Aqueous Solutions Of Potassium Nitrate Research Articles

Laser-Induced Shockwave Crystallization in Supersaturated Solutions and Conceivable Clustering in Undersaturated Aqueous Potassium Nitrate Solutions.

In this study, a newly developed setup based on laser-induced shockwave crystallization coupled with electric conductivity monitoring was employed to study the growth of crystals in supersaturated solutions and to investigate possible clustering in undersaturated solutions of potassium nitrate (KNO3). A comparison was drawn between crystals induced by laser irradiation, by shockwaves, and spontaneously in terms of crystals' mean size, shape, and size distribution. The size distribution of produced crystals by shockwaves was also characterized in terms of laser irradiation time. The results show that produced crystals by shockwaves propagation have the sharpest size distribution and the smallest mean dimensions compared to crystals grown spontaneously or by direct laser induction. Real-time monitoring of nucleation was also performed in supersaturated solutions, while decrease in conductivity was observed in undersaturated solutions as a function of laser irradiation time.

Stainless Steel Surface Coating with Nanocrystalline Ag Film by Plasma Electrolysis Technology

This paper describes the use of a plasma electrolysis technique to apply a nanosilver coating to the surface of stainless steel to achieve hydrophobic properties. We propose an experimental reaction system, which includes stainless steel 316 as the two electrodes and an aqueous solution of potassium nitrate (KNO3), silver nitrate (AgNO3), and ammonium hydroxide (NH4OH) as the electrolyte. Better results with a stainless steel surface coated by nanocrystalline Ag film are obtained using optimal parameters chosen through one-factor-at-a-time experiments. The main parameters consist of electrode distance, KNO3 concentration, and AgNO3 concentration. The experiment focuses on analyzing the impact of the plasma electrolysis technique on processing time. Variations in KNO3 concentration show that 3 wt.% yields the worst result because it causes an uneven surface, whereas 5 wt.% gives excellent results because it creates an even, porous surface and the highest contact angle. An AgNO3 concentration of 0.03 wt.% yields the best contact angle. With the same processing time, silver sediment increases as the KNO3 concentration increases. With respect to variation in electrode distance, we find that when the distance is set at 20 mm, the contact angle exceeds 100° and results in hydrophobic properties on the specimen surface, while other distances yield a contact angle below 80°, resulting in hydrophilic surfaces. The SEM (scanning electron microscope) results show that the surface of the specimen is full of crater-like cavities that directly affect the contact angle. In this experiment, the contact angle yielding optimum hydrophobic properties is 134° ± 10°. Finally, using distribution patterns obtained by elemental analysis, the experimental results lead to an evenly distributed silver coating on the surface of specimens subjected to plasma electrolysis treatment. The study confirms that plasma electrolysis can be used to coat nanosilver onto stainless steel 316.

A Generic Polycarbonate Based Microfluidic Tool to Study Crystal Nucleation in Microdroplets

Crystal nucleation is important to control the product properties in industrial crystallization processes. To investigate crystallization phenomena, methods which rely on microscopic volumes have gained relevance over the last decade. Microfluidic devices are suitable for carrying out crystallization experiments based on a large set of individual droplets in the nanoliter range. In this work, we propose a simple method to manufacture such devices from polycarbonate as an alternative to conventional chips made of poly (dimethylsiloxane). The microfluidic device consists of two main functional parts: A T-junction for droplet generation and a section for storage and observation of up to 400 individual droplets. Using these manufactured devices, it is easy to produce and store highly monodisperse droplets of substances that require either a hydrophilic or hydrophobic surface of the microchannel. Since crystal nucleation is a stochastic process which depends on the sample volume, a reproducible droplet volume is of great importance for crystallization experiments. The versatile applicability of the manufactured devices is demonstrated for substances which are used in different crystallization applications, for example, solution crystallization (aqueous potassium nitrate solution) and melt crystallization (ethylene glycol distearate). Finally, we demonstrate that the manufactured microfluidic devices in our experimental setup can be used to conduct crystal nucleation measurements. Based on these measurements we discuss our results with respect to state-of-the-art nucleation models.

Solubility and solute-solvent interactions of dl-alanine and dl-serine in aqueous potassium nitrate solutions

Present study described the saturated solubilities of dl-alanine and dl-serine in pure and aqueous binary potassium nitrate solutions, were estimated by an analytical ‘formol titration’ procedure at 298.15K. Various physicochemical and thermodynamical parameters like free energy change, density, molar volume, solvent diameter, co-solvent diameter, probable dipole moment of aqueous electrolyte systems, etc., were calculated at 298.15K. The nature and degree of solubilities of such amino acids in aqueous potassium nitrate solutions were analyzed in terms of salting-in effect which was further justified by relative solubility and salting-in constants. Finally, thermodynamics of solute-solvent interactions in terms of transfer Gibbs free energetics were calculated and described the relative stability of the amino acids in pure and binary mixture of solvents.

Coupled jump rotational dynamics in aqueous nitrate solutions.

A nitrate ion (NO3-) with its trigonal planar geometry and charges distributed among nitrogen and oxygen atoms can couple to the extensive hydrogen bond network of water to give rise to unique dynamical characteristics. We carry out detailed atomistic simulations and theoretical analyses to investigate these aspects and report certain interesting findings. We find that the nitrate ions in aqueous potassium nitrate solution exhibit large amplitude rotational jump motions that are coupled to the hydrogen bond rearrangement dynamics of the surrounding water molecules. The jump motion of nitrate ions bears certain similarities to the Laage-Hynes mechanism of rotational jump motions of tagged water molecules in neat liquid water. We perform a detailed atomic-level investigation of hydrogen bond rearrangement dynamics of water in aqueous KNO3 solution to unearth two distinct mechanisms of hydrogen bond exchange that are instrumental to promote these jump motions of nitrate ions. As observed in an earlier study by Xie et al., in the first mechanism, after breaking a hydrogen bond with nitrate ion, water forms a new hydrogen bond with a water molecule, whereas the second mechanism involves just a switching of hydrogen bond between the two oxygen atoms of the same nitrate ion (W. J. Xie et al., J. Chem. Phys. 143, 224504 (2015)). The magnitude as well as nature of the reorientational jump of nitrate ion for the two mechanisms is different. In the first mechanism, nitrate ion predominantly undergoes out-of-plane rotation, while in the second mechanism, in-plane reorientation of NO3- is favourable. These have been deduced by computing the torque on the nitrate ion during the hydrogen bond switching event. We have defined and computed the time correlation function for coupled reorientational jump of nitrate and water and obtained the associated relaxation time which is also different for the two mechanisms. These results provide insight into the relation between the coupled reorientational jump dynamics of solute and solvent molecules.

Synthesis and study of potassium uranates K2U6O19 and K2U4O13·2.2H2O

Potassium uranates K2U6O19 and K2U4O13·2.2H2O were synthesized by the reaction of aqueous solutions of uranyl acetate with aqueous solutions of potassium nitrate under hydrothermal conditions at 200°C. The compounds were examined by chemical analysis, X-ray diffraction, IR spectroscopy, and differential thermal analysis. The decomposition of the compounds was studied.

Volumetric & Transport behavior of neutral amino acids in different concentrations of an Electrolyte at 250C

Apparent molar volumes, V2, ? of glycine, DL-?-alanine, DL-?-amino-n-butyric acid, L-valine and L-leucine in water and in (0.25, 0.5, 0.75, 1.0, 1.5, 2.0) mol?kg-1 aqueous potassium nitrate solutions have been determined at T= 298.15 K from density measurements. The standard partial molar volumes at infinite dilution, V20 obtained from V2, ? , have been used to calculate the corresponding volumes of transfer, ?tV0 from water to aqueous potassium nitrate solutions. The hydration number, nH, side chain contributions and volumetric interaction coefficients of these amino acids have also been calculated. The ?tV0 values for the studied amino acids are positive, and these values increase with an increase in the concentration

Volumetric & Transport Behavior of Neutral Amino Acids in Different Concentrations of an Electrolyte at 250°C

Apparent molar volumes, V2, ? of glycine, DL-?-alanine, DL-?-amino-n-butyric acid, L-valine and L-leucine in water and in (0.25, 0.5, 0.75, 1.0, 1.5, 2.0) mol?kg-1 aqueous potassium nitrate solutions have been determined at T= 298.15 K from density measurements. The standard partial molar volumes at infinite dilution, V20 obtained from V2, ? , have been used to calculate the corresponding volumes of transfer, ?tV0 from water to aqueous potassium nitrate solutions. The hydration number, nH, side chain contributions and volumetric interaction coefficients of these amino acids have also been calculated. The ?tV0 values for the studied amino acids are positive, and these values increase with an increase in the concentration of NaNO3 .

Fischer–Tropsch Synthesis: Effect of Halides and Potassium Addition on Activity and Selectivity of Cobalt

The effect of halides and potassium addition on cobalt Fischer–Tropsch synthesis (FTS) was studied using 1L CSTR at 493 K, 1.99 MPa and H2/CO of 2.0. The potential catalyst poison was co-fed with syngas after reaching steady-state FTS. Halides were added in an aqueous solution of HX (HF, HCl, HBr) and potassium as aqueous potassium nitrate solution along with syngas at various concentration levels ranging from 500 ppbv to 100 ppmv. Fluoride addition did not affect FT performance of cobalt up to 1.0 ppmv level. However, the presence of other halides (Cl− and Br−) decreased the FT activity proportionally. Addition of potassium decreased cobalt FT activity considerably and increases syngas conversion to methane and CO2 at higher potassium concentrations. The observed poisoning effects for metallic cobalt could be attributed to a blocking effect of cobalt metal sites by halides and potassium in agreement with results of H2 chemisorption on used cobalt FT catalysts.

Preparation and characterization of high surface area, high porosity carbon monoliths from pyrolyzed bovine bone and their performance as supercapacitor electrodes

Bovine cortical bone was pyrolyzed to produce a network of conductive carbon entwined with native hydroxyapatite that maintains its macroscopic structure during pyrolysis and prevents collapse of the carbon. Self-supporting conductive carbon monoliths were prepared by removing the hydroxyapatite with acid or ethylenediaminetetraacetic acid. The specific surface areas of these monoliths were determined by nitrogen adsorption, and their chemical structure was characterized using Raman spectroscopy. The monoliths exhibit specific surface areas and Raman spectra similar to those of amorphous carbons. Capacitance was assessed using the monoliths as the working electrodes in three-electrode cells, and two-electrode devices in which both electrodes were monoliths. Individual monoliths exhibit specific capacitances of 134±11F/g in aqueous solutions of potassium nitrate and 108±9F/g in the ionic liquid 1-ethyl-3-methylimidizolium bis(trifluoromethylsulfonyl)imide. The capacitance of individual 6mm diameter by 1mm thick electrodes was typically on the order of 0.2 Farads.

Correlation between ion-exchange properties and swelling/shrinking processes in hexasulfonated calix[6]arene doped polypyrrole films: ac-electrogravimetry and electrochemical atomic force microscopy investigations

Electrogenerated polypyrrole films doped with hexasulfonated calix[6]arenes were subjected to ac-electrogravimetry and electrochemical atomic force microscopy (EC-AFM) studies in aqueous potassium nitrate solutions. The former technique reveals that these films are mainly cation exchangers although solvent molecules (H 2O) and anions (NO 3 −) are also exchanged, in much lower amounts, in the course of the doping/undoping process. Unexpectedly, within the potential range encompassing this process, K + cations were found to be exchanged for more cathodic potentials whereas H 3O + are exchanged for more anodic potentials. EC-AFM investigations revealed substantial shrinking and swelling during the oxidation (doping) and reduction (undoping) processes respectively. An obvious correlation can easily be built between these observations: the oxidation of the polymer films provokes an expulsion of the cations, as expected from cation exchanger polymer films, and therefore a decrease of the volume (and thickness) of these films whereas their reduction causes an insertion of cations and an increase of their volume (and thickness). This electromechanical mechanism is amplified by the simultaneous exchange of free water molecules. Suggestions based on these observations, on structural characteristics of polypyrrole films, and on complexation ability of hexasulfonated calix[6]arenes incorporated in the films are discussed to explain (i) the change of the identity of the exchanged cations as a function of the potential, (ii) the exchange of free water molecules and, (iii) the exchange of small amounts of nitrate ions.

EVALUATION OF A PORTABLE NITRATE ION-SELECTIVE ELECTRODE WITH AQUEOUS POTASSIUM NITRATE AND VEGETABLE JUICE

The nitrate ion content of vegetables has become a concern with regard to human health. A portable nitrate ion-selective electrode (ISE) developed by Horiba, Ltd. was evaluated against an aqueous solution of potassium nitrate and vegetable juice. The ISE exhibited a linear dynamic range from 20 to 6000 ppm NO 3 - in standard aqueous solutions of potassium nitrate. In vegetable juice, the measured nitrate ion concentration decreased proportionately with dilution, and was constant as a function of temperature. In nitrate-spiked samples of raw vegetable juice, the recovery percentage consistently approached 100%. Furthermore, the ISE results were essentially identical to those obtained by ion chromatography (IC), exhibiting a correlation coefficient of R=0.997 (n=7). The use of an ionic strength adjustor was deemed unnecessary in these experiments, which allows for simple implementation in practical applications. The instrument is currently commercially available as the compact nitrate ion meter B-343 (Horiba Ltd, Kyoto, Japan).

Quantitative design of seed load for solution cooling crystallization based on kinetic analysis

Seed load of crystallization has a direct effect on the product qualities. To further reveal the effects of seed load on crystallization kinetics and improve the product size distribution, the aqueous solution of potassium nitrate (KNO 3–H 2O) is employed as a model system and the relevant kinetic experiments are conducted in a batch cooling crystallizer. The crystal nucleation and growth rate parameters are firstly estimated with the concentration and transmittance data using a mathematical model reported in our lab, and then the backward calculations with the help of the model parameters are successfully performed. It is found that the nucleation capacity decreases and growth capacity increases with increasing seed load, and the size distribution of crystal products tends to be more uniform. However, with the increasing of seed load, the linear growth rate of single crystal and the mean size of products both reduce accordingly. Based on the calculational and experimental results, a quantitative design scheme concerning seed load is proposed by further kinetic analyses, and the corresponding verification experiments are carried out. The results show that under the guidance of the proposed scheme, the size distribution of crystal products is more concentrated and the mean size of final particles can also escape from reducing obviously.

Experimental and computational study on the aqueous acidity constants of some new aminobenzoic acid compounds

The acidity constants of three new aminobenzoic acid derivatives were determined using potentiometric and spectrophotometric methods in 0.10 M aqueous potassium nitrate solution as supporting electrolyte. The potentiometric data and UV–Vis absorption spectra of solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, concentration distribution diagrams and number of components involved have been calculated. The relative p K a values for three acids were also calculated using ab initio quantum mechanical method at the HF/6-31G** level of theory in combination with CPCM continuum solvation method. The influence of substituents on the ionization constants of the studied molecular structures was investigated. The satisfactory agreement between the experimentally derived and theoretically calculated p K a values provides solid support for the acid–base reactions proposed in this work.

Microfluidic Droplet Method for Nucleation Kinetics Measurements

In this work, we developed a microfluidic equivalent of the classical droplet method for investigating nucleation kinetics. Our microfluidic device allows us to store hundreds of droplets of small volume ( approximately 100 nL) and to accurately control their temperature. We also monitor directly all the stored droplets, and thus perform statistical measurements on a large number of nucleation events. In the case of aqueous solutions of potassium nitrate, we manage to investigate nucleation kinetics and polymorphs and quantify the influence of impurities. The use of small droplets is crucial in such experiments, since it allows the sample to reach high supersaturations and to separate all the nucleation events. Moreover, we compare our results to the classical nucleation theory, and we demonstrate unambiguously using direct observations of the droplets that nucleation in aqueous solutions of potassium nitrate always occurs using heterogeneous mechanisms.

Crystal structure and thermal properties of a new double salt: K2SiF6·KNO3

AbstractA new double salt K2SiF6·KNO3 was found during determination of the solubility of K2SiF6 in aqueous potassium nitrate solutions. Unit cell parameters (P63/mmc, a = 5.6268(1) Å, c = 14.5186(6) Å, V = 398.09(2) Å3, Z = 2) and crystal structure have been determined. The compound is further characterized by RAMAN spectroscopy and X‐ray powder diffraction. Thermal properties were studied using DTA, DSC and in situ high‐ temperature X‐ray powder diffraction measurements. At 287 °C K2SiF6·KNO3 decomposes into its components KNO3 and K2SiF6 with an enthalpy of decomposition of about + 42 J·g‐1. Further thermal effects could be assigned to phase transformations of KNO3 whereby earlier literature data have been reconfirmed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Vis/NIR spectroelectrochemical analysis of poly-(Azure A) on ITO electrode

Electrochromic behavior of poly-( Azure A) on indium–tin oxide electrode is analyzed in an aqueous potassium nitrate solution. The dependence of the absorbance on the applied potential during cyclic voltammograms proves very interesting at two selected characteristic wavelengths: at 925 nm, attributed to an intermediate species and another at 735 nm, attributed to the oxidized form of the polymer. Molar absorptivity coefficients for both species have been calculated from the relationship between current and the derivative of absorbance with respect to time. Voltammograms of formation of the intermediate are simulated from spectroelectrochemical results.

Caffeine as non-toxic corrosion inhibitor for copper in aqueous solutions of potassium nitrate

Different electrochemical methods were employed in order to confirm the ability of caffeine (1,3,7-trimethylxanthine) to inhibit the corrosion processes of copper in aqueous potassium nitrate solutions in the absence and in the presence of chloride. Some experiments were repeated in potassium perchlorate in order to compare the influence of the medium. The interaction between the organic compound and the electrode surface occurs independently of the electrode potential. However, maximum interaction was observed at 0.0V (Ag/AgCl) in aerated solutions, and at −0.25V (Ag/AgCl) in deaerated solutions.The presence of the organic compound adsorbed on the electrode surface was confirmed by comparing the voltammograms of copper electrode in the absence and presence of 1.5mmolL−1 of dissolved caffeine. The same results were observed by comparing polarization curves in the absence and in the presence of caffeine.Anodic currents decrease noticeably in the presence of the organic compound. Chronoamperometric experiments were conclusive to prove the inhibitor capability of caffeine to decrease the corrosion dissolution processes of copper under anodic polarization.

Selective oxidation of propane to acrylic acid on K-doped MoVSbO catalysts: catalyst characterization and catalytic performance

K-doped Mo V Sb mixed oxides catalysts have been prepared by impregnation of a MoVSbO mixed oxide (previously prepared by hydrothermal synthesis) with an aqueous solution of potassium nitrate, characterized by XRD, SEM-EDX, EPR, XPS, XANES, and FTIR of adsorbed NH 3, and tested in the selective oxidation of propane and propylene in the 593–693 K temperature range. The undoped MoVSbO catalysts presented a selectivity to acrylic acid lower than 15%, while selectivities to acrylic acid of about 40% can be obtained on K-doped catalysts. No appreciable differences between undoped and K-doped catalysts are observed in the nature of crystalline phases present in each case, on the basis of X-ray diffraction analysis. However, important differences in both the oxidation state of surface Sb species (according to XPS evidence) and the number of acid sites (determined from FTIR of adsorbed NH 3) are observed between the undoped and the K-doped catalysts. The high selectivity to acrylic acid on the K-doped catalysts seems to be related to changes in the acid–base properties of the catalysts and most particularly to the elimination of (Brønsted) acid sites. In addition, the role of antimony species in activity and selectivity is also discussed and a reaction network for the partial oxidation reaction is proposed.

Solidification and compositional convection of a ternary alloy

We present the results of an experimental study on the solidification of aqueous solutions of potassium nitrate and sodium nitrate cooled from below. Upon cooling, two distinct mushy layers form, primary and cotectic, separated by an approximately planar horizontal interface. A density reversal between the two mushes causes the residual liquid in the upper, primary mush to be more buoyant than the melt overlying it, while the cotectic mush is compositionally stable. The unstable concentration gradient between the melt and primary mush causes convection that keeps the melt well-mixed and reduces the concentration gradient to zero after a finite time. At this point, the cotectic mush overtakes the primary mush and a transition from a convective regime to a diffusive regime occurs. Our measurements show that this transition is rapid and alters the growth rate of the single (cotectic) mush layer that remains. Concentration measurements taken from within the melt during convection and from within the mush during the diffusive regime show good agreement with the concentration evolution predicted by use of the equilibrium ternary phase diagram. We describe a global conservation model for solidification of a ternary alloy in this regime. Predictions from our model forced with empirical data for the heat and solute fluxes are in good agreement with the measured data for the interface positions of the two mushy layers. We also discuss how solid fractions vary with different melt concentrations in a non-convecting alloy and examine the influence of vertical solute transport in the convecting case. The identification of a density reversal in the solidification of a ternary alloy begins to address the complexities in solidification processes of multi-component alloys.