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Sulfuric Acid Medium (sulfuric + acid_medium)

Distribution by Scientific Domains

Polymers and Materials Science	33%

Selected Abstracts

Effect of phosphonate additive on crystallization of gypsum in phosphoric and sulfuric acid medium

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2002
H. El-Shall
Abstract Understanding the mechanisms of growth and inhibition during crystallization of calcium sulfate is of primary importance for many industrial applications. For instance, inhibition of the crystallization process may be required to prevent scale formation in pipes, boilers, heat exchangers, reactors, reverse osmosis membrane surfaces, cooling water systems, secondary oil recovery utilizing water flooding techniques and desalination evaporators, etc. On the other hand, control growth and morphology of gypsum crystals is desired in achieving higher filtration rate and higher productivity of phosphoric acid from phosphate rocks. In this regard, this basic study is carried out to understand effect of Aminotris (methylenephosphonic acid (ATMP) on calcium sulfate dihydrate (gypsum) crystallization. The time elapsed between the achievement of supersaturation and the appearance of a solid phase (termed as induction time) is measured under different supersaturation ratios ranging from 1.018 to 1.979. The data are used to calculate the surface energy, critical nucleus size, and crystal growth rates of gypsum under different conditions. The results show that, the induction time decreases exponentially with increasing the supersaturation ratio. In addition, the surface energy decreases with ATMP compared to the baseline (without ATMP). Interestingly, with addition of the ATMP, the crystals mean and median diameters are found to decrease. The inhibition efficiency ranges from 16% to 59% depending on supersaturation ratio. [source]

Kinetics and mechanism of the dehydration reaction of sarcosine to a bislactame through diacyclperoxide intermediate in strong acidic medium

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2009
Homayoon Bahrami
The influence of substitution on the amine functional group of glycine in the permanganic oxidation of such an ,-amino acid in moderately concentrated sulfuric acid medium has been investigated. Reaction products analysis has revealed that contrary to the usual ,-amino acid oxidation product, which is an aldehyde species, a valuable compound, namely 1,4-dimethylpiperazine-2,5-dione, has been obtained as the main product via a cheap, simple, efficient, and novel method. Sarcosine has been chosen as a substituted derivative of glycine, and the kinetics and mechanism of its permanganic oxidation have been investigated using a spectrophotometric technique. Conclusive evidence has proven delayed autocatalytic activity for Mn(II) in this reaction, analogous to some ,-amino acids. It has been revealed that such activity can show up when a certain concentration ratio of Mn(II) to sarcosine is built up in the medium, which we call the "critical ratio." The magnitude of the latter ratio depends on the sulfuric acid concentration. Considering the "delayed autocatalytic behavior" of Mn(II) ions, rate equations satisfying observations for both catalytic and noncatalytic routes have been presented. The reaction shows first-order dependence on permanganate ions and sarcosine concentrations in both catalytic and noncatalytic pathways, and apparent first-order dependence on Mn2+ ions in catalytic pathways. The correspondence of pseudo-order rate constants of the catalytic and noncatalytic pathways to Arrhenius and Eyring laws has verified "critical ratio" as well as "delayed autocatalytic behavior" concepts. The activation parameters associated with both pathways have been computed and discussed. Mechanisms for both catalytic and noncatalytic routes involving radical intermediates as well as a product having a diketopiperazine skeleton have been reported for the first time. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 689,703, 2009 [source]

Effect of surfactant micelles on the kinetics of oxidation of D -fructose by cerium(IV) in sulfuric acid medium

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2006
Kabir-ud-Din
Kinetics of the oxidation of D -fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first-order kinetics each in [cerium(IV)] and [D -fructose] and inverse first order in [H2SO4]. The Arrhenius equation is found to be valid for the reaction between 30,50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant Ks that equals to 286 mol,1 dm3 is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na2SO4, NaNO3, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18,25, 2006 [source]

Synthesis and characterization of polyaniline films using Fenton reagent

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008
M. M. Ayad
Abstract The chemical oxidation of aniline to form polyaniline (PANI) films and powder samples was made using Fenton reagent as an oxidizing agent in aqueous sulfuric acid medium. The PANI films were monitored by using the quartz crystal microbalance and the electronic absorption techniques. The optimum concentration was determined and the results were justified by measuring the UV,vis absorption spectra for the in situ PANI films. The conductivity for the PANI films and powder samples, prepared in different conditions, was measured. Also, the IR spectra, X-ray and the thermogravimetric analysis for the PANI powder formed in the bulk were measured and compared with the polymer prepared using ammonium peroxydisulfate. A preliminary investigation to the dielectric properties of the polymer powder was measured and discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Impedance measurements on oxide films on aluminium obtained by pulsed tensions

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2003
K. Belmokre
Anodisation; Elektrochemische Impedanzspektroskopie (EIS); pulsierende Spannung; Alterung von Oxidfilmen Abstract We have performed this study on oxide films sealed or not in boiling water. The films are first obtained on type 1050 A aluminium substrat by pulsed tensions anodizing technique, in a sulfuric acid solution. Afterwards the, Electrochemical Impedance Spectroscopy (EIS) is employed to appreciate the films behaviour in a neutral solution of 3.5% K2SO4, in which the interface processes interest only the ageing phenomenon of the oxide films and not their corrosion. We have also attempted a correlation between pulse parameters of anodization and the electrical parameters characterizing these films. The sealing influence on ageing has been studied as well. For all films, ageing is appreciated using impedance diagrams evolution versus time. The results show: , the existence of two capacitive loops confirming the presence of two oxide layers characteristic of oxide films obtained in a sulfuric acid medium. The first loop, at high frequencies, is related to the external porous layer and the second one, at lower freqencies, is related to the internal barrier layer. , the thickness of the barrier layer varies between 25 and 40 nm in relation with the electrical pulse parameters. , the sealing acts favorably against anodic oxide films ageing. Impedanzmessungen an durch pulsierende Spannung erzeugten Oxidfilmen auf Aluminium Die vorliegenden Untersuchungen wurden an versiegelten und nicht versiegelten Oxidfilmen in kochendem Wasser durchgeführt. Die Filme wurden zuerst auf Aluminiumsubstrat des Typs 1050A durch anodische Technik mit pulsierender Spannung in einer Schwefelsäurelösung erzeugt. Anschließend wurde die elektrochemische Impedanzspektroskopie eingesetzt, um das Filmverhalten in einer neutralen 3,5% K2SO4 -Lösung zu beurteilen, wobei bezüglich der Grenzflächenprozesse nur das Alterungsphänomen der Oxidfilme und nicht ihr Korrosionsverhalten interessierte. Es wurde versucht, eine Korrelation zwischen den Pulsparametern der Anodisierung und den elektrischen Parametern, die diese Filme charakterisieren, zu finden. Ebenfalls wurde der Versiegelungseinfluss auf die Alterung untersucht. Für alle Filme wurde die Alterung mit Hilfe der Entwicklung von Impedanzdiagrammen über die Zeit beurteilt. Die Ergebnisse zeigen: , die Existenz von zwei kapazitiven Schleifen, die die Anwesenheit von zwei Oxidschichten bestätigen, was charakteristisch ist für Oxidfilme, die in einer Schwefelsäurelösung erzeugt wurden. Die erste Schleife, bei hohen Frequenzen, bezieht sich auf die äußere poröse Schicht und die zweite, bei niedrigeren Frequenzen, bezieht sich auf die innere Barriereschicht , die Dicke der Barriereschicht variiert zwischen 25 und 40 nm, abhängig von den elektrischen Pulsparametern , die Versiegelung wirkt günstig gegenüber der Alterung des anodischen Oxidfilms. [source]