Isothermal Mode Research Articles

Oxygen Mobility in the Materials for Solid Oxide Fuel Cells and Catalytic Membranes (Review)

Oxygen transport (including oxygen mobility and surface reactivity) is one of the important factors governing electrochemical activity of solid oxide fuel cells electrodes as well as oxygen and hydrogen separation membranes based on materials with mixed oxide-ionic and electronic conductivity. In this work, oxygen mobility data obtained for a series of materials destined for such devices using modern techniques of oxygen isotope heteroexchange are summarized. Series of solid oxide fuel cells’ and membranes’ materials were studied by isotope exchange of their oxygen with 18O2 and C18O2 in isothermal and temperature-programmed modes using closed and flow reactors and data analysis based on developed model of oxygen diffusion and exchange. For solid electrolytes’ materials (Sc- and Ce-doped zirconia) as well as for proton-conducting materials [Ln5.5(Mo,W)O11.25], the effect of composition heterogeneity on the oxygen mobility was demonstrated. For Ln6 – xWO12 – δ, a strong effect of structure on the oxygen mobility was demonstrated. For oxides with asymmetric structure, where oxygen migration proceeds via cooperative mechanisms [La2(Mo,W)2O9, (Ln,Ca)2NiO4], the doping hampers the cooperative migration, resulting in oxygen mobility deterioration and sometimes forming additional slow diffusion channels. In the PrNi0.5Co0.5O3–Ce0.9Y0.1O2 nanocomposites that are materials of the solid oxide fuel cells’ cathode and functional layer of the oxygen separation membranes, two diffusion channels were observed, where more mobile oxygen corresponds to the fluorite phase and interfaces; less mobile, to the perovskite phase. This is due to special features of cations redistribution between the phases.

Pt–Pd/MnOx–Al2O3 Oxidation Catalysts: Prospects of Application for Control of the Soot Emission with Diesel Exhaust Gases

Together with exhaust gases from motor vehicles with diesel engines, soot and toxic nitrogen oxides are released into the environment. In this work, we consider the possibility of removing diesel soot on the surface of the Pt–Pd/MnOx–Al2O3 oxidation catalyst with a low Pt–Pd content. The rate and activation energy of the catalytic oxidation of diesel soot with oxygen and NOx were studied in the isothermal mode and compared with the kinetic characteristics of the oxidation of charcoal soot and two samples of synthetic soot (Printex U, Vulkan XC-72). The physicochemical properties of soot, such as nano- and microstructure, elemental composition, composition of surface functional groups, determine its oxidative reactivity, which is higher in mixtures with NOx than in oxygen-containing mixtures.

Development of high-strength cast iron for back-up layer of bimetallic products

The article presents chemical composition of the charge and smelting regimes of the newly designed austenitic-bainitic high-strength cast iron with spheroidal graphite (ABHCSG), the analysis of research results of influence of isothermal hardening modes in pseudo-boiling layer on the mechanical properties and structure of cast iron.

Study of the Behavior of Mo40Si40B20 Coatings in the Temperature Range of 1000–1200°С

The resistance of Mo40Si40B20 magnetron coatings to high-temperature oxidation in the 1000–1200°С temperature range is investigated. The main phases of the initial coating are high-temperature β‑MoSi2 with a hexagonal lattice and t-MoB. The phase transition of β-MoSi2 phase into the low-temperature tetragonal α-MoSi2 one proceeds at 1000°С. After annealing, the main structural components of the coating are the t-MoSi2, t-Mo5Si3, and t-MoB phases. The size of the formed crystallites’ of the t-MoSi2, t‑Mo5Si3, and t-MoB phases increases 1.5-fold at 1000–1200°С. The coatings oxidation is studied at 1200°С in the isothermal and non-isothermal modes. After annealing on the surface, a dense oxide SiO2 layer formed and prevented the diffusion of oxygen to the substrate and its subsequent oxidation. In the case of non-isothermal annealing, the protective oxide layer’s thickness increases 2.6–3.6-fold compared to that during isothermal holding for the same holding time.

Gas-Liquid Fluorination of 1,1,1,2-Tetrafluoroethane and Methane with Elemental Fluorine in a Perfluorinated Liquid

The reaction of 1,1,1,2-tetrafluoroethane with fluorine in a gas-liquid reactor with a high-speed stirrer and with perfluorodecalin or perfluoro-1,3-dimethylcyclohexane as a liquid phase occurs as hydrogen substitution without noticeable cleavage of C-C bonds, yielding penta- and hexafluoroethane. The fluorination of methane in perfluorodecalin under the same conditions yields, depending on the methane and fluorine concentrations in their mixtures with an inert gas, products of successive hydrogen substitution by fluorine when the reaction occurs in approximately isothermal mode and products corresponding to the thermodynamic equilibrium when the reaction occurs in the mode of gas-phase diffusion combustion on the gas bubble scale.

Моделирование ex vivo процесса термотерапии стенки кисты Бейкера в изотермическом режиме

Цель работы - определение ex vivo глубины и степени коагуляционных изменений в тканях кисты Бейкера, возникающих при равномерном изотермическом воздействии при различной длительности воздействия. Методика. Для проведения исследования был сконструирован экспериментальный термостолик с возможностью контроля поддержания изотермического режима работы. Иссеченная во время операции капсула кисты Бейкера незамедлительно была разделена на несколько фрагментов. Один из образцов служил контролем, остальные фрагменты выдерживали на поверхности экспериментального термостолика (65-70 °С), в течение различных промежутков времени до 60 с. Все фрагменты, включая интактный, исследовали гистологически. Результаты. В интактном фрагменте кисты Бейкера обнаруживались признаки хронического воспаления, такие как полнокровие сосудов, мукоидное набухание и очаговая периваскулярная инфильтрация лимфоидными элементами. В образцах стенки, подвергнутых термическому воздействию продолжительностью до 30 с, обнаруживались структурные изменения на уровне синовиальной оболочки, в виде пикноза и лизиса ядер синовиацитов. В фрагментах стенки кисты при нагревании в течение 60 с отмечался некроз синовиального слоя, а в подлежащих слоях - признаки отека, разрыхление и фрагментация коллагеновых волокон. Выраженность и глубина деструктивных изменений в стенке кисты Бейкера находились в прямой зависимости от периода непрерывного нагрева. Заключение. Определены закономерности изменений гистологического образца в зависимости от тепловой экспозиции. В период до 30 с теплового воздействия на ткани кисты Бейкера ведущими гистоморфологическими трансформациями являются признаки деструкции синовиального слоя. При увеличении периода нагрева до 60 с имеет место лишь частичное нарушение структуры коллагена в стенке кисты. Aim. To determine ex vivo the depth and degree of coagulation changes in tissues of Baker’s cyst induced by a uniform isothermal exposure of different duration. Methods. An experimental thermo table was constructed for the study with an option to maintain the isothermal mode of operation. The capsule of Baker’s cyst excised during the surgery was immediately divided into several fragments. One of the samples was used as control, the remaining samples were kept on the surface of the thermo table heated to 65-70°C for different time up to 60 seconds. All fragments were examined histologically. Results. The intact fragment of Baker’s cyst showed signs of chronic inflammation, such as plethoric blood vessels, mucoid swelling, and focal perivascular infiltration with lymphoid elements. In samples of the wall exposed to heat for up to 30 seconds, similar structural changes were found at the level of synovial shell in the form of pyknosis and lysis of synoviacyte nuclei. Fragments of the cyst wall heated for 60 seconds showed necrosis of the synovial layer and underlying levels showed swelling, loosening and fragmentation of collagen fibers. Severity and depth of destructive changes in the Baker’s cyst wall directly depended on duration of continuous heating. Conclusion. The study determined some regularities of changes in histological samples related to the thermal exposure. In thermal exposures of Baker’s cyst tissue lasting for up to 30 seconds, the major histological transformation included signs of destruction in the synovial layer. When the heating duration was increased to 60 seconds, only a partial disorder of collagen structure was observed in the cyst wall.

Visualization of Polymer Crystallization by In Situ Combination of Atomic Force Microscopy and Fast Scanning Calorimetry.

A chip-based fast scanning calorimeter (FSC) is used as a fast hot-stage in an atomic force microscope (AFM). This way, the morphology of materials with a resolution from micrometers to nanometers after fast thermal treatments becomes accessible. An FSC can treat the sample isothermally or at heating and cooling rates up to 1 MK/s. The short response time of the FSC in the order of milliseconds enables rapid changes from scanning to isothermal modes and vice versa. Additionally, FSC provides crystallization/melting curves of the sample just imaged by AFM. We describe a combined AFM-FSC device, where the AFM sample holder is replaced by the FSC chip-sensor. The sample can be repeatedly annealed at pre-defined temperatures and times and the AFM images can be taken from exactly the same spot of the sample. The AFM-FSC combination is used for the investigation of crystallization of polyamide 66 (PA 66), poly(ether ether ketone) (PEEK), poly(butylene terephthalate) (PBT) and poly(ε-caprolactone) (PCL).

Thermo-mechanical characterization of carbon fiber composites with different epoxy resin systems

The composite materials have found widespread applications in aircraft, automobiles, sports, space, and defence industries. Understanding the cure behavior as well as resulted thermo-mechanical properties of a thermosetting system are essential in the development and optimization of composite fabrication processes. In this paper, HCU200/A45 carbon fiber prepreg along with HinpoxyC, HinpoxyVB, ARL135 and ARL136 epoxy resin systems with suitable hardeners are used for the development of composites and their characterization. The DMA, isothermal and dynamic modes of DSC, Kissinger equation and the universal tensile test are used to determine various thermo-mechanical properties of composites namely glass transition temperature, heat of reaction, degree of cure, activation energy, pre-exponential factor and tensile strength. The simple additive weighting method is applied to compare different epoxy resin systems and it is found that the overall thermo-mechanical properties for ARL136 resin system are within 5% variation of the same properties measured for the prepreg system.

Influence of diameter on the degradation profile of multiwall carbon nanotubes

Ten multiwall carbon nanotubes purchased from two companies with diameters ranging from 7 to 100 nm with tapped bulk densities from 57 to 250 kg m−3 and with similar lengths and powder sizes were analyzed by thermogravimetric analysis in dynamic and isothermal mode to investigate the importance of the diameter size and tapped bulk density on the degradation behavior of carbon nanotubes. In the case where mass/heat transfer effects were eliminated, results showed that the oxidation temperature depends on diameter only at sufficiently small diameters. The number of surface defects as measured from the ID/IG ratio obtained from Raman spectroscopy was not correlated with degradation stability. The tapped bulk density, on the other hand, dominated the pattern of degradation at high enough heating rates where mass/heat transfer effects become appreciable. As found in previous work which examined nanotubes with roughly constant diameter, tapped bulk density linearly correlated with the ending oxidation temperature at sufficiently high heating rates.

High-pressure in-situ X-ray diffraction and Raman spectroscopy of Ca2AlFeO5 brownmillerite

ABSTRACTThe behavior of Ca2AlFeO5 brownmillerite was studied by in situ synchrotron X-ray diffraction and Raman spectroscopy at 300 K with pressures up to 26.5 and 32.1 GPa, respectively. A reversible structural phase transition was observed. The P–V data were fitted by a third-order Birch–Murnaghan equation of state, and the isothermal bulk modulus was obtained as K0 = 181.9(76) GPa with K0′ = 4.4(17). If K0′ was fixed to 4, K0 was obtained as 183.8(20) GPa. Ca2AlFeO5 brownmillerite shows an axial elastic anisotropy since the b-axis is more compressible than a- and c-axis. Combined with previous results, the isothermal bulk modulus and axial compressibility of Ca2AlFeO5 brownmillerite increase with more Al incorporated in the structure. The Raman spectra of Ca2AlFeO5 brownmillerite were analyzed and the pressure coefficients vary from 2.23 to 4.90 cm−1/GPa. The isothermal mode Grüneisen parameters range from 0.83 to 1.77 and the thermal Grüneisen parameter is determined as 1.08(11).

Isothermal double-cycle catalytic system using DNAzyme and RNase H for the highly selective one-pot detection of oligonucleotides.

With the use of a double-cycle system involving two catalytic reactions by RNase H and DNAzyme, the signal of oligoDNAs has been specifically amplified in an isothermal mode. The precursor of DNAzyme was introduced to the system as a ring-structured and inactivated form, which involves the 6-nt RNA portion being complementary to target oligoDNA. In the presence of target oligoDNA, the RNA portion forms a DNA/RNA hetero-duplex and is cut by RNase H. This scission converts the precursor to catalytically active DNAzyme, which in turn disconnects the molecular beacon to produce the amplified signal. Because the covalent bonds were disconnected to provide discrete structural changes in both cycles, high sensitivity and specificity are obtained, indicating the strong potential of this double catalytic cycle method for versatile applications.

Trifunctional integrated DNA-based universal sensing platform for detection of diverse biomolecules in one-pot isothermal exponential amplification mode.

A biosensor with all the advantages of ultra-high sensitivity, easy operation, straightforward signal output and universal applicability is introduced. The biosensor was demonstrated to work well in the detection of polynucleotide kinase and DAM methyltransferase, thus providing a powerful tool for clinical diagnosis, drug screening and disease therapeutic assay.

The study of the kinetics of formation of gaseous products during thermochemical conversion of woody biomass

The article shows the effect of the stage of internal combustion of biomass (pine sawdust) with insufficient and excessive heat supply. Thermochemical conversion of pine sawdust was carried out first in a dynamic mode to different temperatures of 280, 320, 360, 440 and 440 ° С, and then transferred to the isothermal mode for 1 hour. As a result, the following results were obtained: 1) Hydrogen does not form when heated to 280 ° C; it is formed in small quantities at 320 ° C. From a temperature of 360 ° C and higher, the formation of hydrogen becomes significant. You can also select two modes of education, which is especially noticeable at a temperature of 440 ° C. 2) In the cases of CH4, H2O, CO and CO2, three stages of formation can be distinguished: low-temperature, medium-temperature and high-temperature. For each selected stage, the corresponding kinetic coefficients were calculated.

PHASE EQUILIBRIUM IN SYSTEM (LiF)2 – Li2CO3 – Li2SO4

The liquidus surface of the system (LiF)2-Li2SO4-Li2CO3 was studied by the calculated and differential thermal method of physicochemical analysis. An analysis of the systems of lower dimensionality of the facets of the investigated object showed that the most informative, for the experimental study, is the sections located in the crystallization field of lithium fluoride. A study of the DTA of a number of compositions located at the initially chosen polythermal section in the lithium fluoride crystallization field, the ratios of lithium sulfate and carbonate in the eutectic are determined. The composition of the triple eutectic was revealed by studying a non-invariant cut from the vertex of the triangle (LiF), through a point showing a constant ratio of sulfate and lithium carbonate in the eutectic, to the fusion of the thermal effects of the primary and tertiary crystallizations. The complexity of the study was that lithium carbonate is the most fusible component in the system, and according to the literature, after the melting of lithium carbonate, decomposition begins, which greatly complicates the interpretation of research results. In order to avoid the decomposition of lithium carbonate, each experimentally studied composition was heated to the melting temperature of lithium carbonate and kept in isothermal mode, at a temperature below its melting. Thus, the theoretical melting calculations and the region of location of the non-invariant composition have been extrapolated, allowing to limit the number of experimentally studied samples, and the subsequent experimental investigation of DTA of two polythermal sections revealed a eutectic composition crystallizing at 476 ° C and containing LiF-20 eq.%, Li2SO4 - 51 eq.%, Li2CO3 – 29 eq.%. The discrepancies between theoretical calculations and experimental studies are 8.3% in temperature and 5.05% in composition.

Photo-differential Scanning Calorimetry Study on Photopolymerization of Polyacrylate/E7 Liquid Crystal Blends

Photo-differential scanning calorimetry (photo-DSC) was used to investigate the cure kinetics of a photo-initiated polymerization of tripropylene glycol diacrylate (TPGDA) monomers mixed with a eutectic liquid crystal mixture, E7, chosen due to its significant optical properties. The thermal photo-polymerization reactions were performed in isothermal mode in order to identify and evaluate the different thermal effects occurring during the photo-polymerization reaction under UV light. The results obtained help to better understand the curing mechanisms as well as the kinetics of the curing reactions. The isothermal photo-DSC provided complex thermograms showing the presence of two thermal effects: an exothermic heat (positive activation energy) generated during the conversion of monomers and an endothermic heat produced by the UV lamp. The latter phenomenon was observed in our previous work and was associated to the heating of the polymer dispersed liquid crystals (PDLC) material by the UV irradiation lamp. The dependence of photopolymerization on the time and intensities of the curing UV light were investigated. The results showed that the high intensity UV light heats the material and slows the process of phase separation which, in turn, affects the electro-optical properties of the material under study. The photo DSC results also revealed that the heating of the system was insignificant and can, therefore, be neglected, for materials exposed to UV radiation with an irradiation time of 5 seconds and a low intensity of 13.80 mW/cm2.

Simple Approach to Designing Safe and Productive Operation of Homogeneous Semibatch Reactors Involving Autocatalytic Reactions

In the fine chemical and pharmaceutical industries, design of the safe and productive operating conditions for isoperibolic semibatch reactors(SBRs) involving exothermic autocatalytic reactions is an essential topic. Since determination of the detailed kinetic parameters is a time-consuming process, development of kinetic-parameter-free approach for the above purpose is greatly desirable. In this work, an insight into the desirable QFS (Quick onset, Fair conversion and Smooth temperature profile) operations in isoperibolic SBRs involving autocatalytic reactions is first provided. Then by comparing the thermal performances of SBRs involving autocatalytic reactions in both isothermal and isoperibolic mode, we found that if the MTSR increases with the reaction temperature in isothermal SBRs, the corresponding isoperibolic SBRs with initial temperature equal to the reaction temperature of the isothermal SBRs must be in the QFS region. On the basis of this finding, a facile approach with no requirement of the information on the kinetic parameters is developed to design safe and productive operating conditions for isoperibolic SBRs involving exothermic autocatalytic reactions.

Exploration and practice to improve the kinetic analysis of char-CO2 gasification via thermogravimetric analysis

Kinetic studies of char gasification with CO2 were conducted using thermogravimetric analysis (TGA) under isothermal conditions. A set of improved solutions were proposed to amend the data acquisition and processing in an isothermal TGA mode to reduce the processing error. On this basis, the effects of the external and internal mass transfer limitations on the gasification reactivity and kinetic parameters were investigated. Conventional cylindrical alumina crucibles (CAC) with different sidewall heights and a flat alumina disc (FAD) were used for sample loading. The stagnant gas region in the CAC played an important role in increasing the external mass transfer resistance of CO2 from the bulk flow to the bed surface. The external mass transfer limitation was eliminated in the FAD and, therefore, an abundant provision of CO2 to the surface of char bed was achieved. It was found that the char reactivity decreased linearly with increasing the height of the stagnant gas region but decreased exponentially with increasing bed depth. The mass-independent reactivity can be obtained by carefully striking a balance between the bed thickness and the loading area. The external mass transfers that occurred in the stagnant gas region definitely decreased the reactivity, the activation energy and the frequency factor but had a limited influence on the reaction order. The inter-particle diffusion (bed diffusion) had more significant effects on the reactivity and all the kinetic parameters than the external mass transfers.

Accurate experimental (p, ρ, T) data of natural gas mixtures for the assessment of reference equations of state when dealing with hydrogen-enriched natural gas

The GERG-2008 equation of state is the approved ISO standard (ISO 20765-2) for the calculation of thermophysical properties of natural gas mixtures. The composition of natural gas can vary considerably due to the diversity of origin. Further diversification was generated by adding hydrogen, biogas, or other non-conventional energy gases. In this work, high-precision experimental (p, ρ, T) data for two gravimetrically prepared synthetic natural gas mixtures are reported. One mixture resembled a conventional natural gas of 11 components (11 M) with a nominal mixture composition (amount-of-substance fraction) of 0.8845 for methane as the matrix compound with the other compounds being 0.005 for oxygen, 0.04 for nitrogen, 0.015 for carbon dioxide, 0.04 for ethane, 0.01 for propane, 0.002 each for n- and isobutane, and ultimately 0.0005 each for isopentane, n-pentane, and n-hexane. The other mixture was a 13-component hydrogen-enriched natural gas with a low calorific value featuring a nominal composition of 0.7885 for methane, 0.03 for hydrogen, 0.005 for helium, 0.12 for nitrogen, 0.04 for carbon dioxide, 0.0075 for ethane, 0.003 for propane, 0.002 each for n- and isobutane, and 0.0005 each for neopentane, isopentane, n-pentane, and n-hexane. Density measurements were performed in an isothermal operational mode at temperatures between 260 and 350 K and at pressures up to 20 MPa by using a single-sinker densimeter with magnetic suspension coupling. The data were compared with the corresponding densities calculated from both GERG-2008 and AGA8-DC92 equations of state to test their performance on real mixtures. The average absolute deviation from GERG-2008 (AGA8-DC92) is 0.027% (0.078%) for 11 M and 0.095% (0.062%) for the 13-component H2-enriched mixture, respectively. The corresponding maximum relative deviation from GERG-2008 (AGA8-DC92) amounts to 0.095% (0.127%) for 11 M and 0.291% (0.193%) for the H2-enriched mixture.

Method of researching the influence of isothermic annealing modes on welding of hauling track rails used in mine workings

Modern problems of butt welding of hauling tracks in mine workings are considered. The article describes the method for studying the influence of isothermal annealing modes of a welded joint of samples from rail steel. The cutoff layout of samples used for experiments and the equipment are provided. The developed method allows the temperature to be measured in the weld metal and the heat-affected zone in the process of welding the samples from rail steel. Using the developed method it is proposed to study the effect of thermal cycles of butt welding on the structure of rail steel. The result of using this method is shown as an example.

Isothermal calorimetry of a monoclonal antibody using a conventional differential scanning calorimeter

It has been shown that isothermal calorimetry is able to provide critical information regarding the kinetics of denaturation/aggregation of monoclonal antibodies at temperatures below Tm. Those measurements, however, required sophisticated specialized instrumentation. Here, we demonstrate that similar measurements can be performed using widely available conventional differential scanning calorimeters (DSC) when operated in isothermal scan mode. The denaturation/aggregation kinetics of the anti-HIV monoclonal antibody VRC07-523LS was measured by isothermal DSC at ten degrees below Tm. It is shown that a readily available instrument provides similar kinetic information and can become an important tool for determining the long term stability of biologics.