Alloys containing tungsten

Two alloys containing tungsten are commercially available. The first, containing about 3 wt % rhenium, is used for heating filaments. The rhenium contributes improved resistance to thermal and mechanical shock. The second alloy contains about 25 wt % rhenium. This latter alloy is sold as sheet, rod, and heavy wire and may be fabricated for various uses. An important use of these rhenium alloys is in the constmction of thermocouples. Various combinations, 3 wt % Re—97 wt % W, or 25 wt % Re—75 wt % W, are usehil for measurement of temperatures to 2500°C (see Temperaturemeasurement). 

It is alloyed with iron, nickel and other metals to make Alnico, an alloy of unusual magnetic strength with many important uses. Stellite alloys, containing cobalt, chromium, and tungsten, are used for high-speed, heavy-duty, high temperature cutting tools, and for dies. 

Tantalum and 2kconium exhibit the highest corrosion resistance to HCl. However, the corrosion resistance of 2ironium is severely impaHed by the presence of ferric or cupric chlorides. Tantalum—molybdenum alloys containing more than 50% tantalum are reported to have exceUent corrosion resistance (see Molybdenumand molybdenum alloys) (69). Pure molybdenum and tungsten are corrosion resistant in hydrochloric acid at room temperature and also in 10% acid at 100°C but not in boiling 20% acid. 

Iron carbide (3 1), Fe C mol wt 179.56 carbon 6.69 wt % density 7.64 g/cm mp 1650°C is obtained from high carbon iron melts as a dark gray air-sensitive powder by anodic isolation with hydrochloric acid. In the microstmcture of steels, cementite appears in the form of etch-resistant grain borders, needles, or lamellae. Fe C powder cannot be sintered with binder metals to produce cemented carbides because Fe C reacts with the binder phase. The hard components in alloy steels, such as chromium steels, are double carbides of the formulas (Cr,Fe)23Cg, (Fe,Cr)2C3, or (Fe,Cr)3C2, that derive from the binary chromium carbides, and can also contain tungsten or molybdenum. These double carbides are related to Tj-carbides, ternary compounds of the general formula M M C where M = iron metal M = refractory transition metal. 

Samples were tested on in a melt of salts (75% Na SO, 25% NaCl) at 950°C in an air atmosphere for 24 hours. Micro X-rays spectrum by the analysis found that the chemical composition of carbides of an alloy of the ZMI-3C and test alloys differs noticeably. In the monocarbide of phase composition of an alloy of the ZMI-3C there increased concentration of titanium and tungsten is observed in comparison with test alloys containing chemical composition tantalum. The concentration of more than 2% of tantalum in test alloys has allowed mostly to deduce tungsten from a mono carbide phase (MC) into solid solution. Thus resistance of test alloys LCD has been increased essentially, as carbide phase is mostly sensitive aggressive environments influence. The critical value of total molybdenum and tungsten concentration in MC should not exceed 15%. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

Amorphous Fe-3Cr-13P-7C alloys containing 2 at% molybdenum, tungsten or other metallic elements are passivated by anodic polarisation in 1 N HCl at ambient temperature". Chromium addition is also effective in improving the corrosion resistance of amorphous cobalt-metalloid and nickel-metalloid alloys (Fig. 3.67). The combined addition of chromium and molybdenum is further effective. Some amorphous Fe-Cr-Mo-metalloid alloys passivate spontaneously even in 12 N HCl at 60° C. Critical concentrations of chromium and molybdenum necessary for spontaneous passivation of amorphous Fe-Cr-Mo-13P-7C and Fe-Cr-Mo-18C alloys in hydrochloric acids of various concentrations and different temperatures are shown in Fig. 3.68 ... 

This consists of a hollow cathode, constructed from the element to be analyzed or from an alloy containing the element. The anode is a tungsten wire or ring. 

Ferro-alloys Master alloys containing a significant amount of bon and a few elements more or less soluble in molten bon which improve properties of bon and steels. As additives they give bon and steel better characteristics (increased tensile sbength, wear resistance, corrosion resistance, etc.). For master alloy production carbothermic processes are used for large-scale ferro-sihcon, ferro-chromium, ferro-tungsten, ferro-manganese, ferro-nickel and metallothermic processes (mainly alumino and sihco-thermic) for ferro-titanium, ferro-vanadium, ferro-molybdenum, ferro-boron. 

Commercial ferrotungsten is obtained by reducing wolframite, scheelite, ferberite or hybnerite with carbon in an electric furnace. Iron scrap is added in appropriate amounts to form a ferrotungsten alloy containing about 70 to 80% tungsten. 

In ZnCl2-EMIC (1 1) melt containing Cu(I), the electrodeposition of Cu-Zn alloys on tungsten and nickel electrodes was carried out [180]. The composition of the Cu-Zn deposit was changed by deposition potential, temperature, and Cu(I) concentration in a plating bath. 

The same researchers [184] studied electrodeposition of Zn-Sn alloys on tungsten and GC electrodes from ZnCh-EMIC ionic liquid containing Sn(II). The Zn-Sn codeposits consist of two-phase mixtures of Zn and Sn. 

Tungsten alloys with tantalum in all proportions.1 Alloys of tungsten and tantalum which also contain cobalt, chromium or molybdenum have also been prepared.2... 

A certain iron-base alloy contains 5% Cr and 10% W by weight. It is desired to make a new alloy with molybdenum substituting for tungsten on an atom for atom basis. That is, one atom of Mo replaces one atom of W. What wt.% Mo should the alloy contain The following data are available ... 

The pellets are sometimes graphite coated, copper plated, or nickel plated. Plated shot is normally confined to hard or extra hard shot. The alloying metal is usually antimony, and lead pellets typically contain between 0% and 6% antimony, although up to 12% antimony has been encountered. Tungsten-polymer shot is also manufactured and, as the name implies, contains tungsten metal embedded in some sort of thermoplastic. 

Sea-water, dilute hydrochloric or sulphuric acid has very little action on nickel.4 At the temperature of the water-bath, dilute sulphuric acid containing 63 per cent, of acid exerts the maximum action on nickel.6 The resistance of the nickel is greatly enhanced by alloying with tungsten, the optimum percentage being 18 of tungsten. 

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