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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2021年9月22日星期三

RF Sputtering Method Preparing Nanometer Tungsten Disulfide Membrane

Tungsten disulfide is an excellent solid lubricant material, it has high application value in the field of super solid lubrication.

Tungsten disulfide membrane have layered structure, it has lower hardness and better stability under high temperature, it is suitable to be used as a solid lubricant for friction parts in special environment. There are three main methods for preparing tungsten disulfide membrane which include RF sputtering method, reactive magnetron sputtering method, chemical deposition method.

The method of RF sputtering crystal growth is the method of using RF sputtering to make the components of the crystal material gasified and then recrystallized to grow the crystal. RF sputtering is a sputtering deposition method suitable for all kinds of metal and nonmetal materials, the frequency range is 5~30MHz, the frequency of 13.56MHz is commonly used internationally. It is mainly used to prepare thin membranes and also to prepare small size crystals.

RF sputtering method image

WS2 powder with 99.99% purity was prepared by cold pressing to form WS2 target, the surface of the stainless steel substrate is mechanically polished, and the surface is cleaned by ultrasonic wave. The background vacuum is 3 x 10-3Pa, fill in argon to the working pressure 1Pa, sputtering power 30W, deposition time for 1hour, depositing WS2 on a substrate to form a thin membrane.

The surface of tungsten sulfide membrane prepared by RF sputtering method is smooth, no voids and gaps were observed under SEM, it has high density and good quality, the surface morphology of the samples with different working pressure, different sputtering power and deposition time is similar, and no obvious changes.

Compared with other sputtering methods, RF sputtering method has a wide range of target materials, better advantages of high deposition rate, the RF power can be effectively input by adjusting the discharge impedance and the power impedance matching.

The membrane obtained by this method are generally amorphous. But by strictly controlling the sputtering pressure, power and other technological parameters, the sputtering method is still an important method for the preparation of the laboratory or the production of small workpieces.

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Review on the Effectiveness of Tungsten Disulfide and Molybdenum Disulfide Lubricant

 Solid lubrication is a method of coating or plating on the surface of the friction pairs to form a thin film and reducing friction.

tungsten disulfide and molybdenum disulfide image

The technique of using solid lubricants to lubricate is called solid lubrication. Tungsten disulfide and molybdenum disulfide are excellent solid lubricating materials, in the field of ultra-solid lubrication has a very high value, this technology is applied to the hard disk drive bearing of computer, such as rotation and sliding in ultra high vacuum system.

Molybdenum disulfide has a graphite-like structure, molybdenum and sulfur through the covalent bond to form a hexagonal structure, each molybdenum is surrounded by six sulfur atoms, the molecular layer surface only sulfur atoms, each layer molecular layer thickness of 0.626nm. The thermal stability of MoS2 is better in the air environment lower than 400 degrees. When the temperature is higher than 400 degrees, MoS2 will be oxidized to MoS3 in a short time, MoS3 is a granular material with higher hardness, attached to the friction surface of abrasive formation. But in a vacuum and inert gas environment, the structure of MoS2 at 1100 DEG C can keep steady.

Tungsten disulfide WS2 also has a hexagonal lamellar structure similar to molybdenum disulfide. Tungsten atoms and sulfur atoms covalently bonded, the molecular layer surface only sulfur atoms, between the sulfur atoms between the weak molecular bonds. WS2 is insoluble in almost all media, including acids, alkalis, oils and water, but is sensitive to free gaseous fluoride, hydrofluoric acid and hot sulphuric acid. Compared with MoS2, the thermal stability of WS2 is better than that of MoS2, and the decomposition temperature of WS2 is 510 °C in the air. In 539 degrees will be rapid oxidation, decomposition temperature in vacuum and inert gas is 1150 DEG C. Compared to the molybdenum disulfide, more widely applicable temperature range WS2.

Several domestic and foreign lubricant manufacturers have tungsten disulfide, molybdenum disulfide and graphene three lubrication performance comparison, through the test found that tungsten disulfide is not only stronger than molybdenum disulfide, stronger than graphene. In addition, in the high radiation operating environment, tungsten disulfide has a higher anti-radiation properties, can adapt to more complex operating environment, therefore, the major manufacturers are tungsten disulfide lubricant showed a more intense interest in production.

In the United States, aerospace industry, mainly used as MoS2 solid lubricating material, this is because the United States is the production of molybdenum power, convenience with local resources. In China, we have not only molybdenum more tungsten, relative to molybdenum, tungsten, whether it is heat resistance, physical and chemical stability, or radiation resistance are better than molybdenum, so tungsten disulfide lubricant will be better choice.

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Electrical Properties of Tungsten Disulfide

The structure of tungsten disulfide is a hexagonal layered structure with excellent electrical properties.

In tungsten disulfide, the interaction between the W atoms in the layer and the surrounding S atoms is strong, and the interaction between the tungsten disulfide layer and the layer is weak.

monolayer of tungsten dioxide image

The thermal stability of two tungsten sulfide is stronger than that of molybdenum disulfide. The temperature range is wide, and it is not easy to decompose. Oxidation occurs at 539 degrees centigrade. Therefore, tungsten disulfide is an excellent semiconductor material for indirect bandgap semiconductors. When the thickness of tungsten disulfide is reduced to a single layer, it changes into a direct band gap, which means that tungsten disulfide can effectively pass through the bandgap transition absorb or emit photons. The band gap of monolayer tungsten disulfide is about 2eV. This electrical performance characteristic is the main advantage of tungsten disulfide in semiconductor tubes, transistor applications that can go beyond graphene.

In fact, graphene has a very important defect in the field of semiconductors, which is the lack of band gap between electrons. In theory, graphene has very high mobility electrons that allow it to process data at very high rates, although it's very fast, there's no electron gap, and it's hard to turn it off once it starts to transmit data, this seriously hinders the logical operation, because all the problems in logic operations are open and close. While the two tungsten sulfide with planar high current switch, a higher than the mobility and the effective conductivity modulation performance, there is no logic problem, which can completely replace graphene in transistors, lighting diodes and optical sensors and other devices. The future, even now produce more than 100 times the calculation function of CPU, the use of the material is probably two tungsten sulfide.

In addition, tungsten disulfide also has a very strong photoluminescence properties, can replace the traditional transparent electrode materials and graphene, as a liquid crystal display, touch screen, solar cells and other equipment, transparent electrodes, with the addition of tungsten disulfide, the future of such equipment or will have a folding function.

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Tungsten Carbide / Cobalt Sprayed Coating

Thermal sprayed tungsten carbide / cobalt cermet is widely used in aerospace, metallurgy, machinery and other fields due to its good hardness and toughness.

tungsten carbide / cobalt sprayed coating image

Thermal spraying (spray welding), surfacing and other processes are gradually becoming the commonly used alloy, steel material anti-wear and surface corrosion technology measures. Tungsten carbide / cobalt thermal spraying technology has a simple process compared with other thin film and coating preparation technology, the coating and substrate have a wide range of selection, a large range of coating thickness, high deposition efficiency and easy to form composite coating. 

The wear resistance of alloy is a systematic engineering problem. The material is only an important aspect to measure the grindability. In addition, it is also related to the stress state, surface structure, lubrication conditions, environmental temperature and other factors. The characteristics of thermal spraying powder vary with the milling process. The usual preparation methods include sintering crushing method, agglomeration sintering method, mixing method, coating method, melting method, etc..

The powders prepared by sintering method are generally rough and angular shape, and the particles are compact inside. A large number of WC particles are distributed in the Co matrix, and a single WC particle is combined with the Co matrix. Agglomeration sintering is a kind of solid aggregate particles containing organic binder in the liquid medium. The WC powder and Co powder are mixed evenly and spray drying is formed. Finally, the heat treatment is carried out. 

The mixed powder prepared by WC and Co phase, the WC particles were loose co polymerization together; coating on the surface of WC particles is coated with cobalt form; melting method is made by crushing and melting casting method, powder particle size is generally big. 

With the progress of nanotechnology, a new spraying process cold spraying has been developed in recent years. The nanostructured WC/Co coating prepared by cold spraying has no negative effect on decarburization, there is no porosity, and there is no gap and crack between the matrix and it has good bonding property. Cold spraying is a 100% solid state process without particle melting, which can solve the problems of decarburization, phase transformation and re solidification of nano coating melt particles during the conventional process.

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2021年9月6日星期一

Decoloration Mechanism of Double Doped Zinc Tungstate

The modification of zinc tungstate by doping rare earth elements is an effective way to improve its luminescent properties.

The single crystal of zinc tungstate is rose red, the color makes the luminous efficiency decrease and the decoloration effect is obvious.

After annealing for a long time, the ZnWo4 crystal will disappear gradually, but the annealing of the bulk crystal still has difficulties which can not be overcome. The main problem is that the defect is incomplete and the defects are introduced into the annealing process. 

double doped zinc tungstate image

In single doped rare earth crystals, only cerium doped Ce3+ can recede the color of the crystal, both doped cerium Ce3+ and lithium li3+ have obvious decoloration effect on zinc tungstate crystal, especially, the former can obtain colorless crystal by proper doping.

The removal mechanism of zinc tungstate may be due to the decomposition of CO2 in Li2CO3 crystals, CO2 molecules will be partially retained in the lattice, CO2 molecules and O2 molecules are linear molecules, and the radius of the two has little difference, can replace each other in the hole. Therefore, when the crystal grows, the CO2 molecules fill in the oxygen vacancies to make the crystal clear.

Through the mechanism of doped zinc tungstate, it can be seen that the segregation coefficient of Ce3+ and Sm3+ in ZnWo4 crystal increases after double doping, it is beneficial to obtain high content of crystals, thereby changing the short life of fluorescence and the quenching temperature of luminescence is too low.

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Toughening Properties of Silver and Nickel Contacts Evaluation by Tungsten and Tungsten Oxide

In life, silver-nickel contact materials are widely used in relays, circuit breakers for low current ratings because of their good ductility and low contact resistance.

When current levels exceed 20 A, conventional AgNi contact materials exhibit weaker resistance to soldering and erosion, limiting their range of application. However, by adding a small amount of additives, the electrical properties can be improved, thus expanding its application area. Some scholars have studied that adding tungsten or tungsten oxide can improve the performance of AgNi contact materials. 

silver nickel contact image

The W or WO3, which accounts for 1.5% of the total, was made into silver-nickel contacts (containing 85% of silver content) by powder mixing, isostatic pressing, sintering, extrusion, subsequent wire drawing and riveting. Each contact material was repeated 5 times using the same resistive load in the test. The current and mechanical structure ensured that all tests had comparable arcing energy with supply voltages and load currents of 220 V and 25 A, respectively. After the 5000 operation, the contact is removed from the equipment and cleaned by ultrasonic in alcohol. After drying, the weight is weighed and the weight loss is calculated. 

The comparison of test results shows that the two different additive silver and nickel contact materials with tungsten powder or tungsten oxide have no obvious difference in the microstructure of the material, but there are big differences in the electrical properties such as material transfer and arc erosion. In the simulation of electrical performance test, the tendency of the addition of WO3 is that the mass loss and the microstructure of arc-affected zone are worse than that of tungsten powder. 

The addition of 1.5% W in AgNi contact materials can reduce the maximum welding power and reduce the arc erosion compared with 1.5% WO3. Therefore, tungsten powder may be better applied at low current level AC contactors.

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Tungsten Phosphide Catalyst Desulfurization

The contradiction between the increase of organic nitrides and sulfides in oil and the heavy crude oil.

The strict environmental protection regulations are becoming more and more serious, so it is necessary to conduct deep hydrofining for oil products.

The research shows that although the traditional molybdenum sulfide based catalyst is effective in hydrotreating process, it is far from meeting the requirements of deep hydrodesulfurization. The current approach is to retrofit existing catalysts and find new catalysts that can be used to meet the need for deep hydrotreating of crude oils.

desulfurization of tungsten phosphide catalyst image

In 1990s, the synthesis and performance of tungsten nitride hydrodesulfurization catalyst have been reported abroad, and the structure and desulfurization performance of P, Ni, W catalyst with phosphorus as auxiliary agent have been studied. However, the research on tungsten phosphide seems to be few. Therefore, the Chinese scholars also try to use tungsten phosphide for hydrodesulfurization test, so as to evaluate the non phosphorus catalytic effect.

The catalyst active component tungsten phosphide was synthesized by the method of temperature programmed reduction of phosphotungstic acid with high purity hydrogen. The PW-r-Al2O3 catalyst was prepared by reduction and mixing with r-Al2O3 as the carrier and tested.

The results show that the specific surface area of the tungsten phosphide is 7.228m2/g, and the specific surface area of tungsten phosphide catalyst Al2O3 is 105.543m2/g, which has better thiophene desulfurization performance. When the pressure is 3.0MPa, the space velocity is 4h-1, the volume ratio of hydrogen to oil is 1000 and the temperature is 340 °C, the thiophene hydrodesulfurization rates of the catalysts are respectively 90.2%. In addition, the stability of the catalyst was investigated. When the mixture was injected (thiophene 0.8%, pyridine 1.2%, cyclohexane 76%, octane 2%, cyclohexene 20%), the quality of the catalyst was all mass fraction, under the same reaction conditions, the denitrification rate and the desulfurization rate of the catalyst were only decreased by about 2%, which indicated that the PW-r-Al2O3 catalyst had good stability after 105h.

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Nickel Tungsten Nitrogen Catalyst for Its Catalytic Strength

With the continuous strengthening of human environmental awareness, the quality of living environment has aroused widespread concern.

All countries have formulated strict standards for the quality indicators of sulfur, nitrogen and other harmful substances in petroleum products. The clean production process and green products have become the mainstream trend in the development of petroleum refining and chemical production. In recent years, the transition metal nitrides hydrotreating catalyst has become a hot topic in the field of new catalysts because of its excellent deep hydrodesulfurization, denitrification activity and selectivity.

Some scholars believe that the current research on oil desulfurization catalyst is too focused on the cobalt molybdenum series earlier, and has excellent mechanical and thermal stability and anti poisoning characteristics of nickel tungsten catalysts study less, but in fact, the nickel tungsten nitrogen catalyst has more potential applications. 

nickel tungsten nitrogen catalyst image

By using temperature programmed reduction technology and r-Al2O3 as carrier, the nickel tungsten hydrofining catalyst NiWN/r-Al2O3 with different metal loading was prepared by impregnation method, and its hydrodesulfurization test was carried out.

 The size of the desulfurization activity level and surface acidity of catalyst was correspondence, namely catalyst surface acidity high desulfurization activity of catalyst, desulfurization activity of small low surface acidity. The surface acidity of catalysts, in addition to direct hydrogenolysis and hydrogenation desulfurization desulfurization, isomerization and cracking degree of strengthening, for deep desulfurization, and high desulfurization activity. The test found in NiWN/r-Al2O3 than the surface of the product is 149.5, surface acidity was 0.205, in the process of cracking gasoline showed good catalytic performance, surface acidity of benzothiophene on two is enough to produce catalytic desulfurization effect, the desulfurization rate is only about 91.2%. In this regard, scholars believe that nickel tungsten nitrogen catalyst can be used for catalytic desulfurization of oil, but there is still room for improvement and improvement.

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2021年7月28日星期三

Chemical Deposition Method Preparing Monolayer Tungsten Disulfide

Monolayer tungsten disulfide is a kind of nano material with layered structure, it has better temperature stability than monolayer disulfide.

It has attracted much attention in recent years because of its better optical and electrical properties, in the semiconductor field such as transistors, tungsten disulfide is an indirect bandgap semiconductor, forbidden band width is  2.0eV, it has more space than the application of graphene in the field of electronic tube. At present, the most important methods to prepare monolayer tungsten disulfide in China are three methods: RF sputtering, reactive magnetron sputtering and chemical deposition.

In recent years, the research on the preparation of two-dimensional TMDCs by CVD(chemical vapor deposition) method is mainly focused on molybdenum disulfide, because MoS2 requires lower temperature and it is easy to control the growth process, tungsten disulfide seems much more complex.

monolayer tungsten disulfide image

There are two main ways to prepare tungsten disulfide film by CVD method in laboratory: one step reaction method and two step method. One step reaction is the method that directly make the reaction of S source with W source to generate WS2 and deposit on the target substrate in CVD furnace. The two step method is to pre deposit a layer of metal W film on the target substrate, the WS2 film is then synthesized by sulfidation in CVD furnace. The above two CVD methods do not perfectly solve the large-area controllable monolayer and minority layer WS2 films.

Overall, growth conditions on the preparation of WS2 is critical. In the process of two-dimensional WS2 prepared by CVD method, it has more stringent requirements on the instrument and growth process, and the cost of the experiment is high. We believe that in the near future, WS2 film development bottleneck will soon be widened to promote its device and industrialization process.

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Application of Monolayer Tungsten Disulfide Film in Photoelectric Field

Two dimensional transition metal chalcogenide (TMDCs) is considered as a potential star material for future applications of electronic devices because of its graphene like structure.

The current research more semiconductor materials are tungsten disulfide WS2, molybdenum disulfide MoS2, MoSe2 molybdenum selenide, WSe2 tungsten selenide and so on. Among them, WS2 has the most promising application in electronic devices because of its bipolar electron transport properties.

Single layer two W is a kind of layered material similar to graphite with a layer spacing of 0.7 nm. WS2 is an important photoelectric material. When WS2 is changed from bulk material to single layer, the material changes from indirect bandgap to direct band gap semiconductor, and the band gap will change from 1.3eV to 2.0eV, which makes the monolayer tungsten disulfide thin films have important potential applications in photoelectric detectors and solar cells.

Monolayers of tungsten disulfide films show excellent performance in photodetection device research. Some scholars have found that based on 10-layer thick WS2 thin-film optical transistor devices, has the ability to detect monochromatic light of different wavelengths. When the wavelength is 514 nm, the photoresponse time of the device is about 5.3 MS, and the photoresponse rate is about 10 times of that of the MoS2 film. 

tungsten disulfide film image

In the field of solar cells, tungsten disulfide has shown great potential due to its excellent light response and absorption characteristics, some scholars have constructed ITO /WS2 /Au Schottky solar cells. The test results show that visible photocurrent can be produced under visible light irradiation. They also studied the effects of single layer, double layer and multilayer graphene electrodes on Al/WS2/rGO, Schottky cells. The results show that the Schottky contact between graphene and WS2 film is easy to form, so that the built-in electric field is formed at the interface between graphene and WS2 film, the photoinduced electron flows from the WS2 film to the Al electrode, and the hole flows from the WS2 film to the graphene, the maximum photoelectric conversion efficiency of the solar cell is up to 3.3%.

At present, the mass production of single-layer tungsten disulfide film is still difficult, the finished product quality is unstable and the cost is also high, this may be that tungsten disulfide is not as famous as graphene main surface. In the future, it is still a difficult problem for scientists to find a cheap and large area continuous preparation method of WS2 film and guarantee the quality and quantity.

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How to Make Rare Earth Terbium Zinc Tungstate More Dazzling

Rare earth ions are rich in energy levels, their luminescence wavelengths can change from ultraviolet to infrared. They are often used as luminescent centers in luminescent materials.

Metal tungstate is a kind of important inorganic functional materials, including tungsten ore stone structure of zinc tungstate (ZnWO4) is a self luminous material type. WO42- itself has self excitation fluorescence, emits blue green light under ultraviolet irradiation, and can effectively transfer energy to rare earth ions. Therefore, it is widely concerned that in the chemical industry, the self luminescent tungstate doped rare earth element is the most effective LED light source acquisition scheme to change its fluorescence color.

rare earth terbium zinc tungstate fluorescence image

At present, the synthesis methods of rare earth doped ZnWO4 are sol gel method, combustion method, hydrothermal method and microemulsion method. Hydrothermal synthesis is a commonly used method for the synthesis of green phosphors ZnWO4:Tb3+. In the process of hydrothermal synthesis of  ZnWO4:Tb3+ phosphor, adding proper surfactant can greatly affect the structure and luminescent properties of  ZnWO4:Tb3+ phosphor.

In the rare earth doped ZnWO4 system, due to the unequal price of trivalent rare earth ions Tb3+ and Zn2+, Na+ is usually introduced into the synthesized ZnWO4:Tb3+as a charge compensation to enhance the luminescence intensity of the rare earth. In addition, some scholars have studied the effect of surfactants on the luminescence of rare earth zinc tungstate, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB) and polyethyleneglycol 2000 (PEG-2000) were tested for surface active additives, concluded as follow:

Zinc rare earth terbium tungstate added with different surfactants had almost no effect on the position of the excitation spectrum, but had an influence on the emission intensity. The use of PEG-2000 as a surfactant is most effective for enhancing the luminescence intensity of phosphors. The lifetime of  ZnWO4:Tb3+ phosphors synthesized by using PVP as surfactant is longer than that of PEG-2000 and CTAB as surfactants. Combined with luminescence intensity and fluorescence lifetime, PVP is the most suitable surface additive for rare earth terbium zinc tungstate.

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Zinc Tungstate Whisker

Whisker is a kind of fiber which grows in single crystal form under artificial control.

Whisker's diameter is very small (micron order of magnitude), no defects in the usual materials (grain boundaries, dislocations, voids, etc.). Its atomic arrangement is highly ordered, so its intensity is close to the theoretical value of the complete crystal. Because the whisker reinforced composites have the potential of high strength, the research and development of whiskers have been paid much attention to.

zinc tungstate whisker image

Zinc tungstate whisker is mainly used in metal matrix composites, and it is a key high-tech material. It has been widely used in ceramic cutting tools, space shuttles, automobile parts, chemical industry, machinery and energy production. 

Zinc tungstate has a better scintillation performance than the currently widely used scintillation crystal, but also has the characteristics of not deliquescence and low price, and is a very promising scintillation crystal. The size of zinc tungstate whiskers is generally about 200~500nm, and it is unlikely to have obvious quantum size effect, therefore, scholars believe that the blue shift of the luminescence peak should be due to the crystal structure of the whisker is more complete, less defects, that is, the whisker growth of zinc tungstate is not difficult. 

Zinc tungstate whisker is prepared by solid phase sintering, that is, by mixing tungstic acid and tungsten oxide powder, ball milling, drying, grinding, sieving, tableting, sintering and other technological processes, finally, zinc tungstate whiskers were successfully prepared. Analysis of whisker structure with the XRD, found the structure of wolframite structure, smooth surface, thickness of single whisker is consistent, its cross section is round, the top of the whisker is sharp, and the growth of the whisker is best when the ratio of tungstic acid to tungsten oxide is 4:1, the sintering temperature is 1150 degrees, and the holding time is 240 min.

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2021年6月30日星期三

Inorganic Fullerene / Tungsten Disulfide Composite Lubricant

Fullerene is the third allotrope of elemental carbon was found by a carbon, any elements in spherical, oval shaped structure of the material existence.

In the field of lubricants, tungsten disulfide is a typical layered structure, easy to slip away, it is widely used in the field of lubricants, but tungsten disulfide due to its crystal edge of the unsaturated suspension bond with chemical activity, easy in the friction process oxidized, the tribological properties of graphene are greatly reduced, especially in humid atmosphere. Graphene has good chemical stability, so it is applied in practice, people tend to be tungsten disulfide and graphene compound made of lubricants, but some scholars use inorganic fullerene C60 instead of graphene, and get better results.


The inorganic fullerene structure eliminates the dangling bonds on the edge and has higher chemical inertness. The hollow cage structure can provide higher elasticity and increase the resilience in the load range, in order to reduce the dissipation related to wear, some scholars have used uniaxial shock wave to test the dynamic compressive properties of two tungsten sulfide / inorganic fullerene structures, it is found that the inorganic fullerene structure has excellent compressive wave absorbing ability, and its maximum compressive pressure is high, which is now found in the most tough molecular cage structure, its compressive properties are better than those of other carbon cage like structures, even under lower pressure, it will collapse or transform into other diamond structures. Its compressive properties are better than those of other carbon cage like structures, even under lower pressure, it will collapse or transform into other diamond structures. Therefore, when the inorganic fullerene structure is used as a solid lubricant, it can withstand more graded load conditions, performance is not inferior to graphene / tungsten disulfide composite lubricant, and the environmental strain is stronger than the former.

The study found that the lubricating oil by adding a small amount of inorganic fullerene / two tungsten sulfide composite lubricant can greatly improve its tribological properties, adding a small amount of inorganic fullerene / two tungsten sulfide composite lubricant can significantly prolong the service life of the engine in automobile lubricating oil, reduce fuel consumption of motor vehicles.

Taking spacecraft as an example, the tribological properties of materials in the transition from atmosphere to high vacuum, from low temperature to high temperature and from humid atmosphere to dry atmosphere are extremely demanding, at this point, liquid lubricants are difficult to meet the needs of use. Only inorganic fullerene / two tungsten sulfide can achieve excellent antifriction and wear resistance. In order to reduce the energy consumption of the transmission system, prolong the service life of components and improve the reliability of the system, it provides a new effective way to solve the tribological problems of materials under extreme conditions.

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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...