Thermodynamic Parameters of Nonisothermal Degradation of A New Family of Organometallic Dendrimer with Isoconversional Methods

The objective of this work is to obtain the thermodynamic parameters, namely, the changes of enthalpy, Gibbs free energy, and the entropy of two degradation steps observed in three of a new family of organometallic dendrimers. The isoconversional Flynn-Wall-Ozawa (FWO) model was employed to calculate the effective activation energy and pre-exponential factor. The changes of enthalpy and the entropy was consistent with the activation energy, whereas the change of Gibbs free energy remains positive during the entire degradation process, implying that the degradation is non-spontaneous and thus requires external heat supply.

The Physicochemical Analysis of Bayerite Al(OH)3 → γ-Al2O3 Transformation

It was obtained aluminum hydroxide in the form of bayerite by precipitation with ammonia. The precipitation pH was found by the potentiometric titration. Based on the data of thermal, X‑ray diffraction and IR‑analysis it was identified the sequence of bayerite transitions up to 800 °C. The study of nitrogen adsorption- desorption allowed to determine a specific surface, a volume, and dimensions of pores for boehmite and γ- Al2O3 as 135±2 and 238±10 m2/g; 0.38 and 0.51 cm3/g; 1.7 and 3.8 nm, relatively. The value of effective activation energy for boehmite →γ- Al2O3 transition ((136±5) kJ/mol) was found by means of non- isothermal method (by Avrami equation)

MECHANODESTRUCTION OF ISOPRENE RUBBER. PART 3. KINETICS OF OXIDATIVE DESTRUCTION

Continuation of studies of changes in molecular parameters, in particular, the molecular weight (MM) during the plasticization (P) of SKI-3 isoprene rubber. The kinetics of oxidative destruction (OD) in the temperature range (T) 30-130 °C and time (t) 30–600 s were studied in detail. Plasticization of rubber, as before, was carried out in a laboratory rubber mixer of the company «NFM», and gel chromatographic studies were carried out on a gel chromatograph of the company «Waters». The speed constant OD K0 decreases in absolute value with a decrease in T and an increase in t. The calculated effective activation energy of OD Eeff decreases from 24,4 to 13 kJ/mol in the studied t range. The influence of the oxygen diffusion process on the kinetic features of the OD of SKI-3 at Р is pointed out.

Electrodeposition and Growth of Iron from an Ethylene Glycol Solution

The electrochemical reduction of iron (III) ions into zero-valent iron from a solution of ethylene glycol was accomplished. The kinetics and mechanism of the electroreduction process were investigated by cyclic and linear polarization techniques. The influence of temperature, potential sweep rate, and concentration of iron (III) ions on the electroreduction process was also studied. The observed values of effective activation energy revealed that the investigated electroreduction process is accompanied by mixed kinetics control. Moreover, the results of SEM and X-ray diffraction analysis confirmed the deposition of thin Fe films under the optimized conditions.

SYNTHESIS OF THALLIUM SULPHATE IN A SULFURIC ACID SOLUTION AT POLARIZATION BY CURRENT

Nowadays, the one of the actual problems is the recycling of metal waste and its provision to consumers. However, it is known that there are a number of difficulties with the recycling of thallium waste. By using new recycling methods, it's possible to increase thallium resources and lower prices for thallium-derived products. Therefore, some work was carried out to extract its compounds from thallium waste by studying the electrochemical properties of thallium in our research work. The experimental results showed that thallium electrodes dissolve in an aqueous solution of sulfuric acid under alternating current polarization with the formation of thallium (I) sulfate. In this work, the kinetics of electrochemical oxidation-reduction of thallium in aqueous solutions of sulfuric acid is studied by potentiometry. To characterize the mechanism of thallium electrooxidation, the following parameters were calculated: the order of the reaction and the effective activation energy of the process. The impact of electrolysis modes: current density, concentration and temperature of the electrolyte on the dimensional charac-teristics of the obtained thallium (I) sulfate was investigated.

Solid-State Polymerization as a Vitrimerization Tool Starting from Available Thermoplastics: The Effect of Reaction Temperature

In the current work, solid-state polymerization (SSP) was studied for the synthesis of poly(butylene terephthalate), PBT-based vitrimers. A two-step process was followed; the first step involved alcoholysis reactions and the incorporation of glycerol in the polymer chains. The second step comprised transesterification reactions in the solid state (SSP) in the presence of zinc(II) catalyst resulting in the formation of a dynamic crosslinked network with glycerol moieties serving as the crosslinkers. The optimum SSP conditions were found to be 3 h at 180 °C under N2 flow (0.5 L/min) to reach high vitrimer insolubility (up to 75%) and melt strength (2.1 times reduction in the melt flow rate) while increasing the crosslinker concentration (from 3.5 to 7 wt.%) improved further the properties. Glass transition temperature (Tg) was almost tripled in vitrimers compared to initial thermoplastic, reaching a maximum of 97 °C, whereas the melting point (Tm) was slightly decreased, due to loss of symmetry perfection under the influence of the crosslinks. Moreover, the effect of the dynamic crosslinked structure on PBT crystallization behavior was investigated in detail by studying the kinetics of non-isothermal crystallization. The calculated effective activation energy using the Kissinger model and the nucleating activity revealed that the higher crosslinker content impeded and slowed down vitrimers melt crystallization, also inducing an alteration in the crystallization mechanism towards sporadic heterogeneous growth.

MECHANISM OF HYDROCHEMICAL OXIDATION OF HEAZLEWOODITE IN NITRIC ACID

В работе представлена математическая модель гидрохимического окисления хизлевудита в разбавленных растворах азотной кислоты. Дана физико-химическая интерпретация основных кинетических характеристик процесса растворения: константа скорости и эффективная энергия активации. Установлены режимы взаимодействия хизлевудита с азотной кислотой, выявлены вероятные лимитирующие стадии. По наблюдаемым кинетическим закономерностям при моделировании процесса, предложен механизм гидрохимического окисления хизлевудита. The paper presents a mathematical model of the hydrochemical oxidation of heazlewoodite in dilute solutions of nitric acid. A physicochemical interpretation of the main kinetic characteristics of the dissolution process is given: the rate constant and the effective activation energy. The modes of interaction of heazlewoodite with nitric acid have been established, and probable limiting stages have been identified. According to the observed kinetic regularities in modeling the process, a mechanism for the hydrochemical oxidation of heazlewoodite has been proposed.

INFLUENCE OF THE NANOCLUSTER {MOFE} POLYOXOMETALATE ON OXIDATION OF IODIDE-IONS BY PERSULFATE

Изучены каталитические свойства нанокластерного железомолибденового полиоксометаллата {MoFe} в растворах при реализации окисления персульфатом йодид-ионов. Использована автоматизированная установка на базе спектрофотометрического метода анализа, управляемая компьютером. Сравнение литературных данных и кинетических данных окисления иодида персульфатом показывает, что кеплерат является гетерогенным катализатором. Эти данные позволяют предполагать нерадикальный механизм для разложения персульфата на поверхности молекул кластера на первой стадии реакции окисления иодида калия. Значение эффективной энергии активации процесса указывает на каталитическое воздействие {MoFe} на промежуточной стадии разложения пероксида водорода. Catalytic properties of the nanocluster iron-molybdenum polyoxometalate {MoFe} in solutions during the oxidation of iodide ions by persulfate have been studied. Automated installation based on spectrophotometric method of analysis controlled by computer was used. Comparison of literary data and kinetic datа on the oxidation of iodide with persulfate showed that keplerate {MoFe} is a heterogeneous catalyst. These data allowed to assume a non-radical mechanism for persulfate decomposition on the surface of cluster molecules at the first stage of the potassium iodide oxidation reaction. The value of the effective activation energy of the process indicates the catalytic effect of {MoFe} at the intermediate stage of the decomposition of the hydrogen peroxide.

ELECTROCHEMICAL REDUCTION OF SELENIUM IONS FROM ORGANIC SOLUTION

Due to the unique properties of metal dichalcogenides, they are wide used in various fields of nano- and optoelectronics. Bi2Se3 is one of the promising n-type semiconductor materials belonging to the Av – Bvı group, with a band gap of 0.3 eV. To obtain these compounds by co-electrodeposition, we study the electroreduction of the initial components separately. Therefore, the study is devoted to the electrochemical reduction of selenite ions from the ethylene glycol solution. By drawing cyclic and linear polarization curves on Pt electrodes, the kinetics, the mechanism of the process, and the influence of various factors on the electroreduction of selenite ions are studied. Using the obtained data on the influence of temperature, the effective activation energy was calculated by the Gorbachov method. The calculation results show that the electroreduction of selenite ions from ethylene glycol is accompanied by electrochemical kinetics closer to diffusion

Tunneling Effects in NH3 Annealed 4H-SiC Trench MOSFETs

The interface between the gate oxide and silicon carbide (SiC) has a strong influence on the performance and reliability of SiC MOSFETs and thus, requires special attention. In order to reduce charge trapping at the interface, post oxidation anneals (POAs) are conventionally applied. However, these anneals do not only influence the device performance, such as mobility and on-resistance, but also the gate oxide reliability. We study the oxide tunneling mechanisms of NH3 annealed 4H-SiC trench MOSFET test structures and compare them to devices which received a NO POA. We show that 3 different mechanisms, namely trap assisted tunneling (TAT), Fowler-Nordheim (FN) tunneling and charge trapping are found for NH3 annealed MOS structures whereas only FN-tunneling is observed in NO annealed devices.The tunneling barrier suggest a trap level with an effective activation energy of 382 meV to enable TAT.