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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1. The chemical etchant of tungsten contacts, tungsten copper contacts, silver tungsten contacts, tungsten, nickel and copper contacts, silver-nickel contacts and others is: 50ml of ammonia or 10-30ml of hydrogen peroxide solution (30%). Highlights of use: wipe the surface of the contact material with a freshly prepared solution over 10 seconds.

2. The chemical etchant of tungsten, tungsten carbide or nickel granule in silver tungsten contacts, silver tungsten carbide contacts, copper tungsten contacts, silver-nickel contacts is: potassium ferricyanide mixture, in which,
A. K₃[Fe(CN)₆]     10g         water     90ml
B. NaOH(KOH)    10g         water     90ml
Highlights of use: A and B are mixed and wipe over the surface of the contact material.

3. The chemical etchant of tungsten granule in silver tungsten contacts and copper tungsten contacts is: potassium ferricyanide mixture, hydrochloric acid solution, in which,
A. K₃[Fe(CN)₆]     30g    Water 70ml
B. NaOH(KOH)    10g    Water 90ml
Highlights of use: A and B are mixed and wipe over the surface of the contact material.

4. The chemical etchant of pure copper, copper alloy is: ferric chloride, hydrochloric acid solution, in which,
Ferric chloride                    5g
Hydrochloric acid (concentrated)     50ml
Water                           50ml
Highlights of use: wipe method.

5. The chemical etchant of pure silver, copper graphite is: ferric chloride solution, in which,
Ferric chloride                    10g
Water                           50ml
Highlights of use: wipe method.



 

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The metallographic inspection processes of tungsten contacts:

1. Sampling
This step is necessary to consider the characteristics and processing aspects of tungsten contacts material, and then select the location and test surface of the appropriate and representative sampling.

2. Inlaying
If the shape of the contacts material is irregular or size is not big enough, then you need to insert or holder for easy operation.

3. Coarse grinding
The purpose: to make contacts sample flat and approximately ground to a suitable shape. If it is general steel material, then you need to coarse grinding on the grinder kibble, if it is only relatively soft material, then you can use a file to polish specimens.

4. Finish grinding
The purpose: To eliminate the deep scratches of the contacts material left by coarse grinding, and make it ready for polishing. General material grinding methods can be divided into mechanical grinding and manual grinding.

5. Polishing
The purpose: This is to remove the fine cracks left by finish grinding and to make its surface as bright as a mirror, and no trace. Polishing generally is divided into chemical polishing, electrolytic polishing and mechanical polishing, among which the most commonly used is mechanical polishing.

6. Corroding
You must first carry out corroding process of contacts material so that polishing contacts can be observed under a microscope. Metallographic corroding methods include electrolysis corrosion, chemical corrosion and constant potential corrosion, among which the most commonly used, is chemical corrosion.



 

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The other defect types of tungsten contacts can be shown as follows:

6. The squeezing crack
This is because tungsten contacts have been existed or gathered porous holes before extrusion, which resulting in the formation of cracks under pressure during the extrusion process.

7. The silver belt or strap
In silver tungsten contacts or copper tungsten contacts, because during the pre-sintering process, there are cracks in porous skeleton, and silver or copper will penetrate along the cracks at the time of infiltration sintering, thereby forming a silver belt or strap.

8. The purity of tungsten contacts material
9. The particle size and morphology of tungsten powder

10. The production process for each procedure, etc.
Therefore, in the analysis of the defect types of tungsten contacts material, it should be combined with a variety of factors to determine the causes and resolve them, in order to obtain a good quality of contacts.



 

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you hit your own double after you have become a killer you do kill yourself! Each time a kill occurs, one life is erased from that player's tallies. Once the player has no lives left that player is out of the game. Play continues until the only one player has any life left.

Variations of this game can be played to adjust to the players' level. You could use all triples for stronger players or require a double bull to become a killer. For weaker players, use the thin inner wedge of the number. On occasion, I have had several average players and one "I never picked up a dart before" kind of person. So what I do is set that the "new player" only has to hit the thin or thick single wedge to become a killer or kill while the rest of us have to hit doubles. With all the combinations available it's easy to balance the play to be fun for everyone.

Strategy: There really isn't much strategy to this game but I can offer a couple of tips. First, try not to hit a number right next to some one else. If you do, you will get accidental kills from people who were trying to kill the other player. Also players will tend to aim at that spot with the thought that there is more chance to kill someone if they don't yet have a favorite enemy yet.

Another tip is to try to stay neutral and to kill people evenly. If you blast someone, while ignoring other players it will be remembered for several games and that player will be out to get you.

Often the players try to take out the stronger players who have a better chance of killing them than the weaker players. This can often lead to the worst player wining the game because when the smoke clears, the stronger player will probably only has one life left. The weaker player, on the other hand, probably has all three lives left because that player was left alone. The weaker player now only has to hit one dart to win the game.

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Killers: Killers is a really fun game designed to be played with 3 or more people. The more people playing the more fun it is. It is a great game to play when there are an odd number of people and everyone wants to play tungsten darts.

The Object: To win killers you must simply be the last person on the scoreboard with a life left.

The Scoring: The names are place down the left side of the score board in any order. Generally, after the first game is played, the player who was knocked out first gets to throw first in the next game. For the first game, people usually do a closest to the bullseye with one dart each. Next to each name, three tally marks are placed to indicate the number of lives each player has left.

The Play: Play begins with each player, in order, throwing one tungsten dart left-handed (or right-handed if that player is a lefty). This is to set a random number and that number will be the players number for the rest of the game. Whatever number is hit is written next to that players name. No two players may have the same number, so if a player hits a number that was already taken that player should throw again.

The next step in the game is to become a "killer". You become a killer by hitting the double (the thin outer ring) of your number once. When you hit a double of your number, write a "K" next to your name to show that you are a killer. Note: if you hit a double with your left-handed throw, you automatically become a killer, provided no one else already had that number.

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A tungsten linear accelerator is a highly specialized machine in which a high frequency (alternating) electric field is used to accelerate electrons, producing high energy X-rays (photons) and electrons.

In operation, an electron gun with a tungsten filament produces electrons, which rides on microwaves down an accelerating waveguide at nearly the speed of light (186,000 miles per second). A powerful bending magnet is used to select the appropriate electron energy (measured in millions of electron volts (MeV)) and send these electrons to impact on a thin tungsten target producing photons (deeply penetrating X-rays). With a flip of a switch, the electrons may bypass the tungsten target and hit a scattering foil to generate a beam of electrons used for non-penetrating or superficial treatments, such as in the treatment of skin cancer. On the way to the patient, the chosen type of radiation beam is made flat and symmetric by using a flattening filter with quadrant monitor chambers. The dose is monitored using ionization chambers, and the beam is constrained and shaped using the 120 tungsten leaf multi-leaf collimator, to cover only the projected target area. These beam modifications correlate with the therapy plan, which produced by treatment planning computer to give the proper sculpted radiation dose to the tumor.

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