A coprecipitation method using calcium tungstate was developed to remove ⁸⁷Sr isobaric interference with ⁸⁷Rb prior to measurement of Rb by ID-ICP-MS. Precipitation of calcium tungstate was obtained by adding Ca(NO₃)₂ solution and (NH₄)₂WO₄ solution to the sample, where (NH₄)₂WO₄ was added more than the stoichiometric proportion to precipitate Ca(NO₃)₂ completely and remove Sr effectively. Furthermore, in order to reduce matrix burden to the ICP-MS instrument, the residual (NH₄)₂WO₄ was removed by adding conc. HNO₃. Prior to the application, thorough purification of coprecipitant reagent was carried out to reduce the blank. The effectiveness of the present method was verified by analyzing two brown rice flour certified reference materials (CRMs), NIES CRM 10a and NIES CRM 10b. Finally, the present method was applied to the measurement of Rb in a white rice flour RM sample being developed by National Institute of  Metrology of Japan.

 

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Silver tungsten contacts to produce electric locomotives regulating switch by infiltration process:

Firstly, batching silver powder, tungsten powder and a small amount of nickel powder, and then mixing;
Then pressing the mixing powder to form porous skeleton;
And then stacking the infiltration silver pieces and the porous skeleton, placing them in the burned tungsten boat;
Finally, conducting infiltration sintering, to make the molten silver completely soaked porous skeleton pores, you can get silver tungsten contacts after letting it cool down. Sintering conditions are: putting them in the furnace of molybdenum wire, under the protection of the atmosphere, the temperature range is above the melting point of silver over 100 ℃.

Infiltration processes to produce electric locomotives regulating switch, using silver tungsten as raw material:

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The main methods of silver tungsten contacts’ preparation are re-pressuring method and infiltration method.

1. Infiltration method. Infiltration method is a common method of producing low melting point metal prosthesis alloy and refractory metal. Firstly, pressing and pre-sintering the metal powder with high melting point to form a porous skeleton, and then you should control the temperature higher than the metal with low melting point, and put the metal with low melting point below or above the porous skeleton, to make the metal melt and fill the pores of the porous skeleton, to obtain silver tungsten contacts with high density.

2. Mechanical alloying. In recent years, mechanical alloying as a new material preparation process is gradually stepping into people's vision, the concept was first proposed in the 1960's, and now, mechanical alloying has gradually been developed and is widely used. Mechanical alloying refers to mixing two kinds or more kinds of elements powder by high-energy ball milling for a long time., in this process, powder will withstand friction, impact, shear and compression and other forces and absorb mechanical energy, that is to say, under the role of milling media, the mixing powder will be combined with each other after repeatedly pressing, welding, crushing and fracture process and through solid state reaction or diffusion, in order to achieve alloying.



 

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The process of silver tungsten contacts produced by infiltration method:

Firstly, pressing the silver blank and tungsten skeleton without silver or porous skeleton with partial-induced silver; then, pre-sintering the porous skeleton at high temperature; after stacking up the two parts together, putting them in a special melt infiltration sintering furnace, and then liquid sintering, the sintering temperature is controlled above the melting point of silver. Silver under the molten state fills the pores of the porous skeleton by capillary action, forming silver tungsten contacts with high density eventually. The main process of silver tungsten contacts are as follows:

Tungsten powder + a small amount of silver, adding additional elements → mixing powder → pretreatment →skeleton molding + pure silver → pre-sintering (temperature > melting point of silver + 100 ℃) → infiltration → cold treatment



 

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