According to Varlamov and co-workers, the synthesis of cyclic nitrones (4) can be carried out using H2O2 and a catalytic amount of sodium tungstate dihydrate, at room temperature, with moderate to high yields, as exemplified for 2-benzazepines (3).


 

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Reference standard of tungsten points in interrupter as follows:

On chemical analysis of tungsten in 1984------ GB / T 4324.1-4324.30

About hardness test------ Metallic Rockwell hardness test method in 1991------ GB / T 230

                                     ------ Metallic Vickers hardness test method in 1984------ GB / T 4340

Interrupter in Magneto test method in 1999------ JB / T 9864.2

Technical condition of tungsten rod in interrupter points according to provisions of JB / T 9860.2 in 1999.

Test methods of rod crystals size of tungsten, sintered tungsten bar, molybdenum and alloys refer to GB / T 4197 regulations in 1984.

Batch inspection sampling procedures and sample forms in 1987 (go for continuous checks of batch products) ------ GB / T 2828

 

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The sodium tungstate dihydrate catalyzed oxidation of secondary amines with hydrogen peroxide gives the corresponding nitrones in methanol or water, at room temperature. Acyclic and cyclic nitrones can be obtained from secondary amines in a single step in good to excellent yields.


 

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The following is working principle of tungsten points in automotive relay:
Automotive relay is considered as being composed of main circuit and the control circuit. Tungsten points work in main circuit and the coil working in control circuit. In the control circuit of relay, only tungsten points can control its on-off, because of the small capacity of tungsten points, working current is low and it can’t be used to control the load with larger power consumption directly.

Applying a certain current/voltage at both ends of electromagnetic relay’s coil, and the coil will generate magnetic flux which will flow through the magnetic circuit whose compositions are core, armature, yoke and working air gap magnetic circuit.

Armature will be attracted to core’s pole face under the influence of magnetic field, therefore, normally closed tungsten points will open and normally open tungsten points will close;

When the voltage/current across the coil under a certain value, the mechanical counterforce is more than electromagnetic attraction, armature will back to its initial state; normally closed tungsten points will connect and normally open tungsten points will disconnect.


 

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Very recently, Leonard and co-workers reported that sodium tungstate dihydrate promotes the oxidation of diamine (1) using 90% hydrogen peroxide in sulfuric acid. Since product (2) is very unstable, the authors propose that these reactions should be done with extreme caution, by knowledgeable researchers.


 

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According to the nature of vanadium dioxide which will cause phase change in about 68 ℃. Relevant researchers found that doping can not only reduce the phase transition temperature of vanadium dioxide, but also VO2 film can effectively reduce the VO2powder phase transition temperature. Therefore, using microwave plasma to produce tungsten vanadium dioxide films with nitrogen daped the phase transition temperature can be reduced to 35 ℃. The producing process of tungsten vanadium dioxide as follows: Using microwave plasma method to restore prepared V1.96W0.04O5 film to V0.98W0.02O2 with well controlling response parameter then doping nitrogen in V0.98W0.02O2. This method can make V1.96W0.04O5 which is stoichiometric ratio restore to different nitrogen content‘s tungsten vanadium dioxide (V0.98W0.02O2-XNY). The reaction parameter setting range is as follows: total pressure 1kPa, reactive power 100-200W, N2 flow rate of 20ml / min, H2 flow rate of 20ml/min, the reaction time is 10-30min. By setting different parameters and process conditions can produce V0.98W0.02O2 film with different amounts of nitrogen-doped. The experiment found that with the nitrogen ions incorporation can effectively reduce the phase transition temperature of tungsten vanadium dioxide film, the minimum can be reduced to 35 ℃.

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Vanadium dioxide (VO2) in the temperature range of 68 ℃ is easy cause phase change, which can limit VO2 application scope. Doping can effectively change the VO2 phase transition temperature, making it can widely use in other fields, so now there are many methods for doped VO2. And experiment found VO2 film can be further reduced VO2 powder’s phase transition temperature. Therefore, using microwave plasma method to produce tungsten vanadium dioxide thin films with doping nitrogen has low transition temperature. Using microwave plasma method to produce tungsten vanadium dioxide film is selecting V2O5 and W2O3 as precursors coated in the glass, then by microwave plasma enhanced synthesis method producing. The V1.96W0.04O5 colloids and producing process as follows:
1. A certain amount of V2O5 powder and W2O3 into the pot, stir, placed in a muffle furnace heated to 900 ℃ melted in an air medium.
2. After 15 minutes heat preservation, quickly putting solution in the certain amount deionized water cooling immediately, with vigorous stirring. Until create V1.96W0.04O5sol with stoichiometric ratio.
3. Using spin coating method, with 75% alcohol and deionized water repeatedly cleaned glass then coating prepared V1.96W0.04O5 sol in the glass.

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The study found that vanadium dioxide will occurs first order phase transition in about 68 ℃, during the phase change process, vanadium dioxide (VO2) can occur reversible mutations  in resistivity, magnetic, optical index, refractive index and transmissivity. Although VO2 is vanadium-titanium oxide of MIT characteristic’s which is the closest to room temperature, but its phase transition temperature higher than room temperature is still greatly hindered the application of VO2. It is possible to use doping method to change the temperature of VO2 to improve VO2 range of applications. Way of doping method has cation and anion doping. At present, there has many ways to doping VO2 such as sol - gel method, hydrothermal synthesis doping method, a sputtering doping method, metal organic chemical vapor deposition method and the microwave plasma method, and so on.
The experiment found that by microwave plasma method to produce VO2 film can reduce the VO2 powder phase temperature, the phase transition temperature can be lowered to 35 ℃. And using microwave plasma method to produce tungsten vanadium dioxide film is selecting V2O5 and W2O3 as precursors coated in the glass, then by microwave plasma enhanced synthesis method producing.

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Tungsten points play an important part in automotive relay. Magnetic system, contact system and restoring mechanism can be regarded as constituting an automotive relay. Tungsten points are applied in contact system; restoring mechanism is consisting of tension spring; magnetic system is composed of the core, the coil and the armature.

Due to relay is an automatic control device, the output will change by leaps and bounds when the input reaches up to a certain value.

Harsh conditions of tungsten points in automotive relay:
Bearing high load power;
Withstanding instable voltage;
Owning nice anti-seismic performance and better impact resistance;
Possessing corrosion resistance, tungsten points can resist the erosion of oil, salt, water, sand, dust, and others;
Temperature range: 40 ℃ ~ 125 ℃ around, if it is in other locations, its temperature range is between -40 ℃and 85 ℃.

 

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People’s demand for tungsten points is increasing sharply with the development of automotive industry. Besides, they have strict processing requirements of tungsten points, whose processing requirements as described below:
High hardness;
Good impact toughness;
Smooth rod surface;
Small thermal expansion coefficient;
Excellent and stable arc-resistant performance;
There are no scratches and cracks in rod;
Section crystals fibers should be short;
With uniform and fine section crystals;
Owning better roundness, concentricity and flatness;
Having lower vapor pressure;
Possessing slower evaporation rate;
In order to satisfy people’s demand for tungsten points, the technicians of manufacturers have done lots of study on tungsten points’ physical and mechanical performance. In the producing process, they analyze the defects of tungsten points comprehensively, such as, splitting, brittle fracture, uniform section crystals size and others. What’s more, they have taken a series of measures to avoid the aforementioned problems.


 

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