Hafnium sponge

Refining. KroU-process hafnium sponge and electrowon hafnium do not meet the performance requirements for the two principal uses of hafnium metal. Eurther purification is accompHshed by the van Arkel-de Boer, ie, iodide bar, process (18) and by electron beam melting. 

Hafnium carbide can be prepared industrially from hydrided hafnium sponge at 1500—1700°C or from Hf02 at 2000—2200°C by carburization in vacuum in the presence of hydrogen. The resulting carbide contains almost the theoretical quantity of carbon, 6.30 wt % C, of which a maximum of 0.1 wt % is unbound. 

Physical Properties. Hafnium is a hard, heavy, somewhat ductile metal having an appearance slightly darker than that of stainless steel. The color of hafnium sponge metal is a dull powder gray. Physical properties of hafnium are summarized in Table 1. These data are for commercially pure hafnium which may contain from 0.2 to 3% zirconium. Although a number of radioactive isotopes have been artificially produced, naturally occurring hafnium consists of six stable isotopes (Table 2). Hafnium crystallizes in a body-centered cubic system which transforms to a hexagonal close-packed system below 2033 K. 

If hafnium sponge (3.57 g., 0.020 mole) and resublimed sulfur (1.34 g., a slight excess over 0.040 mole) are used in the above procedure in place of zirconium sponge and sulfur, HfS is obtained. 

Sheets, strip, bars Hafnium Sponge Bar and plate... 

Finely divided hafnium is pyrophoric and can ignite spontaneously in air. Care should be taken when machining the metal or when handling hot sponge hafnium. 

Hafnium Carbide. The need of pure zirconium [7440-67-7] for nuclear reactors prompted the large-scale separation of hafnium [7440-58-6] from zirconium. This in turn made sufficient quantities of hafnium dioxide [12055-23-17, Hf02, or Hf metal sponge available for production of HfC for use in cemented carbides (see Hafniumand hafnium compounds). 

The sponge form of titanium, zirconium, or hafnium is preferable in these syntheses because the tendency for explosive reaction is much less than with the powdered metals. More massive forms, such as wire or shot, react too slowly and less completely. Suitable sources are City Chemical Corp., 132 W. 22d St., New York, N.Y. 10011, and Electronic Space Products, Inc., 854 S. Robertson Blvd., Los Angeles, Calif. 90035. 

The most important commercial methods of production of metalhc zirconium and hafnium are based on furnace reduction, either of MCI4 with magnesium or a Na-Mg mixture (the KroU process), yielding a metal sponge, or of metal fluorides with Ca at 2000 °C to give an ingot. The... 

Grade Plate, strip, bars, wire, sponge and briquettes, powder, foil, technical, pure (hafnium free), single crystals. 

Zircon concentrate Zirconium, hafnium-free Sponge... 

Both zirconium and hafnium metal sponges are generally converted to massive metal by arc melting processes. A consumable-electrode type of furnace is usually preferred, to avoid contamination by electrode impurities. The massive metal may have a Brinell hardness as low as 192. At figures below 300, it can be cut, machined, forged, swaged and rolled. 

The route shown in Fig. 9.12 is one which has been operated commercially in the U.K. on a fairly small scale, quite successfully. As in the case of niobium, it is convenient to use the crude ferro alloy as feed to the chlorination stage. The chloride purification stages lead to pure vanadium trichloride, which is reduced with magnesium in a manner similar to that employed for titanium, zirconium or hafnium. Some of the complexities, applicable in the latter processes owing to the volatile nature of the chlorides, are absent with vanadium. The vanadium metal sponge has some properties in common with the other metal sponges. 

Hafiiium carbide powder is prepared by the reaction of Hf02 with carbon at 1800-2200°C in hydrogen by the carburization of hafoium sponge by the carburization of hafiiium hydride at 1600-1700°C, or by plasma CVD. Hafnium carbide coatings are deposited by CVD, evaporation or sputtering (see Chs. 14 and 15). 

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