Ammonium Tungsten Bronze Nanoparticles Preparation

Tungsten bronze compounds are a series of important inorganic compounds, tungsten ions exist as mixed valence state of W6 +, W5 + and W4 + in such compounds to make a balance in the overall charge. Rich crystal structure, the tunnel structure and this particular valence state lead to its excellent properties, such as electronic and ionic conductivity, superconductivity, optical properties, which has caught widespread research interest in the aspects of the secondary battery, electrochromism, near-infrared absorption and application of chemical sensors.

Currently, methods to synthesize tungsten bronze compounds mainly are the wet chemical method, heat reduction method and thermal decomposition method. Wet chemical method to synthesize ammonium tungsten bronze is to put the starting material in the reducing solvent refluxing for several days, size of the sample obtained by this method is too large, it’s usually between a few to ten micron, and the preparation process requires a long time and high energy consumption. Thermal reduction method is to uniformly mix tungsten oxide, tungsten powder and metal tungstates in proper proportions, then heated in a vacuum or under an inert atmosphere, the reaction temperature is usually about 1000 ℃, and remove unreacted impurities after the reaction is completed. Since the thermal stability of ammonium tungsten bronze difference is poor and decomposition temperature (300 ℃) is lower than the synthesis temperature, the thermal reduction method can not be used to synthesize ammonium tungsten bronze. The thermal decomposition method to synthesize ammonium tungsten bronze is to heat and decompose ammonium paratungstate in a reducing atmosphere (H2 or a mixed gas of H2, Ar, etc.), the size of the resulting sample is too large, and this method can not obtain completely pure phase ammonium tungsten bronze, ammonium content in sample is too low and easy to excessive decomposed into tungsten oxide.

The pure phase ammonium tungsten bronze nano-powder can not be directly obtained in current study, so usually break the large micron-sized particles obtained into small particles by milling, but these compounds are easily to be oxidized and lost live and decompose in the milling process, also accompanied by crystallization performance degradation. For the above problems, some scholars have proposed a synthesis method to directly synthesize ammonium tungsten bronze powder with controllable particle size.

Preparation of reduced state ammonium tungsten bronze nanoparticles: dissolve 0.01~1g tungsten hexachloride or tungsten tetrachloride in 20~40mL oleic acid solution, and stirred to obtain homogeneous solution, then added 4~30mL oleylamine, and mix evenly, move to supercritical reaction kettle, crystallization reaction at 150~350 ℃ for 0.5~48 hours, the powder samples were centrifuged and washed after reaction, dry under vacuum at 40~250 ℃ for 1~12 hours, and the reduced state ammonium tungsten bronze nanoparticles are obtained, the mole fraction of ammonium group in the composition is between 0.2~0.3. In addition, samples obtained by this method have strong near-infrared absorption ability, the film containing nanoparticles can effectively shield the near infrared rays of 780 ~ 2500nm and maintain high visible light transmittance.

It was proposed a synthesis method to directly synthesize ammonium tungsten bronze powder with controllable particle size since the pure ammonium tungsten bronze nano-powder can not be directly obtained in current study.

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Lithium Tungsten Bronze Photocatalyst Preparation II

Taking into account the practicality of the photocatalyst in the decomposition of harmful substances, sunlight as the light source is indispensable. Wavelength irradiated to the surface of the sun at about 500nm has the maximum intensity of visible light, energy of wavelength at 400nm-750nm in the visible region is about 43% of the total energy of sunlight, so in order to efficiently utilize the solar spectrum, finding the catalyst with light visible effect has aroused people's attention. Kinds of photocatalysts with visible effect reported are still limited currently, so it is necessary to research and develop new photocatalyst with highly efficient visible light effect. Tungsten bronze compounds are a series of important inorganic compounds, tungsten ions exist as mixed valence state of W6 +, W5 + and W4 + in such compounds to make a balance in the overall charge. Rich crystal structure, the tunnel structure and this particular valence state lead to its excellent properties.

A kind of oxide containing lithium tungsten bronze structure as visible effect photocatalyst, the chemical formula of lithium tungsten bronze structure oxide is = Ba5LiFe0.5 (NbxTah) λ A. （0 <x <1） preparation steps of lithium tungsten bronze structure oxide are as follows: mix the 99.9% analytically pure chemicals of BaCO3, Li2CO3, Fe2O3, Nb205 and Ta2O5 as formula Ba5LiFe0.5Nb4.75Ta4. 75 O30, put into the mill pot, add zirconia balls and ethanol, milling for 2-8 hours, mix grinding, remove and dry through 200-mesh sieve; the resulting powder material calcine at 1175-1275 ℃, and incubate for 6-8 hours, cool to room temperature, and then pulverized by ball mill so that the particle size gets smaller to 2 μm, then the lithium tungsten bronze structure oxide powder Ba5LiFe0.5Ta9.5O30 is obtained, 0 <x <10. This method is simple, with low cost, photocatalys obtained has excellent catalytic performance, with effects of decomposing harmful chemical substances, organic biomass and bactericidal under visible light irradiation.

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Lithium Tungsten Bronze Photocatalyst Preparation I

Environment pollution has caught great concern from many countries in the world, it has led to the drinking water source of people's lives and industrial water quality continue to decline, which leads to air pollution grow and results in the continuous destruction of the ecological environment,and poses a serious threat for human survival. In order to solve these problems, a variety of methods to control environmental pollution are carried out.

From the late 1970s, it is proposed the use of photocatalyst to decompose pesticides and malodorous substances and other organic matters in water and the atmosphere, as well as application examples like photocatalyst coated solid surfaces self-cleaning and so on. Currently, the photocatalyst is primarily titanium dioxide, which has been used to decompose pesticides and malodorous substances and other organic matter in water and the atmosphere, however the bandgap of titanium dioxide is 3.2eV, can only show activity in the ratio of 400nm shorter ultraviolet light and can only work indoors or where there is an ultraviolet lamp, hardly with visible light, which greatly limits the use of titanium dioxide photocatalyst.

In order to efficiently utilize the solar spectrum, finding the catalyst with light visible effect has aroused people's attention, so the application of oxide containing lithium tungsten bronze structure as visible effect photocatalyst is found.

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Tungsten Bronze Application in Ceramic Capacitors II

Temperature stability is of great importance for the preparation of multilayer ceramic capacitors in electronic products application, and tantalates with tungsten bronze structure having high dielectric constant (> 100) and low dielectric loss, is expected to be the dielectric materials with temperature stability being used in multilayer ceramic capacitors.

Miniaturized drives and speed of the computer transfer more focus into the high-temperature resistant parts, the capacitor must be able to work at 150℃ or even 200℃ in the future. However, the application of PbTiO3-BaTiO3 composite multilayer ceramic capacitor is not desirable, the first reason is 1¾ toxicity, the second one is that easy to decompose in low oxygen partial pressure, and Ni metal electrode will form into low melting point alloy with it. The same problem also appears in BiTiO3 doped by Bi2O3 base solid solution. The ideal new materials require the phase transition temperature is between -50 ℃ ~250 ℃, without PbO or Bi2O3, containing relatively common and inexpensive raw materials.

Recently, domestic and foreign researchers found that a number of tantalates with tungsten bronze structure having high dielectric constant (> 100) and low dielectric loss, is expected to be the dielectric materials with temperature stability being used in multilayer ceramic capacitors. The ceramic dielectric constant ε r  is between 127~175, dielectric loss tan σ is less than 0.009 at 1MHz, the dielectric constant and temperature coefficient τ ε is between -7¾~-2500ppm / ℃. But the dielectric constant and temperature coefficient of these tantalates with tungsten bronze structure are too large, the dielectric constant is too low, thus the practical applications are limited.

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Tungsten Bronze Application in Ceramic Capacitors I

A ceramic capacitor is a fixed value capacitor in which ceramic material acts as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes. The composition of the ceramic material defines the electrical behavior and therefore applications. Ceramic capacitors, especially the multilayer style (MLCC), are the most produced and used capacitors in electronic equipment that incorporate approximately one trillion (1012) pieces per year. Ceramic capacitors of special shapes and styles are used as capacitors for RFI/EMI suppression, as feed-through capacitors and in larger dimensions as power capacitors for transmitters. Ceramic capacitors are divided into two application classes: Class 1 ceramic capacitors offer high stability and low losses for resonant circuit applications. Class 2 ceramic capacitors offer high volumetric efficiency for buffer, by-pass, and coupling applications.

Temperature stability is of great importance for the preparation of multilayer ceramic capacitors in electronic products application. Two or more than two of the polyhydric compounds having opposite temperature coefficient and dielectric constant (τ ε) are mixed to produce a solid solution with small temperature coefficient and dielectric constant, this method is frequently used to realize the temperature stability of the materials; or, such as capacitor for BaTiO3, mixed dopant is dispersed in the ceramic body to produce ferroelectric - paraelectric phase transition near room temperature and the relatively stable material has been obtained. Currently, BaTiO3 compound fits X7R standard, its dielectric constant does not exceed ± 15% in the temperature range of -55 ℃ ~125 ℃ compared to the change rate of dielectric constant at room temperature, the dielectric loss tan σ is less than 0.02 at 1MHz. However, if PbTiO3 (Tc = 4950C) is not doped, the maximum operating temperature does not exceed 130 ℃.

Recently, domestic and foreign researchers found that a number of tantalates with tungsten bronze structure having high dielectric constant (> 100) and low dielectric loss, is expected to be the dielectric materials with temperature stability being used in multilayer ceramic capacitors.

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Tungsten Market Short-Term Shocks

Tungsten price rose sharply in short term, which did not only fail to stimulate the enthusiasm of the industry, but made the upstream and downstream market trade sharply compressed, although raw material prices were pulled up rapidly, the price of terminal tungsten carbide products has not been improved.

Two months of tungsten price continuous rising begins to turn around. On May 25, the average price of 65% wolframite is 76,000 yuan / ton, the price of APT is 120,000 yuan / ton, the price of medium grain tungsten powder is 190 yuan / kg, respectively, the average price fell 2,000 yuan / ton, 3,500 yuan / ton, 2 yuan / kg compared with that on last Friday (May 20).

Affected by tungsten enterprises limited production price and purchasing and storage news, tungsten price rose sharply in short term, which did not only fail to stimulate the enthusiasm of the industry, but made the upstream and downstream market trade sharply compressed, the price of tungsten lacking of market demand to support will eventually fall back, so there are reasonable demands for the price returning in the market itself. Price of tungsten products continued to rise, especially tungsten powder, tungsten carbide powder and other powder products, with the rapid rise. Although raw material prices were pulled up rapidly, the price of terminal tungsten carbide products has not been improved. Some alloy enterprises said that the current orders on hand were signed before a month and unable to increase prices. Some small and medium sized carbide producer claimed that they were prepared to discontinued at any time.

Influence by the high costs of raw materials, on the one hand the downstream business are difficult to accept it, on the other hand with the increasing prices of raw materials, there are attempts to raise the offer of their own terminal products. Combined with that the early result of tungsten concentrate prices rising, traders of tungsten concentrate storing a large number of goods leads to backlog of funds, the divergence of interests in the market of all parties, or cause short-term frequent shocks of price tungsten in the market, the base of the sharp decline is still not enough.

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