Microwave Oven Magnetron Thorium Tungsten Wire Carbonization Secret

In order to improve the stability of magnetron launch, carbonization of magnetron made of thorium tungsten wire is required.

Carbonization is a fixed and assembled magnetron that is placed in the vapor of the hydrocarbon, heated to 2200-2500°C, and when the hydrocarbon vapor is exposed to the tungsten at high temperature, the carbon and hydrogen are decomposed. The carbon is attached to the surface of the thorium tungsten wire and forms tungsten carbide with tungsten and diffuses into the tungsten. Because the binding force of thorium atom and tungsten carbide is larger than tungsten, the thorium tungsten wire of carbonized tungsten reduces thorium to thorium atom at working temperature, thus forming a stable single atomic cover layer on the surface of thorium tungsten wire, making it produce stable electron emission.

In order to prolong the service life of magnetron, thorium tungsten wire used for winding magnetron of microwave oven and its manufacturing method are as follows:

Thorium oxide 0.5-1.5%, potassium 0.0020-0.0080%, tungsten 97%-98%.

(1) After drying the thorium nitrate solution, potassium nitrate solution, aluminum silicate solution and blue tungsten powder in the doping pot, the thorium tungsten powder containing trace potassium is reduced to the reduction furnace. The reduction process is reduced by five stages of temperature control. The temperature of the five section is 550°C, 650°C, 750°C, 850°C and 950°C respectively. They are all 60-80min, and the loading capacity is 300-350g/ boat. The reduction atmosphere is hydrogen, and the hydrogen flow rate is 3-5m3/h.

(2) The thorium tungsten powder is put into ball milling tank containing polyurethane lining, and high energy ball milling for 3-5h. The ball milling medium is tungsten ball.

(3) By using isostatic pressing and pressing force is 145-250MPa, the thorium tungsten bar with single weight between 1.5kg-2.5kg is obtained.

(4) Using direct electrified vertical melting sintering, the sintering process is increased from 0A to 900A after 2 minutes, after 18 minutes current rises to 3100A-3500A, then after 20 minutes current rises to 4000A-4500A, and the vertical melt strip with density of 17.5-18g/cm3 is obtained.

(5) A rotary forging machine is used to process the vertical melt strip from about 17mm to 3.3mm in diameter. During this process, the vertical melting strip is annealed at 9mm and 5mm respectively. The annealing temperature is between 2000-2300°C. The annealing speed is 0.5-2m/min.

(6) The doped thorium tungsten strip is swaged into 3.3mm to wire drawing machine, and the sequence is 2.8-2.4 -2.0 -1.52 -1.24 -1.08- 0.93- 0.77 -0.7- 0.63 -0.57- 0.51mm, and the 0.51mm doped thorium tungsten black wire is obtained.

(7) The black wire with diameter of 0.51mm was polished to 0.50mm by electropolishing, and thorium tungsten wire used for winding magnetron of microwave oven was obtained.

In practical application, in order to improve the properties of thorium tungsten wire, a small amount of noble metal rhenium can be added to the first step, and the thorium tungsten rhenium wire is made with the amount of 0.3-0.5%. The grain is not easy to grow after high temperature carbonization with the magnetron coil of the thorium tungsten rhenium wire around the microwave oven. It can guarantee the stability of the structure and guarantee the package after the production is finished. Loading, delivery and other transportation processes will not cause brittle fracture due to vibration. 

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