shrinkage of the coating during curing, improve the wear resistance and adhesion of the coating, reduce the cost, but also make the coating have good storage stability and heat resistance.
The influence of talcum powder as a filler on the elastic elongation and tensile strength of waterproof coatings shows a similar trend: that is, with the increase of fillers, the elastic elongation and tensile strength of waterproof coatings both increase first, and a maximum value, and then continue to decrease until an optimal value appears in the middle. Considering from the molecular point of view, when the amount of talcum powder is extremely small, the particles without talc powder will be dispersed in the middle of the macromolecular chain segments, so the attraction between the macromolecular chain segments cannot be reduced, and the macromolecular chain segments are very weak. Difficult to move, resulting in small elastic elongation of waterproof coating; with the increase of the amount of talcum powder, its small particles will continue to fill between the chain segments of macromolecules, the movement of the chain segments is strengthened, and the elastic elongation When the small inorganic particles of talcum powder just fill the gaps between the macromolecular chains, the defects in the curing system of the waterproof coating are the fewest, and the tensile strength and elongation of the waterproof coating reach an optimum. value; but too much filler will weaken the force between the macromolecules and reduce the cohesive energy of the waterproof coating, resulting in a decrease in tensile strength.
2. Application of talcum powder in latex paint
Latex paint is one of the essential paints in our lives. Now our country often uses latex paint in the decoration process. Good quality latex paint is very popular. And if you want latex paint to meet the high quality requirements, you must rely on the help of talcum powder.
Adding talcum powder to latex paint can increase the hardness of the paint, so that the difficulty of construction can be reduced when adding latex paint, so that the aesthetics of building construction can also be improved. Talc powder is an essential and important part of paint, and only the paint with talcum powder can have better corrosion resistance. But it should be noted that talcum powder is not added in unlimited quantities. If too much talcum powder is added to the latex paint, it will precipitate the latex paint and reduce the quality of the paint, and if it is used too little, it will affect the practicality and beauty of the latex paint.
In addition, when adding talcum powder, attention must also be paid to its adding temperature, otherwise it will also affect the quality of latex paint.
The difference between crystallization, fusion and spherical silica powder
According to different classification standards, silicon powder is divided into different types, such as ordinary silicon powder, electrical grade silicon powder, electronic grade silicon powder, semiconductor grade silicon powder, etc. according to the use and purity, and can be divided into crystalline silicon powder according to the crystallization characteristics. Micropowder, fused silica powder, etc.; according to particle shape, it can be divided into angular silica powder, spherical silica powder, etc.
At present, the industry often uses two classification methods of crystallization characteristics and particle shape to classify related products. Angular silica powder can be divided into two categories: crystalline silica powder and fused silica powder, while spherical silica powder is further prepared on the basis of angular silica powder.
1. Crystalline silica powder: simple process and low cost
The main raw material of crystalline silica powder is selected high-quality quartz ore, which is a silica powder material processed through grinding, precision classification and impurity removal, which can improve the physical properties such as linear expansion coefficient and electrical properties of downstream products such as copper clad laminates. .
Its advantage lies in its early start, mature and simple process, low requirements for production hardware and relatively cheap price, and it has a great effect on improving the performance of copper clad laminates in terms of stiffness, thermal stability and water absorption. The main disadvantage is that the improvement of the resin system is not as good as that of spherical silica powder. The specific performance is that the dispersibility, sedimentation resistance and impact resistance are lower than that of spherical silica powder, and the thermal expansion coefficient is higher than that of spherical silica powder.
2. Fused silica powder: better performance, middle cost
The main raw material of fused silica powder is selected quartz with high-quality crystal structure, which is refined by acid leaching, water washing, air-drying, high-temperature melting, crushing, manual sorting, magnetic separation, ultra-fine crushing, grading and other processes. Micronized.
Compared with crystalline silica powder, fused silica powder has the advantages of lower density, hardness, dielectric constant, and thermal expansion coefficient. And other industries, its main disadvantages are the high melting temperature in the preparation process, complex process, although the dielectric constant is improved compared with crystalline silicon micropowder, it is still higher, and its production cost is higher than that of crystalline silicon micropowder.
3. Spherical silica powder: good performance and high cost
Spherical silicon micropowder means that the individual particles are spherical, a kind of high-strength, high-hardness, inert spherical particles, which are irregularly shaped and selected angular silicon micropowder particles are instantly melted at high temperature to make them spheroidized under the action of surface tension , and then processed by cooling, grading, mixing and other processes of silica powder. Spherical microsilica powder has good fluidity and a high filling amount in the resin. After being made into a plate, the internal stress is low, the size is stable, the thermal expansion coefficient is low, and it has a higher bulk density and a more uniform stress distribution. Therefore, it can increase the filler. fluidity and reduced viscosity.
In addition, spherical silica powder has a larger specific surface area than angular silica powder, which can significantly reduce the linear expansion coefficient of copper-clad laminates and epoxy molding compounds, improve the reliability of electronic products, and reduce the impact on equipment during the manufacture of related products. and mold wear. Its disadvantage is mainly that the preparation process is complicated and the cost is high.
The three microsilica powders have different application fields due to their different parameters. Generally speaking, the application fields are gradually becoming high-end in the order of crystalline silica powder, fused silica powder, and spherical silica powder. Crystalline silica powder is commonly used in electrical grade applications, such as copper clad laminates for home appliances, switches, wiring boards, chargers, etc.; fused silica powder is often used in electronic grade applications, such as copper clad laminates used in smartphones, tablet computers, and automobiles. Epoxy molding compounds, adhesives, etc. used in chip packaging; spherical silica powder is mainly used in the manufacture of epoxy molding compounds for high-end chips, and as fillers for copper clad laminates for high-frequency and high-speed circuits.
The difference between crystallization, fusion and spherical silica powder
According to different classification standards, silicon powder is divided into different types, such as ordinary silicon powder, electrical grade silicon powder, electronic grade silicon powder, semiconductor grade silicon powder, etc. according to the use and purity, and can be divided into crystalline silicon powder according to the crystallization characteristics. Micropowder, fused silica powder, etc.; according to particle shape, it can be divided into angular silica powder, spherical silica powder, etc.
At present, the industry often adopts two classification methods of crystallization characteristics and particle shape to classify related products. Angular silica powder can be divided into two categories: crystalline silica powder and fused silica powder, while spherical silica powder is further prepared on the basis of angular silica powder.
1. Crystalline silica powder: simple process and low cost
The main raw material of crystalline silica powder is selected high-quality quartz ore, which is a silica powder material processed through grinding, precision classification and impurity removal, which can improve the physical properties such as linear expansion coefficient and electrical properties of downstream products such as copper clad laminates. .
Its advantage lies in its early start, mature and simple process, low requirements for production hardware and relatively cheap price, and it has a great effect on improving the performance of copper clad laminates in terms of stiffness, thermal stability and water absorption. The main disadvantage is that the improvement of the resin system is not as good as that of spherical silica powder. The specific performance is that the dispersibility, sedimentation resistance and impact resistance are lower than that of spherical silica powder, and the thermal expansion coefficient is higher than that of spherical silica powder.
2. Fused silica powder: better performance, middle cost
The main raw material of fused silica powder is selected quartz with high-quality crystal structure, which is refined by acid leaching, water washing, air-drying, high-temperature melting, crushing, manual sorting, magnetic separation, ultra-fine crushing, grading and other processes. Micronized.
Compared with crystalline silica powder, fused silica powder has the advantages of lower density, hardness, dielectric constant, and thermal expansion coefficient. And other industries, its main disadvantages are the high melting temperature in the preparation process, complex process, although the dielectric constant is improved compared with crystalline silicon micropowder, it is still higher, and its production cost is higher than that of crystalline silicon micropowder.
3. Spherical silica powder: good performance, high cost
Spherical silicon micropowder means that the individual particles are spherical, a kind of high-strength, high-hardness, inert spherical particles, which are irregularly shaped and selected angular silicon micropowder particles are instantly melted at high temperature to make them spheroidized under the action of surface tension , and then processed by cooling, grading, mixing and other processes of silica powder. Spherical microsilica powder has good fluidity and a high filling amount in the resin. After being made into a plate, the internal stress is low, the size is stable, the thermal expansion coefficient is low, and it has a higher bulk density and a more uniform stress distribution. Therefore, it can increase the filler. fluidity and reduced viscosity.
In addition, spherical silica powder has a larger specific surface area than angular silica powder, which can significantly reduce the linear expansion coefficient of copper-clad laminates and epoxy molding compounds, improve the reliability of electronic products, and reduce the impact on equipment during the manufacture of related products. and mold wear. Its disadvantage is mainly that the preparation process is complicated and the cost is high.
The three microsilica powders have different application fields due to their different parameters. Generally speaking, the application fields are gradually becoming high-end in the order of crystalline silica powder, fused silica powder, and spherical silica powder. Crystalline silica powder is commonly used in electrical grade applications, such as copper clad laminates for home appliances, switches, wiring boards, chargers, etc.; fused silica powder is often used in electronic grade applications, such as copper clad laminates used in smartphones, tablet computers, and automobiles. Epoxy molding compounds, adhesives, etc. used in chip packaging; spherical silica powder is mainly used in the manufacture of epoxy molding compounds for high-end chips, and as fillers for copper clad laminates for high-frequency and high-speed circuits.