Isothermal Research Articles

Reliable unencapsulated Ag/Ag2S micro-reference electrodes for battery research and other applications in organic media

Reliable electrochemical measurements depend on the availability of robust reference electrodes (RE) with well-defined potentials. While many reliable REs are known, they are not applicable in certain demanding media such as ionic liquids, nor in small confined spaces. Here, we describe the fabrication of a simple yet robust Ag/Ag2S micro-reference electrode (μ-RE) where a micron-thick Ag2S layer is formed by isothermal reaction with sulfur vapor. Scanning electron microscopy, X-ray photoemission spectroscopy, and spectroscopic ellipsometry characterization reveals that the optimal morphology corresponds to a slightly porous Ag2S film. We demonstrate that the Ag/Ag2S μ-RE can be operated in and cycled through a wide variety of polar organic solvents, including common protic solvents (EtOH), aprotic solvents (ACN, DMSO, NMP, DMF) and ionic liquids (EMIM-TFSI, BMP-TFSI), with short equilibration time (tens of seconds) and little drift (<20 mV), without requiring encapsulation, protective liquid junctions, nor special conditioning. A redox potential of 0.54 ± 0.02 V was obtained for ferrocene in acetonitrile, which places this RE at 0.08 V vs Ag/AgCl. We have also successfully embedded the electrode inside the CR2032 coin cell to perform cyclic voltammetry of battery materials. These results underpin the suitability of this simple micro-reference electrode for a wide variety of electrochemical measurements in demanding and/or miniaturized environments.

Achieving unprecedented stability in lyophilized recombinase polymerase amplification with thermostable pyruvate kinase from Thermotoga maritima

Recombinase polymerase amplification (RPA) is an isothermal DNA amplification reaction at around 41°C using recombinase (Rec), single-stranded DNA-binding protein (SSB), strand-displacing DNA polymerase (Pol), and an ATP-regenerating enzyme. Considering the onsite use of RPA reagents, lyophilized RPA reagents with long storage stability are highly desired. In this study, as one of the approaches to solve this problem, we attempted to use a thermostable pyruvate kinase (PK). PK gene was isolated from a thermophilic bacterium Thermotoga maritima (Tma-PK). Tma-PK was expressed in Escherichia coli and purified from the cells. Tma-PK exhibited higher thermostability than human PK. The purified Tma-PK preparation was applied to RPA as an ATP-regenerating enzyme. Liquid RPA reagent with Tma-PK exhibited the same performance as that with human PK. Lyophilized RPA reagent with Tma-PK exhibited higher performance than that with human PK. Combined with our previous results of RPA reagents of thermostable Pol from a thermophilic bacterium, Aeribacillus pallidus, the results in this study suggest that thermostable enzymes are preferable to mesophilic ones as a component in lyophilized RPA reagents.

On-line cure monitoring of phenol formaldehyde resin using embedded fiber Bragg grating sensor

On-line cure monitoring techniques have shown advantages for identifying the stages of curing and can lead to smart curing process of resin system and its composites. In this study, an on-line measuring technique with fiber Bragg grating (FBG) sensors was used to gain clear understanding of the curing stages of phenolic resin, as well as to determine its chemical shrinkage level. The FBG sensors were embedded in phenolic resin and worked under temperature raising and isothermal conditions. Through the interface between FBG sensor and resin, curing shrinkage strain was transferred to the grating, changing the central wavelength of FBG and producing strain. The feasibility of FBG sensors for monitoring chemical shrinkage during curing was verified by employing epoxy and benzoxazine resins that exhibits low chemical shrinkage. For cure monitoring of phenolic resin, the results show that the strain signal can be corresponded to various responses, such as solvent volatilization, hydroxylation and dehydration condensation reactions during temperature raising curing process. Through these strain characteristics, the curing state of phenolic resin can be obtained, which degree of cure ranges from 0.05 to 0.9. In isothermal curing process of phenolic resin, an exponential correlation between chemical shrinkage induced compressive strain and degree of cure of resin was identified, indicating that the real-time compressive strain is proportional to the degree of cure of phenolic resin. By evaluating real-time curing shrinkage levels, the estimation of curing degree of phenolic resin can be achieved utilizing exponential correlation of curing degree and curing shrinkage level.

Evolution mechanism of the core-shell to homogeneous microstructure in immiscible alloy by semi-solid treatment under a high magnetic field

Immiscible alloys possess broad industrial applications, but the presence of immiscible gaps makes them highly susceptible to the formation of segregated microstructures, thus, a new method for obtaining a uniform distribution of fine minor separated phases needs to be explored. The present work focuses on the evolution mechanism of a CuCo immiscible alloy with a core-shell microstructure during semi-solid isothermal processing under a high magnetic field. The results showed that the microstructure changes from the core-shell structure of the initial sample to homogeneous microstructure after semi-solid treatment, regardless of whether a magnetic field is applied. The mechanism of microstructure evolution of the alloy during semi-solid treatment was revealed through in-situ experiment, in which Ostwald ripening and coalescence mechanisms led to grain coarsening, grain boundary remelting caused grain dissociation, and ultimately the grains underwent spheroidization. However, as a high magnetic field was applied, the average radius of the Co-rich particles decreased, and the particles were aligned in the direction of the magnetic field, forming a chain-like microstructure due to dipole-dipole interactions between the grains. The CuCo immiscible alloy with a uniform microstructure after semi-solid treatment exhibited a higher microhardness and saturation magnetization. This study offers a novel perspective for designing immiscible alloys with homogeneous microstructures as well as chain-like microstructures by utilizing semi-solid treatment combined with a magnetic field.

Phasing effects on thermo-mechanical fatigue damage investigated via crystal plasticity modeling

Nickel (Ni)-based superalloys have high strength at elevated temperatures, making them ideal candidates for aerospace components exposed to thermo-mechanical loads. Thermo-mechanical fatigue's (TMF) influence on material failure is highly dependent on the temperature-load phase profile as a consequence of path-dependent thermo-mechanical plasticity. In order to understand the direct influence phasing effects have on TMF performance, a microstructure-based fatigue model has been developed to connect damage mechanisms to crack initiation events. In this work, in-phase (IP) TMF, out-of-phase (OP) TMF, and iso-thermal (ISO) loading profiles are investigated with a temperature-dependent, dislocation density-based crystal plasticity model to pinpoint a relationship between microstructural damage and TMF phasing effects. A crystal plasticity modeling framework with capabilities to isolate phasing (IP, OP, and ISO) effects is presented to locate fatigue damage in a set of statistically equivalent microstructures (SEMs) with an energy-based damage indicative parameter. Local stress, accumulated damage, intragranular misorientiation, grain interactions, and slip alignment activity at the damaged regions are studied under the various temperature-load phase profiles to connect microstructural material damage to TMF performance. Based on the local microstructural material damage, it is postulated the material's stiffness at maximum load influences OP TMF performance, whereas the hardening/plasticity at maximum load influences IP TMF. The results from the presented framework is consistent with experimental evidence that at high mechanical strain amplitudes IP TMF has a shorter life as a consequence of hardening/plasticity influencing path-dependent thermo-mechanical plasticity, whereas at low strain amplitudes OP TMF has a shorter life due to stiffness influencing path-dependent thermo-mechanical plasticity.

Repurposing Co-Fe LDH and Co-Fe LDH/Cellulose micro-adsorbents for sustainable energy generation in direct methanol fuel cells

Spent adsorbents need to be recycled as well as valorized to obtain long-term benefits from the adsorption of contaminants from wastewater. Co-Fe LDH and Co-Fe LDH/cellulose-layered double hydroxide (LDH) were prepared for crystal violet (CV) adsorption. FT-IR, XRD, SEM, TEM, and, zeta potential analyses confirmed the micro-composites. The parameters examined in this study were the initial pH, initial concentration, adsorbent dose, contact time, adsorption isotherm, and adsorption kinetics. The removal percent was 97.5 % and 88 % for Co-Fe LDH and Co-Fe LDH/cellulose, respectively. A maximum adsorption capacity was 69.4 and 50.0 mg g−1 for Co-Fe LDH and Co-Fe LDH/cellulose, respectively, at pH = 9. The Langmuir-Freundlich model can adequately explain the isotherm processes of LDH and LDH/cellulose; R2 was 0.96 and 0.95, respectively. The spent adsorbents (Co-Fe LDH/CV and Co-Fe LDH/Cellulose/CV) were applied once again as catalysts for electro-oxidation in direct-methanol fuel cells. Due to its high stability in the basic medium (NaOH), the waste material was exploited as an active catalyst to support methanol oxidation. It displayed a better efficiency of 74.75 % and a current density of 76 mA/cm2 at 50 mV/s in 1 M methanol for Co-Fe LDH/CV. The suggested technique opens up a completely new channel for reusing waste into high-value materials for application in electrocatalytic energy generation.

Numerical spectral approach for studying activation energy behavior in viscoelastic fluid flow through non-Darcian medium

The work examines the effects of MHD incompressible viscoelastic fluid under nonlinear thermal radiation while flowing in a non-Darcy porous medium. The utilization of the Darcy-Brinkmann-Forchheimer model has thus been implemented in the formulation of the momentum equation. The study posits the existence of a chemical phenomenon which involves elements A and B as two chemical species. The diffusion coefficient of chemical species exhibits inequality when considered for viscoelastic fluid. Numerical solutions are generated using SRM, spectral relaxation technique for governing flow problems. The current algorithm is formulated and implemented using the computational software MATLAB. The results exhibit a considerable degree of agreement with formerly established numerical outcomes within the framework of a specific scenario. The observations from this study provide evidence that chemical species B operates as a catalyst in a subsurface environment that is oriented horizontally. As a result, the connection between the homogeneous-heterogeneous scheme can be observed in the context of isothermal cubic autocatalytic occurrences and processes of the first order, subsequently. The utilization of the heterogeneous reaction parameter offers notable advantages in reducing the concentration of the bulk-fluid while simultaneously enhancing the concentration of the catalyst situated over the surface. The current findings contribute to the exploration of the computational study of diffusivities in MHD viscoelastic fluid flow. Specifically, this research inquires the effects of nonlinear thermal radiation and homogeneous-heterogeneous reactions.

On-site detection of methicillin-resistant Staphylococcus aureus (MRSA) utilizing G-quadruplex based isothermal exponential amplification reaction (GQ-EXPAR)

Methicillin-resistant Staphylococcus aureus (MRSA) has a high incidence in infectious hospitals and communities, highlighting the need for early on-site detection due to its resistance to methicillin antibiotics. The present study introduces a highly sensitive detection system for mecA, a crucial methicillin marker, utilizing an RCA-based isothermal exponential amplification reaction. The G-quadruplex-based isothermal exponential amplification reaction (GQ-EXPAR) method designs probes to establish G-quadruplex secondary structures incorporating thioflavin T for fluorescence. The system, unlike conventional genetic detection methods, works with portable isothermal PCR devices (isoQuark), facilitating on-site detection. A detection limit of 0.1 fmol was demonstrated using synthetic DNA, and effective detection was proven using thermal lysis. The study also validated the detection of targets swabbed from surfaces within bacterial 3D nanostructures using the GQ-EXPAR method. After applying complementary sequences to the padlock probe for the target, the GQ-EXPAR method can be used on various targets. The developed method could facilitate rapid and accurate diagnostics within MRSA strains.

Real‐time dielectric monitoring of isothermal polymerization of methyl cyanoacetate and diethylene glycol dimethacrylate

AbstractDielectric spectroscopy (DS) was employed to monitor the isothermal polymerization processes of P(MCA‐DEGDMA) formed by the alternating copolymerization of methyl cyanoacetate (MCA) and diethylene glycol dimethacrylate (DEGDMA) at different temperatures in real time. P(MCA‐DEGDMA) is a polyether containing functional groups (O, CN, COOCH3) which can promote the transport of ions Li+, thereby having the potential to apply in polymer electrolytes. It is beneficial to investigate the effect of temperature and time on P(MCA‐DEGDMA) polymerization and choose a suitable synthesis strategy through dielectric monitoring. A time‐ and temperature‐dependent relaxation process induced by orientational polarization of the P(MCA‐DEGDMA) chain was observed over a frequency range from 10 kHz to 4 × 106 Hz. The time to reach polymerization equilibrium (tequ) and the dielectric conversion were determined through the time variations of the conductivity at low frequency (κl). The polymerization process shows the characteristic of “fast followed by slow,” and the tequ can be advanced by raising the polymerization temperature. In addition, by discussing the monitoring time dependence of relaxation time (τ) and permittivity (ε), it was concluded that the extent of polymerization (α) for P(MCA‐DEGDMA) at 40°C is the largest, and the optimal polymerization temperature is between 30 and 50°C. Furthermore, the free activation energy (ΔG), activation enthalpy (ΔH), and activation entropy (ΔS) of the relaxation process caused by the motion of the P(MCA‐DEGDMA) chain in three temperature ranges (10–20°C, 30–40°C, 50–60°C) were calculated by using Eyring's equation, from which the physical image of various structures and conformations of the P(MCA‐DEGDMA) chain during monitoring was proposed. Considering the effect of temperature on the generation and migration of free ions, and on the structure and conformation of the P(MCA‐DEGDMA) chain, some suggestions for the synthesis of P(MCA‐DEGDMA) are given: during the polymerization, the temperature is controlled at 10°C in the early stage and then gradually raised to 40°C, which may be beneficial to improving the extent of polymerization of P(MCA‐DEGDMA). Our work may be helpful to investigate the polymerization process of polyether obeying the same synthesis mechanism with P(MCA‐DEGDMA). It can be proven that DS is useful in detecting the inner information of the system changing over time through our work.

Continuous heating aging characteristics of Al-Cu-Mg-Ag alloy based on stress relaxation method

Clarifying the aging characteristics of aluminum alloys during continuous heating is crucial for formulating isothermal and non-isothermal aging (continuous heating aging) processes. This paper investigates the stress relaxation characteristics of an Al-Cu-Mg-Ag alloy under three-point bending during continuous heating. Taking into account the mechanical properties and precipitate analysis, it demonstrates the feasibility of using the stress relaxation method to determine the peak aging temperature during continuous heating. This approach is efficient, requires minimal sample, and yields continuous data. The peak aging temperature of the sample increases from 260 °C to 305 °C when the heating rate increases from 1 to 3 °C/min with the same initial load (3 N). The peak aging temperature is around 280 ℃, when the initial load increases from 1 N to 9 N with the same heating rate (2 °C/min). Under low temperatures (25 ℃∼ 200 ℃), the sample displays the presence of GP zones, and a few Ω precipitates during the continuous heating process of 2 ℃/min. As the temperature increases, the GP zones dissolve and transform into the Ω precipitates. A large number of Ω precipitates appear in the matrix in a continuous precipitation manner when the temperature reaches 235 °C. The precipitation strengthening effect is strongest at 280 °C, and the Ω precipitates begin to coarsen as the temperature exceeds 280 °C.

Quantum Carnot thermal machines reexamined: Definition of efficiency and the effects of strong coupling.

Whether the strong coupling to thermal baths can improve the performance of quantum thermal machines remains an open issue under active debate. Here we revisit quantum thermal machines operating with the quasistatic Carnot cycle and aim to unveil the role of strong coupling in maximum efficiency. Our analysis builds upon definitions of excess work and heat derived from an exact formulation of the first law of thermodynamics for the working substance, which captures the non-Gibbsian thermal equilibrium state that emerges at strong couplings during quasistatic isothermal processes. These excess definitions differ from conventional ones by an energetic cost for maintaining the non-Gibbsian characteristics. With this distinction, we point out that one can introduce two different yet thermodynamically allowed definitions for efficiency of both the heat engine and refrigerator modes. We dub them excess and hybrid definitions, which differ in the way of defining the gain for the thermal machines at strong couplings by either just analyzing the energetics of the working substance or instead evaluating the performance from an external system upon which the thermal machine acts, respectively. We analytically demonstrate that the excess definition predicts that the Carnot limit remains the upper bound for both operation modes at strong couplings, whereas the hybrid one reveals that strong coupling can suppress the maximum efficiency rendering the Carnot limit unattainable. These seemingly incompatible predictions thus indicate that it is imperative to first gauge the definition for efficiency before elucidating the exact role of strong coupling, thereby shedding light on the ongoing investigation on strong-coupling quantum thermal machines.

Towards the Isothermal Gas Compression—A Novel Finned Piston-Cylinder with Increased Efficiency

In this paper, a novel concept of a finned piston system is presented and analyzed in which the compression heat is continuously extracted from the compression chamber. The resulting compression characteristic moves in the direction of an isothermal process, reducing the temperature of the compressed fluid in the compression chamber and reducing the necessary mechanical work required to carry out the process. The finned piston concept consists in an integrated heat exchanger inside of the chamber that is constituted of imbricated flat fins placed on the stator part and on the mobile piston. The internal heat exchange on the surface is strongly increased in comparison with a classical piston/cylinder. The energetic performance of the new system is evaluated with the help of simulation. The pressures, forces, and temperature of the compressed gas are simulated as well as the mechanical work needed. The different curves are compared with the system’s adiabatic and isothermal characteristics.

KINETIC MODELS OF CHAOS IN LINEAR CATALYTIC REACTIONS

Chaos (chaotic oscillations, strange attractors) are aperiodic changes in certain parameters of the dynamic system under study, which differ from other types of oscillations (damped, undamped, multi-periodic) by unusually complex, unpredictable dynamic behavior, and can be observed for an arbitrarily long time. From the theory of dynamical systems it follows that chaotic oscillations can be described by nonlinear systems of ordinary differential equations with three or more independent variables. Until now, such differential equations have been used to construct kinetic models within the framework of the ideal law of mass action, describing chaotic oscillations in homogeneous and heterogeneous catalytic reactions. Moreover, these kinetic models describe chaotic oscillations only for reactions occurring according to stage schemes that are nonlinear with respect to intermediate substances. This article explores the possibility of describing chaotic oscillations by linear systems of ordinary differential equations with three independent variables, which, within the framework of the nonideal Marcelin-de Donde kinetic law, correspond to stage schemes linear in intermediate substances. It is shown that in real conditions, when the Marcelin-de Donde law is satisfied, kinetic models of mechanisms linear in intermediate substances make it possible to describe any complex dynamic behavior of catalytic reactions. Four-stage linear schemes in intermediate substances have been established, the kinetic models of which describe chaotic oscillations of the reactions of interaction between nitrogen monoxides and carbon monoxides (2NO + CO → N2O + CO2) and the oxidation of carbon monoxide (2CO + O2 → 2CO2) on platinum catalysts with Marcelin-de Donde kinetics in an isothermal gradientless reactor. For citation: Kol'tsov N.I. Kinetic models of chaos in linear catalytic reactions. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 5. P. 121-127. DOI: 10.6060/ivkkt.20246705.6956.

A split single-stranded DNA activator-based Cas12a fluorescence biosensor for specific H1N1 detection

We developed a novel CRISPR/Cas12a fluorescence biosensor to specifically detect the H1N1 virus based on splitting single-stranded DNA (ssDNA) activators. Specifically, activators 1 and 2 were generated from dual target nucleic acid sites to induce a three-way junction (3WJ) isothermal amplification process. Two specific H1N1 RNA nucleic acid sites were bound to a set of probes to form a 3WJ, which facilitated repeated extension and nicking reactions to produce high levels of split ssDNA activators via DNA polymerase and nicking endonuclease activity. Amplified activators 1 and 2 fully assembled with Cas12a/crRNA to form complexes. Activated Cas12a trans-cleaved ssDNA reporter molecules to generate fluorescence signals. Under optimal conditions, biosensor dynamic detection range was 1 pM–10 nM, and the detection limit was 205 fM. Thus, our biosensor showed high specificity, reliability, and robustness, which highlights its potential use for H1N1 diagnostics.

The Effect of Isothermal Aging on the Intermetallic Growth between SN100C Lead-Free Solders and ENIG Surface Finish

The selection of substrate material depends on solder joint requirements and will influence intermetallic compound (IMC) layer formation and reliability of the solder joints. Besides, using different solder materials can also affect the microstructure of IMCs formed during soldering and isothermal ageing process. This study investigated the effect of the IMC formation and microstructure evolution during reflow soldering and isothermal ageing using SN100C lead-free solders and ENIG surface finish. The characterization of the IMC formed during both reflow soldering and isothermal ageing in terms of the type, morphology, and thickness is then analyzed by using the Optical Microscope (OM), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX). The result reveals that there are two IMC formed at an interface between SN100C and ENIG which are (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4 where (Ni, Cu)3Sn4 grows beneath (Cu, Ni)6Sn5. The thickness of the IMC formation in the SN100C/ENIG solder joint is also directly proportional to the ageing duration, indicating that the longer the time of the IMC exposed to high temperature affects the thickness of the IMC.

Investigation and Optimization of Biosorbent Capacities of Some Plants Used in Daily Life

In this study, sage, chamomile, and tarragon leaves, which are used as spices and consumed as beverages in daily life, were considered as different biosorbents that can be used in water purification by biosorption. At the same time, the effects of the parameters of initial dye concentration (10-200 mg/L), temperature (20-50 ⁰C) and contact time (0-120 min) on biosorption capacity were investigated. The biosorption processes were found to follow Freundlich isotherm and pseudo-second order (PSO) reaction kinetics. In the study, the process was also modeled using multi-tree evolutionary computation based automatic programming (AP) methods. The methods used initial dye concentration, temperature, and contact time as variables. According to the simulation results, these methods obtained nonlinear mathematical models of the processes with R^2 values as high as 0.99 for each biosorbent. By providing the most accurate models to accurately predict biosorption capacity, this study will make a significant contribution to the field of water treatment using experimental and AP methods.

Effect of Zr on austenite grains growth behaviour of high strength Ti microalloyed low carbon steel

The isothermal grain growth behaviour for three Ti microalloyed steels with different Zr contents (0–0.039 wt-%) at different reheating temperatures (1100, 1150, 1200 and 1250 °C) and for holding times (10, 60, 600 and 1800 s) was investigated. Austenite growth model was established to analyse and predict the functional relationship between austenite grains size and austenitising temperature and time during the isothermal austenitising process in the three tested steels, and the influence of Zr was discussed. The results indicate that the activation energy Q and time index n of austenite grains boundary migration in the tested steels decrease with the increase of Zr content. The addition of Zr can inhibit the growth of primary austenite grains at high temperatures. With the increase of Zr content, the trend of average grain size growth of primary austenite becomes smoother. The addition of Zr improves the high-temperature stability of precipitates, resulting in smaller precipitates and stronger pinning effect for austenite grains boundary in Ti–Zr microalloyed steel compared to that in Ti microalloyed steel at high temperatures.

Real-Time Monitoring of a Nucleic Acid Amplification Reaction Using a Mass Sensor Based on a Quartz-Crystal Microbalance.

Nucleic acid amplification reactions such as polymerase chain reaction (PCR), which uses a DNA polymerase to amplify individual double-stranded DNA fragments, are a useful technique for visualizing the presence of specific genomes. Although the fluorescent labeling method is mainly used with DNA amplification, other detection methods should be considered for further improvements, such as miniaturization and cost reduction, of reaction-monitoring devices. In this study, the quartz-crystal microbalance (QCM) method, which can measure nanogram-order masses, was applied for the real-time detection of DNA fragments in a solution with nucleic acids. This was combined with an isothermal nucleic acid amplification reaction based on the recombinase polymerase amplification (RPA) method, which allowed DNA amplification at a constant temperature. When the DNA amplification reaction was initiated on a QCM sensor plate with an immobilized primer DNA strand, a significant increase in mass was observed compared to when the primer DNA was not immobilized. QCM was shown to be sufficiently sensitive for the in situ detection of amplified DNA fragments. Combining a portable QCM device and RPA offers a sensitive point-of-care method for detecting nucleic acids.

Optimizing strength & ductility combination of medium-carbon TRIP steel via multi-stage work hardening

The effect of the retained austenite (RA) stability on mechanical properties of a medium-carbon transformation-induced-plasticity (TRIP) steel at different deformation temperatures was studied. Two steels were obtained by adjusting the annealing temperature from 780 °C to 820 °C and controlling the isothermal bainitic process, and the carbon content of RA in the steels was 1.2% and 1.4%, respectively. At 25 °C, ultimate tensile strength, yield strength and total elongation of the steel after intercritical annealing at 780 °C were 1390 MPa, 870 MPa and 40%, respectively. When the deformation temperature increased to 200 °C, yield strength nearly kept constant (860 MPa) while total elongation significantly increased to 73%. The stability of RA had a significant influence on the deformation mechanisms of the steel, hence leading to the distinct variation of the mechanical properties. The RA stability increased with increasing deformation temperature to 200 °C, reducing the rate of transformation from RA to martensite and making the TRIP effect more persistently. Meanwhile, due to low solubility of Cu atom and the large number of dislocations acting as fast diffusion channels for Cu and C atoms in transformed martensite, the joint action of the increasing temperature and the continuous TRIP effect promoted the formation of numerous nanosized precipitates including η carbides and Cu particles in the newly formed martensite. As a result, the work hardening rate was significantly increased, improving the ductility without sacrificing the strength. This study provides a strategy to control the deformation mechanisms of medium-carbon TRIP steel, which can tailor the stability of RA according to the requirement of application, so as to obtain a good combination of strength and ductility.

Сорбция ионов Cu(II) и Fe(II) хлопковой целлюлозой, модифицированной диэтилентриамином

The authors have developed new effective sorbent based on chemically modified cotton cellulose. The modification process consists of two stages, including sequential treatment of cellulose with epichlorohydrin and diethylene triamine. The authors present &#x0D; the optimal modification conditions for the obtained sorbent. It allows ones’ to achieve the highest values of sorption capacity for the extraction of iron(II) and copper(II) ions from aqueous solutions. The authors investigated the kinetics and equilibrium of heavy metal ion sorption in the system "cellulose sorbent - aqueous solution of metal sulphate" for original and modified cotton cellulose. Processing of the kinetic experiment results indicates that the kinetics of metal ion sorption is described most correctly in the framework of the pseudo-second-order kinetics model. Isotherms of heavy metal ions sorption clearly indicate the growth of sorption capacity for the modified sorbent in comparison with the original one. Processing of experimental isotherms within the Langmuir model made it possible to determine the values of the maximum sorption capacity (A∞) of original and modified with diethylenetriamine cotton cellulose with respect to Cu(II) and FE(II) ions. It was found that the A∞ of the modified sorbent was about 3 times higher than the ultimate sorption capacity of original cotton cellulose towards iron(II) and Cu(II) IONS. Comparison of IR spectra of the original cellulose samples and cellulose treated with diethylenetriamine indicates the changes that occurred during chemical modification. The paper presents SEM images showing the changes in the surface structure of the modified sorbent compared to the original one.