Layers graphitised

One of the outstanding properties of the austenitic irons is their resistance to graphitic corrosion or graphitisation . In some environments ferritic cast irons corrode in such a manner that the surface becomes covered with a layer of graphite. This compact graphite layer, being more noble than the matrix, markedly increases the rate of attack. The austenitic irons rarely form this... 

The characteristic mode of corrosion of some alloys may be the formation as a corrosion product of a redeposited layer of one of the alloy constituents, as in the case of the brasses that dezincify, or of a residue of one of the components, as in the case of the graphitic corrosion of cast iron. Particularly in the case of the dezincified brass, the adherent copper is not likely to be removed with the other corrosion products, and therefore the mass-loss determination will not disclose the total amount of brass that has been corroded. This is especially important because the copper layer has very little strength and ductility and the extent of weakening of the alloy will not be indicated by the mass loss. In these cases, also, the mass-loss determinations must be supplemented by, or replaced by, mechanical tests or metallographic examination, or both, to reveal the true extent of damage by corrosion. Difficulties in obtaining accurate mass losses of heavily graphitised specimens have been reported... 

These phases are composed of adsorbing materials molecular sieves, alumina, porous glass and gels (such as Chromosorb 100, Porapak and PoraPLOT1 ), and graphitised carbon black. They are mainly used to separate gases or volatile compounds. Capillary columns made by deposition of these materials in the form of very fine particulates are called PLOT (porous layer open tubular) columns. 

The Type VI isotherm, in which the sharpness of the steps depends on the system and the temperature, represents stepwise multilayer adsorption on a uniform nonporous surface. The step height now represents the monolayer capacity for each adsorbed layer and, in the simplest case, remains nearly constant for two or three adsorbed layers. Amongst the best examples of Type VI isotherms are those obtained with argon or krypton on graphitised carbon blacks at liquid nitrogen temperature. 

As mentioned above for pewter objects, the corrosion products may maintain the shape of the object even though no metal is left. One of the best examples of this is observed in cast irons. The iron phase (ferrite) corrodes to form the same corrosion products as already stated above. The graphite flakes in the cast iron are inert and trap the corrosion products and the shape is maintained. This is called graphitisation of cast iron and almost all cast iron artefacts recovered from archaeological sites have graphitised layers on their surface. 

The depth of the recrystallised layer is very small, of the order of 0.01 -0.1 pm. Thus, a possible way to eliminate its effect on p-n junction properties is to perform a drive-in diffusion of aluminium from the epitaxial layer. Unfortunately, the diffusivity of aluminium from an epitaxial layer is extremely slow in SiC. The diffusivity is 3 - 5 orders of magnitude lower than that observed for diffusing aluminium from the vapour phase [70]. The authors of [69] had to employ very high diffusion temperatures, over 2500 °C. The anneal produced a shift of the p-n junction into the crystal bulk and the electrical properties were substantially improved. However, this could not provide the elimination of the weak points of the junctions. The characteristics of the p-n junctions were worse than those with the recrystallised layer removed by sublimation etching. In addition, the surface evaporation and graphitisation at temperatures above 2500 °C severely reduces the reproducibility of the results. 

Sonobe et al. reported the preparation of carbon materials using the interlamellar spaces of montmorillonite as template and polyacrylonitrile, poly(furfuryl alcohol) and poly(vinyl acetate) as carbon precur-They found that carbon precursors were easily graphitised and the obtained carbon materials were two-dimensional film-like graphite, consisting of highly oriented layer planes, which were stacked thin and wide. " Kyotani et al. produced carbons from poly(furfuryl... 

HEAT CAPACITIES OF ETHYL AND TERTIARY BUTYL ALCOHOLS IN ADSORPTIOLN LAYERS ON GRAPHITISED CARBON BLACK. 

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