Nano α-Al2O3 Research Articles

Isothermal Decay Analysis of Thermoluminescence Peaks of Nano-α-Alumina

This study investigates the thermoluminescence (TL) behavior of nano α-Al2O3 (40 nm) within the temperature range of 110 to 160°C to elucidate the kinetic mechanisms governing its TL response. The isothermal decay curves were analyzed to determine the order of kinetics and activation energies of the TL peaks. The ln(I) vs. time plot revealed a nonlinearity starting at 140°C, indicating that the TL peaks do not follow first-order kinetics in this temperature region. Subsequent analysis confirmed that the TL data align with second-order kinetics, with a kinetic-order parameter of b = 2.0 providing the best linear fit. Further examination of the ln(slope) vs. 1/kT relationship revealed a composite structure in the TL response, characterized by three distinct linear sections. These sections correspond to activation energies of 0.6±0.12 eV, 1.07±0.25 eV, and 1.61±0.47 eV, respectively, suggesting the presence of three different centers contributing to the dosimetric peak. The findings underscore the complex nature of the TL response in nano α-Al2O3, highlighting the necessity of considering multiple kinetic components in the analysis of its TL properties. This study enhances our understanding of the thermoluminescent behavior of nano α-Al2O3 and provides a basis for further research into its applications in dosimetry

TEMPERATURE EFFECT ON THERMOLUMINESCENCE KINETIC PARAMETERS OF NANO-ALUMINA

This research explores the fundamental thermoluminescence characteristics of irradiated nano-α-alumina particles, investigating their response to varying heating rates. The study involves recording TL luminescence curves, revealing a distinct peak with a maximum at approximately 202°C. As dose levels increase, the peak consistently shifts towards lower temperatures, indicating adherence to non-first-order kinetics (b≠1). The crystallite size was calculated using XRD analysis and estimated as 40nm. To examine the impact of the heating rate on the TL glow curve and derive kinetic parameters for nano α-Al2O3, specimens were exposed to a 6 kGy dose. Subsequently, TL glow curves were documented over a temperature range from room temperature to 300°C, employing different heating rates (2, 4, 6, 8 and 12°C/s). The peak temperature of the glow peak shifts towards higher temperatures as the heating rate increases and the peak intensity continuously diminishes, aligning with TL theory. The observed decrease in TL glow peak intensity with escalating heating rates is attributed to thermal quenching, where quenching efficiency rises at higher temperatures. Normalizing maximum TL intensities to the lowest heating rate (2°C/s) reveals a substantial 22% decrease in peak intensity.

Exploring the thermoluminescent characteristics of nano α-Al2O3: Influence of heating rate on glow peaks and activation energy

Exploring the thermoluminescent characteristics of nano α-Al2O3: Influence of heating rate on glow peaks and activation energy

Low temperature phase transition mechanism of amorphous Al-oxalate to nano α-alumina

α-Alumina (α-Al2O3), widely used as a raw material or production in advanced manufacturing industry, has attracted much attention in terms of its preparation temperature. A simple dissolution-evaporation-precipitation process was employed to obtain the amorphous Al-oxalate (AAO) precursor, serving as the starting material for the low temperature preparation of nano α-Al2O3. The crystalline structure and thermal behavior of the AAO were compared with commercially available aluminum hydroxide (Al(OH)3) powder using the X-ray powder diffraction (XRD) instrument, the thermal gravity analysis and differential scanning calorimetry (TG-DSC). The phase transition mechanism of AAO was investigated by the fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), and 27Al magic angle spinning nuclear magnetic resonance (27Al-MAS-NMR). The DSC results indicated that AAO underwent a phase transformation at 982 °C. The α-alumina diffraction peaks appeared in AAO at 1000 °C, while α-Al2O3 phase was observed for Al(OH)3 at 1200 °C. Furthermore, an absorption peak at 452 cm−1, corresponding to Al–O bond in α-alumina was detected at 1000 °C. The proposed low-temperature preparation mechanism of α-alumina from AAO is as follows: four coordination Al-oxalate species entities coexist within the AAO sample; with increasing temperature, organic acid functional groups oxidize and volatilize, resulting in the formation of tetra-coordinate [AlO4], penta-coordinate [AlO5], and hexa-coordinate [AlO6] atomic groups; these atomic clusters further polymerize to form a structurally dense α-alumina crystal at the nano-scale (∼50 nm) at around 1000 °C. The experimental findings present a novel approach and method for the low-temperature preparation of nano-sized alumina powder. Additionally, a feasible theoretical reference for the low-temperature phase transition mechanism of amorphous Al-oxalate was provided.

Coordinated regulation for α-Al2O3 and mullite structures in the alumina-mullite fiber based on the different adding form of Fe element

The coordinated regulation for α-Al2O3 and mullite structures in the alumina-mullite duplex fiber poses a challenging yet crucial task in achieving a fiber with exceptional high-temperature properties. In this study, Fe element was added into the alumina-mullite fibers in the form of iron sol and ferric nitrate solution, respectively, with the aim of obtaining a fiber consisting of fine mullite grains embedded with nano α-Al2O3 grains. The results revealed that the addition of Fe element significantly enhances the crystallization process of mullite in alumina-mullite fibers. Specifically, adding iron sol resulted in the reduce of α-Al2O3 formation temperature to 1300 °C, while introducing Ferric nitrate solution promoted the formation of mullite phase. Simultaneous introduction of 1.3 wt% iron sol and 1.3 wt% Ferric nitrate solution contributed to achieve alumina-mullite fiber with tensile strength of 2.06 GPa. In addition, the influence mechanism of Fe source on the phase transformation and microstructures of alumina-mullite fiber were discussed.

Low-temperature preparation of spherical nano α-Al2O3 particles by chelating the structure of anhydrous aluminium sols

α-Al2O3 exhibits excellent physical and chemical stabilities and thus has a wide range of applications in various fields, however the potential application are often called off because of the grains coarsening and vermiculite structures originated from the high-temperature calcination process. In this paper, the calcination temperature has been significantly reduced by selecting the chelating anhydrous aluminium sols as the precursor. It was found that when the chelating agent was malic acid and the addition amount was 0.06 mol, the chelated structure had the highest content of [AlO6] octahedra, which was more favourable for the low-temperature synthesis of α-Al2O3. Kinetic analysis showed that the activation energy for the conversion of γ-Al2O3 to α-Al2O3 in this work was 398.09 kJ mol−1, which has been reduced by nearly 100 kJ mol−1 and thus the complete conversion of γ-Al2O3 to α-Al2O3 was achieved by holding at 900 °C for 2 h. The obtained spherical α-Al2O3 nanoparticles, with a particle size of about 67.2 nm and a uniform morphology. After further extending the holding time to 30 h, the complete conversion of α-Al2O3 was achieved at 825 °C, while the initial nucleation temperature was lower than 760 °C.

Crystal structure, Hirshfeld surface analysis and DFT investigation of new aluminium(III) derivative: A prominent precursor of nano alumina for dye degradation and sensor material

A new homoleptic derivative of aluminium(III) was synthesized quantitatively as white solid by refluxing Al(OPri)3 and C6H5COCH2COC6H5 in 1:3 stoichiometry using anhydrous benzene as a solvent for 8 h and was characterized subsequently by relevant spectral tools. The single crystal X-ray diffraction analysis of the complex reveled that new aluminium derivative is triclinic with space group P1¯ and appearing in hexacoordination around aluminium atom. Crystallinity and purity were verified by powder XRD techniques. Further, the complex [(PhCOCHCOPh)3Al] was analyzed theoretically using Gaussian software at DFT/B3LYP/LanL2DZ and the results were found in accordance with the experimental data. Findings of intermolecular interactions of [(PhCOCHCOPh)3Al] were supported by Hirshfeld surface analysis as it illustrated that packing of the crystal was prominently due to the existence of 51.4% H---H, 21.3% C---H and 16.8% H---C interaction. In addition, nano alumina was also synthesized using this new derivative [(PhCOCHCOPh)3Al] as a precursor via well-established sol–gel technique. The obtained nano alumina was assigned as α- phase by powder XRD and its composition and morphology were characterized using FE-SEM and EDX analyses. Subsequently, nano α-alumina was employed as photocatalyst for congo red (CR) dye and was subjected for electrochemical sensing measurements using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (ESI). The outcomes displayed that the CR dye underwent a remarkable (95%) amount of photodegradation within 10 min on exposure to sunlight. Electrochemical performance of nano α-Al2O3 modified glassy carbon electrode (GCE) demonstrated the oxidation peak at Epa = + 0.2 V in buffer solution with paracetamol and exhibited best sensing performance for the detection of paracetamol. Thus, it might appear as a possible sensor electrode material in the forthcoming investigations.

Influence of NH4BF4 on the alumina phase transition and morphology

The spherical alumina powders including regular morphology, uniform particle size, smooth surface, and reduced particle wear generally give the finished products with the excellent performances. This research presents a novel method to produce the spherical alumina by employing gibbsite precipitated by the Bayer process as raw material mixed with NH4BF4 at 1000 °C, nano α-Al2O3 was characterized by the well-crystallized and monodispersed spherical alumina single crystal particles. The results provide a novel economical method to prepare the spherical alumina from gibbsite.

Mechanical and Thermal Properties of Aluminum Matrix Composites Reinforced by In Situ Al2O3 Nanoparticles Fabricated via Direct Chemical Reaction in Molten Salts

The development of novel methods for industrial production of metal-matrix composites with improved properties is extremely important. An aluminum matrix reinforced by “in situ” α-Al2O3 nanoparticles was fabricated via direct chemical reaction between molten aluminum and rutile TiO2 nanopowder under the layer of molten salts at 700–800 °C in air atmosphere. Morphology, size, and distribution of the in situ particles, as well as the microstructure and mechanical properties of the composites were investigated by XRD, SEM, Raman spectra, and hardness and tensile tests. Synthesized aluminum–alumina composites with Al2O3 concentration up to 19 wt.% had a characteristic metallic luster, their surfaces were smooth without any cracks and porosity. The obtained results indicate that the “in situ” particles were mainly cube-shaped on the nanometer scale and uniform matrix distribution. The concentration of Al2O3 nanoparticles depended on the exposure time and initial precursor concentration, rather than on the synthesis temperature. The influence of the structure of the studied materials on their ultimate strength, yield strength, and plasticity under static loads was established. It is shown that under static uniaxial tension, the cast aluminum composites containing aluminum oxide nanoparticles demonstrated significantly increased tensile strength, yield strength, and ductility. The microhardness and tensile strength of the composite material were by 20–30% higher than those of the metallic aluminum. The related elongation increased three times after the addition of nano-α Al2O3 into the aluminum matrix. Composite materials of the Al-Al2O3 system could be easily rolled into thin and ductile foils and wires. They could be re-melted for the repeated application.

Photonic Sintering of Oxide Ceramic Films: Effect of Colored FexOy Nanoparticle Pigments

Alumina and zirconia thin films modified with colored nano-FexOy pigments were sintered by the flash-lamp-annealing method. We selected a nano α-Al2O3 and micron α-Al2O3 bimodal mixture as the base precursor material, and we doped it with 5 vol% of FexOy red/brown/black/yellow pigments. The coatings were deposited from nanoparticle dispersions both on glass and on flexible metal foil. The characteristics of the thin films obtained with the use of various additives were compared, including the surface morphologies, optical properties, crystallinities, and structures. Flash lamp annealing was applied with the maximum total energy density of 130 J/cm2 and an overall annealing time of 7 s. Based on the simulated temperature profiles and electron-microscopy results, a maximum annealing temperature of 1850 °C was reached for the red Al2O3: Fe2O3 ceramic film. The results show that red α-Fe2O3 pigments allow for the achievement of maximum layer absorption, which is effective for flash lamp sintering. It was also possible to use the selected red α-Fe2O3 particles for the flash-lamp-assisted sintering of ZrO2 on a 30 µm-thin flexible stainless-steel substrate.

Influence of nano α-Al2O3 as sintering aid on the microstructure of spray dried and sintered α-Al2O3 ceramics

Alpha Alumina (α-Al2O3) has traditionally been sintered to near theoretical density by employing variations in raw material properties, particle sizes, grinding methods, compaction pressures, sintering aids or minor quantities of additives and sintering temperatures. All these parameters directly influence the grain growth morphology and microstructure of the sintered alumina ceramic characteristics. Growth of large grained microstructure facilitated by fine grinding of raw material and coalescence of the grains enhanced by dopant additions are well researched. The maximum sintered density and strength of the fired body could be attained through large grained microstructure which include near spheroidal grains. Most of the final sintering is accomplished via additions of suitable aids which also may be promoted by liquid-phase sintering which is considered highly advantageous compared to solid-state sintering for products in many defense applications. In this paper the influence of nano α-Al2O3 (<100 nm particle size) as sintering aid to obtain the desired microstructure in sintered micron sized (1 to 5 µm) α-Al2O3 is being reported. 1.0 and 1.5 wt% nano α- Al2O3 powder were spray dried with 99.0 and 98.5% α-Al2O3 powder respectively, with polyvinyl alcohol binder, compacted into 10 mm dia and 5 mm thick pellets and sintered at 1450 °C with 3 h soak time. In addition to the two different sintering aid additive percentages, other variables included are spray dried powders removed from (i) chamber and (ii) cyclone. The sintered ceramics were characterized for bulk density and fracture surface microstructure via SEM analysis. Nano alumina as sintering aid exhibited significant influence that included generation of microstructure with porosity, precipitation or liquid phase sintering. The study was limited to establishing the definitive role played by nano alumina to influence the sintering of micron alumina.

Adsorptive Removal of Rhodamine B Using Novel Adsorbent-Based Surfactant-Modified Alpha Alumina Nanoparticles.

The objective of the present study is to investigate removal of cationic dye, rhodamine B (RhB), in water environment using a high-performance absorbent based on metal oxide nanomaterials toward green chemistry. The adsorption of sodium dodecyl sulfate (SDS) onto synthesized alpha alumina (α-Al2O3) material (M0) at different ionic strengths under low pH was studied to fabricate a new adsorbent as SDS-modified α-Al2O3 material (M1). The RhB removal using M1 was much higher than M0 under the same experimental conditions. The optimal conditions for RhB removal using M1 were found to be contact time 30 min, pH 4, and adsorbent dosage 5 mg/mL. The maximum RhB removal using M1 achieved 100%, and adsorption amount reached 52.0 mg/g. Adsorption isotherms of RhB onto M1 were well fitted by the two-step adsorption model. The electrostatic attraction between positive RhB molecules and negatively charged M1 surface controlled the adsorption that was evaluated by the surface charge change with zeta potential and adsorption isotherms. Very high RhB removal of greater than 98% after four regenerations of M1 and the maximum removal for all actual textile wastewater samples demonstrate that SDS-modified nano α-Al2O3 is a high-performance and reusable material for RhB removal from wastewater.

Preparation of Continuous Alumina Fiber with Nano Grains by the Addition of Iron Sol.

Continuous alumina fiber exhibits excellent mechanical properties owing to its dense microstructure with fine grains. In this study, alumina fiber was prepared by the sol–gel method using iron sol as a nucleating agent. It was proposed that the α-Al2O3 grain size be adjusted based on the modification of colloidal particle size. The effect of holding temperature and reaction material ratio on the iron colloidal particle size was studied. The microstructure of alumina fiber was characterized by scanning electron microscopy (SEM). The experiment results indicated that iron colloidal particle size increases with the holding temperature and the NH4HCO3/Fe(NO3)3·9H2O ratio. The alumina fiber with uniform nano α-Al2O3 grains was obtained by calcination at 1400 °C for 5 min. The mean grain size tends to rise with the mean colloidal particle size. Using the iron sol as a nucleating agent, the fiber with a mean grain size of 22.5 nm could be formed. The tensile strength of fibers increased with the decrease of grain size.

Effect of in-situ formation of columnar mullite and pore structure refinement on high temperature properties of corundum casatbles

The effects of in-situ synthesis columnar mullite and pore structure on the hot modulus of rupture (HMOR), thermal shock resistance and corrosion resistance of corundum castables have been investigated in this paper. When 2% nano silica was added, the pore diameters of castables could be decreased to 15 nm (at 110 °C), 1 μm (1100 °C) and 6 μm (1500 °C), respectively. The corresponding reducing magnitude of pore size is 98.5%, 83.3% and 33.3%. The HMOR of castables fired at 1500 °C increased by 110% to 3.64 MPa. Furthermore, after three thermal shock cycles, the residual strength ratio of castables increased from 5.2% to 15.3%. A large amount of cross-distributed columnar mullite was formed between nano silica and α-Al2O3 by the two-dimensional nucleation mechanism, which remarkably enhanced the high temperature properties. The penetration index reduced from 30.86% to 19.88%, suggesting that smaller pore size and higher viscosity had a great influence to the penetration process.

Alumina Recovery from Industrial Waste: Study on the Thermal, Tensile and Wear Properties of Polypropylene/Alumina Nanocomposites

The investigation on the influences of alumina (Al2O3) particles in nano-sized retrieved from Aluminium (Al) dross was conducted on the tensile, thermal and wear properties of polypropylene (PP) composites. The thermal decomposition method was used to synthesise the micro α-Al2O3 particles from Al-dross, was followed by the wet-milling method to produce the nano α-Al2O3. The PP composites (nano and micro α-Al2O3 particles) were prepared via melt compounding followed by compression molding. The coupling agent was also added to facilitate the particle dispersion. The tensile tests showed the maximum tensile strength and Young’s modulus of both composites to be corresponding to the samples containing 5 wt% of α-Al2O3. The superiority of nano α-Al2O3 on improving the property of PP had also been evident in the abrasive wear performance. A small amount of α-Al2O3 had been adequate in enhancing the thermal stability of PP than that of neat PP. The study on tensile and worn surface with SEM had revealed better adhesion and interaction between the filler and matrix in composites that were treated with coupling agent. The recovery of nano α-Al2O3 particles from Al-dross potentially decreases the quantity of harmful solid waste and can be an effective alternative filler for thermoplastics.

Very sensitive α-Al2O3:C polycrystals for thermoluminescent dosimetry

New materials have been widely investigated for ionizing radiation dosimetry for medical procedures. Carbon-doped alumina (α-Al2O3:C) have been reported to be excellent thermoluminescent (TL) and optically stimulated luminescence (OSL) radiation dosimeters. In the present study, we have synthetized nano and micro-sized α-Al2O3:C polycrystals, doped with different percentages of carbon atoms aiming to compare their efficiency as TL dosimeters. The dosimetric characteristics for X ray and gamma fields were investigated. Samples doped with different amounts of carbon atoms were sintered under different atmosphere conditions, at temperatures ranging from 1300 °C to 1750 °C. Among the investigated samples, the micro-sized alumina doped with 0.01% of carbon and sintered at 1700 °C under reducing atmosphere, has presented a very high TL output. The main TL peak is centered at 250 °C and has a linear behavior with photon dose in the dose range of 0.02-to-5000 mGy, with correlation coefficient very close to one (0.99991). Samples produced by using nanosized alumina have shown much lower TL output when compared to the samples with microsized alumina. The micro-sized alumina obtained by the methodology used in this work is a suitable candidate to be explored for application in X and Gamma radiation dosimetry.

Simulation study on the melting process of nano-corundum

When the shape of α-Al2O3 product is very complicated, 3D printing technology based on laser or ion beam energy would be the best choice. But it is very difficult at present because of the high melting point and low thermal conductivity of α-Al2O3. So studying the melting process of nano α-Al2O3 with the different particle size can help to provide a guidance for 3D printing of α-Al2O3. In this paper, the melting point and melting process of nanosized α-Al2O3 with the radius of 1–2.2nm were studied by molecular dynamics simulation. Results showed that: The melting points of nano-particles increased along with the radii increased. The melting point of 1.8nm particle was 2200K. Its melting process could be divided into four stages: the thermal expansion stage 300–700K, the surface activation stage 700–1600K, the pre-melting stage 1600–2200K, and the melting stage 2200K. Dominantly due to the migration of O atoms during the melting process, the bond broke at the sites 2.55Å (1nm = 10Å), etc. away from the central atom. The heating rate had a great influence on the melting process of α-Al2O3 nanoparticles. The higher the heating rate, the higher the melting point. The nanoparticle could be superheated and the superheating phenomenon had the dynamic stability limit temperature.

Effect of MgO doping on properties of low zirconium content Ce-TZP/Al2O3 as a joint replacement material

MgO/Ce-TZP/Al2O3 ( Ce-TZP, CeO2 stabilized tetragonal ZrO2，its contents were 5, 10, 15, 20, 25vol%, respectively) nanocomposite powders were prepared by heat-treating the mixture of MgO/Ce-TZP gel and nano α-Al2O3 at 700°C Then the MgO/Ce-TZP/Al2O3 nanocomposites were compacted to bulk pellets and sintered at 1600°Cfor 2h in air. The phase composition, strength, hardness, relative density and microstructure of the nanocomposites were characterized by powder X-ray diffraction (XRD), three-point bending strength testing, Vicker's tester, Archimedes method and scanning electron microscopy, respectively. Stability versus aging of this material was evaluated by low temperature degradation. The results demonstrated that the flexural strength, fracture toughness and hardness of the MgO/10Ce-TZP/Al2O3 nanocomposite ceramic reached up to 703MPa, 12.1MPam1/2 and 17.5GPa, respectively, as the content of 10Ce-TZP and MgO were 20vol% and 0.2wt%, respectively. Moreover, this nanocomposite ceramic has good chemical stability in low temperature degradation.

WITHDRAWN: Preparation of nano α-Al2O3 particles with optimum conditions by the sol–gel method

WITHDRAWN: Preparation of nano α-Al2O3 particles with optimum conditions by the sol–gel method

Reinforcement of poly(amide–imide) containing N-trimellitylimido-L-phenylalanine by using nano α-Al2O3 surface-coupled with bromo-flame retardant under ultrasonic irradiation technique

By the uniform dispersion of nanoparticles into a polymer matrix, a substantial improvement of physicochemical properties can be attained. In this study, a series of poly(amide–imide)/Al2O3 nanocomposites (PANC)s based on various amounts of modified α-Al2O3 nanoparticles (ANP)s were prepared using the ultrasonic irradiation method. In the process of manufacturing the nanocomposites (NC)s, severe agglomeration of ANPs into the polymer matrix can be reduced using 2,3,4,5-tetrabromo-6-[(4-hydroxyphenyl)carbamoyl]benzoic acid as novel coupling agent. The effects of modified ANPs on the morphology and properties of the polymer matrix were studied by means of Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and thermal gravimetric analysis (TGA). The results obtained by TGA showed that the thermal stability of the NCs was improved with the addition of the small amounts of ANPs as effective thermal degradation resistant reinforcement.