Heavy metal alloys

Heavy-media separation plants, 25 442 feed solids content in, 25 443-445 Heavy melting steel, 22 409 Heavy-metal additives, in PVC, 25 682 Heavy-metal alloy process, of tungsten recycling, 25 357... 

The element-rich solid solubility alloys are of importance in the so-called heavy metal alloys. The tungsten phase formed during liquid-phase sintering is saturated with iron (and nickel) and, vice versa, the nickel-iron binder phase with tungsten. 

In 1935, the first tungsten heavy metal alloys were produced as a material group of growing importance that would continue for the next four decades. 

The so-called heavy metal alloys, based on W-Ni-Fe and W-Ni-Cu-(Fe). They are used wherever high density, excellent mechanical properties, and good workability are required. 

FIGURE 6.13. Optical micrograph of a 95 wt% tungsten heavy metal alloy with 3.2 wt% Ni and 1.8 wt% Cu. By courtesy of Plansee AG, Reutte, Austria. 

TABLE 6.1. Properties of Tlmgsten Heavy Metal Alloys"... 

Standard penetrator material [6.29]. Nevertheless, recent environmental considerations have put a strong emphasis on substituting depleted uranium by heavy metals because of its radioactivity. Efforts to improve the ballistic performance through proper processing and compositional modifications have failed [6.29,6.39]. Recent research has therefore focused on alternative matrix alloys, such as tungsten-hafhium, tungsten-uranium composites [6.29], or heavy metal alloys with a spiculating core of WC [6.41]. 

Densimet Heavy Metal Alloys, company brochure, Metallwerk Plansee, Reutte, Austria (1982). 

Country Total Pressure Die Casting Other Light easting Other Heavy metal alloy easting ... 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

Because of its position in the Periodic Table, molybdenum has sometimes been linked to chromium (see Chromiumand chromium alloys) or to other heavy metals. However, unlike those elements, molybdenum and its compounds have relatively low toxicity, as shown in Table 3. On the other hand, molybdenum has been identified as a micronutrient essential to plant life (11,12) (see Fertilizers), and plays a principal biochemical role in animal health as a constituent of several important enzyme systems (see Mineral nutrients). 

Operating parameters include temperature, pressure, oxygen concentration, and residence time. Materials of constmction include stainless steel, nickel, and titanium alloys (the latter for extremely corrosive wastes containing heavy metals). Vented gases from the process may require scmbbing or other emission controls. 

Although metallic antimony may be handled freely without danger, it is recommended that direct skin contact with antimony and its alloys be avoided. Properly designed exhaust ventilation systems and/or approved respirators are required for operations that create dusts or fumes. As with other heavy metals, orderly housekeeping practice and good personal hygiene are necessary to prevent ingestion of (or exposure to) antimony. 

Toxic heavy metals and ions, eg, Pb, Hg, Bi, Sn, Zn, Cd, Cu, and Fe, may form alloys with catalytic metals (24). Materials such as metallic lead, ziac, and arsenic react irreversibly with precious metals and make the surface unavailable for catalytic reactions. Poisoning by heavy metals ordinarily destroys the activity of a precious-metal catalyst (8). 

The corrosion resistance of aluminum and its alloys tends to be veiy sensitive to trace contamination. Veiy small amounts of metalhc mer-cuiy, heavy-metal ions, or chloride ions can frequently cause rapid failure under conditions which otherwise would be fuUy acceptable. 

Neutral or weak acid-salt solutions usually can be handled in lead plants, with the exception of those few heavy metals that may form lead alloys by substitution. The alums and sulfates generally have little action. 

Most simple inorganic salt solutions cause virtually no attack on aluminium-base alloys, unless they possess the qualities required for pitting corrosion, which have been considered previously, or hydrolyse in solution to give acid or alkaline reactions, as do, for example, aluminium, ferric and zinc chlorides. With salts of heavy metals —notably copper, silver, and gold —the heavy metal deposits on to the aluminium, where it subsequently causes serious bimetallic corrosion. 

Other heavy metal impurities (especially copper and nickel) have similar adverse effects on all generic alloy types. In their case sequestering has not proved successful and control of input quality is used to keep their concentration acceptably low. ... 

The analysis of low-melting alloys such as Wood s metal is greatly simplified by complexometric titration, and tedious gravimetric separations are avoided. The alloy is treated with concentrated nitric acid, evaporated to a small volume, and after dilution the precipitated tin(IV) oxide is filtered off heavy metals adsorbed by the precipitate are removed by washing with a known volume of standard EDTA solution previously made slightly alkaline with aqueous... 

The zone elution method has been used for quantitative estimation or recovery of heavy metals in plants and vegetable juices [29], mercury (11) in river and waste waters [52], zinc in different environmental samples [46], nickel and copper in alloys [53], zirconium in Mg-Al alloys [22], cobalt, zinc, nickel, and copper in natural water and alloy samples [54], thiocyanate in spiked photogenic waste water [55], and aluminum in bauxite ores [42],... 

The Alclad alloys have been developed to overcome this shortcoming. Alclad consists of a pure aluminum layer metallurgically bonded to a core alloy. The corrosion resistance of aluminum and its alloys tends to be very sensitive to trace contamination. Very small amounts of metallic mercury, heavy-metal ions, or chloride ions can frequently cause rapid failure under conditions which otherwise would be fully acceptable. When alloy steels do not give adequate corrosion protection—particularly from sulfidic attack—steel with an aluminized surface coating can be used. 

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