2021年11月18日星期四

Mixed Tungsten Oxide Pressing Tungsten Plate

Tungsten plate is a tungsten material pressed by special process, it is mainly used in electronics and semiconductor industry parts manufacturing, tungsten sputtering target, high temperature furnace with tungsten boat, sapphire long furnace components etc.

tungsten plate image

The conventional thin tungsten plate pressing process uses yellow tungsten oxide, because the size distribution of yellow oxide powder is narrow and the particle size of powder is uniform, the gap of particles is not easy to be filled in the process of pressing, which eventually leads to lower strength of pressing.

The physical and mechanical properties of the tungsten plate are closely related to the strength of the compact, the strength of compacts is related to the characteristics of tungsten powder morphology and particle size distribution. There are three types of commonly used tungsten trioxide, yellow tungsten oxide, blue tungsten oxide and purple tungsten oxide, its flagship product is divided into three level: ordinary, fine, superfine granularity. The three kinds of tungsten oxide are mixed in proportion, and the coarse and fine powder can complement each other, so as to achieve the ideal pressure intensity of the tungsten plate pressing.

BTO, VTO and YTO are mixed in a biconical mixer according to the ratio of 2 to 5: 10. After 2 hours, the three kinds of tungsten oxide mixture were used as raw materials, and they were laid in the boatpan and reduced in the reduction furnace. The material layer thickness is controlled between 10-12 mm, and the heating rate is 50°C/h. Hydrogen dew point is -70~-75°C. The five zone reduction temperature distribution is in the range of 700~950°C, and the residence time is 180 min in the high temperature zone. The fine powder will pass through the aperture 0.212 mm wire diameter 0.112 mm and the aperture 0.075 mm wire diameter 0.056 mm sieve twice. Finally, the high pressed compact powder was obtained.

Under the action of external loading, the powder with more fine particles is easier to self adjust, by moving, sliding and rotating, the gap between particles is easy to be filled, so that the large porosity in the blank is reduced. Due to the complex shape of the powder particles, the surface is rough, there is a part of the bridge between particles, forming a loose aggregation structure, which makes the powder clench in the pressing between the particles, so as to improve the strength of compacts, it is conducive to the preparation of high performance tungsten products.

Mix the yellow tungsten oxide, blue tungsten oxide and purple tungsten oxide three and proceed a reduction, it is a simple process, low energy consumption and good quality, no need to change the operation methods and processes, but the quality is already the best.

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Violet Tungsten Oxide for Making Ultrafine Tungsten Powder

 What kind of tungsten oxide can produce high quality cemented carbide?

violet tungsten oxide image

At present, there are yellow tungsten oxide, blue tungsten oxide and violet tungsten oxide which are available in the market. Which kind of raw material is most suitable for cemented carbide production? Violet Tungsten oxide is the best raw material for producing superfine tungsten powder and nanometer metal tungsten powder. Ultrafine tungsten carbide was prepared by ultrafine or nano tungsten powder, and then cemented carbide was produced, the properties and requirements of cemented carbide are better than those made of ordinary. tungsten powder. The alloy with violet tungsten as the raw material has better quality and stronger adaptability, and the violet tungsten can make the penetration capability of the military armour piercing bullet increase by 20%, and the abrasion resistance of the carbide cemented carbide tool can be increased by 12%, etc.

The preparation methods of violet tungsten include hydrogen reduction, reverse hydrogen reduction, and liquid ammonia reduction. No matter what kind of reduction, it needs to be carried out in the high temperature reduction furnace. The reduction temperature is between 790 and -900 degrees centigrade. It is generally believed that the optimum reduction temperature of violet tungsten is between 800°C-850°C. In the pusher type reducing furnace environment, the temperature band range from800 - 850°C is generally set. The thickness of the loading layer can not be too large, and the flow of hydrogen should be controlled properly. The reduction reaction of violet tungsten not only on the surface, but also in the internal reduction process.

The crystal structure of violet tungsten is generally needle shape and micro rod-like crystal shape. It is generally believed that the tungsten powder prepared by the violet tungsten oxide of the needle crystal is finer, while the tungsten powder made by the rod shaped crystal violet tungsten oxide is relatively coarse. Of course, if it is the other crystal form or color, the reduction failure can be basically determined.

In summary, violet tungsten oxide has the advantage of manufacturing ultrafine tungsten powder, tungsten nano powder, and preparation of ultrafine tungsten carbide hard alloy for final production, in addition, violet tungsten is a high quality precursor material for gas sensitive element, but again, violet tungsten does not apply doping, doped work should apply to blue tungsten oxide.

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N-doped Tungsten Dioxide Vanadium Thin Films

Scientists discovered that VO2 has a distinctive phase change function long time ago. When the phase transition temperature is 68°C, it can change reversibly from low temperature monoclinic system to high temperature tetragonal system.

N-doped tungsten dioxide vanadium thin films image

The physical properties such as resistivity, optical transmittance, permeability and so on have changed greatly. Doping method is an effective method to change the phase transition temperature of VO2. The preparation methods of doped VO2 films include sol-gel doping method, hydrothermal synthesis doping method, sputtering doping method, metal organic compound vapor deposition doping method, pulse laser deposition process, inorganic sol-gel doping method, and microwave plasma method. We prepare it by microwave plasma method.

Another main content of the preparation of doped VOthin film is the selected doping compounds. Weigh a certain amount of pure VO5 powder and W2O3 into the pot, then stirring, put in the muffle furnace and under the air medium, heating to 900°C to melt. After 15 min of heat preservation, the molten solution is quickly poured into a certain amount of deionized water to quench and stir violently until a stoichiometric V1.96W0.04O5 sol is formed. The prepared V1.96W0.04O5 sol has been plated on glass sheets cleaned with 75% alcohol and deionized water by spin coating method. Dry naturally at the ventilation, then obtain synthesis of stoichiometric V1.96W0.04O5 thin films.

The V1.96 W0.04O5 films have been prepared by microwave plasma enhanced method, control reaction parameters, the V1.96W0.04O5 thin film was reduced to V0.98W0.02O2 and doped with nitrogen. The reaction time was 10~30 min. The V0.98W0.02O2-x N y thin film was obtained.

The phase transition temperature of VOpowders can be reduced by VO2 film, which is about 6°C, with the addition of nitrogen and tungsten ions, the phase transition temperature of V0.98W0.02O2 -x N y thin film can be effectively reduced, when the nitrogen flow rate is changed, the phase transition temperature of vanadium tungsten dioxide thin film can be reduced to 35°C at minimum. This is the closest phase change material known to be the daily temperature.

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Violet Tungsten Oxide Color Identification

 Violet tungsten oxide, abbreviated as VTO, is named after the appearance of purple. It is the best raw material for the preparation of ultrafine or nanometer tungsten powder.

violet tungsten oxide color identification image

It is produced in the process of producing ammonium paratungstate under the condition of precise control of temperature reduction. Violet tungsten oxide is mainly used in the production of tungsten powder and tungsten carbide.

Violet tungsten oxide sample color can be divided into purple, dark purple, dark blue, blue, the color of violet tungsten oxide and its oxygen index, particle degree of tightness, the aspect ratio of the needle.

Some scholars have invented a way to directly control and detect the quality of violet tungsten oxide. The quality of purple tungsten oxide is determined by the unique color of violet tungsten oxide. This method is called "colorimetric method" in the industry.

The color of violet tungsten oxide is related to the oxygen index, the degree of tightness of the particles and the ratio of length to diameter of the needle. A type of violet tungsten oxide is purple, oxygen index is slightly higher and needle is slightly elongated; B violet tungsten oxide is purple red, and the needle is slightly shorter and slightly thicker. A, B class basically maintained the needle-like morphology of violet tungsten oxide, but there are some small particles are not acicular; Category C violet tungsten oxide is black, the needle is severely shrunk and begins to transform into WO2; D and E are produced abnormally, the color of different particles can be seen with a microscope, and the morphology of the sample is also different by scanning electron microscopy.

By colorimetric method, it is found that the quality of violet tungsten oxide with purple and purple color is the best, and the quality of purple black is slightly worse. If it appears purple blue or blue, it has basically declared failure.

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2021年10月14日星期四

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 sulfide, and acetone and other harmful gases.

The preparation methods of nano tungsten oxide mainly include hydrothermal method, sputtering method, sol gel method and gas phase deposition method. Compared with other synthetic methods, as a new method for composing nano-materials, low heating solid phase chemical reaction has the characteristics of simple operation, friendly environment and mild conditions. 

Mix sodium tungstate and sodium sulfate for 30min, the sample was placed in a cone bottle and placed for 24h to obtain the precursor. Then put the precursor calcined at 600°C in the muffle furnace 2h, nano tungsten carbide was obtained. 

nano tungsten oxide image

Based on the product of nano tungsten carbide test, the material in the lower working temperature of low concentration acetone gas showed the performance of fast response, high selectivity and high sensitivity. This material can be used for the detection of early diabetes, in addition, under the UV light and simulated sunlight conditions it has better performance for the degradation of methylene blue solution, the degradation efficiency of not less than 70%, these excellent properties concern with nano tungsten carbide smaller particle size and surface activity. 

Solid phase chemical synthesis of nano tungsten carbide can be obtained with high purity, good crystallinity and particle size of tungsten oxide nanoparticles, this method overcomes some traditional experimental hard conditions, the tedious experiment process and long reaction time, it is a simple and efficient, new green composing method.

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Tungsten Titanium Thin Films Electrochromic Properties

Electrochromic is the phenomenon that the optical properties of materials change stably and reversibly under the action of applied electric field.

It can cause light penetration through the electric field, changing color with the environment, and no longer need to curtain.

WO3 thin film is one of the most promising electrochromic materials. WO3 thin films have been widely used in photochromic, photochromic, filter, dye sensitized solar cells and so on. 

With the implantation and extraction of ions, the dissolution and ion residues of WO3 thin films will occur, and the electrochromic properties will decline obviously, which limits the wide use of electrochromic devices. TiO2 has excellent stability, and has excellent transmittance in wide waveband. The doping of electrochromic films with TiO2 composite WO3 can improve the stability and lifetime of devices. 

titanium tungsten film image

Pure Ti/WO3 composite films were prepared by radio frequency sputtering method, tungsten titanium alloy with tungsten and titanium content of 5% is used as target material. Indium tin oxide (ITO) conductive glass was selected for thin film substrate. The chamber is pre evacuated to 1 x 10–5 Pa before entering the gas. High purity argon (Ar) was used as working gas, high purity oxygen (O2) was used as reaction gas, base pressure was 0.5 Pa, O2/Ar was 0.15, target base distance was 8 cm, sputtering power was 300 W, sputtering time was 40 min. Finally, Ti/WO3 films were prepared by annealing for 2 hours under N2 atmosphere.

Electrochemical testing results show that Ti doping can improve the reversibility of ion implantation / extraction and improve the cycle stability of the thin films. At the same time, the response speed and optical modulation performance of the films were also improved. The response time of the doped and bleached thin films was reduced from 9.8 and 3.5 s to 8.4 and 2.7 s, respectively. Therefore, the Ti doped WO3 thin films had better electrochromic properties.

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Powdery White Tungstic Acid and Its Application

Tungstic acid can be roughly divided into yellow tungstic acid and white tungstic acid.

More and more practice has shown that tungstic acid not only has an important use in tungsten chemistry, but also has great value in tungsten metallurgy.

Powdery white tungstic acid can compose tungsten niobium and tungsten tantalum Heteropoly salt. Tungsten phosphoric acid and tungstic acid can also be composed. The heteropoly acid prepared from powdered white tungstic acid has better catalytic performance than that prepared with tungstic acid. 

white powdery tungstic acid image

The preparation of white tungstic acid is to drop Na2WO4 solution into dilute acid. In the middle of the process, there is no acid anion, so the precipitation rate is high. In the Na2WOsolution tungsten exists as monomeric WO42-form. The presence of dilute acid immediately results in protonation and formation of tungstic acid precipitation. Generally, the prepared white tungstic acid is a mixture of mono - tungstic acid and poly - tungstic acid. When the mono tungstic acid was converted into poly acid, the tungstic acid was converted into colloid, and its activity was similar to that of yellow tungstic acid.

Pour out method for impurity removal of white tungstic acid. The 0.5-0.8m / L Na2WOsolution was dripped into H2SO4 or H N solution until the pH value <=1, the powdery white tungstic acid can be obtained with a precipitation rate of 100%. When the P, A, s or Si in Na2WOexist in less than 30 m g / L, the resulting white tungstic acid does not contain these three impurities, and these impurities are dissolved in water in the form of twelve tungsten heteropoly acid.

In the preparation of ammonium tungstate, ammonium tungstate, tungsten phosphorus heteropoly acid, white tungstic acid is much better than that of yellow tungstic acid, and the yield is almost 100%. Considering the low acidity and high yield of white tungstic acid, the advantage of white tungstic acid in tungsten metallurgy is more obvious.

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Mixed Tungsten Oxide Pressing Tungsten Plate

Tungsten plate is a tungsten material pressed by special process, it is mainly used in electronics and semiconductor industry parts manufact...