Hard metal

Among the metals, for example, sodium and potassium are similar to each other and form similar compounds. Copper and iron are also metals having similar chemical properties but these metals are clearly different from sodium and potassium—the latter being soft metals forming mainly colourless compounds, whilst copper and iron are hard metals and form mainly coloured compounds. 

Gr. chroma, color) Discovered in 1797 by Vauquelin, who prepared the metal the next year, chromium is a steel-gray, lustrous, hard metal that takes a high polish. 

Gobalt is a brittle, hard metal, resembling iron and nickel in appearance. It has a metallic permeability of about two thirds that of iron. Gobalt tends to exist as a mixture of two allotropes over a wide temperature range. The transformation is sluggish and accounts in part for the wide variation in reported data on physical properties of cobalt. 

Tantalum is a gray, heavy, and very hard metal. When pure, it is ductile and can be drawn into fine wire, which is used as a filament for evaporating metals such as aluminum. Tantalum is almost completely immune to chemical attack at temperatures below ISOoC, and is attacked only by hydrofluoric acid, acidic solutions containing the fluoride ion, and free sulfur trioxide. Alkalis attack it only slowly. At high temperatures, tantalum becomes much more reactive. The element has a melting point exceeded only by tungsten and rhenium. Tantalum is used to make a variety... 

Hardgrove index Hard lenses Hard metals Hardness... 

The main advantages of ECM are that the rate of metal machining does not depend on the hardness of the material, compHcated shapes can be machined on hard metals, and there is no tool wear. 

Cemented Carbides. Cemented carbides contain mostiy tungsten carbide and lesser amounts of other hard-metal components, embedded in a matrix of cobalt (see Carbides, cemented carbides). 

Niobium carbide is used as a component of hard metals, eg, mixtures of metal carbides that are cemented with cobalt, iron, and nickel. Along with tantalum carbide, niobium carbide is added to impart toughness and shock and erosion resistance. The spiraling rise in the price of tantalum has spurred the development of a hafnium carbide—niobium carbide substitute for tantalum carbide (68). These cemented carbides are used for tool bits, drill bits, shovel teeth, and other wear-resistant components turbine blades and as dies in high pressure apparatus (see Carbides). 

The chemistry of Th(IV) has expanded greatly since the mid-1980s (14,28,29). Being a hard metal ion, Th(IV) has the greatest affinity for hard donors such as N, O, and light haUdes such as F and CF. Coordination complexes that are common for the t7-block elements have been studied for thorium. These complexes exhibit coordination numbers ranging from 4 to 11. 

Dreyer and co-workers. Development andTool Efe Beharior of Super-Wear Resistant Multilcryer Coatings on Hard Metals, Book No. 278, Metals Society (London), 1982, pp. 112-117. 

The diboride has a hexagonal stmcture and melts at 3245°C (136) it is considered to have the best oxidation resistance of all the refractory hard metals. The dodecaboride has a cubic stmcture. 

Table 10. Hard Metals and Superalloys for High Temperature Bearings ...

Cemented carbides belong to a class of hard, wear-resistant, refractory materials ia which the hard carbides of Group 4—6 (IVB—VIB) metals are bound together or cemented by a soft and ductile metal biader, usually cobalt or nickel. Although the term cemented carbide is widely used ia the United States, these materials are better known iatemationally as hard metals (see also Refractories Refractory coatings Refractory fibers). 

The impetus for the synthesis of WC and subsequent development of cemented carbides came from the wire drawing industry where the hard metals are stUl used. The most commonly used grade is WC-6 wt % Co with medium grain size (1—2 p.m). Compositions having higher cobalt content are used in drawing tubes, rods, and bars. 

The four most important carbides for the production of hard metals are tungsten carbide [12070-12-17, WC, titanium carbide [12070-08-5] TiC, tantalum carbide [12070-06-3J, TaC, and niobium carbide [12069-94-2] NbC. The binary and ternary soHd solutions of these carbides such as WC—TiC and WC—TiC—TaC (NbC) are also of great importance. Chromium carbide (3 2) [12012-39-0], molybdenum carbide [12011-97-1], MoC, and... 

Carbides of the Iron Group Metals. The carbides of iron, nickel, cobalt, and manganese have lower melting points, lower hardness, and different stmctures than the hard metallic materials. Nonetheless, these carbides, particularly iron carbide and the double carbides with other transition metals, are of great technical importance as hardening components of alloy steels and cast iron. 

Cobalt compounds can be classified as relatively nontoxic (33). There have been few health problems associated with workplace exposure to cobalt. The primary workplace problems from cobalt exposure are fibrosis, also known as hard metal disease (34,35), asthma, and dermatitis (36). Finely powdered cobalt can cause siUcosis. There is Htfle evidence to suggest that cobalt is a carcinogen in animals and no epidemiological evidence of carcinogenesis in humans. The LD q (rat) for cobalt powder is 1500 mg/kg. The oral LD q (rat) for cobalt(II) acetate, chloride, nitrate, oxide, and sulfate are 194, 133, 198, 1700, 5000, and 279 mg/kg, respectively the intraperitoneal LD q (rat) for cobalt(III) oxide is 5000 mg/kg (37). 

FIG. 8-69 Ecc( ntric plii valve shown in erosion-resistant reverse flow direction, Shaded components can he made of hard metal or ceramic materials, Cm 1 li(isy Fislier-R/iseuimini. ... 

Cheapest of all are the particulate composites. Aggregate plus cement gives concrete, and the composite is cheaper (per unit volume) than the cement itself. Polymers can be filled with sand, silica flour, or glass particles, increasing the stiffness and wear-resistance, and often reducing the price. And one particulate composite, tungsten-carbide particles in cobalt (known as "cemented carbide" or "hard metal"), is the basis of the heavy-duty cutting tool industry. 

Other topics recently studied by XPS include the effects of thermal treatment on the morphology and adhesion of the interface between Au and the polymer trimethylcy-clohexane-polycarbonate [2.72] the composition of the surfaces and interfaces of plasma-modified Cu-PTFE and Au-PTFE, and the surface structure and the improvement of adhesion [2.73] the influence of excimer laser irradiation of the polymer on the adhesion of metallic overlayers [2.74] and the behavior of the Co-rich binder phase of WC-Co hard metal and diamond deposition on it [2.75]. 

Figure 3.13. Simple relationships between properties and microstriictural geometry (a) hardness of some metals as a function of grain-boundary density (b) coercivity of the cobalt phase in tungsten earbide/coball hard metals as a function of interface density (after Exner 1996).

Colbalt Hydrogenations of solid fuels and fuel oils Manufacture of terephthalic acid High pressure production of aldehydes Lung irritation (hard metal disease) respiratory sensitization... 

Flame Plating—the deposition of a hard metal coating onto a substrate via application of molten metal at supersonic velocities. 

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