Tungsten dioxydibromide formula is WO2Br2, molecular weight of 375.65, which is a purple-brown solid deliquescent prismatic crystals, decomposition hydrolysis at 200 ~ 300 ℃, the system CAS No.: 13520-75-7. Tungsten dioxydibromide is very sensitive to moisture in the atmosphere. It produces a clear and colorless solution in dilute or concentrated sodium hydroxide solution and ammonia solution. Besides there were not reaction when tungsten dioxydibromide react with hot or cold concentrated hydrochloric acid or drying organic solvent there. Producing tungsten dioxydibromide can mixed an amount of certain stoichiometric tungsten powder, tungsten oxide and bromine.
During synthesis tungsten dioxydibromide when use bromine or iodine need to preheat the reactants in order to prevent the tube explosion, because there is a higher pressure of halogen partial. And during the heating period, only put one end which containing a mixture of tungsten powder and tungsten oxide on the stove, making the initial reaction occurs between the powder mixture and halogen, until halogen substance consumption to the end, and generates a high halide and tungsten oxyhalide so far.

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Tungsten tetrabromide is a black needle-like crystals, the formula is WBr4, a molecular weight of 503.5, is the orthogonal fine structure with a lattice constant α = 0.849nm, CAS number: 12045-94-2. It has anti-magnetic properties and easily oxidized. Generating tungsten hexaboride and tungsten dibromide at 450-500 ℃ by disproportionation, and easily be restore by pyridine, acetonitrile and other nitrogen ligand compound to form the corresponding complexes.
Tungsten tetrabromide producing methods shown as follow: (1) reduction pentabromide tungsten by aluminum or tungsten. (2)Generated by tungsten pentabromide disproportionation under at 180 ℃ and vacuum conditions. (3) tungsten cotton in 1000-1500K reacted with 0.7-6.6kPa bromine to form WBr4. (4) at 550 ~ 700K 10kPa when reacted with bromine vapor is also formed WBr4. (5) putting tungsten powder and WBr5 each at the end of vacuum-sealed quartz tube and heated at 630℃ and 340℃for each end. It can also produce tungsten tetrabromide. Chemical reaction equation is as follows: W + 4WBr5 → 5WBr4.

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Bis (cyclopentadienyl) tungsten dichloride is a green crystal, its physical characteristics are as follows: formula: C10H10Cl2W, molecular weight: 384.93, melting point: 250 ℃, system CAS number: 12184-26-8, PubChem number: 24871096. Although bis (cyclopentadienyl) dichloride tungsten at normal temperature and pressure is stable, but to avoid contact with the material oxides, water or air, to store it in dry place and protected from light. C10H10Cl2W have some irritation, in the operation of the job to wear protective clothing, gloves and goggles and other equipment, to avoid danger. If accidentally in contact, rinse immediately with plenty of water and seek medical advice. Bis (cyclopentadienyl) dichloride tungsten for water usually is not harmful, but without governmental permits cannot release the material to the environment. C10H10Cl2W mainly for tungsten organic intermediates producing, it can produce by dihydro-bis (cyclopentadienyl) tungsten and chloroform reacting with to obtained.

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Tungsten dichloride is a pale gray tungsten powder, easy to form octahedral groups. Its physical properties are as follows: formula: WCl2, MW: 254.76, relative density: 5.436 and it can dissolve in hydrochloric acid, ethanol and ether. Tungsten dichloride in the air is unstable, easily oxidized, and decompose occurs at 500 ℃ condition. It may even be oxidaize by water, when react with water it will occur fierce reaction to release hydrogen. Tungsten dichloride can be saved in excess of hydrogen chloride.
Tungsten dichloride producing in two ways: First, can using aluminum restore tungsten hexachloride in sodium tetrachloroaluminate melting to generation, the second is at 400-450 ℃ the tungsten tetrachloride will cause disproportionation reaction to produce tungsten dichloride.
The reaction is reacting at closed vacuum boron silicate glass tube. Putting tungsten tetrachloride into the end of the tube, and heated to 450-500 ℃, and the other end is kept at room temperature. With the reaction proceeds, tungsten pentachloride can condense at the cold end portion of the tube, thereby separating the tungsten dichloride. Reaction equation: 3WCl4 (s) → WCl2 (s) + 2WCl5 (g).

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Temperature-dependent vibrational (Raman and infrared) spectroscopy and X-ray diffraction studies have been performed on polycrystalline Na₂WO₄ṡ2H₂O and Na₂MoO₄ṡ2H₂O crystals. Raman data at low temperature 13-300 K for sodium tungstate Na₂WO₄ṡ2H₂O was compared with the sodium molybdate Na₂MoO₄ṡ2H₂O. The infrared and the X-ray diffraction obtained in the 80-300 K suggest that both crystals have undergone conformational changes connected with an increase in the Raman intensity of NaO₆ modes and the libration modes of water molecules at about 100-120 K. Additionally, Raman spectroscopy measurements of Na₂WO₄ṡ2H₂O under hydrostatic pressure (from 0 to 5 GPa) were performed. The pressure-dependent studies indicate the starting orthorhombic structure is stable in the 0.0-3.2 GPa pressure range, and undergoes a phase transition at about 3.9 GPa, associated with rotation of WO4-2 units.

 

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Diabetes mellitus leads to bone disorders such as osteopenia and osteoporosis that can increase fracture risk. On the other hand, sodium tungstate is an inorganic compound which exerts anti-diabetic activity in experimental studies due to its suggested insulin-mimetic or antioxidant activity. Therefore this study was designed to investigate the effect of tungstate on bone quality in diabetic rat femurs. The rats were divided into four groups: Control (C), tungstate-treated control (C+Tung), diabetes (STZ-D) and tungstate-treated diabetes (STZ-D+Tung). Diabetes mellitus was induced by single injection of streptozotocin (50 mg/kg). The treated rats received 150 mg/kg/day of sodium tungstate for 12 weeks. Sodium tungstate achieved a little (17%) but significant reduction on blood glucose levels, while it didn't recover the reduced body weights of diabetic rats. In addition, impaired bone mechanical quality was reversed, despite the unchanged mineral density. Sodium tungstate administration significantly lowered the 2-thiobarbituric acid reactive substances and restored the activity of tissue antioxidant enzymes such as glutathione peroxidase, catalase and superoxide dismutase in diabetic rats. On the other hand, glutathione levels didn't change in either case. These findings indicate that tungstate can improve the reduced mechanical quality of diabetic rat femurs due probably to reduction of reactive oxygen species and modulation of antioxidant enzymes as well as reduction in blood glucose levels.

 

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Sodium tungstate solution can be prepared by decomposing wolframite with sodium hydroxide. A new technique is developed for precipitating scheelite from the sodium tungstate solution by the addition of calcium hydroxide. In this study, the effects of several variables on the conversion of sodium tungstate are investigated. Results show that the effects of temperature and sodium tungstate concentration are significant. Specifically, 96.4% WO₄^2 − was converted to scheelite in 2 h at 100 °C with a calcium hydroxide stoichiometric ratio of 1.4 and a stirring speed of 350 rpm. The parent solution containing sodium hydroxide can be recycled as a leaching agent return to the wolframite decomposition process.

Highlights

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Synthesis of scheelite from sodium tungstate solution with addition of calcium hydroxide was successfully achieved.

•

Effects of processing parameters on the conversion of sodium tungstate were presented.

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Optimal processing parameters in the process of synthesizing scheelite were selected.
 

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As mentioned in some researches, the cutting edge geometry could affect the deposition stresses around the tool tip in coating process, in addition, during the machining, the thermal and mechanical loads will be complicated and imposed as well. It is also indicated that chip formation and cutting processes could be severely affected by the radius edge, especially there is a size effect, which is referred to the thickness of the uncut chip is close to or smaller than the edge radius.

In general, for the coated tungsten carbide inserts,on which the cutting edge effects include, with the edge radius increasing, there is a noticeable decrease in deposition residual stresses. On the contrast, the increasing of edge radius will bring up the cutting forces and the with different edge radii and  combined effects, the coated tungsten carbide inserts’wear behavior are complicated.


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Below are the main producing processes of ammonium metatungstate:

1.Use ammonium tungstate solution as raw material, solvent extraction and ion exchange method is first prepared by metatungstate solution, then by evaporation and crystallization Get ammonium metatungstate.

2.Use sodium tungstate as raw material. By solvent extraction solution as raw material in AMT solution, followed by evaporation and crystallization to obtain ammonium metatungstate.

3.The heating thermal dissociation of APT, which lost its part ammonium And the water of crystallization, converted to ammonium metatungstate easily soluble in water, then evaporation and crystallization Get ammonium metatungstate.

4.Mixing APT in the water with acid and neutralize to PH3-4 condition. APT transforms into AMT solution, followed by evaporation and crystallization to obtain ammonium metatungstate.

U.S. mostly uses ammonium tungstate solution as raw material, first obtained ammonium metatungstate solution using solvent extraction or ion exchange method. Some European countries use sodium tungstate solution as raw material using solvent extraction. China mainly uses thermal decomposition method that use ammonium paratungstate (APT) as raw material.



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In practical machining application, it has been pointed out that the cutting edge geometry has compound effects on tungsten carbide inserts coating process, and the cutting edge radius affects the deposition stresses and machining loads in an opposite way. Specially, under different cutting condition, the optimal radius maybe varied from one to another since the edge radius effects on machining loads are depended on machining parameters.

In the coating process like CVD processes, the thermal mismatch between the coating and substrate materials are likely to generate high residual stresses in the tool, and for the tungsten carbide insert’substrate, the cobalt cemented tungsten carbide receive a tensile stress, which tends to have  impacts on the coating functions. Moreover, the geometric changes like cutting edges, will severely alter the local stress fields.


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