Compared to the traditional preparing method, tungsten powder prepared by ammonium paratungstate hydrogen reduction has higher property and green strength. Tungsten powder prepared by this method has uneven particle size and incompletion of crystal. Because of these characters, tungsten powder has greater shaping property and green strength.

Traditional tungsten powder is formed without binder which has low formability. When the pressing pressure is low, the binding strength of powder is insufficient and it is very fragile. It will crack if the pressure rises and cause hierarchy. However tungsten powder prepared by hydrogen reduction under 300MPa, there is no hierarchy and green strength reaches above 2MPa.

Tungsten powder prepared by ammonium paratungstate hydrogen reduction is of irregular shape, during the pressing process, the corner of powder contacts with corner unlike traditional surface contact with surface. The formability thus increases.



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Changing dynamics of four endogenous hormones in normal and aborted ovules of hazelnut（Corylus heterophylla Fisch）was analyzed during fruit development stage，and following ABA and its synthesis inhibitor sodium tungstate solution spraying treatments were carried out to study the effects of ABA on ovules filling process. The results showed that：（1）Content changing curves of IAA，GA₃ and ZR in normal filled ovules were approximately single peak shaped，and their peak value appeared on 80th，90th and 100th day after blooming，respectively. Compared during the same developing period，content of IAA and GA₃ in aborted ovules were lower than that in filled ovules in most cases，while higher ZR content was found to exist in aborted ovules. Eighty to 110 days after blooming was a key period for rapid growth of hazelnut ovule. During the stage，ABA content in developing ovules was significantly higher than that in abortive one.（2）20.0 and 50.0 mg · L^-1 ABA treatments promoted fresh weight of kernel，shell and nut to different degrees，while sodium tungstate had an opposite effects on the above indexes compared with ABA treatments. The results above indicated that ABA was involved in the regulation process of ovule filling in hazelnut.

Tungsten hexafluoride encountered moist air or hydrolyzed, it will emit toxic and corrosive hydrogen fluoride fumes. This smoke will cause very serious injury of people and polluted the environment. Because it has a severe irritant so when during the work the workers should to do all aspects of protection, such as wearing gas masks, protective glasses, wearing protective clothing, in the end of works the workers should to take a shower. The workers who have long been working in such environment should be regular to attend medical examinations.
If accidentally the tungsten hexafluoride leak, all the stuff should be rapid withdrawal from leaking area to a safe area, not to prohibit access to the contaminated area, emergency personnel wearing self-contained breathing apparatus and chemical protective clothing (to ensure complete segregation). In ensuring the safety of plugging, then slowed tungsten hexafluoride volatile by spraying water, but not to directly spray to leak point. Do not allow water to enter the packaging container, drainage (indoor), or powerful ventilation (outdoor). Leaking containers cannot use, and to remove any residual gas through the technical processing.

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Heavy tungsten oxide has several trade names: methenamine, tungsten powder, tungsten oxide and heavy network potassium. Heavy tungsten chemical oxide formula is (CH2) 6N4, industry hexamethylene tetramine of scientific name. It is a white crystalline powder, has a stimulating effect on the skin, the proportion of 1.27 (25 ℃) was dissolved in water, ethanol and chloroform, insoluble in ether, easily agglomerate with moisture, and it can burning a lot of heat when it burn with fire, the combustion flame is colorless.
Heavy tungsten oxide is mainly used in produce phenolic curing agent, aminoplast catalyst, rubber vulcanization accelerator, anti-shrinking agents in the textile industry, the pharmaceutical industry diuretic, urinary antiseptic, military and the RDX explosives and raw material of agricultural pesticides. Heavy tungsten oxide mixed with caustic soda and phenol can be used as masks for phosgene absorber.

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With the different reaction conditions, tungsten react with bromine can produce different product. Such as bromine and tungsten react at 600 ℃ can generate WBr6. In other conditions, it is possible to generate tungsten pentabromide and [W5Br6] Br4.
Tungsten hexabromide is a blue-black glossy needles, chemical formula: WBr6, it is commonly used in the synthesis of organic compounds of tungsten. During at work works should to wear chemical goggles, gloves and respirators, etc., and pay attention away from fire to avoid explosion or fire to produce toxic fumes.
Synthesis methods of tungsten hexabromide are:
(1) Using boron tribromide reacts with and tungsten hexachloride to obtain tungsten hexabromide. Or using boron tribromide reacts with tungsten metal to obtain it.
(2) tungsten powder with stoichiometric bromine reacts in a vacuum at 500-800 ℃ sealed tube, to obtain tungsten pentabromide and tungsten hexabromide.

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Tungsten hexabromide is a blue-black needles crystal, its physical properties are as follows: chemical formula: WBr6, molecular weight: 663.264, relative density: 6.9, melting point: 309 ℃, boiling point: 327 ℃, soluble in carbon disulfide, diethyl ether , insoluble in cold water, hot water decomposition. Tungsten hexabromide easily hydrolyze into tungstic acid in humid air, and decomposes into pentabromide tungsten and bromine. CAS registry number: 13701-86-5. WBr6 can produce tungsten tetrabromide and tungsten pentabromide by disproportionation reaction. It is commonly used in the synthesis tungsten organic compounds.
Tungsten hexabromide should be sealed in storage container, placed in a cool, ventilated, and dry area which has safeguard procedures and away from fire and heat. Besides tungsten hexabromide should be stored separately with oxidant, avoid mixing storage. Keep away from food, drink and animal feed. At the same time the storage room should be equipped with the appropriate variety and quantity of fire equipment and other suitable material for leakage collect.
If tungsten hexabromide leaked first to remove the source of fire to prevent fire or explosion, and use any method to collect leakage with dry media to collect, prevented entering drains. Using water and detergent clean the floor and all the things which contaminated by tungsten hexabromide.

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Tungsten（V） bromide is the inorganic compound with the formula WBr5 and it also be known as tungsten pentabromide. The compound consists of bioctahedral structure with two bridging bromide ligands.
Tungsten pentabromide is the precursor to another tungsten compounds by reduction reactions. For example, tungsten pentabromide can be prepared by reduction with aluminum or tungsten. The WBr4 can be purified by chemical vapor transport. The reaction quotation is: 3 WBr5 + Al → 3 WBr4 + AlBr3. Excess tungsten pentabromide and aluminum tribromide are then by sublimation at 240℃.Tungsten dibromide can then be obtained heating the tetrabromide. At 450-500℃, gaseous tungsten pentabromide is evolved leaving yellow-green residue of WBr2. An analogous method can also be applied to the synthesis of tungsten chloride.
Because it is relatively easy to reduce tungsten pentahalides, they can be used as alternative synthetic routes to tungsten halide adducts. For example reaction of WBr5 with pyridine gives WBr4(py)2. The reaction equation of it is: 2 WBr5 + 7 C5H5N → 2 WBr4(C5H5N)2 + bipyridine + C5H5NHBr.

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Tungsten（V）bromide is a kind of brown-black crystals, easy hygroscopic and it also has another name which is tungsten pentabromide. And it is physical properties is: chemical formula: WBr5, molar mass: 583.39 g/mol, melting point: 286℃, boiling point: 333℃. Besides the CAS registry number is 13470-11-6 and PubChem number is 139467. According to X-ray diffraction, the structure for tungsten pentabromide consists of an edge-shared bioctahedron. What’s more the tungsten bromide consists of bioctahedral structure with two bridging bromide ligands.
Tungsten pentabromide is prepare by treating tungsten powder with bromine in the temperature range 650-1000℃. But the product is often contaminated with tungsten hexabromide.

 

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Results of an extensive investigation of the optical properties of CaWO₄:Sm³⁺are reported. Absorption, fluorescence, and excitation spectra and pulsed fluorescence measurements were obtained at temperatures from below 8 K to room temperature on an undoped single crystal and crystals containing samarium concentrations ranging between 0.01% and 1.0%. An empirical energy-level diagram is determined for trivalent samarium in this host and the existance of several different nonequivalent crystal-field states is established. It is found that host-sensitized energy transfer to the samarium occurs in varying degrees from all four of the lowest excited states of calcium tungstate and the efficiency of transfer is different for different crystal-field sites. The ratios of the integrated fluorescence intensities and decay times were measured and from these the temperature and doping concentration dependences of the energy transfer rate were found for excitation in the different host excited states. A model is proposed to explain the results which is based on energy transfer from self-trapped excitons at low temperatures and thermally activated exciton hopping migration to activator-induced host traps at high temperatures. This model predicts the correct dependences for all of the observed data. Quantitative estimates indicate that exchange is somewhat stronger than dipole-dipole interaction for both migration and transfer and the exciton diffusion coefficient is found to be on the order of 10^-7cm²sec^-1.

 

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Cryogenic processing is referred to a range of below zero heat treatment, which are currently employed by the dozens of materials and components treatment process. Generally, it contains steps to cool the tungsten carbide inserts to the temperatures below -130℃ in order to permanently or semi-permanently alter their microstructures. As in such ways, it could offer tool’s improvement regarded to machining performance, wear resistance and ultimately increased service life.

Cryogenic processing of tungsten carbide inserts commonly involves a use of liquid nitrogen into a thermally insulate tank containing the parts to be treated. The three ways of application of cryogenic fluid include, to perform as a cryo-quench by direct immersion of parts, to cool air within the tank as a working fluid, and to create a dry atmosphere by acting as a gas which circulated by fans.


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