Presence Of Al2O3 Research Articles

The effect of Al2O3 and CaO presence on the kinetics of mechanochemical reduction of MoS2 by Zn

Abstract In this research, a new mechanochemical route has been introduced for solid-state reduction of MoS2 using metallic Zn powder as reductant. Nano particles of Mo and ZnS were synthesized as final product. When MoS2 and Zn were used as the starting mixture, the reaction was completed after 12 h. Whereas this reaction was completed after 5 h and 8 h of milling in presence of Al2O3 and CaO respectively. In this research X-ray powder diffraction (XRD) was employed for studying the reactions’ progress. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and laser particle size analyzing techniques were employed for studying the morphology and size distribution of the ball-milled powders. Results have shown that decreasing in size of particles in presence of Al2O3 and CaO was the main reason of improving kinetic of the reaction.

Transformations of α- and β-ionones in the presence of Al2O3 in a supercritical solvent in a flow reactor

The reactivity of α- and β-ionones under the supercritical conditions in a flow type reactor in the presence of Al2O3 at 200–230°C was studied. α-Ionone was reduced to α-ionol, while β-ionol was unstable already at 200°C and underwent dehydration. The secondary reaction products were the corresponding megastigmatrienes.

Destructive Adsorption of Diazinon Pesticide by Activated Carbon Nanofibers Containing Al2O3 and MgO Nanoparticles

We report the destructive adsorption of Diazinon pesticide by porous webs of activated carbon nanofibers containing Al2O3 and MgO nanoparticles. The results show that, the presence of Al2O3 and MgO nanoparticles in the activated carbon nanofibers increases the amount of destructively adsorbed Diazinon pesticide by activated carbon nanofibers. Moreover, type, amount, and specific surface area of metal oxide nanoparticles affect the adsorption rate as well as the total destructively adsorbed Diazinon. Liquid chromatography proved the degradation of Diazinon by chemical reaction with Al2O3 and MgO nanoparticles. Liquid chromatography-mass spectrometry showed that the main product of reaction between Diazinon and the metal oxides is 2-isopropyl-6-methyl-4-pyrimidinol with less toxicity than Diazinon.

Development of Al356–Al2O3 Nanocomposite Coatings by High Velocity Oxy-fuel Technique

In this research, development of Al356–Al2O3 nanocomposite coatings has been investigated. Al356–Al2O3 composite powders were prepared by mechanical milling of Al356 powder and 5 vol.% micro and nanoscaled alumina particles. The milled powders were used as feedstock to deposit composite coatings on A356–T6 aluminum alloy substrate using high velocity oxy-fuel (HVOF) process. X-ray diffractometry, optical and scanning electron microscopy, microhardness and wear tests were used to characterize the composite powders and coatings. The hardness of composite coatings containing micro and nanosized Al2O3 were 114.1 ± 5.9 HV and 138.4 ± 6.9 HV, respectively which were higher than those for substrate (79.2 ± 1.1 HV). Nano and microcomposite coatings revealed low friction coefficients and wear rates, which were significantly lower than those obtained for Al356–T6 substrate. Addition of 5 vol.% micro and nanoscaled alumina particles improved the wear resistance by an average of 85% and 91%, respectively. This is mainly caused by the presence of Al2O3 in matrix and nanocrystalline structure of matrix. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.

Zn(BH4)2/Al2O3: A new synthetic method for efficient and convenient reduction of organic carbonyl compounds to their corresponding alcohols

Zn(BH4)2 (0.5-2 mmol) in the presence of Al2O3 (1 mmol) reduces varieties of organic carbonyl compounds such as aldehydes, ketones, acyloins, ?-diketones and ?, ?-unsaturated carbonyl compounds to their corresponding alcohols. Reduction reactions were carried out in THF at room temperature in high to excellent yields of products. The chemoselective reduction of aldehydes over ketones was accomplished successfully with this reducing system. In addition, regioselectivity and exclusive 1,2-reduction of conjugated carbonyl compounds to their corresponding allylic alcohols in high to excellent yields was accomplished successfully with this reducing system.

A Study on the Carbon Nitriding Process of BF Slag Containing Titanium

The experiment was done in which the BF slag containing titanium produced by Pangang with vanadium-titanium magnetite was dealt with carbon and nitrogen. The possibility of the carbon nitriding reactions were analyzed theoretically. It is found by thermodynamic calculation that the carbon nitriding of TiO2 is easier than that of other oxides and the temperature of carbon nitriding of perovskite can be reduced with the presence of Al2O3 and SiO2 in slag. The phase composition and microstructure of production from carbon nitriding were studied using X-ray diffraction and SEM. It is approved that the main phase composition of production from carbon nitriding under N2 was Ti(C,N). The influence factors, temperature, holding time and particle size were investigated. The results show, the phase compositions of the slag is mainly perovskite; the most suitable temperature and holding time of carbon nitriding is about 1450°C; the most appropriate holding time was about 2 hours and the most suitable size of the slag particle is about 180 meshes. With the optimization of the process, the size of Ti(C,N) can be increased which will benefit the recycle of Ti(C,N) in ore dressing.

Reactive wetting phenomena of MgO–C refractories in contact with CaO–SiO2 slag

Wetting phenomena between MgO–C and CaO–SiO2 slags were investigated by varying carbon content. A sessile drop technique was adopted to study the wetting phenomena in conjunction with a high speed camera for the observation of intrinsic wetting phenomena. The results show that the high content of SiO2 and the presence of Al2O3 in slags enhance the diffusion of Mg2+, leading to the promotion of reactive wetting. The carbon in MgO–C refractory impedes the penetration of slags by repelling the slag and slowing the diffusion of Mg2+. This accounts for the non-wetting behavior of the slag on MgO–C refractory with 17% (mass fraction) carbon similar to that of graphite.

Cyclization of citronellal in a supercritical solvent in a flow reactor in the presence of Al2O3

The reactivity of citronellal under supercritical solvent conditions in a flow reactor in the presence of Al2O3 is examined. It is shown that at 160°C, the main transformation product of citronellal is isopulegol, and when the temperature is increased to 190°C, they are monoterpenes with a para-menthane framework and myrcene.

Laser-Surface Alloying of Nimonic 80 with Silicon and Aluminum and its Oxidation Behavior

In the current study, laser-surface alloying (LSA) of Nimonic 80 (a Ni-based superalloy) was conducted using a high-power continuous wave (CW) CO2 laser by simultaneous feeding of predetermined proportion of elemental Si and Al powders with an Ar shroud. After LSA, the microstructure of the alloyed zone was carefully analyzed and found to consist of several intermetallic phases of Ni and Si. The microhardness of the alloyed zone was significantly increased to 500 VHN compared with 250 VHN of the as-received substrate. The high-temperature oxidation resistance of the laser-surface-alloyed specimens (under isothermal conditions) was improved (at temperature ranges between 1223 K and 1423 K [950 °C and 1150 °C]) compared with as-received Nimonic. Even though LSA enhanced resistance to oxidation up to a limited period, continued exposure to extended hours (at a given temperature) led to spallation of scale. It seems that a SiO2-rich adherent scale is responsible for enhanced protection against oxidation in the laser-surface-alloyed specimens. However, the presence of Al2O3 in the oxide film enhances the resistance to spallation by increasing the scale adherence at a higher temperature. The results are supported by a suitable thermodynamic calculation.

Performance of supported Mg0.15V2O5.152.4H2O nanowires in dehydrogenation of propane

Catalytic dehydrogenation of propane has recently received considerable attention because of the increasing demand for propane. In this present work, the catalytic performances of layered nanowires of Mg0.15V2O5.152.4H2O with equal weight of either Al2O3 or SiO2 were investigated in propane dehydrogenation and compared with the bulk commercial V2O5, at atmospheric pressure and temperature range of 500–600°C. Both dehydrogenation and cracking reactions products were obtained; which suggested sites of different relativities. The catalysts exhibited propylene, ethylene, ethane and methane as primary products. The highest propylene yield of 17% was obtained in the presence of Al2O3. The nanowire samples exhibited higher selectivity to propylene than bulk samples at similar level of propane conversions. For the nanowire samples, the conversion increased (1–3%) while selectivity to propylene decreased (96–87%). At low propane conversions (<1%), the primary products were propylene and ethylene. As the conversion increased, methane was also formed. But not observable amount of ethane was recorded. In the same partial pressure range (0.14–0.43atm), the bulk samples exhibited lower level of propane conversions (0.2–1.2%) and insignificant change in selectivity to propylene (71–73%). In this case, propylene, ethylene and methane are primary products. Although cracking is only observable at conversion higher than 1% on the nanosized samples, the bulk sample exhibited cracking products even at lower conversions. This implies that the nanowire sample exhibited better performance due to lower population of sites that lead to cracking reactions.

Photo-induced properties of anodic oxide films on Ti6Al4V

Photocatalytic activity and wettability of the anodic oxide layer on Ti6Al4V prepared by anodization in a sulfuric acid electrolyte are explored. The oxide is composed mainly of TiO2 with V2O5, VO2 and Al2O3. The crystal structure of the TiO2 varies from anatase to rutile with the sulfuric acid concentration in the electrolyte. Anatase exhibits better photocatalytic activity compared with rutile, which is different from those on Ti and Ti–Nb–Sn alloy. Contact angles of the oxides decrease with ultraviolet light illumination, and hydrophilicity is observed in the rutile oxide. Both photocatalytic activity and hydrophilicity are inferior to the corresponding Ti and Ti–Nb–Sn alloy, which is explained by the presence of Al2O3 in the anodic oxide.

Cu2Sb–Al2O3–C nanocomposite alloy anodes with exceptional cycle life for lithium ion batteries

Cu2Sb–Al2O3–C nanocomposite alloy material has been synthesized via a mechanochemical reduction of Sb2O3 with Al and Cu metals in the presence of carbon (acetylene black). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) reveal that these nanocomposites are composed of nanostructured Cu2Sb particles in an amorphous Al2O3 and conductive carbon matrix. The presence of Al2O3 in the nanocomposite drastically improves the cycle life of the Cu2Sb–C material and enables a remarkable capacity retention of 80% over 500 cycles (330 mAh/g) after the first cycle. With a tap density of ∼1.4 g cm−3, Cu2Sb–Al2O3–C offers significantly higher volumetric capacity than the commonly used graphite anode. A conductive Cu framework supports the electrochemically-active Sb and results in low impedance and good rate capability, while the matrix of ceramic oxide and conductive carbon reduce the agglomeration of the nanocrystalline Cu2Sb particles and buffer the volume expansion/contraction that occurs during cycling. TEM of the electrodes that were cycled between 1 and 500 cycles shows the evolution of the morphology of Cu2Sb particles in the presence and absence of Al2O3. Because the Cu2Sb–Al2O3–C nanocomposite electrodes can operate well above the potential where lithium plating occurs, it is viewed as a safer alternative to graphite anodes.

Catalytic Steam Reforming of Propane over Ni/LaAlO3 Catalysts: Influence of Preparation Methods and OSC on Activity and Stability

To develop an efficient catalyst for steam reforming of propane, Ni/LaAlO3 catalysts were prepared by deposition precipitation, impregnation, and solvo-thermal methods, and characterized by XRD, BET, H2-TPR, elemental analyses, and TEM. Ni/Al2O3 and Ni/CeO2 catalysts were also synthesized by the solvo-thermal method for comparison. The Ni/LaAlO3 catalysts exhibited better catalytic performance than both Ni/Al2O3 and Ni/CeO2 catalysts, and activities with Ni/LaAlO3 were found to be dependent upon the preparation methods. In particular, the Ni/LaAlO3 catalyst synthesized by the solvo-thermal method exhibited the highest activity presumably because tetrahydrofuran helps distribute generated Ni nanoparticles onto the catalyst surface in a uniform fashion. In addition, the solvo-thermally prepared Ni/LaAlO3 catalyst was found to be highly stable, with its activity being maintained at least during 100 h. The observed high stability is attributed to the excellent oxygen storage capacity of LaAlO3, which was first determined by thermogravimetric methods as well as by soot oxidations in the presence of Al2O3, CeO2, and LaAlO3. Compared to the Ni/Al2O3 and Ni/CeO2 catalysts, Ni/LaAlO3 exhibited suppressed carbon formation even at lower S/C ratios due to the superior oxygen transport ability of the LaAlO3 support.

Effects of Reactor Packing Materials on H2 Production by CO2 Reforming of CH4 in a Dielectric Barrier Discharge

AbstractNon‐thermal plasma has been investigated for CO2 reforming of CH4 in a coaxial DBD reactor with different reactor packing materials placed into the discharge gap. Both the chemical and physical effects on reaction performance have been examined for the addition of quartz wool, γ‐Al2O3 and zeolite 3A, in order to gain a better understanding of plasma interactions with materials during CH4 reforming reactions. Quartz wool was found to enhance the conversion of CH4 and improve H2 yields as a result of changes in the physical properties of the discharge; electrical measurements showed an increase in the intensity of microdischarge filaments over quartz wool. In the presence of Al2O3 and zeolite 3A, the discharge intensity was reduced and consequently CH4 and CO2 conversions were lower for these materials. However, in the presence of zeolite 3A improved selectivities towards H2 and light hydrocarbons acetylene/ethylene were obtained and formation of liquid hydrocarbons was inhibited due to shape‐selectivity determined by the zeolite pore size.magnified image

Preparation and Characterization of Titania−Alumina Mixed Oxides with Hierarchically Macro-/Mesoporous Structures

A series of hierarchically macro-/mesoporous structured TiO2−Al2O3 mixed oxides with various molar ratios of Ti to Al was synthesized under different preparation conditions. The physical properties, that is, textural, morphological, and crystalline phase features of the prepared and calcined TiO2−Al2O3 materials were detailedly characterized by N2 adsorption−desorption, scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermal analysis techniques. The results showed that the preparation conditions, such as the solution pH, the water concentration, the molar ratio of Ti to Al, and the surfactant, can greatly influence the sizes of macropores and mesopores, the specific surface area, the pore volume, and the crystallization process of the mixed oxides. Calcination treatments of the prepared materials revealed their high thermal stability. The 800 °C calcined samples were thermally stable and retained the hierarchically macro-/mesoporous structure. Compared with pure TiO2 and pure Al2O3, the presence of Al2O3 in the TiO2−Al2O3 mixed oxides retarded the anatase-to-rutile phase transformation, while the incorporation of TiO2 promoted the formation of the α-Al2O3 phase in the mixed oxides. The hierarchically structured porous TiO2−Al2O3 materials had high potential applications as catalyst supports.

The features of the catalytic synthesis of methanethiol from dimethyl sulfide

The characteristic features of methanethiol synthesis from dimethyl sulfide and H2S in the presence of Al2O3 at atmospheric pressure and T = 320–500°C have been studied. It has been shown that the yield of methanethiol increases with an increase in the temperature, the H2S-to-dimethyl sulfide ratio, and the contact time, attaining equilibrium values. The methanethiol formation rate is proportional to the dimethyl sulfide partial pressure raised to a power of 0.4 and the H2S partial pressure raised to a power of 0.8. An increase in the specific surface area and the volume of transport pores and a decrease in the particle sizes of Al2O3 facilitate the augmentation of the catalyst activity in methanethiol formation. At T ∼ 400°C, a low H2S concentration, and a long contact time, the side reaction of dimethyl sulfide cracking occurs to result in the release of methane and the deposition of sulfur-containing and carbonaceous compounds on the surface, which lower the activity of alumina. The deactivated catalyst can be regenerated by oxidation.

Dispersive Micro Raman Backscattering Spectroscopy Investigation of Arc Discharge Synthesized CNTs Doped by Boron and Nitrogen

Raman scattering studies reveal the remarkable structure and the unusual electronic and phonon properties of carbon nanotubes. In this study, we directly produced boron, B, and nitrogen doped carbon nanotubes by using DC-arc discharge method which normally can be employed for producing carbon nanotubes. We performed experiments without using catalysts and in the presence of Ar gas for producing boron doped carbon nanotubes. At the second and third stages and in the presence of Al2O3 and MgO nanopowders as catalysts and nitrogen gas were used for producing nitrogen doped carbon nanotubes. In general, our investigation revealed that some major changes caused by B and N dopants can be observed in the related recorded Raman spectra. PACS numbers: 61.46.Fg, 63.22.Gh, 78.67.Ch, 81.07.De

Rim region growth and its composition in reaction bonded boron carbide composites with core-rim structure

Aluminum was detected in reaction-bonded boron carbide that had been prepared by pressureless infiltration of boron carbide preforms with molten silicon in a graphite furnace under vacuum. The presence of Al2O3 in the heated zone, even though not in contact with the boron carbide preform, stands behind the presence of aluminium in the rim region that interconnects the initial boron carbide particles. The composition of the rim corresponds to the Bx(C,Si,Al)y quaternary carbide phase. The reaction of alumina with graphite and the formation of a gaseous aluminum suboxide (Al2O) accounts for the transfer of aluminum in the melt and, subsequently in the rim regions. The presence of Al increases the solubility of boron in liquid silicon, but with increasing aluminum content the activity of boron decreases. These features dominate the structural evolution of the rim-core in the presence of aluminum in the melt.

ZnO/Al2O3 core–shell nanorod arrays: growth, structural characterization, and luminescentproperties

We report an aqueous chemical method to fabricate well-alignedZnO/Al2O3 nanocrystal (NC) core–shell nanorod arrays (NRAs). Structuralcharacterization showed that the shell layers are composed ofα-Al2O3 nanocrystals. Photoluminescence measurements showed the enhancementof near-band-edge (NBE) emission of ZnO NRAs due to the presence ofAl2O3 NC shells.The Al2O3 NC shell layer resulting in the flat-band effect near the ZnO surface leads to a strongeroverlap of the wavefunctions of electrons and holes in the ZnO core, further enhancing theNBE emission. This approach should be very useful in designing many othercore–shell NRAs for creating varieties of high-efficiency optoelectronic devices.

Surface Mediated Synthesis of Unsymmetrical O,O-dialkyl Alkyl Pyrophosphonates using Neutral Alumina: Potential Chemical Weapons Convention Related Compounds

The surface mediated synthesis of unsymmetrical O,O’- dialkyl alkyl pyrophosphonates from O-alkyl alkylphosphonic acid is described. These pyrophosphonates are listed in schedule 2B4 of Chemical Weapon Convention (CWC). The effect of the presence of chromatographic grade of Al2O3on the phosphorylation of a series of alkyl phosphonic acids has also been investigated. For phosphonic acids having different alkyl groups, it was observed that higher yields of the more hindered pyrophosphonates were formed in the presence of Al2O3. This method has an advantage over the conventional methods in terms of easy work-up, reduced reaction time and high yields.