The wide applications of spherical alumina
Due to its larger surface area and uniform distribution compared to other morphologies, spherical alumina powder exhibits superior performance in practical applications compared to other shapes of alumina materials. It can be used not only in ceramics, catalysts and their carriers, but also in various fields such as grinding, polishing, and electronic devices.
Thermal Conductive Filler Field
With the advent of the information age, advanced electronic devices are becoming increasingly miniaturized, and the heat generated by these devices is increasing exponentially, placing many demands on system heat dissipation. Because alumina is widely available in the market, comes in many varieties, and is cheaper than other thermal conductive materials, and can be added in large quantities to polymer materials, it has a high cost-performance ratio. Therefore, most high-thermal conductivity insulating materials currently use alumina as a high-thermal conductivity filler.
Ceramics Field
Adding a certain amount of spherical alumina powder during the production of ceramics can significantly change the properties of the ceramics. The low-temperature brittleness of ceramics greatly affects their application range. Ceramic materials with added spherical alumina powder can be used to manufacture low-temperature ductile ceramics.
Grinding and Polishing Field
Compared with traditional granular or flake alumina, spherical alumina has better dispersibility and fluidity. Spherical alumina powder abrasives can be evenly distributed in the polished product, avoiding abnormal powder accumulation. Furthermore, the smooth surface of the particles prevents scratching the workpiece surface, thus improving the surface finish.
Electronic and Optical Materials Field
Spherical alumina has a wide range of applications in the electronic and optical fields. Using spherical alumina as a substrate and adding rare earth elements as activators, this method can produce red luminescent materials with better performance. Spherical alumina particles are uniform in size and evenly dispersed, exhibiting better luminescence performance compared to other shapes of alumina, and better determining the filling structure of the luminescent material.
Catalyst and Carrier Field
Because alumina has a large number of unsaturated chemical bonds on its surface and a large number of catalytic active centers, it exhibits high chemical activity. Moreover, spherical alumina has the advantages of low particle wear, long service life, and large specific surface area.
3D Printing Field
Spherical alumina is one of the most commonly used materials for 3D printing due to its high strength, high sphericity, and high-temperature resistance.
Surface Protective Coatings
The use of spherical alumina as a spray coating material is currently one of the research hotspots. This spray coating material not only provides protection for polymer materials, glass, metals, and alloys, but also extends the lifespan of stainless steel products such as kitchen cookware.
From all perspectives, fine alumina has become one of the new materials that my country needs to prioritize for development. With its widespread application in traditional fields and rapid penetration into emerging industries such as new energy vehicles and photovoltaic power generation, demand is constantly increasing, and the fine alumina industry has broad market prospects.
Five typical applications of talc powder
When talc's multiple powerful "superpowers" are unleashed in coatings, it can significantly improve material performance while substantially reducing product costs, leading to a comprehensive improvement in coating quality. Therefore, talc is widely used in various coating formulations.
Architectural Coatings
When talc powder is used in architectural coatings, it provides excellent brushability, gloss retention, and leveling properties. At the same time, the drying properties, tackiness, hardness, and corrosion resistance of the coating are significantly improved. It enhances the dry and wet hiding power, matting effect, crack resistance, and scrub resistance of the coating product, and can greatly improve the tinting strength of titanium dioxide, thus reducing product costs. In the use of materials for architectural coatings, talc is an indispensable component.
Industrial Coatings
Talc powder is widely used as a functional filler in various industrial coatings, especially in primer coatings for parts. Due to its good sanding and water resistance, talc powder can completely or partially replace primer fillers. When applied to steel structure coatings, talc powder effectively improves the sedimentation properties of the coating, the mechanical properties of the film, and recoatability. Many products, such as flash-drying primers and coatings for transportation vehicles, prioritize the use of talc powder.
Wood Coatings
Talc also holds a place in wood (furniture) coatings.
The application of talc powder in wood coatings is mainly in transparent primers and solid color topcoats. The low hardness characteristics of talc powder give the paint film good sandability, allowing for partial replacement of high-cost zinc stearate sanding agents. The refractive index of talc is similar to that of resin binders, giving the coating high transparency. This characteristic allows the natural texture of the substrate to be well displayed, and when used in matte topcoats, it can partially replace expensive matting agents.
When talc is used in wood coatings, it can maximize the charm of wooden furniture while satisfying people's pursuit of lifestyle and reducing living costs.
Anti-corrosion Coatings
Talc is still frequently seen in the field of anti-corrosion coatings. Talc's naturally stable lamellar structure increases the viscosity of the paint and provides a shielding effect to the paint film. While effectively preventing the penetration of corrosive media such as acids, alkalis, and salts, it also hinders the penetration of the primer on porous substrates, improving the sealing effect and sandability of the primer. These characteristics significantly improve the anti-corrosion performance of the paint film. In the field of anti-corrosion coatings, talc is a solid and reliable partner, worthy of trust.
Waterproof Coatings
As a filler in waterproof coatings, talc powder not only reduces volume shrinkage during coating curing, improves the wear resistance and adhesion of the coating, and reduces costs, but also gives the coating good storage stability and heat resistance.
More importantly, talc powder has a beneficial effect on the elastic elongation and tensile strength of waterproof coatings: within a certain range of addition, as the amount of talc powder filler increases, the elastic elongation and tensile strength of the waterproof coating both increase. This also means maximum protection for the coated object.
The application of talc in architectural coatings, industrial coatings, wood coatings, anti-corrosion coatings, and waterproof coatings is only a small part of its many application fields. As an inexpensive, non-renewable non-metallic mineral, talc also has wide applications in cosmetics, food, medicine, rubber, ceramics, textiles, printing and dyeing, and the electronics industry. It is believed that in the near future, with further research, humanity's understanding of talc will become increasingly profound, and talc will surely shine brightly in even broader fields.
How does barium sulfate contribute to the creation of high-quality coating materials?
Barium sulfate is highly favored primarily due to its exceptional filling capacity. This means that while maintaining paint film performance, it can effectively optimize formulation costs and is widely used in various fields, from industrial coatings to decorative paints.
More importantly, thanks to its small particle size, uniform distribution, large specific surface area, and excellent fluidity, barium sulfate exhibits very low abrasiveness during processing. This characteristic directly translates into production efficiency: it significantly reduces wear and tear on mixing, pumping, and spraying equipment, extending equipment lifespan and making the production process smoother and more economical.
This advantage is fully demonstrated in the application of automatic primer surface coatings. Even under high filling rate production requirements, barium sulfate ensures excellent stability and leveling properties of the paint slurry, resulting in exceptional uniformity and smoothness. This provides a flawless "canvas" for subsequent topcoat application, which is crucial for achieving efficient, automated, and high-quality coating.
Barium sulfate is far more than just a simple filler. It is a multifunctional additive that combines high filling capacity, low abrasion, and excellent leveling properties. Choosing it means selecting a reliable "foundation of quality" for your coatings, enhancing product performance while also ensuring efficient production.
Applications of advanced ceramic materials
Applications in High-Speed Aircraft
High-speed aircraft are strategic equipment that major military powers are vying to develop. Their supersonic flight and sharp structures lead to serious aerodynamic heating problems. The typical thermal environment for high-speed aircraft involves high temperatures and complex, harsh thermo-mechanical loads. Existing high-temperature alloys can no longer meet the requirements, leading to the emergence of ceramic matrix composites. In particular, SiCf/SiC composite ceramic materials have been widely used in hot structural components such as turbine blades, nozzle guide vanes, and turbine outer rings of aero-engines. Their composite material density is approximately 1/4 that of high-temperature alloys, resulting in significant weight reduction. Furthermore, they can operate at temperatures up to 1400°C, greatly simplifying cooling system design and enhancing thrust.
Applications in Lightweight Armor
Lightweight composite armor is crucial for maintaining the survivability of modern equipment. The development of ceramic fibers and fiber-reinforced ceramic matrix composites is fundamental to the application of lightweight composite armor. Currently, the main protective ceramic materials used include B4C, Al2O3, SiC, and Si3N4. Silicon carbide ceramics, with their excellent mechanical properties and cost-effectiveness, have become one of the most promising bulletproof ceramic materials. Their diverse applications in various armor protection fields, including individual soldier equipment, army armored weapons, armed helicopters, police and civilian special vehicles, give them broad application prospects. Compared to Al2O3 ceramics, SiC ceramics have a lower density, which is beneficial for improving equipment mobility.
Applications in Small Arms
Small arms, as an important component of weaponry, generally include pistols, rifles, machine guns, grenade launchers, and special individual equipment (individual rocket launchers, individual missiles, etc.). Their main function is to launch projectiles to the target area to kill or destroy enemy targets. The operating conditions of small arms include high temperature, low temperature, high altitude, humid heat, dust, rain, dust-rain, salt spray, and immersion in river water. Corrosion resistance is crucial. Currently, the main anti-corrosion processes for small arms include bluing, hard anodizing, ion-controlled penetration technology, diamond-like carbon coatings, and plasma nitriding. Especially for weapons and equipment used in marine environments, the requirement for corrosion resistance in salt spray environments for more than 500 hours poses a significant challenge to traditional coating treatments.
Applications in Gun Barrels
The gun barrel is a core component of projectile weapons. The internal structure of the gun barrel includes the chamber, the forcing cone, and the rifling, with the chamber and rifling connected by the forcing cone. Traditional gun barrels are generally made of high-strength alloy steel. During firing, the inside of the gun barrel is subjected to the combined effects of propellant gases and projectiles, leading to cracks and coating detachment on the inner wall of the barrel. The damage to the gun barrel's bore is a result of the repeated action of high-temperature, high-pressure, and high-velocity propellant gases and projectiles on the barrel wall. The forcing cone and the muzzle are usually the first parts to fail.
To improve gun barrel life, chromium plating of the bore is the most common method, but the oxidation resistance temperature of the chromium plating layer does not exceed 500°C. With the continuous increase in chamber pressure during firing and the exponential increase in gun barrel life requirements, the pressure and temperature borne by the gun barrel are also increasing. Utilizing the high hardness, high strength, and high-temperature chemical inertness of ceramics can effectively reduce gun barrel erosion and extend its service life.
Applications in Ammunition
The main components of ammunition are the warhead and the fuze. As the most direct component for causing damage, the warhead mainly consists of the casing, fragmentation elements, explosive charge, and fuze. Continuously improving the lethality of the warhead has always been a goal pursued in weapon development. Especially for area-effect grenades, the fragments produced by the warhead explosion are the terminal killing elements, and efficient fragmentation technology has always been a research challenge in this field.
Four major application areas of silicon nitride ceramics
Mechanical Field
Silicon nitride ceramics are mainly used as valves, pipes, classification wheels, and ceramic cutting tools in the mechanical industry. The most widespread application is silicon nitride ceramic bearing balls. Silicon nitride ceramics are widely recognized as the best bearing material, and the most critical "core player" in bearings—silicon nitride ceramic bearing balls—are the true "unsung heroes" that support equipment performance. These small ceramic balls, ranging in diameter from a few millimeters to tens of millimeters, may seem insignificant, but with their "lightweight, hard, stable, and insulating" properties, they play a "key role" in new energy vehicles, roller skates, dental drills, and even high-end bicycles.
Aerospace Field
Silicon nitride ceramic materials have advantages such as high strength, high temperature resistance, and good chemical stability, which can meet the stringent requirements for materials in the aerospace field. Silicon nitride ceramics have two classic applications in the aerospace field: firstly, silicon nitride is considered one of the few monolithic ceramic materials capable of withstanding the severe thermal shock and thermal gradients generated by hydrogen/oxygen rocket engines, and is used in rocket engine nozzles; secondly, the excellent properties of silicon nitride ceramics and their composites, such as heat resistance, wave transmission, and load-bearing capacity, make them one of the new generation of high-performance wave-transmitting materials under research.
Semiconductor Field
As electronic devices develop towards miniaturization and high performance, semiconductor packaging requires higher demands on heat dissipation materials. Silicon nitride ceramics have a thermal conductivity of up to 90-120 W/(m·K), and a high degree of matching with the thermal expansion coefficient of third-generation semiconductor substrate SiC crystals, making them the preferred material for SiC power device packaging substrates. Internationally, Japanese companies such as Toshiba and Kyocera dominate the market, while domestic companies such as Sinoma Advanced Materials have achieved technological breakthroughs.
In addition to being a key packaging material, silicon nitride ceramics show broad application prospects in semiconductor manufacturing equipment. In the wafer processing process, silicon nitride ceramics can be used to manufacture high-temperature resistant and thermal shock resistant heating elements, meeting the stringent operating conditions of equipment such as CVD (chemical vapor deposition) and diffusion furnaces.
Biomedical Field
As an emerging bioceramic material, silicon nitride shows great application potential in medical implants due to its excellent mechanical properties and biocompatibility. Specifically, silicon nitride has been used as an orthopedic biomaterial and successfully applied in bearing components of prosthetic hip and knee joints to improve wear resistance and extend the lifespan of the prostheses. Furthermore, silicon nitride materials have been used to promote bone fusion in spinal surgery. Silicon nitride ceramic materials demonstrate excellent stability and reliability in the medical field. Silicon nitride also exhibits strong cell adhesion and osteoconductivity, providing an important biological basis for its application in bone repair. However, the inherent brittleness of silicon nitride ceramics remains a major challenge for its application in bone repair engineering. In addition, silicon nitride materials are difficult to degrade in vivo, which hinders the growth of new bone tissue into the repair site and its complete replacement of the original repair material, thus limiting the breadth of its clinical applications.
Why is aluminum hydroxide so effective in treating stomach problems?
Aluminum oxide, also known as alumina, with the chemical formula Al2O3, is the second most abundant oxide in the Earth's crust after silicon dioxide, and is widely found in minerals such as feldspar and mica. Industrially, it is often refined from natural mineral raw materials—bauxite—to obtain alumina.
In a broader sense, aluminum oxide is a general term for aluminum oxides and aluminum hydroxides, a class of compounds composed of aluminum, oxygen, and hydrogen. Due to its multiple forms and properties, aluminum oxide can be divided into hydrated and anhydrous aluminum oxide.
Common hydrated aluminum oxides include industrial aluminum hydroxide, gibbsite, boehmite, pseudoboehmite, diaspore, corundum, and tohdite. Among these, industrial aluminum hydroxide, gibbsite, and boehmite are trihydrated aluminum oxides, diaspore and corundum are monohydrated aluminum oxides, and pseudoboehmite and tohdite are polyhydrated aluminum oxides.
In a broader sense, aluminum hydroxide is a general term for monohydrated aluminum oxide (meta-aluminum hydroxide) and trihydrated aluminum oxide (ortho-aluminum hydroxide). Hydrated aluminum oxide is not a true hydrate of aluminum oxide, but rather emphasizes a crystalline structure of aluminum hydroxide, where aluminum and hydroxide ions are connected by ionic bonds, and all hydroxide ions are equivalent. Aluminum hydroxide is usually a white powder, odorless, non-toxic, inexpensive, and widely used. Aluminum hydroxide is best known for its use as a flame retardant added to polymer matrix materials, where it exhibits excellent flame retardant properties.
Have you noticed that in daily life, aluminum hydroxide is often used to make stomach medicine? It has antacid, adsorbent, local hemostatic, and ulcer-protective effects. Aluminum hydroxide gel can be used to neutralize stomach acid and has a therapeutic effect on some common stomach diseases.
The principle is simple: aluminum hydroxide is a typical amphoteric oxide; it can react with both acids and bases. Therefore, aluminum hydroxide can neutralize or buffer stomach acid. When aluminum hydroxide reacts with stomach acid, the resulting aluminum chloride has an astringent effect, which can provide local hemostasis, but may also cause constipation as a side effect. Aluminum hydroxide, when mixed with gastric juice, forms a gel that covers the surface of ulcers, creating a protective film. This film isolates the gastric mucosa from irritation and damage caused by gastric acid, pepsin, and other harmful substances, promoting the repair and healing of the gastric mucosa and aiding in the treatment of gastritis, gastric ulcers, and other related diseases.
Secondly, aluminum ions bind with phosphates in the intestines to form insoluble aluminum phosphate, which is then excreted in the feces. Therefore, in patients with uremia, taking large amounts of aluminum hydroxide can reduce the absorption of intestinal phosphates, thereby alleviating acidosis.
Furthermore, nanoscale aluminum hydroxide can be used as a drug carrier to encapsulate drugs or antigens, improving drug stability and targeting. In addition, aluminum hydroxide is often used as a pharmaceutical excipient in the preparation of oral medications and vaccines, ensuring drug stability and safety.
Aluminum hydroxide: Why can't it be used directly?
Inorganic amphoteric hydroxides—aluminum hydroxide (Al(OH)3, ATH)—possess highly efficient flame retardant, smoke suppressant, and filling properties. Upon thermal decomposition, it does not produce toxic or corrosive gases and can be used as a flame retardant filler in polymeric organic materials. Currently, the use of ATH as a flame retardant is increasing year by year, and ATH has become the most important inorganic flame retardant globally.
Modification First, Then Flame Retardancy
Generally, manufacturers typically fill flammable materials with powdered aluminum hydroxide (ATH) or coat the surface of flammable materials with a flame-retardant coating containing ATH to improve the flame-retardant properties of polymeric organic materials.
Furthermore, because ATH contains three hydroxyl groups (-OH), its surface is asymmetrical and highly polar. The surface hydroxyl groups exhibit hydrophilic and oleophobic properties, making it prone to agglomeration when added to polymeric organic materials, directly affecting the material's mechanical properties.
Therefore, aluminum hydroxide needs to be surface modified before use.
Surface Modification of Aluminum Hydroxide
Surface modification is one of the key technologies for optimizing the properties of inorganic powder materials, playing a crucial role in improving the application performance and value of inorganic powders. Surface modification of inorganic particles refers to the adsorption or encapsulation of one or more substances on the surface of inorganic particles, forming a core-shell composite structure. This process is essentially a composite process of different substances.
Types and Characteristics of Modifiers
There are many types of powder surface modifiers, but there is no standard classification method. Modifiers for inorganic powder modification are mainly divided into two categories: surfactants and coupling agents.
(1) Coupling Agents
Coupling agents are suitable for various composite material systems of organic polymers and inorganic fillers. After surface modification with coupling agents, the inorganic material's compatibility and dispersibility with the polymer are increased. The surface of the inorganic material changes from hydrophilic and oleophobic to oleophilic and hydrophobic, increasing its affinity with the organic polymer.
Coupling agents are diverse and can be classified into four main categories based on their chemical structure and composition: organic complexes, silanes, titanates, and aluminates.
(2) Surfactants
Surfactants are substances that can significantly alter the surface or interfacial properties of a material when used in very small amounts. They include anionic, cationic, and nonionic surfactants, such as higher fatty acids and their salts, alcohols, amines, and esters. Their molecular structure is characterized by a long-chain alkyl group at one end, similar to polymer molecules, and polar groups such as carboxyl, ether, and amino groups at the other end.
How can the modification effect be determined?
Is modified aluminum hydroxide reliable? How reliable is it? This requires evaluating and characterizing the modification effect.
Currently, the flame-retardant effect of aluminum hydroxide flame retardants can be evaluated through direct methods such as testing the material's oxygen index, vertical and horizontal flammability index, smoke production, thermogravimetric analysis, and mechanical properties during combustion; or indirectly by measuring powder absorbance, activation index, and oil absorption value to indirectly test its modification effect.
(1) Absorbance
Unmodified ATH has hydrophilic and oleophobic hydroxyl groups on its surface, allowing it to dissolve in water or settle freely to the bottom. After modification, the surface of ATH becomes hydrophilic and oleophobic, with surface properties completely opposite to the unmodified form. It cannot dissolve or settle to the bottom and can only float on the surface. However, modified ATH can dissolve or precipitate well in oils (such as liquid paraffin).
(2) Activation Index
Unmodified ATH has very strong polarity due to the nature of its surface hydroxyl groups (-OH), allowing it to dissolve or settle freely in water with similar properties. After modification, ATH has a layer of lipophilic groups attached to its surface, with surface hydroxyl groups (-OH) encapsulated within. The better the modification effect, the higher the lipophilic group coverage rate of the ATH surface, and the more modified ATH floats on the water surface.
(3) Oil Absorption Value
Measuring the oil absorption value requires adding castor oil to ATH and stirring. Before modification, ATH, due to its hydrophilic and oleophobic properties, requires more castor oil to form spheres. After surface modification, it becomes hydrophilic and oleophobic, improving the dispersibility of ATH in the polymer and reducing voids formed by powder agglomeration.
Understanding Super Strong Materials—NdFeB
Sintered NdFeB, as the earliest preparation process and the most universally applicable, has driven the rapid development of rare earth permanent magnet materials. Sintered NdFeB, with its strong magnetic anisotropy and low-cost raw material input, has become a research target for many countries. Sintered NdFeB permanent magnet materials utilize powder metallurgy. The smelted alloy is made into powder and pressed into a compact in a magnetic field. The compact is then sintered in an inert gas or vacuum to achieve densification. Furthermore, to improve the coercivity of the magnet, aging heat treatment is usually required. The process flow is as follows: raw material preparation → smelting → powder preparation → pressing → sintering and tempering → magnetic testing → grinding → machining → electroplating → finished product.
Unlike sintered NdFeB, the individual powder particles of bonded magnets need to have sufficiently high coercivity. Once the multiphase structure and microstructure required for high coercivity are severely damaged during the powder preparation process, it will be impossible to produce good bonded magnets. Therefore, by using the method of melt-spinning rapid quenching magnetic powder, the hot molten alloy is first poured or sprayed onto a high-speed rotating water-cooled copper wheel to form a thin strip with a thickness of 100 μm.
The manufacture of hot-pressed/hot-deformed magnets requires starting with rapidly quenched Nd-Fe-B magnetic powder, rather than directly using cast alloys. By employing over-quenching (rapid cooling) conditions, finer grains, or even amorphous magnetic powder, are prepared. During hot pressing and hot deformation, the grains are heated and grown to near single-domain size, thus achieving high coercivity in the final magnet. The hot pressing process involves placing the magnetic powder in a mold and applying pressure at high temperature to force it into an isotropic, solid-density magnet.
Application
Permanent Magnet Motors
In permanent magnet motors, the use of permanent magnets for excitation not only reduces power consumption and saves energy, but also improves motor performance.
Magnetic Machinery
Magnetic machinery operates using the repulsive force of like poles or the attractive force of unlike poles in magnets. This requires permanent magnets with high remanence and high intrinsic coercivity. Furthermore, due to the principle of attraction between unlike poles, magnetic drives can be constructed using non-contact transmission, offering advantages such as no friction and noise. Therefore, high-performance Nd-Fe-B magnets are widely used in drive components of mining machinery, magnetic bearings in gyroscopes and turbines in satellites and spacecraft, and rotor bearings in centrifugal pumps for assisting cardiac function in medical equipment.
Aerospace
Rare-earth permanent magnet materials are indispensable for rocket launches, satellite positioning, and communication technologies. High-performance sintered Nd-Fe-B is particularly useful in microwave transmitting/receiving systems for radar. Utilizing the combined effect of a constant magnetic field and an alternating microwave magnetic field, ferromagnetic resonance occurs, allowing for the fabrication of microwave circulators, isolators, etc. Consumer Electronics
3C consumer electronics has always been an important downstream industry for sintered NdFeB. Sintered NdFeB possesses characteristics such as high magnetic energy product, which aligns with the miniaturization, lightweighting, and thinning trends in 3C consumer electronics products. It is widely used in electronic components such as VCMs, mobile phone linear motors, cameras, headphones, speakers, and spindle drive motors.
Neodymium iron boron waste recycling: an unmissable treasure trove
Neodymium iron boron (NdFeB) permanent magnets are widely used in wind power generation, new energy vehicles, and electronic products due to their excellent magnetic properties, earning them the title of "King of Magnets." However, the scrap rate in the NdFeB magnet production process is as high as 30%, and coupled with their limited lifespan, this results in a large amount of NdFeB waste.
These wastes contain up to 30% rare earth elements, far exceeding the content of primary rare earth ores, making them a highly valuable secondary resource. Efficiently recovering rare earth elements from NdFeB waste is crucial for ensuring rare earth resource security, reducing environmental pollution, and promoting sustainable development.
Characteristics and Sources of NdFeB Waste
NdFeB waste mainly originates from scraps, defective products, and retired electronic products containing magnets during the magnet manufacturing process. Its chemical composition is complex; in addition to the main rare earth elements Nd and Pr, elements such as Dy and Tb are often added to improve coercivity, and elements such as Co, Al, and Cu are added to improve overall performance. Based on rare earth element (REE) content, NdFeB waste can be classified into three categories: low rare earth (REEs < 20%), medium rare earth (20%–30%), and high rare earth (> 30%).
Currently, the recycling processes for NdFeB waste are mainly divided into pyrometallurgical, hydrometallurgical, and novel recycling technologies.
(I) Pyrometallurgical Recycling Processes
Pyrometallurgical recycling separates rare earth elements from iron through high-temperature reactions. The main methods include selective oxidation, chlorination separation, liquid alloying, and slag-metal fusion separation.
Selective oxidation is based on the fact that rare earth elements have a much higher affinity for oxygen than iron. At high temperatures, rare earth elements are selectively oxidized to form oxides, which are then separated from metallic iron. Nakamoto et al. successfully prepared mixed rare earth oxides with a purity exceeding 95% and a recovery rate exceeding 99% by precisely controlling the oxygen partial pressure.
Chlorination separation utilizes the strong affinity between rare earth elements and chlorine. Chlorinating agents such as NH4Cl, FeCl2, or MgCl2 are used to convert rare earth elements into chlorides before separation. Uda used FeCl2 as a chlorinating agent, reacting at 800℃, achieving a rare earth recovery rate of 95.9% and a product purity exceeding 99%.
The liquid alloying method utilizes the difference in affinity between rare earth elements and iron for other metals to achieve effective enrichment and separation of rare earth elements and iron. Rare earth element Nd can form various low-melting-point alloys with Ag, Mg, etc.
The slag-metal separation method is based on the characteristic that rare earth elements in NdFeB waste more readily combine with oxygen. All the metals in the NdFeB waste are converted into metal oxides. Simultaneously, under the high temperature of a slagging agent, the iron oxides are converted into metallic Fe by controlling the reducing conditions.
(II) Wet Recovery Process
Wet recovery is currently the most widely used method, mainly including the total dissolution method, hydrochloric acid preferential dissolution method, double salt precipitation method, and solvent extraction method.
(III) New Recycling Processes
New recycling technologies aim to solve the problems of high energy consumption and high pollution associated with traditional methods, including hydrogen explosion, bioleaching, and electrochemical methods.
Comparison of Different Recycling Processes and Environmental Impact
Pyrometallurgical processes have short flow rates and large processing capacities, but high energy consumption and difficulty in separating single rare earth elements; hydrometallurgical processes have high recovery rates and high product purity, but high acid consumption and high wastewater treatment costs; newer processes such as bioleaching and electrochemical methods are environmentally friendly, but are mostly in the laboratory stage and have not yet been applied on a large scale.
In terms of environmental impact, traditional recycling processes often use strong acids, strong alkalis, and high temperatures, generating large amounts of waste liquid and waste gas, increasing the environmental burden. Therefore, developing green and low-consumption recycling processes is crucial.
NdFeB waste recycling is a key way to alleviate rare earth resource shortages and reduce environmental pollution. Through technological innovation and policy guidance, the NdFeB recycling industry will develop towards greening, low cost, short processes, and high recovery rates, injecting new impetus into sustainable development.
Application and development of inorganic powder materials in the rubber industry
Rubber is widely used in transportation, machinery, electronics, defense, and other sectors of the national economy. However, rubber also has its own significant drawbacks, such as weak intermolecular forces, large free volume, and poor self-crystallization ability, resulting in low strength and modulus, and poor wear resistance in rubber materials. Therefore, it is necessary to add inorganic non-metallic fillers to meet the requirements of these applications.
Generally speaking, inorganic non-metallic fillers in rubber mainly serve the following functions: reinforcement, filling (increasing volume) and cost reduction, improving processing performance, regulating vulcanization characteristics, and imparting special functions.
Commonly Used Inorganic Non-metallic Mineral Fillers in Rubber
(1) Silica
Silica is currently the second most widely used reinforcing agent in the rubber industry after carbon black. The chemical formula of silica is SiO2·nH2O. Its particle structure contains many voids. When these voids are in the range of 2nm-60nm, they easily combine with other polymers, which is the main reason why silica is used as a reinforcing agent. As a reinforcing agent, silica can greatly improve the wear resistance and tear resistance of materials. It can also significantly improve the mechanical properties of tires and is widely used in vehicles, instruments, aerospace, and other fields.
(2) Light Calcium Carbonate
Light calcium carbonate is one of the earliest and most widely used fillers in the rubber industry. Large amounts of light calcium carbonate added to rubber can increase the volume of the product, thereby saving expensive natural rubber and reducing costs. Light calcium carbonate filling rubber can achieve higher tensile strength, wear resistance, and tear strength than pure rubber vulcanizates. It has a significant reinforcing effect in both natural and synthetic rubber, and can also adjust consistency. In the cable industry, it can provide a certain degree of insulation. (3) Kaolin
Kaolinite is a hydrous aluminosilicate, a common clay mineral. Its practical application in rubber enhances the rubber's elasticity, barrier properties, elongation, and flexural strength. Adding modified kaolinite to styrene-butadiene rubber (SBR) significantly improves the rubber's elongation, tear strength, and Shore hardness, while also extending its service life.
(4) Clay
Clay can be added during tire manufacturing, depending on the production process requirements. Clay is used as a filler to reduce costs. However, it must be activated clay to facilitate bonding with rubber. Activated or modified clay can partially replace carbon black in the formulation.
Studies show that as the amount of clay increases, the hardness, 300% tensile stress, and tensile strength of the rubber compound decrease slightly, but this can be compensated for by adjusting the vulcanization system. When used in tread formulations, after system optimization, it can also reduce rolling resistance.
(5) Barium Sulfate
It can effectively enhance the anti-aging and weather resistance of rubber products such as tire rubber and belts. In addition, it can improve the surface smoothness of rubber products. As a powdered rubber filler, it can not only improve the powder application rate, but also has obvious advantages in terms of economic cost.
(6) Talc
Talc powder is usually divided into general industrial talc powder and ultrafine talc powder. The former, as a rubber filler, does not play a reinforcing role and has a negligible effect on improving the physical properties of rubber. Therefore, general industrial talc powder is often used as a separating agent. Ultrafine talc powder, on the other hand, has a good reinforcing effect. If it is used as a rubber filler, the tensile strength of the rubber itself is equal to the effect produced by silica.
(7) Graphite
Graphite belongs to the lamellar silicate non-metallic minerals and has good thermal conductivity, electrical conductivity, and lubricity. Using graphite as a rubber filler involves a similar process to that used for montmorillonite, where graphite is broken down into nano-sized particles using a special technique. When these nanoparticles combine with the rubber matrix, various functional properties of the rubber are improved. For example, electrical conductivity, thermal conductivity, airtightness, and mechanical properties are all significantly enhanced.