Current Effect on the Welding Force and Welding Strength of Silver Tungsten Contacts
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- Category: Tungsten Information
- Published on Tuesday, 14 July 2015 15:29
- Written by Yahong
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If you energize silver tungsten contacts for a short time, on one hand, the temperature of its contact surface will be a sharp rise, on the other hand, it would make silver tungsten contacts short-arc because the current lines near the beam area is curved. The above two conditions will make the silver tungsten contacts melt, that is to say, it would lead to silver tungsten contacts welding. If the current through silver tungsten contacts is close to the critical value of welding current, silver tungsten contacts will be welded to some extent. The material of silver tungsten contacts and its surface state will directly affect the welding resistance properties of silver tungsten contacts. You can reinforce silver tungsten contacts’ welding in case of: there are surface film layers and uneven energized treatment.
Silver tungsten contacts materials have high welding force and welding strength. Silver tungsten contacts’ initial welding current is about 1000A, when the current is 0.9 peaks current, its maximum welding force is around 165N; when the current is 4600A, silver tungsten contacts have the largest welding strength of about 750Pa.
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Macro Grain Ammonium Paratungstate formation conditions(Ⅱ)
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- Category: Tungsten Information
- Published on Tuesday, 14 July 2015 14:37
- Written by Cristina
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2. Adding seed crystal and （NH4）2WO4 solution.
During the first nucleary, adding seed crystal will obtain ammonium paratungstate which has largest Fsss grain size and apparent density. Adding complete seed crystal will obtain ideal even ammonium paratungstate. After the nucleary of ammonium paratungstate, adding （NH4）2WO4 solution increase Fsss grain size and apparent density of ammonium paratungstate without changing distrubition of grain size. If the adding speed increases, micro ammonium paratungstate will be formed.
3.Mixture.
Increase the mixture speed, crystal formation rate is controlled by surface reaction instead of distribution. Ammonium paratungstate grain size varies in different mixture speed.
|
Speed |
Grain Size um |
|||||
|
rad/s |
<45 |
45-80 |
80-98 |
98-125 |
125-180 |
>180 |
|
0π |
53.5 |
21.0 |
9.0 |
8.8 |
7.5 |
0.2 |
|
2π |
12.4 |
33.1 |
32.2 |
18.3 |
4.0 |
0 |
|
3π |
36.8 |
50.5 |
7.3 |
4.4 |
1.0 |
0 |
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Tungsten Borides
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- Category: Tungsten Information
- Published on Monday, 13 July 2015 18:13
- Written by xiaoshan
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Tungsten borides are compounds of tungsten and boron, and their most remarkable preoperty is high hardness. The Vickers hardness of tungsten borides or tungsten diboride is about 20GPa, and that of WB4 is about 30 GPa for loads exceeding 3 N. δ-WB and WB2 crystals have metallic resistivities of 0.1 and 0.3 mΩ·cm, respectively. The oxidation of W2B, WB and WB2 is significant at temperatures above 600 °C. The final oxidation products contain WO3 and probably amorphous B2O3 or H3BO3. The melting temnperatures of W2B, WB and WB2 are 2670, 2655 and 2365 °C, respectively.
WB2 has the same hexagonal structure as most diborides such as AlB2, MgB2 and it has several forms, α (tetragobal), β (orthorombic) and δ (tetragonal).
There are the ways for synthesis the tungsten borides. Single crystals of WB2−x, x=0.07–0.17 (about 1 cm diameter, 6 cm length) were produced by the floating zone method, and WB4 crystals can be grown by arc-melting a mixture of elemental tungsten and boron.
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Macro Grain Ammonium Paratungstate formation conditions(Ⅰ)
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- Category: Tungsten Information
- Published on Tuesday, 14 July 2015 14:35
- Written by Cristina
- Hits: 342
Grain size of ammonium paratungstate affects the grain size of tungsten powder. Macro grain ammonium paratungstate has large apparent density and flow ability which promote the property and quality of tungsten powder. Marketing demand for macron ammonium paratungstate enlarges year by year. Macro grain ammonium paratungstate formation conditions include the influence of temperature, adding seed crystal and （NH4）2WO4, the influence of mixture.
1.Temperature. Rapid heating up and reduce the degree of super saturation before boiling up. It will not only improve producing efficiency, also reduce the production rate of metatungstate radical A （HW6O215-）and the conversion rate of metatungstate radical A to metatungstate radical B（H2W12O4210-）.
Medium temperature nucleary. Reduce the formation of crystal nucleus. During nucleary of ammonium paratungstate, raise temperature in a certain degree will make the crystal grain size smaller.
Formation under high temperature. Reduce the rate of second nucleary. After the first nucleary, the distribution of ammonium paratungstate grain size depends on the second nucleary. After the first nucleary, heating up rapidly, reduce mixing time, thus reduce the second nucleary and crystal broken degree.
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Tungsten Silicide Application
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- Category: Tungsten Information
- Published on Monday, 13 July 2015 18:12
- Written by xiaoshan
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On one hand, tungsten silicide is used in microelectronics as a contact material, with resistively 60-80μΩcm and it is often used as a shunt over polysilicom lines to increase their conductivity and increase signal speed. On the other hand, tungsten silicide also finds use in microelectromechanical systems and for oxidation-resistant coatings. Besides, tungsten silicide layer can replace tungsten films which are made by chemical vapor deposition. What’s more tungsten silicide is also used as a barrier layer between silicon and other metals such as tungsten.
Tungsten silicide layers can be prepared by chemical vapor deposition, besides films of tungsten silicade can be plasma-etched using for example nitrogen trifluoride. There is producing process as follow:
1.Using monosilane or dichlorosilane with tungsten hexafluoride as source gases.
2.The deposited film is non-stoichiometric and require annealing to convert to more conductive stoichiometric form.
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