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Vol 516, No 1 (2024)
CHEMISTRY
Thermally induced transformation tert-butyl peroxyethyl esters of carboxylic acids
Abstract
The features of thermolysis of tert-butyl peroxyethyl esters of carboxylic acids (CH₃)₃COOCH(CH₃)OC(O)R are investigated. Based on the identification of reaction products and the analysis of kinetic parameters, the fact of simultaneous transformation of four bonds (O–O, C–O, C–C and C–H) in a molecule with the formation of two molecules was proved for the first time [RC(O)OH and CO] and two free radicals [(CH₃)₃CO• and •CH₃], which, under experimental conditions, do not enter into a cross-break reaction, but detach the hydrogen atom from the solvent. Evidence of the coordinated (simultaneous) transformation of four bonds is the low (compared with the energy of bond dissociation) values of the activation energy and the pre-exponential multiplier, as well as negative values of the activation entropy.
3-7
Synthesis of spherical LiFePO₄ microparticles with encapsulated carbon nanotubes for high-power lithium-ion batteries
Abstract
Lithium ferrophosphate – LiFePO₄ (LFP) – is one of the widely studied and used materials for lithium-ion batteries. However, one of the main drawbacks of LFP is its poor electrical conductivity. To address this issue, we propose an effective approach based on encapsulating carbon nanotubes within the volume of LFP particles in the volume of spherical LFP particles. Electrodes based on the obtained materials exhibit more aTₜᵣactive electrochemical characteristics than LFP obtained by the standard method: increased specific capacity (62 and 92 mAh g–1 at a current density of 20C for LFP and LFP/SWCNT, respectively), stability of cyclic characteristics (preservation of 98% capacity after 100 charge/discharge cycles for LFP/SWCNT and 96.5% for LFP), as well as reduced charge transfer resistance. Encapsulation of SWCNT into the structure of iron phosphate during deposition is an easy-to-implement approach to formation modified LFP-based cathodes with improved characteristics, which expands the possibilities of their practical application in high-power lithium-ion batteries.
8-20
CHEMICAL TECHNOLOGY
The change of phase composition and the morphology of particles of hydrothermal titanosilicate precipitates during their aging
Abstract
During the study of phase formation under conditions of hydrothermal synthesis of alkaline titanosilicate systems (NH₄)₂TiO(SO₄)₂⋅H₂O или TiOSO₄⋅H₂O-Na₂SiO₃-NaOH-H₂O it was found that the formed titanosilicate solid phases differ both in composition and structure. The process of their aging under conditions of long-term exposure without forced heating is accompanied mainly by the loss of free water without noticeable structural and morphological changes. The exposure to the temperature of 70–100°С significantly accelerates the process of solid phase transformation. In these conditions, a porous system of particles is formed, which is confirmed by an increase in their specific surface area and total pore volume, as well as by an increase in the activity of the powders to absorb single- and double-charged cations. The effectiveness of hydrochloric acid treatment of fresh and especially aged precipitates on the ordering of the structure with the formation of crystals of a clear frame shape, inherent in the minerals zorite and ivanyukite, which contributes to increasing the sorption capacity of the final product is shown. The obtained results are used to adjust the technological regulations, which are used to test the technology of titanosilicate sorbent on the pilot plant.
21-29
PHYSICAL CHEMISTRY
Development of an applied variant of the kolmogorov–johnson–mehl theory of crystallization for processing thermal analysis data. Temperatures and enthalpies of melting germanium isotopes
Abstract
An applied kinetic model has been developed for processing DSC peaks of transitions between states, determining the temperature–time dependence of the degree of transition and combining the fundamental theory of Kolmogorov–Johnson–Mehl crystallization, simplified for practice, with the semi-empirical Erofeev model. In the development of this applied model, the concept of a “thermodynamic factor” is introduced, which allows a transition in the kinetics of phase transformations of condensed matter. The application of the new approach is demonstrated by the example of studying the dependences of temperature and enthalpy of fusion on the average atomic mass of stable germanium isotopes, data on which, as new chemical individuals, are of a fundamental nature and can serve as reference information.
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The structure of humates in aqueous solutions and their biological activity
Abstract
When studying humate solutions, it is often not taken into account that humic substances (HS) can form supramolecular formations (SMFs) from molecular particles. These SMFs are highly stable, that is, the particles-molecules of HS do not separate from them spontaneously. It follows that at concentrations of the existence of SMFs, it is they, and not the particles-molecules of HS, that should be in solutions and determine their properties. The purpose of the study is to assess the influence of the form of existence of HS in solutions on their physico-chemical properties and biological activity. Solutions of sodium humate from brown coal were used in the work. The experimental results showed that with an increase in the concentration of humates, an abrupt increase in pH in the range of 30–50 mg l⁻¹ is observed. These concentrations correspond to the literature data on changes in the structure of HC in solutions: at concentrations above 30 mg l⁻¹ – barrier concentration – HS molecules form SMFs by self-assembly. Both molecular particles and SMFs, due to the diphilicity of HS, have the properties of surfactants. That is, in solutions at the interface of the “water–air” phases, HS films form. The strength of the films depends on the size of its constituent particles and the speed of their movement from the thickness to the surface of the solution. When plotting graphs in the coordinates “Film formation time in hours–Log humate concentration, mg l⁻¹”, a jump corresponding to the barrier concentration was detected on the curves. It was also found that during foliar treatment of cucumber shoots with mechanoactivated humate solutions with concentrations below the barrier, the stimulation effect increases, apparently due to the transition from the existence of HS in solution in the form of SMFs to existence in the form of particles-molecules that, due to their small size, can penetrate plant cells.
39-44
Multiplet relaxation transitions in fluorurethane coating after climate aging
Abstract
The relaxation transition from a glassy to a highly elastic state (α-transition) of a fluoropolyurethane coating deposited on the surface of VPS-48/778 glass fiber reinforced plastic was studied using the method of dynamic mechanical analysis. It is shown that the relaxation maximum of the dynamic loss modulus in the initial state is a superposition of α1-, α2-, α3-transitions, corresponding, respectively, to transitions from the glassy to highly elastic state of VE-69 enamel and EP-0215 epoxy primer. The transition temperature α1, which is the glass transition temperature of fluoropolyurethane VE-69, after 3 years of exposure decreases in proportion to the average annual air temperature of the region. The transition temperatures α2 and α3 after full-scale exposure due to post-curing increased by 13−15°C and acquired stable values α2 = 99 ± 1°C, α3 = 122.5 ± 0.5°C, regardless of the climatic conditions of the tests.
45-51
Features of electronic structure of (η⁵-C₅H₅)LuCl₂(THF)₃
Abstract
For the first time, a topological analysis of the electron density distribution function in a crystal for an organolanthanide compound was carried out using the CpLuCl₂(THF)₃ complex as an example. The charges on atoms were determined. A predominantly ionic nature of the Lu–ligand bond was confirmed, but the essentially covalent nature of the Lu–Cp bond was discovered. The energies of the Lu–ligand bonds were determined.
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