Alumina Al2O3 Research Articles

Ferroelectric Aspect and Phase Transitions of Solid Solution of Cadmium Acetate with Aluminium (III) Oxide

The behavior of variation of dielectric constant with temperature of solid solution of Cadmium Acetate Cd(C2H3O2)2 with Aluminium (III) Oxide Al2O3 and other dielectric parameters have been measured between the temperatures 35°C to 100°C using the capacitance bridge model ZENITH-FM89A and Q meter at the frequency of 2000 Hz. In the measurement, it have been observed that the compound has lower value of dielectric constant (ε = 1580) below 36ºC, which rises upto a value of 5600 at the moderate temperature of 45ºC. After this temperature, the dielectric constant of compound decreases upto the value of nearly 3521 at the temperature of 75ºC and a high peak at the temperature of 76°C (ε = 7000) in the heating cycle curve with some fluctuations.. When the variation of dielectric constant was studied in cooling cycle the peak was observed at 62ºC(ε = 6500), above and below this temperature dielectric constant decreases with some intermediate fluctuations and by increasing aluminium oxide content in the mother compound, its quality factor also increases with a little effect on dielectric constant. The cooling cycle curve does not follow heating curve because of the relaxor behaviour of the compound. The results have been explained on the basis of crystal structure changes and the possibility of free internal rotation of acetate groups within the crystal lattice at elevated temperature. One of the advantages of Cd(C2H3O2)2 with Al2O3 is that by varying the Aluminium Oxide content, one can control temperature coefficient of resonant frequency τf without affecting the other properties. This is important for many ferroelectric applications because τf of near about low value is not always required. A non-zero τf is often preferable to compensate for frequency variation due to the effect of temperature change on the resonator housing and dielectric support structure. Solid solution of Cadmium Acetate with Aluminium Oxide suggests for its valuable applications as dielectric material with excellent properties useful in ceramics engineering and communication system. KEY WORDS: Polarization, Quality Factor, Dielectric Constant, Phase Transition, Curie temperature, Resonant Frequency and Ceramics Engineering.

Electrical treeing behavior in XLPE insulation due to content AL2O3 nanoparticles

XLPE is currently commonly used in high voltage underground cables. Several researchers recently chose several nanofillers to improve the electric tree’s strength in the polymer matrix. Alumina AL2O3 nanofiller have been utilized to investigate the effects on the electrical treeing in XLPE. The percentage concentration were used as follows with different amounts “0.3wt.” % and “1wt.”% from weight of base material. The needle-plane electrodes were used in this investigation and gap selected between needle and plane earth is 3 mm. The growth and morphology of treeing in XLPE insulation have been observed by using charge coupled device camera CCDc and microscope system. Scanning of electron microscopes SEM has been investigated the nanoparticles spread in base material. The outcomes show the tree inception voltage TIV values 12.5, and 14.8 KV “0.3wt.” % and “1wt.”%, respectively in XLPE composites that is mean the TIV increase with increase concentration nanofiller, while the tree propagation time at 2mm length increase about 40 min and 2 hours in “0.3wt.” % and “1wt.”% AL2O3/XLPE, respectively compared with unfilled XLPE, as well as the breakdown time BDT enhancement by4.347% and 13.043% for 0.3wt% and 1 wt% nano AL2O3 composites compared with unfilled XLPE insulation. And showed pictures taken with a SEM Diffusion and accumulation of nanoparticles in the XLPE material.

High Performance Hybrid Graphene Nano Filters as a Total dissolved solid remover

Graphene, a single-layer carbon sheet with its distinctive two-dimensional (2D) single-atomic-thick sp2 hybridized hexagonal packed lattice structure which is nearly friction less with high chemical inertness, and pliability which can be manufactured sustainably in great amounts with less expense, has shown many unique properties, Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (GO), offers a wide range of possibilities to produce nano-filters containing graphene membrane which is capable to remove ninety percent of the heavy contaminants from different sources of water and to reduce the level of total dissolved solids, salinity, and neutralizes the pH level further inorganic membrane used in synergism with graphene oxide shows improved efficiency and reduction in cost of production of separation membranes. In this review, we demonstrated real world application of graphene, Fabricated with Several Metal Oxides in synergism to illustrate enhanced photocatalysis properties, Flexural strength and anti-fouling characteristics of the material in comparisons to conventional membrane, photocatalytic metal oxides nanoparticles such as Titania TiO2, Zirconia ZrO2, Alumina Al2O3, and Silica SiO2 functions in the presence of Multiple Spectrums of Light by absorbing photons and releasing Oxygen Radical which degrades harmful water pollutants into less harmful substances.

Highly wear-resistant alumina/graphene layered and fiber-reinforced composites

The wear resistance and tribological characteristics of alumina/graphene layered and fiber-reinforced composites were investigated under dry sliding conditions at applied loads of 10 N and 50 N in the air. The experimental materials were prepared by a combination of electrospinning-calcination-chemical vapor deposition and spark plasma sintering. Graphene-coated Al2O3 microfibers were used to form layers in layered monolithic alumina/graphene-coated Al2O3 microfibers composite, and as reinforcements for the alumina matrix in the fiber-reinforced composite. The microstructure, deformation, and damage characteristics were studied. Both composites show a lower coefficient of friction in comparison to alumina with the lowest value of 0.42 for the fiber-reinforced composite measured at a load of 10 N. At the load of 10 N the composites exhibit very high wear resistance with values of wear rate 2.78 × 10−8mm3/(N·m) for the layered and 1.74 × 10−8mm3/(N·m) for the fiber-reinforced composite, in comparison to the wear rate of Al2O3 with a value of 5.35 × 10−6mm3/(N·m). The significant improvement in the wear resistance of the composites was associated with the improved mechanical properties and formation of a protective tribofilm on the wear tracks by the multilayered graphene present on the surface of Al2O3 microfibers and alumina debris, which provided the lubricating effect for the composites.

Mechanical modelling of microwave sintering and experimental validation on an alumina powder

Microwave sintering (MW) allows fast heating (≤30 min) and densification of ceramic materials, like alumina Al2O3. In order to predict the final material properties (density, size and grain size) the mechanical SOVS (Skorohold Olevsky Viscous Sintering) model is adapted and validated for conventional sintering of alumina. The model is implemented on ABAQUS with UMAT subroutine. Secondly, the SOVS model is modified for the microwave sintering by adapting the shear viscosity Arrhenius type law. Pre-exponential and exponential coefficients are modified for MW sintering. The calculated relative densities are compared to experimental results from conventional and microwave sintering and the relative difference remains under 3%. The coefficients identified for the MW sintering reveal a decrease in the shear viscosity by around 10 and an increase by up to 50 times in the grain boundaries diffusion coefficient.

Development and Mechanical Characterisation of Al6061-Al2O3-Graphene Hybrid Metal Matrix Composites

MMC based on aluminium (Al) were produced for light-weight applications especially in aviation and automobile areas. Present paper deals with the fabrication and mechanical performance of AA6061 matrix composites fortified with Al2O3 (alumina) and graphene particulates. Fluid metallurgy method namely stir casting route was employed for fabricating the hybrid composites. Al2O3p and graphene powder are mixed in different weight fractions in which graphene (1 wt. %) particle reinforcement is held consistent and Al2O3 reinforcement is differed freely with 5, 10 and 15 wt. %. Using optical analyser and SEM equipment, microstructural examination is carried out and the result reveals that the graphene and Al2O3 particles prevalently are homogeneously appropriated on the grain limits of Al matrix and Al2O3 particles are disseminated between graphene in the as-cast AA6061 MMC’s. Detailed analysis on investigation of the microstructure and mechanical aspects of Al6061-graphene-Al2O3p composites is presented by following ASTM guidelines; results uncovered that with increment in reinforcement particles, there is an enhancement in the hardness, ultimate strength, yield strength and a decline in the elongation values was however noticed when contrasted with Al6061 alloy. Fractography investigation revealed dimples in unreinforced alloy and the composite.

A Study of the Thermo-Mechanical Behavior of a Gas Turbine Blade in Composite Materials Reinforced with Mast

The turbine blades are subjected to high operating temperatures and high centrifugal tensile stress due to rotational speeds. The maximum temperature at the inlet of the turbine is currently limited by the resistance of the materials used for the blades. The present paper is focused on the thermo-mechanical behavior of the blade in composite materials with reinforced mast under two different types of loading. The material studied in this work is a composite material, the selected matrix is a technical ceramic which is alumina (aluminum oxide Al2O3) and the reinforcement is carried out by short fibers of high modulus carbon to optimize a percentage of 40% carbon and 60% of ceramics. The simulation was performed numerically by Ansys (Workbench 16.0) software. The comparative analysis was conducted to determine displacements, strains and Von Mises stress of composite material and then compared to other materials such as Titanium Alloy, Stainless Steel Alloy, and Aluminum 2024 Alloy. The results were compared in order to select the material with the best performance in terms of rigidity under thermo-mechanical stresses. While comparing these materials, it is found that composite material is better suited for high temperature applications. On evaluating the graphs drawn for, strains and displacements, the blade in composite materials reinforced with mast is considered as optimum.

On the variety and formation sequence of second-phase particles in nickel-based superalloys fabricated by laser powder bed fusion

We examine by transmission electron microscopy the precipitation state in the as-built microstructure of a hot-cracking sensitive nickel-based superalloy fabricated by laser powder bed fusion. Most observations are carried out on carbon extraction replica to isolate the precipitate signals from those of the matrix. Chemical maps measured by energy dispersive X-ray spectrometry are compared to phase and orientation maps obtained on the same precipitates by automated crystal orientation mapping. The chemical analyses are completed by electron energy-loss spectrometry measurements made on thin foils. The large fields of view investigated allow for achieving a representative picture of the second-phase particles in the as-built microstructure. A large variety of nano-particles is found: (Ti,Nb)(C,N) carbonitrides, (δ) Al2O3 alumina, (Cr,Mo)3B2 and (Cr,Mo)5B3 borides, and the intermetallic phase Ni7Zr2. The precipitates themselves are also complex in terms of their inner structure: carbonitrides can present a core-shell structure of composition and are frequently twinned, alumina particles serve as nucleation sites for carbonitride aggregates, and several crystallographic forms of borides may coexist next to each other. These observations provide the necessary information to retrace the solidification path of the microstructure during fabrication and to discuss the precipitation mechanisms under the extreme processing conditions associated with laser powder bed fusion.

ДОСЛІДЖЕННЯ НАНОКРИСТАЛІТІВ, ОТРИМАНИХ НА ОСНОВІ НАНОПОРИСТИХ МЕМБРАН AL2O3 ІЗ НАСИЧЕНИХ ВОДНИХ РОЗЧИНІВ KH2PO4

Розглядається питання отримання та використання нанокомпозитних матеріалів для радіомереж оптичної та терагерцової смуг частот. Приготовлені нанопористі структури анодованого оксиду алюмінію Аl2О3 (АОА) діаметром пор 40 та 75 нм. Отримано та проведено дослідження кристалічного матеріалу KH2PO4 (KDP) у вигляді нанопроводів та нанотрубок при різних варіантах росту на основі мембрани Al2O3 і насиченого водного розчину KDP.

The Heat Transfer Performance of MWCNT, CuO, and Al2O3 Nanofluids in an Automotive Engine Radiator

The effect of enhancing heat transfer using three nanofluids, Multi-Walled Carbon Nanotubes MWCNT, Copper oxide CuO, and aluminum oxide Al2O3, have been experimentally studied on the automotive radiator with a concentration of 1% vol and different flow rates (4-8) l/min, air velocity of 3 m/s and inlet temperatures range (60-80) °C. The results showed that the use of nanofluids improved the thermal performance compared to the base fluid. Using the (MWCNT-Water) achieved 41.7% of Nusselt number where as, copper oxide (CuO) and aluminum oxide (Al2O3) have improved the Nussult number by 31.7 % and 12.3 % respectively. The Nusselt number showed an increase with the increase in the flow rate and the inlet temperature.

Potential Use of Green Synthesized Al2O3 (Alumina) Nanoparticles from Guava Leaves (Psidium guajava) for the Removal of Methylene Blue from Wastewater

Recently non-harmful nanomaterials have acquired critical significant attention in wastewater treatment containing organic pollutants especially toxic and hazardous dyes. In this regard, a low cost and eco friendly method has been investigated for the green synthesis of alumina nanoparticles (Al2O3 NPs). The alumina nanoparticles were synthesized using an aqueous extract of Psidium guajava leaf as a potential stabilizing agent. The UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques were used to characterize the synthesized nanoparticles. The absorption at 281 nm confirmed the formation of alumina nanoparticles. The FTIR spectra and XRD analysis confirmed the presence of various functional groups and crystalline structures of Al2O3 NPs during the synthesis. The spectrum clearly indicates the organic moieties in Psidium guajava extract are responsible for the biosynthesis of Al2O3 NPs. The suface morphology of Al2O3 NPs was confirmed by SEM and EDS studies. Besides this, the removal of methylene blue through adsorption and kinetic study was also reported.

Исследование фотокаталитической антимикробной активности нанокомпозитов на основе TiO-=SUB=-2-=/SUB=--Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- при воздействии светодиодного излучения (405 nm) на стафилококки

The photocatalytic activity of nanocomposites based on theta-modification of aluminum oxide Al2O3 with different TiO2 content for heterogeneous photocatalysis and biodegradation of pathogenic microorganisms under the action of LED radiation with a wavelength of 405 nm has been studied. It was found that all the investigated nanocomposites have photocatalytic activity. The maximum antibacterial efficiency of composites with a TiO2 content of 8 wt% (reduction of CFU of Staphylococcus aureus 209 P to 86%), which allows us to recommend this nanomaterial as a promising antimicrobial coating.

In English

The paper presents research materials on some hydrogen-containing volcanic glasses of Transcaucasia of acidic composition, concentrated in areas of late Tertiary-Quaternary volcanism, in particular, the central part of the Akhalkalaki plateau, within the Akhaltsikhe valley (Georgia). Studies of natural materials of perlite, obsidian and pechstein were carried out by geological, physico-chemical: petrography, chemical analysis, X-ray diffractometry, and IR spectroscopic methods. The work shows the genesis, structural features and prospects of using these minerals. It has been found that the chemical composition of the minerals studied is characterized by a different content of aluminum oxide Al2O3. It is shown that silicon oxide SiO2, which is a part of volcanic glasses, occurs in an amorphous state. Perlites of the studied deposits differ from each other both visually and in composition. The perlites of the Toloshi deposit are dark gray in color and the Paravani deposits are white. In the perlite spectra of the Tolosh deposit, the vibrational frequencies of both the intratetrahedral and in the intertetrahedral space of Si-O-Si (Al) indicate that silicon is replaced by aluminum to a lesser extent than in the perlite of the Paravan deposit. The prospects of using expanded volcanic glasses are also shown.

Thermal performance of U‐shaped serpentine microchannel heat sink using various metal oxide nanofluids

AbstractThis study aims to evaluate the thermal performance and friction factor characteristics of the U‐shaped serpentine microchannel heat sink using three different nanofluids. Two distinct nanoparticles, namely Al2O3 (alumina) and CuO (copper oxide), were used for the preparation of nanofluids using water and ethylene glycol (EG) as base fluids. Three nanofluids, namely nanofluid I (Al2O3 + water), nanofluid II (CuO + water), and nanofluid III (CuO + EG), have been prepared. The results showed that the thermal conductivity of nanofluids was increased for all concentrations (from 0.01 to 0.3%), compared with base fluids. The theoretical values derived from the relationship between the Darcy friction factor showed a clear understanding of the fully developed laminar flow. Thermal resistance for nanofluid III was lower than other nanofluids, resulting in a higher cooling efficiency. The nanofluid mechanism and the geometry of the U‐shaped serpentine heat sink have led to the improvement in the thermal performance of electronic cooling systems.

Phenomenological approaches for quantitative temperature-programmed reduction (TPR) and desorption (TPD) analysis

Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) are techniques widely used for catalyst characterization, providing information about active sites. However, results from these experiments are usually interpreted with the aid of empirical models, based on the representation of reduction or desorption profiles as summations of empirical reference curves. In this context, phenomenological approaches can present several advantages over this traditional empirical approach, as in this case the extracted information can be based on theoretical models that allows for a deeper understanding of the catalyst properties. For this reason, in the present work, empirical and phenomenological modelling approaches are evaluated for the quantitative analysis of H2-TPR and NH3-TPD profiles, obtained from the characterization of Ni/SiO2 and Al2O3 alumina catalysts, respectively, and results from both approaches are thoroughly compared and discussed for the first time. Our results, obtained from the fitting of both modelling approaches to the whole experimental profile by using nonlinear regression, indicate that the phenomenological modelling approach can be considered better and should therefore be preferred, as it allows for significantly more accurate quantification and correct discrimination of distinct active sites, in addition to simultaneously enabling the determination of reduction or desorption kinetics parameters.

Structural State of High-Entropy Fe40–xNiCoCrAlx Alloys in High-Temperature Oxidation

The evolution of phase composition and mechanical properties and the formation of oxide layers on Fe40–xNiCoCrAlx (x = 5 and 10 at.%) alloys in long-term oxidation at 900 and 1000°C were studied. In the initial cast state, depending on the aluminum content and valence electron concentration, the alloys contain only an fcc solid solution (VEC = 8 e/a) or a mixture of fcc and bcc phases (VEC = = 7.75 e/a). Thin continuous oxide scales containing Cr2O3 and NiCr2O4 spinel formed on the surface of both alloys oxidized at 900°C for 50 h. A further increase in the annealing time to 100 h leads to the formation of aluminum oxide Al2O3 in the scale on the Fe30Ni25Co15Cr20Al10 alloy, having high protective properties. An increase in the oxidation temperature to 1000°C results in partial failure of the protective layer on the alloy with 10 at.% Al. Long-term holding at 900°C (100 h) + 1000°C (50 h) does not change the phase composition of the Fe35Ni25Co15Cr20Al5 alloy matrix, being indicative of its high thermal stability. In the two-phase Fe30Ni25Co15Cr20Al10 alloy, the quantitative ratio of solid solutions sharply changes: the amount of the bcc phase increases from 4 to 54 wt.% and its B2-type ordering is observed. The mechanical characteristics of the starting alloys and those after long-term high-temperature annealing were determined by automated indentation. The hardness (HIT) and elastic modulus (E) of the cast Fe35Ni25Co15Cr20Al5 alloy are equal to 2 and 147 GPa, respectively, and decrease to 1.8 and 106 GPa after a series of long-term annealing operations. The Fe30Ni25Co15Cr20Al10 alloy shows the opposite dependence: HIT increases from 2.5 in the initial state to 3.1 GPa after annealing and E decreases from 152 to 134 GPa. This indicates that the Fe30Ni25Co15Cr20Al10 alloy is promising as a high-temperature oxidation-resistant and creep-resistant material.

Thermal-hydraulic analysis of Al2O3 nanofluid as a coolant in Canadian supercritical water reactor by porous media approach

In this study, thermal-hydraulic analysis of Canadian Supercritical Water Reactor (Canadian SCWR) with nanofluid coolant has been done by porous media approach. In the applied analysis the derived conservation equations of mass, momentum and energy for coolant and conduction heat transfer equation for fuel and clad were discretised by finite volume method and solved numerically using C# program. Nanofluid coolant with various concentration of Al2O3 (Alumina) nanoparticle (up to 40% mass fraction) was selected for this study. Since in Canadian SCWR coolant and moderator are separated, higher mass fraction of nanofluid can be applied in this concept. The achieved results show that by increasing Al2O3 mass fraction, coolant heat transfer coefficient and average coolant temperature grow up in the middle of the core and pressure drop will be raised. Average clad and fuel temperature in the core was calculated. The results show that by using Alumina nanofluid with 40% nanoparticle mass fraction, maximum clad wall and fuel temperatures decrease about 20 °C and 30 °C respectively.

Impact Study of Electron-Beam Heating on the Structure and Properties of Boroaluminized Layers Aimed at Producing New Composite Coatings with Special Properties

Abstract Electron-beam processing is a promising method of surface processing. Electron-beam processing can involve surface melting accompanied by adding alloying elements into the melt (electron-beam alloying), or it can be applied to preliminary obtained diffusion layers on a material’s surface (electron-beam chemical thermal processing). Electron-beam heating both increases the temperature and initiates diffusion processes in the metal. By regulating parameters of electron-beam processing, different types of layers—diffusion, diffusion-crystalized, or liquid phase—are formed. The paper presents the study of the impact of electron-beam heating on the structure and properties of boroaluminized layers in carbon steel 60 (0.6 % carbon), obtained by thermochemical processing (solid-phase boroaluminizing in powder mixture 98 % (70 % aluminum oxide Al2O3) + 10 % boron oxide (B2O3) + 20 % aluminum (Al) + 2 % sodium fluoride (NaF) at T = 950°C, τ = 4 h). The authors studied the influence of electron-heat processing modes on the formation of boroaluminized layers’ structure. The parameters of electron-beam heating were beam current Ic = 20–60 mA and time of impact τ = 15–120 s. The authors conducted metallographic and X-ray microscopic analysis and measured microhardness of boroaluminized layers obtained with a combined method (thermochemical processing and electron-beam heating). It was shown that electron-beam heating of boroaluminized layers leads to changes in the structure and properties as well as in the layer’s morphology. Aluminum is spread evenly in the depth of the layer. The layer’s microhardness changes and the brittleness decreases. The obtained results led to the conclusion that electron-beam heating can be recommended to improve properties of boroaluminized layers and used as a foundation for producing new composite coatings with special properties.

Comparison of Capillary Flow Porometry (CFP) and Liquid Extrusion Porometry (LEP) Techniques for the Characterization of Porous and Face Mask Membranes

This work aims to study the characterization of several membrane filters by using capillary flow porometry (CFP) and liquid extrusion porometry (LEP) to obtain their pore size distributions (PSD) and mean pore diameters (davg). Three polymeric membranes of different materials namely, polyethylene (PET), cellulose nitrate (CN), and FM (face mask), and one inorganic (namely, alumina Al2O3) from ultrafiltration (UF)/microfiltration (MF) and particle separation were analyzed using a pressure constant fluid/liquid extrusion porometer, developed at institute de la filtration et techniques séparatives (IFTS). Several porosimetric fluids have been used to wet and penetrate into the porous/fiber structure. The results show the accuracy of the setup on characterizing membranes in the UF/MF range by CFP, with reasonable agreement with nominal data of the filters. Additionally, LEP extension of the equipment obtained good agreement with nominal data and the CFP results, while filters presenting a microstructure of highly interconnected pores (face mask) resulted in clear differences in terms of resulting PSD and average sizes when CFP and LEP results are compared.

Interaction of components features of the reaction mixture ZO2(m)-Al-C systems when heated

By the complex analysis basis of the interaction theory of the reaction mixture components ZrO2(m)-Al-C when heated to temperatures of 1650-1775°C and experimental data (DTA, x-ray d iffraction analysis), the nature of the formation of final synthesis products is studied. The probability of multistage interaction of components in the heating process with the formation of aluminum oxide Al2O3 and zircon iu m carbide ZrC as final components, which is accompanied by an intermediate stage of formation of i nter m etallid e based on Al and Zr, is noted. The results obtained indicate that it is advisable to further study the laws of phase and structure formation of materials in the considered system in order to obtain high-density functional ceramics of the oxide-carbide type.