e oxide-scale structure and pickling behavior of oxided 2205 duplex stainless steel in the electrolytes containing hydrochloric acid were investigated. e oxide scales mainly consist of two layers: the outer layer is dense Fe 2 O 3 , and the inner granular is FeCr 2 O 4 spinel. During the pickling process, pittings form around the boundaries of FeCr 2 O 4 particles or interfaces of two kinds of oxides, which results in that the electrolyte can directly react with the chromium-depleted layer along the pittings to produce an "undercut" effect so that the pickling efficiency is improved markedly. e pickling mechanism was discussed, and the model was established.
Experiment Procedure2205 duplex phase stainless steel (with a chemical composition of 0.018 wt.% C, 1.2 wt.% Mn, 22.6 wt.% Cr, 5.3 wt.% Ni, and balanced Fe) was hot rolled into a plate, following annealing and blasting treatment (called as oxidized 2205). Specimens (30 mm × 30 mm) were machined from the plater. e phase components of the oxide scale were investigated by a Japan Rigaku D/Max-IIIB X-ray diffractometer with Cu Kα1 radiation (λ �1.5405Å).
Gibbsitic bauxite from Australia was leached by hydrochloric acid in this work. Analysis on kinetics for the extraction of Al2O3was quantitatively studied. It was concluded that the hydrochloric acid leaching process of gibbsitic bauxite was controlled by chemical reaction. Moreover, the mechanism for the dissolution followed the equation,lnk=39.44-1.66×104(1/T), with an apparent activation energy of 137.90 kJ/mol, according to the equation ofk=Ae-Ea/RT. This work aims to provide a good theory support for the process control by using a new method of alumina production from the low grade bauxite.
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