What are the applications of graphene in the field of thermal conductivity?
At present, with the continuous deepening of research, the application of graphene in the field of thermal conductivity has achieved remarkable results, including the formation of graphene films through chemical bonds between sheets, as a filler in thermally conductive composite materials and thermally conductive coatings, and the preparation of graphene. Polyethylene fiber new functional textile materials, etc.
1. Graphene thermal film
Artificial graphite film has been the most ideal choice for thermal conductive films for a long time in the past. It can usually be used as a heat sink in electronic components and is attached to the surface of electronic components that easily generate heat to evenly disperse the heat generated by the heat source. However, since high thermal conductivity graphite films are mainly prepared using the technical route of PI film carbonization-graphitization method, which requires high-quality polyimide films as raw materials, and its research and development and production have high technical barriers, so the industry has always hoped Other alternatives can be found to solve the problem of raw materials being blocked by technology, and graphene thermal conductive film is an ideal alternative.
2. Thermal conductive filler
As a two-dimensional thermally conductive filler, graphene is easier to form a thermally conductive network than granular fillers, and has good application prospects in thermal interface materials and thermally conductive coatings.
a. As a thermal interface material thermally conductive filler
Compared with traditional granular thermally conductive fillers, thermally conductive fillers using graphene as a thermal interface material can not only utilize its ultra-high in-plane thermal conductivity, but its large diameter-to-thickness ratio is also more conducive to the construction of a three-dimensional thermal conductivity network. It has strong advantages in compounding with fillers of other dimensions to improve the thermal conductivity of thermal interface materials.
b. As a filler for heat dissipation coatings
Heat dissipation problem is a big bottleneck restricting the development of lightweight high-performance devices. As a special industrial coating, heat dissipation coating can increase the heat dissipation speed and efficiency of the surface of the object by enhancing the infrared radiation rate of the heat source surface, and reduce the surface temperature of the material. Meet the need for efficient heat dissipation of devices despite space and size constraints.
3. High thermal conductivity graphene fiber functional textiles
High thermal conductivity graphene fiber is a new type of carbon fiber material composed of graphene units assembled and arranged in an orderly manner. It is assembled in an orderly manner using graphene oxide dispersion or functionalized graphene dispersion through wet spinning. . Its main advantage is that it has good mechanical, electrical and thermal properties at the same time, and can be combined with textile technology to produce functional textiles in large quantities through wet spinning.
Currently, the ultra-high thermal conductivity of graphene can be used to produce electric heating clothing that can keep warm and keep out the cold, as well as thermally conductive and cool-feeling textiles. Graphene electric heating clothing mainly uses graphene to convert the energy of the power supply into heat, and then combines the ultra-high thermal conductivity of graphene to evenly transfer heat to the entire body. It can keep the fabric light and soft while providing excellent thermal insulation performance. The thermally conductive and cool-feeling textiles utilize the high thermal conductivity of graphene, which causes rapid heat loss from the skin surface after skin contact with textiles, significantly lowering body temperature and providing people with a more comfortable wearing experience.
Application progress of ball mill in the field of new materials
Since its introduction more than 100 years ago, ball mills have been widely used in industries such as chemical industry, mining, building materials, electric power, medicine and national defense industry. Especially in the fields of complex mineral processing, powder surface modification, powder activation, functional powder synthesis, mechanical alloying, and ultrafine powder preparation, the mechanical ball milling method has a broad research and application market. .
The ball mill has the characteristics of simple structure, continuous operation, strong adaptability, stable performance, suitable for large-scale and easy to realize automatic control. Its crushing ratio can range from 3 to 100. It is suitable for processing various mineral raw materials and wet grinding. And dry grinding can be used as its abrasive method.
Research progress of mechanical ball milling method in the field of new materials
(1) Lithium battery materials
SiOx materials were synthesized by mechanical ball milling in air atmosphere. Used as anode material for lithium-ion batteries, the volume specific capacity of SiOx can reach 1487mAh/cc, which is more than twice that of graphite; its first Coulombic efficiency is higher than that of untreated SiO, up to 66.8%; and it has excellent cycle stability. After 50 cycles at a current density of 200mA/g, the capacity stabilizes at around 1300mAh/g. The results show that SiOx prepared by this method has practical possibility.
(2) Rare earth materials
In terms of rare earth polishing powder, the mechanical ball milling method not only increases the shear force during the chemical reaction, increases the diffusion rate of particles, is conducive to the refinement of reactants and products, but also avoids the introduction of solvents and reduces It eliminates the intermediate precipitation process, reduces the influence of many preparation conditions in the preparation process of polishing powder, and greatly broadens the research scope of polishing materials. In terms of rare earth catalytic materials, the mechanical ball milling method has a simple preparation process and mild conditions, and can process materials in large quantities.
(3) Catalytic materials
In order to change the particle size of TiO2 and improve its photocatalytic performance, Qi Dongli et al. used high-energy ball milling to process TiO2 powder and studied the effect of ball milling time on the micromorphology, crystal structure, Raman spectrum, fluorescence spectrum and photocatalytic performance of the sample. The degradation rate of TiO2 samples after ball milling is higher than that of non-ball milled samples, and the degradation rate of the sample ball milled for 4 hours is the highest, indicating that it has the best photocatalytic performance.
(4) Photovoltaic materials
The chemical reduction-mechanical ball milling method was used to prepare bright flaky silver powder, and the effects of ball milling method, ball milling time and ball milling speed on the parameters and properties of flaky silver powder were studied. The results show that wet ball milling has higher flake formation efficiency, but the flake silver powder prepared by dry ball milling has a larger flake diameter and a brighter silver appearance.
(5) Perovskite materials
Lead-free double perovskite Cs2AgBiBr6 nanopowder was prepared using a mechanical ball milling process. As the ball milling time increases, the Cs2AgBiBr6 nanopowder finally reaches the pure phase, the particle size gradually decreases to about 100nm, and the particle shape changes from rod-shaped to round particles.
(6) Adsorption materials
Non-metallic minerals such as limestone, kaolin, and serpentine are activated through ball milling to strengthen their ability to react with harmful components such as copper, lead, and arsenic in the water phase. This enables an efficient, simple, and low-cost new sewage purification process to be applied to the sewage purification process. Selective precipitation, separation and enrichment recovery of target metal components.
Compared with other methods, during the process of chemical reaction, the ball milling method can significantly reduce the reaction activation energy, reduce the powder particle size, increase the powder activity, improve the particle size distribution, enhance the bonding between interfaces, promote solid ion diffusion and It induces low-temperature chemical reactions to improve the density and optical, electrical, thermal and other properties of the material. The equipment is simple, the process is easy to control, the cost is low, and there is less pollution. It is an energy-saving and efficient material preparation technology that is easy for industrial production.
What are the requirements for thermal interface materials in popular application areas?
In recent years, the explosion of photovoltaics, electric vehicles, 5G communications and mobile electronics has brought increasingly higher requirements for device heat dissipation. Thermal interface material is a typical thermal conductive material that can be widely coated on heating elements (power tubes, thyristors, electric heating piles, etc.) and radiators (heat sinks, heat sinks, etc.) in various electronic products, power batteries, and electrical equipment.
1. New energy power battery
As the main power source of new energy vehicles, power batteries need to arrange as many battery cells as possible in a certain space to increase their cruising range. This results in a very limited heat dissipation space in the power battery. When the vehicle is running, the heat generated by the battery cells Heat will gradually accumulate in a small heat dissipation space, which will reduce the charging and discharging efficiency of the battery and affect the power of the battery; in serious cases, it will cause thermal runaway and affect the safety and life of the system. Therefore, it is necessary to use thermally conductive potting glue with certain thermal conductivity to achieve potting between battery cells, as well as between the entire battery module group and the heat sink plate. Due to new energy power batteries, the optimal operating temperature range of power battery cells is very narrow, generally between 20-40°C and less than 65°C. To ensure the safety of vehicle operation and optimal battery performance, thermal conductive adhesive is generally required The thermal conductivity of the potting glue reaches more than 3W/(m·K).
2. Photovoltaic inverter
Generally speaking, the thermal conductivity of photovoltaic inverters is required to be no less than 2.0W/mK, and the withstand voltage is no less than 5kV/mm. At the same time, in order to protect the control circuit board and components from the influence of the external environment and mechanical forces, and protect the safety and stability of the circuit, the thermally conductive potting glue used in photovoltaic inverters is also required to have certain earthquake resistance, impact resistance, dust resistance, UV resistance, waterproof and moisture-proof, insulation and other properties. In addition, since the life of photovoltaic systems is generally about 20 years, the life requirements for thermal conductive adhesives used in photovoltaic inverters are also relatively high, usually more than 8 years.
3. 5G base station
The base station is a typical closed natural heat dissipation device. Its heat dissipation method is to allow the heat of the power device to be transferred to the casing first, and then conducted from the casing to the air. Considering the processing properties of electronic equipment in 5G base stations, dispensing technology is often used for construction to improve automation efficiency. Therefore, the thermally conductive adhesive needs to be prepared into a gel state with low stress and high compression modulus.
4. Chip packaging, heat dissipation
Thermal conductive silicone grease with good rheological properties is mainly used for filling between the chip and the packaging shell, and the packaging shell and the heat sink. Since the working temperature of the chip often reaches 60-70°C, the thermal conductivity material used at the chip has very high thermal conductivity requirements. High, it needs to be above 5 W·(m·K), and requires basic properties such as low adhesive layer thickness, high flexibility, high thermal conductivity, low contact thermal resistance, and appropriate thermal expansion coefficient.
The emergence of emerging application fields has put forward more diversified requirements for thermal interface materials, which are no longer limited to improving thermal conductivity, but are developing in the direction of multi-functionality, including dielectric, insulation, high-performance Reliability, flame retardancy and other aspects, so as to better adapt to the specific needs of various fields, thereby promoting technological progress and innovation in related industries.
8 Concepts About Bentonite Clay
1. Bentonite
Bentonite, also known as "bentonite" or "bentonite", is a non-metallic mineral with montmorillonite as the main mineral component. It often contains a small amount of illite, kaolinite, zeolite, feldspar and calcite and other minerals. Montmorillonite The stone content determines the utilization value of natural bentonite.
2. Montmorillonite
Smectite is a large family of minerals with complex chemical composition. The International Clay Association has determined that Smectite is the family name, that is, the smectite family, also known as the smectite family. This group of minerals includes two subgroups, dioctahedral and trioctahedral, and more than a dozen mineral species. Bentonite usually contains minerals from the dioctahedral subgroup, such as montmorillonite, beidellite, nontronite, etc.
3. Sodium bentonite and calcium bentonite
Because part of the silicon ions and aluminum ions in the silicon-oxygen tetrahedron and aluminum-oxygen octahedron are often replaced by other low-priced cations, the montmorillonite crystal structure has a permanent negative charge. In order to balance the electricity price, the montmorillonite unit cell will adsorb exchangeable cations.
According to the type, content and crystallization chemical properties of exchangeable cations contained in bentonite, bentonite is divided into calcium bentonite, sodium bentonite, magnesium bentonite and calcium-sodium bentonite. The most common ones are the first two. .
4. Organic bentonite
Organobentonite refers to using organic ammonium cations to replace exchangeable cations in montmorillonite, covering the surface of montmorillonite, blocking the water adsorption center, causing it to lose its water absorption function, and turning into hydrophobic and lipophilic organobentonite. complex.
Organobentonite can be divided into high-viscosity organobentonite, easily dispersible organobentonite, self-activating organobentonite, and high-purity organobentonite according to functions and components.
5. Lithium bentonite
There are very few natural lithium bentonite resources. Therefore, artificial lithiation is one of the main methods for preparing lithium bentonite.
Lithium bentonite can form gel in organic solvents and replace organic bentonite. Lithium bentonite has excellent swelling, thickening and suspending properties in water, lower alcohols and lower ketones, so it is widely used in architectural coatings, latex paints, casting coatings and other products to replace various organic cellulose suspending agents.
6. Activated clay
Activated clay is made from clay (mainly bentonite) as raw material, which is obtained by inorganic acidification or salt treatment. It is a porous white-off-white powder with a microporous structure and a large specific surface area, and has strong adsorption properties. It is mainly used for decolorization and refining of petroleum processing products (lubricating oil, paraffin, petroleum jelly) and industrial animal and vegetable oils, and is used as adsorbent and catalyst carrier in the chemical industry.
7. Pillared montmorillonite
Pillared montmorillonite is a mineral material with two-dimensional pores formed by polymerized inorganic cations or organic ions (molecules) inserted into montmorillonite. It has a large specific surface area, good thermal stability, strong surface acidity and adjustable pore size. It has broad application prospects in petrochemical industry, sewage treatment, antibacterial materials and other fields.
8. Bentonite gel
Bentonite inorganic gel is a high value-added colloidal product produced with bentonite as the main raw material through purification, sodium modification, phosphating modification and gelation. The preparation process mainly includes the purification of bentonite raw ore, There are four major processes: sodium modification, phosphating modification and gelling.
Inorganic gel is a high value-added bentonite deep processing product that can be used as a thixotropic agent, thickener, dispersant, suspending agent, stabilizer, etc. It is widely used in daily chemicals, pharmaceuticals, detergents, ceramics, glass, papermaking, and casting. , battery and other industries.
Learn more about powders: must-know terms and concepts
Crushing/grinding/pulverizing
The process of reducing particle size.
Dry grinding
The process of crushing in air or other gaseous media.
continuous grinding
The process of continuously and evenly feeding the materials to be processed into the crushing device (or system), and at the same time, the crushed materials are discharged in time.
surface grinding
Under the action of external forces such as friction and shear, the grinding process is mainly based on surface grinding and peeling.
impact grinding
The crushing process is realized by utilizing the impact of the high-speed moving working parts of the crushing equipment on the material or the impact of the high-speed moving material and the wall.
Jet pulverizing
The high-speed jet formed by the expansion and acceleration of compressed gas through the nozzle causes impact, collision and friction between particles and between particles and the wall, thereby realizing the crushing process.
Crushing ratio/ratio of size reduction
The ratio of the characteristic particle diameters of the feed material and the discharge material during the crushing operation indicates the degree to which the particle size of the material is reduced after crushing.
grinding efficiency
The output rate of qualified products per unit energy consumption per unit time.
grinding balance
During the crushing process, the particle size of the powder material no longer continues to decrease and the specific surface area no longer continues to increase.
mechano-chemistry
Structural or physical and chemical changes induced by mechanical forces during the material crushing process.
grinding media
It is an object that is loaded in the mill and uses the impact, collision, shearing, grinding and peeling effects generated during its movement to crush the material.
Grinding aid
Additional additives to improve crushing and grinding efficiency.
Dispersant/dispersing agent
It is an additive that directional adsorbs on the surface of the treated particles to prevent them from aggregating with each other and maintain the stability of the particles within a certain period of time.
classification
The process of dividing a material into two or more particle size distribution levels.
Sieving
The process of grading using sieves.
fluid classification
The process of classifying liquid or gaseous media.
Dry classification/wind classification (dry classification)
The process of classification in air or other gaseous media.
gravity classification
The process of classifying particles based on the difference in their final settling velocity in liquid or gaseous media.
centrifugal classification
The process of grading based on the different trajectories of particles in the centrifugal force field.
Cut size
According to the particle size, the material is divided into coarse and fine particles and the separation limit particle size of the product.
classification efficiency
The degree of separation of coarse and fine grade products during the classification process is usually expressed by the ratio of the mass of the fine-grained material after classification to the mass of the graded material smaller than the cutting particle size. It is a measure of the quality of the grading operation. an important indicator.
surface treatment
A general term for processes such as particle shaping, surface modification, and surface coating.
particle functional design
The process of changing the morphology, structure and characteristics of particles for the purpose of material functionalization.
Particle shape modification
A process that changes the shape of particles.
sphericity
The process of processing irregularly shaped particles into spherical or approximately spherical particles.
Degree of sphericity
The particle shape is close to a sphere.
surface modification
The process of changing the surface properties of particles through the adsorption, reaction, coating or coating of surface modifiers on the particle surface.
wet modification
The process of surface modification of materials in a slurry with a certain solid-liquid ratio or solid content.
Dry modification
The process of surface modification of dry or dried powder materials.
physical coating
The process of surface modification using physical methods.
mechano-chemical modification
The process of surface modification is achieved with the help of strong mechanical force in the crushing process.
encapsulation modification
The process of surface modification by covering the surface of particles with a homogeneous and certain thickness film.
high energy surface modification
The process of surface modification using irradiation or radiation.
Surface modifying agent
Substances that modify the surface of particles.
surface coating
The process of forming inorganic coatings on the surface of particles.
Pigment powder ultrafine crushing equipment
Particle size is one of the important indicators of pigments. Generally, pigment particles are required to have stable physical form, uniform particle size, and good dispersion, without agglomeration or precipitation.
Iron oxide pigment is a pigment with good dispersion, excellent light resistance and weather resistance. It mainly refers to the four types of iron oxide red, iron yellow, iron black and iron brown coloring pigments based on iron oxides. Among them, iron oxide red is the main one.
Precipitated (wet) iron oxide pigments are very fine, but during the filtration and drying processes, due to factors such as van der Waals forces, hydrogen bonds, charges, etc., the micro-aggregates aggregate into large aggregates and cannot be directly used in high-end coatings. For coloring, ultrafine crushing is necessary. Jet milling uses the energy of high-speed airflow or superheated steam to ultrafinely grind solid materials. It is one of the most commonly used ultrafine grinding methods.
At present, in the pigment production industry, the application range of airflow crushing is becoming more and more extensive, which mainly comes from the following two factors:
First, the safety of mechanical crushing is poor, because if hard metal falls on the high-speed rotating mechanical teeth, it is easy to produce an open flame, which is very dangerous in a dusty pigment production workshop, but airflow crushing does not have this question;
Second, airflow crushing belongs to ultra-fine crushing. In the production of some special pigments, the fineness of the pigments is required to be higher.
1. Iron oxide pigment
During the filtration and drying process of iron oxide pigments, due to van der Waals forces, hydrogen bonds, charges and other factors, micro-aggregates aggregate into large aggregates, which cannot be deaggregated through general mechanical action. Using a fluidized bed or disc-type jet mill to process iron oxide pigments, the Hagermann fineness can reach: iron oxide red 5.5 to 7.0, the darker the color, the better the fineness; iron oxide yellow 7.5; iron oxide black 7.0 .
After ultra-fine crushing, the iron oxide pigment is depolymerized from large aggregates into small aggregates. When producing paint, it only takes a short time of high-speed stirring process to achieve the required fineness, thereby saving costs and the small size of the pigment. The aggregates are difficult to coarsen into large aggregates, thus ensuring the quality of the paint.
2. Black high temperature resistant manganese ferrite pigment
The fine particles of manganese ferrite pigment that have been surface-coated, surface-modified, dried, and pulverized are flocculated again into coarse particles of varying degrees, and cannot effectively exert the pigment properties of manganese ferrite.
After deep processing and grinding using a fluidized bed or disc-type jet mill, the Hagermann fineness of the manganese ferrite pigment is approximately 7 to 7.5. It has good dispersion and can give full play to its optical and pigment properties.
3. Brown ceramic pigment
The brown ceramic pigment is ultrafinely pulverized using a flat jet mill. When the air pressure is 7.5×105Pa and the feeding speed is 100kg/h, the product d50 is 4.55μm and the maximum particle size is 9.64μm.
At present, common ultra-fine grinding equipment includes jet mill, mechanical impact ultra-fine grinder, stirring ball mill, sand mill, vibration mill, colloid mill, high-pressure jet grinder, planetary ball mill, pressure roller mill, and ring roller mill. etc.
Production technology of high-quality calcium hydroxide
Calcium hydroxide, commonly known as hydrated lime, has a chemical formula of Ca(OH)2. Generally in powder form, it will lose water and become calcium oxide (quicklime) at 580°C under normal pressure. Calcium hydroxide is slightly soluble in water, and its solubility decreases as the temperature increases. The colorless and transparent solution obtained by dissolving in water is commonly known as clear lime water. A milky suspension composed of calcium hydroxide and water is called milk of lime.
Dry calcium hydroxide production process: qualified quicklime is crushed by a jaw crusher. It is sent into the lime silo via bucket elevator and bin-type vibrating conveyor. The lime in the silo is quantitatively added to the hydrated lime pre-digester through star-shaped feeding, and is initially digested under strong stirring by the stirring rod, and then enters the digester to complete the digestion process. The digested lime is input into the slaked lime silo by the slaked lime elevator and the inlet screw conveyor, and then the qualified refined slaked lime is obtained by the ash adding spiral air separator. The refined slaked lime is unloaded into the finished slaked lime silo and then packaged according to user needs. During the dry digestion reaction, the organizational structure changes, causing Ca(OH)2 to form a loose powder, with the volume increasing to 1.5 to 2.0 times the original volume. The product and raw materials have better fluidity, so the dry digestion process can be used in water. The high conversion rate reaction of quicklime can be achieved under the condition of low ash ratio (mass ratio of water to lime).
Calcium hydroxide applications
(1) Flame retardant materials
Calcium hydroxide powder is widely used as a filler in polymer materials. Adding calcium hydroxide to polymer materials can improve the thermal stability and flame retardant properties of composite materials; calcium hydroxide is alkaline and can react with hydrogen chloride (HCl) released when PVC is thermally decomposed, eliminating the degradation of PVC by hydrogen chloride. The autocatalytic effect of the process has a certain thermal stabilization effect.
(2) Degradable polymer materials
Calcium hydroxide can be used as an auxiliary agent for environmental absorption of plastics. It has dechlorination, cracking and alkaline degradation effects on the decomposition of plastics.
(3) Wastewater treatment
The role of calcium hydroxide in wastewater can be basically summarized into four aspects: neutralizing free acids in wastewater, neutralizing acid salts in wastewater, reacting with metal ions to produce water-insoluble precipitates, and adjusting the pH of wastewater. value.
(4) Desulfurizer
In the calcium hydroxide-gypsum wet desulfurization process, the flue gas comes into contact with the Ca(OH)2 absorption liquid over a large area, so that the SO2 in the flue gas dissolves in water and reacts with the calcium hydroxide slurry to form calcium sulfite, which is then blown in Under the condition of a large amount of air, calcium sulfite is oxidized to generate CaS (V2H2O), thereby achieving the purpose of reducing SO2 in the flue gas. In the calcium desulfurization process, calcium ions are actually involved in the sulfur fixation. Calcium carbonate, calcium oxide, and calcium hydroxide can all be used as desulfurization agents.
(5) Medical and health care
Calcium hydroxide is used for disinfection in a variety of places, such as scientific research, laboratories, medicine, factories, etc. It has a long history of use in clinical medicine.
(6) Food processing
Adding a certain amount of food-grade calcium hydroxide to milk powder can not only adjust the pH value of the milk powder and promote the rapid dissolution of the milk powder in water, but also supplement calcium.
4 key points for choosing powder surface modifiers
There are many types of powder surface modifiers on the market with various functions and of course different prices. How to choose the most suitable modifier?
Practice has shown that when selecting surface modifier varieties, the main considerations include: the properties of the powder raw materials, the use or application field of the product, as well as technology, price and environmental protection.
1. Properties of powder raw materials
The properties of powder raw materials are mainly acid, alkalinity, surface structure and functional groups, adsorption and chemical reaction characteristics, etc. Surface modifiers that can chemically react or chemically adsorb with the surface of powder particles should be selected as much as possible, because physical adsorption on It is easy to desorb under strong stirring or extrusion during subsequent applications.
For example, the surfaces of acidic silicate minerals such as quartz, feldspar, mica, and kaolin can bond with silane coupling agents to form stronger chemical adsorption; however, silane coupling agents generally cannot bond with alkaline carbonates. Minerals undergo chemical reactions or chemical adsorption, while titanate and aluminate coupling agents can chemically adsorb with carbonate alkaline minerals under certain conditions and to a certain extent.
2. Product use
The purpose of the product is the most important consideration in selecting a surface modifier. Different application fields have different technical requirements for powder application performance, such as surface wettability, dispersion, pH value, hiding power, weather resistance, gloss, antibacterial properties, UV protection, etc. This means that surface modification should be selected according to the purpose. One of the reasons for the variety of sexual agents.
For example, inorganic powders (fillers or pigments) used in various plastics, rubbers, adhesives, oily or solvent-based coatings require good surface lipophilicity, that is, good affinity or compatibility with the organic polymer base material. , which requires the selection of surface modifiers that can make the surface of inorganic powders hydrophobic and oleophilic; for inorganic pigments used in ceramic blanks, they are not only required to have good dispersion in the dry state, but also require affinity with the inorganic blanks. Good compatibility and can be evenly dispersed in the blank; for surface modifiers of inorganic powders (fillers or pigments) used in water-based paints or coatings, the dispersion and sedimentation stability of the modified powder in the water phase are required. Good compatibility.
For inorganic surface modifiers, they are mainly selected based on the functional requirements of powder materials in the application field. For example, to make titanium dioxide have good weather resistance and chemical stability, SiO2 and Al2O3 must be used for surface coating (film) , in order to make the muscovite pigment have a good pearlescent effect, it is necessary to use TiO2 for surface coating (film).
At the same time, different application systems have different components. When selecting a surface modifier, you must also consider the compatibility and compatibility with the application system components to avoid the functional failure of other components in the system due to the surface modifier.
3. Modification process
The modification process is also one of the important considerations in selecting surface modifiers, such as temperature, pressure and environmental factors. All organic surface modifiers will decompose at a certain temperature. For example, the boiling point of silane coupling agents varies between 100 and 310°C depending on the type. Therefore, it is best to select a surface modifier with a decomposition temperature or boiling point that is higher than the processing temperature of the application.
The current surface modification process mainly adopts dry method and wet method. There is no need to consider the water solubility of the dry process, but the water solubility of the surface modifier must be considered for the wet process, because only if it is soluble in water can it fully contact and react with the powder particles in a wet environment.
Therefore, for surface modifiers that are not directly water-soluble and must be used in a wet environment, they must be saponified, ammonized or emulsified in advance so that they can be dissolved and dispersed in aqueous solutions.
4. Price and environmental factors
Finally, when selecting surface modifiers, price and environmental factors must also be considered. On the premise of meeting application performance requirements or optimizing application performance, try to choose cheaper surface modifiers to reduce the cost of surface modification. At the same time, attention should be paid to selecting surface modifiers that do not pollute the environment.
5 Major Types of Surface Modification Methods For Carbon Fiber
Carbon fiber (CF), as a new type of composite reinforced material, has been widely used in various industries and has attracted much attention. However, the surface of CF is relatively smooth and has no active groups. The fiber surface is chemically inert, so the fiber has poor hydrophilicity and poor adhesion to the matrix, and is easy to fall off. Therefore, it is necessary to improve the interface between CF and matrix reinforcement.
So far, the common surface modification methods of carbon fiber mainly include coating modification, surface graft modification, oxidation modification, plasma modification and joint modification, among which oxidation treatment and surface grafting treatment are more popular. Methods. These modification methods improve the fiber's wettability, chemical bonding, and mechanical interlocking with the matrix to form a transition layer, promote uniform stress transmission, and reduce stress concentration.
The surface of carbon fiber is smooth, has few active groups, and does not adhere firmly to the matrix. In normal applications, it is necessary to improve the adhesion rate. One method is to roughen the smooth carbon fiber surface through physical effects, creating grooves or small holes to increase the contact area with the matrix material. Polymers or nanoparticles can be filled in the fiber. In the grooves on the surface, the fiber and polymer can be mechanically locked together through the rough shape of the fiber surface after curing, resulting in an obvious mechanical interlocking effect between the fiber and the matrix, which is beneficial to improving the interface strength.
1. Coating modification
Carbon fiber coating modification can cover a variety of materials, such as metal salts, metal alloys, carbon nanomaterials, etc., through spraying, physical or chemical deposition, polymers, sol-gel methods and coating processes. After coating, the surface of CFs has different properties.
2. Surface grafting
Carbon fiber surface grafting is a bottom-up, extensively studied CFｓs modification method. Compared with surface oxidation and coating methods, surface grafting can give the grafted polymer better adhesion to the CF surface. Through radiation or chemical reaction, the grafting reaction is triggered on the surface of CFs, and polymers with functional groups are introduced on the surface of CFs, which improves the interface strength of the composite material.
3. Oxidation treatment
Carbon fiber oxidation treatment is a simple modification method that not only increases the pore distribution and pore size on the CF surface, but also introduces different concentrations of oxygen-containing functional groups, which has a significant impact on the material interface adhesion and immobilization efficiency (IE). Influence.
4. Plasma treatment
Plasma treatment is a prominent and successful treatment method for a variety of materials, including carbon materials. High enough energy plasma is used to hit the CF surface, causing the chemical bonds to break and reorganize on the surface, thereby improving the surface structure and performance of the carbon fiber to achieve good adhesion between CF and the matrix material. Plasma treatment has the advantages of simple operation, high efficiency, green and environmental protection.
5. Joint modification
The above-mentioned single modification methods have more or less defects. For example, coating-modified CF has low adhesion between the coating and CF, requires the use of solvents during the manufacturing process, has low preparation efficiency, and is difficult to produce continuously; investment in plasma treatment equipment is expensive; in wet chemical oxidation and electrolysis Some liquid contamination is inevitable during chemical treatment, and the modification conditions should be precisely controlled in gas-phase oxidation to prevent excessive oxidation from destroying the internal structure of CF, and the use of nanomaterials or grafted polymers to modify the surface of carbon fibers is complex.
Therefore, when modifying the surface of carbon fiber, joint modification using multiple modification methods can avoid the shortcomings of using them alone and combine the advantages with each other. This is the main direction of carbon fiber surface modification treatment in the future.
What are the differences between white talc, black talc and hydrotalcite?
At present, the products related to "talc" on the market mainly include white talc, black talc, hydrotalcite, etc. Although they are all called talc, their ingredients, uses, prices, etc. are very different.
1. White talc
Talc is a hydrous magnesium silicate mineral, most commonly found in white, which is white talc. Look at China for the world's talc. The white talc supplied in the international market mainly comes from China. The advantages of Chinese talc are not only reflected in reserves and output, but more importantly, in the extraordinary quality of white talc, especially high-purity white talc.
White talc has high electrical insulation, heat insulation, high melting point and strong adsorption of oil. It is widely used in papermaking, chemical industry, medicine, rubber, ceramics, paint, cosmetics and other industries.
2. Black talc
Black talc is a 2:1 type (T-O-T) magnesium-rich silicate clay mineral. It is soft, has a flaky structure and a slippery feel. It does not contain water between the layers, is odorless and tasteless, has stable chemical properties, small particles, and a large specific surface area. Black talc is gray to black because it contains organic carbon. Its chemical composition, mineral composition and mineral deposit origin are similar to white talc. The main ore components are usually composed of talc, quartz, organic carbon, etc.
At present, most black talc is processed into white talc through whitening technology and then used in the traditional ceramic industry and basic fillers. The research directions are mainly high-efficiency whitening and ultra-fine processing technology.
3. Hydrotalcite
Hydrotalcite is divided into natural hydrotalcite and synthetic hydrotalcite. Since natural hydrotalcite is difficult to mine and its purity is not high, the market supply of hydrotalcite is dominated by synthetic hydrotalcite.
Synthetic hydrotalcites (LDHs) are a class of anionic layered compounds with broad application prospects, mainly composed of hydrotalcite (HT), hydrotalcite-like (HTLC for short) and their intercalation chemical products pillared hydrotalcite (Pillared LDH) constitute.
Synthetic hydrotalcite is a non-toxic dihydroxy compound with a special layered structure. It has physical and chemical properties such as charging properties, anion exchangeability, adsorption properties, catalytic properties, etc. It has a wide range of applications in the field of polymer resin materials. Mainly used as heat stabilizer for polyvinyl chloride (PVC) production and halogen absorber for polyolefin resin production.
The main finished product categories of synthetic hydrotalcite include general synthetic hydrotalcite, highly transparent synthetic hydrotalcite and flame-retardant synthetic hydrotalcite.