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 of Intelligent Equipment for Vanadium Dioxide Doped Tungsten Powder

Among the vanadium oxides, vanadium dioxide is distinguished by its rapid and abrupt phase transition, and its phase transition temperature is 68 °C.

The reversible change from low temperature monoclinic system to high temperature tetragonal system leads to great changes in physical properties such as resistivity, optical transmittance, permeability and so on. This feature makes it very promising in intelligent switches, electronic devices and optoelectronic devices.

However, in daily life, the application temperature of 68 degrees is still too high, so it is necessary to reduce the VO2 phase transition temperature, so that VO2 can be widely used. In recent years, many studies have shown that doping of other elements in VO2 can effectively reduce its phase transition point. Especially the high valence metal ions, such as MO6+, W6+ and so on, doping effect is particularly significant.

The amount of ammonium metatungstate was mixed with vanadium oxide by hydrothermal method. According to the molar mass ratio of tungsten ion to VO2 of 0%, 1% and 2%, a certain amount of ammonium metavanadate and ammonium metatungstate powder, successively added to the 40mL deionized water, stirring on the magnetic stirrer, a certain amount of oxalic acid (and ammonium vanadate molar ratio 1.5: 1) as a reducing agent. When the solution is added into the solution, the liquor is mixed with red wine, and the mixed solution is transferred to a reactor lined with polytetrafluoroethylene in 100 mL, and the filling degree is 60%, In the drying box under 180 DEG C for 24 h insulation, get powder black precipitate, removed and cooled to room temperature, using deionized water and anhydrous ethanol by centrifugal washing 3 times. Then after centrifugation sediment in Petri dish, and the dish is put in a drying box, heat 8 h into dry powder under 80 degrees, with agate mortar grinding. The dried powder is placed in the porcelain boat and placed in the quartz tube. In the quartz tube through the argon, the gas flow rate of 15 mL / min, at 600 °C for 6 h. With the furnace cooled to room temperature, to be doped with different molar mass of tungsten ions than the vanadium dioxide powder.


The test results show that the phase transition temperature of tungsten powder doped VO2 powders decreases with the increase of tungsten doping content. When the doping amount of tungsten increases from 0% to 2%, the phase transition temperature decreases about 12.5 degrees when the doping content increases by 1%, and the phase transition temperature of the powder decreases to 43.17 degrees when doping 2%, and the phase transition temperature is close to the daily temperature. Among the vanadium oxides, two vanadium oxide is distinguished by its rapid and abrupt phase transition, and its phase transition temperature is 68 degrees centigrade.

The reversible change from low temperature monoclinic system to high temperature tetragonal system leads to great changes in physical properties such as resistivity, optical transmittance, permeability and so on. This feature makes it very promising in intelligent switches, electronic devices and optoelectronic devices.

However, in daily life, the application temperature of 68 degrees is still too high, so it is necessary to reduce the VO2 phase transition temperature, so that VO2 can be widely used. In recent years, many studies have shown that doping of other elements in VO2 can effectively reduce its phase transition point. Especially the high valence metal ions, such as MO6+, W6+ and so on, doping effect is particularly significant.

The amount of ammonium metatungstate was mixed with vanadium oxide by hydrothermal method. According to the molar mass ratio of tungsten ion to VO2 of 0%, 1% and 2%, a certain amount of ammonium metavanadate and ammonium metatungstate powder, successively added to the 40mL deionized water, stirring on the magnetic stirrer, a certain amount of oxalic acid (and ammonium vanadate molar ratio 1.5: 1) as a reducing agent. When the solution is added into the solution, the liquor is mixed with red wine, and the mixed solution is transferred to a reactor lined with polytetrafluoroethylene in 100 mL, and the filling degree is 60%, In the drying box under 180 DEG C for 24 h insulation, get powder black precipitate, removed and cooled to room temperature, using deionized water and anhydrous ethanol by centrifugal washing 3 times. Then after centrifugation sediment in Petri dish, and the dish is put in a drying box, heat 8 h into dry powder under 80 degrees, with agate mortar grinding. The dried powder is placed in the porcelain boat and placed in the quartz tube. In the quartz tube through the argon, the gas flow rate of 15 mL / min, at 600 °C for 6 h. With the furnace cooled to room temperature, to be doped with different molar mass of tungsten ions than the vanadium dioxide powder.

The test results show that the phase transition temperature of W doped VO2 powders decreases with the increase of tungsten doping content. When the doping amount of tungsten increases from 0% to 2%, the phase transition temperature decreases about 12.5 degrees when the doping content increases by 1%, and the phase transition temperature of the powder decreases to 43.17 degrees when doping 2%, and the phase transition temperature is close to the daily temperature.

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2021年2月8日星期一

Biodiesel Catalyzed Preparation by Ionic Liquid Phosphotungstic Acid

Biodiesel is usually synthesized from vegetable oils and fats and waste edible oils by simple transesterification.

In the synthesis of biodiesel, the key technology is the selection of the catalyst, the traditional inorganic acid and alkali catalyst, facing strong corrosive and non renewable, easy to cause problems such as saponification reaction against the original intention of the environmental protection of bio diesel. 

Phosphotungstic acid is an environmentally friendly catalyst widely used in catalysis in recent years. It has strong acidity, and many industrial processes that need to be catalyzed by inorganic acids can be replaced by phosphotungstic acid. But in the biodiesel production process, found itself acid soluble in water, for many catalytic processes of catalytic esterification, the esterification rate is generally not high, in addition, the activity of the heteropoly salt group easily lost, so that it can not be used repeatedly, which leads to high cost.


Even so, the omnipotent chemists still found the solution. Ionic liquid is a kind of green solvent and catalyst. Its structure and acidity and basicity can be controlled. Then, morpholine ring cation was combined with heteropoly acid anion to obtain a novel organic heteropolyacid catalyst - morpholine phosphotungstate catalyst [C3SO3Hnhm] 3PW12O40. Through the design of functional structure and heteropoly acid anions for organic cation, the comprehensive performance of adjusting the catalyst, while maintaining the catalytic activity, alleviate the corrosion of traditional catalyst and solid acid and alkali catalyst, high cost and difficult separation.

Some scholars use morpholine phosphotungstate catalyst soybean oil and methanol reaction preparation of biodiesel. The results showed that when the mass fraction of n (methanol): n (soybean oil) = 14: 1, the mass fraction of tungstate catalyst was 4% of the total mass of soybean oil and methanol, the reaction time was 6 hours, the reaction temperature was 100 °C, Yields reached 94. 90%.

More surprising is that morpholine phosphotungstate catalyst not only has a good catalytic effect, the catalyst after the catalyst can be repeated recycling, catalytic 6 times, the recovery rate is still 91%, and the reaction of the [C3SO3Hnhm] 3PW12O40 structure did not change.

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Titanium Tungsten Composite Plasma Material

The ITER device is a superconducting tokamak can produce large-scale nuclear fusion reactions,  aims to create a clean and sustainable energy future of mankind.

ITER uses deuterium and tritium to produce nuclear fusion. Deuterium and tritium fusion in the circulation with millions, tens of millions of billions of temperature, the circulator must be strengthened by high temperature resistant metal, from the engineering point of view, material problems determine the success or failure of fusion energy development.

In fusion materials, a very important type of material is plasma facing material (PFMs), and the general requirement for PFMs is: high temperature resistance, low sputtering, low hydrogen (tritium) retention and compatibility with structural materials. Tungsten is considered to be the most promising PFMs material, which can meet many requirements in this harsh environment. However, tungsten is facing severe brittleness because of its own structural characteristics. Therefore, it is possible to solve the brittleness problem of tungsten by adding tungsten doped titanium element into tungsten matrix composite.



At present, there are many ways to solve the problem of doped tungsten. This paper introduces a new method of doping tungsten powder titration method. In the suspension of ammonium metatungstate (AMT) saturated solution with titanium carbide (TiC) powder and dispersant, ethanol was added dropwise to obtain AMT coated titanium carbide precursor; Tungsten coated TiC composite powders were prepared by high purity hydrogen reduction of precursor, and titanium tungsten composite was prepared by spark plasma sintering (SPS) technique.

The results show that the titanium - tungsten composite material is reduced by 1 °C at 600 °C for 30 min and then at 30 °C for 30 min, and a good spherical like composite powder can be obtained, After 6 °C incubation at 1600 °C, the distribution of TiC in the matrix was uniform after SPS sintering, and the relative density of Ti-tungsten composites was 94.6%, the flexural strength reaches 739 MPa, the microhardness reaches 4.86 GPa, the fracture toughness reaches 7.87 MPa m1 / 2, perfectly solved the brittleness defect of tungsten.

To solve the problem of brittle tungsten, tungsten based alloy materials in the artificial sun will have a greater range of use, in fact, tungsten based materials is not only the main material of artificial sun wall, the main material is divertor.

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High Energy Explosive Loading Spraying Micron Tungsten Powder Technology

Tungsten coating is mainly used in aviation, aerospace, nuclear power, machinery and other industrial fields, and the key parts of friction and movement parts wear protection.

Tungsten coating is difficult to prepare because of its special properties. The basic process of high explosive loading spraying technology can be divided into three stages: 1. The use of explosive detonator is paved on the surface of the powder coating with explosives, explosive detonation wave propagation in detonation, similar to slip in explosive welding of detonation wave, high temperature and high pressure of the detonation product formation; 2. The powder of flying coating moves rapidly downward under the action of detonation wave and detonation products with high speed expansion, which can reach a higher speed. By selecting the type of explosive reasonably, controlling the distance between coating powder and matrix, the target velocity of coating powder can be controlled effectively, and the best velocity domain combined with substrate can be achieved; 3. Plate powder combined with heating and accelerating coating powder particles and matrix high-speed collision, through the larger plastic deformation or thermal fusion, the two are firmly combined together.


Some scholars try to use high-energy explosive spray preparation of tungsten coating to micron tungsten powder as raw material, the use of black baskets of this base explosive pressure packing column, the pillar size φ 50 mm × 50 mm, the burst speed 8200 m / s, the substrate is 2A12 aluminum, dimensions φ 300 mm × 5 mm. The tungsten powder has a particle size of 5 to 10 um, a purity of 99. 98% and a mass of 150 g. In order to ensure that the tungsten powder has a higher plate speed, so set the fried height of 750 mm and 400mm. Before spraying the surface of the aluminum plate grinding treatment, so that the surface has a certain degree of roughness, can improve the surface area of aluminum, is conducive to the combination with the tungsten powder. 

During explosive spraying, the shock wave and detonation product formed by explosive explosion drive the tungsten powder into the aluminum plate at high speed, and serious plastic deformation occurs between the aluminum plate and tungsten powder, forming mechanical bite, and finally forming a coating. The study found that tungsten powder in the spraying process, particles are not completely melted, did not grow up, finally making the tungsten coating prepared by uniform thickness, the porosity is about 3%, showing good compactness, the coating effect is very ideal.

With high explosive explosion with superior technology, better uniformity and compactness of the coating loaded tungsten coating, although there is a concept of this technology, a lot of people, but there is no doubt that this coating technology has very broad prospects for development.

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Surface Copper Plating on Tungsten Powder and Its Action

Tungsten has a high melting point, high density, high hardness, saturated vapor pressure, low coefficient of thermal expansion and other characteristics.

Copper has high thermal conductivity properties, tungsten copper alloy combination is made known to all the materials in aerospace and military fields. The traditional preparation of tungsten copper alloy mainly adopts the method of mechanical mixing, forming and sintering of tungsten powder and copper powder, or using infiltration process. The method is relatively simple, but there are some defects, because of the great difference between tungsten and copper, tungsten and copper can only form pseudo alloy shape, and it is difficult to achieve uniform distribution of tungsten and copper in the interior, resulting in lower or unstable properties. 


With the development of Aeronautics and Astronautics and military industry, the demand for tungsten copper exothermic sweating material is higher and higher, Chinese scholars created a powder plating method in electroless copper plating on the surface of tungsten powder can improve the processability, thermal properties of tungsten and tungsten powder or powder metallurgy and other materials forming performance, application scope of the expansion of tungsten powder.

Usually chemical plating process: filtered tungsten powder → ultrasonic dispersion and degreasing → activation → multiple washing → plating → drying.

1.In order to reduce agglomeration in the process of preparation and storage, tungsten powder was dispersed in 10 min under ultrasonic wave in OP-10 aqueous solution.

2.After tungsten powder cleaning, and then through the coarsening, sensitization, activation treatment, adding to the pH value of 12-13 bath, the solution by the copper sulfate, formaldehyde, potassium tartrate, 2, 2-bipyridyl to make.

3.Copper began to adjust the mechanical stirring speed so that tungsten powder suspended in the bath, so that the tungsten powder and bath full contact to achieve uniform and stable tungsten powder coating. The temperature of electroless copper plating is kept at about 45 degrees by constant temperature water bath heating bath.

4.After spraying for one hour after the tungsten powder becomes red, and in a certain mixing speed tungsten powder has been in the middle of the liquid layer of the solvent. After plating 3 h after the basic colorless bath, and tungsten powder completely red.

5.Drying, copper plating process completed.

The biggest advantage of copper plating on tungsten powder surface is to improve the uniformity of powder, which makes the performance and stability of the final copper tungsten alloy greatly improved, and provides better conditions for the wide application of tungsten copper composite material.

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Solid Phase Chemical Method Composing Nano Tungsten Oxide

Nano tungsten oxide is considered to be one of the most promising new oxides gas sensing materials that detects nitrogen oxides, hydrogen s...