A tracer investigation of chromic acid anodizing of aluminium

A tungsten tracer introduced into a sputtering‐deposited aluminium substrate was employed to investigate pore development in anodic films formed at 3 mA cm^?2 in 0.25 M chromic acid electrolyte at 313 K. The anodized specimens were observed by transmission electron microscopy (TEM), with compositions of films determined by Rutherford backscattering spectroscopy (RBS). The anodic films were found to be similar in thickness to that of the aluminium layer consumed during anodizing and revealed the feathered pore morphology that is a characteristic of the electrolyte. The anodizing efficiency was ～45–48%, with tungsten tracer species, in addition to aluminium species, being lost to the electrolyte at the pore base. These findings, together with the relatively uniform distribution of tungsten species within the film, are consistent with field‐assisted dissolution of the alumina playing a major role in the development of pores. The films contrast with those formed in phosphoric and sulphuric acid electrolytes, for which feathering of pores is absent, the tracer distribution is inverted and the film thickness exceeds that of the consumed metal, features indicative of the influence of material flow in pore development. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermal decomposition of hydrogen peroxide in the presence of sulfuric acid

Hydrogen peroxide (H₂O₂) is popularly employed as a reaction reagent in cleaning processes for the chemical industry and semiconductor plants. By using differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2), this study focused on the thermal decomposition reaction of H₂O₂ mixed with sulfuric acid (H₂SO₄) with low (0.1, 0.5 and 1.0 N), and high concentrations of 96 mass%, respectively. Thermokinetic data, such as exothermic onset temperature (T ₀), heat of decomposition (ΔH _d), pressure rise rate (dP/dt), and self-heating rate (dT/dt), were obtained and assessed by the DSC and VSP2 experiments. From the thermal decomposition reaction on various concentrations of H₂SO₄, the experimental data of T ₀, ΔH, dP/dt, and dT/dt were obtained. Comparisons of the reactivity for H₂O₂ and H₂O₂ mixed with H₂SO₄ (lower and higher concentrations) were evaluated to corroborate the decomposition reaction in these systems.     

Electroluminescence of aluminium during electropolishing in nitric acid

Electropolishing of aluminium in 10 mol dm⁻³ aqueous nitric acid shows the emission of electroluminescence. The very high anodic current densities involved during electropolishing preclude the presence of all but the thinnest of surface oxide films, and this raises the question of the origins of the luminescence. The electroluminescence during electropolishing is compared with that occurring during anodising in phosphoric acid.     

Thermal hazard evaluation of carbon nanotubes with sulfuric acid by DSC

Many concerns over unsafe or unknown properties of multi-walled carbon nanotubes (MWNTs) have been raised. The thermal characteristics regarding stability would represent potential hazards during the production or utilization stage and could be determined by calorimetric tests for various thermokinetic parameters. Differential scanning calorimetry (DSC) was employed to evaluate the thermokinetic parameters for MWNTs at various compositions. Thermoanalytical curves showed that the average heat of decomposition (ΔH _d) of the MWNTs samples in a manufacturing process was about 31,723 J g⁻¹, by identifying them as an inherently hazardous material. In this study, significant thermal analysis appeared in the presence of sulfuric acid (H₂SO₄). From the DSC experiments, the purification process of MWNTs could induce an unexpected reaction in the condition of batch addition with reactants of H₂SO₄. The results can be applied for designing emergency relief system and emergency rescue strategies during a perturbed situation or accident.     

Study of anodizing process on aluminium foam to improve the corrosion behavior

Aluminium foam is obtained by the production of air into metallic melt. This material shows a very low density together with good mechanical properties, high impact energy absorption, and fire resistance. Different production ways to obtain metallic foam are possible. Considering the cost, the Alporas process is particularly interesting. By means of this production method, a block of metallic foam with close cells is obtained. By slicing, foam panels are obtained. The mechanical cut promotes the formation of an open cells texture on the surface. In this last case, the complex morphology of aluminium foam could be a critical point considering the corrosion behavior in aggressive environments, where localized corrosion phenomena, as pitting or crevice corrosion, are likely to occur. The anodizing treatment is one of the most used methods to improve the corrosion resistance of aluminium and aluminium alloys. The aim of this paper is to perform an anodization treatment to enhance the corrosion resistance of aluminium foam. Constant voltage anodization (12 V for 60 min) and pulsed current anodization (0.04 A/cm² for 60 seconds and 0.01 A/cm² for 15 seconds, repeated for 15 cycles) have been carried out in 15 wt% H₂SO₄ at 20°C. The anodized samples are observed in cross section by optical and electronic microscopes to investigate the structure of the anodic oxide layer and the presence of defects and to measure the thickness of the layer. The corrosion protection performance and the compactness of layers are evaluated using acetic salt spray test and electrochemical impedance spectroscopy.     

Equilibrium structure of sulfuric acid

The equilibrium structure of the more stable conformer of H2SO4, of C2 symmetry, has been calculated ab initio using the CCSD(T) method and taking into account the core correlation correction. The accuracy of this structure has been checked by comparing it to that of similar molecules and by estimating the effects of basis set enlargement and of diffuse functions. Furthermore, the quadratic, cubic, and quartic force fields have been calculated at the MP2 level of theory using a basis set of triple-zeta quality. The spectroscopic constants derived from the force field are in satisfactory agreement with the experimental ones. The resulting band origins are compared to literature infrared values, including those for overtone and combination bands. Normal modes of vibration are pictured. Using this force field, semiexperimental equilibrium rotational constants are determined which allows us to check the accuracy of the ab initio structure and to refine it using a mixed regression method.     

Thermal decomposition of aluminium hydroxides

The thermal decompositions of the crystalline aluminium hydroxides hydrargillite, bayerite and nordstrandite were investigated by thermogravimetry, differential thermal analysis, X-ray diffraction and infrared spectrophotometry. It was found that these aluminium hydroxides undergo thermal decomposition in the following sequences: hydrargillite-1

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Zusammenfassung Die thermische Zersetzung von kristallinen Aluminiumhydroxiden, wie Hydrargillit, Bayerit und Nordstrandit, wurde thermogravimetrisch, differentialthermoanalytisch, röntgendiffraktometrisch und IR-spektrophotometrisch untersucht. Es wurde festgestellt, da\ diese Aluminiumhydroxide in der folgenden Reihenfolge zersetzt werden: Hydrargillit-I

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Ionic hydrogenation of olefins in sulfuric acid

Conclusions A mixture of H₂SO₄ with either alcohols or ethers is a convenient medium for running the ionic hydrogenation of olefins with retention of the selectivity of this reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1886–1888, August, 1982.     

Detection of sulfuric acid in insoluble sulfates

Summary Heating of insoluble residue with phosphoric acid and testing the distillate with calcium chloride permits identifying 0.02g sulfate.

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Zusammenfassung Erhitzen des unlöslichen Rückstandes mit Phosphorsäure und Prüfen des Destillates mit Calciumchlorid erlaubt den Nachweis von 0,02g Sulfat.

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Résumé II est possible d'identifier 0,02g de sulfate par chauffage du résidu insoluble en présence d'acide phosphorique et traitement du distillat par le chlorure de calcium.

     

Acid-catalyzed hydrolysis of benzoylhydrazine in sulfuric acid

Conclusions A mechanism is proposed for the acid-catalyzed hydrolysis of benzoylhydrazine; the limiting step in this mechanism is the interaction of the solvated proton with the reactant in ion pair form.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2476–2478, November, 1981.     

The determination of sulfuric acid aerosols

A reliable method has been developed for the chemical determination of sulfuric acid aerosol by simple technique and inexpensive equipment. A similar method is also presented for determining total acidity, including sulfuric acid and volatile acids together with salts that hydrolyze to give protons. The determinations can be performed directly on air samples collected with a sequential tape sampler. The basic chemical reactions involved are specifically controlled by the protons: stoichiometric amounts of bromine are released from a mixture of bromate-bromide by the protons, and the liberated bromine reacts with fluorescein to produce eosin, the color intensity of which is a direct measure of proton concentration. The detection limit for both the methods is 0.5 μg in terms of sulfuric acid and the range for quantitative measurement is 1–10 μg. The new methods are of special significance because of previous lack of reliable methods for determining acidic species in a polluted atmosphere.     

Throwing power of a dilute sulfuric acid copper plating electrolyte during intensive electrodeposition

A method of determination of the throwing power (TP) of electrolytes in conditions of forced convection in a Hull cell with a rotating cylindrical electrode is presented. The method is used to determine TP of a copper plating electrolyte containing 0.15–0.5 M CuSO₄ and 1 M H₂SO₄ at current densities of up to 75 mA cm^-2. The TP decreases with increasing current density at a constant i _av/i _d ratio, where i _av is the average working current density and i _d the limiting diffusion current density. With increasing the i _av/i _d ratio due to an increase in the cathodic polarizability conditions for an increase in TP may be achieved. In optimum (for uniform deposition) modes, i _av/i _d 0.4–0.5. The TP may increase upon diluting electrolyte with respect to its main component.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 91–96.Original Russian Text Copyright © 2005 by Dikusar, Bobanova, Yushchenko, Yakovets.To the Centennial of B.N. Kabanov.     

Extraction of sulfuric acid with TOPO

A study on solvent extraction of sulfuric acid by tri-octylphosphine oxide (TOPO) in n-heptane has been made. Extraction coefficients of H₂SO₄ as a function of H₂SO₄ concentration in aqueous phase, and extractant concentrations in organic phase have been studied. The composition of extracted species, equilibrium constants of extraction reaction have been evaluated. These results are important for interpreting extraction equilibrium data of uranium(VI) or other metal ions with TOPO in sulfuric acid media.     

Microwave investigation of sulfuric acid monohydrate

The complex H2SO4-H2O has been observed by rotational spectroscopy in a supersonic jet. A-type spectra for 18 isotopic forms have been analyzed, and the vibrationally averaged structure of the system has been determined. The complex forms a distorted, six-membered ring with the water unit acting as both a hydrogen bond donor and a hydrogen bond acceptor toward the sulfuric acid. One of the H2SO4 protons forms a short, direct hydrogen bond to the water oxygen, with an H...O distance of 1.645(5) A and an O-H...O angle of 165.2(4) degrees. Additionally, the orientation of the water suggests a weaker, secondary hydrogen bond between one of the H2O hydrogens and a nearby S=O oxygen on the sulfuric acid, with an O...H distance of 2.05(1) A and an O-H...O angle of 130.3(5) degrees. The experimentally determined structure is in excellent agreement with previously published DFT studies. Experiments with HOD in the jet reveal the formation of only isotopomers involving deuterium in the secondary hydrogen bond, providing direct experimental evidence for the secondary H...O interaction. Extensive isotopic substitution has also permitted a re-determination of the structure of the H2SO4 unit within the complex. The hydrogen-bonding OH bond of the sulfuric acid elongates by 0.07(2) A relative to that in free H2SO4, and the S=O bond involved in the secondary interaction stretches by 0.04(1) A. These changes reflect substantial distortion of the H2SO4 moiety in response to only a single water molecule, and prior to the proton transfer event. Spectral data indicate that the complex undergoes at least one, and probably more than one type of internal motion. Although the sulfuric acid in this work was produced from direct reaction of SO3 and water in the jet, experiments with H2(18)O indicate that about 2-3% of the acid is formed via processes not normally associated with the gas-phase hydration of SO3.