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H2SO4 Solution (h2so4 + solution)

Distribution by Scientific Domains
Chemistry80%

Selected Abstracts

Influence of citric acid on calcium sulfate dihydrate crystallization in aqueous media

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2007
S. Titiz-Sargut
Abstract The crystallization of Calcium sulfate dihydrate produced by the reaction between pure Ca(OH)2 suspension and H2SO4 solution was investigated at different pH values, temperatures and citric acid concentrations. Crystal size distributions, filtration rates and zeta potentials of gypsum were determined as a function of citric acid concentrations at pH 3.5 and 65°C. The influence of citric acid on the morphology of gypsum was also investigated and discussed. The average particle size of gypsum was reached to maximum in the presence of approximately 2500 ppm citric acid concentration, where the minimum cake resistance and maximum filtration rate were obtained. In the presence of citric acid, various crystal morphologies such as tabular, plate-like, double-taper leaf-like and flower-like, etc., were obtained. The change of morphology is related to the preferential adsorption of citric acid on different crystallographic faces. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Morphology and Roughness of Silver Deposit Formed by Cementation at Various Temperatures in Pure Sulfuric Acid

HELVETICA CHIMICA ACTA, Issue 11 2006
Grzegorz
Abstract The morphology and surface roughness of silver (Ag) deposit formed on metallic copper (Cu) by cementation conducted in a 0.5M H2SO4 solution was investigated at various temperatures above 25°. The influence of the presence or absence of oxygen (O2) on Ag morphology was studied at an initial Ag+ concentration of 20,mg/dm3. An analysis of distribution diagrams of the surface height calculated from scanning-electron-microscope (SEM) top-view images was performed. The cementation reaction results in a non-homogeneous Ag deposit formed on the surface independently of the presence or absence of O2 in solution. The Ag deposit covers Cu mainly with a uniform and compact layer with separated germs of predendrites, but also a huge ,fern-leaf-shaped' and ,lycopodium-twigs-shaped' dendrites appear occasionally on the surface. The presence of O2 in the system and temperature do not affect significantly the morphology of Ag dendrite as well as a deposit formed on the smooth part of the surface. The roughness of surface with Ag cement varies with temperature only under aerobic conditions where the enhanced Cu corrosion increases the size of anodic sites. The results obtained from the surface-height-distribution diagrams constructed for anaerobic conditions showed that the reaction between Cu+ and Ag+ does not start in the bulk of the solution even at the highest studied temperature. [source]

A study of the relation between current oscillations and pitting

CHINESE JOURNAL OF CHEMISTRY, Issue 10 2003
Hou-Yi Ma
Abstract Anodic polarization behaviors of iron in pure H2SO4 and three mixed acidic solutions, H2SO4 + NaCl, H2SO4 + NaNO3 and H2SO4+ NaCl + NaNO3, were investigated. The potentiodynamic sweep curves showed that the current densities rose and dropped irregularly in H2SO4 + NaCl solution at the more anodic potentials since the iron surface suffered pitting attack in the solution, but the pitting corrosion was inhibited effectively in the presence of nitrate ions. The surface morphological measurements indicated that pits appeared on the iron surface in H2SO4 + NaCl solution and only a few unobvious corrosion spots were observed in H2SO4 + NaCl + NaNO3 solution after the iron electrode was potentiostatically polarized at 1.3 V. The oscillatory properties of iron are associated with the susceptibility of the iron to pitting. In H2SO4 + NaCl solution, the regular potentiostatic current oscillations gradually evolved into the irregular current fluctuations due to occurrence of the pitting; whereas in H2SO4 + NaCl + NaNO3 solution, the current oscillations took place regularly, like the oscillatory behavior in the pure H2SO4 solution. Thus, when the higher the oscillatory frequency, the more irregular oscillatory process and the more sensitive to pitting iron occurred. [source]

Deposition of PtxRu1,x Catalysts for Methanol Oxidation in Micro Direct Methanol Fuel Cells

ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2008
William E. Mustain
Platinum-ruthenium electrodes (PtxRu1-x) have been prepared by electrochemical and electroless deposition and investigated as catalysts for the oxidation of methanol in acidic solutions. PtxRu1-x deposits were electrochemically deposited from acidic chloride electrolytes at potentials between ,0.46 and 0.34 V (vs. NHE). The composition of the electrodeposit was estimated by energy dispersive X-ray spectroscopy and is a strong function of the electrode potential. An empirical model for the deposition process is presented and kinetic parameters are estimated and discussed. Also, the methanol oxidation activity of the PtxRu1-x catalysts was characterized by cyclic voltammetry in 1.0 M CH3OH, 1.0 M H2SO4 solutions. Electroless PtxRu1-x samples were prepared in a modified Leaman bath with hydrazine dihydrochloride as the reducing agent. The kinetic results for the electrochemical deposition of PtxRu1-x were directly applied and the deposition potential was estimated as approximately 0.40 V. [source]

In situ Chemical Deposition of Polyaniline on Activated Carbon for Electrochemical Capacitors

CHINESE JOURNAL OF CHEMISTRY, Issue 1 2006
Zhang-Hua Zhou
Abstract Polyaniline (PA) film was chemically deposited onto the surface of activated carbon (AC) uniformly. Chemical deposition was carried out in 0.1 mol/L aniline plus 0.5 mol/L H2SO4 solution adopting V2O5·nH2O coated on the surface of activated carbon as oxidant. The surface morphologies and structures of the composite materials were characterized by scanning electron microscopy and FT-IR spectra. The electrochemical properties of the composite material electrodes were studied by cyclic voltammetry and constant current charge/discharge tests in 1 mol/L H2SO4 solutions. The specific capacitance of composite materials was exhibited as high as 237.5 F/g at a current density of 1.0 A/g compared with a value of 120 F/g for pure carbon electrode. Good power characteristic and good stability of composite electrodes were also demonstrated. [source]