Surface Modification and Application of Barite Ultrafine Powder
Barite powder is an important barium-containing inorganic mineral raw material, which is quite different from the properties of polymer materials and lacks affinity, which limits its application in the field of polymer materials. In order to further improve its performance and broaden its application field, the surface of barite powder must be modified.
Modification mechanism
The surface modification of inorganic mineral powders is mainly achieved by the adsorption and coating of chemical modifiers on the surface of mineral powders. Surface modification of one or both of the two substances to be carried out by some small molecules or polymer compounds with amphoteric groups, lipophilic and hydrophilic groups, and minerals are made by chemical reaction or physical coating. The surface changes from hydrophilic to hydrophobic, which enhances the compatibility and affinity with organic polymers, and improves the dispersion, so that the organic and inorganic substances can be better combined.
Modification method
Surface modification methods include physical adsorption, coating or physical-chemical methods. Generally speaking, the surface modification methods of mineral particles mainly include the following types.
1 surface coating modification
Use inorganic or organic substances to coat the surface of mineral powder, endowing the particle surface with new properties. This method is to combine the surfactant or coupling agent with the surface of the particle by adsorption or chemical bonding, so that the surface of the particle changes from hydrophilic to hydrophobic, and the compatibility between the particle and the polymer is improved. This method is currently the most commonly used method.
2 Precipitation reaction modification
The chemical precipitation reaction is used to deposit the product on the surface of the mineral powder to form one or more "modified layers", so as to achieve the effect of modification.
3 mechanochemical modification
Using mechanical stress to activate the surface as a means to grind and crush minerals, relatively large particles are made smaller by crushing, friction, etc.
4 graft modification
Some groups or functional groups compatible with polymers are grafted on the surface of particles by chemical reaction, so that inorganic particles and polymers have better compatibility, so as to achieve the purpose of compounding inorganic particles and polymers.
5 surface chemical modification
This modification method is currently the most widely used method in production. It uses surface modifiers to chemically react or adsorb certain functional groups on the mineral surface to achieve the purpose of chemical modification.
6 High Energy Surface Modification
Use the huge energy generated by high-energy discharge, ultraviolet rays, plasma rays, etc. to modify the surface of the particles to make the surface active and improve the compatibility between the particles and the polymer.
Barite products are widely used in petroleum industry, chemical industry, paint industry and metal casting industry. In addition, barite can also be partially used in the manufacture of friction plates for transportation equipment. Modified barite ultrafine powder and organic high polymer have good compatibility and affinity, and can be uniformly dispersed in the matrix; it can replace expensive precipitated barium sulfate in single-sided coated paper, coatings, and paints, reducing production cost. The use of other modifiers to modify barite powder still has great prospects, and it still needs to use higher technical means and methods to continuously explore and develop.
Superfine Powder Classification Technology and Its Typical Equipment
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 low in cost and convenient.
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.
Typical Grading Equipment
(1) wet classifier
The wet classification of ultrafine powder is mainly divided into gravity type and centrifugal type according to the current market situation.
(2) Dry classifier
Most of the dry classifiers use centrifugal force field and inertial force field to classify powder, and they are important fine classification equipment with rapid development at present. The following are several representative devices.
Conical centrifugal air classifier. The conical centrifugal air classifier realizes the separation of coarse powder and fine powder under the action of centrifugal force. The finest particle size of the finished product of this equipment can reach about 0.95μm, and the classification accuracy d75/d25 can reach 1.16.
The equipment does not have any moving parts, and the angle of the deflector can be adjusted between 7° and 15°. The equipment has compact structure, high classification efficiency, and safe and reliable operation.
Surface Coating Technology of Ultrafine Powder
Ultrafine powder (usually refers to particles with a particle size of micron or nanometer) has the characteristics of large specific surface area, high surface energy and high surface activity, so it has excellent optical, electrical and magnetic properties that are difficult to match with many bulk materials. , thermal and mechanical properties. However, due to the small size effect, quantum size effect, interface and surface effect, and macroscopic quantum tunneling effect of ultrafine powder, it is easy to agglomerate in the air and liquid medium. If it is not dispersed, the agglomerated ultrafine The powder cannot fully maintain its specific properties. The most effective way to disperse ultrafine powder is to modify its surface. In recent years, powder surface modification technology has become one of the hot technologies that people pay attention to. Among them, surface coating modification is an important kind of surface modification technology. Coating, also known as coating or coating, is a method of coating the surface of mineral particles with inorganic or organic substances to achieve modification.
At present, there are several classification methods for the surface coating technology of ultrafine powder according to different methods. For example, according to the state of the reaction system, it can be divided into: solid phase coating method, liquid phase coating method, and gas phase coating method; according to the properties of the shell material, it can be divided into: metal coating method, inorganic coating method and organic coating method; Coating properties can be divided into: physical coating method and chemical coating method and so on.
Solid phase coating method
1) Mechanochemical method
2) Solid phase reaction method
The solid-state reaction method is to thoroughly mix the coated substance with metal salt or metal oxide through grinding, and then undergo a solid-state reaction under high-temperature calcination to obtain micro/nano ultra-fine coated powder.
3) High energy method
The method of coating ultrafine particles with high-energy particles such as ultraviolet rays, corona discharge, and plasma radiation is collectively referred to as high-energy methods. This is a relatively new powder coating technology.
4) Polymer encapsulation method
Coating a layer of organic substances on the surface of the powder can enhance its anti-corrosion barrier effect, improve the wettability and stability in organic media, and enhance the interfacial regulation in composite materials, by anchoring active molecules or biomolecules And biologically functional.
5) Microcapsule modification method
Microcapsule method modification is to cover a layer of micron-scale or nano-scale uniform film on the surface of fine particles to modify the characteristics of the particle surface.
Liquid coating method
Liquid-phase coating technology is to achieve surface coating in a wet environment through chemical methods. Compared with other methods, it has the advantages of simple process, low cost, and is easier to form a core-shell structure. Commonly used liquid phase methods include hydrothermal method, precipitation method, sol-gel method, heterogeneous nucleation method, and electroless plating.
1) Hydrothermal method
2) Sol-gel method
3) Precipitation method
The precipitation method is to add the metal salt solution of the coating material to the water suspension of the coated powder, and then add a precipitant to the solution to cause the metal ion to precipitate and precipitate on the surface of the powder to achieve the surface coating effect.
4) Non-uniform nucleation method
5) Electroless plating method
The electroless plating method refers to a coating technology in which the plating solution undergoes a self-catalyzed oxidation-reduction reaction without external current, and the metal ions in the plating solution undergo a reduction reaction to become metal particles deposited on the surface of the powder.
6) Microemulsion method
7) Miscellaneous flocculation method
Vapor coating
The gas phase coating method is to use the modifier in the supersaturated system to gather on the surface of the particles to form a coating on the powder particles. It includes physical vapor deposition and chemical vapor deposition. The former relies on the van der Waals force to achieve particle coating, and the binding force between the core and the shell is not strong; the latter uses gaseous substances to react on the surface of nanoparticles to form solid deposits to achieve the coating effect. Rely on chemical bonding.
With the development of science and technology, powder coating technology will be further improved, and it is expected to prepare multi-functional, multi-component, and more stable ultrafine composite particles, which will open up broader application prospects for composite particles.
The production process of ultrafine powder - Impact pulverization
It is a method that has been widely used since ancient times to mechanically pulverize bulk materials into powder. At present, bulk ultrafine powder still mainly relies on mechanical crushing. Commonly used ultrafine crushing equipment includes: autogenous mill, jet mill, high-speed mechanical impact mill, vibration mill, stirring mill (including various sand mills, tower mills, etc.), Colloid mill (including homogenizer, etc.), ball mill, Raymond mill, etc.
Mechanical pulverization is generally used to produce powders larger than 1 μm. A small number of equipment, such as jet jet mill, can be used to produce materials smaller than 1 μm, which can crush materials to sub-micron level, that is, 0.1+0.5 μm. Its structure is that the compressed air produced by the air compressor is sprayed out from the nozzle, and the powder collides with each other in the jet flow and is crushed.
Raw materials are fed from the hopper, accelerated to supersonic speed by the Venturi nozzle, and introduced into the pulverizer; in the pulverization zone formed by the fluid ejected from the grinding nozzle inside the pulverizer, the material particles collide with each other, rub and pulverize into fine powder. Among them, those who lose centrifugal force and are introduced into the center of the pulverizer are superfine powders; coarse powders do not lose centrifugal force, and continue to be pulverized in the crushing belt.
The jet mill developed in Germany suspends and collides the powder smaller than 0.088mm into superfine powder, so it can produce products of various grades not larger than 44μm, and the average particle size can reach 1, 2, 3, 4μm. This kind of jet mill has high production efficiency, does not pollute the environment, and the product has high purity, fine particles, and no agglomeration. It is an ideal ultrafine grinding equipment. The technical development trend of the mechanical pulverization method is to improve the process technology on the existing basis, develop high-efficiency and low-consumption ultra-fine pulverization equipment, fine classification equipment and supporting auxiliary process equipment, and expand the particle size limit of mechanical pulverization, while improving the processing capacity , forming economies of scale.
In the ultra-fine crushing process, fine grading equipment is also required to separate qualified fine powder materials in a timely manner, improve the efficiency of crushing operations, and control the particle size distribution of products. At present, there are two types of commonly used classification equipment: one is dry classification, generally centrifugal or turbine wind classifier; the other is wet classification equipment, generally using horizontal spiral centrifugal classifier, small diameter and small Cone angle hydrocyclone, and hydrocyclone etc.
Generally, hydraulic classification is used, and the commonly used methods are sedimentation method, overflow method, cyclone method and centrifugation method. The sedimentation method uses the mechanism of different sedimentation speeds in water for different particle sizes to classify; the mechanism of the overflow method is similar to the sedimentation method, the difference is that the water flow speed is greater than the particle sedimentation speed, thereby bringing out the fine powder; the cyclone method The slurry rotates at high speed in the cyclone to generate centrifugal force, and the particle size is different, the centrifugal force is also different, so that the large and small particles can be separated; the centrifugal method is that the slurry rotates at high speed in the centrifuge, and the centrifugal force generated by particles of different sizes is also different.
After classification, the obtained products of various particle sizes are dehydrated and then dried.
In ultrafine grinding, the particle size of the powder is fine, and its specific surface area and surface energy are both large. The finer the particle size, the higher the mechanical strength of the material. Therefore, the energy consumption of ultra-fine pulverization is high, and the powder is easy to agglomerate under repeated mechanical force. In order to improve the crushing efficiency, in addition to strengthening the classification, grinding aids and additives are sometimes added.
The production process of the mechanical pulverization method is simpler than that of the chemical synthesis method, the output is large, the cost is low, and the produced micropowder has no agglomeration. However, it is unavoidable to mix impurities in the crushing process, and the particle shape of the crushed product is generally irregular, and it is difficult to obtain fine particles smaller than 1 μm.
4 major application fields of silica powder
Due to its advantages of acid and alkali corrosion resistance, high temperature resistance, low linear expansion coefficient and high thermal conductivity, microsilica powder is widely used in copper clad laminates, epoxy molding compounds and other fields to improve the performance of related products.
1. Copper clad laminate
Adding silicon micropowder to the copper clad laminate can improve the physical properties such as the linear expansion coefficient and thermal conductivity of the printed circuit board, thereby effectively improving the reliability and heat dissipation of electronic products.
At present, there are five types of silica powder used in copper clad laminates: crystalline silica powder, molten (amorphous) silica powder, spherical silica powder, composite silica powder, and active silica powder.
Spherical microsilica powder is mainly used in high-filling, high-reliability high-performance copper clad laminates due to its unique characteristics of high filling, good fluidity, and excellent dielectric properties. The main indicators of spherical silica powder for copper clad laminates are: particle size distribution, sphericity, purity (conductivity, magnetic substances and black spots). At present, spherical silicon micropowder is mainly used in rigid copper clad laminates, and the proportion of mixed casting in copper clad laminates is generally 20% to 30%; the usage of flexible copper clad laminates and paper-based copper clad laminates is relatively small.
2. Epoxy molding compound
Filling silicon micropowder into epoxy molding compound can significantly increase the hardness of epoxy resin, increase the thermal conductivity, reduce the exothermic peak temperature of the reaction of cured epoxy resin, reduce the linear expansion coefficient and curing shrinkage rate, reduce internal stress, and improve The mechanical strength of epoxy molding compound can reduce the cracking phenomenon of epoxy molding compound, thereby effectively preventing external harmful gas, moisture and dust from entering electronic components or integrated circuits, slowing down vibration, preventing external force damage and stabilizing component parameters.
Common epoxy molding compounds are mainly composed of 60-90% filler, less than 18% epoxy resin, less than 9% curing agent, and about 3% additives. The currently used inorganic fillers are basically microsilica powder, with a content of up to 90.5%. Silica powder for epoxy molding compound mainly focuses on the following indicators:
(1) Purity. High purity is the most basic requirement of electronic products for materials, and the requirements are more stringent in VLSI. In addition to the low content of conventional impurity elements, it is also required that the content of radioactive elements be as low as possible or not. With the advancement of the manufacturing process, the electronics industry has higher and higher requirements for the purity of silicon micropowder.
(2) Particle size and uniformity. VLSI packaging materials require fine silicon powder particle size, narrow distribution range, and good uniformity.
(3) Spheroidization rate. High spheroidization rate is the prerequisite to ensure high fluidity and high dispersibility of fillers. High spheroidization rate and good sphericity of silicon micropowder have better fluidity and dispersion performance, and can be more fully dispersed in epoxy molding compounds to ensure The best filling effect.
3. Electrical insulation materials
Microsilica powder is used as epoxy resin insulating packing material for electrical insulation products, which can effectively reduce the linear expansion coefficient of the cured product and the shrinkage rate during the curing process, reduce internal stress, and improve the mechanical strength of the insulating material, thereby effectively improving and enhancing the insulating material. mechanical and electrical properties.
4. Adhesive
As an inorganic functional filler, silica powder can effectively reduce the linear expansion coefficient of the cured product and the shrinkage rate during curing when filled in the adhesive resin, improve the mechanical strength of the adhesive, improve heat resistance, permeability and heat dissipation performance, thereby improving the viscosity. Knot and seal effect.
The particle size distribution of microsilica powder will affect the viscosity and sedimentation of the adhesive, thereby affecting the manufacturability of the adhesive and the linear expansion coefficient after curing. Therefore, the field of adhesives pays attention to the function of microsilica powder in reducing the linear expansion coefficient and improving mechanical strength. The requirements for appearance and particle size distribution are relatively high, and products of different particle sizes with an average particle size between 0.1 microns and 30 microns are usually used for compound use.
Process properties and application of kaolin
According to the quality, plasticity and sandy content of kaolin ore itself, it can be divided into three types: hard, soft and sandy kaolin. Hard kaolin has a hard texture and no plasticity, but it has a certain plasticity after crushing and grinding; soft kaolin has a softer texture and better plasticity, and the amount of sand contained in it is less than 50%; The sandy kaolin has a looser texture and poor plasticity. It is better after sand removal, and the amount of sand contained in it generally exceeds 50%.
Pure kaolin has high whiteness, soft quality, easy to disperse and suspend in water, good plasticity and high viscosity, excellent electrical insulation properties; has good acid solubility, low cation exchange capacity, good Physical and chemical properties such as fire resistance.
Application of kaolin
1. Application of kaolin in cement-based materials
Kaolin becomes metakaolin due to dehydration. Cement can usually be prepared by alkali activation, or used as an additive to concrete materials. Kaolin can improve the strength, workability and durability of concrete, and at the same time resist the autogenous shrinkage of concrete. Kaolin cement-based materials have excellent performance and a wide range of applications, and their development prospects are worthy of attention.
2. Application of kaolin in ceramic industry
In the ceramic industry, the application of kaolin is earlier than other industries, and the dosage is also very large, usually accounting for about 20% to 30% of the formula. Kaolin can increase the content of A1203 in ceramics, and the formation process of mullite is easier, thus improving the stability and sintering strength of ceramics.
3. Application of kaolin in refractory industry
Because of its high refractoriness, kaolin is usually used in the production and processing of refractory products. Refractory materials are mainly divided into two types: refractory bricks and silicon-aluminum wool, which have the characteristics of high temperature resistance and small deformation under pressure. A series of high temperature resistant clays including kaolin, bauxite, bentonite, etc. are collectively called refractory clay.
4. Application of modified kaolin in coatings
Kaolin has been used as a filler for coatings and paints for a long time because of its white color, low price, good fluidity, stable chemical properties, and large cation exchange capacity on the surface. Kaolin used in coatings generally includes washed superfine kaolin and calcined superfine kaolin.
5. Application of kaolin in paint industry
TiO2, CaC03, talc, and kaolin are the main mineral raw materials used in the paint industry. Among them, kaolin has requirements for its dispersibility, particle size, and content of colored oxides. Because of its white color, low cost, good fluidity and suspension, chemical inertness, strong covering power and other properties, kaolin mainly plays the role of filler and pigment substitute in paints, and can reduce the need for expensive dyes quantity.
6. Kaolin is used in plastic industry
As a filler, kaolin is generally used in an amount of 15% to 60% in plastics. Its function is to make the appearance of plastic products smooth, accurate in size, resist chemical corrosion, reduce thermal shrinkage and thermal fission, and facilitate the polishing process. In the production process of polyvinyl chloride, kaolin is usually used as a strengthening agent to improve the abrasion resistance and durability of plastic products.
7. Kaolin is used to make glass fiber in pond kiln
Kaolin, which is low in iron, is used in fiberglass manufacturing primarily as a source of aluminum and silicon, as well as to dull its luster. The technical content of glass fiber drawing in the pool kiln is relatively high, and for glass fiber forming, it is required to reach the quasi-optical level. The quality and stability of kaolinite homogenized micropowder are the primary factors affecting the kiln glass fiber drawing process, and the alkali-free kiln glass fiber has strict quality requirements for kaolinite homogenized micropowder.
8. Application of kaolin in paper industry
In the paper industry, the international market of kaolin is relatively prosperous, and its sales volume exceeds that of ceramics, rubber, paint, plastics, refractory materials and other industries. In pulp, kaolin usually does not react with its ingredients, has strong stability, and is well retained in paper fibers.
9. Application of kaolin in rubber industry
Kaolin, which is used in the rubber industry, is filled into the colloidal mixture, which can enhance the wear resistance, chemical stability and mechanical strength of the rubber, prolong its hardening time, and can also adjust the mixing, rheological and vulcanization properties of the rubber, and improve the durability of the rubber.
7 advantages of air classifier
The classifier, cyclone separator, dust collector and induced draft fan form a classifying system. Under the action of fan suction, the material moves to the classification area at high speed from the inlet at the lower end of the classifier along with the updraft, and the coarse and fine materials are separated under the strong centrifugal force generated by the high-speed rotating classifying turbine.
The fine particles that meet the particle size requirements enter the cyclone separator or dust collector through the gap between the blades of the classifying wheel to collect. The coarse particles entrain some fine particles and the speed disappears after hitting the wall, and drop down to the secondary air outlet along the cylinder wall. The washing effect separates the coarse and fine particles, the fine particles rise to the classification area for secondary classification, and the coarse particles descend to the discharge port for discharge.
The air classifier, cyclone separator, dust collector and induced draft fan form a complete crushing system. After the compressed air is filtered and dried, it is sprayed into the crushing chamber through the Laval nozzle at high speed, at the intersection of multiple high-pressure airflows.
The materials are repeatedly collided, rubbed, sheared and crushed. The crushed materials are moved to the classification area with the upward airflow under the action of the fan suction. Under the strong centrifugal force generated by the high-speed rotating classification turbine, the coarse and fine materials are separated to meet the particle size The required fine particles enter the cyclone separator and dust collector through the classification wheel to collect, and the coarse particles descend to the crushing area to continue crushing.
The seven advantages of the air classifier are as follows:
●Airflow classifier is suitable for dry crushing of various materials with Mohs hardness below 9, especially for high hardness, high purity and high value-added materials.
●The airflow classifier contains a horizontal classifying device, the top cutting is accurate, the product particle size D97: 2-45 microns is adjustable, the particle shape is good, and the particle size distribution is narrow.
●Low temperature and medium-free crushing, especially suitable for crushing heat-sensitive, low-melting, sugar-containing and volatile materials.
●The crushing process is mainly completed by the collision between the materials themselves, which is different from mechanical crushing which relies on the impact crushing of the materials by blades or hammers, so the equipment is wear-resistant and the product purity is high.
●The equipment is easy to disassemble and clean, and the inner wall is smooth without dead ends.
●The whole system is sealed and crushed, with less dust and low noise, and the production process is clean and environmentally friendly.
●The control system of the air classifier adopts program control, which is easy to operate.
The advantages of metal silicon powder as a refractory material
Features of metal silicon powder:
1. High temperature resistance
Metal silicon powder has strong high temperature resistance, so adding an appropriate amount of metal silicon powder many times in the production of refractories and powder metallurgy can greatly improve the high temperature resistance.
2. Wear resistance
Usually we add metal silicon powder in the production of some wear-resistant castings to improve the wear-resistant performance of the castings.
3. Deoxygenation
Metal silicon powder, as the name suggests, contains a certain amount of silicon, which can have an affinity with oxygen to form silicon dioxide, which reduces the melting reactivity during deoxidation and ensures the safety of deoxidation!
In addition, metal silicon powder has also been widely used in the metallurgical foundry industry. In steelmaking, metal silicon powder can be used as deoxidizer, alloy additive, etc., and the effect is very obvious.
Silicon fume and metal silicon fume are two completely different products. In practice, these two products are often confused because they are inextricably linked.
The silica fume we usually say is also called silica fume and micro silica fume. It is the soot recovered from the production process of metal silicon or ferroalloy. Due to its high content of silica, extremely fine particles and high activity, it can be used in concrete, refractory materials, rubber, paint, etc. There are a wide range of applications in industries such as.
The main component of metal silicon powder is crystalline silicon (Si). Its initial form is lumpy, and it becomes powder after being crushed or ground, which is used in industries such as refractory materials.
The reason why metal silicon powder is turned into powder is because it is physically ground, and silicon powder is naturally formed during the production process.
The chemical composition varies greatly. Silicon powder is mainly silicon dioxide, and the main content of metal silicon is SI element.
Metallic silica fume is generally inert, while silica fume is a pozzolan. The color of metallic silicon powder is usually relatively stable, while the color of silicon powder varies greatly from white to black. Silica fume is widely used. The price of metal silica fume is very high, several times that of micro silica fume
The Progress of Superfine Pulverization Technology in Modern Food Processing
Superfine Grinding (SG) technology, as a new technology developed rapidly in the past 20 years, is a deep processing technology that combines mechanical mechanics and fluid mechanics, overcomes the internal cohesion of objects, and crushes materials into micron or even nanometer powders. Ultrafine pulverization treatment can make the material particle size reach 10 μm or even nanometer level. Since the powder structure and specific surface area are greatly changed compared with ordinary particles, the ultrafine pulverization particles have special properties that ordinary particles do not have, and with the modern equipment With the development of science, superfine pulverization technology has made major breakthroughs in many fields such as food and pharmaceuticals, especially in the extraction of Chinese herbal medicines, the development of functional foods, and the utilization of waste resources.
According to the particle size of processed finished powder, ultrafine pulverization technology can be mainly divided into: micron pulverization (1 μm ~ 100 μm), submicron pulverization (0.1 μm ~ 1.0 μm) and nano pulverization (1 nm ~ 100 μm). The preparation of micron powder generally adopts physical pulverization method; the preparation of submicron and below particle size powder adopts chemical synthesis method. The chemical synthesis method has the disadvantages of low output and high operation requirements, which makes the physical pulverization method more popular in the modern processing industry.
1. Extraction of natural active ingredients of precious Chinese herbal medicine
The demand for precious medicinal materials is high due to their remarkable medicinal effects, and wild resources are almost exhausted. Now they rely on artificial planting for supply, but the market is still in short supply, resulting in high prices. Therefore, it is necessary to make full use of precious Chinese herbal medicines and improve their processing technology.
Researchers generally use methods such as microscopic identification and physical property testing to perform characterization and physical property testing of ordinary Chinese herbal medicine powder and ultrafine powder. It was found that the ultrafine pulverization technology can effectively destroy the cell walls of a large number of cells in medicinal materials, increasing cell fragments, and its water solubility, swelling power, and bulk density are also improved to varying degrees compared with ordinary powder. At the same time, the dissolution rate of active ingredients in the ultrafine pulverization process is improved.
2. Reuse of food and drug processing waste resources
Food and drug processing waste usually still contains certain natural active ingredients, and discarding them will not only cause a lot of waste but also pollute the environment. The emergence of ultrafine pulverization technology provides more possibilities for the reuse of food and drug processing waste resources. In recent years, researchers' research on ultrafine pulverization technology has mostly focused on the reuse of food and drug processing waste resources, usually combined with enzymatic hydrolysis technology. For example, the reutilization of potato pomace, linseed husk, grape seed, coffee peel, etc., mostly focuses on the influence of different particle sizes on the physical and chemical properties and functional properties of ultrafine powders, as well as its influence on the relevant characteristics of food matrices.
3. Development and utilization of functional food processing
Because the cell structure of some raw materials rich in natural active ingredients is tough and not easy to be destroyed, the release rate of the nutrients and functional ingredients contained in them is usually at a low level, which cannot be fully developed and used. Ultrafine pulverization technology brings the possibility to destroy the cell structure and improve its nutrient release efficiency. Studies have shown that proper ultrafine pulverization can improve the hydration properties of raw materials, while excessive pulverization will reduce the hydration properties; at the same time, within an appropriate range, the dissolution rate of active ingredients will gradually increase with the decrease of particle size.
4. Other aspects
Research on ultrafine pulverization technology also focuses on the flavor components of spices, usually using low-temperature ultrafine pulverization technology. At present, some researchers have pretreated rattan pepper, dried pepper, and ginger through ultrafine pulverization technology, and studied their flavor. The research results show that the appropriate particle size will enhance the aroma of raw materials, and the aroma will not be lost in the later storage process; too small particle size will cause the aroma to lose faster with the prolongation of storage time.
Application of jet pulverization equipment in the production of titanium dioxide
1. Titanium dioxide requirements for crushing
Titanium dioxide used as a pigment has excellent optical properties and stable chemical properties. Titanium dioxide has very high requirements on particle size, particle size distribution and purity. Generally, the particle size of titanium dioxide is based on the wavelength range of visible light, that is, 0.15m ~ 0.35m. And as a white basic pigment, it is very sensitive to the increase of impurities, especially iron impurities, and the increase is required to be less than 5 ppm when pulverized. In addition, titanium dioxide is also required to have good dispersibility in different coating systems. Therefore, the general mechanical crushing equipment is difficult to meet the requirements, so the final crushing of titanium dioxide (finished product crushing), at present, jet mills are used at home and abroad.
2. The choice of jet mill for titanium dioxide production
According to the crushing requirements of titanium dioxide: narrow particle size distribution, less increase in inclusions, good dispersibility, etc., and the material characteristics of titanium dioxide: high viscosity, poor fluidity, fine particle size and easy wall attachment, etc. The flat type (also known as horizontal disc type) jet mill with high-level function is used as the final crushing equipment for titanium dioxide;
And use superheated steam as the crushing medium. Because the steam is easy to get and cheap, the pressure of the steam working medium is much higher than that of the compressed air and it is also easy to increase, so the kinetic energy of the steam is larger than that of the compressed air. At the same time, the cleanliness of superheated steam is higher than that of compressed air, with low viscosity and no static electricity. Moreover, while crushing, it can eliminate the static electricity generated by material collision and friction, and reduce the secondary cohesion of powdered materials. In addition, crushing at high temperature can improve the application dispersibility of titanium dioxide and increase the fluidity of titanium dioxide. The energy consumption of superheated steam is low, which is only 30% to 65% of that of compressed air.
In addition, using a flat jet mill, organic additives can be added while pulverizing to organically modify the surface of titanium dioxide to increase the dispersibility of titanium dioxide in different application systems.
3. Factors affecting jet milling equipment
(1) Jet mill: As the most important equipment for jet milling, the quality of the jet mill directly determines the quality of the product. The gas powder machine is required to be reasonably designed, well-made, with high impact kinetic energy, good classification effect, wear resistance and high temperature resistance. Therefore, it is very important to choose a gas powder machine.
(2) Steam quality: The crushing medium of jet milling is superheated steam. If the steam quality does not meet the crushing requirements, it will seriously affect the quality of gas powder. Generally, the requirements for the steam of the gas powder machine are: the pressure is 1.6-2.0 MPa, and the temperature is between 290 ° C and 310 ° C. If the temperature and pressure are lower than the requirements, the impact kinetic energy will be low, the crushing force will be reduced, the heat of the system will not be enough, the material will be easily affected by moisture and many other unfavorable factors, which will affect the crushing effect, block the system, and make it unable to operate normally; if the temperature and pressure are too high, it will damage the damage to equipment within the system.
(3) Process control: Jet milling requires stable and continuous operation, and the fluctuation of steam and feed amount should be controlled within a certain range. The adjustment must be adjusted slowly, and it is strictly forbidden to be suddenly large or small. In addition, once the air-powder system is normal, it should keep running continuously, and avoid frequent driving and parking. Furthermore, the operating procedures should be strictly followed when driving and parking.
(4) System monitoring: In order to ensure the normal operation of the system, necessary monitoring equipment must be installed in a reasonable position of the system, so that timely adjustments can be made according to changes in the situation.