Commercial Alumina Research Articles

WO3 nanowires loaded with cobalt oxide nanoparticles, deposited by a two-step AACVD for gas sensing applications

A two-step procedure was implemented to obtain tungsten oxide nanowires (WO3) doped with cobalt oxide nanoparticles employing W(CO)6 and the metal-organic precursor Co(acac)2. In the first step, tungsten oxide nanowires were grown at 400 °C using an aerosol assisted chemical vapor deposition system (AA-CVD) and subsequently annealed at 500 ºC for 2 h in dry air. Then, cobalt oxide loading (at different dose levels) of the nanowires was performed via a second AA-CVD process. These hybrid nanomaterials were grown on top of commercial alumina substrates that comprised interdigitated electrodes and a heating element. The response of these nanomaterials toward H2S, ethanol H2 and ammonia is investigated and discussed. Co-loaded tungsten oxide is well suited for detecting ammonia under dry conditions and hydrogen sulfide in humid environments.

Novel method and its mechanism of reconstruction of commercial alumina to homogeneous porous alumina composite material

Abstract In this study, a novel method for reconstruction of commercial alumina to a homogeneous porous alumina composite material (HPACM) using an alumina powder, boric acid, and Na2SO4 and Na2CO3 additives is proposed for the first time and experimentally evaluated in detail. The properties of the as-prepared porous materials and their formation mechanisms are investigated. Unlike the traditional complex methods for manufacturing of porous alumina including electrochemical anodisation of aluminium and chemical etching, the HPACM can be simply prepared through sintering and dissolution. Scanning electron microscopy and N2 adsorption–desorption isotherm analyses demonstrate the formation of the HPACM with a diameter distribution centred at ∼20 nm after the sintering and decomposition at high temperatures and dissolution at room temperature. Transmission electron microscopy and X-ray diffraction results show that the main components of the as-prepared HPACM are alumina and sodium aluminate. The formation of the HPACM is attributed mainly to the reactions between the alumina powder, boric acid, and Na2SO4 and Na2CO3 additives at high temperatures and dissolution of the intermediate product of sodium aluminate at room temperature. A NaCl additive does not contribute to the formation of the intermediate product during the sintering process, owing to its considerable vapour loss at low temperatures. Moreover, a nanoindentation test shows that the HPACM has a good mechanical strength.

Influence of test procedure on dielectric breakdown strength of alumina

Dielectric strength testing of ceramics can be performed with various setups and parameters. Comparisons of results from different sources are often not meaningful, because the results are strongly dependent on the actual testing procedure. The aim of this study is to quantify the influence of voltage ramp rate, electrode size, electrode conditioning, and sample thickness on the measured AC dielectric strength of a commercial alumina. Mean values, Weibull moduli, and failure probabilities determined in standardized short time tests are evaluated and related to withstand voltage tests. Dielectric strength values in the range from 21.6 to 33.2 kV mm−1 were obtained for the same material using different testing procedures. Short time tests resulted in small standard deviations (< 2 kV mm−1) and high Weibull moduli around 30, while withstand tests at voltage levels with low and virtual zero failure probability in short time tests resulted in large scatter of withstand time and Weibull moduli < 1. The strong decrease in Weibull moduli is attributed to progressive damage from partial discharge and depolarization during AC testing. These findings emphasize the necessity of a thorough documentation of testing procedure and highlight the importance of withstand voltage tests for a comprehensive material characterization.

Multicomponent cascade reaction catalyzed by basic alumina

Multicomponent polymerization is gaining popularity because of its high efficiency and ease operation. In this work, commercial basic alumina was used as a solid catalyst to catalyze the Knoevenagel condensation and thiol-ene click reaction. The reaction conditions were mild and the resulting products were easily separated and purified.

Preparation of ZrO2 modified Al2O3 nano-sheets supported cobalt catalyst and its performance in Fischer-Tropsch synthesis

Abstract Al2O3 nano-sheet (Al2O3-CN) was synthesized under hydrothermal condition. The cobalt-based catalyst of 20% (mass fraction) was prepared by impregnation method and applied to Fischer-Tropsch synthesis. The Al2O3-CN (226 m2/g) and commercial alumina (Al2O3-C, 249 m2/g) have similar specific surface area, but Al2O3-CN has more narrow pore size distribution. Compared with Co/Al2O3-C catalyst, Co/Al2O3-CN catalyst showed higher reduction degree and more uniform cobalt particle size distribution after impregnation. Thus, Co/Al2O3-CN catalyst exhibited higher CO conversion and lower methane selectivity. In order to further improve the catalytic performance of Co/Al2O3-CN, Al2O3-CN was modified with ZrO2. The characterization results showed that with the increase of ZrO2, the specific surface of Al2O3-CN did not change significantly, and the pore volume and pore diameter increased. The cobalt particle size decreased and the number of active sites increased. Under the same reaction conditions, the CO conversion rate of catalysts modifield by ZrO2 was further improved and selectivity of methane was decreased.

Application of a catalytic membrane reactor to the selective hydrogenation of 1-Butyne

A catalytic membrane reactor (CMR) was applied in order to enhance the selectivity in the hydrogenation of 1-butyne in the presence of 1-butene. The performance of the CMR was studied in batch-wise operation for the hydrocarbon liquid mixture, while hydrogen was continuously fed to keep a constant partial pressure. The reaction was carried out at 44 °C and partial pressures of hydrogen in the range of 1 to 5 bar. The CMR was prepared by impregnating a commercial alumina membrane disk with Pd. Experimental results were compared with those obtained in a conventional fixed bed reactor (FBR), using a commercial catalyst of egg-shell type in its original size, and in a microreactor (MR) with the same commercial catalyst milled to a size of around 40 μm. The CMR presents high activity and selectivity, comparable to the values of the milled commercial catalyst, but significantly higher than for the commercial catalyst in its original size. Kinetic parameters for the hydrogenation of 1-butyne were obtained from the regression of the experimental data. Also, a simulation of a continuous operation of both, CMR and FBR with the commercial catalyst, was carried out to show the advantage in selectivity of the CMR.

New Trends in Automotive Exhaust Gas Purification Materials: Improvement of the Support against Stability of the Active Components

Lanthanum and zirconium oxides are well known to be applied as an additive to improve the properties of the commercial alumina. Such modified aluminas are widely used in different catalytic fields including three-way catalysis. In the present research we have paid attention to the possible effects of the doping on the catalytic performance and stability of bimetallic Pd-Rh catalysts. The samples were prepared via an incipient wetness impregnation of the commercial supports, tested in CO oxidation under prompt thermal aging regime and characterized by physicochemical methods.

Development of non-shrinkable ceramic composites for use in high-power microwave tubes

Al2O3-CaO-SiC-based ceramic composites with four different compositions were sintered at 1700°C for 3 h in an air furnace. The phase analysis, microstructural characterization, and elemental composition determination of the developed composites were performed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDAX) analysis, respectively. The shrinkage, thermal properties, and electrical resistivity of the composites were also studied. The experimental results showed the effects of adding silicon carbide and calcia to alumina on the thermal, electrical, and shrinkage properties of the resultant composites. Among the four investigated ceramic composites, the one composed of 99wt% alumina, 0.5wt% CaO, and 0.5wt% SiC exhibited the best characteristics for use as a potting material in a dispenser cathode of a microwave tube. The material exhibited slight expansion instead of shrinkage during drying or firing. Other properties of the composite powder, such as its thermal properties and electrical resistivity, were comparable to those of a commercial alumina powder.

Steam reforming of n-dodecane over mesoporous alumina supported nickel catalysts: Effects of metal-support interaction on nickel catalysts

Developing a highly active and stable Ni-based catalyst is still a challenge for the generation of on-site hydrogen through steam reforming of long-chained hydrocarbons, such as kerosene fuels. Ni nanoparticles (ca. 5 nm) on mesoporous alumina prepared by atomic layer deposition (ALD) were employed in steam reforming of n-dodecane, and exhibited a turnover frequency (TOF) of 477.6 h−1, whereas Ni nanoparticles on commercial alumina support prepared by impregnation method exhibited a TOF of 100 h−1. The high activity of ALD Ni catalysts was ascribed to high reduction degree, as confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and H2-chemisorption. A deactivation was also observed on the ALD prepared catalysts, which was ascribed to the weak metal-support interaction, as confirmed by H2 temperature-programmed reduction (TPR). The ALD Ni/Al2O3 catalysts were further modified with CeO2 and they showed enhanced stability with 8% deactivation degree in steam reforming of n-dodecane. Further characterizations of spent catalysts showed that the presence of CeO2 was favorable for stabilizing Ni nanoparticles by enhancing moderate metal-support interaction, and reducing the formation of coke on the interfaces of NiCeO2.

Intensifying gibbsite precipitation from sodium aluminate solution by adding a mixed seed

Gibbsite precipitation from sodium aluminate solution was intensified by adding mixed industrial and self-prepared active seeds, and its mechanism was researched preliminarily. The interfacial properties of seed/aluminate solution were determined for separate industrial and active seed. Contact angles of seed/aluminate solution and the specific surface area of seeds were respectively measured by sessile drop and BET method, and the morphology and particle size of precipitates were recorded by SEM and laser diffraction. The results show that, compared with the industrial seed, the active seed has a better wettability, lower interfacial tension, and larger specific surface area, being conducive to enhancing gibbsite precipitation from sodium aluminate solution. SEM analysis of the precipitates indicates that the embedment and accumulation/agglomeration of extremely fine particles on the surface of coarse industrial seed can effectively control the content of fine particles in the precipitation product. With extra 3.1–4.6 g/L active seed, the gibbsite precipitation ratio was increased by 3.23%–3.92%. Moreover, the mass percentage of particles <45 μm in precipitation product has even a slight decrease compared with that for the traditional precipitation product or of the industrial seed itself. The result presented is favorable to developing an intensified gibbsite precipitation process for commercial alumina manufacture.

Rod-shaped porous alumina-supported Cr2O3 catalyst with low acidity for propane dehydrogenation

Direct catalytic propane dehydrogenation (PDH) to obtain propylene is a more economical and environmentally friendly route for propylene production. In particular, alumina-supported Cr2O3 catalysts can have better potential applications if the acidic properties could be tuned. Herein, a series of rod-shaped porous alumina were prepared through a hydrothermal route, followed by calcination. It was found that the acidity of the synthesized alumina was generally lower than that of the commercial alumina and could be adjusted well by varying the calcination temperature. Such alumina materials were used as supports for active Cr2O3, and the obtained catalysts could enhance the resistance to coke formation associated with similar activity in PDH reaction compared to the commercial alumina. The amount of coke deposited on a self-made catalyst (Cr-Al-800) was 3.6%, which was much lower than that deposited on the reference catalyst (15.7%). The lower acidity of the catalyst inhibited the side reactions and coke formation during the PDH process, which was beneficial for its high activity and superior anti-coking properties.

Desarrollo de recubrimientos a partir de silicato de zirconio de origen mineral mediante proyección térmica por llama oxiacetilénica para aplicación sobre ladrillos refractarios

En el presente trabajo se documenta el desarrollo experimental empleado para obtener mediante proyección térmica por llama oxiacetilénica, recubrimientos a partir de arena de circonio (ZrSiO4) de origen mineral y de una mezcla de ZrSiO4 con 50 % en peso de alúmina comercial referencia Oerlikon-Metco 105 SFP. La arena de ZrSiO4 fue molida y tamizada, con el fin de seleccionar las fracciones de tamaño de partícula -37 +25 μm y -25 μm. Diferentes parámetros de proyección térmica fueron simulados con la herramienta computacional Jets et Poudres SPCTS versión 2002-2009 y las condiciones con mayor potencial para obtener recubrimientos fueron verificadas experimentalmente. Los recubrimientos elaborados sobre sustratos refractarios silico-aluminosos fueron caracterizados mediante MEB y DRX, encontrando que aquellos depositados a partir de la fracción de tamaño más fina, utilizando una llama producida con 22 y 70 L/min de acetileno y oxígeno respectivamente, a una distancia de proyección de 10 cm y con una velocidad de desplazamiento de la antorcha de 0,275 cm/s y con una rotación de los sustratos de 34,57 rpm fueron los que presentaron las mejores características estructurales. La porosidad de los recubrimientos fabricados a partir de la arena de circonio y de la mezcla ZrSiO4 con alúmina fueron de 30,5 ± 6,6% y 20,3 ± 9,2% en área y su dureza fue de 3.06±0.70 GPa y 6.0±0.30 GPa, respectivamente. A partir de los resultados obtenidos se concluye que es posible la utilización de este mineral como materia prima en el proceso de proyección térmica oxiacetilénica.

Synthesis and adsorption behavior of mesoporous alumina and Fe-doped alumina for the removal of dominant arsenic species in contaminated waters

Ordered mesoporous Al2O3 and Fe-Al2O3 materials were synthesized at room temperature by an easy and environmentally friendly self-assembly sol-gel route, to be tested for arsenic removal.Solid samples were thoroughly characterized by several techniques. Synthetized and commercial alumina samples were evaluated as adsorbents for the removal of dominant arsenic species under a wide pH range (3.6–11.5). The mesoporous alumina showed higher adsorption capacity (90 mg/g As(V), pHeq 4) than commercial alumina (54 mg/g As(V), pHeq 4), due to its amorphous structure, uniform accessible mesopores and higher surface acidity. The Fe bearing material exhibited strong As affinity.As(III) adsorption resulted much lower than for arsenate (maximum uptake of 16 mg/g, at pH 8), since As(III)-adsorbent interaction is only based on weak Van der Waals force.Arsenic isotherms adjusted well to the Freundlich model and more accurately to the three parameters Sip´s model. The kinetics results fitted the Elovich model.As pH increased, adsorption capacity decreased due to the reduction of electrostatic interactions. Under alkaline conditions arsenic desorption was achieved, although the stability of the material was compromised.The presence of several interfering ions was evaluated. Phosphate ions showed the highest interference. The use of a tap water matrix increased As(V) adsorption, encouraging the use of these materials in the treatment of real polluted waters.

Imidazolium-based Ionic Liquids Impregnated in Silica and Alumina Supports for CO2 Capture

Ionic liquids (ILs) physical immobilization in solid materials is a key strategy for developing efficient and low cost CO2 capture processes. In this work, two porous commercial substrates with different characteristics (silica and alumina) were impregnated with ILs by physical wet method. Imidazolium based IL combined with [Br]- and [Tf2N]- anions were used in impregnation process. CO2 sorption capacity and selectivity (CO2/N2) of these materials were investigated. The best results regarding CO2/N2 selectivity and CO2 sorption were obtained with [Tf2N]- anion. In relation to solid support, commercial alumina exhibited enhanced CO2 uptake and higher selective capacity (CO2/N2) (6.1 (± 0.1)). Combination of commercial alumina as support and 20 wt% of mbmim [Tf2N] resulted in higher CO2/N2 selectivity of 9.5 ± 1.0. In addition, this material also showed fast sorption kinetics when compared to pure IL besides reuse capacity.

Ispitivanje mehaničkih svojstava akrilatnih kompozitnih materijala sa različitim AL2O3 ojačanjima brazilskim testom

Composite materials based on UV-curing acrylates and various alumina-based reinforcements represent material that is suitable for the use in dentistry, but also in other areas. Composites were made using four different types of reinforcement of chemically very similar compositions, but different size and morphologies. In order to monitor the mechanical properties of the composite material, samples were made in the form of discs of defined dimensions suitable for polymerization under UV light. The subject of this study is the examination of the mechanical properties of the Bis-GMA (Bisphenol A glycidyl methacrylate)/TEGDMA (trimethylene glycol dimethacrylate) photopolymer composite material as a matrix. The reinforcements were in the form of commercial nanoparticles and alumina whiskers and their influence on mechanical properties were compared with the influence of synthesized alumina particles doped with iron oxide synthesized sol-gel technique. In order to test the mechanical properties of composite materials, the Brazilian Tests and the testing of the microhardness of samples were employed.

One-pot cascade ethylene oligomerization using Ni/Siral-30 and H-ZSM-5 catalysts

A study on the ethylene oligomerization was carried out using a one-pot cascade continuous flow fixed-bed reactor, loaded with Ni/Siral-30 and H-ZSM-5 catalysts at the same time. The used Siral-30 and ZSM-5 are commercial silica alumina (Sasol, SiO2/Al2O3 = 30/70) and zeolite (Zeolyst CBV 2314) materials, respectively. Compared to the catalytic results from reactions with the single catalysts under identical conditions, the one-pot cascade Ni/Siral-30 + H-ZSM-5 exhibited close to 100% conversion, resulted in a completely reversed Schulz-Flory type product distribution (C10+ > C8 > C6 > C4), and yielded the highest amount of liquid product for the entire reaction time at 250 °C (0.14 and 0.05 g gcat.−1 h−1 of a total liquid and C10+, respectively). A liquid product containing about 30% aromatic compounds, which is one of the important constituents needed for jet-fuel, was obtained from the one-pot cascade reaction. We also confirmed that the results obtained from Ni/Siral-30 + H-ZSM-5 in the gas-slurry autoclave reactor were significantly different than those obtained from the one-pot cascade reaction. The overall results demonstrate that a sequential one-pot cascade catalysis over Ni-containing and Brønsted acidic catalysts can be a good method for improving the production of jet-fuel range hydrocarbons from ethylene conversion.

Synthesis and Characterization of Alumina-ChitosanHydroxyapatite Biocomposites for Load Bearing Application

This study investigated the influence of reinforcing hydroxyapatite (HA) with alumina (Al) and chitosan nanofiber (CH) to enhance its usefulness in load bearing application. Commercial alumina was used while chitosan fiber and hydroxyapatite were synthesized from cowry shells and limestone respectively. The developed composites were characterized with a view to assessing theirsuitability for use as medical implants in load bearing capacity. It was observed that the optimum compressive strength obtained was 181.73 MPa, tensile strength of 172.67 MPa, hardness value of 529.21 HV, fracture toughness of 7.42 MPa.m1/2 , elastic modulus of 8.23 GPa and bending strength of 175.51 MPa. Increasing volume fractions of Al-CH resulted in decrease in compressive strength, hardness and elastic modulus of hydroxyapatite while its tensile strength, bending strength and fracture toughness increased. The result obtained from the Fourier Transform Infrared Spectrometry revealed that the intermolecular hydrogen bond and chelate interaction between the constituents contribute to the good mechanical properties of the composite. X-Ray Fluorescence analysis result indicates that their chemical compositions contain ions which are found in the physiological environment. The dispersion of the alumina-chitosan nano fiber in the HA matrix as revealed by the Scanning Electron Microscope micrographs result in the formation of interfaces which activates different mechanisms that improve the strength of HA. The optimum mechanical property was obtained at 20-20-60 Al-CH-HA composite. Hence, this composite will be a suitable material for load bearing application.

Microstructure and optical properties of alumina sintered from various phases

Self-synthesized and commercial alumina (boehmite, γ-Al2O3, α-Al2O3) powders were consolidated using an identical spark plasma sintering cycle, and optically translucent samples were obtained. The benefit of higher pressure is remarkable grain growth suppression. Additionally, the shorter dwell time at higher pressure advantageously leads to a reduction in grain size while conserving the optical transparency and without affecting the density.

Design and Performance Evaluation of Al2O3-SiC Composite for Direct-Bonded Copper Substrate

A computational material design approach is applied to propose a novel ceramic material for direct-bonded copper (DBC) substrate with enhanced thermal and structural performance. The material design inherently consists of many competing requirements that require careful decisions regarding key trade-offs in terms of material composition, inclusion size, shape, and distribution to achieve the target properties. The alumina-silicon (Al2O3-SiC) composite, as compared to commercial alumina, used in DBC is found to be the most suitable design among other candidates with improved thermal and structural properties. In order to study the performance characteristics and the effects of the new ceramic composite with improved properties in terms of structural behavior and fatigue life of the DBC substrate, the normal working and extreme thermal cycling conditions were simulated and analyzed using finite element method. The temperature, strain, and localized stress distribution within the substrate at a steady-state condition were analyzed, and the improved Coffin–Manson law was used to calculate the fatigue life of the substrate under extreme thermal cycling conditions. The proposed Al2O3-SiC composite is found to be more robust than the commercial alumina as DBC substrates considering the thermal–mechanical performance. The fatigue life cycle of the DBC substrate with the proposed material is predicted to be about two times longer than the commercial alumina DBC ceramic under transient thermal cycling test.

Activated Alumina Granules with nanoscale porosity for water defluoridation

Highly porous alumina granules have been processed by virtue of modified sol–gel method. Activated alumina (AA) granules were obtained through hydrolysis of aluminum nitrate controlled by ammonia in aqueous media and granules were formed in ammonia–paraffin oil bath. The prepared granules were found to be consisting of high porosity amorphous γ- alumina particles which were characterized by XRD, SEM, TEM, FT-IR and Brunauer–Emmett–Teller (BET) techniques. The material prepared via this method were found to be composed of nano-particles with an average grain size of 30 nm and a large BET surface area 447 m2/g which is very high compared with commercial alumina available in the market. The fluoride removal capacity of prepared granules with variation of fluoride dose has also been studied by employing AA in domestic candle type filters. It also shows better regeneration and reusability after ten cycles of usage. Fluoride removal from aqueous solution in continuous mode depends on adsorbent doses and initial concentration of fluoride.