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Aluminum oxide (Al₂O₃) is a widely used ceramic material known for its high-temperature stability, which makes it valuable in a variety of industrial applications. The conversion from bulk to surface modification may lead to substantial changes in their thermodynamic properties. Consequently, this study endeavors to resolve the primary thermodynamic properties of Al₂O₃ by employing DFT calculation. The FP-LAPW+lo method is first used in the WIEN2K software to determine the surface of bulk Al₂O₃ with varying thicknesses. The thermodynamic parameters of Al₂O₃ at high pressure and elevated temperature, such as bulk modulus, thermal expansion coefficient, heat capacity, entropy, enthalpy and Debye temperature are investigated with the help of the quasi-harmonic Debye model in the Gibbs2 package. The calculated thermodynamic parameters of the Al₂O₃ agree with earlier findings. The results reveal that with increasing thickness, the thermal expansion coefficient and entropy decrease while the enthalpy increases, indicating that Al₂O₃ can be a suitable candidate for various energy and electronic industrial applications.

The optical and thermodynamic properties of aluminum oxide (Al₂O₃) were investigated through the density functional theory. In this paper, to examine the structural parameters the GGA-PBEsol potential was used. The Becke–Johnson (TB-mBJ) potential was applied to estimate the optical properties, and the Gibbs2 code was used to examine the thermodynamic behavior of Al₂O₃. The optical analysis shows that the optical properties were improved and the spectrum red-shifted occurs under high pressure. The thermodynamics behavior of the Al₂O₃ in temperatures ranging from 0K to 1400K and the pressure ranging from 0GPa to 60GPa were achieved using the quasi-harmonic Debye model to elucidate the relationships between thermodynamic parameters and temperature under variant pressure. The results show that the optical and thermodynamic properties of Al₂O₃ are significantly improved under high pressure. This enhancement suggests that Al₂O₃ could be used more effectively in many industrial applications, including high-performance ceramics, thermal barrier coatings and as an optical material in devices such as lasers and sensors. In addition, the findings provide important insights into the behavior of Al₂O₃ compounds under high-pressure environments, which could enhance material design procedures for advanced technologies.

We have fabricated and investigated several types of GaN MOSFETs with normally-off operation. The recessed-gate GaN MOSFET is preferred for normally-off operation, because the threshold voltage (V_th) of the device can be easily controlled, but it suffers from relatively modest current drivability which must be improved by adopting appropriate device structure and/or process. Enhanced performances have been achieved in this work by combining the recessed-gate technology with additional processes, such as: the post-recess tetramethylammonium hydroxide (TMAH) treatment to remove the plasma damage, the post-deposition annealing of gate oxide to decrease the gate leakage current, the re-growth of n+ GaN layer for source/drain to improve the access resistance and V_th uniformity, the stress control technology to achieve extremely high 2-D electron-gas density (2DEG) on source/drain and decrease the series resistance, and the use of the p-GaN back-barrier to decrease the buffer leakage current. The GaN-based FinFET with very narrow fin was also investigated as a possible candidate for high performance normally-off GaN MOSFETs.

Al₂O₃ insulator layer was deposited by atomic layer deposition (ALD) technique on p-type Si $〈111〉$ and the Al/Al₂O₃/p-Si metal/insulator/semiconductor (MIS) structures were fabricated. The current–voltage ($I-V$) characteristics of these structures were investigated in two different temperatures. The main electrical parameters such as the ideality factor ($n$), zero bias barrier height (${\mathrm{\Phi }}_{Bo(I-V)}$), and series resistance ($R_s$) values were found for 300 and 400K. The energy density distribution profiles of the interface state density ($N_{ss}$) were determined from the $I-V$ characteristics. In addition, the capacitance–voltage ($C-V$) and conductance–voltage ($G/w-V$) characteristics of devices were investigated in the frequency range 50–1000kHz at room temperature. Frequency-dependent electrical characteristics such as doping acceptor concentration ($N_A$), energy difference between the valance band edge and bulk Fermi level ($E_F$), diffusion potential ($V_{\text{D}}$), barrier height (${\mathrm{\Phi }}_{B(C-V)}$), the image force barrier lowering ($\mathrm{\Delta }{\mathrm{\Phi }}_B$), maximum electric field ($E_m$), and $R_s$ values were determined using $C-V$ and $G/w-V$ plots. In addition, the $N_{ss}$ values were performed using Hill–Coleman method. According to experimental results, the locations of $N_{ss}$ and $R_s$ have an important effect on $I-V$, $C-V$ and $G/w-V$ plots of MIS structure.

Copper aluminium oxide (Cu–Al₂O₃) films were synthesized on Si(111) substrates through RF magnetron sputtering by using the layer stacking technique. Cu and Al₂O₃ targets were used to deposit Cu and Al₂O₃ thin films under Ar atmosphere, respectively and the deposited films were then annealed under N₂ environment at 350${}^{\circ }$C, 450${}^{\circ }$C and 550${}^{\circ }$C for 6h. The structural properties of the films were investigated by using X-ray diffraction (XRD) while the surface morphology and topography of the deposited films were examined through Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX) and Atomic Force Microscopy (AFM). XRD analysis revealed the existence of multiple phases of CuO, Al₂O₃ and CuAl₂O₄ in the deposited films on Si(111) substrates. As a result of the annealing effect, the peak intensities of CuO, Al₂O₃ and CuAl₂O₄ were found to be increased along with the shifting of peak positions. Williamson–Hall (WH) analysis was also implemented to analyze the structural properties such as crystallite size, stress, strain, and energy density. Based on the three models used in WH analysis, the changes in the crystallite size and strain of the films were indicated to be anomalous with the changes in the annealing temperature. Moreover, the strain of films was also showed to be changed from compressive strain into tensile strain. The FESEM results also indicated the formation of various surface morphologies under various annealing temperatures whereas EDX analysis showed an increased atomic percentage of Cu, Al, and O due to the effect of increase in annealing temperature. The AFM analysis showed that the surface roughness of the deposited films increased with the increase in the annealing temperature.

Plasma electrolytic oxidation (PEO) coatings were formed on aluminium alloy in additive Al₂O₃- and TiO₂-containing Na₂SiO₃-based electrolytes, respectively. The effect of these additives on morphology, composition and wearing properties of coatings was investigated. The morphology and composition of coatings were studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). Analysis of wearing properties of coatings were done by friction and wearing experiment. It was found that the use of additives greatly affects the surface morphology of coatings. It is shown that the content of $\alpha$-Al₂O₃ in coatings formed in Al₂O₃-containing electrolytes increased with the addition of Al₂O₃. However, the content of $\alpha$-Al₂O₃ in coatings formed in TiO₂-containing electrolytes first increased and then decreased. Among these coatings, the coating formed in silicate-based electrolytes system containing 7g/L Al₂O₃ showed the most superior wearing properties.

In the current experimental study, grey cast iron (CI) substrate was coated with Inconel718-Al₂O₃ based composite coating with a high-velocity oxy-fuel technique. The effect of changing the Al₂O₃ content (10, 20 and 30 wt.%) on the microstructure, hardness, porosity and electrochemical corrosion performance of Inconel (INC718) coating was studied. Investigations on the corrosion behavior of uncoated and HVOF-coated substrates were carried out at room temperature at 3.5wt.% sodium chloride solution (NaCl) with the help of the potentiodynamic polarization approach. The surface morphologies and compositions of HVOF as-sprayed and electrochemically corroded coatings were studied through SEM and EDS techniques. The various phases existing in the INC718 and Al₂O₃ feedstock powders and HVOF-deposited composite coatings were determined by XRD analysis. The microhardness of INC718-based coatings was found to be increased with the increase in Al₂O₃ content. The highest average microhardness value of about $801\pm 40$HV${}_{0.2}$ was observed in INC718-30wt.% Al₂O₃ coating. The deposited coatings exhibited an increased porosity level with the increased amount of Al₂O₃ contents. However, the coating with 10wt.% Al₂O₃ content exhibited the maximum corrosion resistance. Its improved corrosion performance is attributed to low porosity levels, which causes the penetrating pathways of Cl⁻ ions to be blocked completely.

In this study, Al/Al₂O₃ composites have been fabricated by combined stir casting and accumulative press bonding (APB) processes. The effect of APB method on the bonding properties of bulk samples such as the number of APB process, Al₂O₃wt.% and the pressing temperature has been investigated by the peeling test. It is established that stronger bonding with a good quality can be obtained by increasing the pressing temperature and decreasing the Al₂O₃ particleswt.% as the reinforcement. Also, growing the step number of the APB method increases the bonding strength up to step#2 and then reduces the average peeling force due to the strain hardening result of the metallic matrix during the accumulative pressing. Finally, the effect of the APB method on the peeling surface of samples has been investigated using the scanning electron microscopy.

Presently, there are more new kinds of requirements for the production of advanced ceramic elements in the engineering field. These ceramic elements are to be machined for a better surface roughness value. Surface roughness of the machined elements is one of the main machining characteristics which play a vital role in determining the high quality of advanced ceramic elements in engineering. In this work, some machining tests were done on the advanced aluminum oxide (Al₂O${}_3)$ ceramic work material using a silicon carbide (SiC) grinding wheel under different process parameters. A parametric analytical model was developed using the method of regression analysis by taking into account of four process parameters, such as depth of cut, feed, grain size and spindle speed. The effectiveness of the model is evaluated based on the comparison of experimental results with the regression analysis. The predicted values of surface roughness ($R_a)$ and wheel wear ($W_w)$ with minimum average error are in line to the results of the acquired experiment.

Heat exchanger plays an essential part in industrial sector in transferring the heat energy. Heat is exchanged between fluids in convection and conduction mode through the walls of the heat exchanger. If the heat transfer medium has low thermal conductivity, it will greatly limit the efficiency of the heat exchanger. Whenever the system acts subjected to an increase in the heat load, heat fluxes caused by more power and smaller size, cooling is one of the technical challenges faced by the industries. The objective of this research work is to evaluate the overall heat transfer coefficient through an experimental analysis on the convective heat transfer and flow characteristics of a nanofluid. In our experiment, the nanofluid consists of water and one percentage volume concentration of Al₂O₃-water nanofluid flowing through parallel and counter flow in shell and tube heat exchangers. About 50nm diameter of Al₂O₃ nanoparticles was used in this analysis and found that the overall heat transfer coefficient and convective heat transfer coefficient of nanofluid were slightly higher than those of the base liquid at same mass flow rate and inlet temperature. Here, there are three samples of dissimilar mass flow rates, which have been identified for conducting the experiments and their results are continuously monitored and reported. Finally, the observed results through an experimental investigation were presented and concluded that the enhancement of overall heat transfer coefficient is likely to be feasible by means of increasing the mass flow rate of base fluid and prepared nanofluid on the proportional basis.

Friction stir welding (FSW) is a process that can join many materials by causing minimal internal stress without the need for a direct electric current, contrary to traditional welding methods. The effects of SiC and Al₂O₃ reinforcing powders on the joining of AA6061-T6 and AA7075-T6 plates, which are difficult to join with conventional welding methods by FSW, are investigated in this study. The metallurgical properties of the combined samples are examined in terms of strength characteristics to investigate the effects of the reinforcement powder. In addition, elemental analysis is carried out for the mixing behavior of the powders. Finally, we used the TOPSIS method to select the most appropriate powder types to improve welding quality. Furthermore, a game theory application is presented to determine which powder type is suitable considering the joined aluminum plate’s strength expectations.

AlO is a prevalent oxide compound composed of aluminum and oxygen, with the chemical formula Al₂O₃. This study aims to prepare aluminum oxide nanoparticles using aluminum nitrate nonahydrate Al(NO${}_3{)}_3\cdot$ 9H₂O through direct exposure to a plasma jet system using argon gas, as plasma is the fourth state of matter and a common effective method. The major study in the preparation of Al₂O₃ nanoparticles, which is a physical method, examines the effect of aluminum oxide nanoparticles against bacteria and fungi. Different methods were used for diagnosis. The X-ray diffraction examination showed an average particle size of 37.8 nm. It was also found through the UV-Vis examination that a surface plasmon resonance was formed at 300 nm with an energy gap value of 4.21 eV. The electron microscope field emission scanning (FE-SEM) was used to study the surface morphology. The results of biological testing showed that aluminum oxide nanoparticles have high antibacterial and antifungal activity.

Amorphous alumina films are isotropic and have no grain boundaries, which make them have smooth surfaces, excellent properties, and wide applications in protective coatings, catalysis, and microelectronics. However, high-quality alumina films were usually prepared by vapor-phase approaches which need expensive equipment and long production time. Additionally, amorphous films are long-range disordered, which makes the study of structure–property relationships challenging. Here, a simple sol–gel method is employed to obtain high-quality amorphous Al₂O₃ thin films. The microstructure, morphology, and mechanical properties of amorphous Al₂O₃ thin films were systematically investigated. All the Al₂O₃ thin films heat-treated at 600–800^∘C are in amorphous state with ultrasmooth surface (Ra values about 0.29–0.43 nm) and high mechanical properties (elastic modulus ∼170GPa, hardness ∼20GPa). The mechanical properties (E and H) of Al₂O₃ films gradually increase with the increase of heat-treating temperature. Additionally, the Al coordination of the amorphous alumina films are analyzed by solid-state NMR and correlated with the mechanical properties. The results show that in amorphous alumina, the presence of tetrahedral Al ([4]Al) and octahedral Al ([6]Al) is helpful to improve the mechanical properties, while the five-coordinated Al ([5]Al) is not conducive to improve the mechanical properties. The results demonstrate that sol–gel method is an attractive alternative to time-consuming and expensive vapor-phase approaches and are useful for scale-up to applications and research of amorphous alumina films.

We investigated the characteristics of Al₂O₃ gate pH-ISFET which was fabricated by using the standard complementary metal oxide semiconductor (CMOS)-process techniques. The Al₂O₃ film used to sensing membrane was deposited by atomic layer deposition (ALD). Then, thermal temperature annealing process of the Al₂O₃ film was performed in O₂ ambient for 40 min at a temperature of 500°C, 600°C, 800°C and 900°C. We measured the I_D–V_D, I_D–V_G and transconductance of fabricated FET device in order to confirm stability of device before the fabrication of pH-ISFET. Then, the package process was performed. To investigate the pH response characteristics, we measured the I–V curves of the Al₂O₃ gate pH-ISFET sensor using a 4155 probe station. Form the measured results, we confirmed that sensitivity, hysteresis, and long-term stability of the Al₂O₃ pH-ISFET showed the changed characteristics at various annealing temperature. The characteristics of Al₂O₃ gate pH-ISFET annealed at 600°C indicated the best results of the high sensitivity (56 mV/pH), low hysteresis (0.5 ~ 0.7 mV), and low drift (1.35 mV/h) in comparison to Al₂O₃ gate pH-ISFETs annealed other conditions. As measured results, we confirmed that sensitivity, hysteresis, and long-term stability of Al₂O₃ gate pH-ISFET depend on the thermal annealing temperature of Al₂O₃ film and also it is the very important parameter in the pH-ISFET.

Highly resistive Al₂O₃ ceramics have been widely used for electrostatic chucking of silicon wafer. However, there are some restrictions to use such chuck material on higher resistance substrates, such as glass or sapphire wafer. In this study, Al₂O₃ compositions were modified by various dopants ; TiO₂, CuO and SiO₂, and their sinterability, crystal structure, electrical properties and chucking property were investigated with different doping concentrations and sintering conditions. Both of TiO₂ and CuO were found to be key dopants on controlling the sintering temperature and electrical resistivity. When 2~3 mol% of TiO₂ and CuO, and 1mol% of SiO₂ were added simultaneously, the specimens having lowered resistivity, ~10¹² Ωcm were obtained at a relatively lowered sintering temperature, 1250°C, which means that the electrostatic chuck for display and LED sapphire chip processes can be economically fabricated by using simple ceramic process.

Silicon carbide composite ceramic filtration membrane materials were prepared by air spray technology. In this process, using some organic solvents such as glycerol, ethanol, etc to fabricate a stable, excellent dispersibility inorganic silicon carbide slurry. Using air spray technology and coating the filter membrane. According to some heat treatments that sintering temperature from1350℃ to1450℃ for 3h, we can prepare a well-distributed, jumbo size SiC ceramic composite filtration membrane. The effects of particle size of SiC, sintering temperature, different ceramic binders on SiC filtration membrane were investigated. Meanwhile, the reaction bonding characteristics, phase composition, flexural strength as well as microstructure of SiC composite ceramics filtration membrane were also investigated. It is demonstrated that 22.8μm silicon carbide sintered at 1450℃ will obtain a better performance. With particle size increases, silicon carbide porous ceramic surface oxide layer thinner prepared at the same temperature. When 15wt% ceramic binder was added, a flexural strength of 36.6MPa was achieved at an open porosity of 35.3%. Al(OH)₃ used as a ceramic binder is very suitable due to its outstanding connectivity and better uniformity.