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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Super Wave Absorbing Material—Nanometer Tungsten Disulfide/Fullerene

Microwave absorbing material is an important stealth form in stealth technology.

High temperature absorbing composites with new wave absorbing materials should be a kind of structure and function integrated material, which can replace metal parts and realize dual functions of bearing and stealth.

Fullerene is characterized by cage-like structure, hollow in the middle, and the most common fullerene is C60. Because of the particularity of inorganic fullerene hollow cage-like structure, it is found that the inorganic fullerene’s structure has excellent resistance to compression and wave absorption. Its maximum compressive resistance is up to 25Gpa, which is the most hard molecular cage structure found recently, and its compressive resistance performance is better than other carbon cage like structures. Even when it under lower pressure, the collapse or transformation to other diamond structures will occur. Therefore, when inorganic fullerene structure is used as wave absorbing material, it can withstand more hard load conditions, such as high temperature oxidation. 

F35 absorbing materials image

The reason why nano tungsten disulfide / fullerene has excellent absorbing electromagnetic wave property lies in that: (1) nano tungsten disulfide / fullerene particles have small size and large specific surface area, the quantum size effect causes the splitting of the electronic energy levels, and the splitting energy levels are in the energy range corresponding to the microwave, which creates a new absorbing channel for the materials. (2) The atomic and electronic properties of tungsten disulfide / fullerene increase the efficiency of electromagnetic energy conversion to thermal energy, thus increasing the absorption properties of electromagnetic wave. (3) nano tungsten disulfide / fullerene has higher coercive force, it can cause large hysteresis loss, and it is conducive to the absorption of radar waves and other heat energy conversion and consumption.

In summary, inorganic fullerene/ nano tungsten disulfide is an excellent microwave absorbing material. It is not enough to use stealth materials only against single frequency bands. Only a wide spectrum stealth material that can resist a variety of detection instruments can meet the needs of military equipment stealth. Therefore, the stealth material in the military field is a more complex material system engineering.

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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...