Increase In Activation Energy Research Articles

Microplastics in dyeing sludge: Whether do they affect sludge incineration?

Microplastics (MPs), as emerging contaminant detected in dyeing sludge (DS), inevitably affected the subsequent treatment and disposal of DS. However, the effect of MPs on the predominant disposal path (incineration) of DS remains far from explicit. This study used thermogravimetry-mass spectrometry (TG-MS) method to explore the effect of representative MPs, polyethylene terephthalate (PET) and polyvinyl chloride (PVC), on combustion characteristics, gas evolution and kinetics on DS combustion. Results showed that PET inhibited the whole combustion of DS by physical barrier. Relatively, PVC delayed the combustion of light volatile but promoted heavy volatile and char reaction due to HCl catalyst. Generally, MPs deteriorated the combustibility, burnout performance and combustion stability of DS. MPs aggravated HCl and gaseous N emissions. Noticeably, the interactions between DS and PVC accelerated the emissions of gaseous pollutants, especially under high dose condition. DAEM and FWO models could well describe the combustion kinetic of DS containing MPs. MPs led to an increase in activation energy of DS, namely, it deteriorated the combustion efficiency of DS. The combustion mechanisms could be divided into two stages: (1) diffusion (D3) stage: melted MPs blocked the gas channels, (2) chemical reaction (F3): the residual chars were thermally stable.

Thermal Quenching Mechanism of Metal-Metal Charge Transfer State Transition Luminescence Based on Double-Band-Gap Modulation.

Bi3+-related metal-to-metal charge transfer (MMCT) transition phosphors are expected to become a new class of solid-state luminescent materials due to their unique broadband long-wavelength emission; however, the main obstacle to their application is the thermal quenching effect. In this study, one novel thermal quenching mechanism of Bi3+-MMCT transition luminescence is proposed by introducing electron-transfer potential energy (ΔET). Y0.99V1-xPxO4:0.01Bi3+ (YV1-xPxO4:Bi3+) is used as the model; when the band gap of the activator Bi3+ increases from 3.44 to 3.76 eV and the band gap of the host YV1-xPxO4 widens from 2.75 to 3.16 eV, the electron-transfer potential energy (ΔET) decreases and the thermal quenching activation energy (ΔE) increases, which result in the relative emission intensity increasing from 0.06 to 0.64 at 303-523 K. Guided by density functional calculations, the thermal quenching mechanism of the Bi3+-MMCT state transition luminescence is revealed by the double-band-gap modulation model of the activator ion and the matrix. This study improves the thermal quenching theory of different types of Bi3+ transition luminescence and offers one neo-theory guidance for the contriving and researching of high-quality luminescence materials.

Kinetics of antigorite dehydroxylation for CO2 sequestration

Heat-treatment of serpentine minerals generates structural amorphicity and increases reactivity during subsequent mineral carbonation, a strategy for large-scale sequestration of CO2. This study employs thermal analyses (TGA-DSC) in conjunction with in-situ synchrotron powder X-ray diffraction (PXRD) to record concurrent mass loss, heat flow, and mineralogical changes during thermal treatment of antigorite. Isoconversional kinetic modelling demonstrates that thermal decomposition of antigorite is a complex multi-step reaction, with activation energies (Eα) varying between 290 and 515 kJ mol−1. We identify three intermediate phases forming during antigorite dehydroxylation, a semi-crystalline chlorite-like phase (γ-metaserpentine) showing an additional reaction pathway for the decomposition of Al2O3-rich antigorite into pyrope, and two distinct amorphous components (α and β-metaserpentine) which convert into forsterite and enstatite at higher temperature, respectively. The combination of isoconversional kinetics with in-situ synchrotron PXRD illustrates, for the first time, that local crystal structure changes, related to intermediate phase and forsterite formation, are responsible for the steep increase in activation energy above 650 °C and only 49% dehydroxylation can be achieved prior to this increase. This suggests that the high thermal stability of Al2O3-rich antigorite would severely limit Mg extraction during application of mineral carbonation under flue gas conditions.

Electrical Characteristics of Dry Cement – Based Composites Modified with Coconut Husk Ash Nanomaterial

Abstract Coconut husk is generated yearly as waste in large quantities but majorly under-utilized. Also, as a result of high embodied carbon, cement production is one of the largest contributors to construction sector carbon footprint. Since accumulation of unmanaged agro-waste like coconut husk has an increased environmental concern due to its pollution effect, recycling it into sustainable construction materials is a viable solution for future generation. In this study, experiments were performed to investigate the influence of coconut husk ash nanomaterial (CHAN) inclusion on electrical characteristics of plain cement paste (BCP) and mortar (CSM) samples at curing ages of 7 and 28 days. The results showed increase in electrical resistivity, thermal constant, and activation energy with curing duration for heating and cooling cycles of BCP and CSM. With inclusion of CHAN, the developed cement paste (CAP) and mortar (CASM) possessed lower values in all cases compared to their counterparts. Also, during heating at 28 days, both the CAP and CASM exhibited decrease in thermal constant. Though electrical resistance of all the samples varied inversely with temperature, CAP and CASM were found to possess greater potentials to make building structures intrinsically smart. Hence, in addition to solving disposal problems, utilization of coconut husks as described herein could enhance development of safe, inexpensive, and sustainable buildings that have large temperature sensing volume.

Dendrite-free alkali metal electrodeposition from contact-ion-pair state induced by mixing alkaline earth cation

Alkali metals are expected to be used for rechargeable metal anode batteries owing to their low electrode potentials and large capacities. However, they face the well-known fatal problem of “dendritic growth” while charging. Here, we present a detailed investigation on electrolytes where alkaline earth salts are introduced to inhibit dendrite growth in alkali metal electrodeposition. Specifically, focusing on CaTFSA 2 as an exemplary additive, we reveal that dendrite-free morphology upon alkali metal electrodeposition can be attained by modifying the solvation structures in dual-cation electrolytes. Addition of Ca 2+ promotes alkali cation (Li + or Na + ) to form the contact ion pairs (CIPs) with the counter anions, which replaces the solvent-separated ion pairs that commonly exist in single-cation electrolytes. The strong binding of the CIPs slows the desolvation kinetics of alkali cations and, consequently, realizes a severely constrained alkali metal electrodeposition in a reaction-limited process that is required for the dendrite-free morphology. • Additive divalent cations lead to flat morphology in Li and Na electrodeposition • Li + /Na + tends to form strong CIPs to alleviate interaction among divalent cations • Increased activation energy of CIPs enables to retain a uniform diffusion field Li et al. report that mixing divalent cations with alkali cations in electrolytes can modify the solvation structure and consequently obtain flat morphology in alkali metal electrodeposition. This finding may represent a step toward active control of reaction kinetics toward metal anode batteries.

Investigation of Hot Deformation Behavior and Microstructure Evolution of Lightweight Fe-35Mn-10Al-1C Steel

The deformation behavior of lightweight Fe-35Mn-10Al-1C steel with an elevated concentration of Mn was investigated. Hot compression tests at temperatures of 950–1150 °C and strain rates of 0.1–10 s−1 were carried out using the thermomechanical simulator, Gleeble 3800. Strain compensated constitutive model of hot deformation behavior with high accuracy (error was 4.6%) has shown significant increases in the effective activation energy (410–460 kJ/mol) in comparison with low Mn steels. The significant influence of the strain rate and temperature on the grain size was shown. The grain size decreases from the initial value of 42 ± 6 μm to the value of 3.5 ± 0.7 μm after the deformation at 1050 °C and 10 s−1. The model of the microstructure evolution of the investigated steel was constructed. The average error of the constructed model was 8.5%. The high accuracy of the constructed models allows for their application for the optimization of the hot deformation technologies using finite element simulation.

Thermo-economic analysis of solar drying of Jerusalem artichoke (Helianthus tuberosus L.) integrated with evacuated tube solar collector and phase change material

In the present work, the experimental studies performed through the thermo-economical analysis of Jerusalem artichoke slices dried by an indirect cabinet solar dryer with evacuated tube collectors and phase change materials. It shows that in the drying process of 5 mm thickness of Jerusalem artichoke slices the effect of using phase change materials in the solar dryer on the movement of the water content from the crops was significant (P < 0.05). The drying time decreased with increasing the airflow rate, but it was not significant (P > 0.05). Using phase change materials increased activation energy (33.4 kJ/mol) and improved the overall drying efficiency 1.51–7.81%. Specific energy consumption with PCM usage decreases from 14.51 to 13.38 MJ/kg. In addition the exergy efficiency for the drying process about 35.3–59.7%. The optimized condition for the system was obtained, and it showed that payback time for the solar dryer with optimized condition could be decreased to 22 months which was lower than basic condition (15%). Moreover, artificial neural network, computational fluid dynamic and evolutionary polynomial regression were considered to predict the variations of thermal behavior of the system. The values of RMSE and COV for artificial neural network method are lower and R2 is higher than the computational fluid dynamic method. The result of evolutionary polynomial regression implied that it predicted outlet temperature, and the collector thermal efficiency with the acceptable accuracy (R2 > 0.98). According to the exergetic, economic and quality consideration the proper condition was obtained with 0.9 kg/s for air flow rate assisted with PCM.

Realization of homojunction PN AlN diodes

Aluminum nitride (AlN) is an insulator that has shown little promise to be converted to a semiconductor via impurity doping. Some of the historic challenges for successfully doping AlN include a reconfigurable defect formation known as a DX center and subsequent compensation that causes an increase in dopant activation energy resulting in very few carriers of electricity, electrons, or holes, rendering doping inefficient. Using crystal synthesis methods that generate less compensating impurities and less lattice expansion, thus impeding the reconfiguration of dopants, and using new dopants, we demonstrate: (a) well behaved bulk semiconducting functionality in AlN, the largest direct bandgap semiconductor known with (b) substantial bulk p-type conduction (holes = 3.1 × 1018 cm−3, as recently reported in our prior work), (c) dramatic improvement in n-type bulk conduction (electrons = 6 × 1018 cm−3, nearly 6000 times the prior state-of-the-art), and (d) a PN AlN diode with a nearly ideal turn-on voltage of ∼6 V for a 6.1 eV bandgap semiconductor. A wide variety of AlN-based applications are enabled that will impact deep ultraviolet light-based viral and bacterial sterilization, polymer curing, lithography, laser machining, high-temperature, high-voltage, and high-power electronics.

A Thermic Effect on Degradation Kinetics of Sugar Cane Bagasse Polypropylene Composites

In this study, thermal degradation mechanisms and the kinetics of PP (Polypropylene) composites containing alkali and saline treated SC (Sugar cane bagasse) have been evaluated using a non-isothermal thermogravimetric analysis under consistent nitrogen atmosphere. The study indicates dynamics of kinetics that need to be considered should the composites be applied in high temperature applications. NaOH treated composites revealed a reduced fiber size compared to the other composites. The presence of SC generally reduced the functional group intensities of FTIR peaks, however some peaks re-emerged after the treatments. The composites indicated higher thermal stability and char content than the pristine polymer. In fact, NaOH treated composite is more thermally stable, while the saline is the least stable of the rest. Well known reliable degradation kinetics methods were employed in order to unpack thermal degradation behavior and possible metaphors. Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) thermal degradation kinetic models are in agreement that the presence of both SC and those in the PP matrix that have been treated lead to increased activation energy values with the competing reactions in the degradation process. Nonetheless, the linear relation is not absolutely perfect and the competing reactions seem complex at lower temperatures as there are overlying inconsistencies in activation energies. Interestingly, bagasse indicated some effect on the mechanism that included the hindering of free radicals that emanated from the first cleavage of PP.

Effect of microwave‐assisted vacuum drying on the drying kinetics and quality parameters of Moringa oleifera leaves

AbstractMicrowave‐assisted vacuum drying (MAVD) has been studied to improve drying kinetics and physical and antioxidant properties of dried moringa leaves. Microwave power and vacuum level produced a significant reduction (p &lt; .05) in drying time and improvement of drying rate. It was further confirmed by an increase in effective diffusivity value (Deff) by an increase in power and vacuum levels. The reliance of Deff on microwave power was further confirmed by an increase in activation energy from 13.564 to 17.31 W/g with an increased power level. Fitting experimental moisture ratio to the thin layer drying models revealed that the Midilli et al. model could better describe the MAVD of moringa leaves with the highest R2 values. Physical characteristics such as color and rehydration ratio were better for MAVD samples than hot air‐dried samples. Increased drying rate and rehydration ratio were due to the open porous structure of the moringa leaves dried by MAVD, as revealed from the SEM imaging. The vacuum level and power level were significant (p &lt; .05) to the total color difference but the change in color at power levels of 270 and 450 W were insignificant (p &gt; .05). Also, the vacuum level was significant (p &lt; .05), and the microwave power level was insignificant (p &gt; .05) to the rehydration ratio of the MAVD moringa leaves. Phenolic composition and antioxidant properties of MAVD moringa leaves showed increased phenolic content and improved antioxidant activity. Microwave power showed a significant effect (p &lt; .05) on antioxidative properties, whereas vacuum level (p &gt; .5) showed an insignificant effect. The highest power level of 450 W and vacuum level of 500 mmHg produced better quality moringa leaves with good physical and antioxidative properties.Practical ApplicationsDrying is the most common and oldest preservation method for storing food for a longer time. It is very much important to dry moringa leaves that have high moisture content and very less shelf‐life. But conventional drying methods cause great nutritional and textural changes. Microwave‐assisted vacuum dryer combines the advantage of quick and shorter drying of microwave system and lower temperature process as in vacuum system. This eventually reduces the drying time and temperature stress on the food product. This study aids in scale‐up and design a MAVD system for moringa leaves based on its drying kinetics. MAVD of moringa leaves was best modeled by Midilli et al. model. Evaluation of physical characteristics of leaves after drying and its comparison with hot air‐dried one revealed better color and rehydration property that is considered as the key character of dried samples. MAVD also produced increased antioxidant properties with good retention of phenolic components. So, the method of Microwave Assisted Vacuum Drying (MAVD) has got tremendous importance that could be industrially exploited in Moringa leaf processing plants.

New insight into the interface of TiO2/C as nanocomposite electrode for lithium-ion batteries

Coating the carbon layer onto the surface of TiO2 electrode is seen as an effective strategy to improve the electrochemical performance of lithium-ion batteries, particularly the reduced charge transfer resistance. The reduced charge transfer resistance was attributed to the chemical bonding between the phases. In this paper, however, we show that it is not only the chemical bonding but also the change of the activation energy differences that is responsible. Herein, we fabricate the carbon layer coated TiO2 electrode (TiO2/C) and combine the recently proposed modified Planck-Nernst-Poisson coupled Frumkin-Butler-Volmer (MPNP-FBV) model to address the above-mentioned issues. By combining the experimental results with the electrochemical model, the charge transfer resistance and the interface behaviors are analyzed. The results show that the performance of TiO2/C electrode based cells is determined by the carbon layer/TiO2 interface, while the cells based on TiO2 electrodes are limited by the electrolyte/TiO2 interface. Comparison between the electrochemical simulations and the experimental data indicates that this increased activation energy difference leads to the decrease of the charge transfer resistance. These results imply that activation energy difference across the interfaces can be a critical parameter for designing high performance batteries.

Dynamic recovery and recrystallization mechanisms in secondary B2 phase and austenite matrix during hot deformation of Fe–Mn–Al–C-(Ni) based austenitic low-density steels

In present study two different austenitic based low-density steel (LDS) grades with compositions of Fe–28Mn–9Al-0.9C and Fe–15Mn–9Al-0.9C–5Ni (in weight percent) were produced by vacuum induction melting. The former alloy was a single-phase austenitic grade, whereas the latter alloy contained coarse B2 ordered Fe(Ni)Al secondary phase along with fine κ-carbides in austenite matrix. Hot deformation behaviour of these two LDS grades was studied in as-cast plus homogenized condition under compression over a range of temperature (1173–1423 K) and strain rate (0.005–5 s−1). The stress-strain curves were analysed to evaluate the role of secondary B2 phase on the stress exponent and activation energy of deformation. The evolution of microstructures in these steels as a function of test temperature, strain rate and strain was examined in-detail by electron backscattered diffraction. Both the low-density steels exhibited nearly similar stress exponent value of ∼4; however, the presence of B2 phase led to an increased activation energy of deformation. The effect of B2 phase on flow behaviour and microstructure evolution during hot deformation was found to be more pronounced at low test temperatures. The B2 containing steel showed slower recrystallization kinetics than that of B2-free alloy and is presumably due to the Ni addition, the presence of undissolved κ-carbides and the strain rate-temperature dependent strain partitioning between γ and B2 phases in the former alloy. The examination of microstructural evolution with progress of deformation revealed that the austenite (γ) matrix grains undergo discontinuous dynamic recrystallization, while B2 grains display continuous dynamic recrystallization along with fragmentation.

Improved melt strength and processability of impact copolymer polypropylene by introducing long‐chain branching via reactive extrusion with “ene” functionalized dendrimer

AbstractA generation two dendrimer (G2) having eight terminal double bonds has been prepared via esterification reaction from a dendritic precursor having eight hydroxyl end groups (G1). The reactive extrusion of impact co‐polymer polypropylene (ICP) with G1 resulted in improved processability while leading to enhanced melt strength in the case of linear low‐density polyethylene (LLDPE). G2 being an extension of G1, was melt grafted on ICP using a radical initiator to introduce long‐chain branching in the polymer backbone. The prepared samples were analyzed for their molecular weight distribution, thermal, rheological properties, and mechanical properties. Thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) analysis showed higher thermal stability and slightly higher crystallization temperature with grafting of G2 on ICP. The rheological analysis through melt flow index measurements and parallel plate rheometer indicated higher processability, melt strength, complex viscosity, and zero‐shear viscosity for ICP grafted with an optimized amount of G2. The presence of long‐chain branching was confirmed with an increase in activation energy for ICP modified with G2 as compared to neat ICP. Modified ICP samples retained their bulk mechanical properties as neat ICP.

Microsolvation effect on chlorination reaction of simple alcohols

AbstractThe microsolvation effect was investigated on bimolecular nucleophilic substitution () mechanism for chlorination of methanol, ethanol, and propanol using water as explicit solvent. Based on theoretical calculations, within Density Functional Theory (DFT) combined with polarizable continuum model (PCM) and explicit solvent molecules, it was possible to compare the effect of hydration on the nucleophile and on the leaving group, for the main extremal points of potential surfaces, that is, pre‐complex, transition state (TS), and post‐complex. The possible disposition of water molecules was also investigated raging from one to four explicit molecules. This study was carefully and systematically done for methanol and the main conclusions were used to guide the corresponding study for ethanol and propanol. The results point out to an increase of activation energy with the number of explicit water molecules, showing the importance of hydrogen bond on the stabilization of structures, effect not captured by PCM alone.

Low‐temperature synthesis and oxidation resistance of random combination of Hf, Nb, and Ta carbides microcuboids

AbstractBased on the dissolution‐precipitation mechanism, this article successfully synthesized binary and ternary transition metal carbide microcuboids with random combinations of Hf, Nb, and Ta by annealing monocarbides/cobalt powders. Accelerated mass transport rate through the flow of molten alloys (Co‐Hf‐Nb‐Ta) instead of slow solid diffusion made the low‐temperature pressureless sintering technique (1500°C) a reality. Furthermore, the equilibrium morphology was driven by the gradient Gibbs potential of carbides induced by the different local curvature of powders and anisotropic interfacial energy. (Hf0.5Ta0.5)C possessed the optimal oxidation resistance among all mentioned carbides, even competed with (Hf1/3Nb1/3Ta1/3)C. During the isothermal oxidation at 800∼1200°C, the doping of Nb and Ta in carbides assisted the monoclinic‐orthorhombic HfO2 transition at ambient pressure, besides, TaC can also restrain the orthorhombic‐monoclinic transition of Nb2O5. Moreover, oxidation kinetics parameters concluded that the addition of HfC and TaC contributed to the decreasing reaction order and the increasing activation energy, respectively.

Influence of tetraethylammonium cation on electrochemical CO2 reduction over Cu, Ag, Ni, and Fe surfaces

Enhancing the selectivity and activity of desired CO2 reduction products while suppressing hydrogen evolution reaction (HER) will facilitate the commercialization of electro-reduction of CO2 to hydrocarbons. Except for gold, polycrystalline surfaces of all transition metals used for the electrochemical CO2 reduction reaction (CO2RR) suffer from low CO2RR selectivities and activities at lower overpotentials. As ionic liquid cations stabilize key CO2RR intermediates and destabilize the HER intermediates, we studied the influence of tetraethylammonium (TEA+) cation on CO2RR and HER activities, experimentally, over transition metal electrodes (Cu, Fe, Ag, and Ni). We observed an enhancement in CO2RR activity and major CO2RR product formation in the presence of TEA+ cation on Cu and Ag. In addition, HER activity was enhanced on Ni and Fe surfaces but suppressed on Ag and Cu surfaces. Density functional theory (DFT) based computational studies were employed to rationalize these observations. Experimental and computational results suggest that the decreased activation energy for water dissociation enhanced the HER activity on Ni and Fe. Further, the increased activation energy for water dissociation suppressed HER activity on Cu and Ag. Moreover, the increase in *COO– (or CO2–⋅) binding energy in the presence of TEA+ cation is crucial for enhancing CO2RR activity and major CO2RR product formation on Cu and Ag. Thus, this study of the influence of TEA+ cation on CO2RR/HER activity over transition metal electrodes helps in exploring other ionic liquid cation-electrode combinations in terms of CO2–⋅ intermediate stabilization and water dissociation suppression for selective electrochemical CO2 reduction to fuels.

On the effects of CO2 atmosphere in the pyrolysis of Salicornia bigelovii

This study focuses on understanding the effects of a CO2 atmosphere on the pyrolysis of Salicornia bigelovii by performing a detailed kinetic analysis and investigating the pyrolysis products. In comparison to N2 pyrolysis, CO2 pyrolysis increased the amounts of acids, phenols, amines/amides and N-aromatics in the bio-oil. Biochar showed a 6.5% increase in carbon and a 5.8% decrease in oxygen due to the presence of CO2 in the pyrolysis atmosphere. CO2 also inhibited the volatilization of certain functional groups, such as phenols, tertiary alcohols and aromatics from the biochar, and the surface area of the biochar was 12 times larger than pyrolysis in N2 atmosphere. Pyrolysis in CO2 led to an increase in the average apparent activation energy from 146.5 kJ mol−1 in N2 to 163.4 kJ mol−1. The kinetic equation was found to conform to a three dimensional diffusion mechanism. Finally, the pre-exponential factor was determined for each reaction.

Thermodynamic and Adsorption Analysis of Corrosion Inhibition of Mild Steel in 0.5M HCl Medium &amp;lt;i&amp;gt;via&amp;lt;/i&amp;gt; Ethanol Extracts of &amp;lt;i&amp;gt;Phyllanthus mellerianus&amp;lt;/i&amp;gt;

The corrosion of mild steel is a problem in industrial processes based on its deterioration on exposure to acids, alkalis, and salt solutions. This issue has prompted an increase in research interest in order to mitigate the harmful effects of corrosion on metals and their alloys. The thermodynamic and adsorption analysis of mild steel in 0.5M hydrochloric acid solutions <i>via ethanol leaf extract of Phyllanthus mellerianus</i> was investigated using weight loss and hydrogen evolution techniques. The powdered sample was extracted with ethanol and concentrated with a rotary evaporator. The phytochemical analysis reveals the presence of tannins, flavonoids, phenols, and terpenoids at reasonable percentages. The inhibition efficiency, enthalpy, enthropy, activation energy, Gibbs free energy, and adsorption isotherms were extrapolated with some models. The inhibition efficiency increased with an increase in the concentration of the extract. The values of change in Gibbs free energy obtained at 303K, 313K, and 323K were negative, indicating that the leaf extract of <i>Phyllanthus mellerianus</i> was strongly adsorbed on mild steel surfaces and stable at high temperatures. The enthalpy of activation ranges from 43.08kJ/mol to 80.64kJ/mol. An increase in activation energy with inhibitor concentration confirmed the physical (physisorption) adsorption mechanism for the corrosion of mild steel surfaces. The R² values obtained from the linear regression are strongly fitted to the Langmuir and freundlich isotherms. The inhibitory effectiveness of extracts has been attributed to the presence of the hetero atoms N, O, and S present in their phytochemical composition.

Study of SO2 into nanoporous silica Y Zeolite: Molecular dynamics simulation

The dynamic, structure, and thermodynamic properties of sulfur dioxide guest gas inside nanoporous fixed silica Y zeolite were studied by molecular dynamics simulation at different loadings of SO2 per unit cell and within a range of temperature. At loading 20, greater deviation from Fickian behavior is observed. Generally, self-diffusion coefficient increases with temperature. The activation energy for diffusion follows a decreasing trend by loading increase, except at loading 20, which shows an increase in activation energy. The velocity autocorrelation function demonstrates oscillating behavior and cage effect decrease with temperature. From the radial distribution function (RDF) between gas and zeolite framework, it is found that the first layer around the central atom at a low temperature is established more easily and the first peak of the RDF appears at a short distance with more intensity. The interaction between S and Si atoms was examined by the potential of mean force that is independent of loading. The results indicate that SO2 is able to disperse homogeneously into the zeolite at all concentrations and temperatures without much perturbation.

Исследование особенностей высокотемпературной деформации керамик из чистого карбида вольфрама с различным размером зерна

The mechanism of high-temperature creep deformation during compression tests of binderless tungsten carbide specimens with different initial particle size was studied. Tungsten carbide samples with high relative density (96.1 – 99.2 %) were obtained by high-speed spark plasma sintering (SPS) from nano-, submicron-, and micron-sized α-WC powders. The creep tests were carried out in two modes: isothermal soaking at different temperatures (1300 – 1375 °C) at a given stress, allowing to estimate the activation energy of creep, and tests by “stress jumps” at 1325 °C, allowing to estimate the value of the coefficient n in the creep equation. It is shown that the value of creep activation energy in ultrafine grained tungsten carbide with grain size ~ 0.15 µm sintered from plasma chemical nanopowders is ~ 31 kTm. This value is 1.5 – 2 times higher than the creep activation energy in fine-grained tungsten carbide samples obtained by SPS from submicron (~ 0.8 μm) and micron (~ 3 μm) industrial powders. It was found that the value of the coefficient n varies from 2.4 to 3.1, which corresponds to the case of motion of lattice dislocations in the field of uniformly located point obstacles. It has been suggested that one of the reasons for the increase in creep activation energy in tests of tungsten carbide is an increased volume fraction of W2C low carbide particles formed during high-speed sintering of plasma-chemical α-WC nanopowders with an increased concentration of adsorbed oxygen.