Study of the behavior of chromium(III) in potassium nitrate solutions at 25°C

Solubility in the KNO₃-Cr(NO₃)₃-H₂O system at 25°C was studied by an isothermal method. The existence of solid phases of potassium nitrate and chromium(III) nitrate nonahydrate was confirmed by constructing a phase diagram, chemical analysis, and IR spectroscopy. Crystallization of potassium nitrate from aqueous solutions was studied. Potassium nitrate does not interact with chromium(III) nitrate within the range of micro and macro concentrations. The capture of chromium(III) by KNO₃ crystals is due to adsorption and occlusion of a mother solution.     

Differential scanning calorimetry of sodium and potassium nitrates and nitrites

Differential scanning calorimetry (DSC) experiments were performed with NaNO₃, KNO₃, (Na,K)NO₃, NaNO₂ and KNO₂ over the temperature range 350–990 K. Endothermic peaks, indicative of decomposition reactions, were observed to occur in the single salts above their melting points. The equimolar mixture of sodium and potassium nitrate did not decompose in the temperature range specified. The nitrites began to decompose at 800±10 K. Sodium nitrate began to decompose at 840±10 K and potassium nitrate began to decompose at 820±20 K. These results were compared with previously reported differential thermal analysis investigations of NaNO₃ and KNO₃.     

Solubility of some phenolic compounds in aqueous alkali metal nitrate solutions from (293.15 to 318.15) K

This paper is continuation of the study concerning the solubility-temperature dependence data for some phenolic compounds (PhC), contained in olive mill wastewater (OMWW), in two nitrate salts (KNO₃ and NaNO₃) aqueous solutions. The solubilities of PhC were determined in the temperature ranging from (293.15 to 318.15) K. It has been observed that the solubility, in aqueous nitrate solutions, increases with increasing temperature. Results showed that alkali metal nitrate has a salting-out effect on the solubility of PhC. The effect of the anion of the electrolyte on the solubility of PhC is observed by comparing these results with values reported in the previous papers for the effect of LiCl, NaCl and KCl. For each cation, the solubilites of the phenolic compounds are higher with nitrate anion than with chloride anion. Results were interpreted in terms of the salt hydration shells and the ability of the solute to form hydrogen-bond with water. The solubility data were accurately correlated by a semi empirical equation. The standard molar Gibbs free energies of transfer of PhC (Δ_trG^°) from pure water to aqueous solutions of the nitrate salts have been calculated from the solubility data. The decrease in solubility is correlated to the positive Δ_trG^° value which is mainly of enthalpic origin.     

Topotaxial decomposition of calcite-type KNO3 crystals

The calcite-like form of potassium nitrate, KNO₃, decomposed under the transmission electron microscope to form KNO₂ which subsequently decomposed giving the high-temperature β form of K₂O. Two closely related orientation relations were observed for KNO₂. Referred to the four-molecule cell of KNO₃, they were [111]_NNO3∥[111]_KNO2, (0$\text{1}$1)_KNO3∥(0$\text{1}$1)_KNO2; and [100]_KNO3∥[111]_KNO2, (001)_KNO3∥(001)_KNO2. These and a different published orientation relation for the decomposition of cadmium carbonate conform, respectively, to orientations resulting from a corresponding structural phase transformation in rubidium nitrate. β-K₂O formed with its cube axes parallel to those of KNO₂. Both nitrate and carbonate reactions can be regarded as topotaxial. Application of the crystallographic approach to orientations and accommodation of misregistry is discussed.     

Study of magnesium nitrate behavior in sodium nitrate solutions at 25°C

Solubility in the system KNO₃-Mg(NO₃)₂-H₂O at 25°C was studied by the isothermal method. Crystallization of potassium nitrate from aqueous solutions was studied. Coefficients of the removal of magnesium nitrate admixture were calculated.     

Solubility in the diagonal sections of the 2KCl + Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> ⇆ 2KNO<Subscript>3</Subscript> + CaCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Solubility data in the diagonal sections of the quaternary reciprocal 2KCl + Ca(NO₃)₂ → 2KNO₃ + CaCl₂–H₂O system at 25 and 15°C are presented. It has been shown that the quaternary system has no stable diagonal at the studied temperatures, but contains a stable pair of salts, namely, potassium nitrate and calcium chloride. The obtained data can be used to optimize the thermal and concentrational parameters of the synthesis of potassium nitrate from calcium nitrate and potassium chloride.     

A study of the differential capacitance of zinc in aqueous solution with potassium silicate additions

The differential capacitance of the polycrystalline zinc electrode has been studied in aqueous solutions of KCl, KNO₃ and KOH both with and without the addition of potassium silicate. Double layer capacitance measurements can be made in KCl and KNO₃ without the interaction of OH^? at low pH values < 3.0. The reduction of the nitrate ion takes place at the zinc electrode in aqueous potassium nitrate.The silicate ion is adsorbed on the zinc electrode in aqueous KOH solutions at a potential close to the dissolution potential. This results in inhibition of metal dissolution, due to limited interaction of OH^? with the metal surface. The electrode resistance is increased by this adsorbed layer of silicate ion. In alkaline solution the h.e.r. is stimulated by the addition of potassium silicate.     

Activity coefficients of sodium,potassium, and nitrate ions in aqueous solutions of NaNO3, KNO3, and NaNO3+KNO3 at 25°C

Ion selective electrodes have been used to measure the activity coefficients at 25°C of individual ions in aqueous solutions of NaNO₃ up to 3.5 molal, KNO₃ up to 3.5 molal and mixtures of NaNO₃ and KNO₃ up to 2.4 molal total nitrate ion concentration. The experimental results confirm that the activity coefficient of anion and cation in aqueous single electrolyte solutions of NaNO₃ and KNO₃ were different from each other over the whole range of concentrations studied. These effects are attributed to the ion-ion and ion-solvent interactions. The results also show that the activity coefficients of nitrate ions in the presence of sodium and potassium counterions do not depend significantly on the nature of the counterions present in the solution. The experimental data obtained in this study were correlated by a model proposed previously.     

Potassium cobaltinitrite

Potassium cobaltinitrite K₃[Co(NO₂)₆] has been synthesized by three methods. The crystalline products have been characterized by scanning electron microscopy, X-ray powder diffraction, IR spectros-copy, and thermal and sedimentation analyses. A comparative analysis of the synthetic methods has been carried out. The highest yield, the smallest particle size, and the highest purity of the product are attained by reacting potassium nitrite with cobalt nitrate in an acid medium in the same way as in the synthesis of sodium cobaltinitrite: 2CH₃COOH + Co(NO₃)₂ + 7KNO₂ → K₃[Co(NO₂)₆]↓ + 2KNO₃ + 2CH₃COOK + NO↑ + H₂O. All of the resulting potassium cobaltinitrite samples are hygroscopic. The water release and nitrite ion elimination temperature intervals have been determined.     

Effect of Ammonium Ions on the Radiation Degradation of Potassium Nitrate

The formation and thermal conversion of paramagnetic centers in -irradiated single crystals of potassium nitrate with an ammonium nitrate impurity was studied by EPR spectroscopy. It was found that the presence of ammonium nitrate decreased the radiation-chemical yield of nitrite ions, which are one of the final radiolysis products of nitrate-containing compounds. An analysis of the results of a study on NO₂ orientation in the KNO₃ crystal lattice with an impurity of NH⁺ ₄ allowed us to propose a mechanism for selective N–O bond rupture in the radiation-stimulated dissociation of the nitrate ion in a potassium nitrate matrix.     

Theoretical calculations of the ionic strength dependence of the ionic product of water based on a mean spherical approximation

A modified version of the restricted primitive model for electrolyte solutions based on the mean spherical approximation (MSA) is applied to estimate the ionic strength dependence of the ionic product of water in aqueous solutions containing different salts, which are commonly used as background electrolytes (NaCl, KCl, KNO₃, and NaC10₄). The modification involves the use of permittivity of the solvent as concentration-dependent parameter and a single average effective diameter. This is a way of including effects originated from the solvent which do not exist in the primitive model. In the case of potassium nitrate and sodium perchlorate, a complete methodology to calculate the effective diameter and density dependence of the dielectric constant has been proposed and developed. Fits between calculated and experimental pK_w values are possible over wide concentration ranges using a single adjustable parameter, namely, the average hard core diameter of water.     

Polytherm of the CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>–KNO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O phase diagram

The crystallization polytherm of the ternary CO(NH₂)₂–KNO₃–H₂O system is plotted for the first time via visual polythermal analysis and calculating ternary eutonics characteristics from data on the boundary elements of two-component systems. The ternary eutonics modeling error does not exceed 3.5%. In addition to the crystallization fields of individual components, the field of the redox reaction that occurs in the system between potassium nitrate and carbamide is shown in the CO(NH₂)₂–KNO₃–H₂O diagram by a dashed outline.     

Temperature standard reference materials for thermal analysis

The feasibility of the use of potassium nitrate and potassium perchlorate as temperature standards in Differential scanning calorimetry has been studied. The solid-state phase transition temperatures of KNO₃ and KClO₄ were determined by means of DSC. The metrological properties of these salts as calibration materials were examined. The reliability of KNO₃ and KClO₄ calibrations was investigated by twofold determination of the bismuth melting temperature after the apparatus had been calibrated with indium and lead, and with KNO₃ and KCl_O4. Conclusions were drawn concerning the suitability of these salts for use as DSC temperature calibrants.

---

Zusammenfassung Es wurde die Möglichkeit der Verwendung von Kaliumnitrat und Kaliumperchlorat als Temperaturstandard für DSC untersucht. Die Bestimmung der Temperaturen für Feststoff-Phasenumwandlungen von Kaliumnitrat und Kaliumperchlorat wurde mittels DSC erreicht. Weiterhin wurden die meßtechnischen Eigenschaften der untersuchten Salze (KNO₃ und KClO₄) als Bezugssubstanzen geprüft. Die Zuverlässigkeit der Kalibrierung mittels KNO₃ und KClO₄ wurde durch eine zweifache Bestimmung der Schmelztemperatur von Wismut überprüft: einmal nach der Kalibrierung des Gerätes mit Indium und Blei und andererseits nach der Kalibrierung mit Kaliumnitrat und Kaliumperchlorat. Angesichts der Resultate kann man feststellen, daß die untersuchten Salze zur Temperaturkalibrierung in der DSC geeignet sind.

     

Solubility in the 2KNO3 + MgCl2 ? 2KCl + Mg(NO3)2-H2O system

Solubility in the 2KNO₃ + MgCl₂ ↔ 2KCl + Mg(NO₃)₂-H₂O four-component reciprocal system was studied for the first time at 25 and 50°C in order to determine the feasibility of preparing potassium nitrate and magnesium chloride at near-ambient temperatures.     

LiNO_3-KNO_3-H_2O三元体系相平衡研究

本文采用等温法分别测定了KNO3-H2O体系的溶解度相图以及LiNO3-KNO3-H2O体系在273.15和298.15K的等温溶解度相图。结果表明在273.15K时LiNO3-KNO3-H2O体系的溶解度等温线有2条分支,对应的固相分别为KNO3和LiNO3·3H2O,共饱点组成为31.55wt%LiNO3和7.07wt%KNO3。该体系在298.15K的等温线有3条分支,对应的固相分别为KNO3,LiNO3和LiNO3·3H2O,2个共饱点组成分别为50.42wt%LiNO3,22.18wt%KNO3,和55.74wt%LiNO3,10.9wt%KNO3。     

δ 15N measurement of organic and inorganic substances by EA-IRMS: a speciation-dependent procedure

Little attention has been paid so far to the influence of the chemical nature of the substance when measuring δ ¹⁵N by elemental analysis (EA)–isotope ratio mass spectrometry (IRMS). Although the bulk nitrogen isotope analysis of organic material is not to be questioned, literature from different disciplines using IRMS provides hints that the quantitative conversion of nitrate into nitrogen presents difficulties. We observed abnormal series of δ ¹⁵N values of laboratory standards and nitrates. These unexpected results were shown to be related to the tailing of the nitrogen peak of nitrate-containing compounds. A series of experiments were set up to investigate the cause of this phenomenon, using ammonium nitrate (NH₄NO₃) and potassium nitrate (KNO₃) samples, two organic laboratory standards as well as the international secondary reference materials IAEA-N1, IAEA-N2—two ammonium sulphates [(NH₄)₂SO₄]—and IAEA-NO-3, a potassium nitrate. In experiment 1, we used graphite and vanadium pentoxide (V₂O₅) as additives to observe if they could enhance the decomposition (combustion) of nitrates. In experiment 2, we tested another elemental analyser configuration including an additional section of reduced copper in order to see whether or not the tailing could originate from an incomplete reduction process. Finally, we modified several parameters of the method and observed their influence on the peak shape, δ ¹⁵N value and nitrogen content in weight percent of nitrogen of the target substances. We found the best results using mere thermal decomposition in helium, under exclusion of any oxygen. We show that the analytical procedure used for organic samples should not be used for nitrates because of their different chemical nature. We present the best performance given one set of sample introduction parameters for the analysis of nitrates, as well as for the ammonium sulphate IAEA-N1 and IAEA-N2 reference materials. We discuss these results considering the thermochemistry of the substances and the analytical technique itself. The results emphasise the difference in chemical nature of inorganic and organic samples, which necessarily involves distinct thermochemistry when analysed by EA-IRMS. Therefore, they should not be processed using the same analytical procedure. This clearly impacts on the way international secondary reference materials should be used for the calibration of organic laboratory standards.

Superstructure of α‐phase potassium nitrate

The structure of potassium nitrate, KNO₃, has been redetermined at room temperature. The compound surprisingly shows a 2 × 2 × 1 superstructure and crystallizes in space group Cmc2₁. This result contrasts with that found in former investigations, which gave the supergroup Pmcn, neglecting the superstructure. The improved results are due to the employment of a CCD area detector.     

热力学模型研究KNO3-K2SO4-H2O和KNO3-KCl-H2O体系溶解度

用Pitzer-Simonson-Clegg热力学模型(PSC模型),分别拟合KCl-H2O、K2SO4-H2O、KNO3-H2O体系以及KNO3-K2SO4-H2O和KNO3-KCl-H2O体系水活度和溶解度实验数据,得到二元参数和三元离子相互作用参数,并以此计算3个二元盐水体系溶解度相图,及2个三元盐水体系在不同温度下的溶解度,结果表明计算值与实验值一致。     

One-step synthesis of nitrogen-doped porous carbon for supercapacitors utilizing KNO<Subscript>3</Subscript> as an electrolyte

Nitrogen-doped porous carbons were prepared using a facile method, with low-biotechnology fulvic acid potassium salts as a precursor. The prepared carbons had a high surface area (1623 m² g^?1) and good electrochemical properties, making them suitable electrode materials for supercapacitors. Nitrogen-doped porous carbons were tested as an electrode in both 6 M KOH aqueous solution and different concentrations KNO₃ aqueous solution. The nitrogen-doped porous carbons with unique microstructure and nitrogen functionalities exhibited a capacitance of 235 F g^?1 in a 6 M KOH aqueous solution. Electrochemical investigation showed that the nitrogen-doped porous carbons exhibited a broad potential operational window in a 2.5 M KNO₃ aqueous solution. Furthermore, a high capacitance retention of 88.1 % was achieved even after 5000 cycles at 1.7 V. Potassium nitrate solutions in a wide range of concentrations were also proven to be promising electrolytes for electrochemical capacitors because they are cheap, noncorrosive, electrochemically stable, and compatible to diverse current collectors.     

Phase Modification of Ammonium Nitrate by Potassium Salts

Modification of the room temperature phase (IV-III) of ammonium nitrate (AN) has been attempted using a variety of potassium salts namely, KF, KCl, KI, KNO₃, K₂CO₃, K₂SO₄, KSCN and K₂Cr₂O₇. No phase transition was observed when AN containing 1–2% by mass of these potassium salts is heated from room temperature (25°C) onwards in DTA and DSC scans, but the linear expansion due to phase transition was still observable in TMA measurements. Complete arrest of the linear expansion occurs only when a higher concentration of the additive is used. Similarly, in thermal cycling experiments, complete phase modification in the temperature range -80 to 100°C occurs only with a higher percentage of the potassium salt. The extent of modification, however, is found to be dependent both on the concentration, and the type of the anion. Potassium dichromate when used as an additive modifies the phase as well as the decomposition pattern of AN. This revised version was published online in July 2006 with corrections to the Cover Date.