14 methods of surface coating of ultrafine powder
Ultrafine powders usually refer to particles with a particle size of micrometers or nanometers. Compared with bulk conventional materials, they have larger specific surface area, surface activity and higher surface energy, thus showing excellent optical, thermal, electrical, magnetic, catalytic and other properties. Ultrafine powders have been widely studied as a functional material in recent years and have been increasingly widely used in various fields of national economic development.
However, due to the unique agglomeration and dispersion problems of ultrafine powders, they have lost many excellent properties, which seriously restricts the industrial application of ultrafine powders.
Methods for coating the surface of ultrafine powders
1. Mechanical mixing method. Use mechanical forces such as extrusion, impact, shearing, and friction to evenly distribute the modifier on the outer surface of the powder particles, so that various components can penetrate and diffuse into each other to form a coating. The main methods currently used are ball grinding, stirring grinding, and high-speed airflow impact.
2. Solid-phase reaction method. Mix and grind several metal salts or metal oxides according to the formula, and then calcine them to directly obtain ultrafine coated powders through solid-phase reaction.
3. Hydrothermal method. In a closed system of high temperature and high pressure, water is used as a medium to obtain a special physical and chemical environment that cannot be obtained under normal pressure conditions, so that the reaction precursor is fully dissolved and reaches a certain degree of supersaturation, thereby forming a growth unit, and then nucleating and crystallizing to obtain a composite powder.
4. Sol-gel method. First, the modifier precursor is dissolved in water (or an organic solvent) to form a uniform solution, and the solute and the solvent are hydrolyzed or alcoholyzed to obtain a modifier (or its precursor) sol; then the pretreated coated particles are uniformly mixed with the sol to make the particles uniformly dispersed in the sol, and the sol is treated to be converted into a gel, and calcined at a high temperature to obtain a powder coated with a modifier on the surface, thereby achieving surface modification of the powder.
5. Precipitation method. Add a precipitant to a solution containing powder particles, or add a substance that can trigger the generation of a precipitant in the reaction system, so that the modified ions undergo a precipitation reaction and precipitate on the surface of the particles, thereby coating the particles.
6. Heterogeneous coagulation method (also known as "heteroflocculation method"). A method proposed based on the principle that particles with opposite charges on the surface can attract each other and coagulate.
7. Microemulsion coating method. First, the ultrafine powder to be coated is prepared by the tiny water core provided by the W/O (water-in-oil) type microemulsion, and then the powder is coated and modified by microemulsion polymerization.
8. Non-uniform nucleation method. According to the LAMER crystallization process theory, the coating layer is formed by the non-uniform nucleation and growth of the modifier particles on the coated particle matrix.
9. Chemical plating method. It refers to the process of metal precipitation by chemical method without applying external current. There are three methods: replacement method, contact plating method and reduction method.
10. Supercritical fluid method. It is a new technology still under research. In supercritical conditions, reducing the pressure can lead to supersaturation, and can achieve a high supersaturation rate, so that the solid solute crystallizes from the supercritical solution.
11. Chemical vapor deposition. At a relatively high temperature, the mixed gas interacts with the surface of the substrate, causing some components in the mixed gas to decompose and form a coating of metal or compound on the substrate.
12. High energy method. The method of coating nanoparticles using infrared, ultraviolet, gamma rays, corona discharge, plasma, etc. is collectively referred to as high energy method. The high energy method often uses some substances with active functional groups to achieve surface coating of nanoparticles under the action of high energy particles.
13. Spray thermal decomposition method. The process principle is to spray a mixed solution of several salts containing the required positive ions into a mist, send it into a reaction chamber heated to a set temperature, and generate fine composite powder particles through reaction.
14. Microencapsulation method. A surface modification method that covers a uniform film with a certain thickness on the surface of the powder. The particle size of the microcapsules usually prepared is 2 to 1000 μm, and the wall material thickness is 0.2 to 10 μm.
Ultrafine nickel powder: small size, big effect!
Ultrafine nickel powder generally refers to nickel with a particle size of less than 1μm. According to the particle size, ultrafine nickel powder is often divided into micron-grade nickel powder (average particle size ≥ 1μm), submicron-grade nickel powder (average particle size 0.1-1.0μm) and nano-grade nickel powder (average particle size 0.001-0.100μm). Ultrafine nickel powder has the characteristics of small size, high surface activity, good conductivity and excellent magnetic conductivity. It is widely used in cemented carbide, chip multilayer ceramic capacitors, magnetic materials, high-efficiency catalysts, conductive slurries, absorbing materials, electromagnetic shielding materials and other fields. Many fields have high requirements for the purity, dispersibility and sphericity of nickel powder, so the preparation of spherical ultrafine nickel powder with good sphericity, high purity and high dispersibility has become the current research focus in the preparation of nickel powder.
Ultrafine nickel powder is widely used in many high-tech and industrial fields due to its high specific surface area, excellent conductivity, catalytic activity and magnetic properties.
Electronics and semiconductor fields
Multilayer ceramic capacitors (MLCC): Ultrafine nickel powder is a key material for the internal electrodes of MLCC, replacing the traditional precious metal palladium/silver alloy, significantly reducing manufacturing costs, while meeting the needs of high-frequency and miniaturized electronic components.
Conductive paste and packaging: Due to its high conductivity and dispersibility, it is used in electronic pastes and printed circuit board (PCB) conductive coatings to improve the conductivity and heat dissipation performance of electronic devices.
Semiconductor materials: As a conductive filler in chip packaging, it enhances the thermal conductivity and mechanical stability of the material.
Energy storage and conversion
Lithium-ion batteries: As a positive electrode material (such as LiNiO2), it significantly improves the battery energy density and cycle life, especially for new energy vehicles and energy storage systems.
Fuel cells: Used as a catalyst (such as a hydrogen-oxygen reaction catalyst) to improve reaction efficiency, reduce the use of precious metal platinum, and reduce costs.
Supercapacitors: Enhance the charge storage capacity of electrode materials through nanostructure optimization.
Catalysis and environmental protection
Petrochemicals: used as an efficient catalyst in hydrogenation, dehydrogenation and other reactions to improve yield and product purity, such as toluene hydrogenation to produce methylcyclohexane.
Environmental protection: used for waste gas and wastewater treatment, catalytic degradation of pollutants, and reduction of harmful substance emissions.
New energy catalysis: in hydrogen energy production, efficient hydrogen production through steam reforming reaction (SMR) promotes the development of clean energy.
Magnetic materials and wave absorbing technology
Magnetic fluid and storage medium: dispersed in the carrier liquid to form magnetic fluid, or used in high-density magnetic storage devices (such as quantum disks).
Electromagnetic shielding and wave absorbing materials: ultrafine nickel powder has excellent electrical and magnetic properties. Electromagnetic wave shielding materials can be prepared by compounding ultrafine nickel powder with polymer matrix materials. Multi-component composite materials such as copper and nickel have good wave absorbing and shielding properties in the high-frequency region, and can be used as stealth materials in the high-frequency region. Based on ultrafine nickel powder conductive coating, it is widely used in military stealth technology and civilian electronic equipment.
Aerospace and high-end manufacturing
High-temperature alloys: As additives to improve the high temperature resistance and corrosion resistance of alloys, suitable for aircraft engine parts.
Cemented carbide: Replace cobalt as a bonding metal, used in cutting tools and wear-resistant parts, reducing costs and improving performance.
Biomedicine and new materials
Drug carriers and diagnosis and treatment: Utilize its magnetic responsiveness and biocompatibility for targeted drug delivery and magnetic marker detection.
3D printing and composite materials: As a filler for metal injection molding (MIM), it improves the mechanical properties and molding accuracy of complex parts.
The advantage of ultrafine nickel powder is that it replaces more expensive precious metal materials, greatly reducing production costs. However, these application fields require the nano nickel powder used to have regular spherical structure, small size and uniform particle size distribution, good dispersibility, high tap density, strong antioxidant ability and other properties, which also poses a challenge to the preparation process of nano nickel powder.
Advantages of carbon materials in thermal conductivity and heat dissipation
In the current electronics and optoelectronics industries, as electronic devices and their products develop towards high integration and high computing, the dissipated power has doubled. Heat dissipation has gradually become a key factor restricting the sustainable development of the electronics industry. Finding heat management materials with excellent thermal conductivity is crucial for the next generation of integrated circuits and three-dimensional electronic product designs.
The thermal conductivity of traditional ceramic materials (such as boron nitride, aluminum nitride) and metal materials (such as copper, aluminum) is only a few hundred W/(m·K) at most. In comparison, the thermal conductivity of carbon materials such as diamond, graphite, graphene, carbon nanotubes, and carbon fiber is even more amazing. For example, graphite has a theoretical thermal conductivity of up to 4180W/mk in the direction parallel to the crystal layer, which is almost 10 times that of traditional metal materials such as copper, silver, and aluminum. In addition, carbon materials also have excellent properties such as low density, low thermal expansion coefficient, and good high-temperature mechanical properties.
Graphene
Graphene is a single-layer carbon atom surface material peeled off from graphite. It has a honeycomb-shaped two-dimensional plane structure composed of single-layer carbon atoms tightly arranged in regular hexagons. The structure is very stable. The connection between carbon atoms inside graphene is very flexible. When external force is applied to graphene, the carbon atom surface will bend and deform, so that the carbon atoms do not have to rearrange to adapt to the external force, thereby maintaining structural stability. This stable lattice structure gives graphene excellent thermal conductivity.
Carbon nanotubes
Since the discovery of carbon nanotubes in 1991, it has been a focus, attracting many scientists to study the thermal conductivity of carbon nanotubes. Carbon nanotubes are made of single-layer or multi-layer graphite sheets curled up, and are divided into three types: single-walled, double-walled and multi-walled.
The special structure gives carbon nanotubes extremely high thermal conductivity. Some researchers have calculated that the thermal conductivity of single-walled carbon nanotubes at room temperature is 3980 W/(m·K), the thermal conductivity of double-walled carbon nanotubes is 3580 W/(m·K), and the thermal conductivity of multi-walled carbon nanotubes is 2860 W/(m·K).
Diamond
The crystal structure of diamond is a close arrangement of carbon atoms in tetrahedrons, and all electrons participate in bonding. Therefore, its room temperature thermal conductivity is as high as 2000~2100 W/(m·K), which is one of the materials with the best thermal conductivity in nature. This feature makes it irreplaceable in the field of high-end heat dissipation.
Carbon fiber
Carbon fiber is treated by high-temperature carbonization to form a turbostratic graphite structure. If its axial graphite lattice is highly oriented, it can achieve ultra-high thermal conductivity. For example, the thermal conductivity of mesophase pitch-based carbon fiber is 1100 W/(m·K), and the thermal conductivity of vapor-grown carbon fiber can reach 1950 W/(m·K).
Graphite
Graphite has a hexagonal crystal structure, consisting of six facets and two close-packed basal planes. The first layer of the hexagonal grid of carbon atoms is staggered by 1/2 of the hexagonal diagonal line and overlapped in parallel with the second layer. The third layer and the first layer are repeated in position, forming an ABAB... sequence. The thermal conductivity of natural graphite along the (002) crystal plane is 2200 W/(m·K), and the in-plane thermal conductivity of highly oriented pyrolytic graphite can also reach 2000 W/(m·K).
The above carbon materials all have extremely high thermal conductivity, so they have attracted much attention in the field of high heat dissipation requirements. Next, let's look at several classic carbon-based conductive/heat dissipating materials.
Carbon materials, with their unique crystal structure and physical and chemical properties, have demonstrated irreplaceable advantages in the field of thermal conductivity and heat dissipation. With the advancement of preparation technology and the expansion of application scenarios, carbon-based materials such as graphene and diamond are expected to promote heat dissipation solutions in industries such as electronics and aerospace to a higher level.
Application of powder preparation based on thermal plasma technology in thermal management materials
The miniaturization and integration of electronic devices put forward higher heat dissipation requirements for polymer-based thermal management materials. The development of new high thermal conductivity fillers to construct effective thermal conduction paths is the key to achieving high-performance thermal management materials.
Thermal plasma technology has great advantages in the preparation of nano- and micron-shaped spherical powders, such as spherical silicon powder and alumina powder, due to its high temperature, controllable reaction atmosphere, high energy density and low pollution.
Thermal plasma technology
Plasma is the fourth state of matter in addition to solid, liquid and gas. It is an overall electrically neutral aggregate composed of electrons, cations and neutral particles. According to the temperature of heavy particles in plasma, plasma can be divided into two categories: hot plasma and cold plasma.
The temperature of heavy ions in hot plasma can reach 3×103 to 3×104K, which basically reaches the local thermodynamic equilibrium state. In this state, the thermal plasma has the following relationship: electron temperature Te = plasma temperature Th = excitation temperature Tex = ionization reaction temperature Treac, so the thermal plasma has a uniform thermodynamic temperature.
Plasma preparation of spherical powders
Based on the characteristics of high temperature and fast cooling rate of high-frequency thermal plasma, physical vapor deposition technology is used to prepare nanopowders.
There are two main ways to prepare spherical powders with plasma.
One is to pass irregularly shaped and large-size raw material powders into the high-temperature arc of thermal plasma, and use the high-temperature environment generated by thermal plasma to quickly heat and melt the raw material particles (or melt the surface). Due to the surface tension, the melted powder forms a sphere and solidifies at a suitable cooling rate to obtain a spherical powder. The second is to use irregular powders or precursors as raw materials and thermal plasma as a high-temperature heat source. The raw materials react with the active particles therein and are rapidly cooled and deposited to generate ideal powder materials.
Taking advantage of the characteristics of high temperature, high energy, controllable atmosphere and no pollution of thermal plasma, high-purity, high-sphericity, and different-size spherical powders can be prepared by controlling the parameters in the preparation process such as feeding, cooling rate, and plasma power. Therefore, the use of plasma technology to prepare spherical powders has been increasingly widely used in energy, aerospace, chemical industry and other fields.
Main application areas and characteristics of silicon micropowder
Silica powder is an inorganic non-metallic material with silicon dioxide as the main component. It is made of crystalline quartz, fused quartz, etc. as raw materials, and is processed by grinding, precision grading, impurity removal and other processes. It has excellent dielectric properties, low thermal expansion coefficient, and high thermal conductivity. It is widely used in copper clad laminates, epoxy molding compounds, insulating materials, adhesives, coatings, ceramics and other fields.
1. Copper clad laminate
Copper clad laminate is an important substrate for the manufacture of printed circuit boards with a structure of "copper foil + dielectric insulation layer (resin and reinforcement material) + copper foil". It is an upstream basic material for various circuit systems.
The choices of fillers for copper clad laminates include silicon micropowder, aluminum hydroxide, magnesium hydroxide, talcum powder, mica powder and other materials. Among them, silicon micropowder has relative advantages in heat resistance, mechanical properties, electrical properties and dispersibility in resin systems. It can be used to improve heat resistance and moisture resistance, improve the rigidity of thin copper clad laminates, reduce thermal expansion coefficient, improve dimensional stability, improve drilling positioning accuracy and inner wall smoothness, improve the adhesion between layers or between insulating layers and copper foil, etc., so it is favored in copper clad laminate fillers.
Spherical silicon micropowder has the best performance but high cost, and is only used in the field of high-end copper clad laminates. In terms of thermal conductivity, filling, thermal expansion and dielectric properties, the performance of spherical silicon micropowder is better, but in terms of price, angular silicon micropowder is lower. Therefore, considering the comprehensive performance and cost, spherical silicon micropowder is currently mainly used in the field of high-end copper clad laminates, such as high-frequency and high-speed copper clad laminates, IC carriers, etc., and the higher the application scenario, the higher the addition ratio.
2. Epoxy molding compound
Epoxy molding compound is a powdered molding compound made of epoxy resin as base resin, high-performance phenolic resin as curing agent, silicon powder as filler, and a variety of additives. It is an essential material for semiconductor packaging such as integrated circuits (more than 97% of semiconductor packaging uses epoxy molding compound).
3. Electrical insulation material
Silicon powder used in electrical insulation products can effectively reduce the linear expansion coefficient of the cured product and the shrinkage rate during the curing process, reduce internal stress, and improve the mechanical strength of the insulating material, thereby effectively improving and improving the mechanical and electrical properties of the insulating material. Therefore, the functional requirements of customers in this field for silicon micropowder are more reflected in low linear expansion coefficient, high insulation and high mechanical strength, while the requirements for its dielectric properties and thermal conductivity are relatively low.
In the field of electrical insulation materials, single-specification silicon micropowder products with an average particle size of 5-25µm are usually selected according to the characteristics of electrical insulation products and the requirements of their production process, and high requirements are placed on product whiteness, particle size distribution, etc.
4. Adhesives
Silicon micropowder filled in adhesive resin can effectively reduce the linear expansion coefficient of the cured product and the shrinkage rate during curing, improve the mechanical strength of the adhesive, improve heat resistance, anti-permeability and heat dissipation performance, thereby improving the bonding and sealing effect.
The particle size distribution of silicon micropowder will affect the viscosity and sedimentation of the adhesive, thereby affecting the processability of the adhesive and the linear expansion coefficient after curing.
5. Honeycomb ceramics
Honeycomb ceramic carriers for automobile exhaust purification and cordierite material automobile exhaust filter DPF for diesel engine exhaust purification are made of alumina, silicon micropowder and other materials through mixing, extrusion molding, drying, sintering and other processes. Spherical silicon micropowder can improve the molding rate and stability of honeycomb ceramic products.
Titanium dioxide coating modification
The coating modification of titanium dioxide (titanium dioxide) is an important means to improve its performance (such as dispersibility, weather resistance, glossiness, chemical stability, etc.). Common coating modification methods mainly include three categories: inorganic coating, organic coating and composite coating. The following is a specific classification and brief introduction:
Inorganic coating modification
By coating a layer of inorganic oxides or salts on the surface of titanium dioxide particles, a physical barrier is formed to improve its chemical stability and optical properties.
1. Oxide coating
Principle: Use the hydrate of metal oxides (such as SiO₂, Al₂O₃, ZrO₂, etc.) to precipitate on the surface of titanium dioxide to form a uniform coating layer.
Process: Usually through liquid phase deposition method, metal salts (such as sodium silicate, aluminum sulfate) are added to the titanium dioxide slurry, and the pH value is adjusted to precipitate and coat the metal oxide hydrate.
2. Composite oxide coating
Principle: Coating two or more metal oxides (such as Al₂O₃-SiO₂, ZrO₂-SiO₂, etc.), combining the advantages of each component.
Features: Better overall performance, for example, Al₂O₃-SiO₂ coating can simultaneously improve dispersibility and weather resistance, suitable for high-demand automotive paints and coil coatings.
3. Salt coating
Principle: Use metal salts (such as phosphates, silicates, sulfates, etc.) to form a poorly soluble salt layer on the surface of titanium dioxide.
Organic coating modification
Through the reaction of organic compounds with the hydroxyl groups on the surface of titanium dioxide, an organic molecular layer is formed to improve its compatibility with organic media.
1. Coupling agent coating
Principle: Using the amphiphilic structure of coupling agent molecules (such as silanes, titanates, aluminates), one end is combined with the hydroxyl group on the surface of titanium dioxide, and the other end reacts with the organic matrix (such as resin, polymer).
Silane coupling agent: Improves the dispersibility of titanium dioxide in water-based systems, commonly used in water-based coatings and inks.
Titanate/aluminate coupling agent: Enhances compatibility in oily systems such as plastics and rubbers, and reduces agglomeration during processing.
2. Surfactant coating
Principle: Surfactants (such as fatty acids, sulfonates, quaternary ammonium salts, etc.) attach to the surface of titanium dioxide through physical adsorption or chemical reaction to form a charge layer or hydrophobic layer.
Function:
Anionic surfactants (such as stearic acid): Improve dispersibility in oily media, commonly used in plastics and rubber.
Cationic surfactants (such as dodecyltrimethylammonium chloride): Suitable for polar systems to improve stability.
3. Polymer coating
Principle: Graft polymers (such as acrylates, epoxy resins, siloxanes, etc.) on the surface of titanium dioxide through polymerization reactions.
Function:
Form a thick coating layer to further isolate chemical erosion and improve weather resistance and mechanical properties.
Improve compatibility with specific resins, suitable for high-performance composite materials and coatings.
4. Silicone coating
Principle: Use the low surface energy characteristics of polysiloxane (silicone oil, silicone resin, etc.) to coat titanium dioxide particles.
Function: Reduce surface tension, improve dispersibility and smoothness, commonly used in inks and cosmetics.
III. Composite coating modification
Combining the advantages of inorganic and organic coatings, double coating is carried out in stages or simultaneously to achieve complementary performance.
1. Inorganic first and then organic coating
2. Inorganic-organic synchronous coating
Other special coating technologies
1. Nano coating
2. Microcapsule coating
Principle: Encapsulate titanium dioxide particles in polymer microcapsules, release titanium dioxide by controlling the capsule rupture conditions (such as temperature, pH value), suitable for smart coatings and slow-release systems.
Magnesium alloy materials in the low-altitude economy
As a lightweight material, magnesium alloy has become an ideal choice for low-altitude economic aircraft due to its low density, high strength, shock absorption and electromagnetic wave shielding capabilities. Compared with traditional materials, magnesium alloy is lighter, can significantly extend the flight time and improve energy efficiency. In addition, the shock absorption and electromagnetic shielding capabilities of magnesium alloy can also improve the operating safety and electromagnetic compatibility of aircraft in complex environments.
Electric vertical take-off and landing aircraft (eVTOL)
Fuse frame: The density of magnesium alloy is only 2/3 of that of aluminum alloy and 1/4 of that of steel. Using it for the fuselage frame can significantly reduce the weight of the aircraft, improve the load capacity and range. For example, Fengfei Aviation's 2-ton cargo eVTOL uses magnesium alloy to manufacture some fuselage frame components, which effectively achieves lightweight while ensuring structural strength.
Wing structure: Magnesium alloy has high specific strength and can maintain the structural stability of the wing under large aerodynamic loads, while reducing the weight of the wing, which helps to improve the flight performance of the aircraft.
Motor housing: Magnesium alloy has good thermal conductivity and electromagnetic shielding properties, which can effectively dissipate the heat generated by the operation of the generator, protect the internal circuit of the motor from electromagnetic interference, extend the service life of the motor, and improve the operating efficiency of the motor. For example, the motor housing of Xiaopeng Huitian's Traveler X2 smart electric flying car is made of magnesium alloy material.
Battery compartment: Magnesium alloy can be used to manufacture battery compartments. Its low density helps reduce the overall weight of the aircraft, and its electromagnetic shielding performance can prevent the battery from being interfered with by external electromagnetic interference, ensuring the safety and stable operation of the battery.
Instrument panel bracket: The magnesium alloy instrument panel bracket has good rigidity and stability, and can support various devices and display devices of the eVTOL instrument panel. At the same time, its lightweight characteristics also help to reduce the overall weight of the aircraft.
UAV
Fuselage frame: Magnesium alloy has low density, which can significantly reduce the weight of the drone, increase the endurance and load capacity, and the high specific strength can ensure that the fuselage can withstand various stresses during flight. For example, the multi-rotor drone "Hybrid Flyer" with a magnesium alloy frame is about 30% lighter than the traditional material frame, and the endurance time is also extended.
Wings and tails: can be used to manufacture the internal support structure or overall skin of wings and tails, while ensuring structural strength and aerodynamic performance, reducing the flight resistance and energy consumption of drones, and improving flight efficiency and flexibility.
Control circuit board bracket: provides stable support for the control circuit board. Its lightweight characteristics help to lower the center of gravity of the drone and improve flight stability. At the same time, the electromagnetic shielding performance can reduce electromagnetic interference between circuit boards and ensure accurate transmission of control signals.
Sensor housing: used to encapsulate various sensors, such as cameras, GPS modules, etc., while protecting the sensors, reducing the payload weight of drones, allowing drones to carry more equipment or extend flight time, and the corrosion resistance of magnesium alloys can adapt to the working requirements of sensors in different environments.
Propellers: magnesium alloys can be used to manufacture propellers. Low density and high specific strength help improve propeller rotation efficiency, reduce energy consumption, reduce weight, and thus improve the overall performance of drones.
Magnesium's light weight, low cost and high reserve make it more advantageous than traditional materials, and it is expected to solve the dilemma of high raw material costs and low operating efficiency in low-altitude economic construction. With the continuous advancement of magnesium alloy production technology, large-scale production will further reduce costs, thereby promoting its large-scale application in the low-altitude field.
Glass fiber composite material properties
Fiberglass is a material composed of many extremely fine glass fibers. It is made by forcing molten glass through a sieve, which spins it into threads and then combines to form glass fibers.
Fiberglass composites are a reinforced plastic material consisting of glass fibers embedded in a resin matrix. Fiberglass composites have excellent specific strength, are light in weight but have mechanical properties close to metal; they are rust-proof and can withstand acid, alkali, moisture and salt spray environments for a long time, and have a longer service life than traditional metal materials; performance can be optimized by adjusting the fiber layup and resin type, and can be processed into complex shapes; they are non-conductive and transparent to electromagnetic waves, and are suitable for special functional components such as electrical equipment and radomes; compared with high-end composite materials such as carbon fiber, fiberglass is cheaper and is an economical high-performance material choice.
Glass fiber composite materials used in low altitude economy
Widely used in the field of drones
Fuselage and structural components: Glass fiber reinforced plastic (GFRP) is widely used in key structural components such as the fuselage, wings and tail of drones due to its lightweight and high strength.
Blade Materials: In drone propeller manufacturing, fiberglass is used in combination with materials such as nylon to increase rigidity and durability.
Important materials for electric vertical take-off and landing aircraft (eVTOL)
Fuse frame and wings: eVTOL aircraft have extremely high requirements for lightweight, and glass fiber reinforced composite materials are often used in combination with carbon fiber to optimize the fuselage structure and reduce costs.
Functional components: Glass fiber is also used in eVTOL avionics devices (such as RF power amplifiers), and its high temperature resistance and insulation properties make it an ideal choice.
As a strategic basic material in the low-altitude economy, glass fiber has broad application prospects in drones, eVTOL and other fields. With policy support and technological progress, its market demand will continue to grow and become an important force in promoting the development of the low-altitude economy.
The neglected gold: rare earth polishing powder
Rare earth cerium-based polishing powder is the mainstream rare earth polishing powder at present. It has excellent polishing performance and can improve the surface finish of products or parts. It is known as the "king of polishing powder". The glass processing industry and the electronics industry are the main downstream application fields of rare earth polishing powder. The waste of rare earth polishing powder that fails after polishing accounts for about 70% of the output each year. The waste components mainly come from rare earth polishing powder waste residue, waste liquid, glass fragments from polishing workpieces, grinding skin (organic polymer) from polishing cloth, oil and other impurities, and the proportion of rare earth components is 50%. How to dispose of the failed rare earth polishing powder has become a major problem for downstream application companies.
Currently, the commonly used methods for recycling rare earth polishing powder waste are physical separation and chemical separation.
Physical separation method
(1) Flotation method
In recent years, flotation technology has been widely used in solid waste treatment. Due to the difference in hydrophilicity of the components in waste rare earth polishing powder, different flotation agents are selected to improve the affinity of the components in aqueous solution, leaving the hydrophilic particles in the water, thereby achieving the purpose of separation. However, the size of the polishing powder particles affects the flotation recovery rate, and the recovery purity is not enough.
During flotation, different collectors are selected, and the impurity removal effect varies greatly. Yang Zhiren et al. found that when the pH of styrenephosphonic acid is 5, the recovery rate of cerium oxide and lanthanum oxide after flotation reaches 95%, while the recovery rate of calcium fluoride and fluoroapatite is only 20% at most. Particles with a diameter of less than 5 microns need to be further separated to remove impurities due to poor flotation effect.
(2) Magnetic separation method
Waste rare earth polishing powder has magnetism. Based on this, Mishima et al. designed a device with a vertical magnetic field to recover rare earth polishing slurry. When the flow rate of the waste powder slurry is 20 mm/s, the circulation time is 30 min, the slurry concentration is 5%, and the pH of the slurry is 3, the separation efficiency of cerium dioxide and iron flocculant can reach 80%. If the magnetic field direction is changed to a horizontal gradient and then MnCl2 solution is added, silicon dioxide and aluminum oxide with opposite magnetic properties can be separated from cerium dioxide.
(3) Other methods
Takahashi et al. froze the waste powder slurry whose particles were not easy to settle at -10°C, and then thawed it in an environment of 25°C. The impurities and rare earth oxides formed a layer, which facilitated the aggregation and recovery of useful substances in the waste.
Chemical separation method
The chemical method mainly adopts the recovery process after acid dissolution and alkali roasting, and uses a reducing agent as an auxiliary reagent to obtain rare earth polishing powder raw materials through impurity removal, extraction, and precipitation. This method has a high rare earth recovery rate, but the process is long and the cost is high. Excessive strong acid or strong alkali produces a large amount of wastewater. (1) Alkali treatment
Aluminum oxide and silicon dioxide are the main impurities in rare earth polishing powder waste. Use 4 mol/L NaOH solution to react with rare earth polishing powder waste for 1 hour at 60°C to remove silicon dioxide and aluminum oxide impurities in rare earth polishing powder waste.
(2) Acid treatment
When recovering rare earth elements from polishing powder waste, nitric acid, sulfuric acid and hydrochloric acid are often used for leaching. Cerium dioxide, the main component of rare earth polishing powder waste, is slightly soluble in sulfuric acid.
(3) Reducing agent assisted acid leaching
If CeO2 is directly leached with acid, the effect is not ideal. If a reducing agent is added to reduce Ce4+ to Ce3+, the rare earth leaching rate can be improved. Using the reducing agent H2O2 to assist hydrochloric acid leaching of rare earth polishing powder waste can significantly improve the experimental results.
Six process paths for high-purity quartz glass
Quartz glass has high purity, high spectral transmittance, low thermal expansion coefficient, and excellent resistance to thermal shock, corrosion, and deep ultraviolet radiation. It is widely used in high-end industrial manufacturing fields such as optics, aerospace, and semiconductors.
Quartz glass can be classified according to the preparation process. There are two main types of raw materials for preparing quartz glass. The first type is high-purity quartz sand, which is used for electric melting and gas refining to prepare fused quartz glass at high temperatures exceeding 1800°C; the second type is silicon-containing compounds, which are used to prepare synthetic quartz glass through chemical reactions.
Electric melting method
The electric melting method is to melt the powdered quartz raw material in the crucible by electric heating, and then form quartz glass through a vitrification process of rapid cooling. The main heating methods include resistance, arc and medium frequency induction.
Gas refining method
Industrially, gas refining method is slightly later than electric melting method. It uses hydrogen-oxygen flame to melt natural quartz, and then gradually accumulates it on the quartz glass target surface. The fused quartz glass produced by gas refining method is mainly used for electric light sources, semiconductor industry, spherical xenon lamps, etc. In the early days, large-caliber transparent quartz glass tubes and crucibles were directly melted with high-purity quartz sand on special equipment using hydrogen-oxygen flame. Now gas refining method is commonly used to prepare quartz ingots, and then the quartz ingots are cold or hot processed to make the required quartz glass products.
CVD method
The principle of CVD method is to heat volatile liquid SiCl4 to make it gaseous, and then let the gaseous SiCl4 enter the hydrogen-oxygen flame formed by the combustion of hydrogen and oxygen under the drive of carrier gas (O2), react with water vapor at high temperature to form amorphous particles, deposit on the rotating deposition substrate, and then melt at high temperature to form quartz glass.
PCVD method
The PCVD process was first proposed by Corning in the 1960s. It uses plasma to replace hydrogen-oxygen flame as the heat source for preparing quartz glass. The temperature of the plasma flame used in the PCVD process is much higher than that of ordinary flames. Its core temperature can be as high as 15000K, and the average temperature is 4000~5000K. The working gas can be appropriately selected according to the specific process requirements.
Two-step CVD method
The traditional CVD method is also called the one-step method or direct method. Since water vapor is involved in the reaction, the hydroxyl content in the quartz glass prepared by the one-step CVD method is generally high and difficult to control. In order to overcome this shortcoming, engineers improved the one-step CVD method and developed the two-step CVD method, also called the indirect synthesis method.
Thermal Modification
The thermal modification method first softens the quartz glass base material by heating it, and then obtains the desired product through methods such as trough sinking and drawing. In the thermal modification furnace, the furnace body is heated by electromagnetic induction heating. The alternating current passed through the induction coil in the furnace generates an alternating electromagnetic field in space, and the electromagnetic field acts on the heating element to generate current and heat. As the temperature rises, the quartz glass base material softens, and at this time, a quartz glass rod/tube can be formed by pulling down with a tractor. By adjusting the temperature in the furnace and the pulling speed, quartz glass rods/tubes of different diameters can be drawn. The coil arrangement and furnace structure of the electromagnetic induction heating furnace have a great influence on the temperature field in the furnace. In actual production, the temperature field in the furnace needs to be strictly controlled to ensure the quality of quartz glass products.