2019年1月31日星期四

【Know Tungsten】What Is Tungstic Acid?

Tungstic acid is the generic term of all kinds of hydrates of tungsten oxide (WO3), polymer compound which formed by the combination of tungsten trioxide WO3 and then united with water at different ratios and formations.


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How to Increase The Fluorescence Yield of Lead Tungstate

Lead tungstate crystals have become a new generation of scintillating materials due to the high density, short radiation length and Moliere radius fast flicker decay time, strong anti-radiation damage ability, air deliquescence, chemical stability and low price.

In recent years, lead tungstate crystals have also attracted attention in the field of nuclear medical equipment applications, especially in the positron emission tomography (PET) and other nuclear medicine imaging has become a hot research at home and abroad. However, lead tungstate scintillation crystals have many advantages, but lower fluorescence yields limit the use of lead tungstate crystals in high energy applications. Therefore, to improve the fluorescence yield of lead tungstate, we can better expand its field of application.

lead tungstate crystals image

At present, there are commonly used ways to improve the low light yield of lead tungstate crystals: (1) Improve the growth conditions, improve the purity of raw materials and adjust the ratio of raw materials to remove as much as possible on the luminous properties of impurities; (2) Doping the ions in the lead tungstate matrix, and the new luminescent center is introduced by compensating the defects so that the doping ions emit light in the blue band; (3) By optimizing and establishing a reasonable annealing process to compensate for oxygen vacancies and reduce defects.

The blue luminescence of lead tungstate crystals lies near 420 nm, in order to improve the low light yield of lead tungstate crystals, it is necessary to have high transmittance in the range of the emission wavelength to reduce the self absorption of the crystal in this band. By optimizing the annealing conditions can compensate for oxygen vacancies, reduce defects, improve the lead tungstate crystal transmittance, thereby increasing the low light yield of the crystal. Therefore, it is important to explore the optimum annealing conditions to improve the low light yield of lead tungstate crystals.

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Sodium Tungstate Promotes Nitrogen Fertilizer Plants Absorption Tips

Nitrate nitrogen refers to the nitrate fertilizer contained in nitrate, which is mainly used in fruit trees. It can stop the development and deformity of fruit.

It is one of the main fertilizers for crop growth and prolonging crop growth and harvesting period,it plays a crucial role in the growth of crops. However, the use of nitrate nitrogen is a double-edged sword, on the one hand, nitrogen fertilizer can improve the yield of crops, on the other hand, the excessive use of nitrogen fertilizer will also pollute the rivers and lakes, soil and underground water, resulting in major rivers appear eutrophication, algal growth, leading to ecological extinction. How can you find a balance between efficiency and the environment? Scientists have been trying to find the answer. Some scholars think of sodium tungstate.

Sodium tungstate has been widely used because of its low toxicity, no harm to environment, human body and crops, and no breeding of microorganisms. Some scholars have added a small amount of tungstate to the nitrate nitrogen in citrus cultivation, but a small change has resulted in unexpected returns.

citrus trees image

Studies have shown that in citrus cultivation, the addition of a small amount of tungstate can promote the plant to better absorb nitrate nitrogen fertilizer useful elements, this is because the nitrate reductase (NR) is the key enzyme in the process of nitrate nitrogen action and rate limiting enzyme, this is because the nitrate reductase (NR) is a key enzyme in the process of nitrate nitrogen action and rate limiting enzyme, its activity reflects the ability of plants to restore and transform nitrate nitrogen, and is closely related to the ability of plants to absorb and accumulate nitrate nitrogen, the enzyme is a water-soluble molybdenum protein, with the same poly-subunit protein.

Each subunit contains three auxiliary: Flavin adenine dinucleotide (FAD), cytochrome (Cytc), and molybdenum cofactor (MoCo), each auxiliary group is a redox process in which molybdenum atoms (Mo) act as an important component of the enzyme and participate in the reduction of nitrate nitrogen to ammonium. The properties of tungsten atom (W) in sodium tungstate (Na2WO4) are similar to that of molybdenum atoms, which can directly replace molybdenum in the nitrate reductase complex, in short, sodium tungstate can play a role in inhibiting reductase activity, so that the plant water to absorb nutrients, and the nutrients just right to pass on the fruit, rather than overeating caused by loss of nitrogen fertilizer to the soil, this is also the secret of citrus fruit being more sweet and full catalyzed by sodium tungstate.

To sum up, adding appropriate amount of sodium tungstate can promote the better absorption of nitrogen fertilizer plants, so as to enhance the efficiency of nitrate use, while improving crop quality while reducing the amount of nitrogen fertilizer, in order to achieve efficiency and environmental balance.

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How Does Sodium Tungstate Delay Metal Corrosion

Corrosion inhibitor is a kind of substance which can prevent or retard the corrosion of metal in environmental medium under low concentration.

It can be divided into three kinds: inorganic inhibitor, organic inhibitor and polymer inhibitor. Commonly used cooling water corrosion inhibitors are chromate, nitrite, phosphate and so on, but they all have one characteristic, that is, toxic. With the enhancement of human's environmental protection consciousness, the development and application of low toxic or nontoxic inhibitors have been paid attention to.

Sodium tungstate is one of inorganic inhibitors. It is used as a metal corrosion inhibitor because of its low toxicity, no harm to environment, human body and crops, and no microorganism breeding. Using sodium tungstate as a metal is a corrosion inhibitor, not only effective, but also green.

submarine pipeline image

Some scholars used sodium tungstate inhibitor to test the corrosion inhibition of sea water on carbon steel, in the experiment, sodium tungstate and sodium lauroyl sarcosine (SLS) were used to draw the conclusion under suitable concentration, the composite corrosion inhibitor of sodium tungstate has a good corrosion inhibition effect on seawater Q235 carbon steel, and the corrosion inhibition efficiency increases with the increase of its concentration. The adsorption of sodium tungstate on carbon steel is a mixture of physical adsorption and chemical adsorption, capable of being adsorbed on a clean metal surface to form a monolayer, to prevent water and dissolved oxygen diffusing to the metal surface, the inhibition efficiency is more than 95%. The corrosion rate was reduced to below 0.075 mm/a, and the effect was satisfactory.

By the test results, we can envision sodium tungstate has very broad application prospects in terms of delaying the metal corrosion, such as oil pipeline, corrosive environment water supply pipeline, bridge foundation, electroplating equipment, electroplating factory, as well as the use of a large number of sand of the coastal city of the real estate industry in building. Sea sand will also corrode steel, if in the concrete synthesis process, adding appropriate sodium tungstate complex type corrosion inhibitor can also extend the life of the building, and of course, this takes a long time to see the results.

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2019年1月4日星期五

Tungstate Makes LED Colorful

Tungstate is the most classic one of the inorganic luminescent materials, as early as in 1896, scientists found that CaWO4 can be applied to X-ray emission.

LED light glows image

In 1906 for the first time to be used as X phosphor materials, tungstate materials quickly penetrate into all aspects of human life. In 1948, people found that the brightness of tungstate with compound purity increases, tungstate can be launched by some elements, these rare earth elements doped tungstate lattice, can make it shine with special properties.

In recent years, the energy-saving lighting industry has developed vigorously. However, the efficient lighting products are unable to avoid the mercury pollution problems while saving electricity and reducing energy consumption, with the developing of tungstate phosphors, LED has gradually become the market mainstream. Tungstate phosphors are those that can absorb energy (the absorbed energy including electromagnetic wave (including visible light, ultraviolet X rays, ), electron beam or ion beam, thermal and chemical reaction), and then through the energy conversion after the release of visible light material.

In the lighting, the LED light-emitting principle is different colors are added with different fluorescent powder, we see the white LED itself is not white, is generally blue light to stimulate the yellow fluorescent light emitting white light, the main material is mostly phosphor tungstate, with rare earth tungstate, similar to the color palette, tungstate blends many colors for LED.

The tungstate phosphor has been used in the presence of mono succinates and two tungsten hydrochloric acid of the CaWO4 scheelite structure. But recently, the application of tungstate doped with rare earth ions such as Eu3+, Tb3+ and Dy3+ has become very active in the field of white LED, and its applications have become more and more widely.

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Tungsten Heteropoly Acid Photocatalyst

A tungsten heteropoly acid phtocatalyst is composed of heteropoly acid and its salt, it consists of a central (hetero) atom (P, Si, etc.) and a coordinated (multi) atom W.

photocatalysis image

A group of metal complexes of oxygen groups bridged by oxygen atoms into space, which can be widely used in homogeneous and heterogeneous catalysis systems.

Because of the development of petrochemical industry, especially the fine chemical industry, the multifunction of catalysts has become a new research target, tungsten heteropoly acid photocatalyst is a bifunctional catalytic material with acidity and basicity and redox property. It is an environmentally friendly catalyst and can reduce environmental pollution and equipment corrosion. Therefore, it is of great significance to study the new catalytic process. Under visible light or UV irradiation, tungsten heteropoly acid is excited to become a strong oxidant and can oxidize various organic compounds in water. Its photocatalytic activity is almost as high as TiO2.

Some scholars use PW12O403- as a catalyst, under the excitation of ultraviolet or near visible light, and the pesticide fenitrothion photodegradation were studied, the results showed that the light mineralization of fenitrothion, eventually transformed into PO43-, SO42-, NO23-, NO3 and other inorganic ions. The study of the catalytic mechanism shows that the reaction is mainly caused by the oxidation of OH radical. Some scholars also used water-soluble H3PW12O40 as catalyst and stimulated by ultraviolet visible light, the fluorinated polyacrylate (NFPA) can be decomposed into F- and CO2 at room temperature, and no harmful by-products such as CF4 and CF3H are produced.

Heteropoly compounds have the characteristics of strong acidity, oxidation and no pollution. They have laid a solid foundation for their important position in the field of catalysis. In recent years, these catalysts have shown an attractive prospect in photocatalytic chemistry, making it possible to make greater use of sunlight.

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Nano Lead Tungstate Preparation by Precipitation Method

Lead tungstate is a kind of tungstate. It has attracted extensive attention because of its luminescent properties and radiation resistance.

nano lead tungstate structure image

The results show that the lead tungstate crystal can exhibit blue, green and red absorption at a certain wavelength, and the requirement of attenuation time and radiation damage is far beyond the requirement of light yield.

The main preparation methods of lead tungstate are solid phase method and liquid phase method. But for the preparation of nano lead tungstate, liquid phase method is usually adopted, and precipitation method is one of liquid phase method.

The starting materials prepared by precipitation of  nano lead tungstate particles with 99% purity of lead nitrate and 99.5% sodium tungstate, with deionized water as solvent, polyethylene glycol (PEG 200) as a dispersant to prepare nano lead tungstate  powder.

According to the chemical dosage ratio of lead nitrate and sodium tungstate were dissolved in deionized water, stirring until completely dissolved, then to adding PEG 200 solution of lead nitrate and sodium tungstate, in order to achieve the effect of particle dispersion. In order to regulate the pH value of the reaction and to facilitate the reaction, a proper amount of ammonia was added into the sodium tungstate solution, the lead nitrate solution is then directly added to the sodium tungstate solution to give lead tungstate.

After the reaction was complete, the mixture was stirred for another 10 min to give a slightly yellowish turbid solution. After settling the turbidity liquid for about 120 min, lead tungstate could be found at the bottom of the vessel, the precipitate of sodium tungstate was washed with deionized water several times, and the precipitated precipitate was dried at 100 °C for a slight amount of nano lead tungstate powder. 

In the nano lead tungstate powder preparation process, control the quantity of PEG 200 is one of the key can achieve the best dispersion effect, because PEG 200 plays a key role in solving the agglomeration between particles, when it is added to the solution, one end of the polymer chain can be attracted tightly to the surface of the particle, the other end extends into the liquid as much as possible to reduce the attraction between particles, thus achieving steric stabilization.

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Photocatalytic Degradation of Molasses Alcohol Wastewater by Lead Tungstate

Molasses alcohol wastewater is produced by molasses fermentation in alcohol workshop of sugar refinery and high concentration and high chroma organic wastewater discharged later.

photocatalytic degradation of molasses alcohol wastewater by lead tungstate image

It riches in protein and other organic compounds, but also contains more N, P, K, Ca, Mg and other inorganic salts and higher concentrations of SO42- and so on, most of these acidic waste water, and high chroma, will seriously pollute the water, the environment, or cause compaction of soil acidification, crop long illness.

The main methods of treating molasses alcohol wastewater are irrigation, concentration, anaerobic and aerobic methods, biological products and EM bacteria technology, in addition to not producing biological products, other methods continue to harm the environment, or the cost is too high, unrealistic, will there be a feasible strategy for the best of both worlds?

In recent years, with the development of photocatalytic technology of nano tungstate, more and more tungstate chemicals have been used to purify environmental pollution, for example, some scholars have used lead tungstate as a photocatalyst to degrade molasses alcohol wastewater. How can the effect be?

Lead tungstate crystal is a new scintillation material because of its large density and good scintillation, generally used as a probe for electromagnetic calorimeters, the idea of being used as a photocatalyst is unique, but the effect is unexpectedly good.

According to a research report by Qin Zuzeng, a scholar at Guangxi University, PbWO4 can effectively catalyze the photocatalytic activity of molasses alcohol wastewater under UV irradiation, and the process is a first-order kinetic reaction. For 30 times diluted molasses alcohol wastewater, the addition of 4.0 g of L-PbWO4 photocatalyst was carried out by introducing 126 L h-1 air without changing the pH value of the waste water and without adding the co-oxidant H2O2, 120 min reaction at 300 W under the irradiation of high-pressure mercury lamp, the decoloration rate of PbWO4 photocatalytic degradation of molasses alcohol wastewater was 90.2%, the removal rate of COD was 78.6%, and good degradation was achieved.

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