Al2O3and TiO2 Research Articles

Comprehensive phenotyping and transcriptome profiling to study nanotoxicity inC. elegans

Engineered nanoparticles are used at an increasing rate in both industry and medicine without fully understanding their impact on health and environment. The nematode Caenorhabditis elegans is a suitable model to study the toxic effects of nanoparticles as it is amenable to comprehensive phenotyping, such as locomotion, growth, neurotoxicity and reproduction. In this study, we systematically evaluated the effects of silver (Ag) and five metal oxide nanoparticles: SiO2, CeO2, CuO, Al2O3 and TiO2. The results showed that Ag and SiO2 exposures had the most toxic effects on locomotion velocity, growth and reproduction, whereas CeO2, Al2O3 and CuO exposures were mostly neurotoxic. We further performed RNAseq to compare the gene expression profiles underlying Ag and SiO2toxicities. Gene set enrichment analyses revealed that exposures to Ag and SiO2consistently downregulated several biological processes (regulations in locomotion, reproductive process and cell growth) and pathways (neuroactive ligand-receptor interaction, wnt and MAPK signaling, etc.), with opposite effects on genes involved in innate immunity. Our results contribute to mechanistic insights into toxicity of Ag and SiO2 nanoparticles and demonstrated that C. elegans as a valuable model for nanotoxicity assessment.

Fireworks: How to Simulate the Manufacture and Operation in the Atmosphere with the Substitution of Ultrasonic Spray Pyrolysis

Background: This review provides a closer look at recent work in the field of fireworks manufacture, which could see the replacement of micron-sized particles with their nano-scaled counterparts. Moreover, we also discuss micron-sized particles as well as nanoparticles (NPs) from K, Fe, Al, Ti, Ba, etc., that are produced in the atmosphere as a result of these fireworks. One of the possible technological substitutes for fireworks is presented in detail, i.e., the use of ultrasonic spray pyrolysis (USP) technology. Method: We searched Google, Web of Science and PubMed for a literature survey of fireworks and their products: firecrackers, micron-sized and nanoparticles. Moreover, we used some of our own knowledge and experimental data to strengthen the possibility of simulating the synthesis of firework products on the laboratory scale. Results: The use of nano reactants and oxidisers has seen a substantial increase in the sound efficiency and a decrease in the amount of chemicals used, making fireworks more eco-friendly. The application of Al- and Ti-based nano flash powder in the size range from 35 nm to 50 μm resulted in a significant improvement in the ignition properties of the fireworks. Under changing aerodynamic conditions, it is difficult to collect them as samples for real-time monitoring, needed for their characterization or the testing of their harmfulness under laboratory conditions. As a result, NPs below 100 nm in the surroundings could be easily inhaled into the lungs and cause more pulmonary and respiratory problems than micron-sized particles. USP produces nanoparticles in the laboratory that could replace the conventional micron-sized firecracker raw materials, or nanoparticles that are similar to those formed by fireworks. It will also help to identify the physiochemical properties of the airborne particulates in order to understand and evaluate their impact. This review could be valuable for a controlled economic synthesis through USP, and in the use of nanopowders in pyrotechnology that could reduce pollution to a great extent, thus contributing to the growth and good practise of the fireworks industry. With respect to the USP synthesis, we have also discussed in detail the physical (size, shape) and chemical (composition) characteristics of Al2O3 and TiO2 NPs from different precursors and their temperature ranges. An in-depth explanation for a comparative analysis for the formation mechanism of nanoparticles through both fireworks and USP is presented in the final section. Conclusion: We can produce nanoparticles in the laboratory with ultrasonic spray pyrolysis that have similar properties to those produced from fireworks and can then be used for further testing.

Insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor devices with Al2O3 or AlTiO gate dielectrics

We have investigated insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor (MIS) devices with Al2O3 or AlTiO (an alloy of Al2O3 and TiO2) gate dielectrics obtained by atomic layer deposition on AlGaN. Analyzing insulator-thickness dependences of threshold voltages for the MIS devices, we evaluated positive interface fixed charges, whose density at the AlTiO/AlGaN interface is significantly lower than that at the Al2O3/AlGaN interface. This and a higher dielectric constant of AlTiO lead to rather shallower threshold voltages for the AlTiO gate dielectric than for Al2O3. The lower interface fixed charge density also leads to the fact that the two-dimensional electron concentration is a decreasing function of the insulator thickness for AlTiO, whereas being an increasing function for Al2O3. Moreover, we discuss the relationship between the interface fixed charges and interface states. From the conductance method, it is shown that the interface state densities are very similar at the Al2O3/AlGaN and AlTiO/AlGaN interfaces. Therefore, we consider that the lower AlTiO/AlGaN interface fixed charge density is not owing to electrons trapped at deep interface states compensating the positive fixed charges and can be attributed to a lower density of oxygen-related interface donors.

Optical Response of High-Density Solid Micro- & Nano-Particles in Turbulent Flows

Optical Visualization Techniques are gaining steady ground as a much favored method for observing and recording the physics of complex flows. These methods use a solid particle dispersed into the concerned flow to analyze the fluid motion. The particles are assumed to be of spherical shape (an acceptable relaxation), wherein the diameter is assumed to be constant this means that the particles have a normal distribution of size, with a sharp peak at the given diameter. Scattering of high-frequency laser light by these particles is the basis of image formation which depicts the flow physics. The fluid phase, which is the carrier phase, is required to impart sufficient momentum to the particulate phase for the particles to trace the flow of the fluid. For this reason, the particles are required to be of sizes not greater than 100 microns, in keeping with the increasing density with size. Alumina and Titania (Al2O3and TiO2) are the most commonly employed seed particles for this purpose. Laser scattering is also dependent on the luminescence prop-erties of the seed particles interactions between particle luminescence and external illumination plays a major role in determining the quality of results. With time, porous particles and artificial materials have found their acceptable places for use in this field. Silica, Glass and Ceramics provide a good balance of density (or weight) and surface area, which is difficult to obtain in metallic particles. The present paper proposes to evaluate the optical response characteristics of dispersed particles vis-a`-vis the operating/flow conditions and the laser systems used. The flow regimes com-monly considered for such studies include turbulence, mixing, reactions, phase changes and so on. Keywords Optical Response; Flow Seeding; Visualization; Multi-phase Flow: Flow Regimes; Particle Dispersion; Laser Diagnostics

Extractive-Pyrolytic Method for Au/MeO<sub>x</sub> Nanocomposites Production

Au/MeOx(MeOx- SiO2, Al2O3and TiO2) nanocomposites have been produced by the extractive-pyrolytic method. An organic extract – a solution of n-trioctylammonium tetrachlorolaurate ([Oct3NH]AuCl4) in toluene – was used as a gold-containing precursor. The produced samples were analyzed by IR spectroscopy, X-ray diffraction and scanning electron microscopy. The performed studies have shown that the mean size of the metal crystallites vary within wide limits: on Al2O3from 60 nm to 35 nm; on SiO2from 33 nm to 23 nm; on TiO2from 50 nm to 13 nm.

High Temperature Oxidation Behaviour of Nickel Based Nanostructured Composite Coatings

The electrodeposition of nanostructured composite coatings involves the co-deposition of nanosized oxide particles such as TiO2, Al2O3 and Y2O3 into a corrosion resistant metal matrix such as nickel to improve the high temperature oxidation and erosion resistance of nickel coatings. The technique has several advantages over other methods for producing nanostructured composite coatings such as thermal metal spraying. Some of the main advantages are lower cost for equipment setup and lower material cost and the ease with which the process can be controlled. Although electrodeposited nanostructured coatings are being developed for various aerospace and marine applications, they have not yet been considered for protecting surfaces of components and piping that is used in technologies for the oil sands industry such as the In-Situ Combustion (ISC) process. The challenge with in-situ combustion oil production is that the combination of high temperature combustion gases and the presence of moving sand particles create an extremely severe environment in which high oxidation and erosion rates are expected. As a result there is a need to develop function specific coatings that can withstand both high temperatures and erosive environments in the oil sands industry. This paper presents results of high temperature oxidation behaviour of nickel coatings containing two types of nanosized oxide dispersions (TiO2 and Al2O3). High temperature oxidation tests were conducted in dry air for 500°C and 700°C. The oxidized specimens were examined by metallographic surface analysis and surface composition techniques such as Scanning Electron Microscopy (SEM), Wavelength Dispersive X-Ray Spectroscopy (WDS). The effects of nanosized oxide particles on high temperature oxidation behavior of nickel coatings have been studied. The results show an improvement in the high temperature oxidation resistance of nickel coatings dispersed with Al2O3 and TiO2.

Surface Analyses of High-Temperature Oxidized <i>In Situ</i> Synthesized Ti-40Al-2.0C Composites

With the reaction between titanium (Ti) sponge, high purity aluminum (Al) and TiC/Al inter-alloy, non-consumable arc melting technique has been successfully used in situ synthesize Ti matrix composites of Ti-40Al-2.0C. The composites oxidized at 700~900°C for different time in static air. The influences of oxidation time and temperature to oxidation kinetics of composites were analyzed. The surface morphologies and components of the oxidation scales were examined by scanning electron microscope (SEM) with energy dispersive spectrometer (EDS). The results show that the isothermal oxidation kinetic curves of composites mainly follow parabolic rate law. When the composites oxidized at low temperature for short time, the color of oxidation surface is olivine which is similar to the color of the matrix and the oxides exist in non-uniform mixture state of Al2O3 and TiO2. While the composites oxidized at high temperature for long time, the color of oxidation surface is deep yellow and the oxides are mainly columnar hexagonal TiO2.

High Temperature Oxidation Behavior of (Ti, Al) C Ceramic Coatings on Carbon Steel Prepared by Electrical Discharge Coating in Kerosene

Multi-component metal ceramic coating（Ti, Al）C was prepared on the 0.45% carbon steel by electrical discharge coating (EDC) in a hydrocarbon medium. The coating of the samples before and after oxidation was analyzed by different methods including X-ray diffraction (XRD), scanning electron spectroscopy (SEM) and energy disperse spectroscopy (EDS).The thermogravimetric technique was used to approximate the kinetics of oxidation of the coated and the uncoated samples.The results indicated that the thickness of the coating was about 20μm, and the composition of the ceramic coating mainly consisted of (Ti, Al) C and a little Ti3AlC. An oxide film with compact structure formed after 600°C oxidation for 200h, and it was mainly composed of Al2O3and TiO2, which inhibited further oxygen diffusion into the coating. The (Ti, Al) C ceramic coating possessed slow oxidation rate and high temperature oxidation resistance.

Characterization of supported rhenium oxide catalysts: effect of loading, support and additives

The nature of the surface rhenium oxide species present in supported rhenium oxide catalysts was determined as a function of the oxide support, rhenium oxide loading and secondary metal oxide additives. The catalysts were prepared using the incipient wetness impregnation method with dilute aqueous perrhenic acid as the precursor and characterized using Raman, FTIR and X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) experiments. The Raman and XPS studies reveal that the surface rhenium oxide species are well dispersed on the Al2O3 and TiO2 supports. Under dehydrated conditions, Raman and IR studies reveal that the surface rhenium oxide species is independent of oxide support (Al2O3 and TiO2) and it appears that the same isolated rhenium oxide species is formed for all loadings. The structural details of this dehydrated isolated rhenium oxide species are, however, not clear. TPR measurements suggest that the reducibility of the surface rhenium oxide species depends strongly on the specific oxide support: the surface rhenium oxide species on TiO2 is more reducible than the surface rhenium oxide species on Al2O3 . The difference in reducibility is related to the bridging Re–O–support bond strength. The secondary metal oxide additives, sodium and vanadium, can be categorized as interacting and non-interacting, respectively. The non-interacting additive (vanadium oxide) coordinates directly to the oxide supports without significantly affecting the structure and reducibility of the surface rhenium oxide species. The interacting additive (sodium oxide), however, directly coordinates with the surface rhenium oxide species and changes its structure and hydrogen reducibility.