Al2O3 Samples Research Articles

Assessment of the Hydrophilic-Hydrophobic Balance of Alumina Oxidized at Different Temperatures via H<sub>2</sub>O and C<sub>4</sub>H<sub>10</sub> Vapor Adsorption

The hydrophilic-hydrophobic surface area of alumina powder (Al2O3) oxidized at different temperatures was determined on the base of adsorption of water and butane vapor at 25°C. In the order to study the influence of thermal oxidation upon hydrophilic/hydrophobic character of the surface, samples of Al2O3 were characterized using granulometry, SEM and BET surface area measurement. SEM results showed that the thermal treatment does not affect the morphology of the Alunima. However, the increase of treatment temperature from 250 to 900°C results in changing of the hydrophilic-hydrophobic balance of Al2O3 surface.

Liquid-Phase Hydrogenation of Internal and Terminal Alkynes on Pd–Ag/Al2O3 Catalyst

The structure and catalytic properties of a bimetallic Pd–Ag/α-Al2O3 catalyst are studied in the liquid-phase hydrogenation of substituted internal and terminal alkynes using diphenylacetylene, phenylacetylene, 1-phenyl-1-propyne, and 1-phenyl-1-butyne as sample alkynes. IR spectroscopy of adsorbed CO, X‑ray diffraction (XRD), and electron microscopy were used to show that the active sites on the Pd–Ag nanoparticle surface are Pd1 sites. The synthesized Pd–Ag/α-Al2O3 catalyst shows a much higher selectivity in the hydrogenation of internal symmetric and asymmetric alkynes compared to the monometallic Pd/α‑Al2O3 sample. Also, it was found in the hydrogenation of diphenylacetylene and 1-phenyl-1-propyne on Pd–Ag/α-Al2O3 that the rate of the stage of desired olefin hydrogenation substantially decreases, which favors the kinetic control of the process.

Tunable microstructures and tensile mechanical properties of oxide-dispersion-strengthened Cu by extrusion and secondary processing

In this paper, the influence of extrusion ratio and secondary processing of hot rolling on microstructural features and tensile mechanical properties of samples produced by extrusion of mechanically alloyed Cu-5vol.%Al2O3 alloy powders is investigated. The results show that the extrusion ratio and subsequent rolling greatly affect the sizes of Cu grains and Al2O3 particles, spatial distribution of Al2O3 particles and dislocation density in the prepared bulk Cu-5vol.%Al2O3 alloys. This readily results in the samples prepared by various processing ways displaying different Al2O3 particle size and spatial distributions, Cu grain size distributions as well as dislocation densities. As a result, a total tensile elongation of over 10% and a tensile strength of approximately 600 MPa are attained in an extruded and rolled Cu-5vol.%Al2O3 sample, which are difficult to obtain concurrently in the commercial Al2O3-dispersion-strengthed Cu materials prepared by internal oxidation. To understand these prominent mechanical combinations, we analyze and discuss the different tensile behaviors observed in the fabricated samples on the basis of their specific microstructural characteristics.

Microstructure and electrical conductivity of Ce0.85Y0.15O1.925-Al2O3 composite ceramics

The polycrystalline Ce0.85Y0.15O1.925 (YDC)-xmol%Al2O3 (x=0, 5, 10, 20, 30) composite ceramic was sintered and prepared at 1300 °C for 10 h in the air atmosphere to investigate the effects of the YDC/Al2O3 heterogeneous interface on its electrical conduction properties. The main phase of YDC exists in all samples, and the second phase of Al2O3 starts to appear in the XRD patterns when its content is beyond the solid solubility limit in YDC. No severe reaction between YDC and Al2O3 occurs in the composite samples at 1300 °C. The average grain size of the composite ceramics decreases from 510 nm to 330 nm with the rise in Al2O3 content from 0 to 30%. The specific grain boundary electrical conductivity of YDC-xAl2O3 samples decreases with the Al2O3 content from 0 to 20% and then begins to increase when the Al2O3 content rises from 20% to 30%. The YDC-30%Al2O3 sample shows a higher specific grain boundary conductivity than YDC-20%Al2O3, which mainly originates from the higher volumetric fraction of YDC/Al2O3 heterogeneous interface in YDC-30% Al2O3 as well as the higher oxygen ion mobility in YDC/Al2O3 heterogeneous interface region.

The Use of Laser Induced Breakdown Spectroscopy (LIBS) to Study Catalyst Deactivation of V2O5/γ‐Al2O3 as Compared to Inductively Coupled Plasma Optical Emission Spectrometry

Laser Induced Breakdown Spectroscopy (LIBS) method is introduced as a novel approach in this work to study catalyst deactivation of V2O5/γ‐‐Al2O3 for gas‐phase dehydration of glycerol and producing acrolein. The LIBS results of V2O5/γ‐Al2O3 samples are compared with those data that are obtained by Inductively Coupled Plasma Optical Emission Spectrometry (ICP‐OES). Experimental data of LIBS data specify that line intensities of vanadium are decreased by deactivation of V2O5/γ‐Al2O3 catalyst. A comparison between the results of LIBS test as well as ICP‐OES analysis shows that the amount of vanadium is decreased in the catalyst. Moreover, coke formation changes the surface of the catalyst. The results of deactivation of V2O5/γ‐Al2O3 are also compared with Pd/C catalyst deactivation.

Thermal stability of nanoparticle supported on Al2O3 with different morphologies

Al2O3 nanocrystals with four various morphologies have been synthesized and used to support Pt nanoparticles and their structural stabilities under high temperature treatment were tested. The results show that Pt supported on a novel coral-like Al2O3 sample synthesized by methanol solvothermal method showed the highest thermal stability due to the strongest interaction between Pt and the support. But the Pt nanoparticles diameters of all the samples tend to be bimodal distributed, centered around 1–3 and 10–20 nm, which is mainly because the different content of coordinatively unsaturated pentahedral Al3+ sites.

Ceramic based multi walled carbon nanotubes composites for highly efficient electromagnetic interference shielding

In this work, for the first time a highly conductive ceramic composite was made by incorporating multi-walled carbon nanotubes (MWCNT) in aluminum (Al)/alumina (Al2O3) matrix by a simple mechanical mixing technique. The different weight percentage (wt%) of MWCNT incorporated with Al/Al2O3 and their role on the electrical and electromagnetic interference shielding effectiveness (EMI SE) of ceramic composites were investigated. The high electrical conductivity of 280 S/m was achieved for MWCNT@Al/Al2O3 composites with 8 wt% MWCNT content which is 280 times higher than MWCNT@Al/Al2O3 composites (1 S/m) with 1 wt% MWCNT. In addition, MWCNT@Al/Al2O3 sample showed a high EMI SE value of 46 dB for the X-band which is capable to block more than 99.9% of incident electromagnetic radiation. The high electrical conductivity and EMI SE properties of MWCNTs embedded ceramic composite system has originated from the homogenous distribution of conducting carbon nanotubes to form a percolated network at low filler loading. This work presents a strategy to develop a conductive ceramic composites for the excellent EMI shielding and electrical properties by a simple mechanical mixing approach.

Numerical simulation of sintering for 3D-printed ceramics via SOVS model

Abstract Today, rapid progress can be seen in ceramic 3D printing processes and their application to the manufacturing of complex-shaped parts. However, the significant deformation of parts during sintering is a major impediment to the broad introduction of the technology. Hence, the application of mathematical modeling methods to simulate the behavior of a part during sintering has become a valuable tool to finely tune the process parameters. The purpose of this paper is to share the experience acquired in the application of the Skorohod-Olevsky Viscous Sintering (SOVS) model for the simulation of the sintering process of Al2O3 samples manufactured with a stereolithography technology. The SOVS model was implemented in the ABAQUS modeling suite using the subroutine mechanism. The modeling results demonstrate an acceptable convergence with the experimental data in terms of the shrinkage and final density of a material.

Neutron resonance transmission analysis of cylindrical samples used for reactivity worth measurements

A characterization of cylindrical samples by neutron resonance transmission analysis (NRTA) at the GELINA facility of JRC Geel (Belgium) is presented. The samples were designed and produced for reactivity worth measurements in the MINERVE reactor of CEA Cadarache (France). NRTA was applied to determine the nuclide composition of UO2, Al2O3 and liquid samples that were doped with silver. The volume number densities of 238U, 107Ag and 109Ag obtained by NRTA are within 2% fully consistent with the values that are quoted by the manufacturer. In addition, the NRTA data reveal a tungsten contamination which is not reported by the provider. It is shown that such a contamination contributes by up to 5.7% to the reactivity worth.

Multiphase Hydrodechlorination of 1,3,5-Trichlorobenzene on Palladium Catalysts Supported on Alumina: Effect of the Support Properties and Modification by Heteropoly Acid Based on Silicon and Tungsten

Catalytic systems 2 wt % Pd/Al2O3 were prepared using noncalcined boehmite (NC) and two types of alumina support: one was prepared by the calcination of boehmite at 600°C (C) and the other produced by Engelhard (E). To prepare 2 wt % Pd/HPC–Al2O3 samples, these supports were modified by impregnation by a heteropoly compound (HPC) (20 wt % Н8[Si(W2O7)6] ⋅ 6Н2О). The effect of the Al2O3 structure and its modification by the heteropoly compound on the physicochemical properties, activity, selectivity and stability of catalysts in the reaction of multiphase hydrodechlorination of 1,3,5-trichlorobenzene (TCB) was studied. All catalysts showed activity in the considered reaction with the predominant formation of benzene but were deactivated in the reaction medium. Modification by the heteropoly compound resulted in increased stability and was especially effective for catalyst supported on Al2O3(E). The method of scanning electron microscopy (SEM) was used to determine the morphological differences of supports. According to the data of transmission electron microscopy, all catalysts contained palladium in the form of particles less than 20 nm in size. The particle size and width of the size distribution increases in the series Pd/Al2O3(NC) < Pd/Al2O3(C) < Pd/Al2O3(E). Modification by the heteropoly compound was favorable for the decrease in the size of palladium particles. The method of temperature-programmed reduction with hydrogen (TPR-H2) showed that all catalysts included in their composition palladium hydride along with more strongly surface-bound metal forms that are reduced at elevated temperatures, and their content decreases after modification by the heteropoly compound and increases after catalytic tests. According to diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the deposition of a heteropoly compound leads to a change in the type of Lewis acid sites on the alumina surface and in the electronic state of palladium. According to the results of infrared spectroscopic studies of adsorbed CO, the relatively large particles of Pd0 are the main form on the surface of nonmodified catalysts. The catalysts modified by the heteropoly compound contain single Pd+ and Pd2+ cations, and the fraction of Pd0 is substantially smaller. The specific features of the Lewis acidity of the catalyst surface determine the possibility of 1,3,5-trichlorobenzene adsorption and activation on the support and the spillover of hydrogen from Pd0. An increase in the catalyst stability as a result of support modification by the heteropoly compound can be explained by the appearance of new active sites in the interaction of palladium with the heteropoly compound or its thermal decomposition products.

Cross-linked porous polymer separator using vinyl-modified aluminum oxide nanoparticles as cross-linker for lithium-ion batteries

A cross-linked porous polymer membrane using vinyl-functionalized aluminum oxide (Al2O3) nanoparticles was prepared and used as a separator for lithium-ion batteries (LIBs). Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was first blended with a mixture solution containing poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), vinyl-functionalized Al2O3 nanoparticles (VTMO@Al2O3) as the cross-linker and poly(vinyl pyrrolidone) (PVP) as the pore-forming agent. Subsequently, the membrane was obtained by free radical copolymerization of the above-mentioned mixture and after-treatment. The preparation and properties of the membranes were investigated. It has been found that, under the action of the pore-forming agent of PVP, the obtained membrane (PMAv) had high ionic conductivity (1.37 mS cm−1) at ambient temperature. On account of the existence of the Al2O3 as cross-linking points, the PMAv membrane showed good mechanical strength of 30.4 MPa and excellent thermal stability at 180 °C. Moreover, comparing with the system without PVP or Al2O3 samples, the cell with the PMAv membrane showed the best discharge capacity and most stable capacity retention and cycle performance, indicating that the PMAv membrane is a good polymer separator for LIBs.

Thermodynamic and catalytic properties of Cu- and Pd- oxides over mixed γ–χ–Al2O3 for methanol dehydration toward dimethyl ether

The development of catalytic systems to generate alternative energies capable of replacing diesel is a great challenge. Methanol dehydration (2CH3OH → CH3OCH3 + H2O) is one of the most suitable catalytic reactions to produce dimethyl ether (DME). In DME synthesis, CuO/γ–Al2O3 based-materials showed to be catalytically active at high pressures, but these lack high performance under atmospheric conditions. In this work, we synthesized CuO/γ–χ–Al2O3, PdO/γ–χ–Al2O3, and CuOPdO/γ–χ–Al2O3 by a facile impregnation method for methanol dehydration at atmospheric pressure. Catalytic results showed that the CuOPdO/γ–χ–Al2O3 sample performed the highest activity. All catalysts reached selectivity of 100% toward DME, regardless of the reaction temperature. Remarkably, the bimetallic catalyst containing low loadings of copper and palladium retained stability during 48 h of reaction at 275 °C, and after its regeneration they showed a similar trend. The activation energies (Ea) for the methanol dehydration using the catalyst that performed the highest catalytic activity CuOPdO/γ–χ–Al2O3 compared with the material with the lowest catalytic activity γ–χ–Al2O3 were obtained. The activation energy values of the γ–χ–Al2O3 and CuOPdO/γ–χ–Al2O3 catalysts were 112.57 kJ/mol and 45.73 kJ/mol, respectively.

Dissolution behaviour of Al2O3 in mould fluxes with low SiO2 content

A kinetic model of the dissolution of Al2O3 into mould fluxes with low SiO2 content was established, and the restrictive step of the dissolution process was investigated by employing a rotating cylinder method. Then, the effects of the relative moving speed between the Al2O3 sample and the flux as well as the effects of the temperature and composition on the dissolution rate of Al2O3 were analysed. The results showed that the dissolution of Al2O3 is controlled by the diffusion in the product layer. The dissolution rate increases with the increase in the relative moving speed and temperature. The activation energy of the dissolution of Al2O3 into mould fluxes A-1, A-2, and B were 150.8 kJ mol−1, 156.1 kJ mol−1, and 131.4 kJ mol−1, respectively. The dissolution accelerates with increasing (CaO+BaO)/(Al2O3 +SiO2) ratio and Na2O, Li2O, B2O3, and F− contents. The result of the analysis of the Al2O3/flux interface by scanning electron microscopy–energy dispersive X-ray spectroscopy showed that a product layer was formed in the dissolution process, with interfacial products BaO·6Al2O3 and BaO·2CaO·4Al2O3.

Tribological Investigation of Multilayer Graphene Reinforced Alumina Ceramic Nanocomposites

We investigated the wear resistance properties of high-frequency induction heat (HFIH) sintered alumina (Al2O3) ceramic nanocomposites containing various multilayer graphene (MLG) concentrations. The tribology of the monolithic Al2O3 and nanocomposites samples was assessed against spherical ceramic (Si3N4) counter sliding partner at sliding loads ranging from 6 to 40 N using ball-on-disk wear test configuration. Compared with the monolithic Al2O3, the incorporation of 1.0 vol % MLG reduced the friction coefficient by 25% and the wear rate by 65% in the MLG/Al2O3 nanocomposites tested under 40 N sliding load. Based on the mechanical properties, brittle index, and microstructure, the active wear mechanisms for the nanocomposites were analyzed. The MLG contributed in the nanocomposites tribology process, indirectly, by enhancing the mechanical properties and, directly, by reducing the friction between the counter sliding partners. The synergistic role of MLG thin triboflim and twirled MLG for improving the tribological performance of the nanocomposites is discussed.

Wear behavior of silica and alumina-based nanocomposites reinforced with multi walled carbon nanotubes and graphene nanoplatelets

Spark plasma sintering (SPS) technique has been employed to fabricate silica (SiO2) and alumina (Al2O3) based nanocomposites having multiwalled carbon nanotubes (MWCNTs) and exfoliated graphite nanoplatelets (xGnPs) as reinforcement phase. The influence of MWCNTs and xGnPs on the wear behavior of the nanocomposites is analyzed. SiO2-MWCNT, SiO2-xGnP nanocomposites having 0.5, 3 and 5 vol% and Al2O3-MWCNT, Al2O3-xGnP nanocomposites having 0.2, 0.8, 3 and 5 vol% of the respective nanofiller were developed. SiO2-based nanocomposites were fabricated at 1350 °C under a pressure of 40 MPa whereas Al2O3-based nanocomposites were prepared at 1450 °C under a pressure of 50 MPa. Experimental results indicate that the wear behavior of various SiO2 and Al2O3-based nanocomposites improves with the introduction of carbonaceous nanofillers like MWCNTs and xGnPs. With the addition of these nanofillers, a continuous supply of graphitic reinforcement phase at the ceramic interface provided a better lubrication to the reinforced nanocomposites, which was not found in the case of monolithic SiO2 or Al2O3 samples. Both MWCNTs and xGnPs effectively withstand the applied stress during the wear test owing to their structural morphology once subjected to the wear strain. A remarkably varied wear behavior of both SiO2 and Al2O3 based nanocomposites was observed. SiO2 based nanocomposites depict narrower wear tracks with high wear rates whereas Al2O3 based nanocomposites were found to depict broader wear tracks with low wear rates.

Characterization of reticulated ceramic foams with mercury intrusion porosimetry and mercury probe atomic force microscopy

This study addresses the question of whether mercury intrusion porosimetry is an appropriate measurement devise for the porosity characterization of reticulated ceramic foams which features three kinds of pores: functional pores, material pores and strut cavities remaining after decomposition of the polymeric foam. Reticulated ceramic foam samples made of Al2O3 and Al2O3-C and with functional pore sizes between 10 and 60 ppi (pores per inch) were investigated. The results show that it is feasible to measure the strut cavities and the entryways of the material pores with the help of the mercury intrusion porosimeter. The results for the strut cavity diameter depends strongly on the ppi number of the polyurethane foam used for the preparation of the ceramic foam.For the reticulated Al2O3-C foam samples no extrusion of the mercury is observed. Reasons for the missing extrusion of mercury are discussed.Furthermore, atomic force microscopy (AFM) measurements on Al2O3 and Al2O3-C samples are carried out using a recent AFM method to examine interactions between a mercury droplet and rough surfaces. Factors like approach/retrace speed, reproducibility and applied force are investigated. It is seen that for Al2O3 larger attractive forces are measured than for Al2O3-C.

Effect of addition of SiC and Al2O3 refractories on Kapitza resistance of antimonide-telluride

Invoking Effective Media Percolation theory (EMPT), Hasselaman-Johnson effective media theory (EMT), and Nan and Birringer EMT, the effect of addition of SiC and Al2O3 nanoparticles on Kapitza resistance (RBd) of Ni0.05Mo3Sb5.4Te1.6 was investigated. Pore size and their volume distribution, and surface area were characterized using BET technique to correlate pore effect and surface area on RBd. Bounds for effective thermal conductivity were determined using Lipton–Vernescu model. Variation of thermal conductance with respect to temperature was studied and compared with the results of other materials. According to EMPT, RBd in Ni0.05Mo3Sb5.4Te1.6/SiC composites ranged from 3.84 × 10-7 to 5.42 × 10-7 m2KW–1 and 3.36 × 10-7 to 3.86 × 10-7 m2KW–1 for Ni0.05Mo3Sb5.4Te1.6/Al2O3 composites. Kapitza radius (aK) for SiC samples was ranged between 2.01 – 2.84 μm; for Al2O3 samples it was 1.86 μm. Hasselman-Johnson model gave RBd values 55%, 51%, and 8% more than what EMPT is predicting, but of the same order and aK values 3.5 μm, 4 μm, 3 μm for SiC samples and 1.2 μm, 0.6 μm, 0.55 μm for Al2O3 samples. Nan-Birringer model yielded large aK of 7.25 μm and RBd ∼ 1.4 × 10–6 m2KW–1 for Ni0.05Mo3Sb5.4Te1.6/SiC. So obtained parameters are reasonable estimates. Variation of effective thermal conductivity in Al2O3 samples is more sensitive to particle size compared to SiC samples. Mechanical properties were studied using micro–indentation technique and their effect on effective thermal properties was ascertained. Addition of Al2O3 nanoparticles have aided in enhancing mechanical properties of bulk material.

Enhanced dielectric characteristics of Ba0.94Bi0.04(Fe0.5Nb0.5)O3 coated with SiO2 and SiO2/Al2O3 over a broad frequency and temperature range

Pure phase of Ba0.94Bi0.04(Fe0.5Nb0.5)O3 (BBFN) nano-particles were obtained by chemical co-precipitation method. The core-shell structure of BBFN@SiO2 and BBFN@SiO2/Al2O3 particles and the target ceramics were successfully prepared by aqueous chemical coating approach. The microstructures and dielectric properties of BBFN@SiO2 and BBFN@SiO2/Al2O3 were studied. Both the BBFN@SiO2 and BBFN@SiO2/Al2O3 samples show significantly decreased dielectric loss and good frequency and temperature stability on relative permittivity. Compared to the rapid decline of relative permittivity of BBFN@SiO2, the synergistic effect of SiO2 and Al2O3 in BBFN@SiO2/Al2O3 ceramics made the relative permittivity of which remains a relatively high level with very low dielectric loss, making it more suitable in colossal permittivity applications. Based on the impedance analysis, the grain boundary effect and IBLC models play the important role for the improvement of dielectric properties of BBFN@SiO2/Al2O3 samples.

Random Multiple Scattering Enhanced Photoacoustic Gas Spectroscopy with Disordered Porous Ceramics.

Light-gas interaction can be enhanced by using disordered porous materials because multiple random scattering increases light intensity near the surface of the material. Here we report signal enhancement of photoacoustic gas spectroscopy with disordered porous ceramics. The amplitude and frequency characteristics of photoacoustic signal due to gas absorption in disordered materials are modeled theoretically. Experiment with a porous Al2O3 sample demonstrates photoacoustic signal enhancement of ∼4 times at 5 kHz.

Acoustic phonon spectrum engineering in bulk crystals via incorporation of dopant atoms

We report results of Brillouin—Mandelstam spectroscopy of transparent Al2O3 crystals with Nd dopants. The ionic radius and atomic mass of Nd atoms are distinctively different from those of the host Al atoms. Our results show that even a small concentration of Nd atoms incorporated into the Al2O3 samples produces a profound change in the acoustic phonon spectrum. The velocity of the transverse acoustic phonons decreases by ∼600 m/s at the Nd density of only ∼0.1%. Interestingly, the decrease in the phonon frequency and velocity with the doping concentration is non-monotonic. The obtained results, demonstrating that modification of the acoustic phonon spectrum can be achieved not only by traditional nanostructuring but also by low-concentration doping, have important implications for thermal management as well as thermoelectric and optoelectronic devices.