Formation of Heterotypic Substitutional Solid Solutions (NH4)10–xKx[H2W12O42] · n H2O in the Ammonium Paratungstate ‘Z'/Potassium Paratungstate ‘Z' System

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Category: Tungsten Information
Published on Tuesday, 08 December 2015 10:31
Written by xinyi
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The synthesis of four solid solutions (NH4)10–xKx[H2W12O42] · n H2O (x/n: 6.9/9.7, 5.9/9.5, 3.3/8.5, and 2.6/9.0) with the structure of triclinic K10[H2W12O42] · 10 H2O (I) and two solid solutions (x/n: 3.1/4.0, and 2.6/4.0) with the structure of monoclinic (NH4)10[H2W12O42] · 4 H2O (II), was accomplished by a new method from ammoniacal monotungstate solution by adding the appropriate amount of potassium hydroxide and the release of ammonia during evaporative crystallization. The preparation of corresponding single crystals was achieved by slow evaporation of saturated solutions of the corresponding polycrystalline samples according to the method of isothermal evaporation.
 
The study of coordination and space filling behavior of the potassium and ammonium cations, crystal water molecules, and the paratungstate ‘Z' anion revealed that the predominance of the triclinic structure (2.6 ≤ x ≤ 10.0) in the system is effected by the bulkiness of NH4+. The transition area (2.6 ≤ x ≤ 3.1; 4 ≤ n ≤ 8.5) with coexisting triclinic and monoclinic mixed crystals represents the miscibility gap, typical for a heterotypic substitutional solid solution. The ‘resistance' of three specific K+ positions, to be substituted by NH4+, is caused by peculiarities of bond lengths, coordination numbers, and character of coordinated neighbors.
 
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Ammonium Paratungstate Tetrahydrate and Highly Pure Ammonium Paratungstate Tetrahydrate Method Producing

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Category: Tungsten Information
Published on Tuesday, 08 December 2015 10:22
Written by xinyi
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The invention is directed to a method for the production of ammonium paratungstate tetrahydrate by thermal treatment of ammonium paratungstate decahydrate in an aqueous suspension. The ammonium paratungstate tetrahydrate can be produced with high purity and high yield. The production method may furthermore be carried out in a simple and energy-efficient manner.
 
The invention is related to a process for preparing ammonium paratungstate tetrahydrate which comprises converting ammonium paratungstate decahydrate suspended in an aqueous phase into ammonium paratungstate tetrahydrate by heating.
 
In the light of this prior art, it is an object of the present invention to provide an economical process which allows a highly pure ammonium paratungstate tetrahydrate to be prepared in a high product yield in a simple process.
 
A further object of the invention is to provide an ammonium paratungstate tetrahydrate having a very high purity.
 
Example 
100 liters of an ammonium- and tungsten-containing solution containing 3.5 g/l of NH3, 45.2 g/l of W and 50 liters of deionized water were placed in a heatable 200 liter stirred reactor. 200 kg of APT decahydrate were added while stirring. The suspension was subsequently treated at 85° C. for three hours while stirring. The NH3 concentration of the liquid phase was 3.5 g/l at an NH3:W molar ratio of 0.83:1. The pH at room temperature was 6.9. The mass ratio of solid to aqueous solution was 1.14:1. After the treatment, the suspension was filtered, the product was washed with 10 liters of deionized water and finally dried at 100° C. The amount of product was 190 kg. This corresponded to a yield of 98.1%.
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Co-doped Effects on Tungsten Copper Electrode II

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Category: Tungsten Information
Published on Monday, 07 December 2015 16:30
Written by xiaobin
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Adding activate element to promote tungsten dissolution, and of the solid phase sintering and liquid phase diffusion densification during sintering tungsten particles dissolved in the liquid phase precipitation, round and accumulation, to obtain a high density. Its addition can remarkably improve the material properties, reduce the sintering temperature and shortening the sintering time.

However, the addition of these elements will be activated in a certain extent, reduce the thermal conductivity and electrical conductivity of tungsten copper electrode. Therefore, this kind of method is suitable for the occasions, which has lower demands of thermal conductivity and electrical conductivity. The effect of different content of Co on the density of tungsten copper electrode as follow:

tungsten copper electrode















The graph shows that the reaction of tungsten copper electrode density is sensitive to the adding Co element, which increases at the beginning, 14.9g/cm3 rapidly increases to 16.6g/cm3. Afterwards, the content of Co increases constantly, the density of tungsten copper electrode changes a little and has a decreasing trend.

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Co-doped Effects on Tungsten Copper Electrode III

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Category: Tungsten Information
Published on Monday, 07 December 2015 16:37
Written by xiaobin
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Sintering additives, which can dissolve tungsten, can be used for decreasing the porosity of tungsten copper electrode. The most common method is to add active elements, which takes advantage of active elements to dissolve tungsten and improve phase precipitation, round and accumulation, to obtain a high density. It can remarkably improve the properties of tungsten copper, decrease the sintering temperature and shorten the sintering time. The effect of different content of Co element on the hardness of tungsten copper electrode as follow:

tungsten copper electrode















We can learn from the graph that the effect of Co element on the hardness of tungsten copper electrode is similar to the density of tungsten copper electrode, which remarkably increases at the beginning and tends to stabilization or decrease. When the content of cobalt is about 0.3%, the density and hardness of tungsten copper electrode reaches the maximum 16.69g/cm3, and HB311.6.

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http://news.chinatungsten.com/en/tungsten-information/81018-ti-10447 
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Thermal Decomposition of Ammonium Paratungstate Hydrate in Air and Inert Gas Atmospheres

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Category: Tungsten Information
Published on Monday, 07 December 2015 09:50
Written by xinyi
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In this study, the thermal decomposition of ammonium paratungstate hydrate was investigated in dynamic air and inert gas (nitrogen and argon) atmospheres by simultaneous thermo-gravimetric analysis (TGA), differential thermal analysis (DTA) and mass spectroscopy (MS). The intermediate and end products obtained during thermal decomposition of ammonium paratungstate hydrate were characterized by X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR).
 
It was found that the kind of gas was not effective on the thermal decomposition mechanism of ammonium paratungstate hydrate below 665 K. In the first decomposition step, anhydrous ammonium paratungstate was obtained by dehydration. In the second decomposition step, only deammoniation occurred and ammonium hydrogen tungstate was obtained. During the third decomposition step, dehydration, deammoniation and reduction of some tungsten atoms to lower valences were observed. At this stage, first, ammonium hydrogen tungsten oxide bronze and later ammonium tungsten oxide bronze were formed by two serial reactions. In the fourth step which occurs after 665 K, ammonium tungsten oxide bronze formed stoichiometric tungsten oxide in air atmosphere and tungsten suboxide in inert gas atmosphere.
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  4. Co-doped Effects on Tungsten Copper Electrode
 

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