Coking metal dusting

The term, metal dusting, was first used about this time to describe the phenomenon associated with hydrocarbon processing. Butane dehydrogenation plant personnel noted how iron oxide and coke radiated outward through catalyst particles from a metal contaminant which acted as a nucleating point. The metal had deteriorated and appeared to have turned to dust. The phenomenon has been called catastrophic carburization and metal deterioration in a high temperature carbonaceous environment, but the term most commonly used today is metal dusting. 

S. Strauss, R. Krajak and H. J. Grabke, Coking by Metal Dusting of Ni-base Alloys, Materials and Corrosion, 50 622-627 (1999). 

Cadmium oxide, calcined dolomite, calcium chloride, calcium oxide, carbomethylcellulose (CMC), carbonates, catalysts, cellulose acetate, ceramics, charcoal, clay, coal, cocoa powder, coffee powder, coke, copper, corn starch Detergents, dextrine, dimethylterephthalate (DMT), dolomite, ductile metals, dusts, dyes Earthy ores, eggshells, elastomers, emulsifiers, epoxy resins... 

Fig.l. Metal dusting attack on Fe3Al, vast outgrowth of coke after 7 d exposure at 650°C and a( = 10, the arrow indicates the sample from which the coke has grown. 

Group Di Acetone, alcohol, gasoline, petroleum fractions, lacquer solvents, and similar vapors Group El Metal dust Group Fi Carbon black, coal or coke dust Group 6 Grain dust... 

The features of this failure case were similar to the previous case materials loss was observed, coke was detected and the internal wall showed a carburised zone in the metallographic cross-section. The outer surface was partially covered with the red scale and one tube had even cracked locally. Near the crack there were deposits in the tube and the microstructure of the steel indicated strong overheating. The new 9%Cr tube obviously failed due to metal dusting, coke formation inhibiting the heat transfer and locally increased temperatures. 

Results of a laboratory study on the metal dusting of four steels in butane-hydrogen. The coke formation within two days exposure was taken as a measure of metal dusting attack, (a) Temperature dependence of attack, (b) effect of H2S additions on metal dusting at 650 °C. 

Copper is thought to be noneatalytic to carbon deposition in all gas atmospheres, and owing to the extremely low solubility of carbon in copper, inert to the metal dusting reaction. Copper-based alloys have recently been reported in the patent literature [13, 14] to be resistant or immune to earburisation, metal dusting and coking. Thus, the addition of copper to niekel, which forms a near perfect solid solution, may be able to suppress or... 

Binary nickel-copper alloys have already been investigated as substitutes for nickel catalysts in order to reduce the amount of coking because of the noncatalytic nature of copper [15-18], Nickel-copper alloys, however, have never been tested for their resistance to metal dusting. The aim of this work was to study the effects of adding copper on the behaviour of nickel metal dusting and associated coking. 

The objective of the present study is to examine the behavior of both metal dusting and coking for transition metals and Ni-Cu binary alloys exposed in a carbonaceous gas, which simulates the synthetic gas produced in the reforming process. The experimentally observed phenomena are also theoretically discussed from the viewpoint of electronic properties under the chemical reactions of CO with transition-metal surfaces. 

Metal dusting is a special form of catastrophic corrosion that takes place in carbon-containing environments where the carbon activity exceeds a value of 1 [26,27]. For Fe-based materials the principles are shown schematically in Figure 13.17. The catalytic effect of the metal or cement-ite surface leads to a dissociation of the carbon-containing gaseous species (CO , C ,Hy) with the effect of carbon uptake into the metal subsurface zone and carbon deposition (amorphous coke) on the surface. This mechanism is evidently influenced by the crystallographic situation of the metal grains on the material surface [28]. For carbon monoxide (CO) adsorbed on metal... 

Strauss S, Krajak R, Grabke H J, Coking by metal dusting of Ni-base alloys . Materials and Corrosion, 1999 50 622-627... 

Bose S K, Grabke H J, Diffusion coefficient of carbon in Fe-Ni anstenite in the temperature range 950-1100°C , Z. MetaUkunde, 1978 69 8-15 Maier M, Norton J F, Frampton P D, Metal dusting of 9-20 Cr steels in increased pressure environments at 560°C , Materials and Corrosion, 1998 49 330-335 Muller-Lorenz E M, Grabke H J, Coking by metal dnsting of steels . Materials and Corrosion, 1999 50 614-621... 

The isolation of zinc, over 90% of which is from sulfide ores, depends on conventional physical concentration of the ore by sedimentation or flotation techniques. This is followed by roasting to produce the oxides the SO2 which is generated is used to produce sulfuric acid. The ZnO is then either treated electrolytically or smelted with coke. In the former case the zinc is leached from the crude ZnO with dil H2SO4, at which point cadmium is precipitated by the addition of zinc dust. The ZnS04 solution is then electrolysed and the metal deposited — in a state of 99.95% purity — on to aluminium cathodes. 

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