Pyrochlore type oxide, tungsten oxide (often referred to as H2W2O7 or WO • -0.5H2O) to WO6 distorted octahedral structural motifs, by a rigid skeleton top corner WO6 construct a layered structure with the bore having a six-membered ring, in layers formed between road. Which has an n-type semiconductor properties and microwave absorption properties, as a new industrial materials, it photochromic, electrochromic, gas discoloration caused by aspects, catalysis have a very important significance. In addition, the tungsten oxide pyrochlore type after the firing energy directly into tungsten trioxide, tungsten trioxide can be prepared as intermediates.

Currently preparation of tungsten oxide pyrochlore type used mainly soft chemical synthesis method and hydrothermal synthesis. Hydrothermal synthesis method is widely applied in the field of inorganic materials synthesis, the advantage of easy-to-control hydrothermal conditions, the resulting product of high purity, good dispersion, size and easy to control. Currently Hydrothermal Synthesis of tungsten oxide pyrochlore type usually sodium tungstate solution for raw materials, hydrothermal reaction after acidification some time to prepare. According to the findings of the different researchers, sodium tungstate solution pH in the range of 2.0 to 8.9 can hydrothermal synthesis of tungsten oxide pyrochlore type, but its synthesis mechanism is not clear, no direct evidence to determine the reaction precursor, study needs further. The presence of an acidic environment with a variety of tungsten ions and more heteropolyacid ion, and the transformation of the structure of the situation is complex and varied, this article focuses on the basic system of tungsten oxide pyrochlore-type hydrothermal synthesis mechanism.

Pure sodium tungstate solution for the reactants, hydrochloric acid as an additive, in an alkaline environment pyrochlore type hydrothermal synthesis of tungsten oxide. Use FT-IR analysis of the infrared spectra of the test method change under different rules and acidification of the reaction solution Na2WO4 different time period, to analyze WO2-4, W7O6-24, H2W12O10-42 and W2O2-7 whether to prepare tungsten oxide pyrochlore-type reaction precursors, ruled out the use of exclusion H2W12O10-42, W2O2-7 possibility before the reaction the body as that of the precursor should WO2-4 and W7O6-24, and assisted by thermodynamic calculations prove.

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Pyrochlore type oxide, tungsten mostly A bit deletion type of layered perovskite tissue, wherein a water molecule is formed directly in contact with the two-dimensional layer structure of tungsten by hydrogen bonding interactions between the layers. Chinese name is pyrochlore type oxide, tungsten foreign names Pyrochlore-type H2W2O7, Formula H2W2O7WO3 • 0.5H2O it for layered composites, sensing field, tungsten oxide calcined preparation.

1988 French Coucou, who first synthesized by soft chemistry type of pyrochlore oxide, tungsten, they (NH4) 10W12O41 • 5H2O as precursor glycol solution is heated in an acidic reflux get [(NH4) 2O] xW2O6, will its repeated washing in acid solution, and the resulting powder is heated to remove water at 100 ℃, which obtained pyrochlore type tungsten oxide powder.

It applies layered composite materials, sensing field, tungsten oxide calcined preparation. Greenstone focus of the present study is not fully oxidized tungsten, still unable to mass production, so many applications yet to be developed.

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Standard curve

A purity of more than 99.9% WO3 into a porcelain crucible, porcelain crucible and then placed in a muffle furnace and calcined at 800℃ 1 hour coolish placed in a desiccator, cool room temperature. Accurately weighed 0.25g tungsten trioxide into 100ml beaker, with 20% NaOH20ml, heating completely dissolved, after cooling into 250ml volumetric flask, dilute to the mark and shake, this solution was transferred to a plastic bottle dry spare.
Standard curve: accurate absorption 1.00mg / ml solution 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0ml Guarantee 100ml flask were placed with 0.85N ~ NaOH complement to 10ml, plus 50 percent potassium thiocyanate 5ml, plus 1: 1HCL50ml, plus 1% TiCl32ml, diluted with water to the mark and shake for 10 minutes, measured at 721 spectrophotometer extinction 0.5cm cuvette with a wavelength of 420 nm, as a reagent blank reference, drawing working curve, the measured slope of the curve K.

Solid phase analysis

Weigh a sample in 50ml of 0.200 ~ 0.500g iron crucible, adding sodium peroxide 4g, was stirred with dry round a glass rod, a small piece of filter paper Sassafras net glass rod, the filters were put in a crucible, in addition to the low temperature furnace H2O , add a muffle furnace at a temperature of 700 ~ 750 ℃ ​​burn for about 10 minutes until pink, remove coolish, leaching into the 250ml beaker containing 100ml of hot water, and washed with water crucible, cooled to room temperature later, into 250ml volumetric flask, dilute to the mark, shake, filtration.Imbibe filtrate G2ml (tungsten oxide content may be) in 100ml volumetric flask, fill 0.85N sodium hydroxide to 10ml, following the same standard curve drawing methods.

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Because tungsten oxide has excellent physical and chemical properties and widespread concern researchers. They have been used to produce the electrochromic windows, infrared switch, write read rub optical devices, detect NO2, H2S, H2, NH3, O3 gas sensing components, as well as humidity and temperature-sensitive components. Meanwhile, tungsten oxide is a very good catalyst and high-temperature superconducting materials. In addition, recent studies have found that the tungsten oxide nanowires have many new properties and uses, such as excellent field emission performance, can be prepared as WS2 nanotube structure precursor.

Back in the 1950s, people began the study of tungsten oxide whisker, originally mixed gas of argon and water vapor in the 1000 ~ 1200 ℃ react with tungsten system. In recent years, there are many literature reports the preparation of one-dimensional nano material of the tungsten oxide methods, such as template method, calcined mesoporous precursor (WO-L) method, the organic solution synthesis method, a high-temperature oxidation method, and an infrared heating oxidation, etc. . In addition, high-temperature reaction of tungsten and SiO2 and WS2 and O2 respectively prepared miniature tree structure containing tungsten oxide nanorods and miniature pine tree containing micron tungsten oxide tubes and fibers. Although one-dimensional tungsten oxide nanomaterials prepared a lot, but there are generally complex process, small yield and other shortcomings. Therefore, it is necessary to further explore new and practical method of preparation.

By W powder and Ni (NO3) 2 • 6H2O in molybdenum reaction kit package prepared pompon micron scale structure of tungsten oxide. Velvet globular structure by a few hundred microns in length, an outer diameter of the tube 1 ~ 10μm micron and sub-micron diameter 100500nm fibers. X-ray diffraction and transmission electron microscopy analyzes showed that: the product is a good crystal structure along the [010] W18O49 growth direction of the monoclinic structure. These pompon structure of tungsten oxide by Vapor-Solid (VS) growth mechanism of formation because it has a huge surface area, has great prospects in terms of micro-sensitive semiconductor components.

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