2021年4月7日星期三

Preparation Method of High Crystallinity Tungsten Carbide Powder

Tungsten carbide-based cemented carbide is widely used in cemented carbide, and high-quality tungsten carbide powder is the basis for preparing high-performance cemented carbide. What is the preparation method of high crystallinity tungsten carbide powder?

A preparation method of tungsten carbide powder with high carbonization crystal integrity and fast carbonization rate includes the following steps:

1) After mixing tungsten powder and carbon black, press the compact into a compact by a press; 2) Carburize the compact in step (1), after the carbonization is completed, ball milling and sieving can obtain high crystallinity tungsten carbide powder.

Precautions for this preparation method:

1. In step (1), the F.S.S.S. particle size of the tungsten powder is 3-40μm, and the particle size of the tungsten powder is too fine and it is not easy to form during pressing. The pressing pressure of the press is 1.0-2.0mpa. The mixing is ball mill mixing, and the mixing time is 1~6h.

2. In step (2), the carbonization temperature is 1500-2500°C. As a preference, when the tungsten powder's F.S.S.S. particle size in step (1) is 3-13μm, the carbonization temperature is 1500-2000°C. When the particle size is greater than 13μm, the carbonization temperature is generally 2000-2500°C.

3. In step (2), the carbonization should be carried out in a vacuum, inert gas or hydrogen atmosphere. The carbonization time is 1 to 6 hours, preferably 2 to 4 hours. The ball milling time is 0.5 to 4 hours. The sieving is twice sieving, the first sieving, the sieve mesh is 100-264 mesh, the second sieving, the sieve mesh is 60-180, the second sieving sieve aperture is larger than the first time.

The principle of the preparation method: in the process of producing tungsten carbide powder, the main function of using a press to press the mixture of tungsten powder and carbon black into a compact includes the following aspects: (1) The compacting effect makes the carbon black particles and the tungsten powder particles close together, and shortens the carbonization reaction distance. (2) Thermal insulation, make full use of the exothermic heat of the carbonization reaction to increase the speed of the carbonization reaction. (3) Forming function, the massive tungsten carbide does not need to be pre-crushed, directly enters the next ball milling process. (4) Isolation. There is no surface penetration of tungsten powder and carbon black compacts and sintering vessels during the carbonization process, which eliminates the surface dirty phenomenon in the traditional carbonization process and improves the quality of tungsten carbide.

Compared with the tungsten oxide reduction-carbonization method widely used in the mass production of tungsten carbide at home and abroad, the method introduced in this article can prepare high-quality tungsten carbide powder and is relatively simple to implement. It only needs to put a press in traditional tungsten carbide production lines.

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Six Preparation Methods of Spherical Tungsten Powder

Spherical tungsten powder is used as a raw material in industries such as tungsten and tungsten alloy 3D printing, porous materials, and high-density powder spraying, and its preparation methods have attracted attention. So, what are the 6 preparation methods for spherical tungsten powder?

The main domestic methods for preparing spherical tungsten powder are as follows:

1.Using the technology of secondary oxidation and reduction of tungsten powder, quasi-spherical tungsten powder can be obtained, and the manufacturing cost is low, but the spheroidization is not sufficient.

2. Using the granulation and sintering method to produce spherical powder for thermal spraying, spherical tungsten powder with a particle size of 40-750μm can be obtained. The density of the tungsten powder is not high, and the particle diameter is relatively large, and the powder is relatively coarse.

3. Use tungsten hexafluoride as raw material to prepare fine-particle (3~5μm) spherical tungsten powder. This method involves a strong corrosive gas and the production conditions are relatively harsh. In today's society, there is a high environmental protection requirement. There is still a certain distance from large-scale production.

4. The tungsten rod uses the rotating electrode DC arc plasma method to prepare spherical tungsten powder. This method can only used for preparing coarser particles (150-1700μm), but cannot prepare fine spherical tungsten powder, and the equipment cost is very expensive.

The main methods for preparing spherical tungsten powder abroad are as follows:

1. Obtain large particle size (40~650um) spherical tungsten powder from tungsten hexafluoride by vapor deposition. Because the process involves strong corrosive hydrofluoric acid, the production conditions are harsh and the environmental protection requirements are high, so It is difficult to gain widespread popularity in practical applications.

2. Spheroidizing and air-cooling Cr, Ta, Mo, W, MgO and other powders with an inductively coupled plasma torch can obtain spherical tungsten powder, but this preparation method requires a large cooling chamber, which must be using high-purity argon gas, the cost is very high, and the spheroidization rate of the powder after one treatment can only reach 85%. If you want to obtain all spherical powders, you need to perform multiple sorting and re-spheroidization processes. This obviously greatly increases production costs.

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Tungsten Oxide Boosts the Achievement of Carbon Neutral

 Carbon neutral refers to the use of afforestation, energy saving and emission reduction to offset the carbon dioxide emissions generated by itself and achieve "zero emissions" of carbon dioxide. Carbon neutral is a solution proposed in response to global warming.

Climate warming is the most concerned climate issue of humans all over the world today, and the core of climate warming is the increase in greenhouse gas carbon dioxide emissions caused by the increase in human activities.

In response to this issue, from the 2009 United Nations Climate Change Conference in Copenhagen to the 2015 United Nations Climate Change Conference in Paris, all emphasis was placed on reducing carbon emissions.

Up to now, the European Union, China, Japan, South Korea, etc. have all proposed carbon neutrality goals. The US President-elect Biden also proposed in his speech that the United States should return to the Paris Agreement. The basic requirement is the time when the United States should propose carbon neutral schedule. In other words, within the next year, all major economies in the world will participate in the process of achieving carbon neutrality.

Two important speeches this year in China both mentioned the need to control carbon emissions, and the Economic Work Conference also list carbon peaking and carbon neutral as one of the eight key tasks for next year. The 14th Five-Year Plan will become the key stage for China's carbon peak and carbon neutral. China promotes of carbon neutral also has the meaning of ensuring energy security, promoting economic transformation and promoting global development.

Two paths for tungsten oxide to help achieving the goal of carbon neutral:

First, carbon reduction at the power generation end: including photovoltaic, wind power, hydropower, nuclear power, and UHV links. As the main raw material of photovoltaic silver, tungsten oxide has excellent electrical conductivity.

Second, carbon reduction on the consumer side: including promoting the consumption of new energy vehicles, the development of energy storage, the use of degradable plastics, and green buildings. Because of its larger specific surface area and higher theoretical capacity, tungsten oxide has gradually become an ideal choice for replacing cobalt as a cathode material for lithium batteries.

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Ammonium Metatungstate Thermal Insulating Agricultural Membrane

Due to the intensification of the global greenhouse effect, extreme climate changes have been caused, resulting in a significant reduction in the area of arable land and making crops difficult to grow. Greenhouse cultivation can reduce the disasters caused by the climate to agricultural production, and maintain the stable production of crops, and solve the famine problems that may be faced in the future. 

It is a gradual trend in crop planting methods. Due to the increasingly serious problem of oil shortage and global warming, the promotion of energy conservation and reduction of carbon dioxide emissions have become the goals of various governments. Among them, the promotion of energy-saving green buildings is a key project, so energy-saving greenhouses that can reduce energy use have also become a new development trend.

The greenhouse shell shoulders the important functions of sheltering wind, rain, light regulation, heat insulation or heat preservation. The light-transmitting covering material is the main structural component that affects the exchange of light, heat and air inside and outside the greenhouse. The temperature in the greenhouse rises to very high in summer, which is not conducive to plant growth and personnel work. Artificial cooling measures also waste energy and increase cultivation costs. Although the high-performance greenhouse light-transmitting covering material has the opportunity to isolate the heat radiation part of the sun, and maintain high light transmission, solve the problem of indoor overheating. However, the currently commercially available greenhouse light-transmitting covering materials are insufficiently insulated, and there is still much room for improvement.

The wavelength of solar thermal energy reaching the surface of the earth is mainly at 280~3000nm. Among them, 280~380nm is ultraviolet light, 380~780nm is visible light, and 780~3000nm is infrared light. For plants, light in the 400-700nm wavelength range is required for photosynthesis, especially the strongest absorption band of chlorophyll is in the blue-violet light 400-480nm and red-orange light region 600-680nm, which has a great impact on plant growth. The response of plants to the length of day and night is the photoperiod. Red light and far-red light have a significant impact on the photoperiod effect. The red light of 600~700nm will inhibit the elongation of the stem and the divergence of the plant, and sometimes cause the leaves to be small and thick, and affect the flowering of the plant. The far-red light of 700~780nm will promote the elongation of stems and affect the flowering of plants. Ultraviolet light 280~380nm generally has an adverse effect on plants, but UVB at 280~315nm has minimal impact on morphology and physiological processes. The major impact is UVA at 315~380nm, which will affect the photoperiod effect and prevent stem extension. Long, plants are easy to burn, stimulate the germination of fungal spores, pathogens and viruses are also easy to invade, but it can make the flowers or fruits of plants brighter.

Optical performance requirements for greenhouse films

1. High light transmittance and stable

2. High light scattering

3. High infrared light barrier

4. Proper UV light barrier properties

The thermal insulation dispersion prepared by ammonium metatungstate and acrylic glue are used to make a nano organic-inorganic hybrid coating, and then this coating is coated on the surface of the polyester film to form a high-performance thermal insulating agricultural membrane. This transparent nanoparticle coating film can provide high see-through rate while blocking infrared rays, thus achieving high light transmission and high heat insulation effects. The optical properties of the thermal insulation film are related to the dispersibility of the thermal insulation powder in the resin. Generally speaking, the overall light transmittance of the heat insulation film can be maintained at 60~80%, and the infrared light blocking rate can reach 78~98%. Compared with the optical performance of the top-level thermal insulation films on the market, the optical performance of each other is not much different. Therefore, the use of nano-coating methods can produce products comparable to the top-level commercially available thermal insulation film, which has the advantages of simple manufacturing process and low cost. Therefore, greenhouse films will have great market demand in the future to maintain stable production of crops.

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2021年2月25日星期四

Corrosion Inhibition Mechanism of Sodium Tungstate

In order to protect the environment, human efforts to develop new, efficient, low toxicity, pollution-free corrosion inhibitors, sodium tungstate quickly favored by people.

Sodium tungstate was first used as a corrosion inhibitor for organic antifreeze, and subsequently developed in other functional packages. Tungstic acid can be used in different corrosive media, such as fresh water cooling water, seawater cooling water, oil recovery in the oil field, molten salt, water-cooled internal combustion engine antifreeze, adsorption type refrigerant circulating fluid and coal slurry. You can also add anti-rust paint and mold resin material from the role of corrosion inhibition.


Sodium tungstate alone has some inhibition, but the corrosion rate is not high, and the amount is large, the cost is difficult to control, therefore, sodium tungstate is mixed with other organic compounds in general industry, which can significantly improve the corrosion inhibition performance and reduce the cost of sodium tungstate.

Sodium tungstate can not only inhibit the uniform corrosion of metals, but also inhibit the pitting corrosion. Before the metal is immersed in the solution, the coverage of the surface metal oxide is quite high due to the action of oxygen in the air, and the oxidation rate is further increased after entering the solution, so that the anode area decreases and the anode current density increases. While WO42- can discharge rapidly at high current density, at this time, its oxidation ability is very strong, Fe2+ can be oxidized to Fe3+, which promotes the formation of iron oxide film, therefore, tungstate does not play a major role in the formation of metal passive film. It only acts as the maintenance and repair function of the film.

In addition to the oxidizing sodium tungstate inhibitor has in common, its specificity can not be ignored, such as: the oxidation of tungstate is relatively low, and the atomic weight of tungsten is larger; Tungstate can form a very small salt with many metal ions. Therefore, whether the passivation film theory or the characteristic adsorption theory, we only need to know that sodium tungstate has good metal corrosion inhibition, and it is the ideal material to inhibit metal corrosion, so that is enough.

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Polyimide / Zirconium Tungstate Composite Film

Polyimide (PI) is one of the best comprehensive performance of organic polymer materials, with excellent mechanical, dielectric and other properties, is widely used in many fields.\

Zirconium tungstate (ZrW2O8) is a kind of expansive material with isotropic negative thermal excellence, modern industry it with the prepared polyimide composite, PI/ZrW2O8 composite film, this film has very important applications in industry.


PI/ZrW2O8 composite films with ZrW2O8 content of 0%, 3%, 6%, 10%, 25%, and 50% ZrW2O8 were successfully prepared by in situ polymerization, through the contrast test found that after joining ZrW2O8, the high temperature strength of PI/ZrW2O8 composite films had a very big impact, no change in quality and thermal effect in the wood between 200 and 450 °C. It was further verified that the polyamic acid was fully imidized at 350 °C, indicating that the material had high heat resistance and high decomposition temperature. The thermal decomposition temperature of the film filled with ZrW2O8 powder increases with the increase of ZrW2O8 powder content.

Polyimide / zirconium tungstate composite films can be used for wrapping material slot insulation of motor and cable, transparent polyimide film can be used as a solar cell plate soft, can be used in the manufacture of gas separation membrane, used for a variety of separation, such as hydrogen / nitrogen and nitrogen / oxygen / nitrogen or carbon dioxide, methane, etc., it can also be used as pervaporation membrane and ultrafiltration membrane from air hydrocarbon raw material gas and alcohol. Polyimide / zirconium tungstate composite film is of great importance in separation of organic gas and liquid because of its excellent heat resistance and resistance to change.

Polyimide / zirconium tungstate composite film picture polyimide / zirconium tungstate composite film is a kind of polymer negative thermal expansion material which is widely used. It is widely used in aerospace, aviation,

microelectronics and other high-end industries.

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Process for Preparing Aluminum Based Zirconium Tungstate Composite

Thermal expansion is a common problem in many fields, such as mechanical, electronic, optical and structural materials.  

Aluminum and zirconium tungstate are negative thermal expansion materials. Aluminum is a metal type negative thermal expansion material, which is characterized by excellent conductivity and thermal conductivity, and the material price is relatively cheap, it can deal with the general application. But in the high temperature and cold environment, but its negative thermal expansion is less than zirconium tungstate, but zirconium tungstate production cost is higher, the performance and price trade-off dilemma.


Fortunately, zirconium tungstate has good compatibility and can be used to form composite particles with aluminum. The traditional preparation technology of aluminum based zirconium tungstate composite material is heating sintering and pressing.

Preparation process of aluminum based zirconium tungstate composite: 1. The zirconium tungstate powder was pressed into a preform with a diameter of 45 mm under 30 MPa pressure, and then preheated in 500~550 °C heat-resistant steel mould for 1 h.; 2. 6013 aluminum alloy were smelted at Al-1%Mg-2.4%Cu-2.4%Si 800~900 (mass fraction) and melted in the heat resisting steel mould after degassing and slag removal; 3. In the hydraulic press through the die on the aluminum liquid pressure, the pressure of 377MPa, 30 seconds after the pressure relief, after cooling off the system made of zirconium tungstate / 6013Al composite material.

The results show that aluminum based zirconium tungstate composite has lower thermal expansion coefficient and more stable performance than single aluminum alloy, the aluminum base zirconium tungstate composite can greatly enhance the thermal shock resistance of the material, and maintain the dimensional stability and the service life of the material when it is used in the variable temperature situation, that is, the performance of zirconium tungstate is close to that of zirconium tungstate, and it has the advantage of cheap and easy access to aluminum.

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Preparation Method of High Crystallinity Tungsten Carbide Powder

Tungsten carbide-based cemented carbide is widely used in cemented carbide, and high-quality tungsten carbide powder is the basis for prepar...