Surface disordering of classic and superionic crystals: A description in the framework of the stern model

The surface potential (φ_S) in ionic crystals: binary compounds of the type NaCl and superionic oxygen conductors of the type M _{1 ? c} ^IV Me _c ^III O_{2 ? c/2} are calculated with the aid of the Stern model. Effect of the energy of formation of defects, concentration of accessible sites (N _S), and concentration of admixtures on the temperature dependences of φ_S(T) is studied. Instances of high and low potentials are analyzed. It is demonstrated that the surface potential increases proportionally to the difference between the adsorption energies of individual defects, provided the absolute value of |ΔG _i| (ΔG _i < 0) and concentration N _S are sufficiently large. Values of isoelectric temperatures in NaCl crystals doped with admixtures of other valence are calculated. An attempt is undertaken to describe experimental data for silver halides with the aid of the model. Calculations of the surface potential in superionic oxygen conductors show that increasing concentration of surface vacancies is accompanied by segregation of the admixture cations in the surface layer.     

A comparison of energy changes accompanying growth processes by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Calculations are made using the equations Δ_r G = Δ_r H ? TΔ_r S and Δ_r X = Δ_r H ? Δ_r Q where Δ_r X represents the free energy change when the exchange of absorbed thermal energy with the environment is represented by Δ_r Q. The symbol Q has traditionally represented absorbed heat. However, here it is used specifically to represent the enthalpy listed in tabulations of thermodynamic properties as (H _T  ? H ₀) at T = 298.15 K, the reason being that for a given substance TS equals 2.0 Q for solid substances, with the difference being greater for liquids, and especially gases. Since Δ_r H can be measured, and is tangibly the same no matter what thermodynamics are used to describe a reaction equation, a change in the absorbed heat of a biochemical growth process system as represented by either Δ_r Q or TΔ_r S would be expected to result in a different calculated value for the free energy change. Calculations of changes in thermodynamic properties are made which accompany anabolism; the formation of anabolic, organic by-products; catabolism; metabolism; and their respective non-conservative reactions; for the growth of Saccharomyces cerevisiae using four growth process systems. The result is that there is only about a 1% difference in the average quantity of free energy conserved during growth using either Eq. 1 or 2. This is because although values of TΔ_r S and Δ_r Q can be markedly different when compared to one another, these differences are small when compared to the value for Δ_r G or Δ_r X.     

Electrical-percolation effects in micellar solutions of alkyltrimethylammonium bromides

Specific conductivity K of aqueous solutions of alkyltrimethylammonium bromides has been studied in a wide range of concentrations c of surfactants containing 10, 12, 14, and 16 carbon atoms in alkyl chains. In general, three break points have been observed in the K(с) dependences. The first point observed upon increasing overall solution concentration corresponds to critical micelle concentration CMC₁. The CMC₁ values of alkyltrimethylammonium bromides decrease with an increase in the alkyl chain length. They are in satisfactory agreement with the published data. It has been supposed that the second break point in the K(с) dependences corresponds to the formation micellar structures as clusters and the appearance of channels with a higher specific conductivity, which is provided by the contribution from the overlap of electrical double layers existing in the vicinities of micelles. Surfactant concentrations corresponding to these break points have been called “critical percolation concentrations” (CPCs). The position of a CPC in the concentration scale strongly depends on alkyl radical length. All K(с) curves exhibit a third break, which corresponds to second critical micelle concentration CMC₂, at which the properties of ionic-surfactant solutions may substantially change because of the appearance of supramicellar structures. The experimental data obtained have been used to evaluate the parameters of the model of electrical percolation for micellar solutions, i.e., effective conductivity \({\tilde K_m}\) and effective micelle radius r ₀.     

The thermodynamic properties of 5-vinyltetrazole and poly-5-vinyltetrazole over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 350 K

The temperature dependences of the heat capacities of 5-vinyltetrazole and poly-5-vinyltetrazole were measured by adiabatic vacuum calorimetry over the temperature range 6-(350–370) K with errors of ～0.2%. The results were used to calculate the thermodynamic functions of the compounds, C _p ^° , H ^°(T) - H ^°(0), S ^°(T), and G ^°(T) - H ^°(0), over the temperature range from T → 0 to 350–370 K. The energy of combustion of 5-vinyltetrazole and poly-5-vinyltetrazole was measured in an isothermic-shell static bomb calorimeter. The standard enthalpies of combustion Δ _c H ^° and thermodynamic characteristics of formation Δ_f H ^°, Δ_f S ^°, and Δ_f G ^° at 298.15 K and p = 0.1 MPa were calculated. The results were used to determine the thermodynamic characteristics of polymerization of 5-vinyltetrazole over the temperature range from T → 0 to 350 K.     

The kinetic patterns of CO oxidation on WO<Subscript>3</Subscript> promoted with Pt or Pd

The kinetic peculiarities of CO oxidation on WO₃ promoted with Pt or Pd were studied. In the region of low catalyst activity (the degree of CO conversion below 20%), the reaction was found to be zero-order in CO and first-order in oxygen. In the high-activity region (CO conversion above 95%), the reaction order was first with respect to CO and zeroth with respect to oxygen. Hysteresis phenomena were observed for the r ? c(O₂) and r ? c(CO) dependences at certain temperatures. A reaction scheme combining the heterogeneous and heterogeneous-homogeneous mechanisms was suggested.     

Thermodynamic Properties of Polyphenylquinoxaline in the Temperature Range of <Emphasis Type="Italic">T</Emphasis> → 0 to 570 K

The thermodynamic properties of amorphous polyphenylquinoxaline in the temperature range of 6 to 570 K are studied via precision adiabatic vacuum calorimetry and differential scanning calorimetry. The thermodynamic characteristics of glass transition are determined. Standard thermodynamic functions C^°_p, H°(T) ? H°(0), S°(Т) ? S°(0), and G°(T) ? H°(0) in the range of T → 0 to 570 K and the standard entropy of formation at T = 298.15 K are calculated. The low-temperature (T ≤ 50 K) heat capacity is analyzed using a multifractal model for the processing of heat capacity, fractal dimension D values are determined, and conclusions on the topological structure of the compound are drawn.     

Thermodynamic properties of first- and third-generation carbosilane dendrimers with terminal phenyldioxolane groups

The heat capacities of first- and third-generation carbosilane dendrimers with terminal phenyldioxolane groups are studied as a function of temperature via vacuum and differential scanning calorimetry in the range of 6 to 520 K. Physical transformations that occur in the above temperature range are detected and their standard thermodynamic characteristics are determined and analyzed. Standard thermodynamic functions C_p^ο(T), [H°(T) ? H°(0)], [S°(T) ? S°(0)], and [G°(T) ? H°(0)] in the temperature range of T → 0 to 520 K for different physical states and the standard entropies of formation of the studied dendrimers at T = 298.15 K are calculated, based on the obtained experimental data.     

Heat capacity and thermodynamic functions of new cobalt manganites NdM<Subscript>2</Subscript><Superscript>I</Superscript> CoMnO<Subscript>5</Subscript> (M<Superscript>I</Superscript> = Li,Na, and K) in the range of 298.15–673 K

Temperature dependences of the heat capacity of cobalt manganites NdM₂ ^I CoMnO₅ (M^I = Li, Na, and K) are studied by means of dynamic calorimetry in the range of 298.15?673 K. It is found that λ-shaped effects are observed on the C _p ^° ~ f (T) curve of cobalt manganites, due probably to second order phase transitions. Based on the experimental data, equations for the temperature dependences of the heat capacity of cobalt manganite are derived with allowance for the temperatures of phase transitions. The values of thermodynamic functions Н°(T)–Н°(298.15), S°(T), and Ф^хх(T) are calculated.     

Thermodynamic Properties of Zincate-Manganites of LaM<Subscript>2</Subscript> <Superscript>II</Superscript>ZnMnO<Subscript>6</Subscript> (М<Superscript>II</Superscript> = Mg,Ca, Sr,Ba) Composition

Temperature dependences of the heat capacity of new zincate-manganites of LaM₂^IIZnMnO₆ (M^II = Mg, Ca, Sr, Ba) composition are studied via experimental calorimetry in the interval of 298.15–673 K. It is found that all compounds have λ-shape effects on the curve of dependence C_p° ~ ?(T) with respect to phase transitions of the second kind. Equations for the temperature dependence of the heat capacity are derived with allowance for phase transition temperatures, and thermodynamic functions H°(T) ? H°(298.15), S°(T) and Φ^xx(T) are calculated on the basis of experimental data on C_p°(T) and the calculated S°(298.15) value.     

Thermodynamic properties of a liquid crystal carbosilane dendrimer

The temperature dependence of the heat capacity of a first-generation liquid crystal carbosilane dendrimer with methoxyphenyl benzoate end groups is studied for the first time in the region of 6–370 K by means of precision adiabatic vacuum calorimetry. Physical transformations are observed in this interval of temperatures, and their standard thermodynamic characteristics are determined and discussed. Standard thermodynamic functions C_p^°(T), H°(T) ? H°(0), S°(T) ? S°(0), and G°(T) ? H°(0) are calculated from the obtained experimental data for the region of Т → 0 to 370 K. The standard entropy of formation of the dendrimer in the partially crystalline state at Т = 298.15 K is calculated, and the standard entropy of the hypothetic reaction of its synthesis at this temperature is estimated. The thermodynamic properties of the studied dendrimer are compared to those of second- and fourth-generation liquid crystal carbosilane dendrimers with the same end groups studied earlier.     

Simulation of copper(II) cations sorption on goethite from aqueous solutions of complexons

Effect of complexons of polyaminopolycarboxylic acid series (IDA, NTA, EDTA, and DTPA) and polyphosphonic acid series (HEDP, NTP, and EDTP) on Cu(II) cations sorption on goethite (α-FeOOH) from aqueous solutions has been studied. Obtained results have been considered in the context of complexation reactions in bulk solution and on sorbent surface. It has been found that all complexons (except for EDTA), depending on nature, produce on goethite surface (≡FeOH) triple complexes of type A (surface–metal–complexon) of composition ≡FeOCuLH _i ^1+i?n and ≡FeOCuL(OH) _j ^1?j?n or type B (surface–complexon–metal) of composition ≡FeLH _i Cu^3+i-n and ≡FeLCu(OH) _j ^3?j?n . pH-Ranges for complex existence and stability constants for the surface complexes have been determined. Factors affecting the character of complexon effect (immobilization/remobilization) on the sorbed metal have been analyzed.     

Thermodynamic properties and functions of condensed Bi<Subscript>8</Subscript>O<Subscript>11</Subscript>

The values of ΔH°₂₉₈, S°₂₉₈, H°₂₉₈–H°₀, T, ΔH _fus, and C _p(T), as well as the temperature dependences of the Gibbs energy function, are calculated for Bi₈O₁₁ oxide by proven computational methods.     

Elastic properties of a nematic in a tetrapalladium organyl-pentadecane system

The temperature dependences of birefringence Δn, anisotropy of permittivity ?_a, and elastic constants K ₁₁ and K ₃₃ in the nematic phase of a tetrapalladium organyl-pentadecane system with a pentadecane content of 55 wt % have been investigated experimentally. It has been shown that, as temperature is elevated, ?_a, K ₁₁, and K ₃₃ values decrease and Δn remains unchanged. Elastic constants K ₁₁ and K ₃₃ have been established to vary from 3.4 × 10^?7 to 5.6 × 10^?6 dyn and from 1.3 × 10^?6 to 27.4 × 10^?5 dyn, respectively. The value of ?_a has been revealed to vary over the range 0.2–0.5. It has been found that, at temperatures above the N₂ → Cr phase transition by 6°C, an imposed electric field induces the growth of tetrapalladium organyl crystals.     

Dissolution kinetics of silver metal nanoparticles in their reaction with nitric acid in an reverse micelle solution of AOT

The dissolution of silver nanoparticles in their reaction with aqueous HNO₃ solubilized to an reverse micelle solution of sodium bis(2-ethylhexyl)sulfosuccinate in decane is studied spectrophotometrically. A physicochemical model is advanced for quantifying the process kinetics on th basis of the following autocatalytic scheme: Ag⁰ + H⁺ + NO ₃ ^? → Ag⁺ + products (k ₁), and Ag⁰ + Ag⁺ + NO ₃ ^? → 2Ag⁺ + products (k ₂). The effective rate constant k ₂ decreases with decreasing solubilization capacity V _S/V _O (where V _S is the volume of the solubilized dispersed aqueous phase and V _O is the volume of the micelle solution); the solubilization capacity determines the size of the micelle cavities in which the reaction between Ag⁰ and HNO₃ occurs: k ₂ = 74 (V _S/V _O) · 100% ≈ 3.8%), 41 (2.9), and 35 (2.0) L/(mol s). The effective constant k ₁ is determined with a high uncertainty; the effect of V _S/V _O on k ₁ has the opposite tendency.     

Structure and Chemical Bonding of the B<Subscript>3</Subscript>S<Stack><Subscript>n</Subscript><Superscript>0/−</Superscript></Stack> (<Emphasis Type="Italic">n</Emphasis> = 2–4) Boron Sulfide Clusters: A Density Functional Theory Investigation

A density functional theory investigation on the structural and bonding properties of B₃S _n ^?/0 (n = 2–4) series has been performed. Based on B3LYP and CCSD(T) calculations, we present the linear D _∞h B₃S₂ ^? (1, ³Σ_g) and D _∞h B₃S₂ (2, ²Π_u), the Y-shaped C _2v B₃S₃ ^? (3, ¹A₁) and C _2v B₃S₃ (4, ²B₂), and perfectly planar structures C _2v B₃S₄ ^? (5, ¹A₁) and C _2v B₃S₄ (6, ²B₂) that contain rhombic B₂S₂ rings. The 1–6 ground-state structures are planar with linear “B–B–B” core, in which the first and the second S atoms prefer to bond terminally to the terminal B, and the third S atom bonds to the center B, however, when the third S atom is added with the fourth, the atoms tend to be in the bridging positions of two adjacent B atoms. The growth pattern of B₃S _n ^?/0 (n = 2–4) clusters helps to understand the structural properties of the other small boron sulfide clusters. Bonding analyses reveal that a dual or single three-center one-electron (3c–1e) π hypervalent bonds located over the “B–B–B” core of D _∞h B₃S₂ ^? (1) and B₃S₂ (2), respectively. While C _2v B₃S₄ ^? (5) and B₃S₄ (6) with rhombic B₂S₂ rings as the center with –BS and –S units all possess 4c–4e bonds (o-bonds) in the rhombic B₂S₂ rings.     

XPS spectra of vanadium-doped disulfides CuCrS<Subscript>2</Subscript>

The charged state of atoms in layered cation-substituted disulfides CuCr_1?x V _x S₂ (x = 0?0.4) was studied using X-ray photoelectron spectroscopy. The study was performed with polycrystalline powder and ceramic samples of chromium-copper disulfides. CuCr_1?x V _x S₂ samples were shown to comprise differently charged atoms of chromium, copper and vanadium, the charged state of which varies with the concentration of vanadium cations (x).     

Thermochemical study of the complex formation of copper(II) and nickel(II) iminodiacetates with amino acids in aqueous solutions

The formation of mixed-ligand complexes in the M(II)–Ida–L systems (M = Cu, Ni, L = His, Orn, Lys), where Ida is the iminodiacetic acid residue, was studied by pH-metry, calorimetry, and spectrophotometry. The thermodynamic parameters (logK, Δ_rG⁰, Δ_rH, Δ_rS) of formation of the complexes were determined at 298.15 K and the ionic strength I = 0.5 (KNO₃). The most probable mode of coordination of the chelating agent and the amino acid in the mixed-ligand complexes was elucidated.     

Thermodynamic characteristics of complexation between Ho<Superscript>3+</Superscript> and ethylenediamine-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>'-disuccinic acid in aqueous solutions at 298.15 K

The thermodynamic characteristics of complexation between ethylenediamine-N,N'-disuccinic acid (H₄Y; EDDA) and Ho³⁺ ion were determined calorimetrically and potentiometrically at 298.15 K and ionic strengths of 0.1, 0.5, 1.0, and 1.5 (KNO₃). The logK, Δ_rG, Δ_rH, and Δ_rS values for the formation of HoY^– and HOHY complexes were calculated at the studied and zero ionic strength values. The changes in thermodynamic parameters of the reactions are discussed.     

Thermodynamics of the terpolymer of carbon monoxide,ethylene, and 1-butene

The heat capacity and the temperatures and enthalpies of physical transformations of the alternating terpolymer of carbon monoxide, ethylene, and 1-butene (the content of butene units is 10.7 mol.%) were studied by adiabatic and differential scanning calorimetry in the temperature range from 6 to 520 K. The energy of terpolymer combustion was measured at 298.15 K on an calorimeter with an isothermal shell and static bomb. The standard thermodynamic functions C°_p(T), H°(T)–H°(0), S°(T)–S°(0), and G°(T)–H°(0) for the range from Т → 0 to 400 K, the standard enthalpy of combustion, and the thermodynamic parameters of formation of the partially crystalline CO—ethylene—1-butene terpolymer at 298.15 K, as well as the thermodynamic characteristics of its synthesis in the range from T → 0 to 400 K were calculated.     

Thermodynamic characteristics of the formation of complexes of nickel(II) with L-homoserine

The formation of complexes of nickel(II) with L-homoserine at 298.15 K and ionic strengths I = 0.5, 1.0, and 1.5 (KNO₃) are investigated by potentiometry and calorimetry. Standard characteristics of studied equilibria (log K°, Δ_rG°, Δ_rH°, and Δ_rS°) are determined.