Cobalt hard metals

Hartung M, Schaller KH and Brand E (1982) On the question of the pathogenic importance of cobalt for cobalt hard metal fibrosis of the lung. Int Arch Occup Environ Health 50 53-57. 

Lison D, Lauwerys R, Demedts M and Nemery B (1996) Experimental research into the pathogenesis of cobalt /hard metal lung disease. Eur Respir J 9 1024-1028. 

Grain-growth inhibitor in WC-cobalt hard metals In steel alloys where it forms during melting... 

Sliding friction, wear, ceramic, oscillation, coating, NbC, niobium carbide, cobalt, hard metal INTRODUCTION... 

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. 

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). 

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. 

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). 

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. 

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).

The use of tungsten carbide alloyed with cobalt, well known as Hard Metal is used for cutting tools because of its excellent wear resistance but finds little use as a corrosion resistant material. 

Toxicology. Cobalt causes skin irritation, allergic contact dermatitis, and occupational asthma interstitial pulmonary fibrosis is associated with exposure to hard metal dust (tungsten and cobalt). 

In the occupational setting, exposure to cobalt alone occurs primarily in the production of cobalt powders. With other industrial exposures, such as hard metal exposure, additional... 

Cobalt (Co) Inhalation exposure "hard metal" pneumoconiosis Alloy in metals - but also associated with vitamin Bq2... 

Shirakawa T, Kusaka Y, Fujimura N, et al. 1990. Hard metal asthma - cross immunological and respiratory activity between cobalt and nickel. Thorax 45 267-271. 

Cobalt is an essential element that is part of vitamin B12, or cobalamin, a coenzyme that is essential in the formation of proteins, nucleic acids, and red blood cells. Although cobalt poisoning is not common, excessive levels can be harmful. Most cases of human exposure to toxic levels of cobalt have occurred through inhalation in the workplace. Many exposures have been suffered by workers working with hard metal alloys of cobalt and tungsten carbide, where very fine particles... 

DFG MAK DFG TRK 0.5 mg/m calculated as cobalt in that portion of dust that can possibly be inhaled in the production of cobalt powder and catalysts hard metal (mngsten carbide) and magnet production (processing of powder, machine pressing, and mechanical processing of unsintered articles) other cobalt alloys and compounds 0.1 mg/m calculated as cobalt in that portion of dust that can possibly be... 

Cobalt is an essential nutrient at low levels ( 40mgday ). In industrial settings, inhalation of high concentrations of cobalt compounds has led to hard-metal pneumoconiosis, which may result in interstitial fibrosis. Workers with this condition typically develop hypersensitivity to cobalt compounds (symptoms include coughing and wheezing). A few workers have developed skin hypersensitivity after dermal contact with cobalt and its compounds. Cobalt can cause cardiomyopathy and (if inhaled as a dust) interstitial lung disease. 

Lison D, Lauwerys R. Cobalt bioavailability from hard metal particles Further evidence that cobalt alone is not responsible for the toxicity of hard metal particles. Arch Toxicol 1994 68 528-31. 

Cobalt salts are responsible for inducing OA in approximately 5 per cent of exposed workers and should be distinguished from hard metal (mixture of cadmium and cobalt) diseases that result in interstitial pneumonitis and pulmonary... 

KUSAKA, Y NAKONA, Y SHIRAKAWA, T. MORIMOTO, K. (1989) Lymphocyte transformation with cobalt in hard metal asthma. Industrial Health, 27, 155-163. 

SHIRAKAWA, T KUSAKA, Y FUKIMURA, N GOTO, S. MORIMOTO, K. (1989) Occupational asthma from cobalt sensitivity in workers exposed to hard metal dust. Chest, 95, 29-37. 

Lustrous, hard metal hexagonal, cJose-packed structure. d 12.45. mp about 2450" bp about 4150", Sp heat (O ) 0,057 cal/g/°C. Does not react with acids, even aqua regia. Net oxidized by air in the cold on heating combines readily with oxygen the powdered metal forms the dioxide on ignit -mg in air. Supeficially attacked by coned alkaline hypochlorites, The powdered metal is attacked by chlorine above 200" by bromine between 300-700. Oxidized by fused alkali hydroxides. Forms alloys with platinum, palladium, cobalt, nickel, tungsten forms definite compds with zinc and with tin. 

---