A typical formulation and method of preparation is given for the calcium‐silicate‐tungstate (CST) phosphor. The wave length of the peak fluorescent emission of the tungstate phase is a function of its lead content. From spectral distribution of the emission of a CST phosphor, one can determine the lead content and the luminous efficiency to be expected from the tungstate phase. The effect of calcium fluoride as a batch addition in increasing average particle diameter of CST phosphor is shown.

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With regard to the determination of foreign elements in tungsten, cinchonine has been widely used as a precipitant of tungsten. This paper, however, deals with the flame-photometric determination of calcium in ammonium paratungstate (A. P. T.) by the following isolation procedure of tungsten. A. P. T. is dissolved in a mixture of conc. hydrochloric acid and hydrogen peroxide, and the solution is heated until the decomposition of hydrogen peroxide is completed, and tungsten is precipitated as hydrous tungsten oxide. Methyl alcohol is added to eliminate the adsorption of calcium on the precipitate, and to decrease the solubility of the precipitate, then the precipitate is filtered off, and calcium is analyzed flame-photometrically.

 

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The metallographic testing steps of tungsten points:

1. Sample
Select the tungsten points’ material required for metallographic testing to determine the location and cut mode.

It is necessary to take the properties and processing aspects of tungsten points’ material into account, and then select representative sampling.

2. Inlay

If points’ materials have irregular shape or too small size, insert or holders for easy operation are needed.

3. Coarse and finish grind

(1) Coarse grind
The objective: flat points sample and grind to a suitable shape approximately. It should be coarse grinded on the grinder kibble when general steel material are needed, a file is needed if it is only soft material.

(2) Finish grind

The objective: eliminating deep cracks of the points’ material left by coarse grind, and make it ready for polish. In general, material grind methods can be divided, manual grind and mechanical grind.

4. Polish

The objective: removing fine cracks left by finish grind and to make its surface as bright as a mirror without trace. Generally polish is divided, electrolytic polish, chemical polish and mechanical polish, and mechanical polish is the most commonly used.

5. Corrosion

Corrosion process of points’ material is needed to polish points, so it is observed under a microscope. Metallographic corrosion methods contain chemical corrosion, electrolysis corrosion and constant potential corrosion, and chemical corrosion is the most commonly used.



 

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Bismuth tungstate, as a novel photocatalyst is an efficient, non-toxic, inexpensive material, has wide application prospect in the dielectric, sterilization, photocatalysis. Because it’s microscopic morphology affects the performance quality of the product and effective use in life and industry. And by exploring the controllable factors of material producing can obtain a specific shape, size, surface structure powder material, so as to achieve visible light photocatalytic performance.
Using hydrothermal method producing bismuth tungsten the procedures are as follows:
1. Weigh 2.419g Na2WO4 • 2H2O and 4.851g Bi (NO3) • 5H2O dissolved in 100ml deionized water, adjusting solution‘s PH value by nitric acid and sodium hydroxide.
2. Adding a certain amount of cetyl trimethyl ammonium bromide (CTAB), after stirring for 30 minutes, the solution was placed in a tetrafluoroethylene reaction tank (filling of about 75%), placed in a stainless steel reactor, after sealing the reaction placed in an oven at 180 ℃ for 24 hours.
3. Then cooled to room temperature to give a yellow precipitate. Washed several times with water and ethanol, at 80℃ constant temperature to dried to obtain sample.

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1. The chemical etchants of silver tungsten points, tungsten copper points, tungsten points, silver-nickel points, tungsten, copper and nickel points and other points are:
Ammonia                            50ml
Or hydrogen peroxide solution (30%)      10-30ml.
Use of points as follows: using a freshly prepared solution to wipe the surface of the points about 10 seconds.

2. The chemical etchants of tungsten, nickel or tungsten carbide particles in silver-nickel points, copper tungsten points, silver tungsten points, silver tungsten carbide points are: potassium ferricyanide mixture, among them,
A. NaOH(KOH)    10g         water     90ml
B. K₃[Fe(CN)₆]     10g         water     90ml
Use of points as follows: mixing A and B, and wiping the surface of the points.

3. The chemical etchants of tungsten particles in copper tungsten points and silver tungsten points are: hydrochloric acid solution and potassium ferricyanide mixture, among them,
A. NaOH(KOH)    10g    Water 90ml
B. K₃[Fe(CN)₆]     30g    Water 70ml
Use of points as follows: mixing A and B, and wiping the surface of the points.

4. The chemical etchants of pure copper, copper alloy are: hydrochloric acid solution and ferric chloride, among them,
Ferric chloride                    5g
Water                           50ml
Hydrochloric acid (concentrated)     50ml
Use of points as follows: wiping.

5. The chemical etchants of pure silver, copper graphite are: ferric chloride solution, among them,
Ferric chloride                    10g
Water                           50ml
Use of points as follows: wiping.

 

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Tungstate and other semiconductor materials because it’s unique structure and physico-chemical properties, increasingly people's attention. Tungstate which has a light responsive photocatalysts is: bismuth tungstate, zinc tungstate, and silver tungstate, these tungstate semiconductor photocatalysts facilitate removal and degradation of organic pollutants and decomposition of water.
Wherein the bismuth tungstate as a new photocatalyst, the chemical formula of it is Bi2O12W3 and molecular weight is 1161.4736. There is some related system number of bismuth tungtate as follows: 13595-87-4, EINECS number: 237-033-7. In addition, it is an efficient, non-toxic, inexpensive material, in terms of the dielectric, sterilization and photocatalysis has a wide range applications. Meanwhile bismuth tungstate is kind of narrow gap material which has diverse topography. Thereby controlling its production conditions can produce nano bismuth tungstate with different morphologies and structure, so that effectively improve their physical and chemical properties to improve the catalytic performance and develop the new applications.

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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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