Relationship between the solubilities and separation factors for the co-crystallization of lanthanide ethylsulphates

Co-crystallization coefficients of lanthanide ethylsulphates [Ln(H₂O)₉] (C₂H₅SO₄)₃ were determined and compared with the solubility of these salts. In contrast to the common opinion denying any simple correlation between co-crystallization coefficients and solubilities it was established that a simple relationship does exist for ethylsulphates of light lanthanides. It was concluded that in the case of light lanthanides an almost complete compesation of activity coefficients in the RATNER equation is due to the similar structure of the hydrated cations [Ln(H₂O)₉]³⁺ in both the solid and the aqueous phase. For ethylsulphates of heavy lanthanides such a compensation was not observed, since in this case the cations in the aqueous phase are probably hydrated by 8 water molecules, while in the solid phase the coordination number is still 9. The solubility of Pm, Pu, Am and Cm ethylsulphates was determined by the method “from matrix”. Presented in part at the Italian-Polish Meeting on the Properties and the Development of Methods for Separating Lanthanide Fission Products and Transuranian Elements in Post-Irradiation Analysis of Nuclear Fuels, held in Rome, 19–26 November 1974.     

Some mechanistic considerations of hindered amine uv stabilisers

Hindered amines are good uv stabilisers. Tetra-substituted hindered amines are usually better uv stabilisers than tri-substituted ones. Among bicyclo tri-substituted amines the uv stabilisation activity appears to depend on the degree of hindrance around the nitrogen atom and the way in which the two rings are fused together.This conclusion is based on the finding that 2,2,4-trimethyl-trans-decahydroquinoline (trans-TDQ) is a better uv stabiliser than cis-TDQ in polypropylene. The same trend was found between 1-(2-hydroxyethyl)-2,2,4-trimethyl-trans-decahydroquinoline (trans-HETDQ-1) and cis-HETDQ-1. The difference in the uv stabilisation activity of these isomers is explained in terms of the relative stability of the nitroxyl radical of trans and cis TDQ.     

Some factors influencing the selectivity of styrene oxidation by active oxygen donors catalyzed by three generations of ironporphyrins

In this work, we used representatives of 3 generations of metalloporphyrins [Fe(TPP)Cl, 1st generation; Fe(Cl₆P)Cl, 2nd generation; and Fe(Cl₁₄P)Cl, 3rd generation] as catalysts in the oxidation of styrene by PhIO and t-BuOOH to evaluate the influence of the reaction conditions on the mechanisms and catalytic efficiency of these catalysts. Increased substitution of hydrogen atoms on the phenyl groups and β-pyrrolic rings for electron-withdrawing elements such as halogens makes the catalytic species more reactive and prevents ironporphyrin self-destruction. However, an excess of such substituents in the 3rd generation complex is not a guarantee of high product yields, because of the steric effect of these substituents on the reaction mechanisms. In turn, other parameters such as solvent, oxidant, and axial ligands can be set up in order to favor the mechanism responsible for the high selectivity for the desired product. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 4, pp. 572–580. This text was translated by the authors.     

On the factors influencing the dispersion of radioiodines

Radioactivities dispersed from 0.1 N sodium hydroxide solutions of 123I, 125I, or 131I were measured, and the factors influencing dispersion of radioiodines were analyzed. The radioiodines dispersed were trapped by glass fiber filters, charcoal filters, and separable paint. The factors influencing the dispersion of radioiodines are discussed in terms of the dispersal rate, which defined as the ratio of total activity of three kinds of traps in a unit time to whole activity. In order to clarify the factors influencing the dispersal rate, we carried out the experiments; on the effect of reducing agent, that of radioactive concentration of radioiodine, that of mixing the 125I solution with 131I, and that of scavenging hydrated electrons and hydroxyl radicals. It could be concluded from experimental results that the principal factors influencing dispersion of radioiodines are the number of atoms of radioiodine per volume and the energy absorbed in solution from radioiodines. In regard to the absorbed energy, we thought that the dispersion of radioiodines is influenced mainly by hydrated electron, not markedly by hydroxyl radical.     

Solvent effects on the solubilities of reference electrolytes

Solubilities of bis(biphenyl)chromium(I) tetraphenylborate were measured in 25, solubilities of tetraphenylarsonium tetraphenylborate in nine and solubilities of bis(biphenyl)chromium(0) in seven nonaqueous solvents. Linear dependences of the pK_s-values for these compounds as well as the pK_s values for tetraphenylstibonium tetraphenylborate, tetraphenylmethane and tetraphenylgermane were observed. The relations between the pK_s-values of the above mentioned compounds and solvent parameters as well as solvent structure are discussed.     

Olivine thermal diffusivity influencing factors

Titanium and its alloys are used in production of implants such as knee and hip prostheses due to their superior properties. Ti–Nb–Zr ternary alloys are preferred over other metallic implant materials due to the presence of non-toxic elements, high corrosion resistance, good biocompatibility, and proper mechanical properties. The aim of this work is to investigate the effect of zirconium addition on α → β phase transformation, microstructure, and mechanical behavior of Ti–16Nb alloy. In doing so, Ti–16Nb–xZr (x: 0, 5, 10, 15 mass%) alloys are produced by powder injection molding, which offers advantages such as low cost, net shape, and easy production of complicated parts for implant fabrication. X-ray diffraction analysis and scanning electron microscope images showed that zirconium behaves as a β stabilizer and according to differential thermal analysis, and it decreases α to β transition temperature approximately 30 °C. It is also revealed that increasing zirconium content caused finer microstructure and hardness of the alloy was raised from 336 HV_0.5 to 412 HV_0.5 while elastic modulus remains approximately steady between 103 and 110 GPa. It is concluded that Ti–Nb–Zr alloys have been found to be a good alternative to known metallic implant materials.     

Thermal decomposition of some metal sulphates

The thermal decomposition temperatures of some metal sulphates (iron, copper, cobalt, nickel, zinc and lead sulphates) have been investigated by TG and DTA. The mechanism of decomposition of these sulphates is discussed, making use of additional information obtained from isothermal studies and X-ray diffraction measurements. The activation energies of these reactions were calculated and found to increase, with almost the same increments, in the order Zn<Fe<Co<Ni<Cu.     

Assessing factors influencing the release of hexazinone from clay-based formulations

New designs of pesticide formulations based on organoclays are receiving increasing attention in reducing offsite movement of pesticides in the environment and in prolonging the efficacy of soil-applied pesticides. In the present article, we report the results of laboratory and field experiments conducted to evaluate the influence of the saturating cation, the sorbent : herbicide ratio, and the type of preparation on the controlled release properties of organoclay-based formulations of the herbicide hexazinone. Two organoclays with different affinities for hexazinone (hexadecyltrimethylammonium-exchanged Arizona montmorillonite, HDTMA-SA, and phenyltrimethylammonium-exchanged Arizona montmorillonite, PTMA-SA), two herbicide loadings (10% and 20% AI), and three types of preparation were assayed. Laboratory experiments showed that hexazinone formulations based on HDTMA-SA displayed slow-release properties in water, retarded herbicide leaching through soil columns, and maintained a herbicidal efficacy similar to that of the currently available commercial hexazinone formulation (wettable powder). In contrast, PTMA-SA formulations released the herbicide instantaneously and did not display slow-release properties. High organoclay-herbicide ratios and the use of organic solvent made the interaction between HDTMA-SA and the herbicide more intimate and reduced the release rate of hexazinone, suggesting that a range of release and leaching behaviours can be achieved by selecting the type of preparation and the herbicide loading in the formulations. A field experiment confirmed the usefulness of HDTMA-SA formulations of hexazinone to reduce herbicide leaching while maintaining weed-control efficacy.     

Mechanism and kinetics of inorganic sulphates decomposition

Thermal decomposition of different inorganic sulphates are presented. A number of techniques, but mainly TG and DTA, are used to prove the mechanism and kinetics of CaSO₄, BaSO₄, FeSO₄·xH₂O, Al₂(SO₄)₃·xH₂O under various gas atmospheres. It is shown how the partial pressure of gas components and heating rate may effect the mechanism and kinetic parameters. There are also examples on the effects of some additives and initial treatment on the thermal processes. On the base of the results obtained some recommendations are given concerning the precautions to be taken into account in the thermal decomposition studies and the sulphur recovering.     

Chromatographic determination of solubilities in superheated water

Superheated water (SHW) is an effective solvent for the extraction of a variety of environmental pollutants, but knowledge of the solubilities in water at elevated temperatures necessary to maximise the efficiency of the process is often lacking. Ambient temperature aqueous solubilities have been measured by reverse‐phase HPLC from correlations with retention factors, k, but for poorly soluble organics the eluent must contain a proportion of organic modifier followed by extrapolation to pure water. The use of SHW as mobile phase allows direct determination of aqueous solubility from measurement of k on a modified HPLC system in which the eluent is cooled before detection to improve baseline stability. Alumina‐bonded octadecylsilane columns were found to be more stable in SHW chromatography than their silica‐bonded counterparts. To validate the procedure, measurements of k were made between 100 and 200°C for toluene and correlated with literature solubilities; the solubilities at 170°C of a number of related aromatics were then determined from their k‐values.     

The solubilities of azobenzene derivatives in water

Summary The solubilities of azobenzene derivatives in water have been determined at 5 °C intervals from 0° to 40 °C to obtain the information both about the effect of polar groups on the solubility of aromatic compounds in water and about the action of polar groups to the iceberg-formation in the vicinity of hydrophobic part of the solute in water environment. From the results the imaginary super cooled pure liquid has been taken as a standard state and the thermodynamic parameters of solution of azobenzene derivatives in water have been calculated.     

The factors influencing coordination numbers in solids

An empirical plot of average principal quantum number ($\text{n}$) versus average AX electronegativity difference (Δχ) for A_nX_m structures shows resolution of four-, six-, and eight-coordinate solid state structures (Pearson diagrams). A simple molecular orbital (and therefore covalent) analysis of the coordination number problem suggests that it is determined by the balance between X-X nonbonded repulsions and the number of stabilizing interactions (both of which increase with coordination number). A-A repulsions may also be important if A is significantly larger than X. The approach provides an alternative to the ionic model for structure rationalization but it is still not clear how relatively important covalent and ionic factors are in determining the structures of even “ionic” solids.     

A theoretical study of imine-ene reaction influencing factors

Potential energy surfaces of the imine-ene reaction between methanimine and propene have been calculated using restricted and unrestricted density functional theory at the B3LYP level. The results show that a concerted mechanism with an exo configuration for lone pair electrons transition structure is more favourable for the intermolecular bare imine-ene reaction. In addition, the C-C bond formation and the migration of the propene α-hydrogen occur simultaneously. The promoting effect of seventeen Lewis acids was also studied. When a Lewis acid is used as a promoter, the corresponding activation and reaction energies decline greatly compared to those of the bare imine-ene reaction. A good correlation (R(2) > 0.9) was found between the activation barriers and the polar character of the transition states. Lewis acids and electron-withdrawing substituents on methanimine were proven to facilitate the imine-ene reaction, whereas electron-donating groups, conjugated groups or a bulky group hinders the reaction. The steric factor is the most unfavourable. The reactivity indices defined by the conceptual density functional theory were also studied and there is a good correlation between the activation barrier and electrophilicity. Frontier molecular orbital theory gives a good explanation for the above results.     

Cavities in molecular liquids and the theory of hydrophobic solubilities

Thermal configurational data on neat liquids are used to obtain the work of formation of hard spherical cavities of atomic size in six molecular solvents: n-hexane, n-dodecane, n-undecyl alcohol, chloroform, carbon tetrachloride, and water. These results are used to test a recent suggestion that the differences between nonaqueous solvents and liquid water in solvation of inert gases are not principally due to the hydrogen-bonded structure of liquid water but rather to the comparatively small size of the water molecule. The frequencies of occurrence of cavities in liquid water can be meaningfully distinguished from those in the organic solvents. Liquid water has a larger fractional free volume, but that free volume is distributed in smaller packets. With respect to cavity work, water is compared to a solvent of the same molecular density and composed of hard spheres of the same size as the water molecule. That comparison indicates that the hard-sphere liquid finds more ways to configure its free volume in order to accommodate an atomic solute of substantial size and thus, would be more favorable solvent for inert gases. The scaled particle model of inert gas solubility in liquid water predicts cavity works 20% below the numerical data for TIP4P water at 300 K and 1.0 g/cm3 for cavity radii near 2.0 angstroms. It is argued that the sign of this difference is just the sign that ought to be expected and that the magnitude of this difference measures structural differences between water and the directly comparable hard-sphere liquid. In conjunction with previous data, these results indicate that atomic sized cavities should be considered submacroscopic.     

Mutual solubilities of hydrocarbons and water with the CPA EoS

The knowledge of hydrocarbon/water phase equilibria is important in the design and operation of equipment for petroleum transport and refining and petrochemical plants. The presence of water in a hydrocarbon mixture can affect the product quality and damage the operation equipment due to corrosion and formation of gas hydrates. Tracing the concentration of hydrocarbons in aqueous media is also important for technical purposes like preventing oil spills and for ecological concerns such as predicting the fate of these organic pollutants in the environment.     

Mechanisms and factors influencing the removal of microcystin-LR by ultrafiltration membranes

In this study, we investigate the application of ultrafiltration (UF) for the removal of the cyanotoxin, microcystin-LR, and determine the dominant removal mechanisms. System variables examined included membrane characteristics, feed concentration, water recovery and operating pressure. While adsorption dominated rejection for most UF membranes, at least at early filtration times, both size exclusion and adsorption were important in removing microcystin-LR by the tight thin-film (TF) membranes. Adsorption was primarily attributed to hydrophobic interactions, although hydrogen bonding and physical surface properties such as surface roughness, thickness, and porosity may also play a role. Polysulfone membranes, the most hydrophobic membrane examined, significantly adsorbed microcystin-LR (91%), whereas the more hydrophilic cellulose acetate membranes adsorbed little or no microcystin-LR. The initial feed concentration had a significant influence on the adsorption capacity of TF membranes for microcystin-LR, which could be described based on a linear adsorption isotherm. An increase in water recovery and/or operating pressure led to an increase in the adsorption of microcystin-LR, probably due to increased convective transport. On the other hand, microcystin-LR rejection through size exclusion was reduced for higher water recovery and/or applied pressure.