Application and market of silicon powder
Silicon micropowder is a kind of non-toxic, odorless and non-polluting silica powder processed by grinding, precision classification, impurity removal, high-temperature spheroidization and other processes as raw materials of crystalline quartz, fused quartz, etc. It is an inorganic non-metallic material with excellent properties such as high heat resistance, high insulation, low linear expansion coefficient and good thermal conductivity.
Classification and varieties of silica powder
Purity (%) by use and w(SiO2): ordinary silicon powder (>99%), electrical grade silicon powder (>99. 6%), electronic grade silicon powder (>99. 7%), semiconductor grade silicon powder (>99.9%) etc.
According to chemical composition: pure SiO2 silicon powder, composite silicon powder with SiO2 as the main component, etc.
According to particle shape: angular silicon powder, spherical silicon powder, etc.
In addition, there are classifications based on particle size, surface activity, etc.
- Angular silicon powder
According to the types of raw materials, it can be further subdivided into crystalline silicon powder and fused silicon powder.
Crystalline silicon powder is a silica powder material made of quartz block, quartz sand, etc., which is processed through grinding, precision classification, and impurity removal. It improves the linear expansion coefficient and electrical properties of copper clad laminates and epoxy resins. The performance of packaging materials and other products.
Fused silica powder is made of fused silica, glass, etc. as raw materials, and is made through grinding, precision classification and impurity removal processes, and its performance is greatly improved compared with crystalline silica powder.
- Spherical silica powder
Using selected angular silicon micropowder as raw material, it is processed into spherical silica powder material by flame method and other processes. It has excellent characteristics such as good fluidity, low stress, small specific surface area and high bulk density.
Compared with spherical silicon powder, the production process of angular silicon powder is relatively simple, and the application field is relatively low, so the value is relatively low; while spherical silicon powder has better fluidity, it can be used as a filler to obtain higher filling rate and uniformity, and the price Relatively high, so the price is 3 to 5 times that of angular silicon powder.
Spherical silicon powder is classified according to its particle size and can be divided into three types: micron spherical silicon powder (1-100μm), submicron spherical silicon powder (0.1-1.0μm) and nano-spherical silicon powder (1-100nm).
With the rapid development of the global electronic information industry and the continuous improvement of 4G, 5G and other technologies, higher technical requirements have been put forward for the lightness, thinness and shortness of electronic products, the packaging performance of the chip and the carrier board for carrying the chip. The spherical silicon micropowder is also moving towards Development in the direction of small particle size and excellent performance. Submicron spherical silica powder has the advantages of small particle size, proper particle size distribution, high purity, smooth surface and no agglomeration between particles, which can make up for the shortcomings of micron spherical silica powder.
Preparation methods of submicron spherical silicon powder: gas phase method, chemical synthesis method, flame method, self-propagating low-temperature combustion method, VMC method... ...
Gas phase method：the prepared product contains high impurities such as HCI and low pH. It cannot be used as the main material in electronic products. It can only be added in a small amount to adjust the viscosity and increase the strength. In addition, the raw materials are expensive, the equipment requirements are high, and the technology More complicated.
Chemical synthesis method：the prepared sub-micron spherical silicon powder is usually low in density, often contains more pores, resulting in a large specific surface area, and there are disadvantages such as the production process is not environmentally friendly.
Flame method：The raw materials used are silicon-source organics, and the safety design requirements of the feed system are stricter and the price of the raw materials is higher, which often results in higher production costs.
Self-propagating low-temperature combustion method：large-scale industrial production has not yet been achieved, and whether it can be industrialized requires further verification.
VMC method：the sub-micron spherical silica powder prepared from metallic silicon has the characteristics of smooth surface and high amorphous content. However, the raw material metallic silicon used is prone to dust deflagration, and there is a greater safety hazard in the production process.
Application and market overview of silicon powder
As a functional filler, silica powder products have unique physical and chemical properties such as high heat resistance, high insulation, low linear expansion coefficient and good thermal conductivity. They can be widely used in copper clad laminates, epoxy plastic packaging materials, electrical insulation materials, adhesives, Ceramics, coatings, fine chemicals, advanced building materials and other fields have penetrated deeply in consumer electronics, household appliances, mobile communications, automotive industry, aerospace, defense and military industry, wind power and other industries. The good development prospects of the downstream application industry provide a good guarantee for the market growth space of the silicon powder industry.
- Copper Clad Laminate
Copper clad laminate is an electronic basic material made by impregnating glass fiber cloth or other reinforcing materials with a resin matrix, one or both sides with copper foil and hot pressing. Fillers are required between the base material and the reinforcing materials. In order to improve the heat resistance and reliability of the printed circuit board (PCB board).
Silicon micropowder has excellent performance in reducing linear expansion coefficient, reducing dielectric properties, improving thermal conductivity, and high insulation. Adding silicon micropowder can improve the physical properties of printed circuit boards such as linear expansion coefficient and thermal conductivity, thereby effectively improving the performance of electronic products. Reliability and heat dissipation; and because the silicon powder has good dielectric properties, it can improve the quality of signal transmission.
At present, the filling ratio of resin in industry practice is about 50%, and the filling ratio of silicon powder in the resin is generally 30%, that is, the weight ratio of silicon powder in the copper clad laminate can reach 15%.
Copper clad laminate is a basic electronic material, and PCB is the key support for circuit components and devices in electronic products, and it is the main downstream industry of copper clad laminate. At present, PCB output value in Asia has accounted for more than 90% of the world's total, and China's PCB output value has accounted for more than 50%.
- Epoxy molding compound
Epoxy molding compound is a key material used to encapsulate chips in electronic products. The filling ratio of silicon micropowder in epoxy molding compound is between 70% and 90%. Taking the average filling ratio of 80% for calculation, the market capacity of silicon micropowder in the domestic epoxy molding compound industry is 80,000 tons.
High-performance integrated circuits have high requirements for materials, and the penetration rate of high-end silicon powder continues to increase. Ultra-large-scale and ultra-large-scale integrated circuits represented by high-end chips have extremely high requirements for packaging materials, not only requiring the use of ultra-fine fillers in packaging materials, but also requiring high purity and low radioactive element content. Traditional angular silicon micropowders have been difficult to meet the requirements. . Spherical silicon powder, especially sub-micron products, has excellent properties such as high heat resistance, high humidity resistance, high filling rate, low expansion, low stress, low impurity, and low friction coefficient, making it indispensable in ultra-large-scale and ultra-large-scale integrated circuit packaging materials. Missing functional filling materials. Therefore, the domestic semiconductor design, manufacturing, packaging and testing and other links continue to be replaced by localization, and the demand for high-end silicon powder has also grown rapidly.
- Demands for honeycomb ceramics, coatings, and high-end building materials are all in force
The main raw materials of honeycomb ceramic products are talc, microsilica powder, alumina, kaolin, cellulose, etc., and microsilica powder for coatings has also increased objectively. Silica powder has a similar structure to titanium dioxide, has excellent performance and low cost, and can effectively replace titanium dioxide.
Benefiting from the implementation of national environmental protection standards, industries such as environmentally friendly adhesives and artificial quartz panels have obtained better development opportunities. Special adhesives used in bridges and high-rise buildings, automotive ignition coil packaging, wind turbines and other fields have quickly obtained With the development, the high-end artificial quartz board industry has also improved. In addition, with the promotion of the country's circular economy and the upgrading of the green environmental protection industry, artificial marble is expected to continue to replace traditional ceramic tiles and natural stones and become a new type of advanced environmentally friendly building materials. It is predicted that in 2025, the demand for silicon powder in the field of advanced building materials may increase by 358%.
Article source: China Powder Network
Air classifier can be used to classify, break up and remove large particles
Airflow classifiers are widely used in chemical, mining, metallurgical and other industries and various dry powder materials to superfine, break up and remove large particles, and can classify spherical, flake and fibrous particles; suitable for chemical, mineral, and building materials , Electronics, pharmaceuticals, pesticides, coatings, dyes, metallurgy and other industries, can perform dry classification of various organic and inorganic substances.
The air current classifier is composed of a set of classification system with cyclone separator, dust collector and induced draft fan. The materials are first moved to the classification area from the inlet of the lower end of the air flow classifier under the suction of the fan, and then move to the classification area at a high speed with the ascending airflow. The gap of the classification wheel blade enters the cyclone separator or dust collector to collect, and the speed of the coarse particles entrained by the part of the fine particles hits the wall and disappears, and then descends along the cylinder wall to the secondary air outlet. The coarse and fine particles are separated, the fine particles rise to the classification zone for secondary classification, and the coarse particles fall to the discharge port for discharge.
Structural characteristics of air classifier:
(1) The air flow classifier is under the action of the high-speed rotating impeller with the jet fine particle ring. When the pressure of the gas flowing through the impeller rises, the high-pressure airflow will flow out of the impeller and pass through the jet fine particle ring. Curved shape, the airflow classifier has a large inlet cross-sectional area and a small outlet cross-sectional area, so the airflow pressure at the outlet is reduced, the speed increases, and it flows out in a rotating direction, which is conducive to classification.
(2) The adjustment mechanism of the air classifier is equipped with three adjustment rods, and a chain is used to keep it moving in synchronization. When the adjusting lever moves upward, the fine powder increases; when the adjusting lever moves downward, the fine powder decreases. The classification point can be continuously adjusted and the particle size of the classification product can reach D97: 3～150 microns. The air flow classifier is suitable for the fine classification of dry micron products.
(3) The control ring is equipped with a control ring to ensure that a suitable cross section is formed between the control ring and the injection fine particle ring, and the flow rate of the control airflow is stable.
(4) The residual air vent is avoided from the dry materials to bring in excess gas, and the temperature in the classification room is higher, and the air will expand, so a residual air vent is designed to keep the airflow in the classification room stable and balanced.
Application scope of air classifier:
1. The air flow classifier for high hardness materials is suitable for silicon carbide, various corundum, boron carbide, alumina, zirconia, garnet, zircon sand, diamond, etc.
2. In terms of non-metallic minerals, the air classifier is used for quartz, graphite, kaolin, calcium carbonate, mica, barite, mullite, medical stone, wollastonite, talc, pyrophyllite, etc.
3. In terms of chemical technology, aluminum hydroxide, silica gel, various dyes, epoxy resins, various additives, etc.
4. In terms of food, the jet mill is used for pollen, hawthorn, pearl powder, various vegetable powder, various Chinese herbal medicines, various cosmetics, antibiotics, etc.
5. In terms of metal materials, jet mills are also used for aluminum powder, magnesium powder, zinc powder, tin powder, copper powder, etc. Jet mills are also used in ceramic materials, refractory materials, electronic materials, magnetic materials, rare earth materials, phosphors, copy material powder, etc.
Working principle and applicable industries of airflow ultrafine pulverizer
The jet mill is a large-scale jet ultrafine pulverizer that uses airflow to carry out superfine pulverization. The jet mill, cyclone separator, dust collector, and induced draft fan constitute a complete pulverization system. The crushing process is to filter and dry compressed air into the crushing cavity through a Laval nozzle. After multiple jets of high-pressure airflow, it will form an intersection. The material is repeatedly collided, rubbed, and sheared at the intersection of the high-pressure airflow. After being cut and crushed, the crushed materials move to the classification area with the upward air flow under the action of the fan suction. Under the strong centrifugal force generated by the rotating classification turbine, the coarse and fine materials are separated, and the fine particles that meet the particle size requirements enter the cyclone through the classification wheel. The separator and the dust collector collect, and the coarse particles that do not meet the particle size requirements drop to the crushing area and continue to be crushed.
The airflow ultrafine pulverizer is more suitable for dry pulverization of various materials with a Mohs hardness of 9 or less, and is especially suitable for the pulverization of materials with high hardness, high purity and high added value. The particle size of the material crushed by the airflow ultrafine pulverizer is adjustable between D50:1~45μm, with good particle shape and narrow particle size distribution. And in the crushing process, there is no medium for low-temperature crushing, which is especially suitable for crushing heat-sensitive, low melting point, sugar-containing and volatile materials. The pulverization process of the airflow ultrafine pulverizer relies on the collision between the materials themselves, which is different from the mechanical pulverization which relies on the impact of blades or hammers on the materials, so the equipment is wear-resistant and the product purity is good.
The airflow superfine pulverization, easy disassembly and washing, smooth inside without dead corners, the pulverization process is airtight, no dust pollution, low noise, and the production process is very clean and environmentally friendly. The control system adopts program control, and the operation is simple.
Airflow ultra-fine pulverizers are widely used in chemical, mining, abrasives, refractory materials, battery materials, metallurgy, building materials, pharmaceuticals, ceramics, food, pesticides, feed, new materials, environmental protection and other industries and the ultra-fine grinding of various dry materials, It has a wide range of applications for breaking up and shaping particles.
What are the factors affecting the fineness of the jet mill
In recent years, with the development of technology, new industries have brought a ray of life. Many chemical industries and applications of ultra-fine pulverization of polymer materials (such as carbon black) will use airflow ultra-fine pulverizers. The airflow superfine pulverizer has many advantages. Under the action of the airflow, the material itself can collide to achieve the required fineness, thus ensuring the purity of the material. The better the brittleness of the material, the finer the crushing process, the greater the output.
Jet mill, also known as jet mill, jet mill or fluid energy mill, is a device that uses the energy of airflow (300-500m/s) or superheated steam (300-400℃) to pulverize solid materials. As one of the commonly used ultra-fine grinding equipment, jet mills are widely used in ultra-fine grinding and dispersing forming of ultra-hard materials such as chemical materials, medicines and foods, and metal powders.
The jet mill has a wide range of crushing particle sizes and is simple and convenient to operate. However, in the crushing process, the crushing effect is often different. The crushing effect of the jet mill is mainly affected by the following factors: gas-solid ratio, feed particle size, temperature and pressure of the working fluid, and crushing aids.
- Gas-solid ratio
The gas-solid ratio of the jet mill during smashing is an important technical parameter and also an important index. If the gas-solid ratio is too small, the kinetic energy of the air flow will be insufficient, which will affect the fineness of the product. However, if the gas-solid ratio is too high, not only energy will be wasted, but also the dispersion performance of some pigments will be deteriorated.
- Feed size
When crushing hard materials, there are also strict requirements for the particle size of the feed. As far as titanium powder is concerned, it is necessary to control 100-200 mesh when crushing the calcined material; the material after crushing surface treatment is generally 40-70 mesh, not exceeding 2-5 mesh.
- Working fluid temperature
When the temperature of the working fluid is too high, the flow rate of the gas will increase. Taking air as an example, the critical speed at room temperature is 320m/s. When the temperature rises to 480℃, the critical speed can be increased to 500m/s, that is, the kinetic energy increases by 150%. Therefore, increasing the temperature of the working fluid is beneficial to improve the crushing performance. Effect.
- Working fluid pressure
The pressure of the working fluid is the main parameter that produces the jet flow velocity, and it is also the main parameter that affects the pulverization fineness.
Generally speaking, the higher the working fluid pressure and the faster the speed, the greater the kinetic energy. The crushing pressure mainly depends on the crushability and fineness requirements of the material. For example, when superheated steam is used to pulverize titanium powder, the vapor pressure is generally 0.8-1.7MPa, while the pulverized and calcined material is generally higher, and the surface-treated material after pulverization can be lower.
Jet mills are widely used in chemical, mining, abrasives, refractory materials, battery materials, metallurgy, building materials, pharmaceuticals, ceramics, food, pesticides, feed, new materials, environmental protection and other industries and the ultrafine grinding of various dry powder materials. Dispersion and particle shape shaping have been widely used.
Jet mill has outstanding advantages for processing ternary cathode materials
Generally speaking, there are basically two kinds of ternary cathode materials, one is nickel cobalt lithium aluminate NCA and the other is nickel cobalt manganese lithium NCM. The main purpose is to use in ternary cathode material batteries.
In the processing of ternary materials, the main steps are in three aspects. The first is: mixed abrasives, the second is: high temperature sintering, and the third is: crushing and decomposition. The material particles can be pulverized by a purchased jet pulverizing classifier to achieve the appropriate particle size requirements, and then sieved through classification to obtain the desired ideal particles of ternary materials. The ideal particle is usually around 42μm, and the fluctuation cannot exceed 6μm. This kind of particle can be processed by a jet mill.
The jet mill has outstanding advantages for processing ternary cathode materials, and its performance lies in:
- It has the ability to shape the particles and control the particle size. The finished particles have excellent shape and can be used for different material characteristics and requirements.
- The material distribution is narrow, and the finished product has a high tap density.
- Over-grinding is low, and the finished product rate can reach over 96%.
- The equipment is lined with wear-resistant materials, the equipment wears little, and the finished product has high purity.
- Using frequency converter for precise control, the material fineness can be adjusted arbitrarily between 0.5-100 μm.
- Full negative pressure operation, low noise, no dust pollution.
The jet mill used to crush ternary materials has a built-in high-precision turbine classification system, which can accurately separate the specified particle size after crushing, and the whole machine adopts closed-circuit operation to effectively prevent dust pollution.
Application of powder materials in different kinds of coatings
1. Application of powder materials in coatings
1) Extender pigments (heavy calcium, light calcium, kaolin, etc.) can improve the "dry hiding power" effect of latex coatings, replacing part of the amount of titanium dioxide used (called contrast ratio or hiding ratio) to reduce manufacturing costs.
2) Application of wollastonite powder in intumescent latex fireproof coating
In fire retardant latex coatings, fire retardants and emulsions are important for fire resistance. Although the proportion of fillers used in fire retardant latex coatings is not large, wollastonite, aluminum hydroxide and hollow microspheres are used as fillers in fire retardant latex coatings to account for 5%, 2% and 4%. Among them, wollastonite plays the role of the skeleton of the coating film, aluminum hydroxide plays the role of flame retardant, smoke suppression and cooling, and the air beads play the role of carbon layer strength.
Kaolin and wollastonite with the same fireproof effect of the carbon layer have high expansion, the highest is wollastonite, followed by kaolin, and the lowest time sequence of talc powder is wollastonite>kaolin>talc powder, which means that when the carbon layer reaches a honeycomb shape, The higher the expansion height, the better the heat insulation and fire protection effect. Of course, the carbon layer should not be too high, otherwise it will cause the separation between the carbon layer and the steel plate, which will not play the role of fire prevention. The coating containing Al(OH)3 has the least amount of smoke, especially the longest fire resistance time, and is a very good flame retardant additive.
The order of comparing the five inorganic fillers is: Al(OH)3 >wollastonite>kaolin>talc>CaCO3, so it is the most ideal to use Al(OH)3 as a flame retardant with wollastonite. In the formula, silica fume Stone 5%, Al(OH)3 2% is the most ideal filler layer, with the longest fire resistance time and the least amount of smoke.
3) Application of sericite (muscovite) in latex paints for exterior walls of buildings
Sericite silicate flakes have a strong extinction shielding function, can absorb more than 80% of ultraviolet rays, close to the ultraviolet absorption rate of titanium dioxide, good wear resistance, insulation, good chemical stability, acid and alkali resistance, Water permeability. When adding 5% to latex paint for exterior walls, it can improve the weather resistance of the coating, delay the chalking, discoloration and cracking of the coating, and increase the hardness and toughness of the coating film. A 600-hour artificial aging test was carried out on the latex coating containing Ca4 wet sericite and the latex coating. The aging performance and appearance have been improved from blistering and peeling to non-foaming peeling and no cracking, and the discoloration has changed from level 2 to level 1. Chalking changes from level 3 to level 0 (no chalking), but sericite is not suitable for the obvious matting effect of high-gloss exterior wall latex paint on the paint.
2. The role of powder materials in coatings
Powder materials for coatings include extender pigments, anti-rust pigments, coloring pigments, special pigments, and functional pigments. Among them, extender pigments are a major branch of the powder particle system. Due to the particle size, particle shape, oil absorption, density characteristics of the extender pigment, or the unique characteristics after modification, it has a certain effect and influence on the coating. Especially ultra-fine powder materials until nano-scale materials have a more obvious effect on coatings, and roughly have the following effects:
1) The hiding power of the pigment can be used efficiently
2) The solid content of the paint can be increased, and the limit of harmful volatile organic compounds (VOC) in the paint can be controlled.
3) It can improve the scrubbing resistance of the coating and control the gloss of the coating
4) It can control the sedimentation of the coating system and increase the tensile strength of the coating film.
5) It can adjust the viscosity of the coating system and improve the adhesion of the coating
6) It can improve the abrasion resistance and slip resistance of the coating
7) When the pigment physique concentration in the coating formulation is less than the critical pigment physique concentration, the dry covering power of the coating film can be improved
8) Can be used as a reinforcement and extender for coatings
9) It can improve the stain resistance and corrosion resistance of the coating.
10) A buffering agent that can control the pH of water-based latex coatings
11) It can improve the hand feel of the coating and the hardness of the coating when it feels wet and dry. Extender pigments are not only used as fillers to reduce the cost of coating manufacturing, but also specially processed extender pigments play a role in improving the performance and function of the coating.
Article source: China Powder Network
Factors affecting the production efficiency of fluidized bed jet mill
The fluidized bed jet mill, in the dry mill, has a simple structure and can realize continuous feeding and discharging. It will neither make the material too fine nor too thick. Only materials of qualified size can be used. It is delivered continuously and timely, and its particle size distribution is steep.
Due to the crushing principle of this model, a specially designed nozzle generates a supersonic high-speed airflow. Under the acceleration of the supersonic airflow, the materials to be crushed collide, squeeze and rub against each other and are instantly crushed at the intersection of the nozzles. Since the material does not violently collide with internal parts such as the vessel wall, the equipment is durable and more importantly, it ensures the high purity of the material after crushing. Another important feature is that the gas ejected from the nozzle forms adiabatic expansion in the crushing chamber, and the temperature of the material will not rise during the crushing process. On the contrary, the material is pulverized instantly at low temperature. This pulverization method can pulverize heat-sensitive materials without adding additional refrigerant, and it can also ensure that its physical and chemical properties remain unchanged.
However, the energy consumption per unit output of the fluidized bed jet mill is relatively high. Although this model has many advantages, it still seems to be overburdened for products with low added value.
Nevertheless, people still place great enthusiasm and expectations on the fluidized bed jet mill. Some scholars believe that if the working efficiency of the fluidized bed airflow ultrafine pulverizer can be increased by 1 to 2 times, it will be a very meaningful thing. Due to the improved working efficiency of this model, it will open up a wider range of applications. prospect.
In our long-term experience in the research, development and use of fluidized bed jet mills, we have accumulated a certain amount of practical experience.
If you want to improve the working efficiency of the jet mill, you should first consider two parts, that is, the mill itself and its operating conditions.
(1) Strictly control the feed volume: the feed speed should be appropriate and uniform. In addition, we must also consider which feeding method to use. Some materials need to use a screw feeder, and some materials need to be oscillated. The feeding method should be determined according to the characteristics of the material itself. The most important thing is to ensure that the energy in the crushing room is continuously supplied with materials to meet a certain concentration of materials in the crushing room. Practice has proved that whether the material concentration is too low or the material concentration is too high, it will have an adverse effect on the output of the finished product. The material concentration is low, the probability of contact between materials is small; the material concentration is high, which will affect the airflow speed, both of which are not conducive to the improvement of efficiency. The feed rate of the material should be strictly controlled according to the air pressure, material characteristics and the characteristics of the body itself.
(2) Increase the air velocity and the probability of particle impact. This must be agreed from two aspects. First of all, the nozzle design must be reasonable, and the nozzle layout is also very important. Only by meeting the above two requirements can the goal of improving production efficiency be achieved.
The jet mill breaks the traditional mode of setting nozzles. In the same plane of the crushing chamber, it forms a certain angle with this plane, and several nozzles are arranged symmetrically downwards. In addition, at the bottom of the crushing chamber, the opposite is set A vertically upward nozzle, and the center line of the other nozzles, point to the same focal point. Under the combined action of the air currents ejected from all nozzles, the materials form a conical shape and gather at the focal point, and the materials are instantly crushed. In addition, a mixing tube is installed in front of the nozzle, so that there is no blind zone in the crushing chamber, and the impact probability of particles is increased. Only this modification can increase the efficiency by 150-200%.
(3) Optimize the hierarchical structure. Classification is a crucial part of the ultrafine pulverization system. One of the most notable features of the fluidized bed jet mill is that it can realize continuous feeding and discharging, preventing the material from being finely crushed and causing unnecessary energy consumption. According to the principle of turbine classification, appropriately increasing the diameter of the classifying wheel, increasing the speed, and reducing the air flow are the fundamental guarantees to ensure that the classifier separates the particle size. The relationship between the above three should be controlled according to the characteristics and specific requirements of different materials.
(4) The original material entering the jet mill should be as small as possible. In order to achieve this goal, an ordinary grinder should be used for pre-crushing treatment before ultra-fine pulverization. This is the most direct and effective method to save energy and increase unit output.
(5) Ensure that the fluidized bed jet mill, the airtightness requirements of the entire closed system, including the fully enclosed devices of pipelines, valves, and equipment, should not leak. In short, it is necessary to concentrate precious aerodynamic energy on the nozzles, and strive to increase the gas flow rate and pressure.
(6) The product collection and dust collector should ensure smooth air supply and should not have excessive resistance. This part of the system equipment must not only ensure the collection of qualified products, but also ensure that the environmental requirements are not polluted, but after the equipment is too complicated, things will bring too much burden to the overall work.
Application of calcium carbonate in coatings
Calcium carbonate is a non-toxic, odorless, non-irritating white powder, and it is one of the most widely used inorganic fillers. Calcium carbonate is neutral, basically insoluble in water but soluble in acid. According to the different production methods of calcium carbonate, calcium carbonate can be divided into heavy calcium carbonate, light calcium carbonate, colloidal calcium carbonate and crystalline calcium carbonate.
Calcium carbonate is a common substance on earth. It exists in aragonite, calcite, chalk, limestone, marble, travertine and other rocks. It is also the main component of animal bones or shells. Calcium carbonate is an important building material and has a wide range of industrial uses.
1 Application in latex paint
1.1 The role of heavy calcium
(1) As an extender pigment, it has a filling effect to make it fine, uniform and high whiteness.
(2) It has a certain degree of dry covering power. Generally, ultra-fine products are used. When the particle size is close to that of the titanium dioxide, the covering effect of the titanium dioxide can be improved.
(3) It can improve the strength, water resistance, dryness and scrub resistance of the paint film.
(4) Improve color retention.
(5) Reduce costs and use 10%~50%. Disadvantages: high density, easy to precipitate, the usage amount should not be too large.
1.2 The role of light calcium
(1) As an extender pigment, it has a filling effect, is delicate, and increases whiteness.
(2) Has a certain dry covering power.
(3) The density is small, the specific surface area is large, and it has a certain degree of suspension, which plays a role of anti-settling.
(4) Reduce costs.
(5) Increase the feel. Disadvantages: easy to whiten, swell and thicken, the usage amount should not be too large, and it can not be used in exterior wall coatings.
2 Application in powder coatings
(1) It can be used as a filler for high-gloss coating products.
(2) Semi-gloss paint products can generally be prepared by directly adding calcium carbonate without adding matting agents, which saves costs.
(3) It is a white inorganic pigment that can be used in conjunction with titanium dioxide to reduce costs.
(4) Compared with other fillers, calcium carbonate is most suitable for some environmentally friendly products that require low heavy metal content, such as children's toys and strollers.
(5) It can increase the powdering rate and spraying area of the paint, especially when it is used in mixed powder.
(6) If outdoor weather resistance is required, it cannot be used as a filler.
(7) Because of its high oil absorption, it is easy to cause orange peel on the surface of the paint film. At this time, a little hydrogenated castor oil can be added to the base material.
(8) It acts as a skeleton to increase the thickness of the paint film and improve the wear resistance and durability of the coating.
3 Application in wood coatings
(1) Used as a filler for colored primers to reduce costs.
(2) Increase paint film strength and wear resistance.
(3) Light calcium has a little thickening effect, is easy to thixotropy, and has good anti-settling properties.
(4) Heavy calcium reduces the sandability in the paint film and is easy to precipitate in the tank, so attention should be paid to strengthen the anti-settling property.
(5) Improve the gloss, dryness and whitening of the paint film.
(6) It is not suitable to use with alkali-resistant pigments and fillers.
4 Application in automotive paint
Superfine calcium carbonate with a particle size of less than 80nm is used in car chassis anti-stone coatings and topcoats due to its good thixotropy. The market capacity is 7000~8000 t/a, and the price in the international market is as high as US$1100~1,200 /t.
5 Application in ink
Ultra-fine calcium carbonate is used in ink, showing excellent dispersibility, transparency, excellent gloss and hiding power, as well as excellent ink absorption and drying. It must undergo activation treatment, and the crystal form is spherical or cubic.
Article source: China Powder Network
Ceramic lined jet mill solves the problem of material adhesion
Because of their special material properties, some materials may adhere during the crushing process, which may cause blockage or agglomeration, which brings considerable trouble to the crushing work. After long-term accumulation of experience and continuous innovation and improvement, the ceramic-lined jet mill is specially introduced for the phenomenon of material adhesion.
The fluidized bed jet mill that uses high-hardness engineering ceramics to make all flow-through parts is an ideal crushing equipment for high-hardness, brittle materials, elastic plastic materials, agglomerated materials, and fibrous materials, such as zircon, alumina, rutile titanium White powder, zirconia, talc, kaolin, graphite, paint, pesticide, fertilizer, pollen, food raw materials and other materials are crushed.
Ceramic-lined jet mill not only has the advantages of general fluidized bed jet mills, but also, because the machine's lining is made of high-strength, wear-resistant and high-temperature engineering ceramics, it can not only adapt to high temperature and overheating up to 400℃ The steam working medium does not pollute the material to be pulverized. It is a necessary equipment for high-quality ultra-fine pulverization. At the same time, the cost of airflow ultra-fine pulverization is mainly the cost of the pulverizing working medium, and the superheated steam working medium is higher than the compressed air working medium. The cost is reduced by a quarter. In addition, the superheated steam working fluid will not generate static electricity, so it will not cause wall sticking. Therefore, it is suitable for the production of some materials that will stick to the wall with compressed air at room temperature, such as: titanium dioxide .
The ceramic-lined jet mill is mainly composed of a feeding device, a crushing chamber, a discharge port, a steam distribution pipe and a nozzle. The material of the feed nozzle and the crushing nozzle is made of high-strength, wear-resistant and high-temperature-resistant special alloy, and the nozzle structure is supersonic design; the rest of the flow-through parts are lined with high-strength, wear-resistant and high-temperature engineering ceramics. The material venturi tube, ceramic middle ring, discharge port lining, ceramic upper cover and ceramic lower cover are made of high-strength reaction sintered silicon carbide; the steam distribution pipe and the main engine cover are all made of stainless steel and polished, and the whole machine has a beautiful appearance compact. The ceramic-lined jet mill can be used in conjunction with the jet classifier. According to the physical characteristics of the material and the purity requirements of the finished product, ceramic sheets are lined inside the equipment to increase wear resistance, reduce the impact of materials on the equipment, and increase the use of the equipment Life, and accurately control the iron content of the material in the crushing and grading process. Successfully solved a series of problems such as the adhesion of battery materials, poorly made, and inaccurate classification.
The working principle of the ceramic-lined jet mill: After being filtered and dried, compressed air is sprayed into the milling chamber at high speed through Laval nozzles, and the animal material is repeatedly collided and rubbed at the intersection of the high-pressure airflow to smash. The pulverized coarse and fine mixture is under negative pressure. The fan reaches the classification zone. Under the action of the strong centrifugal force generated by the high-speed rotating classification turbine, the coarse and fine materials are separated. The materials that meet the particle size requirements are collected by the cyclone separator and dust collector through the classification wheel, and the coarse particles drop to the crushing zone to continue. Shattered.
The ceramic-lined jet mill has the following performance advantages:
1. It is suitable for dry pulverization of various materials with Mohs hardness below 9, especially suitable for the pulverization of materials with high hardness, high purity and high added value.
2. The breakthrough of particle acceleration technology has greatly improved the pulverization efficiency and reduced the energy consumption. The pulverization is small, the particle shape is good, the particle size distribution is narrow and there are no large particles, and the product particle size D97=3-74 microns can be adjusted arbitrarily.
3. During the crushing process, the airflow temperature is reduced due to the rapid expansion of the airflow, which is especially suitable for the crushing of heat sensitive, low melting point and volatile materials.
4. The crushing of materials by collision with each other is different from the mechanical crushing which relies on the impact crushing of the materials such as blades or hammers, plus a full range of ceramic lining, so the equipment is less abraded and the product purity is high.
5. It can be used in series with a multi-stage air classifier to produce products with multiple particle sizes at one time.
6. The ceramic-lined jet mill has a compact structure, easy to disassemble and clean, and the inner wall is smooth and has no dead corners.
7. The entire system runs in a closed negative pressure, no dust, low noise, and the production process is clean and environmentally friendly.
8. The dust collector eliminates the problems of low negative pressure and sticking to the machine.
The difference between heavy calcium carbonate and light calcium carbonate
Calcium carbonate, commonly known as limestone, stone powder, marble, and calcite, is a compound with a chemical formula of CaCO3, which is alkaline and basically insoluble in water but soluble in acid. It is a common substance on the earth. It exists in aragonite, calcite, chalk, limestone, marble, travertine and other rocks, and is also the main component of animal bones or shells.
Heavy calcium carbonate and light calcium carbonate are classified according to different methods of calcium carbonate production. They can be distinguished from the following aspects:
1. Powder characteristics
The particles of heavy calcium carbonate are irregular in shape and are polydisperse powder. Its particle size is large, the average particle size is generally 5-10μm, and the distribution is wide. It is almost insoluble in water, soluble in water containing ammonium salt or ferric oxide, and insoluble in alcohol. It will boil and dissolve in dilute acetic acid, dilute hydrochloric acid, and dilute nitric acid. It is decomposed into calcium oxide (CaO) and carbon dioxide (CO2) when heated.
Light calcium carbonate particles have regular shapes and can be regarded as monodisperse powders, but they can be in various shapes, such as spindle, cubic, needle, chain, spherical, flake, and quadrangular prism. These different shapes of calcium carbonate can be prepared by controlling the reaction conditions. Its particle size is small, the average particle size is generally 1-3μm, and the distribution is narrow. It is hardly soluble in water and alcohol, soluble in acid, and emits carbon dioxide at the same time, showing an exothermic reaction. Also soluble in ammonium chloride solution. It is stable in the air and has a slight moisture absorption capacity.
Heavy calcium carbonate and light calcium carbonate are different in shape, particle size, etc. It is these differences that make them have different effects on physical and chemical properties and produce different effects.
2. Production process
The heavy calcium carbonate adopts the crushing method, and the white stone containing more than 90% CaCO3 is crushed, classified and separated with a Raymond mill or other high-pressure mill to obtain the finished product.
Light calcium carbonate adopts the carbonization method, which is the finished product is obtained by mixing limestone and white coal in a certain proportion, calcination at high temperature, water digestion, carbonization of carbon dioxide, centrifugal dehydration, drying, cooling, crushing and sieving.
The production process of light calcium carbonate is relatively complicated, and different production methods make them shine in different fields.
3. Purpose
Heavy calcium carbonate has a wide range of uses. It can be filled in rubber to obtain higher tensile strength, tear strength and abrasion resistance than pure rubber vulcanizates. It can play a role as a skeleton when used in plastic products, which has a great effect on the dimensional stability of plastic products, and can also increase the hardness of the products, and improve the surface gloss and surface smoothness of the products. It is used in the water-based coating industry to make the coating non-settling and easy to disperse. The heavy calcium carbonate used in papermaking can ensure the strength and whiteness of the paper, and the cost is low. Heavy calcium carbonate is used in concrete in the construction industry to play an important role, which can increase the toughness and strength of the product. It is used in the floor tile industry to increase the whiteness and tensile strength of the product, improve the toughness of the product, and reduce the production cost.
Light calcium carbonate can be used as a filler in industries such as rubber, plastics, papermaking, coatings and inks, and is widely used in the production of organic synthesis, metallurgy, glass and asbestos. It can also be used as a seeding agent for industrial wastewater, an antacid for gastric and duodenal ulcers, an antidote for acidosis, an SO2 scavenger in SO2-containing exhaust gas, an additive for dairy cattle feed, and an anti-sticking agent for linoleum. . It can also be used as a raw material for tooth powder, toothpaste and other cosmetics.
With the continuous advancement of powder technology, the application fields of calcium carbonate are constantly expanding, and they will also exert greater advantages in the future.
Article source: China Powder Network