Cemented containing cobalt

Separation of two metals from a leach solution - as examples, mention may be made of solutions containing cobalt and copper, and nickel and copper. The former solution is treated by metallic cobalt to precipitate copper, and the latter by metallic nickel to precipitate copper. In both cases, the metal added to cement the copper is recovered afterwards. 

Contact allergy to cobalt is common and is often associated with concomitant allergy to nickel or chromate (Chaps. 66, 67). This is interpreted as simultaneous sensitization due to combined exposure, because nickel is often contaminated with cobalt, and cement contains chromium as well as cobalt. Solitary cobalt allergy is seen mainly among hard-metal workers (Chap. 68) and in the glass and pottery industries. 

A ductile phase in a multiphase ceramic is found to increase the fracture strength. An example to cite is the case of cemented carbide. This composite contains cobalt as the ductile phase. In this material, cracks tend to originate... 

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). 

Occupational exposure to dust of cemented carbide that contains more than 2% cobalt must be controlled so that employees are not exposed at a concentration greater than 0.1 mg cobalt/m air, determined as a TWA concentration for up to a 10-h workshift in a 40-h workweek. 

Calorised Coatings The nickel- and cobalt-base superalloys of gas turbine blades, which operate at high temperatures, have been protected by coatings produced by cementation. Without such protection, the presence of sulphur and vanadium from the fuel and chloride from flying over the sea promotes conditions that remove the protective oxides from these superalloys. Pack cementation with powdered aluminium produces nickel or cobalt aluminides on the surfaces of the blade aerofoils. The need for overlay coatings containing yttrium have been necessary in recent times to deal with more aggressive hot corrosion conditions. 

Special carbide tools also will often contain various percentages of titanium, tantalum, niobium icolumbium). and hafnium carbides, along witii die tungsten carbide. Chromium and vanadium carbides are also added to produce special, fine-grain-size grades of cemented tungsten carbide-cobalt materials. See Fig. 1. 

R. Earnshaw, Investments for casting cobalt-chromium alloys, part 11, Br. Dent. J., 108 (1960) 429-440. E.G. Sherif and Edwin S. Michaels, East-setting cements from liquid waste phosphorous pentoxide containing materials, US Patent 4,487,632, 1984. 

Catastrophic failure of two cemented cobalt-containing femoral stems that had been used in conjunction with the impacting bone-grafting technique has been reported in two cases (5). 

Zinc Process [11.1,11.2,11.5,11.6]. In this process, cemented carbide scrap is treated in molten zinc or zinc vapor, which reacts with the binder to form intermetallic phases and a zinc-cobalt alloy. These reactions lead to a volume expansion of the binder and bloat the scrap. After vacuum distillation of zinc, the material is liiable and can be readily disintegrated. The condensed Zn can be re-used. The reclaimed carbide/metal sponge contains less than 50 ppm Zn. 

For information about hazardous substances in the production of tungsten alloys, such as thoriated tungsten, cobalt, or nickel-containing cemented carbides, see Chapter 14. 

Cemented carbide parts are used for demanding wear applications. They are primarily made of tungsten carbide and contain a small percentage of binder such as nickel or cobalt to provide structural homogeneity. Cemented carbides products include knives, blades, nozzles, jets guides, valve seats, seal parts, etc. The properties and design of cemented carbides strongly influence part life and overall equipment reliability. 

Tungsten carbide (WC), the hard phase, together with cobalt (Co), the binder phase, forms the basic cemented carbide structure from which other types of cemented carbide have been developed. In addition to the straight tungsten carbide - cobalt compositions - cemented carbide may contain varying proportions of titanium carbide (TiC), tantalum carbide (TaC), and niobium carbide (NbC). These carbides are mutually soluble and can also dissolve a high proportion of tungsten carbide. Also, cemented carbides are produced which have the cobalt binder phase alloyed with, or completely replaced by, other metals such as iron (Fe), chromium (Cr), nickel (Ni), molybdenum (Mo), or alloys of these elements. 

Cemented carbides normally contain 70-90% of hard particles together with 10-30% cobalt binding metal. In general, the more cobalt that is present, the tougher the cemented carbide. Unfortunately, however, this increase in toughness, obtained by increasing the cobalt content, results in decreased hardness and abrasion resistance. 

Prior to electrowirniing zinc, all zinc plants must purify the electrolyte, and in particular cobalt has to be removed, usually by cementation with zinc powder. Such a cement can be re-processed to recover its metal values, in particular cobalt. Hydrometal S.A. a subsidiary of Jean Goldschmidt Int. S.A. (JGI) processes such cobalt-containing cements at its plant in Engis, Belgium (31). Cements from various sources are treated, with typical content of 15-20% Cu, 2-5% Ni, 20-30% Zn and 5-7% Co. A simplified process flowsheet is presented in Figure 16. 

All the equations so far listed, with the exception of equation (5.52), are based on analyses of wholly brittle monolithic ceramic systems. More recent considerations of the application of the indentation technique to the determination of Kic parameters for cemented carbides containing ductile cobalt as a binder have resulted in the following two equations, which apply to Palmqvist cracks. 

Hard-metal workers are exposed to dusts of cemented tungsten carbide containing 5-10% of cobalt. However, due to the solubility of metallic cobalt in the lung environment (Lison et al. 1994), particle analysis of lung tissue or BALF of hard metal workers show only trace amounts of cobalt (Dumortier et al. 1989). 

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