Chemical metallisation

Chemical metallisation and galvanisation as a method for development of electroconductive polyacrylonitrile fibres... 

Scheme of the galvanisation setup with (1, 2) rolling cathodes, (3) chemically metallised yarn, (4) electrolyte solution, (5) galvanisation bath and (6) anodes. 

Table 11.9 Relative variations of amount of nickel and specific electrical resistance in individually cut PAN-fibre pieces obtained through chemical metallisation and galvanisation...

This results in PAN fibres obtained by chemical metallisation and galvanisation with the following properties ... 

Molybdenum hexafluoride is used in the manufacture of thin films (qv) for large-scale integrated circuits (qv) commonly known as LSIC systems (3,4), in the manufacture of metallised ceramics (see MetaL-MATRIX COMPOSITES) (5), and chemical vapor deposition of molybdenum and molybdenum—tungsten alloys (see Molybdenumand molybdenum alloys) (6,7). The latter process involves the reduction of gaseous metal fluorides by hydrogen at elevated temperatures to produce metals or their alloys such as molybdenum—tungsten, molybdenum—tungsten—rhenium, or molybdenum—rhenium alloys. 

Nylon is similar ia its general chemical stmcture to the natural fiber wool, and therefore all the previously described processes for wool are appHcable to dyeiag nylon with acid, metallised, and other dyes. There are, however, significant differences. Nylon is synthetic, it has defined chemical stmcture depending on the manufactufing process, and it is hydrophobic (see Fibers, POLYAMIDES). 

Metallisation is a process in which a metal ion is absorbed by a conventional fibre, followed by chemical reduction of the absorbed metal ions to its metallic phase. In this case, conduction is also obtained through the entire fibre but with a limited rate, dependent on the density of metal ion absorbed in the fibre and adsorbed at the surface of the fibre. 

In this chapter, a relatively simple method is described to metallise polyacrylonitrile (PAN) fibres with a two-step process (ab/adsorption and reduction of Ni(II) in one bath solution followed by galvanisation), and making use of relatively cheap chemicals in order to offer a simple and economically feasible metallisation method and related metallised product. 

Metallisation of fibres is not only a physical process determined by absorption capacity of the fibres for the metal and diffusion capacity of the metal in the fibre structure, but also depends on chemical parameters such as chemical structure of the fibres, presence of functional groups, reactivity of the fibre and the metal, oxidation state of the metal and the presence, necessity and reactivity of supporting chemicals (e.g. reducing agent). Therefore, it was necessary first to study metallisation at different types of fibres in order to investigate which structure is most useful for further research. In this respect, viscose, cotton, natural silk and polyacrylonitrile fibres were investigated because of their different structure and properties and their availability in the New Independent States of the former Soviet Union (Uzbekistan, Kazakhstan, Kyrgyzstan). 

The metal ion uptake profiles are shown in Fig. 11.1 for variations of NaCNS concentration (Fig. 11.1a), temperature (Fig. 11.1b) and plasticisation drawing (Fig. 11.1c) of the precipitation bath for Co uptake. Similar curves were obtained with Ni. Table 11.2 shows the data for different parameters related to a fully metallised fibre obtained after metallisation of PAN fibres, produced under different experimental conditions of the precipitation bath. Despite the fact that the uptake profiles are considerably different and the data obtained (diffusion coefficient) confirms this, no remarkable changes are observed in the total amount of metal absorbed by the fibre. This means that saturation for metal uptake is obtained independently of the precipitation bath parameters. The role of these parameters is limited to the rate of metal uptake, and a choice for the optimal value of these parameters should be based on economic reasons first the consumption of chemicals and energy and, secondly, the processing time. Taking these two criteria into account, a NaCNS concentration of about 12%, a temperature of 283 K and a plasticisation drawing of 500% are further used. 

Metallising Applying a thin coating of metal to a non-metallic surface. May be done by chemical deposition or by exposing the surface to vaporised metal in a vacuum chamber. 

These are produced by several conversion processes (evaporation, sputtering, chemical plasma deposition). Evaporation is the same method as that used to create metallisation using aluminium. A material is heated in a crucible by either a resistive heat or an electron beam gun (hence the name electron beam deposition), whereby the material evaporates and subsequently condenses on a chilled film in a vacuum chamber. In the case of Sit), coatings, the aluminium used in metallisation is replaced by SiO/Si02. 

This Datareview has described the known surface phases which exist on both a- and P-SiC. Surface treatments by annealing in UHV, by ion bombardment and by laser irradiation are not suitable to prepare SiC surfaces for further study. Chemical reduction of surface oxides is the preferred route to surface preparation, particularly using a Si flux at temperatures < 1000°C. A distinction is drawn between ideal surfaces prepared in UHV and practical ones where substrates are chemically treated or ion bombarded prior to metallisation. Processes occurring during deposition of the first few monolayers of metal and subsequent treatments are discussed in terms of chemical and physical properties. A total of 15 metal-SiC combinations are reviewed and discussed in terms of silicide and carbide formation. 

Aylett BJ, Harding IS, Earwaker LG, Forcey K, Giaddui T (1996) Metallisation ofporous silicon by chemical vapour infiltration and deposition. Thin Solid Films 276 253... 

Die passivation layers were first introduced to protect the metallisation of integrated circuits from mechanical damage during assembly. However, it soon became apparent that the passivation layer was a crucial factor in determining the failure rate in moist ambients. Originally, pure chemical vapour deposition (CVD) silicon dioxide was used, but later phosphorus was added to relieve strain in the layer and thus prevent cracking and loss of adhesion. There is also interest in, and limited use of, other forms of passivation such as silicon nitride, oxynitride and polyimide. 

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