Powder metallurgy techniques

The metal is isolated commercially by a complex chemical process, the final stage of which is the hydrogen reduction of ammonium ruthenium chloride, which yields a powder. The powder is consolidated by powder metallurgy techniques or by argon-arc welding. 

F. H. Froes, "Synthesis of MetaUic Materials For Demanding Applications Using Powder Metallurgy Techniques," P/M in Merospace and Defense Technologies, Metal Powder Industries Federation, Princeton, N.J., 1991. 

Fig. 5. Micrographs of the microstructure of fully hardened and tempered tool steels produced by the powder metallurgy technique, showing uniform distribution and fine carbide particles in the matrix, (a) M-42 (see Table 6) and (b) cobalt-free AlSl T-15 having a higher concentration of fine carbide...

Consolidation. Because of its high melting point, tungsten is usually processed by powder metallurgy techniques (see Powder metallurgy). Small quantities of rod are produced by arc or electron-beam melting. 

The preferred method for synthesis of complex carbides is the powder metallurgy technique. Hot-pressed powder mixtures must be subjected to prolonged annealing treatments. If low melting or volatile components are present, autoclaves are used. 

Consolidation and Fabrication. Chromium metal may be consoHdated by powder metallurgy techniques or by arc melting in an inert atmosphere (8,13,24,25) (see Metallurgy Metallurgy, powder). 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

Finally, it may be pointed out that none of the rare metals can be smelted directly from the ore. The concentrate must first be converted to a pure chemical compound which is utilized as the raw material for the production of the metal. The refractory rare metals are often obtained in the form of a powder or sponge. They are consolidated and refined by powder metallurgy techniques or by arc melting or by electron beam melting. In fact, the current refractory rare metals technology has been crucially dependent on the development of vacuum metallurgical techniques and processes. 

Potassium perrhenate (KRe04) is reduced by hydrogen in two stages. The first operation is carried out at 500 to 550 °C. The reduced product is washed to remove the hydroxide. The powder is then subjected to a second reduction at a higher temperature (900 to 1000 °C). The product is washed, first with dilute hydrochloric acid and then with water, and dried in vacuum or in a current of hydrogen. Solid rhenium is made by powder metallurgy techniques. 

Powder metallurgy techniques, wick formation by, 23 232 Powder pattern, 26 429 Powder pattern structure determination diffractometers in, 26 428 Powder perfumes, 23 364 Powder processing... 

The term cermet derives from the combination of ceramic and melal. Cermets are produced by powder metallurgy techniques and represent Ihe bonding of two or more metals. They are particularly useful at high temperatures (850- I250"C). Chromium is used in several cermet combinations, including chromium-bonded aluminum oxide, metal-bonded chromium carbide, and metal-bonded chromium horide. 

VOIDS. Empty spaces of molecular dimensions occurring between closely packed solid particles, as in powder metallurgy. Their presence permits barriers made by powder metallurgy techniques to act as diffusion membranes for separation of uranium isotopes in the gaseous diffusion process. 

Bismuth-Manganese Alloy, developed at the Naval Ordnance Laboratory, White Oak,Md, is a suitable substitute for permanent magnets Alnico or the expensive Pt-Co alloy. The Bi -Mn alloy can be used in various electronic devices(Ref 3). The Bi-Mn alloy known as "Bismanol , prepd by powder metallurgy techniques, is claimed to possess a coercive force of 3000 oersteds(Ref 5)... 

Powder metallurgy techniques have been used to produce a very wide range of compacts containing molybdenum disulphide in such metals as mixed iron-palladium, iron-platinum , tantalum , iron-tantalum , molybdenum-tantalum , and molybdenum-niobium . The concentration of molybdenum disulphide in these compacts has risen to 90% compared with less than 35% in earlier materials. Composites containing nickel were found to be unsatisfactory because of high friction and wear. 

Occurrence Ontario, South Africa, Siberia. Derivation Occurs with platinum, from which it is recovered during the purification process. Available forms Produced as powder that can be fabricated by casting or powder metallurgy techniques. Single crystals are available. 

Derivation (1) Reduction of thorium dioxide with calcium (2) fused salt electrolysis of the double fluoride ThF4 KF. The product of both processes is thorium powder, fabricated into the metal by powder metallurgy techniques. Hot surface decomposition of the iodide produces crystal bar thorium. 

---