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.
Processing technology and requirements of quartz sand for plates
Artificial quartz stone is a kind of artificial stone, which refers to an artificial stone made of unsaturated polyester resin (UPR) as the binder, quartz sand and glass particles as the main aggregate, and quartz powder as the main filler. . Quartz stone inherits the advantages of hard texture, corrosion resistance and wear resistance of natural granite as well as exquisite color and high grade of natural marble.
The main aggregates and fillers in quartz stone slabs are quartz sand and quartz powder respectively. Except for a few high-end products with high whiteness and high transparency, the general requirements are relatively low, mainly for whiteness, transparency, impurities, and particle size. .
1. Quartz sand aggregate processing technology and index requirements
Quartz sand plays the role of aggregate in quartz stone slabs, and other aggregate raw materials include glass, metal, alumina or other minerals (such as granite).
According to the transparency of quartz sand, it can be divided into transparent sand, semi-permeable sand and ordinary sand. On some high-end panels, in order to pursue the three-dimensional layering of the pattern and texture and simulate the high-end pattern and texture of natural stone as much as possible, it is necessary to use quartz sand with high permeability. The higher the permeability of quartz sand, the less impurities, the higher the purity, and the higher the price.
In order to produce high-quality plates, it is necessary to use high-quality quartz sand as raw material. First, a good mineral source must be selected, and then the quartz ore should be washed, sorted and polished to remove miscellaneous stones, and then crushed or ball-milled and sieved to obtain the specified target. Number of pellets or powder. Extremely high-quality quartz ore can be broken directly without pickling to produce fine sand; however, there are fewer and fewer high-quality ore sources of this grade, and most quartz ore need pickling in the sand-making process to obtain high-quality plate sand: for large stones Carry out pickling, and then crush it into sand, with little acid residue, which has little effect on the performance of the later plate; after pickling the sand broken into fine particles, the residual acid must be removed, otherwise the quartz stone plate surface will have the problem of yellowing in the later stage .
2. Quartz powder filler processing technology and index requirements
Quartz powder is divided into ordinary quartz powder and modified quartz powder (that is, quartz powder treated with surfactant). Modified quartz powder improves the compatibility with resin and can reduce the amount of resin.
The surface modifier of quartz powder is mainly a silane coupling agent. There are three main methods of surface chemical modification: dry modification, wet modification and chemical coating modification: dry modification is to add a small amount of diluent and The treatment agent made of silane is added into the quartz powder in the form of spray under high-speed stirring, dispersion and certain temperature conditions, and the material is discharged after stirring for a certain period of time.
Wet modification is to use the prepared surface modifier and auxiliary agent to mix and prepare the treatment liquid, to modify the surface of the quartz sand powder under stirring dispersion and certain temperature conditions, and then dehydrate and dry.
Mechanical grinding and chemical coating modification refer to the addition of modifiers in the process of mechanical force or fine grinding and ultrafine grinding, and the surface modification of the particles is carried out as the particle size of the quartz sand powder decreases.
The current surface modification technology of quartz powder is seriously lagging behind the development of the quartz stone industry. A close relative of quartz stone—resin-type artificial granite, the filler used in it—calcium powder, the current surface modification technology has made great progress, and the oil absorption rate can be below 17%. In contrast, quartz powder, after modification The oil absorption rate of quartz powder hovers around 20% for a long time, which leads to high resin consumption and high cost of quartz stone plates, and has adverse effects on some properties of quartz stone finished products - expansion coefficient, hardness, etc.
The higher the whiteness of the quartz powder, the higher the price, and the produced quartz stone plate has high whiteness, high grade and high price. The higher the transparency of the quartz powder, the higher the price. The produced quartz slabs have a good texture and a strong three-dimensional effect, which can better simulate the texture of natural stone.
The commonly used quartz powder mesh numbers of plate manufacturers are: 100~200 mesh, 325 mesh (or 400 mesh), 800 mesh, 1250 mesh, etc.
Three types of surface modification methods for barite powder
Barite is a sulfate mineral of orthorhombic (orthorhombic) crystal system, with relatively stable physical and chemical properties, insoluble in water and hydrochloric acid, high density, good filling, non-toxic, non-magnetic, easy to absorb radiation, good Optical performance and other advantages, it is an important inorganic chemical product, widely used in petrochemical, building materials, plastics, coatings, rubber, automobile brake pads and other industries.
At present, the most effective method is to modify the surface of barite, so that the modifier forms an adsorption layer or a monolayer film on the surface of barite, changes its surface characteristics, and improves its dispersion and compatibility with organic matter. Sex, expand its scope of application, and increase the added value of the product.
The surface modification of barite and its application as a filler have been extensively studied, but there are still two issues in the modification of barite that need to be further studied: one is the selection of suitable modification methods and new modification methods. The first is the development of permanent methods to meet the needs of different types of barite and their application objects; the second is the optimization of modifiers and the development of new modifiers to meet the needs of products with higher performance.
At present, the modification methods for barite mainly include surface chemical coating method, mechanochemical method, chemical deposition method and so on.
1. Surface chemical coating method
The surface chemical coating method is a method of uniformly and stably coating the modifier on the particle surface by chemical action, thereby changing the surface characteristics of the particle.
The mechanism of chemical coating modification on the surface of barite: the surface modifier is adsorbed on the surface of barite or reacts with the hydroxyl groups on the surface to form chemical bonds, so as to organically coat the barite, and use steric repulsion or electrostatic interaction Prevent the collision between particles and cause agglomeration, thereby improving the dispersion of barite.
2. Mechanochemical method
The mechanochemical method mainly uses mechanical force to activate the surface of the particle, and promotes the chemical reaction between the particle and the modifier to achieve the coating of the particle surface.
Mechanochemical modification mechanism of barite: it mainly uses ultra-fine pulverization and other strong mechanical force to activate the surface free energy of powder particles purposefully, so as to change the surface structure, structure and performance of powder, and produce lattice distortion And dislocations, enhance its reactivity with the modifier, greatly improve the powder activity and improve the uniformity of particle distribution and enhance the interface between it and the matrix.
The mechanochemical modification process is relatively simple, the production cost is low, and it has been widely used in practical applications. It is mainly suitable for barite with larger particles, but for nano-barite with smaller particles, a single mechanical Mechanochemical modification is not effective. Further improve the uniformity of the action of the powder and the modifier in the modification process and reduce the amount of the modifier, improve the coating effect by combining with other modification methods, introduce new modification equipment to simplify the process, reduce energy consumption, and improve The environmental protection of the modification process, such as: jet mill, honeycomb, will be the development direction of mechanochemical modification.
3. Chemical deposition method
The chemical deposition method is to add a modifier or a precipitant to carry out a precipitation reaction on the surface of the particle, and after washing, filtering, drying, roasting and other steps, a coating film is firmly formed on the surface of the particle, thereby improving the optical, electrical and magnetic properties of the particle. , heat and other properties.
The mechanism of barite chemical deposition method modification: mainly through the chemical reaction to deposit the modifier on the barite surface to form one or more coating layers, this coating treatment can reduce the surface activity of the particles and prevent them Agglomeration improves the dispersion and stability of barite in different media. This method is mainly suitable for the modification of inorganic surface modifiers, but the reaction process is not easy to control to obtain a uniform coating layer. Therefore, it is necessary to further explore the process conditions and the influencing mechanism that affect the deposition uniformity in the chemical deposition process, so as to improve the controllability of the process.
About Ultrafine Powder Classification Technology
Ultrafine powder is not only the basis for preparing structural materials, but also a material with special functions. field is required. With the application of ultra-fine powder in modern industry more and more widely, the position of powder classification technology in powder processing becomes more and more important.
1. The meaning of classification
In the pulverization process, only a part of the powder usually meets the particle size requirements. If the products that have reached the requirements are not separated in time, and then pulverized together with the products that do not meet the particle size requirements, it will cause energy waste and over-crushing of some products. .
In addition, after the particles are refined to a certain extent, the phenomenon of crushing and agglomeration will appear, and even the crushing process will deteriorate due to the larger particle agglomeration. For this reason, in the process of ultrafine powder preparation, it is necessary to classify the product. On the one hand, the particle size of the product is controlled to be within the required distribution range; Then crush to improve the crushing efficiency and reduce energy consumption.
With the improvement of the required powder fineness and the increase of output, the difficulty of classification technology is getting higher and higher. The problem of powder classification has become the key to restrict the development of powder technology, and it is one of the most important basic technologies in powder technology. one. Therefore, the research on ultrafine powder classification technology and equipment is very necessary.
2. The principle of classification
Classification in a broad sense is to divide the particles into several different parts by using the different characteristics of particle size, density, color, shape, chemical composition, magnetism, and radioactivity. Classification in a narrow sense is based on the fact that particles of different particle sizes are subjected to centrifugal force, gravity, inertial force, etc. in the medium (usually air and water), resulting in different motion trajectories, so as to realize the classification of particles of different particle sizes.
3. Classification of classifiers
According to the medium used, it can be divided into dry classification (the medium is air) and wet classification (the medium is water or other liquids). The characteristic of dry classification is that air is used as fluid, which is relatively cheap and convenient, but it has two disadvantages. One is that it is easy to cause air pollution, and the other is that the classification accuracy is not high. Wet classification uses liquid as the classification medium, and there are many post-processing problems, that is, the classified powder needs to be dehydrated, dried, dispersed, and waste water treatment, etc., but it has the characteristics of high classification accuracy and no explosive dust.
According to whether it has moving parts, it can be divided into two categories:
(1) Static classifier: There are no moving parts in the classifier, such as gravity classifier, inertia classifier, cyclone separator, spiral airflow classifier and jet classifier, etc. This type of classifier has a simple structure, does not require power, and has low operating costs. The operation and maintenance are more convenient, but the classification accuracy is not high, so it is not suitable for precision classification.
(2) Dynamic classifier: There are moving parts in the classifier, mainly referring to various turbine classifiers. This type of classifier is complex in structure, requires power, and consumes a lot of energy, but it has high classification accuracy and is easy to adjust the particle size of the classifier. As long as the rotation speed of the impeller is adjusted, the cutting particle size of the classifier can be changed, which is suitable for precision classification.
Application of active wollastonite powder
Active wollastonite powder is a white, fine, soft powder. The difference from ordinary wollastonite powder is that a layer of fatty acid soap is adsorbed on the surface of the particle, which makes it have colloidal activation performance, and its relative density is lower than that of ordinary wollastonite (approx. 2.3-2.5), the production process is basically the same as that of ordinary wollastonite powder, except that a surface treatment process is added.
Application range: Wollastonite powder after high temperature activation has a wide application range, and has been widely used in natural rubber, synthetic rubber, epoxy resin, phenolic resin, thermoplastic polyester, thermosetting polyester, polyolefin, polypropylene, polyethylene , polyvinyl chloride, unsaturated resin, leather, nylon, glass steel, ceramics, paint and coatings and other industries. Its body shape can replace harmful substances such as asbestos and glass fiber. It can replace some expensive titanium dioxide, and can replace 30% lithopone in paint. The advantage of activated wollastonite powder itself containing silicon dioxide can replace 50%-80% of white carbon black. Wollastonite has acicular shape and white glass luster and has been applied to various industrial fields. It has the reputation of industrial monosodium glutamate.
Active wollastonite powder is used in the rubber industry: firstly, it can reduce the production cost of the product and increase the bulk density; more importantly, it can improve the comprehensive performance of the product as a functional filler. Such as strengthening and reinforcing products; adjusting the fluidity of rubber and the plasticity of mixing, anti-shrinkage, surface properties, etc., can improve the chemical properties of rubber products, such as reducing permeability, changing interface reflection, water resistance and weather resistance, Fire retardant, oil resistant coloring and opacity. It can also improve the heat resistance and electrical insulation of the product. Increase the heat distortion temperature of the product; reduce the specific heat and increase the thermal conductivity. It can replace white carbon black, and the main properties of its products have been improved to varying degrees; such as hardness, elongation, breaking strength, permanent deformation and volume wear, etc. are superior to white carbon black. It has a very good reinforcing effect. Especially suitable for high wear-resistant products such as rubber shoes and tires.
Active wollastonite is used in some products of paints and coatings: it replaces part of lithopone and titanium dioxide to improve the fluidity of coatings. The particle shape of wollastonite is a good suspending agent for coatings. Enhancer for clean paints with high loading due to low oil absorption. The consumption of adhesive substances is reduced, so the cost of coatings is greatly reduced. The alkaline nature of wollastonite is very suitable for polyvinyl acetate coatings, so that the coloring can be evenly dispersed. It can connect pigments suitable for acidic media, and can also be made into bright colored coatings. The surface has uniform distribution and good spraying performance. As a filler; it can improve the corrosion resistance of the fresh coating. It is suitable for water-based coatings such as polyvinyl formal, and can also be used for low-grade paints, intermediate coatings, road marking coatings; sound-proof coatings; fire-resistant coatings, asphalt coatings can replace asbestos. Wollastonite powder can be used as a reinforcing agent in self-cleaning paint. It can be used in white alkyd enamel to replace part of titanium dioxide; wollastonite powder after silane surface treatment can be used in iron red epoxy ester primer and iron red alkyd primer to replace all talcum powder, precipitated barium sulfate and smelted zinc oxide .
Application of Superfine Pulverization Technology in Food Industry
Ultrafine pulverization technology is to use mechanical or fluid power methods to crush materials, and the particle size reaches micron level, so that the structure and surface area of materials are changed. The plant cell wall can be broken by the ultrafine pulverization technology, so that the effective substances in the cells can be released quickly. Ultrafine pulverization can be divided into dry pulverization and wet pulverization. According to different pulverization principles, dry pulverization includes airflow type, high-frequency vibration type, rotating ball (rod) grinding type, hammering type and self-grinding type. ; There are colloid mill and homogenizer for wet pulverization.
Application of Superfine Pulverization Technology in Food Industry
1. Soft drink processing
At present, the soft drinks that have been developed by using the airflow micro-grinding technology include powdered tea, bean solid drinks and calcium-enriched drinks formulated with ultrafine bone powder. Tea culture has a long history in China. If tea leaves are made into powdered tea (with a particle size of less than 5 μm) at room temperature and in a dry state, the human body’s absorption rate of its nutrients can be improved. Adding tea powder to other foods can also develop new tea products.
2. Fruit and vegetable processing
Vegetables are ground into micro-paste powder at low temperature, which not only preserves nutrients, but also makes the fiber taste better due to the micronization. Such as loquat leaf powder, sweet potato leaf powder, mulberry leaf powder, ginkgo leaf powder, bean protein powder, jasmine flower powder, rose pollen, licorice powder, dehydrated vegetable powder, chili powder, etc. In addition, ultrafine grinding can also be used in the preparation of pumpkin powder, garlic powder, celery powder, etc.
3. Grain and oil processing
Adding ultra-finely pulverized wheat bran powder, soybean micropowder, etc. to flour can be made into high-fiber or high-protein flour; soybeans are processed into soybean milk powder after ultrafine pulverization, which can remove fishy smell; mung beans, red beans and other beans It can also be made into high-quality bean paste, soybean milk and other products after ultrafine grinding. Rice, wheat and other grains are processed into ultra-micron powder due to the fine particle size and the activation of surface state starch. The food made by filling or mixing it has excellent processing performance, and is easy to ripen, with good flavor and taste.
4. Aquatic product processing
Spirulina, kelp, pearl, turtle, shark cartilage and other superfine powders have unique advantages. Yang Jun ultrafinely pulverized the turtle shell to less than 10 μm. Animal experiments showed that the animals had enhanced calcium absorption and enhanced immune regulation ability.
5. Functional food processing
6. Seasoning processing
Superfine pulverization can finely crush traditional seasonings (mainly spices) into fine ultrafine particles with uniform particle size and good dispersibility. As the particle size decreases, its fluidity, solubility and absorption rate all increase, and the huge porosity makes the aroma contained in the cavity last for a long time, so the aroma and taste of the superfine powder condiment are very strong, pure, and delicious. It is also better, suitable for the production of instant and convenience food. Sun Junshe and others superfinely pulverized seasoning, stewed meat king, thirteen spices, and cumin to 10-25 μm, which improved the color, aroma, taste and processing characteristics of food.
7. Fresh bone meal (mud) processing of livestock and poultry products
Green meat powder food is now gradually becoming a hot spot in the market. Various livestock and poultry fresh bones are not only rich in protein and phospholipids, but also high in calcium, iron and vitamins and other nutrients. If the fresh bone is multi-stage pulverized into ultrafine bone paste or dehydrated into bone meal by airflow ultrafine pulverization technology, more than 95% of nutrients can be maintained and the absorption rate can be improved.
8. Ice cream processing of cold food products
Ultrafine powder can be used as stabilizer, filler, flavor fixative, nutritional binder and antifreeze agent of ice cream. Health-care cold drinks can be developed by using ultra-fine raw materials that are both used for medicine and food.
Advantages of fluidized bed jet mill
Since the advent of jet milling and grading equipment in the 1930s, the types have been continuously updated and the structure has been continuously improved. Bed (on-spray) jet mill, etc.
The fluidized bed jet mill is a new model that was put into use in the late 1970s and early 1980s. It has the characteristics of low energy consumption, light wear, low pollution, low noise, fine particle size and uniform distribution, etc. It is used in synthetic resin, phenolic Production of resins, PVC, pigments and dyes, powder coatings, couplers, pharmaceuticals, cosmetics, advanced ceramics, magnetic powders, abrasives, metal powders, food, spices, stearic acid, fats, waxes, mineral powders, pesticides and wettable powders been widely used in.
The fluidized bed jet mill superimposes the unidirectional jet flow and the reverse counter jet flow, and the unidirectional jet flow enters the grinding chamber through the nozzle. , a concentric reverse jet flow field is formed in the crushing area, and the crushed materials are fluidized under the action of pressure difference. Fluidization refers to the expansion of the particle bed at the critical fluidization velocity in the flow field, and the solid particles in the bed have the flow characteristics of the fluid.
The crushed materials in the crushing area are accelerated in the high-speed counter-jet flow field, and violent impact, collision, friction and shear are generated at the intersection of the jets from each nozzle, resulting in the crushing of the materials. The pulverized materials form an upward airflow around the intersection point, and the materials are brought to the upper horizontal turbine sorter for automatic classification. The powder particles that meet the requirements are selected by the sorter and then collected by the cyclone. Coarse particles slide back to the grinding chamber along the wall and continue grinding until they are separated. Therefore, the powder with good dispersibility and narrow particle size distribution can be obtained through the pulverization and classification treatment of the fluidized bed jet mill.
(1) Change the line and surface impact crushing of the traditional jet mill to the three-dimensional impact crushing of the space, and make full use of the high-speed airflow generated by the jet impact in the flow of materials in the crushing chamber, so that the crushing area is similar to a fluidized state Excellent gas-solid crushing and graded circulation flow effect, which improves the efficiency of impact crushing and the comprehensive utilization of energy. Compared with other traditional methods, the energy consumption is reduced by 30-40% on average;
(2) Since the impact crushing area and the gas-solid flow belt are placed in the middle space of the crushing chamber, the impact and abrasion of the materials driven by the high-speed airflow on the wall of the crushing chamber are avoided, and the most serious wear problem in jet impact crushing is improved, and greatly reduced. the potential for the material to be contaminated;
(3) Protective gases such as high-purity nitrogen or argon are used as the working medium to prevent oxidation, and the closed-loop operation has low gas consumption and reduces costs;
(4) There is no dust flying during the complete closed-loop operation, no pollution to the environment, and no harm to the human body;
(5) After jet milling, the activity of the powder increases. The energy of the high-speed jet flow in the jet mill crushing and classification process can not only cause the particles to be impacted and crushed, but also change the internal structure of the particles, especially the surface state, to a certain extent. The energy of the gas flow removes atoms or ions from the particle lattice, causing a mechanical loss of the crystalline structure. In this way, while the powder material is ultrafinely pulverized, the surface energy or internal energy of the particles increases, and the activity of the particles increases. The increase in the activity of the particles is not only beneficial to the chemical reaction, but also beneficial to the adsorption and coating of the particles.
(6) The particle size of the product is fine, the output is large, and it is suitable for large-scale production; the particle size classification accuracy is high, so the particle size distribution of the product is narrow, and the particle size of the product is also easy to adjust.
Dry fine grinding technology applied in the field of agricultural chemistry
Production Process
The reason why pesticide manufacturers develop specific components and dosage forms is to make the active ingredients effective in reducing the factors that are unfavorable to crop growth (such as pests, weeds or fungi... ). Therefore, plant protection agents can be said to be essentially a mixture of different ingredients. These ingredients can basically be summarized into three categories:
active ingredient in the formulation.
Fillers for diluting active substances, such as clay, talc, kaolin or silica.
Auxiliaries and additives to improve formulation quality (e.g. stabilizers, wetting agents, protective agents, defoamers, etc.)
In the pesticide production process, the first step is feeding and mixing; the second step is grinding. Through different types of grinding equipment as shown below, the mixed material particles are ground and dispersed to the target fineness to meet the application requirements. After grinding, it goes through a sieving process to prevent possible oversized particles. Finally, the additives or fillers that do not need to be ground are added, and the dispersive mixing is carried out again.
Reasons why pesticide particles are required to be ultrafine particles and narrow particle size distribution:
The finer the active ingredient particles, the more potent the action, which means that a smaller amount can be used to achieve the same medicinal effect. Here are the safety, environmental and economical factors:
Reduce toxic effects on persons in the spray area.
Reduce pollution to the environment.
Reduce pesticide production costs and increase profits by reducing the amount of the most costly active ingredient used in the formulation.
Narrow particle size distribution facilitates the simplification of pesticide application steps:
The powder is dispersed in water before application on crops. The finer the particles, the more stable the suspension and no settling occurs during handling.
In the process of pesticide spraying, it effectively reduces the problem of large particles clogging the nozzle of the spraying system.
Mechanical impact mills can be used for fine grinding of soft to medium hard materials. Typical fineness ranges for the median particle size are 20 to 500 μm. The peripheral speed is 25 to 150 m/s. NETZSCH can also provide another model with counter-rotating method and a speed of up to 250 m/s. The air flow depends on the rotor type, thus ensuring temperature-stabilized grinding. The rotor is mounted horizontally and the shaft seal is of the non-contact labyrinth type due to the high shaft speed.
Mechanical mill CSM with grading function
This type of grading mill offers the possibility of simultaneously achieving both grinding and grading functions in one system. CSM classifier is a combination of fine impact classifier and guide wheel classifier. Driven by two independent motors, one for the grinding disc and the other for the classifying wheel, the CSM can precisely adjust the classifying wheel speed to obtain a wide range of final product fineness from d97=9μm to 200μm. By utilizing the geometric shape of the impeller of the classifier and the gap air seal between the classifier wheel and the top cover of the machine, the precise control of the upper limit of the particle size of the grinding material is ensured, thereby achieving fine classification.
The Fluidized bed jet mill is suitable for ultra-fine grinding of materials of various hardness (soft to extremely hard). In the grinding area, the particles are driven by the high-speed airflow to collide and grind each other, without additional grinding parts, and the dynamic classifier controls the maximum particle size. The air velocity at the outlet of the nozzle in the grinding chamber can reach 500 to 600 m/s. Because of the high grinding energy and impact velocity that can be generated in the fluidized bed, it is possible to achieve a D50 fineness of 1 to 5 μm.
Due to this structural feature, the jet mill has a very attractive feature: there is no temperature rise in the grinding chamber during the grinding process. The reason is that the heat generated when the particles collide with each other is offset by the cooling phenomenon of the expanded compressed gas, so that the temperature in the grinding chamber remains constant, and the active substance molecules will not be destroyed.
As a machinery manufacturer, ALPA has been devoting itself to designing grinding equipment and systems, and the machines have many designs that are convenient for customer maintenance. The design of the top cover with the grading wheel assembly can be fully opened, the rotating cavity shape and the properly selected maintenance door make it very easy for users to access the internal components. It is constructed of stainless steel, finely polished, and has a drain valve at the bottom of the grinder so it can be cleaned with water for easy cleaning.
Natural Zeolite Modification Technology and Its Application in Wastewater Treatment
Among many water treatment technologies, adsorption method has become an ideal wastewater treatment technology due to its advantages of simple operation, low energy consumption, good removal effect and high selectivity. The development of low-cost and high-efficiency adsorbents is the core of adsorption methods. Compared with other synthetic high-efficiency adsorbents, low-cost natural adsorbents have higher economic benefits and environmental protection value.
The abundant pores and channels in natural zeolites and the negative charge on the surface make them have good adsorption capacity for cations and little adsorption capacity for anions. This greatly limits the application of natural zeolites in the removal of anionic pollutants in water. For this reason, many studies have been carried out on the modification of natural zeolites in order to increase the affinity for anions. Surface modification is an effective way to increase the affinity of natural zeolites for anionic pollutants.
Different modification methods will have different effects on the physical and chemical properties of zeolite, such as changing the internal pore structure and size of zeolite, as well as hydrophilic and hydrophobic and surface functional groups. The main purpose of physical modification is to remove some impurities on the surface of zeolite and increase the specific surface area. The purpose of chemical modification is: (1) to remove impurities and dredge pore channels to facilitate the entry and transfer process of target substances, (2) to introduce new functional groups to change the surface properties of zeolite, such as hydrophobicity, thereby providing Novel binding sites for target pollutants.
Composite modification can achieve the purpose of synergistic modification by combining multiple modification methods. In order to better balance the preparation cost and removal effect, it is a better choice to improve the adsorption capacity of natural zeolite to anionic pollutants in water by means of compound modification.
There are still many challenges in the practical wastewater treatment of zeolites. For example, the pore size of natural zeolites usually belongs to the category of micropores, which are smaller than the radius of anions, which will hinder their migration and diffusion inside the zeolite, which is not conducive to the adsorption process. Moreover, the components in the actual wastewater are complex and changeable, and zeolites are easily affected by coexisting ions and pH values, resulting in poor adsorption effects and even structural damage. In addition, the saturated zeolite may be transformed into a new pollution source if it is not properly disposed of.
(1) The surface modification method will affect the physical and chemical properties of natural zeolite. Composite modification is an effective way to improve the anion adsorption performance of natural zeolite. For example, by introducing mesoporous materials to expand the pore size of zeolite and improve the diffusion efficiency of anions in the internal structure of zeolite. By introducing functional groups with affinity for target pollutants, the adsorption sites of zeolites can be enriched and the adsorption selectivity can be improved.
(2) Combining natural zeolite with other water treatment processes or materials can effectively improve its application potential in actual wastewater treatment. The pollution components in actual wastewater are complex and changeable, and the combined use of multiple materials/processes has become the mainstream way to improve the effect of actual wastewater treatment. Materials or combined processes containing natural/modified zeolites have been widely used in the treatment of wastewater, domestic sewage, rivers and lakes, etc. Natural zeolites and their modified forms have good application prospects in practical wastewater treatment.
(3) The modification and regeneration process of zeolite may involve toxic solvents, causing great harm to the environment and human health. A safe, pollution-free preparation and regeneration scheme should be sought, or a stable encapsulation method developed as a practical solution for final and safe disposal of zeolites.