Chemical, Hr-Xrd and Spectroscopic Approaches to Short-Time Dissolution Behavior of Kaolin1tic Soils

1996 ◽  
Vol 432 ◽  
Author(s):  
N. Malengreau ◽  
G. Sposito
Keyword(s):  
Solid Phase ◽  
Release Kinetics ◽  
Ph Dependence ◽  
Significant Loss ◽  
Dissolution Behavior ◽  
X Ray Diffraction ◽  
Spin Resonance ◽  
Ph Range ◽  
Short Time ◽  
Kinetics Of

AbstractBatch experiments were conducted at varying proton concentrations on a representative tropical soil in order to investigate its dissolution behavior over a 12h period. The release kinetics of Al, Fe, Si and C were investigated over a 2 to 6 pH range. The pH-dependence exhibited a “point of minimum dissolution” at pH ≈ p.z.n.c. Light scattering measurements on supernatant solutions indicated that colloids were dispersed mainly at pH > p.z.n.c. These results suggested a two-pathway dissolution process, with organic matter playing a role in both pathways. High-resolution X-ray diffraction as well as electron spin resonance and diffuse reflectance spectroscopies, were applied to characterize solid-phase transformations in the course of dissolution. With the exception of quartz, all mineralogical phases (kaolinite, and minor phases such as Fe-, Al- and Ti-oxides) remained unchanged or were slightly affected. A significant loss of quartz (about 10% by mass) was observed after a 12h dissolution at pH 2. Minor phases might have played an important role in stabilizing kaolinite, and dissolved silica may have hindered the dissolution of minor phases.

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

A nuclear magnetic resonance study of the equilibria and kinetics of the reaction of penicillamine with cystine and related disulfides

1985 ◽  
Vol 63 (8) ◽  
pp. 2225-2231 ◽  
Author(s):  
Yvon Theriault ◽  
Dallas L. Rabenstein
Keyword(s):  
Random Distribution ◽  
Ph Dependence ◽  
Thiol Group ◽  
Nuclear Magnetic Resonance Study ◽  
Mercaptoacetic Acid ◽  
Exchange Reactions ◽  
H Nmr ◽  
Mixed Disulfide ◽  
Ph Range ◽  
Kinetics Of

The thiol/disulfide exchange reactions of penicillamine (PSH) with cystine and several related disulfides (RSSR) have been studied by 1H nmr. The reactions take place in two steps:[Formula: see text]The equilibria and kinetics of the reactions of PSH with cystine were characterized over the pH range 5–8, while the reactions with the disulfides of cysteamine, homocysteine, 2-mercaptoethanol, mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptosuccinic acid were studied at neutral pH. From the pH dependence of the rate of the reaction of PSH with cystine, the reactive species are identified as penicillamine with its amino group protonated and its thiol group deprotonated and cystine and penicillamine–cysteine mixed disulfide with their amino groups protonated. For all the disulfides studied, the extent to which the first reaction occurs is within a factor of 2–3 of that predicted by a random distribution, while the extent to which the second reaction occurs is considerably less than for a random distribution. This is attributed to steric effects due to the two methyl groups next to the sulfur of penicillamine.

X-Ray Diffraction Analysis of Oxide Layers of Zr-Based Alloys

2007 ◽  
Vol 567-568 ◽  
pp. 237-240
Author(s):  
Galina Gosmanová ◽  
Ivo Kraus ◽  
Michal Kolega ◽  
Věra Vrtílková
Keyword(s):  
Residual Stresses ◽  
Diffraction Analysis ◽  
X Ray Diffraction ◽  
Transient Conditions ◽  
Oxide Layers ◽  
X Ray ◽  
Corrosion Kinetics ◽  
Short Time ◽  
Kinetics Of ◽  
Tubular Specimens

The results of X-ray diffraction analysis of macroscopic stresses σ and crystallite size D in oxide layers are presented in this contribution. The oxide layers were formed on tubular specimens of Zircaloy 4 and Zr1Nb alloys which were simultaneously oxidized for various times under temperature transient conditions (oxidation in water at 360 °C with a short-time shock in steam at 500 °C). A qualitative relation was outlined between the residual stresses in oxide layers and corrosion kinetics of the alloys under investigation.

Studies on Horseradish Peroxidase. VII. A Kinetic Study of the Oxidation of Iodide by Horseradish Peroxidase Compound II

1971 ◽  
Vol 49 (18) ◽  
pp. 3059-3063 ◽  
Author(s):  
R. Roman ◽  
H. B. Dunford ◽  
M. Evett
Keyword(s):  
Ionic Strength ◽  
Horseradish Peroxidase ◽  
Kinetic Study ◽  
Rate Constant ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Acid Dissociation ◽  
Ph Range ◽  
Compound Ii ◽  
Kinetics Of

The kinetics of the oxidation of iodide ion by horseradish peroxidase compound II have been studied as a function of pH at 25° and ionic strength of 0.11. The logarithm of the second-order rate constant decreases linearly from 2.3 × 105 to 0.1 M−1 s−1 with increasing pH over the pH range 2.7 to 9.0. The pH dependence of the reaction is explained in terms of an acid dissociation outside the pH range of the study.

scholarly journals Synthesis and Characterization of Erythromycin Loaded PLGA and PCL Microspheres: Antimicrobial Application

2021 ◽  
Author(s):  
Lamia Bennabi ◽  
Ilham Abedelemalek ◽  
Abedelkader Ammari ◽  
Khaldia Sediri ◽  
Fatima Bennabi ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Glycolic Acid ◽  
Release Kinetics ◽  
Synthesis And Characterization ◽  
X Ray Diffraction ◽  
X Ray ◽  
Complementary Effect ◽  
Kinetics Of ◽  
Scanning Electron

Abstract We presents in this work the preparation of several formulations, based on biocompatible biodegradable polymers: polycaprolactone (PCL) and poly(lactic-co-glycolic) acid (PLGA) loaded with Erythromycin (ERYT) antibiotic. These biocompatible materials were used to prepare microspheres with and without immobilized ERYT via simple evaporation method by simple emulsion. The particle size was determined by scanning electron microscopy and the absence of the interaction with ERYT was confirmed via X-ray diffraction and infrared spectroscopy. The release kinetics of ERYT were studied and then, ERYT loaded PCL and PLGA blends microspheres were used for the inhibition of gram-positive S. aureus strain. The microbial activity was carried-out by Agar diffusion disc method. The results show that PCL/PLGA blend and PCL alone inhibited the strain by ERYT present in kinetic aliquots with the complementary effect of the polymers. A numerical model was proposed for modeling the kinetics reported in our study.

Kinetics and Mechanism of Ligand Substitution in Binuclear Copper(II) Complexes as Model Compounds for Hemocyanin

1990 ◽  
Vol 45 (5) ◽  
pp. 607-618 ◽  
Author(s):  
Siegfried Schindler ◽  
Horst Elias ◽  
Helmut Paulus
Keyword(s):  
Ph Dependence ◽  
Orthorhombic Space Group ◽  
Electronic Interactions ◽  
Pyridine Complex ◽  
Amine Complex ◽  
Kinetic Effects ◽  
Ph Range ◽  
Group D ◽  
Kinetics Of ◽  
Ethyl Amine

A series of binuclear, hydroxyl-bridged copper(II) complexes 1-10 with the general formula [Cu2(LR2D2)(OH)](ClO4)2 was prepared and characterized. The mono basic, five- or sevendentate ligands HLR2D2 were obtained either by reduction of the Schiff bases derived from the condensation of 2,6-diformyl-4-methylphenol and the amines H2N – D (complex 1: D = -(CH2)2-NH2; 2: -(CH2)2-NMe2; 3: -(CH2)2-NEt2; 4: -(CH2)3-NEt2; 5: -(CH2)2-4-imidazolyl; 6: -CH2-2-pyridyl; 7: -(CH2)2-2-pyridyl) or by reacting 2,6-di-(chloromethyl)-4-methylphenol with 2-[(2-methylamino)ethyl]pyridine (complex 8), Ν,Ν,N′,N′-tetraethyldiethylenetriamine (complex 9) or bis[2-(2-pyridyl)ethyl]amine (complex 10) under HC1 elimination. The UV/VIS spectra of complexes 1-8 with two four-coordinate copper centers and of 9 and 10 with two five-coordinate copper centers are discussed. An X-ray structure analysis of complex 6 (= [Cu2(LR2D2)(OH)](ClO4)2 with R = H and D = -CH2-2-pyridyl) was carried out. 6 crystallizes in the orthorhombic space group Pbca and the two copper centers have practically co-planar, doubly O-bridged cis-N2O2 coordination geometries with one perchlorate anion being weakly coordinated to each copper. Stopped-flow spectrophotometry was used to study the kinetics of copper removal from [Cu2(LR2D2)(OH)]2+ with EDTA in the pH range 8.5-6.6 at 20 °C and I = 0.2 M (NaClO4). The reaction is first-order in both complex and EDTA, the rate law being: rate = k[complex][EDTA]total. At pH 8.0 second-order rate constants k range from 40.3 x 103 M -1s-1 (complex 6) to 3.72x 10-2 M-1s-1 (complex 9). It follows from the pH dependence of k that both species H2EDTA2- and HEDTA3- react independently with [Cu2(LR2D2)(OH)]2+, the reactivity of H2EDTA2- being considerably greater than that of HEDTA3-. The experimental facts support the operation of an associative (A) mechanism with the removal of the first copper being rate-controlling. The kinetic effects of the donor group D and substituent R are attributed to steric and/or electronic interactions.

Kinetik der Reaktion von Papain mit Bromacetamid / Kinetics of the reaction of papain with bromoacetamide

1971 ◽  
Vol 26 (1) ◽  
pp. 43-46 ◽  
Author(s):  
Hans-Gerhard Löffler ◽  
Friedhelm Schneider ◽  
Helmut Wenck
Keyword(s):  
Rate Constants ◽  
Turning Point ◽  
Ph Dependence ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Ph Range ◽  
Kinetics Of

The pH-dependence of the second order rate constants of the reaction of papain with bromoacetamide in the pH-range 5,5-8,5 is described by a curve with a turning point corresponding to a pK 7,3 ± 0,1 at 25°. This is the pK of a catalytically essential imidazole residue. The activation parameters of the reaction of papain with bromoacetamide were determined. The second order rate constants at pH 7 for the reaction is 200 times greater than for the reaction of bromoacetamide with simple SH-compounds.

Effect of ECAP Strain on the Precipitation Kinetics of the AlMg3 Aluminium Alloy

2018 ◽  
Vol 275 ◽  
pp. 3-14
Author(s):  
Przemysław Snopiński ◽  
Tomasz Tański
Keyword(s):  
Aluminium Alloy ◽  
Grain Refinement ◽  
Shear Bands ◽  
Solution Treatment ◽  
Artificial Ageing ◽  
X Ray Diffraction ◽  
Angular Pressing ◽  
Solution Treated ◽  
Short Time ◽  
Kinetics Of

Variation of hardness and microstructure evolution in a solution treated AlMg3 aluminium processed by equal channel angular pressing and subjected to subsequent artificial ageing are investigated. The microstructure features of the UFG aluminium alloy are studied by light, electron microscopy and using X-ray diffraction analysis. Microstructural observations showed significant grain refinement. After four ECAP passes microstructure consist of elongated grains with average widths of shear bands of ∼100 nm. A significant increase in the microhardness was observed in the ECAPed samples due to the grain refinement and strain hardening. Prior ECAP solution treatment and a short time artificial ageing can additionally increase the strength of AlMg3 aluminium alloy.

Studies on Horseradish Peroxidase. XII. A Kinetic Study of the Oxidation of Sulfite and Nitrite by Compounds I and II

1973 ◽  
Vol 51 (4) ◽  
pp. 588-596 ◽  
Author(s):  
R. Roman ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Ground State ◽  
Ph Dependence ◽  
Intermediate Formation ◽  
Ion Concentration ◽  
Compound I ◽  
Hydrogen Ion Concentration ◽  
Ph Range ◽  
Compound Ii ◽  
Kinetics Of

The kinetics of the oxidation of sulfite and nitrite by horseradish peroxidase compounds I and II have been studied as a function of pH at 25° and ionic strength 0.11. The pH dependence of the rate of the reaction between compound I and sulfite over the pH range 2–7 is interpreted in terms of two ground state enzyme dissociations with pka values of 5.1 and 3.3, and that for the compound II reaction with sulfite in terms of a single ground state enzyme dissociation with a pKa value of 3.9. Whereas the reaction between compound I and sulfite produces the native enzyme without the intermediate formation of compound II, the reaction of compound I with nitrite yields compound II. The second-order rate constants for the reactions of compounds I and II with nitrite increase linearly with increasing hydrogen ion concentration over the pH range 6–8.

Solubility of Niobium(V) under Cementitious Conditions: Importance of Ca-niobate

2004 ◽  
Vol 824 ◽  
Author(s):  
Caterina Talerico ◽  
Michael Ochs ◽  
Eric Giffaut
Keyword(s):  
Solid Phase ◽  
Empirical Relation ◽  
Oxide Phase ◽  
X Ray Diffraction ◽  
Ph Values ◽  
Wide Range ◽  
Ph Conditions ◽  
Predicted Values ◽  
Ph Range ◽  
Good Agreement

AbstractThe solubility of niobium was investigated for Ca and pH conditions relevant for cementequilibrated solutions. For the pH range considered (9.5-13.2), the dissolved Nb concentration decreases with increasing pH. Overall, experiments lead to Nb concentrations between 2·10-5 M and 2·10-9 M. For all pH values, the dissolved Nb concentration also decreases systematically with increasing Ca concentration. X-ray diffraction measurements of selected experiments confirmed the presence of a solid Ca-Nb-oxide phase, with CaNb4O11·8H2O (hochelagaite) being the most likely composition. On the basis of these findings an empirical regression model for the prediction of Nb solubility data as a function of pH and Ca concentration was derived. This empirical relation is consistent with the presence of a solubility limiting Ca-Nb solid phase and permits to predict aqueous Nb solubility values in cementitious environments over a relatively wide range of conditions. Predicted values are in good agreement with independent experimental results.

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