In recent years, researchers have found that a series of tungstate having a light responsive photocatalysts, such as bismuth tungstate, zinc tungstate and silver tungstate. These tungstate semiconductor photocatalysts facilitate removal and degradation of organic pollutants and decomposition water. In addition normal particle tungstate compared to nano particle tungstate has unique crystal structure and surface properties which conducive to catalyst activity and improved selectivity.
The following will introduce the producing process of nano zinc tungstate:
1. Adding mixed surfactant solution which include 0.1452g (0.5mmol) zinc nitrate and 1g PVP or SDBS into 40ml deionized water and stirring.
2. Putting 0.165g (0.5mmol) sodium tungstate into above solution with stirring for 30 minutes to ensure that all reagents can be uniformly dispersed.
3. The mixture was added to 50ml Teflon autoclave, adding deionized water until 80% of the the autoclave total volume. And then sealed autoclave and heated to 180 ℃. Besides, maintain this temperature for up to 24 hours, then naturally cooled to room temperature.
4.The white precipitate was collected and washed with deionized water several times and anhydrous ethanol. And then the samples were baked at 60 ℃ in vacuum for 6 hours.

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Defect types of tungsten points described as below:

1. Pores, porous holes
The relatively large gas content of tungsten powder;
When mixing powder the pressure applied is insufficient;
When sintering the porous tungsten skeleton the infiltration is not sufficient;
Due to the uneven particle size of tungsten powder, this is a common defect type for preparing tungsten points in powder metallurgy.

2. Uneven distributed organization
The existence of added element makes the added element or poor oxide aggregated in crystals boundaries.

3. Inclusions
The existence of inclusions in tungsten points may because non-metallic inclusions are mixing in tungsten points or other foreign metal inclusions are mixing with them under normal conditions.

4. Bubbling
Because tungsten ingot itself has small holes, and the inner oxide will appear when pressing, so crushed holes will expand foe forming bubbles.

5. Delaminating cracks
Because there are micro cracks gathering in tungsten ingot itself, and the stress during the oxidation process will make the cracks delaminating.



 

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This topic focuses on nano-CaWO₄ by hydro-thermal synthesis through taking the citric acid as capping agent.The TEM and XRD results indicate the most superior conditions to attain the product is: pH is 7,the amount of surfactant used is 1∶4,the final appearance of product is rod,which is remarkably influenced by the amount of surfactant used.When the certain amuont of rare earth ion adding to the sample,it will not change the structure and the appearance of nano-CaWO4,when the amount of Ce³⁺ is 2% and Eu³⁺ is 4%,it will improve the fluorescence performance.

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The other defect types of tungsten points can be described as follows:

6. The squeezing cracks
There are porous holes existing or gathering in tungsten points before extrusion. And that would lead to, during the extrusion process, the formation of cracks under pressure.

7. The silver belt or strap
During pre-sintering process, there are cracks in porous skeleton of silver tungsten points or copper tungsten points, so when in infiltration sintering silver or copper will penetrate along the cracks, therefore, form the silver belt or strap.

8. Tungsten points’ purity
9. Tungsten powder’s particle size and morphology

10. Each procedure during production process and so on.
So, when analyzing the defect types of tungsten points, you should take a variety of factors into account to find out the reasons and deal with them to get tungsten points with good quality.



 

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Zinc tungstate is often used in Ge-doped decoloration technology, zinc tungsten single crystal Ge-doped decoloration technology belonging tungstate crystal production series areas. This technology generally doping Sb2O3 or Bi2O3 or silver as the toner, but the common deficiency is not drawn out of the large size of colorless crystals.
After the studies found, using GeO2 as doped material, when the weight ratio of ZnO:WO3:GeO2 is 1:1-X:X, X between 0.05% to 0.1%, the pulling rate in 1 ~ 3mm/h, rotation rate at 20 ~ 30 rev/min, the cooling rate of after growth at 150~200 ℃/ h can be achieved large ZnWO4 colorless crystals. Besides light-emitting properties slightly better than the ZnWO4, energy resolution up to about 12.9%.
And when preparing zinc tungstate crystal use Nb2O5 as doped material, the total weight ratio of between it and ZnWO4 is 2 × 10 ~ 1 × 10, the pulling rate at 3 ~ 6mm/h, rotation rate at 20~30 rev/min, the cooling rate after growth at 40~60 ℃/h, to obtain a colorless crystal large zinc tungsten, but the light-emitting properties is no different with zinc tungsten, the energy resolution up to 13 % to 14%.

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Are you thinking about setting up a dart board in one of your rooms? If so, then there are a lot different considerations that you need to make like the Dart Board Height and the Dartboard Distance before start with your dartboard setup. There are some specific things that you can do to make sure that your dart board is placed in a location that is safe and fun for you to play darts. Here are a few tips that may help you in placing your dart board in the correct location.

It's important that you think very carefully about where you are going to place your dart board. You need to carefully consider a location where the dart board can be positioned flat against the wall. You also want to make sure that the dart board has enough space around it so that an aimless dart does not damage anything surrounding the board that might be expensive and that the wall is high enough to reach the correct Dart Board Height. You also want to make sure that there are no doorways in the vicinity, because you don't want to accidentally hit someone who happens to be walking through the door. So, you need to make sure that your dartboard setup is in a low traffic area so that you do not hurt someone.

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Zinc tungstate is a white powder, also known as tungsten zinc oxide, which is stable at normal temperature and pressure. Its chemical formula is ZnWO4 and molecular weight is 313.23. In addition, it has a certain irritation, so when during the operation the worker should to take some certain protective measures, such as protective glasses, gloves and protective clothing. Zinc tungstate, usually is not harmful to water, but if there is no permission of relevant government departments, it can not be discharged into the surrounding environment. There are some related systems numbers of ZnWO4 which are as following: CAS registry number: 13597-56-3, EINECS number: 297-053-6. Besides it should be sealed and stored at somewhere has room temperaturecool dry and ventilated, but avoid light, fire and high temperatures.
Zinc tungstate is often used in Ge-doped decoloration technology, zinc tungsten single crystal Ge-doped decoloration technology belonging tungstate crystal production series areas. This technology generally doping Sb2O3 or Bi2O3 or silver as the toner, but the common deficiency is not drawn out of the large size of colorless crystals.

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The high density, transparency, and chemical inertness of calcium and cadmium tungstates, together with their reasonable luminescent efficiencies when stimulated with high energy radiation, strongly suggest their use as phosphors in scintillation counters for gamma-ray detection. Some of the properties of these crystals are reported and compared with anthracene. It is shown that with proper design, the total anode current produced by a given source is several times greater with the tungstates than with anthracene, although the latter has a more favorable pulse size distribution. Cadmium tungstate has a zero temperature coefficient of luminescence up to 40°C and shows no afterglow after exposure to intense radiation.

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A theory is developed for the coupled substitution e.g., of Nd³⁺ and Na⁺ in Ca²⁺ sites in the scheelite (CaWO₄) lattice. Allowance is made for Schottky defect formation.

The results fit the CaWO₄: Nd system up to 2 % Nd, the CaWO₄: Nd: Na system up to 15 % Na and 5 % Nd, and the CaWO₄: Nd: K system up to 8 % K and 2% Nd.

Equilibrium constants resulting from the theory give the vacancy concentrations in O and Ca sites as 0.054 % each and the free energy of formation of a pair of vacancies as 55 kcal or 2.4 eV, all in pure CaWO₄ in air at the melting point.

Energies are also obtained for the various other substitution arrangements. For exactly balanced substitution of one Na⁺ for each Nd³⁺ in the crystal, it is necessary to use 4.05 Na for each Nd in the melt. This also results in the minimum number of vacancies in the crystal.

 

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Shear of metallographic specimen of tungsten contacts materials can not be arbitrarily taken, it should be in accordance with the relevant technical standards required for the implementation of the materials, such as, specimen site, amounts, data and other factors should represent the interior of the materials properties and its internal aspects of its biggest change since shearing representative and appropriate contacts materials specimen is an important step of metallurgical analysis, if you ignore the importance of this step, the test results will affect the reliability of contacts material and accuracy. Furthermore, the specimen site, direction and other factors with different research purposes should also be different.

Because the surface of the tungsten contacts materials will attach to a layer of metal or unevenly distributed layer component segregation area due to the properties of the production process, so contacts materials specimen site is:

1. Ingots. At the end of the ingots, the shear of ingots should a cross-section which is perpendicular to the die wall;
2. Wire (line) or strip. The Shear of longitudinal section and cross-section at its two ends is needed;
3. Sheet or plate. Shearing its cross-section is needed.



 

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