Metal Oxide Nanopowders Research Articles

Effect of the chemical nature of metal oxide on adhesion to the polyacrylate matrix in filled nanocomposites

The morphology, particle size, and thermochemical properties of the surface of oxides Al2O3, NiO, TiO2, ZnO, and ZrO2 obtained by the wire electroexplosion method were studied. The nanoparticles are spherical, with a mean diameter of 54–86 nm depending on the nature of the oxide. The hydrophilicity of the surface of metal oxide nanopowders was found to change in the series NiO-ZrO2-TiO2-ZnO-Al2O3. Nanocomposites with widely varied compositions were obtained from butyl methacrylate copolymer with 5 wt % methacrylic acid and the oxides under study. The enthalpies of dissolution of the composites in chloroform were determined by Calvet calorimetry. The enthalpies of copolymer mixing with oxides were calculated using the thermochemical cycle. The limiting enthalpies of copolymer adhesion to the oxide surface were calculated from the thermochemical data. The limiting adhesion enthalpy was shown to be negative for all oxides under study; these values decreased in magnitude as the surface hydrophilicity increased. The results were analyzed from the viewpoint of balance between the specific and dispersion interactions at the interface.

A comparative experimental study on the natural convection heat transfer of different metal oxide nanopowders suspended in turbine oil inside an inclined cavity

An experimental study is conducted to investigate the effects of inclination angle on the natural convection of nanofluids inside a cubic cavity with the side size of 10cm. One of the surfaces of the cavity is kept in cold temperature and another one (opposite side) in hot temperature while the other four surfaces are insulated. The mixtures of three different types of nanoparticles including Al2O3, TiO2, and CuO within turbine oil (TO) are used as the heat transfer fluid. The heat transfer in the cavity is investigated in three inclination angles with respect to the horizontal position including 0°, 45° and 90° where the weight fractions of nanoparticles are 0.2%, 0.5%, and 0.8%. The Nusselt number results are presented for the three types of nanofluids, and different angles of inclination, Rayleigh number, and weight fraction of nanoparticles. The results reveal that the turbine oil has the highest Nusselt number in any inclination angle of the cavity compared to the nanofluids. Also, it is found that at the inclination angle of 90°, and the weight fraction 0.2%, the application of TiO2 particles results in the maximum Nusselt number while for weight fraction of 0.8%, the maximum Nusselt number is associated with the CuO nanopowders.

Semiconductor-Type MEMS Gas Sensor for Real-Time Environmental Monitoring Applications

Low power consuming and highly responsive semiconductor-type microelectromechanical systems (MEMS) gas sensors are fabricated for real-time environmental monitoring applications. This subsystem is developed using a gas sensor module, a Bluetooth module, and a personal digital assistant (PDA) phone. The gas sensor module consists of a NO2 or CO gas sensor and signal processing chips. The MEMS gas sensor is composed of a microheater, a sensing electrode, and sensing material. Metal oxide nanopowder is drop-coated onto a substrate using a microheater and integrated into the gas sensor module. The change in resistance of the metal oxide nanopowder from exposure to oxidizing or deoxidizing gases is utilized as the principle mechanism of this gas sensor operation. The variation detected in the gas sensor module is transferred to the PDA phone by way of the Bluetooth module.

Comparative study between metal oxide nanopowders on thermal characteristics of nanofluid flow through helical coils

Abstract Nanofluids and helical coils are two different techniques to enhance thermal performance of highly efficient heat exchangers. By combining these techniques together, energy efficiency of equipments could be increased dramatically. The present study is an experimental comparison of heat transfer behavior between metal oxide nanofluid flows through helical coiled tube with uniform heat flux boundary condition. Nanofluids with required volume concentration of 0.25–1.0% were prepared by dispersing specified amounts of Al 2 O 3 (35 nm) and TiO 2 (50 nm) nanoparticles and appropriate amount of surfactants in distilled water. The experiments covered a range of Reynolds number from 500 to 4500. Experimental results indicated that a considerable heat transfer enhancement is achieved by both nanofluids. In addition, because of greater thermal conductivity and smaller size of Al 2 O 3 nanoparticles compared to TiO 2 nanoparticles, Al 2 O 3 /water nanofluid showed better heat transfer augmentation. Moreover, due to the curvature of the tube when fluid flows inside helical coiled tube instead of straight one, convective heat transfer coefficient and the pressure drop of both nanofluids grew dramatically. Besides, experiments indicated that the effect of coil pitch spacing is to some extent weaker than the curvature ratio effect on the heat transfer rate. Finally, it was studied that the experimental and predicted results of Nusselt number and pressure drop held reasonable agreement.

Influence of Mg doping on the microstructure and PL emission of wurtzite ZnO synthesized by microwave processing

In this paper, we report the synthesis of nano-structured Zinc Oxide (ZnO) and Magnesium doped Zinc Oxide (ZnO:Mg) using air stable and inexpensive chemicals, by microwave assisted processing. The as-synthesized ZnO and ZnO:Mg nanopowders were annealed at 800 °C for 1 h. The samples were further characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and room temperature photoluminescence (PL) spectra. The crystallite size of ZnO decreased from 24 to 16 nm, and the intensity of most prominent vibration band of ZnO becomes weak when Mg dopant is added. SEM images of Mg doped ZnO showed clearly distinct hexagonal shaped nanoparticles with good crystalline quality and size contrast to ZnO. The PL result indicate that the ZnO exhibit strong and sharp UV emission peak at 380 nm. Our result showed that, by doping magnesium into ZnO, the UV emission peak shift towards the lower wavelength at ~370 nm with increasing intensity, which may be attributed to the size confinement. From this study, the microwave processing method has been proved to be successful for preparing other metal oxide nanopowders with good crystal quality.

Evidence for the Predominance of Condensed Phase Reaction in Chemical Looping Reactions between Carbon and Oxygen Carriers

This study investigates the use of metal oxides as an oxygen carrier in chemical looping combustion applications. The initiation and decomposition of C/CuO and C/Fe2O3 are investigated using a time-resolved T-jump/ time-of-flight mass spectrometer (T-Jump/TOFMS). Heating of the metal oxide nanopowders produces gaseous O2, but when mixed with the fuel (carbon), gaseous O2 forms temporally after the primary combustion product, CO2. This indicates condensed phase reaction between the metal oxide and carbon as the predominant reaction mechanism rather than gas phase release of O2 and subsequent burning of carbon, at least in the initiation phase. In situ heating TEM, and SEM are used to further investigate the reaction. The oxidation rate of carbon in the present experiment is estimated to be 3 to 5 orders of magnitude greater than that predicted using the Nagle Strickland-Constable model. The activation energy of C/CuO, C/Fe2O3, and C/Bi2O3 are determined using the Ozawa iso- conversion method and are found to be 110, 170, and 230 kJ/mol, respectively. The condensed phase nature of this reaction is compared to our previous studies on aluminum nanothermites and is considered to be further evidence toward a reactive sintering initiation mechanism.

Dielectric properties of nanopowder dispersions in paraffin oil

This work contributes to the study of nanofluids, by investigating polarization phenomena induced by nanoparticle inclusions in paraffin oil, an insulating organic liquid. Fine metal oxide powders and nanopowders of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , CuO, Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> were dispersed at concentrations up to 5% w/v in the liquid matrix, using ultrasonic treatment. The relative dielectric constant and loss tangent (tanδ) of both pure oil and the prepared nanofluids were recorded in the 20 Hz-1 MHz frequency range. Results depend both on grain size and on the specific compound. In the case of alumina nanoparticles, dielectric behavior is dominated by grain surface polarization phenomena induced by adsorbed water. This effect can be partially cancelled out by the addition of titania nanoparticles. Titanium and (to a lesser extent) ferric oxide increased the dielectric constant at middle and high frequencies. Cupric and cuprous oxides exhibit a distinct relaxation mechanism at the high end of the examined frequency range.

Production of Nanopowders of Metal Oxides Using Pulsed Electron Beam in Low Pressure Gas

The installation for production of metal oxide nanopowders was created. The method involves evaporation of the target by a pulsed-electron beam, condensation of the vapors of the material in a low-pressure gas, and deposition of nanopowders on a cold large-area crystallizer. In a new installation, a higher-power electron gun with a hollow cathode, which ensures the formation of the current pulse of the electron beam with amplitude up to 1 A and a duration of 100 μs, and a crystallizer of a larger diameter (0.3 m) and length (0.5 m), which makes it possible to decrease the agglomeration, were used. The results of the evaporation of targets made of YSZ, CeGdOx, Zn-ZnO, Al2O3, and ZnO were presented. Room-temperature ferromagnetism has been observed in YSZ, Zn-ZnO, and Cu(Al)-doped Al2O3. The proposed method makes it possible to obtain nanopowders of oxides with a characteristic particle size of 3–5 nm and agglomerates consisting of them 20–600 nm in size, specific surfaces of up 338 m2/g, productivity of up to 12 g/h, and a specific power consumption ≥112 (W h)/g.

Novel Ion‐Exchange Process for the Preparation of Metal Oxide Nanopowders from Sodium Alginate

A novel and generic sol–gel method has been developed for the production of high purity metal oxide nanopowders using sodium alginate. This has been demonstrated successfully employing nickel oxide (NiO) as a model material in this instance. The results of this investigation indicate that the final particle size of ~20 nm can be obtained after calcination of the predried beads at 500°C for 3 h in ambient air. An insight into the calcination process has been obtained using simultaneous thermo‐gravimetric analysis and differential scanning calorimetry (TGA/DSC) and high temperature X‐ray diffraction (HT‐XRD). Powder X‐ray diffraction (XRD) confirms that the obtained samples are single phase cubic NiO powders with no trace of impurity. During the phase transformation, NiO + NiO2 have been found to coexist between 250°C and 350°C and a reaction scheme is proposed to account for this. The mean crystallite sizes calculated from XRD analysis using Rietveld refinement method is in good agreement with the morphological features observed using transmission electron microscopy (TEM). The NiO nanopowders produced in this study exhibit negligible strain as indicated using Rietveld refinement procedure. The XRD and TEM analyses indicate that there is a significant influence of calcination temperature and time on the particle size, which increases with increasing temperature and annealing time. This new sol–gel method is a simple, environmentally friendly, and nontoxic route for a large scale production of high purity single phase nanopowders in a cost‐effective manner at significantly low temperatures. The process described in this study can yield 200 kg of NiO nanopowders per ton of dried Ni‐ALG beads.

Hydrothermal Synthesis of Rare-Earth Oxide Nanocatalysts for Automotive Exhaust Clean-Up

Three rare-earth metal oxide nanopowders (CeO2, PrO2, and TbO2) were synthesized using a facile hydrothermal method in a Teflon-lined autoclave. The rare-earth metal oxide nanocrystals with variable morphology were prepared by controlling the synthesis conditions with temperatures in the range of 70−220 °C. X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and temperature programmed reduction (TPR) were used to characterize the average structures and redox properties of these materials. Transmission electron microscopy (TEM) was used to investigate the morphology, particle size, and formation and growth mechanisms of the rare-earth metal oxide nanoparticles in solution-based environment.

Exciton Formation at Solid–Solid Interfaces: A Systematic Experimental and ab Initio Study on Compressed MgO Nanopowders

An important and so far neglected class of structural elements affecting the overall properties of metal oxide nanopowders are interfaces between individual nanocrystals. In this work, we show experimentally that these defects inside a powder of compressed MgO nanocubes are subject to photoexcitation in the UV light range. In particular, we identify a so far unobserved photoluminescence emission process at 2.5 eV. First-principles calculations of the optical properties of nanocrystal interfaces provide plausible candidates for both light absorbing and emitting sites, which involve different types of interface features. It was found that edge dislocations that arise from interfaces between nanocube edges and terraces induce a significant electrostatic perturbation of the interfacial electronic states. This leads to exciton generation and luminescence at even lower energies than those related to corners and edges of MgO nanocubes.

X-Ray micro-tomography of freeze dried nickel alginate beads and transformation into NiO nanopowders

A generic ion-exchange mediated sol–gel method has been developed for the production of high purity nickel and other metal oxide nanopowders using sodium alginate precursor. X-Ray micro-tomography (XMT) shows that the nickel ions have been uniformly cross-linked in the alginate structure and remained stable after freeze drying as evidenced by the bright green color of the freeze dried beads. The freeze dried nickel alginate beads exhibit a porous foam-like structure composing of a thin nickel alginate film and a dominant fraction of voids. The porous nickel alginate beads when calcined at 700 °C for 1 h in ambient air yielded spherical nickel oxide nanoparticles of ∼50 nm in size. Powder X-ray diffraction (XRD) confirms that the sample is single phase cubic NiO powders with no trace of impurity. The mean crystallite sizes calculated from XRD analysis using the Rietveld refinement method agree with the morphological features observed by transmission electron microscopy (TEM).

Nanocrystalline TiO2/SnO2 composites for gas sensors

TiO2/SnO2 nanocomposites are studied as potential candidates for gas sensors. Commercial metal oxide nanopowders milled for 1 h in ethanol are used for preparing nanocomposites with varied composition from 100 mol% TiO2 to 100 mol% SnO2. Brunauer–Emmett–Teller (BET) adsorption isotherms served to determine specific surface area, SSA. The particle size distribution is established by means of Dynamic Light Scattering, DLS technique. Differential Thermal Analysis and Thermogravimetry, DTA/TG measurements within the temperature range of 20–900 °C indicate better stability of nanomaterials composed of bigger particles or agglomerates. The total mass loss varies from 0.9 to 8.5% for 100 mol% SnO2 and 100 mol% TiO2, respectively. The only gaseous products of decomposition are water and carbon dioxide. X-ray diffraction analysis of nanocomposites indicates two separate phases of different crystallite size, i.e., smaller rutile TiO2 (9 nm) and larger cassiterite SnO2 (28 nm). Gas sensor dynamic responses at 400 °C to the reducing gas—ammonia (NH3) are detected in the concentration range extending from 100 ppm to −5000 ppm. Nanosensor of 50 mol% SnO2/50 mol% TiO2 is stable and sensitive to the interaction with NH3 and gives the highest response at 400 °C.

High‐Energy Al/CuO Nanocomposites Obtained by DNA‐Directed Assembly

AbstractOver the next few years, it is expected that new, energetic, multifunctional materials will be engineered. There is a need for new methods to assemble such materials from manufactured nanopowders. In this article, we demonstrate a DNA‐directed assembly procedure to produce highly energetic nanocomposites by assembling Al and CuO nanoparticles into micrometer‐sized particles of an Al/CuO nanocomposite, which has exquisite energetic performance in comparison with its physically mixed Al/CuO counterparts. Using 80 nm Al nanoparticles, the heat of reaction and the onset temperature are 1.8 kJ g−1 and 410 °C, respectively. This experimental achievement relies on the development of simple and reliable protocols to disperse and sort metallic and metal oxide nanopowders in aqueous solution and the establishment of specific DNA surface‐modification processes for Al and CuO nanoparticles. Overall, our work, which shows that DNA can be used as a structural material to assemble Al/Al, CuO/CuO and Al/CuO composite materials, opens a route for molecular engineering of the material on the nanoscale.

Production of nanopowders of metal oxides by evaporation in the pulsed electron beam

Based on practical experience, the installation for production of metal oxide nanopowders is updated. The method involves evaporation of the target by a pulsed electron beam, condensation of the vapors of the material in a low-pressure gas, and deposition of nanopowders on a cold large-area crystallizer. In a new installation, a higher-power electron gun with a hollow cathode, which ensures the formation of the current pulse of the electron beam with an amplitude up to 1 A and a duration of 100 μs, and a crystallizer of a larger diameter (0.3 m) and length (0.5 m), which makes it possible to decrease the agglomeration of nanoparticles, are used. The results of the evaporation of targets made of YSZ and CeGdOx are presented. The proposed method makes it possible to obtain nanopowders of oxides with a characteristic particle size of 3–5 nm and agglomerates consisting of them 20–600 nm in size, specific surfaces of up to 250 m2/g, productivity of up to 10 g/h, and a specific power consumption ≥120 (W h)/g.

Transition metal oxide nanopowder and ionic liquid: an efficient system for the synthesis of diorganyl selenides, selenocysteine and derivatives

We have developed an efficient method for the synthesis of diorganyl selenides and β-seleno amines using Zn, catalytic amounts of ZnO nanopowder, as a catalyst and ionic liquid as a recyclable solvent. This ZnO/ionic liquid system shows high efficiency in catalyzing these transformations with the formation of the desired products in high yields.

Fluidization enhancement of agglomerates of metal oxide nanopowders by microjets

AbstractThe quality of gas–solid fluidization of agglomerates of nanoparticles has been greatly enhanced by adding a secondary flow in the form of a high‐velocity jet produced by one or more micronozzles pointing vertically downward toward the distributor. The micronozzles produced a jet with sufficient velocity (hundreds of meters per second), turbulence, and shear to break‐up large nanoagglomerates, prevent channeling, curtail bubbling, and promote liquid‐like fluidization. For example, Aerosil R974, an agglomerate particulate fluidization (APF) type nanopowder, expanded up to 50 times its original bed height, and difficult to fluidize agglomerate bubbling fluidization (ABF) type nanopowders, such as Aeroxide TiO2 P25, were converted to APF type behavior, showing large bed expansions and homogeneous fluidization without bubbles. Microjet‐assisted nanofluidization was also found to improve solids motion and prevent powder packing in an internal, is easily scaled‐up, and can mix and blend different species of nanoparticles on the nanoscale. © 2009 American Institute of Chemical Engineers AIChE J, 2010

A Novel Approach for the Synthesis of Ti- and Zr-oxo Species as Precursors for Metal Oxide Nanopowder

ABSTRACT Thermal and microwave irradiation treatment of Ti(OPri)4 and Zr(OBu)4 leads to the formation of homogenous and transparent oxo-alkoxy derivatives of titanium and zirconium in a quantitative yield. The oxo-alkoxy derivatives were characterized with the help of FT-IR, NMR, UV, Raman, GC–mass spectroscopy, and elemental analysis. The physicochemical properties of gel differ considerably from their corresponding parent metal alkoxides. Hence, the gel can be considered as an immediate precursor for the preparation of functional metal oxide nanomaterials under mild conditions with control over particle size and its distribution, surface chemistry, and particle agglomeration. The morphology of the metal oxides strongly depends on the nature of the precursor and as well as synthetic methodology.

Comparative studies of the influence of different nano-sized metal oxides on the hydrogen sorption properties of magnesium hydride

The influence of the catalytic activity of metal oxide nanoparticles on the hydrogen sorption properties of nanocrystalline MgH 2 prepared by mechanical (ball) milling was investigated. The simple geometrical model nano-sized particles distributed on the surface of a micro-sized particle is presented. Some trends relating different geometrical features and densities for both powders are shown. With this model, the weight quantities of some metal oxide nanopowders were calculated, and their hydrogen absorption and desorption catalytic activities were compared. The commercial MgH 2 powder was mixed with the nanoparticles of different metal oxides (Cr 2O 3, TiO 2, Fe 3O 4, Fe 2O 3, In 2O 3, ZnO) and subsequently ball milled for 20 h in an inert atmosphere. The hydrogen absorption and desorption kinetics were evaluated using a volumetric Sievert's apparatus and characterized at 325 °C or 300 °C under 1 bar and 10 bar of hydrogen pressure during desorption and absorption, respectively. In both the absorption and desorption reactions, the superior catalytic effect of Cr 2O 3 and TiO 2 was observed. The catalytic effect of the investigated metal oxides is also expressed in the lowering of the activation energy of the dehydriding reaction. The decomposition enthalpies seem not to be affected by the introduction of nano-sized metal oxides.

Synthesis of WS2 and MoS2 fullerene-like nanoparticles from solid precursors

Inorganic fullerene-like WS2 and MoS2 nanoparticles have been synthesized using exclusively solid precursors, by reaction of the corresponding metal oxide nanopowder, sulfur and a hydrogen-releasing agent (NaBH4 or LiAlH4), achieved either by conventional furnace heating up to ∼900 °C or by photothermal ablation at far higher temperatures driven by highly concentrated white light. In contrast to the established syntheses that require toxic and hazardous gases, working solely with solid precursors permits relatively safer reactor conditions conducive to industrial scale-up.