Papers by Keyword: Activation Energy

Abstract: This paper presents experimental results on the processing of complex concentrated alloy with a nominal composition of A_0.35CoCrFeNi. The alloy was produced by vacuum induction melting and tilt casting. The microstructure of the as-cast CCA consists of dendritic and interdendritic regions homogenized by heat treatment at 1360 °C. After rotary swaging at room temperature, the microstructure is characterized by an abundance of dislocations and continuously intersecting slip bands. Annealing experiments were carried out in the temperature range of 1150 °C – 1300 °C and different holding times to determine the parameters of grain growth kinetics. Phase and chemical analysis were investigated using XRD and EDS methods. The activation energy of recrystallization in the studied composition was 458 kJ mol^-1. The influence of grain size on room temperature mechanical properties and tensile properties was determined. The hardening coefficients k_h and k_σ, calculated using the Hall-Petch relation, were 277.5 HV µm^-1/2 and 655 MPa µm^-1/2, indicating the effectiveness of grain boundary hardening in the studied single-phase CCA.

Abstract: The microstructure and growth kinetic of alumina (Al₂O₃)-modified aluminide coating were investigated at 650°C, 680°C, and 700°C for various durations (4, 6, 8, and 10 hours) using the slurry aluminizing process. The heat-treated samples were analyzed through scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) to assess microstructural evolution, elemental composition, and phases of the coating. SEM observations revealed a two-layer aluminide coating, comprising an Al-rich intermetallic (FeAl₃) and a Fe-rich intermetallic (FeAl). Microhardness tests showed that FeAl₃ had hardness values ranging from 880 to 990 HV, while FeAl, with values between 610 and 700 HV. The growth kinetics indicated that the thickness of the aluminide layers increased with both the aluminizing temperature and time, following a parabolic growth law. The activation energy for the growth of FeAl was 343.15 kJ/mol.

Abstract: The focal concern of this study is to examine the behaviour of bio-convective flow featuring micropolar nanofluids over an inclined permeable stretching surface while considering the influence of radiative activation energy. This investigation addresses the complex interplay of factors such as biological activity, convective heat and mass transfer, unique attributes of micropolar fluids, the dynamics of nanofluids, and radiative effects. This analysis employed Buongiorno’s model, considering thermal radiation and activation energy on the bioconvective flow of micropolar nanofluids over an inclined stretching surface. Some suitable similarity variables were used to obtain a set of non-linear differential equations from the initial partial differential equations which were then solved numerically using the Runge-Kutta Fehberg method along with shooting technique. The effects of some physical parameters were examined on the velocity, temperature, concentration, and microorganism density profiles of the flow. The result revealed that each increase in the heat source/sink, thermal radiation, thermophoresis, and Brownian motion lead to a corresponding increase in the thermal boundary layer; activation energy increased the concentration while Peclet number and bioconvective Lewis number declined the microorganism density profile. Insights gleaned from this study can find applications in biomedical fields. Understanding the behavior of bio-convective nanofluids has implications for controlled heat transfer in medical applications like hyperthermia treatments or targeted drug delivery, thereby impacting patient care.

Abstract: The current investigation deals with the utilization of the Differential Scanning Calorimetric (DSC) experimental data of Se-Te-Sn Chalcogenide materials at various heating rates, 10,15,20, and 25 Kmin^-1. With the help of glass transition temperatures, T_g, fragility index, m is evaluated using Starink and Vogel-Flutcher-Tammanni (VFT) models. m is also correlated with mean coordination number (Ω) and the conclusions are derived. Sreeram et al. (modified Gibbs-DiMarzio) expression is scrutinized, which relates a verifiable link between T_g and Ω .

Abstract: This article discusses the use of solar dryers as a method for stabilizing and reducing the volume of residual sludge produced by wastewater treatment facilities. The study focused on the convective drying behavior of sewage sludge produced by the wastewater treatment plant of Meknes City under convective solar drying. The study aimed to investigate the drying kinetics of sewage sludge and emphasize the effect of temperature and water content on the evolution of the drying rate. The measured water content values showed a decrease as drying time increased. The results revealed the presence of phase II, which characterizes the decreasing rate drying period, and the absence of phase I, which describes the constant rate drying period.The study developed an empirical model to describe the kinetic behavior of convective solar drying of Moroccan domestic sludge. The model can be used to predict the shape of a drying curve under other aerothermal conditions. Additionally, the study analyzed the thermal diffusivity and activation energy of sewage sludge using an experimental macroscopic method based on Fick's diffusion model and the Arrhenius equation. The measured diffusion coefficient values range from 0,71 10^-9 m².s^-1 to 1,47 10^-9 m².s^-1, and the value of activation energy was evaluated at 17.54 kJ/mol.

Abstract: Iron substituted Lead zirconate titanate nanoparticles Pb (Zr_0.52Ti_0.48) _1-x Fe_xO_3-x (PZTFx) (for (x=0.00, 0.025, 0.05, 0.075, 0.10, 0.15 and 0.20) was prepared using the sol-gel route in the morphotropic phase boundary (MPB) region. The X-ray diffraction data revealed the formation of both rhombohedral and tetragonal structures. The microstructural properties of the compounds were examined through the scanning electron microscopy (SEM) technique. The impedance spectroscopy and conductivity spectroscopy were carried out over a wide range of temperatures (RT–400°C) and frequencies (100 Hz–2 MHz) to investigate the grain and grain boundary effect on the electrical properties of PZTFx. The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters. Cole– Cole plots indicate Debye-type dielectric relaxation and the grain boundaries resistance is dominant at room temperature. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of PZTFx ceramics. The dielectric properties of (PZTFx) ceramics as a function of temperature are studied and displayed a resonance phenomenon for all samples. Temperature-dependent conductivity behavior indicated an Arrhenius type of thermally activated process in the low-temperature region. Activation energy has been calculated from the temperature-dependent DC electrical conductivity measurements for all the samples.

Abstract: In this study, activation energies required for the static recrystallization behavior during the annealing process after cold deformation of Al-Mg-Si alloy to which zirconium was added in various proportions were investigated. Depending on the zirconium content, the activation energies of the alloys were found and compared both experimentally and by calculation. For this purpose, alloys containing 0.1, 0.2 and 0.3 wt-% Zr were cold rolled after taking into solution and quenching. And then, the alloys were annealed at 375 °C and 500 °C for different annealing times. After the alloys were prepared metallographically, their grain structures were examined microscopically. Depending on the temperature, recrystallization-% was found by image analysis and experimental recrystallization-% curves were drawn. The time taken for recrystallization-50% to experimentally find the activation energy required for recrystallization to occur was found from the curves. These values were replaced in the relevant formulations and the required activation energy was experimentally found from the slope of the Arrhenius equation and the ln t_50% and 1/T graph. In order to find the recrystallization-% by calculation, the nucleation rate and growth rate of the new recrystallized grains were found by image analysis. By substituting these values in Johnson-Mehl-Avrami equation, the calculated recrystallization-% curves of the alloys were found. From here, using the relevant equations, Arrhenius equation was passed and the activation energy was calculated from the slope of ln k and 1/T graph. The results showed that the activation energy increased with the increase of the zirconium ratio, and even the most effective zirconium ratio was between 0.1-0.2% by weight in increasing the activation energy. Therefore, this ratio should be considered in processes where recrystallization, which also affects other properties of the alloy, is not desired.

Abstract: We investigate the temperature-dependent resistivity (ρ(T)) and Hall coefficient (R_H(T)) of heavily Al-doped 4H-SiC and discuss the underlying conduction mechanisms. The sign of R_H(T) changes from positive to negative in nearest-neighbor hopping (NNH) and variable-range hopping (VRH) conduction, whereas it is positive in band conduction because Al-doped 4H-SiC is a p-type semiconductor. We propose a general physical model to explain why R_H(T) in hopping conduction becomes negative at low temperatures, which is applicable to both NNH and VRH conduction. Moreover, we elucidate why the activation energy for negative R_H(T) becomes similar to that of ρ(T) in NNH conduction.

Abstract: This study investigates entropy production analysis in the flow of micropolar nanoliquid due to its application in thermal engineering systems for the identification of the factors which causes the destruction in the available energy and consequently affects overall performance of the thermal devices. The model is built on a two-dimensional porous stretching sheet with an incompressible fluid assumption and steady with the influence of variable thermal conductivity, nonlinear thermal radiation, haphazard motion and thermo-migration tiny particles. A prescribed surface temperature is adopted as the thermal heating condition while the impact of the reaction order and activation energy are incorporated into the concentration field. The model equations are restructured to ordinary derivative system, which is computationally solved by Fehlberg Runge-Kutta technique. The results agree well with previous outcomes for limiting situations while the effects of the embedded terms are presented graphs. The analysis reveals that a rise in variable thermal conductivity, the material term and viscous dissipation leads to a rise in the irreversibility process.

Abstract: Ultrasonic Spray Pyrolysis (USP) technique was used to prepare undoped and (2, 4, 6 and 10 at. %) Zn-doped iron oxide (Fe_xO_y:Zn) thin films for use in photocatalytic applications. The effect of Zn ion substitution on structural, optical, and electrical properties was studied. The X-ray diffraction patterns showed that there are two different phases of iron oxide, a hematite phase (α‑Fe₂O₃) and a magnetite phase (Fe₃O₄) that crystallized in the prepared samples. The nominal fractions of α‑Fe₂O₃ and Fe₃O₄ phases changed from 74 % to 42 % for the hematite phase and from 26 % to 58 % for the magnetite phase and this confirmed that the Zn doping favored the growth of Fe₃O₄ phase. The crystallite size decreased from 15.43 nm to 8.99 nm, while the micro-strain changed from 0.0056 to 0.0215 and the dislocation density from 0.0099 nm^‑2 to 0.0639 nm^‑2. The unit cell parameters were also improved when the doping rate was changed. Optical measurements showed that the energy gap decreased from 2.26 eV to 2.16 eV, the film thickness changed from 569 nm to 479 nm while the refractive index increased from 2.99 to 3.51 and the Urbach energy from 544 meV to 558 meV. Electrical measurements performed by the two-point probe method showed that the electrical conductivity increased directly with increasing Zn concentration reaching 18.5 10^‑15 (Ω.cm)^‑1 with 10 at. % Zn concentration. The variation of the electrical conductivity curves versus the sample heating temperature as well as the activation energy showed a semiconductor behavior of the films. Zinc doped iron oxide thin films exhibit 51.85 % photocatalytic degradation efficiency for methyl green organic dye.