Th is a radioactive tetravalent metal element, in the form of compounds in mineral (e.g. stone monazite and thorium), usually linked together with the rare earth metal is mainly as the isotope with mass number 232, half-life of 1.39 × 10 10 years, the formation of new particles emitted α thorium 1 [thorium] - element symbols Th, Th external electronic arrangement is 6d27s2, extranuclear arrangement of 2,8,18, 32,18,10,2. Isotopes and radiation with Th-226 [30.6m], Th-227 [18.72d], Th-228 [1.91y], Th-229 [7340y], Th-230 [75400y], Th-231 [1.06d], Th-232 (discharge α [14000000000y]), Th-233 [22.3m], Th-234 [24.1d]. Density 11.7 g / cm 3. Melting point of about 1750 ℃, boiling point of about 4000 ℃. 1400 ℃ the following atoms arranged in a face-centered cubic crystal; when the heating temperature is reached, they changed the body-centered cubic crystal. Silver-white metal, long-term exposure to the atmosphere fade to gray. Relatively soft, malleable. Insoluble in acid and hydrofluoric acid, but soluble in fuming hydrochloric acid, sulfuric acid and aqua regia. Nitric acid to make thorium purification. Caustic it had no effect. High temperature with halogen, sulfur, nitrogen effect. Radioactive half-life of approximately 1.4 × 1010 years. All thorium salts showed +4. Chemically zirconium, hafnium similar.

Thorium tungsten electrode is the earliest use of rare earth tungsten electrodes, welding performance is so far the best varieties of tungsten electrodes, so the species on a global scale tungsten electrodes highest market share, but because thorium tungsten electrode grinding and polishing powder metallurgy and rolling will occur during radioactive contamination, so European countries limit the production of the varieties electrode, but because of its excellent welding performance, its use is not restricted.


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Cerium is a chemical element , its chemical symbol Ce, atomic number 58 , atomic weight 140.115 , belonging to the lanthanide elements, but also one of the rare earth elements . Element name comes from the asteroid Ceres, the English name . 1803 German chemist Klaproth , Swedish chemist Berzelius discovered the cerium oxide , respectively . Cerium has four kinds of natural stable isotopes : cerium 136,138,140,142 . Cerium content in the crust of about 0.0046% , is the most abundant of the rare earth elements . Gray soft metal . In monazite accounted for over 40% of total rare earth . Cerium chemically active , firing in air using Daogua ie , soluble in acid , insoluble in alkali . Cerium is iron gray metallic , malleable , melting point 799 ° C, the boiling point of 3426 ° C, density of 6.657 g / cm ³. Cerium is in addition to the rare earth elements europium outside the most active . Cerium oxide at room temperature, it is easy ; slow decomposition in cold water , hot water reaction speed ; most cerium salt solution as its orange-red to orange-yellow , with a strong anti- magnetic properties and oxidation. Cerium oxide for polishing precision glass products, but also do glass to color agent and used to produce colored glass , cerium nitrate used in the manufacture incandescent hood .

Lanthanum is a chemical element , its chemical symbol is La, its atomic number is 57 , belonging to the lanthanide elements for rare earth metals is the most reactive metal in the air is easily oxidized. Lanthanum quarry alone accounted for 25% of total rare earth . A soft silver-white metal , malleable . With water effect. Soluble in dilute acid . Easily oxidized in air ; heating can burn to form oxides and nitrides. Heated in hydrogen generation hydride . It is the second most abundant rare earth elements , often along with other rare earth elements present in monazite , fluorocarbon lanthanum strontium ore . It is uranium, thorium or plutonium fission of radioactive products . It gives the refractive index of the special properties of the glass , the glass having a higher refractive index . Preparation of lanthanum general dehydration of hydrated lanthanum chloride , the use of calcium metal restore , or anhydrous lanthanum chloride electrolysis and after melting in the system. Used to manufacture an expensive camera lens . 138La is a radioactive half-life of 1.1 × 1011 , the trial was to treat cancer .

Lanthanum tungsten electrode is the European country in the 1980s with the hope for alternative thorium tungsten products, improved varieties, once launched, its excellent welding performance attracted much attention in the international welding industry and is very popular, especially by European Welding School in the pursuit, for this reason, the export volume of lanthanum tungsten electrode tungsten thorium behind , while in the domestic market awareness is not high. Its characteristics are the closest conductive properties of 2% thoriated tungsten electrodes , durable high burning rate of the current minimum .


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Stainless steel electrode melting point of pure tungsten (3650K), the electron emission capability, high modulus , low vapor pressure , the first to be used as an electron -emitting material , but the pure tungsten emission efficiency is low , and at a high temperature to form equiaxed recrystallized shaped grains become brittle and easy to break. To overcome these shortcomings , countries Materials workers dedicated to research and development of new electrode materials , tungsten -based doping several high melting point, low power electronic escape rare earth metal oxides, can improve the recrystallization temperature , and can activate the electron emission . However, in the rare earth tungsten electrodes on the basis of research , despite some achievements , but the current global market, replace the use of tungsten electrodes still a long way .

In our country the 1990s, in order from the system with excellent performance and pollution tungsten electrode, tungsten trioxide powder of lanthanum oxide is added , after reduction , suppression, melt down , swaging , stretching lanthanum tungsten electrode was obtained . After analysis, the lanthanum of the tungsten electrode electrical performance than cerium tungsten and tungsten thorium , lanthanum, tungsten and lanthanum oxide evaporation rate is low migration rate , to form a better lap dovetail microstructure , has good high temperature resistance creep. High-energy ball milling and vacuum hot pressing sintering prepared bulk nanocrystalline tungsten - lanthanum oxide electrode materials, the effects of different lanthanum oxide nanocrystalline tungsten content on the electrical properties of the electrode material , while using scanning electron microscopy and energy dispersive spectrometer measured fuel La arc electrode tip distribution and microstructure . The results showed that: nanocrystalline tungsten - lanthanum oxide electrode was superior to the conventional powder metallurgy coarse-grained tungsten electrodes . When the lanthanum oxide content of 6% to 8% , the thermal electron emission capability and stability of the best , but with increasing the content of rare earth lanthanum oxide , lanthanum tungsten electrode moldability and processability more difficult.


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