Ball mill and classifying production line of silica powder

With the ultrafine processing of non-metallic minerals, ultrafine crushing and grading technology has become one of the most important deep processing technologies, which is of great significance to the development of modern high-tech industries.

Silicon micropowder (SiO₂) is an extremely widely used inorganic non-metallic material, with acid and alkali corrosion resistance, abrasion resistance; high insulation, high thermal conductivity, high thermal stability; low expansion coefficient, low dielectric coefficient, and low thermal conductivity. It is widely used in the fields of chemicals, electronics, integrated circuits (IC), electrical appliances, plastics, coatings, advanced paints, rubber, and national defense.

According to the level, it is divided into ordinary silicon powder, electrical grade silicon powder, fused silicon powder, ultra-fine silicon powder, and spherical silicon powder; according to the purpose, it is divided into silicon powder for paint and coating, silicon powder for epoxy floor, silicon powder for rubber, and sealing Silicon powder for glue, electronic grade and electrical grade silicon powder for plastic packaging, and silicon powder for precision ceramics; according to the production process, it is divided into crystalline powder, cristobalite powder, fusion powder, and various active powders.

The preparation of crystalline powder, cristobalite powder, fusion powder and various active powders all need to go through a grinding and classification process. The grinding and classification of silicon micropowder generally adopts dry ball milling and classification.

Ball Mill and Classifying Production Line

All kinds of crushed, beneficiated, calcined or melted silicon powder raw materials → hoist → silo → electromagnetic vibrating feeder → ball mill → classifier → cyclone collector → bag dust collector

• Characteristics of ball mill classification production line

Large output, simple equipment operation, low maintenance costs, flexible selection of grinding media and liners, low pollution to high-purity processing of materials, reliable overall equipment operation, and stable product quality.

The application of silicon powder can make the product high in whiteness, good gloss and stable quality index.

• Ball mill classification production line output

In actual production, in order to maximize the benefits, the output matching of the ball mill and the classifier is very important. Proper cooperation can give full play to their own characteristics, complement each other's advantages, and are highly efficient. Poor coordination will result in functional constraints, high energy consumption and low efficiency.

The influencing factors of the output of the ball mill include the fineness of the feed, the effective diameter of the mill body after lining, the speed of the ball mill, the selection and gradation of the ball mill media, the filling amount, the effective length of the mill body, and the size of the feeding amount.

The factors affecting the output of the classifier include powder concentration, turbine classifier speed, air volume and pressure, classification efficiency, particle size distribution, and product fineness.

Therefore, the output of the two equipment should have the following relationship: the output of the classifier = the processing capacity of the classifier-the amount of coarse material after classification; the output of the ball mill = the amount of raw material feeding + the return amount of coarse material after classification; the processing capacity of the classifier = The output of the ball mill.

Market Outlook of Silicon Micropowder

With the development of the high-tech industry, the use of silicon micropowder is becoming wider and wider, and the amount used is increasing. For the huge high-end market demand in the future, it is necessary to improve the quality of silicon raw materials, improve the technical level of silicon powder production, strengthen the testing and control of the production process, and break the technical barriers as soon as possible, so as to produce various specifications that meet the quality requirements of various fields according to market demand Silicon powder to meet the needs of domestic and foreign markets.

Article source: China Powder Network

by ALPA Powder

Powder metallurgy process & application

Powder metallurgy is a process technology for preparing metal or using metal powder (or a mixture of metal powder and non-metal powder) as raw materials, forming and sintering, to produce metal materials, composite materials and various types of products.

The powder metallurgy products industry in a broad sense includes iron and stone tools, cemented carbide, magnetic materials and powder metallurgy products. The powder metallurgy products industry in the narrow sense only refers to powder metallurgy products, including powder metallurgy parts (most of them), oil-bearing bearings and metal injection molding products.

Powder metallurgy process characteristics

Compared with other processes, the material utilization rate of powder metallurgy is the highest, reaching 95%, and the energy consumption of parts is the lowest!

The density of the products is controllable, such as porous materials, high-density materials, etc.; uniform microstructure, no component segregation; near-shaped forming, raw material utilization rate>95%; less and no cutting, only 40-50% of cutting processing; material group The element is controllable, which is conducive to the preparation of composite materials; the preparation of insoluble metals, ceramic materials and nuclear materials.

The basic process of powder metallurgy

The basic process of powder metallurgy is powder making → mixing → forming → sintering → vibration grinding → secondary processing → heat treatment → surface treatment → quality inspection → finished product.

Flour milling

Flour milling is the process of making raw materials into powder. Commonly used milling methods include mechanical and physical and chemical methods.

The mechanical method does not change the chemical composition of the raw material, and prepares the powder by cutting/grinding the metal to split the material to create a new interface. The mechanical method can reduce or increase the particle size of the powder, and the metal powder will be hardened after grinding, but the shape of the powder is irregular and the powder fluidity becomes poor.

The physical and chemical method is to make liquid metal prepare powder by physical methods such as cooling and atomization; in addition, it can also be prepared by reducing metal oxides and salts with reducing agents based on chemical reactions such as reduction and dissociation. Atomization powder technology can effectively reduce the segregation of alloy components, so the obtained alloy powder composition is relatively uniform. Since the water atomization method uses higher density water as the atomization medium, the shape of the powder obtained is generally irregular.

Solid particles with a size greater than 0.001mm and less than 1mm are called powders. Generally, the shape of powder particles includes spherical, nearly spherical, polygonal, flake, dendritic, irregular, porous sponge, and butterfly shapes.

Mix

Mixing is the process of mixing various required powders in a certain proportion, and homogenizing them to make green powder. It is divided into three types: dry, semi-dry, and wet, double cone mixer, V-type mixer , Dual motion mixers are used for different requirements.

The mixing of powder is not uniform, the forming process is easy to delamination and fracture, the sintering process is easy to burst and deform, and the mechanical properties such as product hardness and density do not meet the requirements.

Forming

Forming is the process of putting a uniformly mixed mixture into a compression mold and pressing it into a parison with a certain shape, size and density under a pressure of 15-600 MPa. There are two methods of pressure forming and non-pressure forming. Pressure forming The most widely used is compression molding.

Sintering

Sintering is a key process in the powder metallurgy process, and the formed compact is sintered to obtain the required final physical and mechanical properties.

Sintering is divided into unit sintering and multi-component sintering. In addition to ordinary sintering, there are loose sintering, immersion method, and hot pressing method.

Sintering is different from metal melting, at least one element is still in the solid state during sintering. During the sintering process, the powder particles undergo a series of physical and chemical processes such as diffusion, recrystallization, fusion welding, compounding, and dissolution, and become metallurgical products with a certain porosity.

Post-processing

The treatment after sintering can adopt various methods according to different product requirements. Such as finishing, oil immersion, machining, heat treatment and electroplating, steam treatment, etc. In addition, in recent years, some new processes such as rolling and forging have also been applied to the processing of powder metallurgy materials after sintering, and have achieved ideal results.

• Impregnation

Use the capillary phenomenon of the porosity of the sintered parts to be immersed in various liquids. For lubrication purposes, it can be soaked in lubricating oil; in order to improve the strength and anti-corrosion ability, it can be soaked in copper solution; for surface protection, it can be soaked in resin or varnish.

• Steam treatment

Due to the existence of pores in powder metallurgy products, this brings difficulties to surface protection. Steam bluing treatment is very important for meters, military industry and powder metallurgy products with anti-corrosion requirements, and can improve the rust resistance and airtight gaps of powder metallurgy parts.

• Cold surface pressure

To improve the dimensional accuracy of the parts and reduce the surface roughness, shaping can be used; to increase the density of the parts, multiple pressing can be used; to change the shape of the parts, fine pressing can be used.

• Heat treatment

Due to the existence of pores, for products with porosity greater than 10%, liquid carburizing or salt bath heating shall not be used to prevent salt solution from immersing in the pores and causing internal corrosion; for products with porosity less than 10%, it can be used with general steel The same heat treatment methods, such as overall quenching, carburizing quenching, carbonitriding quenching, etc.; heat treatment can improve the strength and hardness of iron-based products.

Application of powder metallurgy

The application range of powder metallurgy products is very wide, from general machinery manufacturing to precision instruments, from hardware tools to large-scale machinery, from electronics industry to motor manufacturing, from civil industry to military industry, from general technology to cutting-edge high technology. The figure of metallurgical craftsmanship.

Powder metallurgy materials can be divided into powder metallurgy porous materials, powder metallurgy structural parts, powder metallurgy anti-friction materials, powder metallurgy tool and die materials, powder metallurgy friction materials, powder metallurgy electromagnetic materials, powder metallurgy high temperature materials, etc.

Typical application: automotive industry

Powder metallurgy valve seats, valve guides, VCTs and sprockets, etc., can have high strength, high wear resistance and excellent heat resistance. Such as intake and exhaust valve seats, gears.

Typical application: aerospace industry

Special functional materials are mainly used for auxiliary machines, instruments and airborne equipment of aircraft and engines. High-temperature and high-strength structural materials are mainly used for important structural parts of aircraft engines. Such as high-pressure turbine powder disc for engine, aviation brake pair-BY2-1587.

Typical application: electronics

Such as mute button, power button, volume plus and minus buttons, SIM card tray, 8PIN data cable socket, built-in N41 feet, built-in vibration motor rotor.

The development direction of powder metallurgy

Powder metallurgy technology is developing in the direction of high densification, high performance, integration and low cost. The details are as follows:

1. Representative iron-based alloys will develop into large-volume precision products and high-quality structural parts.

2. Manufacture a high-performance alloy with uniform microstructure, difficult to process and completely dense.

3. The enhanced densification process is used to produce special alloys that generally contain mixed phase compositions.

4. Manufacture of non-uniform materials, amorphous, microcrystalline or metastable alloys.

5. Processing unique and non-general composite parts of shape or composition.

Article source: China Powder Network

by ALPA Powder

Classifier for powder industry

Classification is based on the principle that the solid particles have different sedimentation speeds in the medium due to different particle sizes, and the particle group is divided into two or more particle size levels. Classification is an indispensable part of the crushing process, and the broad classification includes sieving.

Comparison of sieving and classification

The commonly used fluid media for classification are water (called wet classification or hydraulic classification) and air (called dry classification or wind classification). The classifier system consists of air classifier, cyclone separator, dust collector, induced draft fan, electric control cabinet, etc.

Horizontal multi-rotor classifier system layout diagram

Dry classification equipment

• Gravity Air Classifier

The classification is carried out by using the different sedimentation speed and movement trajectory of the particles in the gravity and air medium resistance. Its structure is simple, the pressure drop is small, the processing capacity is large, but the classification accuracy is poor.

Gravity air classifiers include vertical flow type gravity classifiers, horizontal flow type gravity classifiers, and special flow type gravity classifiers.

• Inertial air classifier

Inertia is an inherent property of matter and is determined by mass. During the movement, when particles are subjected to a force that changes the direction of their movement, different inertias will form different trajectories to achieve classification. Its structure is simple, there are no moving parts inside, and the classification accuracy is high, but the output is low.

Inertial air classifiers include jet-type inertial classifiers, jet-type inertial classifiers, and other types of inertial classifiers.

• Centrifugal Force Air Classifier

The classification is achieved under the combined action of air resistance, gravity and centrifugal force, with high classification accuracy and large processing capacity.

Centrifugal classifiers include free vortex type centrifugal classifiers, quasi-free vortex type centrifugal classifiers, forced vortex type centrifugal classifiers, forced vortex type centrifugal classifiers include traditional fan blade type forced vortex centrifugal classifiers, cage rotor type forced vortex centrifugal classifiers Classifiers, rotary wall forced vortex centrifugal classifiers, other types of forced vortex centrifugal classifiers.

• Combined classifier

It is a combination design of the previous models, which can often integrate multiple advantages. It is the main method of setting the classifier before a new breakthrough in classification theory has been achieved.

Wet classification equipment

Equipment that uses gravity or centrifugal force to classify materials according to the sedimentation law of particles in the fluid, such as spiral classifiers, hydrocyclones, cone classifiers and trough classifiers, etc.; control the size of the screen holes and classify materials according to the particle size The equipment, such as vibrating screen, curved screen and fine screen, etc.

The role of classification

The qualified products of grinding can be separated in time to avoid over-grinding, and at the same time, unqualified coarse sand can be separated and returned to grinding. This can well guarantee the sorting effect and effectively improve the grinding efficiency.

Application of classifier

All kinds of powders are super finely graded, remove impurities, and break up; classification of coarse particles entrained by ultra-fine powder and nano powder; classification of materials with strong viscosity, agglomeration, difficult to disperse, and poor fluidity; quartz, ceramics, refractory materials, zirconium Classification of superhard materials such as British sand and silicon carbide.

The function of the fine grading equipment is to ensure that the particle size distribution of the product meets the needs of the application, and to improve the efficiency of the ultra-fine grinding operation.

According to the classification medium, fine classifiers can be divided into dry classifiers with air as the medium (mainly rotor (turbine) airflow classifiers) and wet classifiers with water as the medium (ultrafine hydrocyclones, horizontal Type screw centrifuge, sedimentation centrifuge, etc.).

The development trend of fine classification equipment is fine particle size, high precision, high efficiency, large processing capacity, low energy consumption per unit product, and low wear.

Article source: China Powder Network

by ALPA Powder

Jet mill for titanium dioxide production line

The scientific name of titanium dioxide is titanium dioxide, the molecular formula is TiO₂, and the crystal form is anatase, rutile, and brookite. The plate-titanium type is an unstable crystal type and has no practical value in industry. The anatase type is stable under normal mixing, but will be transformed into rutile type at high temperature; rutile type is the extremely stable crystal form of titanium dioxide with compact structure.

At present, jet mills are used at home and abroad to complete the final product pulverization of titanium dioxide.

Why choose jet mill?

The jet mill can pulverize solid materials into sub-micron level, and the particle size distribution is very narrow, the pollution is small, and the pulverization process does not generate hot stars, and simple chemical reactions can be carried out in the jet mill. In comparison, the Raymond mill is not suitable for the crushing of titanium dioxide.

Know the jet mill

Jet mill, also known as fluid energy mill, is a device that uses the energy of high-speed airflow or superheated steam to make particles impact, collide, and rub each other to achieve ultrafine pulverization or deaggregation.

The compressed air/superheated steam enters the Laval nozzle, the air/steam accelerates into a supersonic airflow, and the high-speed jet moves the material at a high speed, causing the particles to collide and rub against each other and be crushed. The crushed material reaches the classification zone with the airflow. The materials with the required fineness are collected by the trap, and the materials that do not meet the requirements are returned to the crushing chamber to continue crushing.

Studies have proved that more than 80% of the particles are crushed by the impact control between the particles, and less than 20% of the particles are crushed by the impact control and friction between the particles and the wall of the crushing chamber.

Features: The product has fine particle size, narrow particle size distribution, and good particle shape dispersion; low-temperature pulverization without medium, no heat is generated during the pulverization process; the system is closed with less dust, low noise, clean and environmentally friendly production process; suitable for heat sensitivity, low melting point sugar and Crushing of volatile materials.

Which jet mill to choose?

There are five types of jet mills: counter-jet (collision) jet mills, circulating tube jet mills, fluidized bed jet mills, target jet mills, and flat jet mills.

In the production process of titanium dioxide, a flat type (also known as a horizontal disc type) jet mill is used for pulverization. Compared with other types of jet mills, it has the following advantages: the flat type (also known as the horizontal disc type) jet mill has a self-grading function, and organic additives can be added while pulverizing, which can organically modify the surface of the titanium dioxide. , It is beneficial to increase the dispersibility of titanium dioxide in different application systems.

Which grinding medium to choose?

Use superheated steam as the grinding working medium. Steam is easily available and cheap, and the pressure of the steam working medium is much higher than that of compressed air and is also easy to increase, so the flow energy of steam is greater than that of compressed air. Superheated steam has higher cleanliness than compressed air, low viscosity and no static electricity. At the same time of grinding, it can eliminate static electricity generated by collision and friction of materials, and reduce the phenomenon of secondary cohesion of powdered materials. Crushing under high temperature conditions can improve the application dispersibility of titanium dioxide and increase the fluidity of titanium dioxide. Low energy consumption, only 1/3-2/3 of compressed air.

As an important equipment for ultra-fine grinding, the jet mill plays an irreplaceable important role in the production of titanium dioxide. The development of jet grinding can basically meet the needs of titanium dioxide production, but the service life and crushing of the jet mill The effect still needs to be further improved, and the configuration and automatic control of the jet grinding system still need to be improved, and the high-efficiency jet grinding with large capacity still needs to be developed. With the development of science and technology and the application of new materials, jet mills will also play a more active role in promoting the development of the titanium dioxide industry.

Article source: China Powder Network

by ALPA Powder

About powder surface modification technology

Powder surface modification refers to the use of physical, chemical, mechanical and other methods to treat the surface or interface of powder materials, and purposefully change the chemical properties of the surface of powder materials to meet the development of modern new materials, new processes and new technologies. need. It is a new technology that integrates powder processing, material processing, material properties, chemicals, and machinery.

The purpose of powder surface modification

Improve the dispersion, stability and compatibility of the powder particles; improve the chemical stability of the powder particles, such as drug resistance, light resistance, weather resistance, etc.; change the physical properties of the powder, such as optical effects, mechanical strength, etc. ; For the purpose of environmental protection and safe production.

Method for surface modification of powder

• Physical coating

The surface modification process of the powder by using surface modifiers such as polymers or resins to physically treat the surface of the powder.

• Chemical coating

A method of modifying the surface of particles by adsorption or chemical reaction.

• Precipitation coating

Using the precipitation reaction to form one or more layers of "coating" on the surface of the particles to achieve a method of improving the surface properties of the powder.

• Mechanochemical modification

Using ultrafine pulverization and other strong mechanical action to activate the powder surface.

• High energy modification

Using ultraviolet, infrared, corona discharge and plasma irradiation methods for surface treatment.

• Other surface modification methods

graft modification, acid-base treatment, chemical weather precipitation (CVD), physical precipitation (PVD).

Process of powder surface modification

• Dry process

The process is simple, and it is suitable for various organic surface modifiers, especially non-water-soluble various surface modifiers.

• Wet process

The surface modifier is well dispersed and the surface is evenly coated. It is suitable for various water-soluble or hydrolyzable organic surface modifiers, inorganic surface modifiers, etc.

• Combining crushing and surface modification into one process

The process is simple, and the crushing efficiency is improved to a certain extent, but the temperature is not easy to control, the coating rate is not high, and the surface modifier may be damaged.

• Combine drying and surface modification into one process

The process can be simplified, but the drying temperature is generally above 200 ℃, and it is difficult to ensure a uniform and firm coating.

ALPA's powder surface modification equipment includes: Turbo mill, ULM-C series Rotor Mill, Three-roller Mill, Pin Mill, High-speed Blender.

Main factors affecting the surface modification effect of powder

• The nature of the powder raw material

Specific surface area, particle size, particle size distribution, specific surface energy, surface physical and chemical properties, agglomeration

• Surface modification process

The consideration factors are the characteristics of the surface modifier, such as water solubility, hydrolysis, boiling point or decomposition temperature, etc.; the process surface modification method of the front-stage crushing or powder preparation operation.

• Surface modifier formulation

variety, dosage and usage

• Surface modification equipment

The performance of the surface modification equipment depends on the characteristics of the selected process, not the speed of the speed or the complexity of the structure.

Application of powder surface modification technology

Organic/inorganic composite materials (plastics, rubber, etc.), paints, coatings, organic/inorganic composite materials, adsorption and catalytic materials, health and environmental protection, anti-agglomeration in the preparation of ultrafine and nanopowders.

Research direction of powder surface modification technology

• Surface modification process and equipment

Strengthen the research of surface modification process, improve technology, and update equipment to realize the monolayer adsorption of surface modifier on the particle surface, reduce the amount of modifier, stabilize product quality and facilitate operation.

• Surface modifier

On the one hand, it adopts advanced technology to reduce production costs, especially the cost of various coupling agents; on the other hand, it develops new surface modifiers with good application performance, low cost, and special properties or special functions.

• Powder surface modification "soft technology"

First, select powder materials and "design" the powder surface according to the performance requirements of the target material; secondly, use advanced calculation methods, calculation techniques and intelligent technologies to assist in the design of powder surface modification processes and modifier formulations. , In order to achieve the best application performance and application effect.

Article source: China Powder Network

by ALPA Powder

Application of non-metallic mineral fillers in coatings

Coating is a fluid (viscous liquid) or powdery substance. It can be dried and solidified to form a hard film on the surface of the object. It has good adhesion and can evenly cover the surface of the object. Regardless of whether it contains pigments, it is commonly referred to as paint.

The main film-forming substances of coatings include oil, resin, and inorganic cementing materials, and the secondary film-forming substances include coloring pigments, extender pigments, and special pigments, all of which are curing components. The auxiliary film-forming substances of coatings include additives and solvents, which are volatile components.

Extender pigments, also known as fillers, are derived from natural minerals and industrial by-products and are inexpensive. Initially they were used in coatings to reduce costs. It has no tinting power and hiding power in the coating film. With the development of technology, it is found that it can be used in conjunction with coloring pigments to increase the thickness of the coating film and improve the performance of the coating. Therefore, extender pigments are not pigments.

Pigments include stone green, cinnabar, mineral pigments, phthalocyanine green, phthalocyanine blue, etc., and extender pigments include calcium carbonate, talc, kaolin, bentonite, and sulfuric acid dam.

The basic requirements of coatings for fillers

High whiteness; soft texture, good dispersion; low oil absorption; can make the coating have good leveling; it has good compatibility with other ingredients in the coating without chemical reaction; it has a proper surface area; Definite particle shape and crystal form; with definite particle size and narrow particle size distribution.

Non-metallic mineral fillers include calcium carbonate, barium sulfate, talc, wollastonite, kaolin, bentonite, diatomite, etc.

Application of non-metallic mineral fillers in coatings

• Calcium carbonate

Heavy calcium is the world's largest filler in coatings. It can be used in various internal and external coatings. It is most suitable for water-based coatings. Its poor acid resistance hinders its application in external coatings.

The heavy calcium used in the coating industry is mainly used to partially replace titanium dioxide and color pigments, replace light calcium and precipitated calcium carbonate, anti-corrosion, and partially replace anti-rust pigments, in addition to being used for increments.

When heavy calcium is used in interior architectural paint, it can be used alone or in combination with talc. Compared with talcum powder, calcium carbonate can reduce the pulverization rate, improve the color retention of light-colored paints and increase the anti-fungal properties.

Compared with heavy calcium, light calcium has a small particle size and a narrow particle size distribution range, high oil absorption and brightness. Light calcium can be used where the greatest matting effect is required. It is more common to mix light calcium and heavy calcium in semi-gloss, dull paint and matt latex paint.

• Barium sulfate

Low oil absorption, high whiteness, fine texture, anti-blooming, anti-rust pollution, often used in anti-corrosion coatings, powder coatings, and floor coatings. It can improve the hardness and abrasion resistance of the paint film. It is one of the commonly used fillers for coatings. The disadvantage is that the density is high and the paint is easy to precipitate.

• Talcum powder

It is not easy to settle and can suspend the pigment. Even if it sinks, it is very easy to stir up again, which can prevent the paint from sagging. It can absorb expansion and contraction stress during application, avoid the morbid state of cracks and voids, and is suitable for outdoor paint and washable and wear-resistant paint. Talc can be used in a variety of industrial coatings, especially primers. The primer for steel structure can be used in whole or in part with talcum powder, which can improve the precipitation of the coating, the mechanical force of the coating film and the recoatability. It is suitable for metal primer and paint for transportation vehicles.

• Wollastonite

It can improve the abrasion resistance and durability of the coating film, and can be used as a paint filler to prepare high-quality white paint and bright and pure color paint. It can be used as a good flattening agent, can make the coating smooth and delicate, can overcome the shortcomings of peeling and peeling of the coating, and has good anti-chalking ability.

• Kaolin

Kaolin has a soft texture, and when used in latex paint, it can improve the suspension, prevent pigment settling, increase the hiding power of titanium dioxide in the paint, and increase the thickness of the coating film, but it has greater water absorption.

• Bentonite

Bentonite is mostly yellow or pink in color, and its application amount for formulas that require high whiteness is limited to a certain extent.

• Diatomite

With large porosity, strong adsorption, light weight and high melting point, it can be used as an additive for latex paint functional materials for thermal insulation, mildew resistance and sound absorption.

Article source: China Powder Network

by ALPA Powder

Ten characteristics of ultra-fine powder

Generally speaking, we define powder with a particle size of less than 1μm as ultrafine powder. Ultrafine powder has different surface effects and volume effects from the original solid materials or coarser particles, and exhibits properties such as optics, electricity, magnetism, heat, catalysis, and mechanics.

Surface effect

The significant difference between ultrafine powder and macroscopic objects is the increase in the number of surface atoms, its large specific surface area, and the surface effect cannot be ignored.

Physically speaking, surface atoms are not the same as internal atoms, and internal atoms are subjected to the force of symmetrical surrounding atoms. The space position where the surface atoms are located is asymmetric, and it is unilaterally attracted by the atoms in the body, which means that the energy of the surface atoms is higher than that of the atoms in the body.

Quantum effect

The quantum effect refers to the phenomenon that when the particle size drops to a certain value, the electrons near the metal Fermi level change from quasi-continuous to discrete.

According to the energy band theory of solids, conduction electrons no longer belong to a single atom when moving in the periodic potential field of a crystal, but belong to the entire crystal. As a result of this publicization, the energy state of the electron in the crystal becomes quasi-continuous. Energy band, that is, the energy difference between adjacent energy levels is much smaller than thermal energy.

Optical properties

The color of metal particles is often different from that of bulk materials. When the size of the metal particles is less than a certain value, they usually appear black due to the total absorption of light waves. In addition to the absorption of light waves, ultrafine particles also have a scattering effect.

For ultrafine dispersed particles smaller than a few tenths of the wavelength of light, the intensity of scattered light is inversely proportional to the fourth power of the wavelength. Therefore, the scattering of sunlight by the dust in the atmosphere makes the clear sky blue.

The ultrafine clay solution highly dispersed in water, when viewed from the side against a dark background, appears blue-white, as if it is a bit turbid. In fact, this is the result of the ultrafine clay particles in the solution scattering part of the incident light.

Electrical properties

Metallic materials have conductivity, but the conductivity of nano-metal particles is significantly reduced. When the electric field energy is lower than the interval of the splitting energy level, the conductivity of the metal will be transformed into electrical insulation.

Magnetic properties

The magnetic properties of ultrafine powders, especially the dependence of the magnetic properties of ferromagnetic particles on the particle size, have long been a subject of interest.

For bulk magnetic materials, when in the magnetic neutral state, many magnetic domains are usually formed, and the magnetic moment in each magnetic domain will be spontaneously magnetized along the direction of its lowest energy. Between the magnetic domain and the magnetic domain, there is a transition layer whose magnetization direction changes continuously, which is called a magnetic wall.

The arrangement of the chaotic orientation of the magnetic domains actually obeys the principle of the minimum energy of the entire ferromagnet, which will cause the macroscopic magnetization to be zero in the magnetic neutral state. The orientation of the magnetic domain vector in the magnetic domain generally depends on the type of magnetic anisotropy.

Magnetic ultrafine powders are widely used. As magnetic recording media, there are γ-Fe₂O₃, FeCo metal , CrO₂ , Ti_xCO_xO₁₉ , BaFe₁₂-2x,Fe₄N and Co-γ-Fe₂O₃. As the magnetic fluid, there are various nano ferrite powders such as Fe₃O₄ and nano particles of iron, nickel, cobalt and their alloys. When used as a magnetic liquid, the surface of the microparticles must be wrapped with a layer of organic long-chain molecules.

Due to the small size of the nano-powder and the large specific surface area, the surface coating also has a greater influence on its magnetic properties.

Thermal properties

The change in particle size leads to a change in the specific surface area, which changes the chemical potential of the particles and changes the thermodynamic properties. The particle size has a great influence on the thermodynamic properties. As the particle size becomes smaller, the surface energy will increase significantly, so that the ultrafine powder can be melted or sintered at a temperature lower than the melting point of the bulk material.

Catalytic properties

For heterogeneous catalytic reactions, in order to improve the catalytic efficiency, increase the specific surface area of the catalyst and reduce the particle size is necessary, but not the only one.

Some catalysts tend to show the maximum value of catalytic efficiency when the particle size is appropriate. Therefore, it is necessary to study the influence of the particle size and surface state of the catalyst on the catalytic activity.

Mechanical properties

The hardness of traditional metal materials increases with the refinement of grains, and the basic mechanical properties of coarse-grained metal materials increase with the decrease of grain size.

For some pure metal nano-solids, such as palladium, copper, silver, nickel, selenium, etc., the microhardness at room temperature increases significantly compared with the corresponding coarse grains. But for nanomaterials of intermetallic compounds, when the size is below a certain critical size, as the grain size becomes smaller, the hardness decreases instead.

Atom arrangement in nanosolid

In the study of mechanical properties of nanomaterials, people are most interested in nanoceramic materials. Nano-ceramic materials have good chemical stability, high hardness, and high temperature resistance, which are expected to overcome the shortcomings of inability to be machined, brittleness, and non-ductility.

Magnetoresistive properties

The so-called magnetoresistance effect is the change in resistivity caused by a magnetic field.

Regardless of the particle film or multilayer film, in order to obtain a large magnetoresistance effect, the particle size or the thickness of the magnetic and non-magnetic layer must be less than the mean free path of electrons. In this way, in addition to spin-related scattering, electrons are transported in the process Less subject to other scattering, the orientation of the spin can remain unchanged.

Since the mean free path of electrons is usually a few nanometers to 100 nm, the giant magnetoresistance effect can only appear in nano-scale systems.

Solution properties

• Movement of ultrafine particles in solution

In a solution or suspension with ultrafine powder particles as the solute, the ultrafine particles also have a diffusion effect from a high concentration area to a low concentration area. At the same time, there is also Brownian motion.

• Adsorption of ultrafine particles in solution

Adsorption is one of the interfacial phenomena between different phases in contact with each other. It is a phenomenon in which the adsorbate is adsorbed in the very thin contact layer on the interface or surface of the adsorbent liquid or solid. Ultrafine particles have large specific surface area, high surface energy and large adsorption capacity.

• Rheology

Rheology is the science of studying the flow and behavior of matter. As discussed above, as the particle size becomes smaller, the particles gradually exhibit properties or behaviors different from those of the original solid. The rheology of the so-called particle dispersion system or colloid in which particles below 1 μm are dispersed in a liquid is a very meaningful research object in theory and in practice.

Article source: China Powder Network

by ALPA Powder

The relationship between gray calcium powder, light calcium and nano calcium carbonate

Speaking of decoration, what do you think of? Is it a simple and atmospheric layout? A magnificent chandelier? Or is it high-end and atmospheric furniture? I don’t know if anyone is like me, thinking of all kinds of walls. From rough and dim cement to smooth and beautiful walls, it can be said to turn decay into magic.

Those who have renovated should know that putty powder is indispensable for wall treatment. It is a kind of base material used for wall repair and leveling, and can lay a good foundation for the next step of decoration (painting and pasting wallpaper), and putty The main ingredients in the powder include gray calcium powder and calcium carbonate. Today, we will talk about three materials that are inseparable from calcium carbonate, gray calcium powder, light calcium, and nano-calcium carbonate.

About raw materials

CaCO₃ is commonly known as graystone, limestone, stone powder, marble, etc., and its scientific name is calcium carbonate. It is an inorganic compound, the main component is calcite, which is white solid, tasteless and odorless, and has two forms: amorphous and crystalline.

CaO, commonly known as quicklime, scientific name calcium oxide, is an inorganic compound. The surface is white powder, the impure ones are off-white, when it contains impurities, it will be light yellow or gray, and it is hygroscopic.

Ca(OH)₂ is commonly known as slaked lime, slaked lime, scientific name calcium hydroxide, is a white powdery solid. After adding water, there are two upper and lower layers. The upper aqueous solution is called clarified lime water, and the lower suspension is called lime milk or lime slurry. It has alkali properties and is corrosive to skin and fabrics.

About the production area of ​​calcium carbonate

The main production areas of calcium carbonate in China are Baoxing Heavy Calcium, Wenchuan Jiangyou Heavy Calcium, Dujiangyan Mianzhu Light Calcium, Chizhou City in Anhui Province, Quzhou City in Zhejiang Province, Lianzhou City in Guangdong Province, and Hezhou City in Guangxi Province.

About comparison

About the relationship between the three

The raw materials of gray calcium powder, light calcium and nano calcium carbonate are limestone (CaCO₃), which are prepared through different processes. The preparation process is complicated: nano calcium carbonate> light calcium> gray calcium powder

About the application

• Gray calcium powder is often used in putty powder, architectural coatings, latex paint, thermal insulation mortar, wires and cables, plastic steel doors and windows, flue gas desulfurization, and sewage treatment.
• Light calcium is often used in rubber, plastics, papermaking, metallurgy, glass production, and asbestos production.
• Nano calcium carbonate is often used in chemical building materials, inks, coatings, sealants, and adhesives.

About development

• Gray calcium powder

Gray calcium powder is easy to cause white pollution in the production process, but the green products produced are a contradiction. To solve this contradiction, improve equipment, and work hard to eliminate white pollution, gray calcium products will have long-term development.

• Light calcium

Light calcium is artificially synthesized, and its crystal form and composition are easy to control, so it can endow light calcium with a variety of functions. The relatively high specific surface makes the powder better in the coating. Mainly used for anti-corrosion coatings. In addition to being used as fillers, ultra-fine light calcium also has a certain degree of water resistance and corrosion inhibition.

• Nano calcium carbonate

Industrialization has been achieved in China, with increasing scale, increasing output, and expanding application fields, from rubber, ink and other industries to plastics, coatings, adhesives, paper and other industries, and the demand is increasing at an annual rate of 20%. , High-end products continue to be put on the market, meeting the increasing demands of the two major markets at home and abroad.

Summary

Nowadays, functional calcium carbonate has become a major demand point in the calcium carbonate application market. In the face of market demand, different users have different requirements for products. In addition to the product's calcium carbonate particle size, but also product performance and quality, a variety of functionalized special calcium products can have stronger market competitiveness. Therefore, more efforts can be made on the application performance of nano-scale calcium carbonate, and more functional and special-purpose nano-calcium carbonate can be developed. The same is true for the functional development of other inorganic powder materials.

Article source: China Powder Network

by ALPA Powder

View the ball mill from the perspective of powder

When it comes to building materials, what do you think of? Is it the first thing that comes to mind is cement! The cement production process can be summarized in four words: "two grinding and one burning", that is, raw meal preparation, clinker calcination, cement grinding, and the grinding process uses a ball mill.

Do you know what a ball mill is?

Ball mill is the key equipment for crushing materials after crushing. Ball mill is one of the high-fine grinding machines widely used in industrial production. It is suitable for grinding various ores and other materials, and is widely used in mineral processing, building materials and chemical industries.

Why is it called a "ball" mill, and what does "ball" mean?

The pulverization of materials by the ball mill is achieved by grinding media. The transmission mechanism transmits mechanical energy to the grinding media, and the materials are crushed through various mechanical forces generated between the media. The grinding media in the mill is mainly steel balls (steel sections), so it is called a ball mill.

What is the structure of the ball mill?

The ball mill is composed of a liner, a compartment plate, a cylinder, a transmission system, a feeding and discharging device, and a main bearing.

What is the state of the grinding body?

Leakage type: the speed is too slow, the grinding body cannot be brought to a suitable height, it only has a grinding effect on the material, and the impact force is very small.

Throwing type: the speed is moderate, the grinding body is brought to a certain height and then falls in a parabolic motion, which has a greater grinding effect and impact on the material.

Circumferential type: the speed is too fast, the grinding body and the material are close to the wall of the cylinder without falling, and the grinding body does not have any grinding and impact effects on the material.

How to choose a grinding body?

• Quantity

The smaller the quantity, the higher the rotation speed of the cylinder, and the smaller the grinding effect; on the contrary, the lower the rotation speed of the cylinder, the greater the grinding effect.

• Particle size

Generally, it is appropriate to control the particle size of the material to be milled to <15mm. For large-scale mills, due to its strong crushing ability, the particle size of the incoming materials can be increased to 25-30mm. However, the particle size of the material entering the grinding of a large vertical raw mill can reach 100mm, so the specific particle size of the material entering the grinding should be determined according to different conditions.

• Size

For materials with larger or harder particle size, the average size of the grinding body is large and the quantity is small; on the contrary, the average size of the grinding body is small and the quantity is large.

What are the requirements for grinding media?

• Relative density of grinding media

The relative density of different grinding media materials will naturally vary greatly. So far, the relative density of the grinding media commonly used in the industry is in the range of 2.2~14gcm2. It is generally believed that the relative density of the media is related to the viscosity of the slurry.

• Media size

The medium size is small, the contact points of the medium ball are many, and there are many opportunities to grind the material. Generally speaking, the feed size is small, and the finer the product size, the smaller the diameter of the medium.

• Media shape

The more the media contact type changes, the narrower the particle size distribution of the milled product.

• Dielectric ball shape and indicated roughness

The artificial grinding media are mostly spherical, and the steel ball of the ball mill is not well made. When the shape of the steel ball is poor, the rotation motion is blocked, which is not conducive to pulverization, and on the contrary, the wear is increased.

• The mechanical strength and chemical stability of the dielectric ball

The mechanical strength of the media ball refers to the ability of the media ball to resist compression and impact under normal working conditions. For steel balls and cemented carbide balls, such problems generally do not exist, while glass balls and ceramic dielectric balls are very important. The grinding media ball should not produce chemical reaction with the material to be ground, and the pH value is stable. The grinding media usually uses oxides to improve stability.

How to classify ball mills?

According to the grinding media, it can be divided into ball mills, rod mills, and gravel mills; according to the shape of the barrel, it can be divided into short barrel mills, long barrel mills, and conical mills; according to the discharging method, it can be divided into tail unloading, The middle part unloads the grinding; according to the rotation mode, it can be divided into center rotation and edge rotation; according to the operation process, it can be divided into dry mill and wet mill.

What are the advantages and disadvantages of ball mills?

• Advantages

Strong adaptability to materials; large crushing ratio; can be operated dry or wet, and drying and grinding can be carried out at the same time; simple structure, high operation rate, reliable operation.

• Shortcoming

The grinding efficiency is low, and the effective utilization of electric energy is low; the equipment is heavy and the one-time investment is large; the noise is large, and the vibration is strong; the speed is low, and it needs to be equipped with deceleration equipment.

What are the application areas of ball mills?

The beneficiation production line in the beneficiation industry, the refractory materials and new building materials in the building materials industry, the fertilizer and silicate products in the chemical industry.

Summary

Generally speaking, the longer the milling time, the less obvious the particle size reduction. Ordinary ball milling can only reach 1-10μm, and circulating stirring ball milling can reach about 1μm. To reach nanometer-level particles, an ultra-fine ball mill is required, and the maximum can reach tens of nanometers.

According to the data, the particle size of some high-energy ball mills can reach about 1 micron, and the limit of sub-micron level is about 500nm. Using planetary ball milling, ball milling can reach about 70nm in 48h, but it depends on the nature of the powder. Among them, the ball-to-material ratio, medium, etc. will affect the ball milling effect. At the same time, attention should be paid to the problem of agglomeration when grinding to nanometer level.

In the field of fine grinding, the market demand for granular materials continues to grow, which provides an excellent opportunity for the development of ball mills. With the continuous deepening of reform and opening up, the domestic ball mill industry is resurging in recent years. On the basis of drawing on foreign advanced technology, China is moving towards the direction of large-scale ball mills.

Article source: China Powder Network

by ALPA Powder

Application of ultrafine powder in different fields

Functional materials are one of the most active fields in the research, development, production and application of polymer materials, and they have a very important position in materials science. Ultrafine powder is not only a kind of functional material, but also plays an extremely important role for the compounding of new functional materials, making it have broad application prospects and has a wide range of applications in various fields.

1. The application of ultrafine powder in the plastics field

Ultrafine powders are widely used in the chemical industry. They are widely used in coatings, plastics, rubber, papermaking, catalysis, pyrolysis, organic synthesis, chemical fibers, inks and other fields. In the plastics industry, the compounding of ultrafine powder and plastics can play a role in strengthening and toughening. For example, after surface modification of nano-calcium carbonate, the toughening effect on the notched impact strength and double notched impact strength of the material is very significant. And the processing performance is still good.

In addition, the addition of ultrafine powder can improve the aging resistance of composite materials, prevent plastic light radiation aging, and increase the service life of plastic products. At the same time, the ultrafine powder can also functionalize composite materials, such as antistatic plastics, flame-retardant plastics, and self-cleaning plastics.

2. Application in the catalyst industry

Used as a catalyst, the ultrafine powder mainly relies on its large specific surface area and incomplete surface atom coordination to increase the active sites on the surface and more active centers on the surface. The surface effect of ultrafine powder determines its good catalytic activity and selectivity of catalytic reaction. Catalysts are one of the important areas of ultrafine powder applications. The fourth generation of catalysts has been researched and developed internationally. The use of nano-scale catalysts can greatly increase the speed of chemical reactions, greatly shorten the time to complete chemical reactions, and greatly improve production efficiency. , The heat of combustion per gram of fuel can be doubled.

3. Application in the field of coatings

The ultrafine powder can be used to prepare nano-modified coatings and nano-structured coatings. Some functions of nanoparticles can be used to modify existing coatings and improve the performance of coatings. Nano-modified coatings are coatings that use a special preparation process and add ultra-fine nano-materials, so that the nano-coatings have optical, mechanical and environmental protection functions, such as: nano-ceramic coatings, nano-non-stick coatings, self-cleaning coatings, and aviation ablative coatings Wait.

4. Application of ultra-fine powder in the field of materials

The application of ultrafine powder in the field of materials is mainly reflected in the application of ceramic materials, building materials, and special functional materials. In the field of ceramic applications, the superfine powder has the properties of high surface energy, large number of surface atoms, and strong activity. It can be used as an activator in the sintering process to speed up the sintering process, shorten the sintering time, and lower the sintering temperature. At the same time, the ultrafine powder can significantly improve the microstructure of ceramic materials, optimize their performance, and achieve the purpose of densification by sintering at a lower temperature, so it is particularly suitable for the preparation of electronic ceramics.

In the application field of special functional materials, the surface properties of ultrafine powder determine that it is very sensitive to the external environment, such as temperature, light, moisture, etc. The changes in the external environment will quickly cause the surface or surface ion valence and electron transport. Change, that is, cause a significant change in its resistance. The unique properties of ultrafine powder make it the most promising material for sensors. Sensors with fast response speed, high sensitivity, and good selectivity can be developed for different purposes.

5. Application of ultra-fine powder in the field of daily chemical industry

Nanotechnology has broad prospects in antibacterial, deodorization, and air purification. The photocatalytic performance and biodegradable sterilization performance of nano titanium dioxide and nano zinc oxide have been verified in products such as air purifiers, nano washing machines, nano refrigerators, nano toothbrushes, and nano towels. In skin care, cosmetics, clothing, etc., the role of ultra-fine powder is also very important.

For example, the use of nanometer titanium dioxide in sunscreen cream can greatly improve the quality of the cream and the effect of sunscreen and skin care. In toothpaste, shampoo, detergent, and decontamination powder, various powders are also used in large quantities. If these powders are ultra-fine, their use performance will inevitably be greatly improved.

6. The application of ultra-fine powder in the fields of medicine and biology

In the fields of medicine and biology, the controlled release drug delivery system in pharmacy uses physical and chemical methods to change the structure of the preparation, so that the drug is automatically released from the dosage form at a constant rate within a predetermined time and acts on Organs or specific target tissues, and maintain the drug concentration within the effective concentration for a long time.

As a drug delivery system, microparticles or nanoparticles are prepared from materials that are basically non-toxic, have good biocompatibility, have a certain degree of mechanical strength and stability, and do not chemically react with drugs. When the microparticles and nanoparticles are administered parenterally, the materials are required to be biodegradable. The microparticles and nanoparticles system is absorbed by the liver, spleen, lung, etc., which are rich in reticulocytes, and are used as foreign matter by macrophages. Some particles can Attacked by the enzyme system in the lytic enzyme body, causing it to crack and release the drug, the particle size directly affects its distribution in the body. The ultra-fine powder also has excellent properties such as targeting, which can protect the coated material from damage. Processing the medicine into superfine powder can increase its residence time in the body and improve its bioavailability. The application of ultrafine powder technology in the fields of medicine and biology is very important.

by ALPA Powder