Influence of Ionic Strength and pH-value on the Silicon Dioxide Polishing Behaviour of Slurries Based on Pure Silica Suspensions

2010 ◽  
Vol 1249 ◽  
Author(s):  
Ulrich Kuenzelmann ◽  
Kathrin Estel ◽  
Johann W Bartha ◽  
Erwin-Peter Meyer ◽  
Herbert Barthel
Keyword(s):  
Ionic Strength ◽  
Fumed Silica ◽  
Ph Value ◽  
Acidic Ph ◽  
Experimental Conditions ◽  
Ph Values ◽  
Pure Silica ◽  
Silica Sols ◽  
Ph Range ◽  
Silica Suspensions

AbstractIn this study, the effect of the addition of electrolytes in a given ionic strength to various high-purity silica suspensions was investigated by measurement of the removal rates (RR's) in CMP processes on oxide layers under the same experimental conditions. As so-called slurries the following suspensions were used: i) silica sols produced by the Stöber process, ii) conventional silica sols based on alkali silicate as well as iii) suspensions of fumed silica, with the same SiO2 concentration in each suspension. Ionic strength of the added electrolyte was adjusted to e.g. 0.065 mol/l, with the electrolytes being HCl, NH4Cl, KOH, or binary mixtures of these substances.These investigations revealed significant differences of the polishing behaviour between the different types of silica dispersions as slurries. While for the Stöber sols investigated, the RR's are highest in the acidic range and almost negligible in the alkaline pH range, fumed silica suspensions show an entirely different behaviour: RR is very low for acidic pH-values, and increases with the alkalinity of the slurry. In contrast to these observations, the RR's of slurries based on conventional silica sols are highest around the neutral point, and show a decrease for both more alkaline and acidic pH-values. In comparison to the other two types of material, these suspensions have a high amount of electrolyte background, originating from their manufacturing process.A model is developed to explain these results in a comprehensive manner. It involves effects of the electrolyte type and the ionic strengths as well as influences of the particle size.

scholarly journals Zinc adsorption in highly weathered soils

2008 ◽  
Vol 43 (1) ◽  
pp. 131-139 ◽  
Author(s):  
José Carlos Casagrande ◽  
Marcio Roberto Soares ◽  
Ernesto Rinaldi Mouta
Keyword(s):  
Ionic Strength ◽  
Ph Value ◽  
Batch Adsorption ◽  
Adsorption Mechanisms ◽  
Ionic Strength Effect ◽  
Ph Values ◽  
Effects Of Ph ◽  
Ph Range ◽  
Highly Weathered Soils ◽  
Zinc Adsorption

The objective of this work was to assess the effects of pH and ionic strength upon zinc adsorption, in three highly weathered variable charge soils. Adsorption isotherms were elaborated from batch adsorption experiments, with increasing Zn concentrations (0-80 mg L-1), and adsorption envelopes were constructed through soil samples reactions with 0.01, 0.1 and 1 mol L-1 Ca(NO3)2 solutions containing 5 mg L-1 of Zn, with an increasing pH value from 3 to 8. Driving force of reaction was quantified by Gibbs free energy and separation factor. Isotherms were C-, H- and L-type and experimental results were fitted to nonlinear Langmuir model. Maximum adsorption ranged from 59-810 mg kg-1, and Zn affinity was greater in subsoil (0.13-0.81 L kg-1) than in the topsoil samples (0.01-0.34 L kg-1). Zinc adsorption was favorable and spontaneous, and showed sharply increase (20-90%) in the 4-6 pH range. No effect of ionic strength was observed at pH values below 5, because specific adsorption mechanisms predominated in the 3-5 pH range. Above pH 5, and in subsoil samples, Zn was adsorbed by electrostatic mechanisms, since ionic strength effect was observed. Despite depth and ionic strength effects, Zn adsorption depends mainly on the pH.

scholarly journals Mechanism of the process of decomposition of apatitis with phosphoric acid

2019 ◽  
Vol 81 (1) ◽  
pp. 294-297
Author(s):  
R. F. Sabirov ◽  
A. F. Makhotkin ◽  
Yu. N. Sakharov ◽  
I. A. Makhotkin ◽  
I. Yu. Sakharov
Keyword(s):  
Phosphoric Acid ◽  
Ph Value ◽  
Batch Reactor ◽  
Experimental Studies ◽  
Hydrogen Ions ◽  
Experimental Conditions ◽  
Monocalcium Phosphate ◽  
Ph Values ◽  
Whole Process ◽  
Proportional Increase

Experimental studies of the kinetics and mechanism of the process, decomposition of apatite by phosphoric acid, in the Apatite-H3PO4-H2O system without the addition of sulfuric acid have been performed. The study of the decomposition process of Kovdorsky apatite with certain particle sizes was carried out in a batch reactor with a volume of 1 dm3 with stirring of the reaction mixture, and an initial concentration of phosphoric acid of 17% by weight, at a temperature of 78–82 °C. Observation of the process was carried out by determining the concentration of phosphoric acid and the concentration of monocalcium phosphate. The acidity of the reaction mixture was determined by the pH meter readings (pH-105 MA with a glass combined-ESC-10603 electrode). It was shown that during the whole process a constant smooth increase in the pH value of the reaction mixture to pH 6 occurs. Comparison of the pH values of the reaction mixture during the actual at the time of determining the concentration of phosphoric acid and pH of phosphoric acid of the corresponding concentration in the aqueous solution shows that the pH value of the reaction mixture is significantly affected by the presence of monocalcium phosphate gel. During the process, during the first thirty minutes, the concentration of phosphoric acid decreases from 17 to 10% by weight, the corresponding quantitative formation of monocalcium phosphate gel and a proportional increase in the pH of the reaction mixture. Then, as the concentration of phosphoric acid decreases, the process slows down and does not proceed to the end under the experimental conditions. The dependence of the concentration of hydrogen ions in the reaction mixture on the time of the process of decomposition of apatite in phosphoric acid, which is presented in logarithmic coordinates, shows that the mechanism of formation of hydrogen ions during the whole process does not change. Thus, it is shown that the process of decomposition of apatite by phosphoric acid in the Apatite-H3PO4-H2O system proceeds with the formation of an intermediate product - monocalcium phosphate gel. When this occurs, a corresponding significant change in the pH values of the reaction mixture occurs. During the whole process there is a constant decrease in the concentration of phosphoric acid.

Why is the hydrolytic activity of acetylcholinesterase pH dependent? Kinetic study of acetylcholine and acetylthiocholine hydrolysis catalyzed by acetylcholinesterase from electric eel

2018 ◽  
Vol 73 (9-10) ◽  
pp. 345-351 ◽  
Author(s):  
Alena Komersová ◽  
Markéta Kovářová ◽  
Karel Komers ◽  
Václav Lochař ◽  
Alexander Čegan
Keyword(s):  
Catalytic Activity ◽  
Ionic Strength ◽  
Ph Value ◽  
Hydrolytic Activity ◽  
Initial Substrate ◽  
Electric Eel ◽  
Value Range ◽  
Ph Dependent ◽  
Ph Range ◽  
Initial Substrate Concentration

AbstractThe dependence of the activity of acetylcholinesterase from electric eel at a pH value range of 4.8–9.8 (phosphate buffer), regarding acetylcholine and acetylthiocholine hydrolysis, was determined at 25 °C, ionic strength of 0.11 M, and initial substrate concentration of 4 mM. At a pH range of 4.8–9.8, the dependencesA(pH) form a sigmoid increasing curve with the maximum catalytic activity at a pH range 8–9.5. For acetylcholine hydrolysis, the kinetic reason for such an increase inAconsists mainly of an increase in the rate constantk2(Michaelis-Menten) model with increasing pH of the reaction mixture. For acetylthiocholine hydrolysis, the kinetic explication of the determined dependenceA(pH) is more complicated.

Analysis of conditions for the preparation of BSA/MMT composites

2013 ◽  
Vol 20 (3) ◽  
pp. 221-226 ◽  
Author(s):  
Yinghai Lv ◽  
Xiaolu Su ◽  
Fuli Ren ◽  
Hong-qiang Kan ◽  
Ying Kong
Keyword(s):  
Ionic Strength ◽  
Acetate Buffer ◽  
Acetate Buffer Solution ◽  
Buffer Solution ◽  
Experimental Conditions ◽  
Ph Values ◽  
Fixation Effect ◽  
The Impact ◽  
Adsorption Quantity ◽  
Better Than

AbstractThis study describes a new method for protein fixation that has high, stable, and good repeatable fixation effect without deactivating protein. This method involves intercalating bovine serum albumin (BSA) into montmorillonite (MMT) under different experimental conditions, i.e., the concentration of coupling agent KH570, pH values, ionic strength, and the impact of buffers. The study showed the interaction of buffer systems with pH values had the most significant influence on adsorption quantity. The existence of the buffer increased the adsorption quantity and helped with slow protein releasing, while the phosphate buffer worked better than acetate buffer. More BSA was adsorbed on KH570 treated than untreated MMT, and among the treated samples the most protein released was on MMT treated with KH570 in 100% ethanol and in the acetate buffer solution. Adsorption quantity of the BSA initially increased and then decreased with the increase of the ionic strength. The research on the preparation of MMT/BSA materials provides further information on the study of protein composites.

scholarly journals Experiments and Thermodynamic Modeling of Chukanovite (Fe2(OH)2CO3) to High Ionic Strengths

MRS Advances ◽  
2017 ◽  
Vol 2 (13) ◽  
pp. 747-752 ◽  
Author(s):  
Sungtae Kim ◽  
Justin Dean ◽  
Jandi Knox ◽  
Leslie Kirkes ◽  
Je-Hun Jang
Keyword(s):  
Free Energy ◽  
Ionic Strength ◽  
Room Temperature ◽  
Xrd Analysis ◽  
High Ionic Strength ◽  
Model Parameters ◽  
Second Phase ◽  
Experimental Conditions ◽  
Ph Values ◽  
Decreasing Ph

ABSTRACTWhile conducting siderite (FeCO3) solubility experiments in NaCl-Na2CO3 brines, evidence for a second phase was detected. Experiments, in which synthesized siderite was reacted with high ionic strength (0.18 – 7.5 m) solutions at room temperature and high pH (>10), were conducted in a glovebox. As the aging time of siderite-bearing experiments increased, the pH of the solution decreased, signaling formation of a hydroxyl-bearing phase. Decreasing pH values are interpreted to indicate that a hydroxyl-bearing phase, such as chukanovite, is the reaction controlling solid in the solid assemblage. Chukanovite was tentatively identified by XRD analysis. We set out, therefore, to determine the thermodynamic stability of chukanovite under the experimental conditions. Aqueous thermodynamic model parameters were determined with experimentally analyzed Fe(II) solubility data, and subsequently yielded a proposed formation free energy of chukanovite (-1149.8 kJ/mol).

scholarly journals Immunocytochemical localization of luteinizing hormone-releasing hormone (LHRH) and LHRH-like material in brain. Influence of fixation solution at various pH values.

1983 ◽  
Vol 31 (11) ◽  
pp. 1329-1332 ◽  
Author(s):  
D T Piekut
Keyword(s):  
Luteinizing Hormone ◽  
Pineal Gland ◽  
Ph Value ◽  
Acidic Ph ◽  
Immunocytochemical Localization ◽  
Luteinizing Hormone Releasing Hormone ◽  
Releasing Hormone ◽  
Ph Values ◽  
Rat Pineal Gland ◽  
The Brain

The amount and distribution of luteinizing hormone-releasing hormone (LHRH) immunoreactive (ir) material in the hypothalamus, and of a LHRH-like immunostained substance in the rat pineal gland were examined employing Bouin's and Zamboni's fixation solutions at various pH values, and antisera generated against synthetic LHRH. The hypothalamic LHRH immunoreaction product is optimally visualized in this study when the pH value of the fixation solution is basic; conversely, the pineal LHRH-like ir material is seen only with an acidic pH value of the fixation solution. The present study demonstrates that the pH value of the fixation solution contributes substantially to the amount and distribution of some peptides visualized immunocytochemically in the brain.

An alternative method for serum protein depletion/enrichment by precipitation at mildly acidic pH values and low ionic strength

PROTEOMICS ◽  
2015 ◽  
Vol 15 (11) ◽  
pp. 1935-1940 ◽  
Author(s):  
Ann-Kristin Henning ◽  
Dirk Albrecht ◽  
Katharina Riedel ◽  
Thomas C. Mettenleiter ◽  
Axel Karger
Keyword(s):  
Ionic Strength ◽  
Serum Protein ◽  
Acidic Ph ◽  
Protein Depletion ◽  
Ph Values ◽  
Alternative Method ◽  
Low Ionic Strength

Isotope Effects of Uranium by Ion Exchange in the System Dowex 50 / α-Hydroxyisobutyrate

1974 ◽  
Vol 29 (3-4) ◽  
pp. 190-194 ◽  
Author(s):  
Jorma Aaltonen ◽  
Klaus G. Heumann ◽  
Pikka Pietilä
Keyword(s):  
Ion Exchange ◽  
Isotope Effect ◽  
Separation Factor ◽  
Ph Value ◽  
Isotope Effects ◽  
Uranyl Ions ◽  
Distribution Factor ◽  
Ph Values ◽  
Ion Exchange Column ◽  
Ph Range

In this investigation the isotope effect of uranium in the system Dowex 50 resin/ α- hydroxyisobutyrate solution was studied by mass spectrometry. A recycle ion exchange column was used for the separation experiments. The dependence of the isotope effect on the pH value and on the concentration of the α-hydroxyisobutyrate solution used as eluent was investigated. In the case of a 0.07 ᴍ and a 0.22 ᴍ α-hydroxyisobutyrate solution the elementary separation factor of uranium was calculated to be 1.00019 and 1.00006, respectively. In both cases an enrichment of 235U in relation to 238U was found in the solution.In addition the distribution factor of the uranyl ions in the investigated system was determined in the pH range between 2 and 6. The distribution factor depends strongly on the pH value. With increasing pH values the distribution factor decreases.The results obtained for the elementary separation factor and the distribution factor are compared with other investigations.

The Coagulability of Partially Lysed Fibrinogen Effect of pH and Ionic Strength

1971 ◽  
Vol 25 (02) ◽  
pp. 346-353 ◽  
Author(s):  
D. C Triantaphyllopoulos ◽  
Mary Torres
Keyword(s):  
Ionic Strength ◽  
Human Plasma ◽  
Ammonium Sulfate ◽  
Inverse Relationship ◽  
Ph Value ◽  
Distilled Water ◽  
Human Fibrinogen ◽  
Ph Values ◽  
Ph Dependent ◽  
Limited Digestion

SummaryAddition of thrombin to plasma obtained from dogs injected with plasmin clotted more fibrinogen when the plasma was diluted with saline than when it was diluted with distilled water. In contrast, more fibrin was formed in dilutions with distilled water when thrombin was added to intact plasma obtained prior to the injection of plasmin.The same phenomenon was observed with purified human fibrinogen submitted to limited digestion with plasmin and was found to be pH dependent. When the pH was greater than 7.3 more fibrin was formed if the fibrinogen was diluted with saline than if it was diluted with distilled water. The opposite was observed at pH values lower than 7.2.Similar results were obtained with the fraction of partially lysed human fibrinogen which precipitates at 25% saturation with ammonium sulfate. The same fraction, however, obtained from partially digested bovine fibrinogen did not react exactly the same way. In dilutions with distilled water there was an inverse relationship between the pH value and the amount of protein which clotted; but the reverse did not apply to the same extent in dilutions with saline.At variance to the above observations the clottability of purified intact fibrinogen was not significantly altered by changes in pH or in ionic strength.The clottability of partially lysed human plasma could be reversed (more fibrin in distilled water than in saline) after exhaustive dialysis against oxalated (pH 7.0) but not against citrated (pH 7.8) saline indicating that the change in clottability was due to a change in pH.

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