The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Patrick S. Nicholson - One of the best experts on this subject based on the ideXlab platform.
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Influence of Acidity on the stability and rheological properties of ionically stabilized alumina suspensions in ethanol
Journal of the American Ceramic Society, 2004Co-Authors: Gonghou Wang, Patrick S. NicholsonAbstract:The ionic stability of alumina particles in moderately concentrated ethanol suspensions is studied. Surface chemistry and interparticle forces are manipulated by controlling the Acidity of the suspensions without dispersants. The Acidity of ethanol solution is determined using ion transfer functions, wherein the relationships between Acidity, alumina particle surface charge, zeta-potential, stability, and suspension rheological behavior are established. Positive isoelectric point (IEP) shift is observed for alumina in ethanol on increasing the solids concentration. However, dilute and concentrated aqueous suspensions of alumina give the same IEP. The viscosity and flow curves for alumina/ethanol suspensions are Acidity dependent. The flow curves of the suspensions follow the Casson model, and the Casson yield value is used to evaluate suspension stability.
Gonghou Wang - One of the best experts on this subject based on the ideXlab platform.
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Influence of Acidity on the stability and rheological properties of ionically stabilized alumina suspensions in ethanol
Journal of the American Ceramic Society, 2004Co-Authors: Gonghou Wang, Patrick S. NicholsonAbstract:The ionic stability of alumina particles in moderately concentrated ethanol suspensions is studied. Surface chemistry and interparticle forces are manipulated by controlling the Acidity of the suspensions without dispersants. The Acidity of ethanol solution is determined using ion transfer functions, wherein the relationships between Acidity, alumina particle surface charge, zeta-potential, stability, and suspension rheological behavior are established. Positive isoelectric point (IEP) shift is observed for alumina in ethanol on increasing the solids concentration. However, dilute and concentrated aqueous suspensions of alumina give the same IEP. The viscosity and flow curves for alumina/ethanol suspensions are Acidity dependent. The flow curves of the suspensions follow the Casson model, and the Casson yield value is used to evaluate suspension stability.
Richard T Bush - One of the best experts on this subject based on the ideXlab platform.
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Liberation of Acidity and arsenic from schwertmannite: Effect of fulvic acid
Chemical Geology, 2014Co-Authors: Chamindra L. Vithana, Leigh A Sullivan, Edward D Burton, Richard T BushAbstract:Abstract Schwertmannite is one of the major components that produces Acidity in acid mine drainage (AMD) and acid sulfate soils (ASS) and is also known to be an effective scavenger of Arsenic (As) in such environments. Fulvic acid (FA) is an active component of natural organic matter (NOM) and is known to interact strongly with both schwertmannite and As. Two main environmental hazards related to schwertmannite are Acidity liberation and potential re-mobilization of adsorbed or co-precipitated As upon hydrolysis. This study focused on understanding the behaviour of As-substituted schwertmannite with regard to the potential of Acidity liberation, the effect of FA on Acidity liberation from both pure and As-substituted synthetic schwertmannites, and the effect of FA on arsenic mobilization from As-substituted synthetic schwertmannite. This was investigated by means of short-term (48 h) titrations. The liberation of Acidity from As-substituted schwertmannite and the effect of FA were examined at two pH values (i.e. 4.5 and 6.5) typical for ASS environments. As-substituted schwertmannite liberated a greater amount of Acidity in comparison to pure schwertmannite at both pHs. Concentration of FA and pH each showed a strong influence on the liberation of Acidity from both pure and As-schwertmannite. At the acidic pH (4.5), FA inhibited Acidity liberation from schwertmannite. At the near neutral pH of 6.5, the concentration of FA played a critical role in affecting the liberation of Acidity from schwertmannite. The initial liberation of Acidity was enhanced from pure schwertmannite at pH 6.5 by low FA concentration (1 mg L− 1) and from As-schwertmannite by both low (1 mg L− 1) and moderate (10 mg L− 1) FA concentrations. Interestingly, higher FA concentrations (25 mg L− 1) inhibited Acidity liberation from both types of schwertmannite in comparison to the control (pure/As-schwertmannite titrated without added FA). FA enhanced the liberation of As from the As-schwertmannite at both pHs under oxidising conditions and the rate of As liberation was greater at the near neutral pH. The present study provides new insights on the effect of As-substitution on Acidity liberation from schwertmannite and the role of FA on: a) liberation of Acidity, and b) As mobilization, from schwertmannite.
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Acidity fractions in acid sulfate soils and sediments: contributions of schwertmannite and jarosite
Soil Research, 2013Co-Authors: Chamindra L. Vithana, Leigh A Sullivan, Richard T Bush, Edward D BurtonAbstract:In Australia, the assessment of Acidity hazard in acid sulfate soils requires the estimation of operationally defined Acidity fractions such as actual Acidity, potential sulfidic Acidity, and retained Acidity. Acid–base accounting approaches in Australia use these Acidity fractions to estimate the net Acidity of acid sulfate soils materials. Retained Acidity is the Acidity stored in the secondary Fe/Al hydroxy sulfate minerals, such as jarosite, natrojarosite, schwertmannite, and basaluminite. Retained Acidity is usually measured as either net acid-soluble sulfur (SNAS) or residual acid soluble sulfur (SRAS). In the present study, contributions of schwertmannite and jarosite to the retained Acidity, actual Acidity, and potential sulfidic Acidity fractions were systematically evaluated using SNAS and SRAS techniques. The data show that schwertmannite contributed considerably to the actual Acidity fraction and that it does not contribute solely to the retained Acidity fraction as has been previously conceptualised. As a consequence, SNAS values greatly underestimated the schwertmannite content. For soil samples in which jarosite is the only mineral present, a better estimate of the added jarosite content can be obtained by using a correction factor of 2 to SNAS values to account for the observed 50–60% recovery. Further work on a broader range of jarosite samples is needed to determine whether this correction factor has broad applicability. The SRAS was unable to reliably quantify either the schwertmannite or the jarosite content and, therefore, is not suitable for quantification of the retained Acidity fraction. Potential sulfidic Acidity in acid sulfate soils is conceptually derived from reduced inorganic sulfur minerals and has been estimated by the peroxide oxidation approach, which is used to derive the SRAS values. However, both schwertmannite and jarosite contributed to the peroxide-oxidisable sulfur fraction, implying a major potential interference by those two minerals to the determination of potential sulfidic Acidity in acid sulfate soils through the peroxide oxidation approach.
P. C. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Surface Acidity of solid pharmaceutical excipients. II: Effect of the surface Acidity on the decomposition rate of acetylsalicylic acid
European Journal of Pharmaceutics and Biopharmaceutics, 1995Co-Authors: B. W. Glombitza, P. C. SchmidtAbstract:The aim of this study was to adjust the surface Acidity (pHeq) of dicalcium phosphate anhydrous (DCP) by granulation with buffer solutions and to evaluate the influence of the surface Acidity on the decomposition rate of a hydrolyzable drug. The surface acidities of excipients were determined by application of a spectrophotometric method, using pH indicators. Acetylsalicylic acid (ASA) was used as the model hydrolyzable drug. Stability studies were performed with the surface Acidity adjusted using excipients coated with ASA at 30 o C, 12% relative humidity (r.h.) and 30 o C, 56% r.h. Decomposition rate constants were calculated using a model based on a power function. As result, surface Acidity-decomposition-rate profiles were drawn and compared to pH rate profiles of ASA in solution. It was shown that surface Acidity-decomposition-rate profiles were similar to pH-rate profiles of ASA in solution. This effect was attributed to decomposition taking place in water layers around the particles
A J Smout - One of the best experts on this subject based on the ideXlab platform.
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24-h Recording of Intragastric pH: Technical Aspects and Clinical Relevance
Scandinavian Journal of Gastroenterology, 1999Co-Authors: M A Van Herwaarden, M Samsom, A J SmoutAbstract:BACKGROUND: Information about gastric acid secretion and gastric Acidity can be obtained using several techniques but, presently, continuous intragastric pH recording is probably the one applied most frequently. This paper aims to review the technical aspects and some important applications of intragastric pH monitoring in research and clinical practice. METHODS: Literature review. RESULTS: Most studies on intragastric pH are performed with either glass or antimony electrodes. Optimal measurement of 24-h intragastric pH requires accurate calibration of the pH measuring system, exact positioning of the pH electrodes, and a sufficient sample rate. Depending on the aim of the study the results of intragastric pH monitoring are expressed either as median H+ activity or as median pH values. Gastric Acidity shows a circadian rhythm, modified by buffering meals and nocturnal duodenogastric reflux. In health, age, gender and smoking habits are known to influence gastric Acidity. In duodenal ulcer disease an increased gastric Acidity is found and in patients with gastric ulcer gastric Acidity is decreased. In GERD, no relation between reflux oesophagitis and gastric Acidity is found. Helicobacter pylori affects intragastric pH most pronounced during acid inhibitory therapy, both in DU patients and in healthy subjects. In the absence of H. pylori the effect of proton-pump inhibitors on intragastric pH is much less than in the presence of the microorganism, whereas the effect of ranitidine on intragastric pH is barely affected by the H. pylori status. CONCLUSIONS: Despite some limitations, intragastric pH monitoring provides important information about gastric acidit
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24-h recording of intragastric pH: technical aspects and clinical relevance.
Scandinavian journal of gastroenterology. Supplement, 1999Co-Authors: M A Van Herwaarden, M Samsom, A J SmoutAbstract:Information about gastric acid secretion and gastric Acidity can be obtained using several techniques but, presently, continuous intragastric pH recording is probably the one applied most frequently. This paper aims to review the technical aspects and some important applications of intragastric pH monitoring in research and clinical practice. Literature review. Most studies on intragastric pH are performed with either glass or antimony electrodes. Optimal measurement of 24-h intragastric pH requires accurate calibration of the pH measuring system, exact positioning of the pH electrodes, and a sufficient sample rate. Depending on the aim of the study the results of intragastric pH monitoring are expressed either as median H+ activity or as median pH values. Gastric Acidity shows a circadian rhythm, modified by buffering meals and nocturnal duodenogastric reflux. In health, age, gender and smoking habits are known to influence gastric Acidity. In duodenal ulcer disease an increased gastric Acidity is found and in patients with gastric ulcer gastric Acidity is decreased. In GERD, no relation between reflux oesophagitis and gastric Acidity is found. Helicobacter pylori affects intragastric pH most pronounced during acid inhibitory therapy, both in DU patients and in healthy subjects. In the absence of H. pylori the effect of proton-pump inhibitors on intragastric pH is much less than in the presence of the microorganism, whereas the effect of ranitidine on intragastric pH is barely affected by the H. pylori status. Despite some limitations, intragastric pH monitoring provides important information about gastric Acidity.
