Interaction of Dowex A-1 chelating resin with sparingly soluble calcium salts

The interaction between Dowex A-1 and sparingly soluble salts obeys the mass action law if no other salts are present in the solution. Increasing the total amount of charged species in the solution causes a decrease in the distribution coefficients of calcium, the decrease being in accordance with a simple function of the concentrations of the sodium ion and the precipitating anion in solution. The relations between the adsorbability and the solubility products have also been derived.     

Mechanism of dissolution of sparingly soluble electrolytes

Recent constant composition dissolution studies of sparingly soluble calcium phosphates have revealed an interesting and unusual behavior in that the rates decreased, eventually resulting in effective suppression, even though the solutions remained undersaturated. Contrary to traditional theories of dissolution, these experimental results indicated the importance of not only the particle size on the dissolution rate but also the participation of critical phenomena. In these theories, it is assumed that when the dissolution reactions are initiated, they continue spontaneously until all solid phase has disappeared. In terms of these mechanisms, there are no critical phenomena in the dissolution mechanism. Although the crystal size decreases during dissolution, when the reaction is controlled by polypitting (formation and growth of pits), the edge free energy increases at the very first stage due to the creation of pits and dissolution steps. The constant composition experimental results demonstrate the development of surface roughness as the dissolution steps are formed, implying an increase of the total edge length during the reactions. In an exactly analogous mechanism to crystal growth, the participation of critical conditions involving dissolution steps is a possibility. In contrast to crystal growth, dissolution is a process of size reduction and, when the particle size is sufficiently reduced, critical phenomena become important so that the influence of size must be taken into consideration. This paper proposes such a model for dissolution reactions, and although these unusual phenomena probably apply to all mineral phases, they are more evident for sparingly soluble electrolytes in which the critical conditions are attained much more readily.     

Homogeneous nucleation of some sparingly soluble salts

The homogeneous nucleation of barium, strontium and lead sulphates and lead carbonate has been studied by particle counting, and values for the interfacial tension and radius of each critical nucleus calculated. The changes in crystal size and shape that occur near S(crit) are reported.     

Solubility and thermodynamic studies of sparingly soluble tellurite salts

Journal of Thermal Analysis and Calorimetry - In the past few years, tellurium has attracted much attention as it is widely used in a large number of important industrial applications. Despite its...     

Nucleation and the interfacial tension of sparingly soluble salts

Summary Critical supersaturations required for the onset of homogeneous nucleation of sparingly soluble salts from solution have been determined by nephelometry. The data so obtained are used, in conjunction with nucleation theory, to calculate values for the interfacial tension and radius of the critical nucleus. The dimensions of these critical nuclei are close to those of the unit cell and consequently relatively few ions are involved in the nucleation of crystals in solution.

---

Zusammenfassung Die für den Beginn homogener Keimbildung in Lösungen schwerlöslicher Salze nötige kritische Übersättigung wurde nephelometrisch bestimmt. Die Ergebnisse wurden in Zusammenhang mit der Theorie der Keimbildung zur Berechnung der Oberflächenspannung und des Radius der kritischen Keime verwendet. Deren Ausmaße entsprechen weitgehend denen einer Kristalleinheit.Es sind also nur relativ wenige Ionen an der Bildung von Kristallisationskeimen in einer Lösung beteiligt.

---

Résumé On a déterminé par néphélométrie les sursaturations critiques nécessaires pour l'attaque de la nucléation homogène de sels à peine solubles dans la solution. Les chiffres obtenus de cette manière, en accord avec la théorie de la nucléation, sont utilisés pour le calcul des valeurs de la tension interfaciale et du rayon du germe critique. Les dimensions de ces germes critiques sont liées à celles de la maille, et par conséquent relativement peu d'ions sont mis en jeu dans le phénomène de germination des cristaux en solution.

     

Interaction between water soluble polymers and surfactants

Based on literature data and some own results a short review of regularities, driving forces and mechanisms of interaction for different classes of polymers and surfactants is given. The main investigation methods of polymer‐surfactant systems are described.     

The nucleation of sparingly soluble salts from solution

The relationship between heterogeneous and homogeneous nucleation of sallts from solution has been examined. These concepts enable both new and older published data to be interpreted in terms of the Volmer-Becker-Döring theory. The results and some of their implications in surface chemistry and crystallization processes are discussed.     

Kinetics and precipitation mechanism of sparingly soluble alkaline earth sulfates

Summary Phenotypical and genotypical characteristics of the precipitation phenomena of barium, strontium and calcium sulfates have been determined and compared to each other. The kinetics of the transition from homogeneous dynamic systems into heterogeneous quasi static systems have been investigated by tyndallometric light scattering technique, by electrophoretic determination the charge sign on particles. In the obtained general precipitation diagrams stress the outer precipitate — clear solution boundaries as well as discontinuities in the structure of the precipitate itself.

---

Zusammenfassung Es wurden phenotypische und genotypische Eigenschaften der Präzipitationsprozesse von Barium-, Strontium- und Calcium-Sulfat bestimmt.Die Kinetik wurde mittels der Lichtstreuungsmethode und elektrophoretischer Bestimmungen untersucht.Die Ergebnisse wurden in Präzipitationsdiagrammen dargestellt.

---

---

With 3 figures     

Incorporation of sparingly soluble species in mesostructured surfactant-polymer films

Recently we have investigated the formation of novel thick, solid, mesostructured films of polymer/surfactant mixtures which form spontaneously at the air-solution interface. Here we report studies of the effect of adding a series of sparingly soluble species to the precursor solution, to alter the mesostructure of cetyltrimethylammonium bromide/polyethylenimine films and to investigate the incorporation of small molecules within the films. Small-angle neutron scattering confirmed that cyclohexane and decane evenly swell the micelles in film forming solutions, while cyclohexanol extends the prolate micelles along their long axis. Although the presence of these additives in solution did not greatly affect the formation of the film, it was observed that they did influence the structure of the films. Films produced with decane consisted of a cubic phase rather the conventional 2-D hexagonal phase, whilst both cyclohexane and cyclohexanol enhance the level of ordering in low MW polymer films. Benzene was found to have no significant effect on the film.     

Potentiometric investigation of sparingly soluble metal-ligand systems using metal-ion buffers

A novel approach based on metal-ion buffers has been used to determine metal-ligand formation constants for a variety of sparingly soluble systems. It is suggested that the approach will be particularly useful in the study of metal binding by pharmaceuticals.     

Motion and dissolution of drops of sparingly soluble alcohols on water

The dissolution of liquids with low mutual solubility is typically slow. However, drops of sparingly soluble, low-density, low-surface-tension liquids often dissolve rapidly on water due to surface tension instabilities and gradients. We report observations of the motion and dissolution of drops of aliphatic alcohols of a wide range of alkyl chain lengths as they dissolve in water. The alcohol drops are rendered visible by adding small amounts of iodine or other dyes. These drops display dewetting instabilities, fragmentation, fingering, and oscillation. As the length of the alcohol carbon chain increases from n = 4 to n = 9, dissolution slows dramatically. The roles of alcohol solubility and water surface area in promoting rapid dissolution are discussed.     

Thermometric and other titrations of sparingly soluble compounds in aqueous micellar media

Several organic acids and bases that are very sparingly soluble in water have been determined by acid-base and redox titrimetry after solubilizing them in micellar suspensions of sodium dodecylsulfate or cetyltrimethylammonium bromide. Thermometric titrations are much more rapid, convenient, accurate, and precise than the corresponding potentiometric ones. Titrations in such media can effect some differentiations that cannot be made in water and are also much more economical than titrations in non-aqueous solvents.     

Effect of phosphonic and carboxylic acids on crystallization of sparingly soluble salts

The mechanism of the action of phosphonic and carboxylic acids on the nucleation and crystal growth of carbonates has been studied under sedimentation-simulating conditions.     

Interaction forces between waterborne bacteria and activated carbon particles

Activated carbons remove waterborne bacteria from potable water systems through attractive Lifshitz-van der Waals forces despite electrostatic repulsion between negatively charged cells and carbon surfaces. In this paper we quantify the interaction forces between bacteria with negatively and positively charged, mesoporous wood-based carbons, as well as with a microporous coconut carbon. To this end, we glued carbon particles to the cantilever of an atomic force microscope and measured the interaction forces upon approach and retraction of thus made tips. Waterborne Raoultella terrigena and Escherichia coli adhered weakly (1-2 nN) to different activated carbon particles, and the main difference between the activated carbons was the percentage of curves with attractive sites revealed upon traversing of a carbon particle through the bacterial EPS layer. The percentage of curves showing adhesion forces upon retraction varied between 21% and 69%, and was highest for R. terrigena with positively charged carbon (66%) and a coconut carbon (69%). Macroscopic bacterial removal by the mesoporous carbon particles increased with increasing percentages of attractive sites revealed upon traversing a carbon particle through the outer bacterial surface layer.     

Determination of dissociation constants of sparingly soluble phenothiazine derivatives by second-derivative spectrophotometry

The dissociation constants (pK_a) for sparingly soluble phenothiazines (promazine, chlorpromazine, trifluoropromazine) in water were measured by second-derivative spectrophotometry. The intense background signals in the absorption spectra due to the turbidity caused by the precipitation of insoluble free base of the phenothiazine derivatives were eliminated in the second-derivative spectra, and the solubilities of the phenothiazine derivatives could be easily determined from the peak-to-trough lengths (D values) of the second-derivative signals. The pK_a values were calculated from the pH dependence of the D values. The pK_a values obtained agreed well with reported values and the standard deviations for 6–10 determinations were ? 0.02. The solubilities of the free bases of the phenothiazines were also determined.     

Supersaturation control in aragonite synthesis using sparingly soluble calcium sulfate as reactants

Sparingly soluble calcium salts were studied as reactants in the synthesis of needle-like precipitated calcium carbonate (PCC). The morphology and aspect ratio of the PCC particles were characterized with SEM. Polymorphs and crystal size were characterized using X-ray diffraction. The counterions of the sparingly soluble salts influenced the growth kinetics of PCC as well as the polymorphism and morphology of product particles. Either chrysanthemum-like or needle-like aragonite can be synthesized from calcium sulfate and sodium carbonate depending on the supersaturation and synthesis conditions. Low concentration and slow addition rate of sodium carbonate solution were favorable to the formation of aragonite. Addition of sodium sulfate to the reaction system (calcium chloride and sodium carbonate) promoted the formation of aragonite and decreased the crystal size of aragonite due to the decrease of supersaturation and adsorption of sulfate ion. Too much added sodium sulfate, however, did not further increase the aragonite fraction. An optimal temperature for the formation of aragonite was found to be ca. 60 degrees C. Slow dissolution kinetics of sparingly dissoluble salt also is very important for controlling PCC polymorphism and morphology.     

Study on heterogeneous equilibria in saturated solutions of sparingly soluble diprotic acids

Heterogeneous equilibria in saturated solutions of sparingly soluble diprotic acids: 1,2-, 1,3- and 1,4-benzenedicarboxylic acid, and octanedioic acid, respectively, at ionic strengthI=1 (NaCl) and the temperature of 25 °C, have been investigated. The corresponding equilibrium constants were determined by the application of three independent methods: the formation function method, the method of protons bound to the acid in the solution and the solubility method. The results obtained by these three different methods are in good agreement.

---

Untersuchung heterogener Gleichgewichte in gesättigten Lösungen schwerlöslicher diprotischer Säuren

Zusammenfassung Es wurden die heterogene Gleichgewichte in gesättigten Lösungen schwerlöslicher diprotischer Säuren (Benzol-1,2-, -1,3- und-1,4-dicarbonsäuren und Oktandisäure) bei einer IonenstärkeI=1 (NaCl) und der Temperatur von 25 °C untersucht. Die entsprechende Gleichgewichtskonstanten wurden mit drei unabhängigen Methoden bestimmt: mit der Methode der Bildungsfunktion, der Methode der an die Säure in Lösung gebundenen Protonen, bzw. mit der Methode der Löslichkeitsbestimmung. Die erhaltenen Ergebnisse stehen in guter Übereinstimmung.