The objective of this research was to study the purification of industrial-grade phosphoric acid (P2O5) by conventional electrodialysis. The experiments were conducted using a three-compartment cell with anion and cation membranes, and industrial acid solution was introduced into the central compartment. The elemental analysis of the diluted solution indicated that the composition of magnesium, phosphates, and sodium was reduced in the central compartment. The ratios of the concentration of the ions and the phosphates were essentially unchanged by the process. Consequently, electrodialysis could not purify the acid in the central compartment, and the migration of phosphate ions to the anolyte produced a highly concentrated phosphoric acid solution containing sulfates and chlorides as impurities. However, the migration of the phosphate ions across the membrane consumed a large amount of energy. Detailed speciation diagrams were constructed in this study. These diagrams showed that metal-phosphate complexes were predominant in the industrial phosphoric acid solution. This result explains why the ratios of the concentrations of the ion metals and the phosphates did not change in the purification process. The energy consumed in the electrodialysis indicated that the metal-phosphate complexes were less mobile than the free-phosphate ions. The speciation diagrams explained the experimental results satisfactorily.
We present the results of a study of H202:HF:C406H6(tartaric acid):H20 solution for chemical polishing of GaSb wafers. The influence of etching solution composition on surface morphology was studied. The solutions investigated varied in H202 (2.0-3.0 mol) and HF (0.0-5.0 mol) concentrations, but contained a constant concentration of tartaric acid (0.7 mol). It was found that the etchant has excellent polishing properties for GaSb wafers when the HF concentration was less than 1.5 mol. For HF concentration larger than 1.5, the etchant solution produced rough surfaces. The dependencies of the etching rate on solution composition, temperature, and etching time were studied.
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This work reports the electro-oxidation of formic acid using Pd as catalyst supported on third generation TiO2 nanotubes. The results indicate that it is possible to carry out the electro-oxidation of formic acid in acidic medium, and shows an increase in the oxidation of formic acid, by increasing the Pd electrodeposition time on TiO2NTBs.
The electrochemical formation of atomic adlayers introduces significant changes in the electrocatalytic properties of electrode surfaces. In the present contribution, we study the surface properties of Au nanoparticles analysing the electrochemical responses associated to the copper underpotential deposition (upd) in acid pH. The Au nanoparticles were synthesised by the chemical method, using HAuCl4 and trisodium citrate with an average diameter of 19.2 ± 1.2 nm. Three-dimensional networks of Au nanoparticles were assembled via electrostatic layer-by-layer adsorption employing poly-L-Lysine (PLL) on In-doped SnO2 electrodes (ITO). The electrochemical studies in sulfuric acid (Figure 1A) show the voltammetry behavior, while (Figure 1B) in copper sulfate (CuSO4) show the potentiostatic current transients of Cu onto Au nanoparticles. Detailed electrochemical analysis of the responses showed that the average Cu coverage on a single Au nanoparticle is close to those observed at extended Au surfaces. These results demonstrate that each individual nanoparticle in the assembly participate in the electrochemical copper deposition.
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