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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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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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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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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