Volumetric Properties of Aqueous Solutions of Tetramethyl-<Emphasis Type="Italic">bis</Emphasis>-urea between 278.15 and 338.15 K at Atmospheric Pressure

Densities of aqueous solutions of tetramethyl-bis-urea (TMbU) with solute mole fractions ranging up to 7.0×10⁻² have been measured with an uncertainty of 1.5×10⁻⁵ g⋅cm⁻³, at 278.15, 298.15, 318.15, and 338.15 K using a vibrating-tube densimeter. The partial molar volumes and expansibilities of TMbU (down to the infinite dilution) and water have been computed. The effects of solute concentration and temperature on the volume packing changes, caused by dissolution (and hydration) of TMbU in an aqueous medium, have been considered.     

The Hydrolysis of AuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> and the Stability of Aquachlorohydroxocomplexes of Gold(III) in Aqueous Solution

The equilibria AuCl₄⁻+jOH⁻+kH₂O⇌AuCl_4−j−k (OH) _j (H₂O) _k ^k−1+(j+k)Cl⁻, β _jk (0≤j,k≤4) have been studied spectrophotometrically at 20 °C in aqueous solution. For I=2 mol⋅dm⁻³(HClO₄) the conventional constants, β _i ^*, of the equilibria, Au^*+iCl⁻ ⇌AuCl _i ^*, are equal to log ₁₀ β ₁^*=(6.98±0.08); log ₁₀ β ₂^*=(13.42±0.05); log ₁₀ β ₃^*=(19.19±0.09); and log ₁₀ β ₄^*=(24.49±0.07), where [AuCl _i ^*]=∑[AuCl _i (OH) _j (H₂O)_4−i−j ] at i=const. The hydrolysis and other transformations of AuCl₄⁻ in aqueous solution are discussed. On the basis of new and known data, a full set of equilibrium constants, β _jk , or their estimates has been obtained.     

Thermodynamic Model for ThO<Subscript>2</Subscript>(am) Solubility in Alkaline Silica Solutions

No thermodynamic data for Th complexes with aqueous Si are available. To obtain such data, extensive studies on ThO₂(am) solubility were carried out as functions of: (1) a wide range of aqueous silica concentrations (0.0004 to 0.14 mol⋅L⁻¹) at fixed pH values of about 10, 11, 12, and 13; and (2) and variable pH (ranging from 10 to 13.3) at fixed aqueous Si concentrations of about 0.006 mol⋅L⁻¹ or 0.018 mol⋅L⁻¹. The samples were equilibrated over long periods (ranging up to 487 days), and the data showed that steady-state concentrations were reached in < 29 days. X-ray diffraction, FTIR, and Raman analyses of the equilibrated solid phases showed that the Th solids were amorphous ThO₂(am) containing some adsorbed Si. The solubility of ThO₂(am) at pH values ranging from 10 to 13.3 at fixed 0.018 mol⋅L⁻¹ aqueous Si concentrations decreases rapidly with an increase in pH, and increases dramatically with an increase in Si concentrations beyond about 0.003 mol⋅L⁻¹ at fixed pH values > 10. The data were interpreted using both the Pitzer and SIT models, and required only the inclusion of one mixed-hydroxy-silica complex of Th [Th(OH)₃(H₃SiO₄)₃²⁻]. Both models provided similar complexation constant values for the formation of this species. Density functional theory calculations predict complexes of this stoichiometry, having six-fold coordination of the Th cation, to be structurally stable. Predictions based on the fitted value of log ₁₀ K ⁰=−18.5±0.7 for the ThO₂(am) solubility reaction involving Th(OH)₃(H₃SiO₄)₃²⁻[ThO₂(am)+3H₄SiO₄+H₂O↔Th(OH)₃(H₃SiO₄)₃²⁻+2H⁺], along with the thermodynamic data for aqueous Si species reported in the literature, agreed closely with the extensive experimental data and showed that under alkaline conditions aqueous Si makes very strong complexes with Th.     

Isopiestic Determination of the Osmotic Coefficients and Pitzer Model Representation for the Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>+LiCl + H<Subscript>2</Subscript>O System at <Emphasis Type="Italic">T</Emphasis>=298.15 K

Isopiestic molalities and water activities have been measured for the Li₂B₄O₇+LiCl + H₂O system at T=298.15 K using an improved isopiestic apparatus. Two types of osmotic coefficients, φ _S and φ _E, were determined, where φ _S is based on the stoichiometric molalities of the solute Li₂B₄O₇(aq) and φ _E is based on equilibrium molalities calculated by consideration of the equilibrium speciation of Li₂B₄O₇ to partially form H₃BO₃, B(OH)₄⁻ and B₃O₃(OH)₄⁻. The stoichiometric equilibrium constant K _m for the aqueous speciation reaction was estimated. Two representations of the osmotic coefficients of Li₂B₄O₇ + LiCl + H₂O were made with Pitzer’s ion-interaction model. Model (1) involved representing the φ _S values with six parameters based on considering the ionic interactions between Li⁺, Cl⁻, and B₄O₇²⁻; and model (2) involved representing the φ _E values based on the calculated equilibrium speciation. Reasonable agreements were obtained between the experimental osmotic coefficient data and those calculated using the above models, with standard deviations of 0.075 and 0.0229, respectively, for these two models. The thermodynamic osmotic coefficients for the complex system containing polymeric boron anions and lithium cation was modelled and explained by use of Pitzer’s ion-interaction model, with minor modifications in combination with speciation reaction equilibria.     

Physico-Chemical Processes Induced by Electrical Breakdown and Discharge Responsible for Memory Effect in Krypton with &lt; 10 ppm Nitrogen

In order to analyze the processes induced by electrical breakdown and discharge responsible for memory effect in krypton-filled tube at low pressure, experimental data mean value of electrical breakdown time delay \(\bar{t}_{d}\) as a function of afterglow period τ (memory curve) was used. Analysis showed that in the 1 μs < τ < 7 ms interval positive ions formed in the previous discharge and in afterglow have a dominant role in secondary emission of electrons from the cathode which lead to initiation of breakdown. In the 7 ms < τ < 30 s interval N(⁴S) atoms have a dominant role in secondary electron emission. These atoms are formed during breakdown and discharge by dissociation of nitrogen molecules that are presented as impurities in krypton. For τ > 30 s the concentration of N(⁴S) atoms decreases significantly so that the dominant role in initiation of breakdown is taken over by cosmic rays and natural radioactivity. The increase in discharge current leads to the decrease in \(\bar{t}_{d}\) in the 1 μs < τ < 7 ms interval due to the increase in positive ion concentration. The increase in applied voltage decreases the values of \(\bar{t}_{d}\) for τ > 7 ms due to the increase in probability for breakdown. It has also been show that exposure of krypton-filled tube to low dose of gamma ray irradiation as well as UV irradiation with wavelength higher than 300 nm leads to the decrease in \(\bar{t}_{d}\). This decrease occurs for τ > 7 ms, when N(⁴S) atoms play a dominant role in breakdown initiation.     

Experimental and Theoretical Determination of the Limiting Partial Molar Volume of Indole in CCl<Subscript>4</Subscript>, Tetrahydrofuran and Acetonitrile at 293.15 K: A Comparative Study with Benzimidazole and Benzothiophene

The partial molar volumes of indole(Ind) at infinite dilution (V₂^￥V_{2}^{\infty}) in carbon tetrachloride (CCl₄), acetonitrile (ACN) and tetrahydrofuran (THF) as solvents, were estimated from densitometry measurements at 293.15 K. The results indicate that $V_{2}^{\infty}\mbox{(ACN)}>V_{2}^{\infty}\mbox{(CCl$V_{2}^{\infty}\mbox{(ACN)}>V_{2}^{\infty}\mbox{(CCl $\approx V_{2}^{\infty}\mbox{(THF)}$\approx V_{2}^{\infty}\mbox{(THF)}. The values determined in this study are close to the values calculated from reported density for Ind in the solid state. In order to make a comparison the partial molecular volume of benzimidazole (Bim) and benzothiophene (BT) in solvents with appropriate solubility were measured too, and the results have revealed that $V_{2}^{\infty}\mbox{(BT)}>V_{2}^{\infty}\mbox{(Ind)}$V_{2}^{\infty}\mbox{(BT)}>V_{2}^{\infty}\mbox{(Ind)} in CCl₄ and $V_{2}^{\infty}\mbox{(Ind)}>V_{2}^{\infty}\mbox{(Bim)}$V_{2}^{\infty}\mbox{(Ind)}>V_{2}^{\infty}\mbox{(Bim)} in THF. In this work the role of solvent reorganization around to solute cavity, and specific and nonspecific interactions on the volumetric behavior of these molecules in solution are discussed using the Terasawa-Itsuki-Arakawa model, the Lee-Graziano model, molar volumes of solutes calculated at the DFT-B3LYP/cc-pVTZ and aug-cc-pVTZ level in the gas phase and considering solvent presence with the Onsager’s reaction field, and the van der Waals volume. This analysis suggests that the molecular volumes of solutes are overestimated by the quantum methods employed in this work and that the volumetric contribution from the van der Waals components to the limiting partial molecular volumes of solutes is important, with the exception of Ind in CCl₄ where the solvent reorganization is the dominant factor.     

Thermodynamic Protonation Parameters of some Sulfur-Containing Anions in NaCl<Subscript>aq</Subscript> and (CH<Subscript>3</Subscript>)<Subscript>4</Subscript>NCl<Subscript>aq</Subscript> at <Emphasis Type="Italic">t</Emphasis>=25 °C

Protonation constants of one thiocarboxylate (thioacetate) and four sulfur-containing carboxylates (2-methylthioacetate, thiolactate, thiomalate, 3-mercaptopropionate) were determined by potentiometric measurements in a wide ionic strength range [0≤I≤5 mol⋅L⁻¹ in NaCl and 0 ≤I≤3 mol⋅L⁻¹ in (CH₃)₄NCl] at t=25 °C. For two of these ligands (2-methylthioacetate and thiolactate), the protonation enthalpies were also determined by calorimetric measurements in NaCl ionic medium [0 ≤I≤5 mol⋅L⁻¹] at t=25 °C. Individual UV spectra of the protonated and unprotonated 3-mercaptopropionate species, together with values of the protonation constants, were obtained by spectrophotometric titrations. Results were analyzed in terms of their dependence on the ionic medium by using different thermodynamic models [Debye-Hückel type, SIT (Specific ion Interaction Theory) and Pitzer’s equations]. Differences among protonation constants obtained in different media were also interpreted in terms of weak complex formation.     

Cross-sections for formation of <Superscript>178m2</Superscript>Hf and <Superscript>179m2</Superscript>Hf through reactions on natural hafnium at neutron energy 14.8 ± 0.2 MeV

The cross sections for formation of metastable state of ¹⁷⁸Hf (^178m2Hf, 574.215 keV, 31 y) and ¹⁷⁹Hf (^179m2Hf, 362.55 keV, 25.05 d) through reactions induced by 14.8 ± 0.2 MeV neutrons on natural hafnium were measured for the first time. The monoenergetic neutron beam was produced via the ³H(d, n)⁴He reaction on ZF-300-II Intense Neutron Generator at Lanzhou University. Induced gamma activities were measured by a gamma-ray spectrometer with high-purity germanium (HPGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The neutron fluence were determined by the cross section of ⁹³Nb(n, 2n)^92mNb reaction. The neutron energy in the measurement were by the cross section ratios of ⁹⁰Zr(n, 2n)^89m+gZr and ⁹³Nb(n, 2n)^92mNb reactions.     

Comparison of sorption of Pb<Superscript>2+</Superscript> and Cd<Superscript>2+</Superscript> on Kaolinite clay and polyvinyl alcohol-modified Kaolinite clay

Kaolinite clay obtained from Ubulu-Ukwu, Delta state in Nigeria was modified with polyvinyl alcohol (PVA) reagent to obtain PVA-modified Kaolinite clay adsorbent. Scanning Electron Microscopy (SEM) of the PVA-modified adsorbent suggests that Kaolinite clay particles were made more compact in nature with no definite structure. Modification of Kaolinite clay with PVA increased its adsorption capacity for 300 mg/L Pb²⁺ and Cd²⁺ by a factor of at least 6, i.e., from 4.5 mg/g to 36.23 mg/g and from 4.38 mg/g to 29.85 mg/g, respectively, at 298 K. Binary mixtures of Pb²⁺ and Cd²⁺ decreased the adsorption capacity of Unmodified Kaolinite clay for Pb²⁺ by 26.3% and for Cd²⁺ by 0.07%, respectively. In contrast, for PVA-modified Kaolinite clay, the reductions were up to 50.9% and 58.5% for Pb²⁺ and Cd²⁺, respectively. The adsorption data of Pb²⁺ and Cd²⁺ onto both Unmodified and PVA-modified Kaolinite clay adsorbents were found to fit the Pseudo-Second Order Kinetic model (PSOM), indicating that adsorption on both surfaces was mainly by chemisorption and is concentration dependent. However, kinetic adsorption data from both adsorbent generally failed the Pseudo-First order Kinetic model (PFOM) test. Extents of desorption of 91% Pb²⁺ and 94% Cd²⁺ were obtained, using 0.1 M HCl, for the Unmodified Kaolinite clay adsorbent. It was found that 99% Pb²⁺ and 97% Cd²⁺, were desorbed, for PVA-modified Kaolinite clay adsorbents within 3 min for 60 mg/L of the metal ions adsorbed by the adsorbents.     

Experimental and the Theoretical Studies of the Dielectric Properties of DMSO–H<Subscript>2</Subscript>O Mixtures

This paper focuses on the measurement of the permittivity of dimethyl sulfoxide (DMSO)–water (H₂O) mixture solutions, at 2.45 GHz by using a resonant cavity perturbation method. A specific phenomenon was found, in that the imaginary part of the permittivity for the mixture solution was larger than the imaginary part for each component. Theoretical calculation indicated that the reason for that phenomenon was that the high frequency friction of the mixture was larger than that of each component. When comparing the theoretical results with the experimental data, it was found that the classical Debye equation must be modified in order to calculate the complex permittivity.     

Crystallization study of Se<Subscript>86</Subscript>Sb<Subscript>14</Subscript> glass

The present study concerns with high-accuracy determination of crystallization activation energy (\(E_{\text{c}}\)), the frequency factor (\(k_{0}\)), the kinetic exponent (n) for Se₈₆Sb₁₄ glass. Different three methods have been used to investigate the \(E_{\text{c}} \,{\text{and}}\,k_{0 }\) values. It was found that the deduced value of k ₀ based on Kissinger’s method is too small compared with the others. Therefore, it can’t be used to investigate k ₀ value. Where \(E_{\text{c}} \,{\text{and}}\,k_{0}\) values are already known, the overall reaction rate \(k = k_{0 } { \exp }\left( { - E_{\text{c}} /\left( {R \cdot T} \right)} \right)\) at any temperature can be calculated. Now, Avrami’s equation (\(\chi = 1 - { \exp }\left( { - \left( {kt} \right)^{\text{n}} } \right)\)) contains only one unknown which is the kinetic exponent (n). This method enables us to determine n value without any approximations. The values’ crystallization fraction \((\chi_{\text{th}} )\) that theoretically calculated is the same as that experimentally investigated \((\chi_{{{ \exp } .}} )\).     

Trendwatcher or trendsetter; 50 years of MTAA

The development on neutron activation analysis (NAA) into a technique of practical interest effectively started about 60 years ago, when nuclear reactors became available and widely accessible as intense sources of neutrons. During 50 out these 60 years, the series of Modern Trends in Activation Analysis (MTAA) Conferences acted as a true companion and facilitator of this growth. As trendwatcher they signalized the many initiatives that contributed to the development of activation analysis and its applications. A period has come to an end of impressive development resulting from sometimes revolutionary changes in radiation detection and data processing, and much improved irradiation facilities, NAA has reached a full stage of development, with emphasis on routine application and with remaining developments of in marginal impact. NAA is being challenged increasingly in the last 30 years by alternative techniques for multi trace element analysis. The MTAA Conference and with it the ICAA, the International Committee on Activation Analysis, can play an important and active role in this process of identifying and selecting key areas, and even promoting concerted action in those areas. Such an evolution of focus from retrospective to prospective, from trendwatcher to trendsetter, may well allow the MTAA Conference to continue and even expand its role in future development of NAA and its applications. The ideas about the future of the MTAA Conferences and its organization are elaborated upon and some possible subjects for focused development activities are indicated.     

Degradation of 81 keV <Superscript>133</Superscript>Xe gamma-rays into the 31 keV X-ray peak in CsI scintillators

Pacific Northwest National Laboratory uses beta-gamma coincidence detectors in a number of xenon sampling and measurement systems to enable simultaneous, sensitive measurements of ¹³¹Xe, ¹³³Xe, ^133mXe, and ¹³⁵Xe for treaty monitoring applications. In recent years, a new style of beta–gamma detector was developed to improve upon the detector module used in the Automated Radioxenon Sampler/Analyzer. The results of an MCNP5 Monte Carlo simulation of the new detector cell are presented, with particular emphasis on the identification of an energy deposition sequence with the potential to introduce significant error into the detector efficiency calibration. This sequence occurs when an 81 keV gamma from ¹³³Xe is absorbed in an inactive region of the CsI(Na) scintillator, followed by emission of a 31 keV X-ray from cesium (or possibly a 28.5 keV X-ray from iodine). These X-rays add excess counts into the 31 keV peak observed in the decay of ¹³³Xe. The impact of this effect on different efficiency calibration techniques is discussed.     

Decomposition of 8 mol·L<Superscript>−1</Superscript> Urea Solution at 298.15 K

Degradation of urea in 8 mol·L^?1 aqueous solution (20% w/w N) has been studied at 298.15?±?0.01 K over a time period of 150 days. The data were obtained by periodicaly measuring the electric conductivity, acidity, and concentrations of the main species of the solution, such as cyanate, ammonim carbonate and ammonium hydrogencarbonate. The concentration of un-ionized ammonia was calculated on the basis of the data for the total ammonia content in the solution.     

Excess Volumes,Isentropic Compressibilities and Viscosities for Binary Mixtures of <Emphasis Type="Italic">tert</Emphasis>-Butylamine with Alkyl Acetates at 303.15 K

The data on excess volume (V ^E), density (ρ), viscosity (η) and speeds of sound (u) for the binary mixtures of tert-butylamine (TBA) + methyl acetate (MA), + ethyl acetate (EA), + butyl acetate (BA) and + isoamyl acetate (IAA) at 303.15 K were measured experimentally over the entire range of composition. Speeds of sound were evaluated using Jacobson’s free length theory (FLT) and Schaaffs’ collision factor theory (CFT). The viscosity data were analyzed on the basis of the corresponding states approach and the Grunberg and Nissan treatment. The experimental results for excess volume, deviation in isentropic compressibility and deviation in viscosity were discussed in terms of molecular interactions between unlike molecules. A Redlich-Kister type equation was used to fit the experimental data on excess volume, deviation in compressibility and deviation in viscosity.     

A kinetic and statistical model for carbon deposition on Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in the steam methane reforming

An experimental and statistical study was performed for the carbon deposition on Ni/Al₂O₃ catalyst in the methane steam reforming process. Carbon deposition plays a significant role in the catalyst deactivation. Thus, applying a statistical model and a kinetic rate for carbon deposition is so valuable. The central composite design (CCD) was used for the modeling of the carbon deposition process. The statistical analysis of model, as obtained from the CCD method, revealed that a polynomial equation with the F-value = 456.94, the p value < 0.0001, and the R ² = 0.9919, could appropriately predict the experimental data. Based on the established models, an increase in steam to methane ratio (S/C) caused carbon deposition sharply decreased. As pressure increased from 1.81 to 4.19 bar, carbon deposition slightly increased. When temperature varied from 540 to 600 °C, whisker carbon was produced and its activity increased with temperature. As temperature exceeded 600 °C, carbon deposition slightly increased that can be attributed to formation of pyrolytic carbon. The minimum of carbon deposition was occurred in low pressure, high S/C and at 600 °C. So, the kinetic rate of carbon deposition was suggested in these conditions using generalized reduced gradient nonlinear method. The proposed kinetic rate of methane decomposition reaction can accurately predict the experimental rate data.     

Thermophysical Properties of H<Subscript>2</Subscript>O–Ar Plasmas at Temperatures 400–50,000 K and Pressure 0.1 MPa

The article presents the calculation of thermophysical properties of the mixture water steam–argon which has been used to further enhance the characteristics of plasma torches stabilized by the water wortex. The calculations were performed at the temperatures 400–50,000 K and at 0.1 MPa. First, the composition and thermodynamic properties are determined by classical methods. Further the calculations of viscosity, electrical conductivity and thermal conductivity of the mixture are computed in the 4th approximation of the Chapman–Enskog method. The computation of collision integrals is described with special respect to the interactions of charged particles where the necessary calculations for the Coulomb potential screened at the Debye length were enlarged to cover the 4th approximation. Then the formulae describing the method based on the variational principle of solving the system of Boltzmann integrodifferential equations are shortly introduced and the transport coefficients are presented.     

Heat Capacities and Thermodynamic Properties of Aqueous SrCl<Subscript>2</Subscript> Solutions in the Temperature Range from 80 to 320 K

The molar heat capacities of three different concentrations of aqueous SrCl₂ solutions, 0.1212, 0.4615 and 1.878 mol⋅kg⁻¹, were measured, using a precision automated adiabatic calorimeter in the temperature range from 80 to 320 K. Solid–liquid phase transitions were observed at 272.83, 270.18 and 255.15 K, respectively, for these three solutions. The molar enthalpies and entropies of the phase transitions were evaluated. The experimental heat capacity data were fitted to polynomial equations, and based on the polynomial equations and thermodynamic relationship, the thermodynamic functions relative to 298.15 K, [H _T −H _298.15 K] and [S _T −S _298.15 K], of the three solutions were derived in the range of 80 to 320 K with an interval of 5 K.     

Textile with silver silica spheres: its antimicrobial activity against <Emphasis Type="Italic">Escherichia coli and Staphylococcus aureus</Emphasis>

The aim of this study was to investigate antimicrobial activity of textiles doped with silver in different forms. Three types of textiles were prepared and examined: textiles doped with commercially available Ag nanoparticles, textiles doped with commercial colloidal silver and textiles doped with silver silica SiO₂/Ag spheres. The specimens of silica submicron spheres were synthesized by the sol–gel method as a matrix for biological active silver. The results of microbiological tests revealed that among three kinds of Ag doped textiles only these doped with SiO₂/Ag spheres are bacteriostatically active. During the experiments minimal inhibiting bacteria growth concentration of active SiO₂/Ag spheres added to textiles was determined.     

Dioxouranium(VI) Hydrolysis at 75 and 100 °C in 3.6 mol⋅kg<Superscript>−1</Superscript> LiClO<Subscript>4</Subscript> Aqueous Medium

This work is concerned with the acidic properties of the uranyl ion, UO₂²⁺, at 75 and 100 °C in 3.6 mol⋅kg⁻¹ LiClO₄ aqueous medium. The investigation was carried out with a coulometric-potentiometric technique. Direct and reverse acid-base titrations were carried out in order to check whether equilibrium had been reached. Moreover, in order to determine whether or not the solutions were oversaturated, a further check was carried out with fresh saturated hydrolyzed solutions.