Tang Chaobo

Thermodynamic Research of Leaching Copper Oxide Materials with Ammonia-ammonium Chloride-water Solution

Abstract The solubilities of copper hydroxide Cu(OH)2, copper oxide CuO, atacamite Cu(OH)1.5Cl0.5, malachite Cu2(OH)2CO3 and chessylite Cu3(OH)2(CO3)2 in an ammonia-ammonium chloride-water solution were calculated using an exponential computation method based on both mass balance and charge balance equations. The range of stability of each solid phase was also established. A group of experiments were designed to validate the veracity of the results of the thermodynamic calculation.

Effect of Bromide Ions on the Pitting Corrosion of Hafnium in Anhydrous t-Butanol and Acetonitrile

Pitting of Hf in Et4NBr t-butanol and acetonitrile (ACN) solutions was studied by means of cyclic voltammetry, potentiodynamic anodic polarization, galvanostatic, potentiostatic and impedance techniques. The potentiodynamic anodic polarization curves did not exhibit an active dissolution region near corrosion potential due to the presence of an oxide film on the electrode surface, which was followed by pitting corrosion resulting from the passivity breakdown by the aggressive attack of bromide (Br−) ion. The pitting potential (E pit) increased with increasing potential scanning rate but decreased with increasing temperature and Br− concentration. Cyclic voltammetry and galvanostatic measurements allowed the pitting potential (E pit) and the repassivation potential (E p) to be determined. Analysis of the potential/time transients revealed that the applied anodic current density had a significant influence on the values of E pit. On the other hand, the E p values were independent on the applied current density. The current/time transients indicated that the incubation time (t i) for passivity breakdown decreased slightly with increasing potential and solution temperature. The impedance spectra showed that the resistance of passive layer decreased with increasing potential.