The effect of copper (Cu) addition on the active corrosion behavior of hyper duplex stainless steels in sulfuric acid was investigated. The addition of Cu in the base alloy enhanced the resistance to general corrosion by decreasing the critical and corrosion current densities, and increasing the polarization resistance. There are two primary reasons for the considerable enhancement of the corrosion resistance of the experimental alloys containing Cu. First, the protective surface film was enriched with the noble metallic copper (Cu) due to the selective dissolution of the active metallic Cr, Fe, and Ni, and the electrochemical dissolution of the corrosion products such as iron-sulfide (FeS 2), iron sulfate (FeSO 4), ferrous oxide (FeO) and hydrous iron sulfate (FeSO 4 •7H 2 O). Second, chromium oxide (Cr 2 O 3), chromium trioxide (CrO 3), nickel oxide (NiO), molybdenum dioxide (MoO 2), molybdenum trioxide (MoO 3), and tungsten trioxide (WO 3) in an oxide state, molybdenum oxy-hydroxide (MoO[OH] 2) and chromium hydroxide (Cr[OH] 3) in a hydro-oxide state, molybdate (MoO 4 2¹) and tungstate (WO 4 2¹) as corrosion inhibitors in an ion state, and ammonium (NH 4 +) elevating the pH in an ion state were increased and assisted in improving the corrosion resistance.
Metallic silicon powder has been widely used for the production of various industrial materials and parts such as refractory ceramics, solar cells, military parts and so on. Herein, we attempted to prepare pure silicon powder from SiO 2 by a magnesium thermal reduction process. A mixed-phase, Mg 2 Si + MgO, was obtained by the reduction of SiO 2 powder by magnesium gas at 1223 K for 20 h. To extract pure silicon powder, Mg was separated by evaporation under vacuum through Mg 2 Si decomposition above 1073 K, leading to the formation of Si + MgO, and the MgO by-product was eliminated by dissolution in an aqueous hydrochloric acid solution. X-ray diffraction analysis confirmed the formation of pure Si powder and particle size shown in microstructure and oxygen content were analyzed to be 1³5 µm and 1.5³6 wt.%, respectively.
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