Rate-controlling Mechanism Research Articles

Kinetic analysis of fullerene C60 thermal degradation via deconvolution method

This study aims to employ the deconvolution method to investigate the thermal oxidation kinetics of fullerene C60 under non-isothermal conditions where STA (TGA-DSC) with various heating rates was used. Results revealed that the oxidation rate curves consisting of two overlapped peaks are composed of three steps deconvoluted by the Frazer-Suzuki function. Afterward, the kinetic analyses were conducted for each step to determine kinetic parameters. The kinetic model F1 (first-order reaction; g(α) = −ln(1-α)) was identified for steps (I) and (II) with E ≈ 115 and 108 kJ mol−1 and lnA = 12.2, and 11.4 min−1, respectively, and the model R3 (contracting sphere model; g (α) = 1-(1-α)1/3) was determined as the rate-controlling mechanism of step (III), with E ≈ 122 kJ mol−1 and lnA = 13.8 min−1. Electron microscopes like FESEM and TEM were employed to confirm the models obtained for the oxidation process. The results obtained in the case of fullerene C60, with presented thermal oxidation kinetic analyses based on the deconvolution method, indicate that this method can be regarded as a very valuable technique for studying thermal stabilities and complex oxidation kinetics of solid nanomaterials.

Boyd’s film diffusion model for water contaminant adsorption: Time for an upgrade?

The Boyd film diffusion model is widely used in liquid phase adsorption studies for its mathematical simplicity and straightforward data analysis. However, a lack of awareness regarding its restrictive assumptions has led to widespread misuse. The Boyd model assumes film diffusion as the rate-controlling mechanism and rests on two additional pivotal assumptions: adsorption occurs under infinite bath conditions and follows a linear equilibrium relationship. This study examines the recurrent breaches of these assumptions across a growing body of research on water contaminant adsorption. Nearly all kinetic data have been derived from finite bath experiments governed by nonlinear isotherms, which directly contradict the Boyd model’s assumptions. Consequently, applying the Boyd model to such data can yield misleading results and interpretations. To address these challenges, alternative models tailored for finite bath conditions and capable of accommodating both linear and nonlinear isotherms should be considered. These models offer more accurate insights into adsorption kinetics under realistic experimental settings. While the Boyd model remains valuable under specific conditions, its stringent assumptions restrict its broader applicability. Researchers should critically assess the validity of these assumptions and explore alternative models when analyzing liquid phase adsorption kinetics to ensure robust and reliable results.

The impact of precipitation on recrystallization in a severely plastically deformed CoCrFeMnNi multi–principal element alloy

The present study investigated the rate-controlling mechanism for recrystallization kinetics in a severely plastically deformed (SPD) multi–principal element alloy. For this purpose, an equiatomic Cantor alloy (CoCrFeMnNi) was subjected to equal channel angular processing (ECAP) at room temperature and annealed at 773–973 K. The major recovery process was found to be concurrent recrystallization with precipitation. The recrystallization kinetics, investigated in the frame of the Johnson–Mehl–Avrami (JMAK) theory, gives a retarded recrystallization with a high recrystallization temperature of above 0.54Tm and an anomalous low JMAK exponent value of 1.1–1.8. The measured apparent activation energy for recrystallization exhibited a steady increase over the duration, with initial values of 220.8 ± 7.5 kJ/mol rising to 313.9 ± 23.8 kJ/mol towards the end. The systematic analysis leads to the conclusion that the rate-controlling mechanism for recrystallization in ECAP processed CoCrFeMnNi MPEA is the grain boundary migration-determined grain growth instead of nucleation. During this process, the Zener pinning effect exerted by precipitates from the concurrent precipitation with recrystallization plays the dominant role.

Dynamic mechanical behaviors of pearlitic U71MnG rail steel: Deformation mechanisms and constitutive model

Pearlitic rail steels with excellent mechanical and wear properties are widely employed for high-speed railways. During the service period, the presence of track irregularities, switches, as well as crossings can cause intense dynamic loadings, which accumulate the severe deformation of rails, and sometimes even facilitate crack initiation and failure. Knowledge of the dynamic mechanical response and damage behaviors of the rail steels is therefore important for the service performance estimation of railways. In this study, the pearlite U71MnG rail steel was deformed using a split Hopkinson pressure bar (SHPB) apparatus to reach a wide range of strain rates and temperatures. Microstructures including the grain morphology, deformation characteristic of cementite lamellae, dislocation substructures in ferrite lamellae, and phase transformation at pearlite colony boundaries were characterized. Based on the microstructural observations, the rate-controlling strengthening mechanism and temperature-dependent softening mechanism of the steel were revealed when the process for the dynamic loading-induced cementite decomposition at boundaries was discussed. In consideration of the athermal deformation mechanism, thermally activated mechanism, and viscous-drag effect, a physically based constitutive model was proposed to describe the dynamic mechanical response of the pearlite rail steel. The predicted flow stresses were found to be consistent with the experimental one for all strain rates and temperatures.

Selective dissolution and kinetics of leaching zinc from lime treated electric arc furnace dust by alkaline media

The EAF steelmaking process generates 10–20 kg of dust per ton of steel, containing 15–30% zinc, making it a valuable secondary zinc resource. In this work, selective dissolution and kinetics of leaching zinc from lime (CaO) treated EAF dust using NaOH, KOH, and LiOH alkaline solutions were investigated. By reacting with CaO, insoluble ZnFe2O4 in EAF dust is converted to soluble ZnO and stable Ca2Fe2O5. Optimal zinc leaching conditions were achieved after 2 h at 70 °C and a S/L ratio of 1/300 (mg/ml). Among the alkaline solutions used, the zinc leaching rate was highest using 2 M NaOH solution at 99% zinc recovery. On the other hand, thermodynamic solubility calculations indicate that KOH is a better candidate for practical extraction as it can dissolve 6–8 times more zinc than NaOH. The prevailing rate-controlling mechanisms when using NaOH, KOH, and LiOH solutions were found to be the same. From 25 °C to 50 °C, chemical reaction was primarily rate-limiting. In contrast, from 50 °C to 70 °C, the controlling step later shifted to a product layer diffusion control – implying that higher temperatures and finer particle size are vital to achieving high zinc leaching rates. Finally, a solid by-product containing Ca2Fe2O5 and CaO only, which can be recycled in the iron and steelmaking process, was obtained via calcination at 500 °C.

Effect of CO2 on HCl removal from syngas using normal and modified Ca-based hydrotalcites: A comparative study

MSW pyrolysis and gasification technologies have been recognized as effective means to enhance the resource utilization of MSW and promote a circular economy. However, the presence of HCl gas can significantly impact the quality and application of syngas. To maximize syngas resource utilization, develop highly efficient HCl adsorbent, this study investigates the performance and mechanism of HCl removal from syngas using a conventional hydrotalcite (Mg-Al-CO3) and modified Ca-based hydrotalcite (Ca-Mg-Al-CO3). The impact of CO2, a component naturally presents in syngas, on the performance of both materials, were also investigated. Characterization techniques, including XRD, TGA, SEM, and analysis of pore properties and specific surface area, were employed to understand the underlying reaction mechanism. The results demonstrated that the performance of Ca-Mg-Al-CO3 was significantly superior to that of conventional Mg-Al-CO3 sorbents, particularly in the presence of CO2 However, the presence of CO2 had a detrimental impact on the performance of Ca-Mg-Al-CO3 in HCl removal, and this effect became increasingly pronounced with higher concentrations of CO2. TGA results revealed a competitive relationship between HCl and CO2 during the adsorption process. Additionally, the fitting results of adsorption kinetics suggested that the adsorption reaction of HCl and CO2 by Ca-Mg-Al-CO3 followed multiple rate-controlling mechanisms.

Plasticity of solid solution Al-Mn and Al-Mn-Si alloys

The influence of Mn and Si on the mechanical properties of solid solution Al-Mn and Al-Mn-Si alloys have been studied at 4 K, 78 K, and 298 K. The solute strengthening potency of the yield strength increases with decreasing temperature. The addition of Si stimulates the precipitation of Mn-containing dispersoids and decreases the solubility of Mn in the Al matrix, reducing the strengthening effect. The alloys exhibit Stage III of declining work hardening rate with the flow stress during the plastic flow at three temperatures. The mean slip length Λ in the work hardening model of Nabarro, Basinski, and Holt (NBH) evaluated from σΘ curves correlates with the scale of the microstructure. The strain rate sensitivity (SRS) measurements conducted at 78 K show positive SRS of Al and the alloys. At 298 K, one observes a change in SRS due to the change of the mechanism from solute-dislocation to dislocation-dislocation dominated interactions. Mn and Si decrease SRS at 298 K. Al-Mn-Si alloys exhibit negative SRS and jerk flow at a sufficiently low strain rate at 298 K. Analysis of the apparent activation volume, distance, and work has been conducted at 78 K and 298 K to understand the rate-controlling mechanisms. The results indicate that dislocation intersections are rate-limiting processes, but the atomistic mechanism of dislocation cutting varies vastly depending on the temperature and alloy composition. It is suggested that at 78 K, forest obstacles are passed by the formation of jogs and sequential activation of individual partials without making constriction to the perfect defect. At 298 K, the cutting involves constriction, the creation of jogs, and the creation of point defects at each intersection site. The calculated activation work and distance provide signatures of these processes.

Kinetic Analysis of Hydrogen Reduction of Nickel Compounds

A review on the hydrogen reduction kinetics of NiO, NiCO3, and Ni(OH)2 hydrogen was conducted, and the most significant experimental values and results were summarized from the past two decades. Isothermal hydrogen reduction experiments of NiO, NiCO3, and, Ni(OH)2 experiments were carried out at 300 °C, 400 °C, and 500 °C, and the obtained data were fitted to multiple different solid-state kinetic models in order to compare the suitability of the models. Non-isothermal reduction in H2 (0 °C→\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ o $$\\end{document} 900 °C) showed the decomposition of NiCO3 at a temperature range of 230 °C to 300 °C and Ni(OH)2 at 220 °C to 300 °C. The calculated Ea values for NiCO3, Ni(OH)2, and NiO varied between 30 and 35, 36 and 37, and 21 and 26 kJ/mol, respectively. Most of the used models were well fitted making the choice of unequivocally the best suitable model difficult and the identification of the mechanism behind the reaction. It was concluded that an increase in temperature accelerates the reduction process, and the reaction rate-controlling mechanism requires more extensive investigation.

Novel Zinc/Silver Ions-Loaded Alginate/Chitosan Microparticles Antifungal Activity against Botrytis cinerea.

Addressing the growing need for environmentally friendly fungicides in agriculture, this study explored the potential of biopolymer microparticles loaded with metal ions as a novel approach to combat fungal pathogens. Novel alginate microspheres and chitosan/alginate microcapsules loaded with zinc or with zinc and silver ions were prepared and characterized (microparticle size, morphology, topography, encapsulation efficiency, loading capacity, and swelling behavior). Investigation of molecular interactions in microparticles using FTIR-ATR spectroscopy exhibited complex interactions between all constituents. Fitting to the simple Korsmeyer-Peppas empirical model revealed the rate-controlling mechanism of metal ions release from microparticles is Fickian diffusion. Lower values of the release constant k imply a slower release rate of Zn2+ or Ag+ ions from microcapsules compared to that of microspheres. The antimicrobial potential of the new formulations against the fungus Botrytis cinerea was evaluated. When subjected to tests against the fungus, microspheres exhibited superior antifungal activity especially those loaded with both zinc and silver ions, reducing fungal growth up to 98.9% and altering the hyphal structures. Due to the slower release of metal ions, the microcapsule formulations seem suitable for plant protection throughout the growing season. The results showed the potential of these novel microparticles as powerful fungicides in agriculture.

Hair relaxation after shaping - A kinetic approach.

Hair fibres have been shaped via either a thermal route or via a chemical route. The time-relaxation transients of the shaped hairs in air, and in water, respectively, were evaluated. The collected data were kinetically modelled in order to reveal information about the rate controlling mechanism of the recovery process. Hair fibres were thermally shaped at different temperatures between heated plates and left to relax in an environment of controlled humidity and temperature. Different hair fibres were chemically shaped and left to relax in water of different controlled temperatures. Relaxation data were used for modelling the kinetics of the recovery processes by using exponential and logarithmic kinetic laws. The fitting of the models to the two sets of data has been checked by using the residual sum of squares for matching the proper model to each set of data. The processes of shaping and recovery were assimilated with a sequence of two successive quasi-chemical reactions, occurring at the used temperatures. Based on chemical and physical assumptions, the two groups of experiments were modelled by two different laws: an exponential law, suggesting a first-order process as the rate-determining step of the relaxation of thermally shaped fibres, and a logarithmic law, suggesting a slow relaxation, based on percolation theory, for the chemically shaped fibres. This allowed use of chemical kinetics tools for calculating the values of the activation energy in each case. The evaluated values of activation energy of the relaxation processes for both thermal and chemical shaping were found to be close to each other, in spite of the different methods of shaping. The kinetic analysis suggests that despite different reaction sequences occurring during the different shaping-relaxation processes, the rate-controlling mechanism that manages the recovery process is the same in all cases; and this process is proposed to be the thiol-disulphide reformation of intra-protein bonds inside hair.

Magnetic Hydrogel Beads as a Reusable Adsorbent for Highly Efficient and Rapid Removal of Aluminum: Characterization, Response Surface Methodology Optimization, and Evaluation of Isotherms, Kinetics, and Thermodynamic Studies.

Biopolymers such as alginate and gelatin have attracted much attention because of their exceptional adsorption properties and biocompatibility. The magnetic hydrogel beads produced and used in this study had a core structure composed of magnetite nanoparticles and gelatin and a shell structure composed of alginate. The combination of the metal-ion binding ability of alginate and the mechanical strength of gelatin in magnetic hydrogel beads presents a new approach for the removal of metal from water sources. The beads were designed for aluminum removal and fully characterized using various methods, including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, microcomputed tomography, and dynamic mechanical analysis. Statistical experimental designs were employed to optimize the parameters of the adsorption and recovery processes. Plackett-Burman Design, Box-Behnken Design, and Central Composite Design were used for identifying the significant factors and optimizing the parameters of the adsorption and recovery processes, respectively. The optimum parameters determined for adsorption are as follows: pH: 4, contact time: 30 min, adsorbent amount: 600 mg; recovery time: reagent 1 M HNO3; and contact time: 40 min. The adsorption process was described by using the Langmuir isotherm model. It reveals a homogeneous bead surface and monolayer adsorption with an adsorption capacity of 5.25 mg g-1. Limit of detection and limit of quantification values were calculated as 4.3 and 14 μg L-1, respectively. The adsorption process was described by a pseudo-second-order kinetic model, which assumes that chemisorption is the rate-controlling mechanism. Thermodynamic studies indicate that adsorption is spontaneous and endothermic. The adsorbent was reusable for 10 successive adsorption-desorption cycles with a quantitative adsorption of 98.2% ± 0.3% and a recovery of 99.4% ± 2.6%. The minimum adsorbent dose was determined as 30 g L-1 to achieve quantitative adsorption of aluminum. The effects of the inorganic ions were also investigated. The proposed method was applied to tap water and carboy water samples, and the results indicate that magnetic hydrogel beads can be an effective and reusable bioadsorbent for the detection and removal of aluminum in water samples. The recovery values obtained by using the developed method were quantitative and consistent with the results obtained from the inductively coupled plasma optical emission spectrometer.

Creep mechanism in ductile dual-phase aluminum alloys with a fully continuous fiber state

To understand the creep behavior of a practical alloy that has a multiphase consisting of a matrix and several types of precipitate phases, the role of individual phases needs to be studied. However, it is difficult to elucidate the contribution of each phase to creep owing to their complex microstructural morphologies and very complex creep behavior. To understand the role of individual phases and the creep behavior, fundamental creep theories for ductile dual-phase (DDP) alloys must be established initially for specimens with simple microstructural morphologies. To apply these theories practically, they must also be experimentally verified. In this study, DDP alloys composed of 99.99 % Al (matrix phase) and an Al–Mg solid-solution alloy (reinforced phase) were fabricated as a fully continuous fiber state by accumulative roll bonding. Tensile and creep tests at elevated temperatures were performed on alloys composed of systematically varying volume fractions of the reinforced phase. Tensile data at 546 K indicated a linear relationship between the maximum stress and volume fraction of the reinforced phase; the lines were also connected to the data from single-phase materials of the matrix and reinforced phase. Thus, the amount of strain in the matrix and reinforced phases was the same as that during the tensile test, and the relationship between the maximum stress and volume fraction of a DDP alloy followed the classical linear law of mixtures (CLLM). The creep data for Al + Al–2Mg (DDP alloy) at 546 K were nearly equal to those calculated using the CLLM. Thus, the matrix and reinforced phases deformed at the same creep rate. Creep tests were also conducted for Al + Al-1M(5ARB), which had a fine-grained reinforced phase. The creep data for Al + Al-1M(5ARB) at 523 K were also a good approximation to the lines representing the data calculated using the CLLM. Hence, although the grain sizes of the two phases were very different, corresponding to different rate-controlling mechanisms, the creep data for a DDP alloy could be analyzed using the CLLM. Consequently, the creep behavior of the DDP alloys was a superposition of the creep behavior in both phases, and the interpretation of the creep data for DDP alloys using the creep theory of single-phase materials would lead to incorrect conclusions. These findings will contribute to a better understanding of the creep behaviors of practical alloys and will aid in the correct estimation of the creep lifetime.

Passive control of flow rate change due to the input pressure fluctuation based on microchannel deformation

Precise and controlled drug delivery is crucial in continuous infusion systems used for drug treatment, anesthesia, cancer chemotherapy, and pain management. Elastometric pumps are commonly utilized in continuous infusion systems for their ease of use and cost-effectiveness. However, the infusion accuracy is often compromised due to the fluctuating supply pressure of elastomeric pumps, requiring an additional flow regulator to stabilize the output flow rate. We, here, present a novel approach to passively control a flow rate even under the fluctuating pressure environment based on a channel deformation. The flow rate control is enabled by a flow regulator consisting of an open-end microchannel, a closed-end microchannel, and a flexible membrane in the middle. The pressure within an open-end microchannel decreases in the downstream direction, while the pressure within a closed-end microchannel remains equal to the input pressure, creating the pressure difference between the two channels. The membrane deforms in response to this pressure difference, allowing for adjustment of the output flow rate by decreasing the flow path area with the increase in the input pressure. It is found that this concept successfully works by maintaining a steady output flow rate over a target pressure range of 40–50 kPa. Fluid–structure interaction numerical simulations and theoretical analysis are used to explain the flow rate control mechanism of the device. The results show that the present approach offers a promising solution for achieving stable drug delivery in continuous drug infusion systems, addressing the limitations of conventional elastomeric pumps.

Investigation of the rate-controlling process of intermetallic layer growth at the interface between ferrous metal and molten Al–Mg–Si alloy

In this study, we focused on unraveling the intricate world of intermetallic compound formation at the interface of solid Fe and liquid Al–Mg–Si alloy. Our primary aim was to shed light on the phenomenon of Fe degradation in molten Al alloys. Our investigation led us to discover two distinct intermetallic phases, namely Fe2Al5 and Fe4Al13, each exhibiting unique growth dynamics influenced by the interplay of volume diffusion and interface reactions. Moreover, delving deeper into the mechanics of these processes, we meticulously analyzed the rate-controlling mechanisms governing layer growth, exploring both volume diffusion and interface reactions. Furthermore, we quantified the activation enthalpy associated with these phenomena, enriching our understanding of the energy barriers involved in atom or molecule diffusion across solid-liquid interfaces. The implications of our findings extend far beyond the confines of the laboratory, holding significant promise for real-world applications. These insights into Fe degradation prevention and the enhancement of Al alloy performance when in contact with Fe materials offer exciting prospects for materials design and process optimization across diverse engineering and industrial domains.

Pivotal role of retained austenite as a low temperature creep controlling mechanism in a martensitic spring steel

The rising demand for electric vehicles urges automotive suppliers to push their limits on the sag resistance of suspension coil springs. However, the mechanism contributing to sag loss in a coil spring or low temperature creep (LTC) in a spring steel is still unclear. Furthermore, the LTC rate-controlling mechanism remains elusive. In the current study, an attempt has been made to unfold the LTC controlling mechanism in a SAE 9254 steel grade. A combined analysis by means of (i) a mechanism-based exhaustion creep model (ECM) and (ii) advanced microstructural characterization prior to and post LTC suggests that dislocation glide, mainly localized in the metastable γ phase, is considered as one LTC contributing mechanism in martempered SAE 9254. Furthermore, stress-assisted martensitic transformation (SAMT) is considered as additional LTC contributing mechanism in SAE 9254 up to the temperature T≤323K. Beyond that temperature strain-induced martensitic transformation (SIMT) takes the place of SAMT. Our approach includes that the LTC rate-controlling mechanisms are stress-assisted recovery (SAR), SAMT, and SIMT especially at elevated temperature T.

Degraded creep resistance induced by static precipitation strengthening in high-pressure die casting Mg–Al–Sm alloy

Relationship between precipitation strengthening and creep resistance improvement has been an important topic for the widespread applications of magnesium alloys. Generally, static precipitation strengthening through thermal stable precipitates would generate satisfactory creep resistance. However, an opposite example is presented in this work and we propose that the size of precipitates plays a crucial role in controlling the operative creep mechanisms. In addition, the precipitate components along with their crystal structures in the crept Mg–4Al–3Sm–0.4Mn samples with/without pre-aging were thoroughly studied using Cs aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Previous aging generates a large density of fine precipitates (< ∼5 nm) homogeneously distributing in Mg matrix and exhibiting satisfactory strengthening effect. However, the number density of precipitate strings consisting of several or even dozens of relatively coarse precipitates (∼10 nm) was significantly decreased at the same time. As revealed in this work, the relatively coarse particles in Mg matrix are much more efficient than the fine precipitates in promoting dislocation climb. Therefore, the rate-controlling mechanisms are transferred from dislocation climb to dislocation slip after previous aging, thus leading to degradation of creep resistance. Moreover, there are mainly five types of precipitates/clusters, namely β″-(Al, Mg)3Sm, Al5Sm3, ordered Al–Sm cluster, ordered Al–Mn cluster and ordered/unordered AlMnSm clusters. The crystal structures of the former two precipitates were discussed and the formation mechanisms of the precipitates/clusters were revealed.

Comparative study on the microstructure evolution and crystallization behavior of precursor-derived and mechanical alloying derived SiBCN

In this study, the chemical reactions and structural change during the transformation of the precursor into PDCs-SiBCN ceramic were investigated. Besides, the crystallization behaviors of precursor-derived (PDCs-SiBCN) and mechanical alloying derived (MA-SiBCN) SiBCN ceramics at different temperatures (1200–1700 ℃) were compared. Due to different amorphous structures derived from pyrolysis and amorphization processes, the silicon atoms units bonded by sp3 hybridization in PDCs-SiBCN and MA-SiBCN ceramics are SiC4 and SiC(4-x)Nx tetrahedral structure, respectively. Due to the phase separation of SiC(4-x)Nx tetrahedral structure at higher temperatures (>1400 ℃), PDCs-SiBCN ceramic has a higher resistance to crystallization but will suffer obvious carbothermal reduction process of Si3N4 during crystallization. Finally, the crystallization kinetics of SiC in MA-SiBCN ceramic were investigated. The temperature dependence of SiC crystallization in MA-SiBCN ceramic obeys the Arrhenius-type law with different activation energies in the low and high temperature ranges respectively due to the transition of the rate-controlling mechanisms.

Preparation of low-cost activated carbon from Doum fiber (Chamaerops humilis) for the removal of methylene blue: Optimization process by DOE/FFD design, characterization, and mechanism

Within the context of a circular economy, this work aims to valorize local lignocellulosic biomass of Doum fiber (Chamaerops humilis), as a highly promising adsorbent material for the removal efficiency of methylene blue (MB) dye via the adsorption process. Thus, this study investigates the potential of both raw (RDF) and activated carbon from Doum fiber (ACDF) as adsorbents. The first task was to enhance the adsorption efficiency of MB onto activated carbon by systematically optimizing its synthesis conditions. To achieve this, a full factorial design (FFD) approach of four factors (activation time, activation temperature, contact time, and concentration of H3PO4) at two levels was employed, using H3PO4 as the activating agent. A series of batch experiments were performed to characterize the adsorption properties of MB onto RDF and ACDF by describing the adsorption conditions, determining the kinetic and isotherm models, and evaluating the thermodynamic parameters. The results obtained revealed that ACDF had significantly higher surface affinity for MB than RDF, with an adsorption capacity of 83.82 mg. g−1. The adsorption process was found to be spontaneous and endothermic for ACDF, while for RDF, it was exothermic. The adsorption data for both ACDF and RDF exhibited a good fit to the Langmuir isotherm model, indicating monolayer adsorption. Furthermore, the kinetic data demonstrated excellent agreement with the pseudo-second-order model, suggesting a three-step rate-controlling mechanism. According to the results of density functional theory (DFT) calculations, the adsorption mechanism of MB mainly involves electrostatic interactions, hydrogen bonds, and n-π, π-π interactions with the two adsorbents.

Exploring the high-temperature deformation behavior of monocrystalline silicon – An advanced nanoindentation study

Knowing the mechanical behavior of silicon at elevated temperatures is crucial for many high-temperature applications and processes. This work aims to expand the knowledge of these properties, especially on length scales relevant to miniaturized silicon structures. Therefore, nanoindentation experiments were performed on two differently doped (1 0 0) silicon wafers with varying oxygen content, from room temperature up to 950 °C. Residual impressions were microscopically characterized via confocal laser scanning microscopy. From this dataset covering an exceptionally large temperature range the elastic modulus and hardness as well as strain rate sensitivity, activation volume, and energy were evaluated. Generally, a change in deformation behavior can be identified between 300 °C and 400 °C. Above this transition temperature, the hardness drops exponentially. Also, the material becomes strain rate sensitive. These observations support the assumption that the deformation mechanism shifts from high-pressure phase transformation to dislocation-controlled plasticity with increasing temperature. Furthermore, a change in strain rate sensitivity, activation energy, and activation volume above 800 °C implies a further shift in the rate-controlling mechanism of dislocation motion. Lastly, the more strongly doped sample with the higher oxygen content showing higher mechanical strength is discussed regarding solid-solution strengthening and dislocation locking by oxygen atoms.

Rapid epitaxy of 2-inch and high-quality α-Ga2O3 films by mist-CVD method

High thickness uniformity and large-scale films of α-Ga2O3 are crucial factors for the development of power devices. In this work, a high-quality 2-inch α-Ga2O3 epitaxial film on c-plane sapphire substrates was prepared by the mist-CVD method. The growth rate and phase control mechanisms were systematically investigated. The growth rate of the α-Ga2O3 films was limited by the evaporation of the microdroplets containing gallium acetylacetonate. By adjusting the substrate position (z) from 80 to 50 mm, the growth rate was increased from 307 nm/h to 1.45 μm/h when the growth temperature was fixed at 520 °C. When the growth temperature exceeded 560 °C, ε-Ga2O3 was observed to form at the edges of 2-inch sapphire substrate. Phase control was achieved by adjusting the growth temperature. When the growth temperature was 540 °C and the substrate position was 50 mm, the full-width at half maximum (FWHM) of the rocking curves for the (0006) and (10-14) planes were 0.023° and 1.17°. The screw and edge dislocations were 2.3 × 106 and 3.9 × 1010 cm-2, respectively. Furthermore, the bandgaps and optical transmittance of α-Ga2O3 films grown under different conditions were characterized utilizing UV-visible and near-IR scanning spectra.