Al2O3 Molecules Research Articles

The effects of Al (111) and Al2O3/Al (111) surfaces on the decomposition of ammonium perchlorate: A DFT-D study

Ammonium perchlorate (AP) is a crucial oxidizing agent in composite solid propellants, where aluminum (Al) is used as an additive to increase the energy density of composite solid propellants. The interaction between AP and Al significantly improves the ignition and combustion performance of propellants, but the mechanism of their interactions still lacks essential understanding, especially the interaction between AP and Al, as well as the Al surface containing aluminum oxide (Al2O3). To solve this problem, the adsorption and decomposition processes of AP and its decomposition products such as perchloric acid (HClO4) and ammonia (NH3) on the pure-Al (111) and Al2O3/Al (111) surfaces were studied by using the density functional theory (DFT). The effects of temperature and pressure on the adsorption and reactions were discussed. AP tends to adsorb on the pure-Al (111) surface with O-termination, while under the influence of Al2O3, AP is more inclined to adsorb on the surface of Al2O3/Al (111). At the low-temperature stage, the Al2O3 molecules on the surface of Al (111) promote the disengagement H of AP decomposition and the adsorption and decomposition of NH3, while at the high-temperature stage, the pure Al surface is more conducive to the AP disengagement H and NH3 decomposition. The increase in the pressure is in favor of NH3 adsorption, but the effect gradually decreases. HClO4 cannot adsorb on the pure-Al (111) and AP (001) surfaces, but it can adsorb on the surface of Al2O3/Al (111). In the gas phase, the decomposition of HClO4 priors to NH3. At the high temperature and pressure, the pure-Al (111) surface can contribute significantly to the adsorption and activation of NH3. The findings are very valuable for regulating the combustion of solid propellants.

Ultrasensitive Molecular Detection by Imaging of Centimeter-Scale Metasurfaces with a Deterministic Gradient Geometry.

Highly sensitive detection of trace amounts of substances is crucial for broad applications in healthcare, environmental monitoring, antiterrorism, etc., where cost effectiveness and portability are often demanded. Here, an ultrasensitive sensor is reported that can detect an angstrom-thick layer of adsorbed molecules through image acquisition and processing. The sensor features a centimeter-scale plasmonic metasurface with spatially varying geometry, where the light scattering is dependent on both the adsorbed substances and spatial locations. When illuminated with narrowband light (such as from a light emitting diode), the intensity pattern recorded on the metasurface changes with the surface-adsorbed molecules, enabling label-free, sensitive, and spectrometer-free molecular detection. The centimeter-scale size of the sensing area interfaces well with consumer-level imaging sensors on mobile devices without the need for microscopic optics and offers a high signal-to-noise ratio by leveraging the multimillion pixels for noise reduction. It is experimentally demonstrated that a single layer of Al2 O3 molecules deposited on the sensor, with a thickness of approximately one angstrom, can be detected by analyzing the images taken of the sensing chip. Furthermore, by integrating the sensor into a microfluidic setup, quantitative detection of BSA/anti-BSA immune complex formation events is demonstrated, which agrees well with the Langmuir isotherm model.

Defect Filling Method of Sensor Encapsulation Based on Micro-Nano Composite Structure with Parylene Coating.

The demand for waterproofing of polymer (parylene) coating encapsulation has increased in a wide variety of applications, especially in the waterproof protection of electronic devices. However, parylene coatings often produce pinholes and cracks, which will reduce the waterproof effect as a protective barrier. This characteristic has a more significant influence on sensors and actuators with movable parts. Thus, a defect filling method of micro-nano composite structure is proposed to improve the waterproof ability of parylene coatings. The defect filling method is composed of a nano layer of Al2O3 molecules and a micro layer of parylene polymer. Based on the diffusion mechanism of water molecules in the polymer membrane, defects on the surface of polymer encapsulation will be filled and decomposed into smaller areas by Al2O3 nanoparticles to delay or hinder the penetration of water molecules. Accordingly, the dense Al2O3 nanoparticles are utilized to fill and repair the surface of the organic polymer by low-rate atomic layer deposition. This paper takes the pressure sensor as an example to carry out the corresponding research. Experimental results show that the proposed method is very effective and the encapsulated sensors work properly in a saline solution after a period of time equivalent to 153.9 days in body temperature, maintaining their accuracy and precision of 2 mmHg. Moreover, the sensors could improve accuracy by about 43% after the proposed encapsulation. Therefore, the water molecule anti-permeability encapsulation would have broad application prospects in micro/nano-device protection.

Effect on combustion of oxide coating formed on aluminum nanoparticles burned in steam

A model of combustion of aluminum nanopowder in water vapor has been analyzed with allowance for the formation of a condensed phase of aluminum oxide on aluminum particles. Various processes affecting the growth rate of the oxide coating have been considered including adsorption and surface diffusion of Al2O3 molecules on aluminum particles, and condensation of the molecules on the oxide coating. Model calculations have yielded the time profiles of system temperature, phase and fractional composition, as well as the shape of oxide coated aluminum particles. The heterogeneous processes forming the condensed phase of aluminum oxide on Al particles have shown to increase heat generation in the system. On the other hand, shielding aluminum particles by oxide coating retards aluminum evaporation. The competition of these processes during the formation of oxide coating is one of the factors affecting the combustion of aluminum nanopowder in water vapor.

Influence of Al2O3 Nanoparticles Addition to AA6082-T6 on Mechanical Properties by Stir Casting Technique

The work aims at investigating the effects of the addition of Al2O3 nanoparticle as an enhancer on the mechanical characteristics of AA6082-T6 Metal Matrix Nano Composites (MMNCs) compounds. During the experiment, different weight fractions of Al2O3 nanoparticles (5, 10, 15, 20, 25, and 30 %) were added to molten AA6082-T6 using stir casting technique (SCT). Samples were formed at solidification and tested for mechanical properties, including the ultimate tensile strength (UTS), hardness (BHN), and density (ρ). Furthermore, the samples were evaluated for Yung’s coefficient (E) and yield strength (YS). From the results of the investigations, the developed method was found successful in ensuring the homogenous dispersion of the nanoparticles in the MMNCs. Increases in the proportion of the nanoparticles were found to increase the hardness (18.48%), density (15.89%), UTS (22.95%), Youngs modulus (27%), and YS (19.86%) while decreased were observed in the ductility (57.14%) as the proportion of the nanoparticles increases. Finally, Nano Al2O3 molecules were found to be a good material for the promotion of AA6082-T6 compounds.

A green and facile approach to the efficient surface modification of alumina nanoparticles with fatty acids

A general, green and facile approach to the efficient surface modification of alumina and other metal oxide nanoparticles with fatty acids have been proposed. In this process, only water was used as the dispersing medium, the modified metal oxide nanoparticles were automatically separated from water, and water can be recycled. The modification efficiency, using oleic acid as an example, of this water alone method was 36% higher than that of the water-ethanol method, which is a result of higher opportunity of interfacial reaction between oleic acid and Al2O3 molecules on the surface of alumina nanoparticles dispersed in water only. The modification efficiency increases with increasing chain length of the fatty acids. After modification with fatty acids, the crystalline structure of alumina remains unchanged, the agglomeration of alumina nanoparticles was largely reduced, and much better dispersion of modified alumina nanoparticles in organic matrix than the raw ones was achieved.

Effect of suboxides on dynamics of combustion of aluminum nanopowder in water vapor: Numerical estimate

The model of dynamics of combustion of a pre-prepared mixture of aluminum nanoparticles and water vapor under adiabatic conditions is considered and the results of numerical calculations are presented. The formation dynamics of the condensed phase of aluminum oxide (c-phase) in the form of aerosol particles is modeled with allowance for the homogeneous nucleation of Al2O3 molecules, and the processes of condensation, evaporation and coagulation. The condensation process is considered with participation of unstable Al2O3 gas molecules, and heterogeneous processes involving gaseous and adsorbed suboxides of aluminum: AlO, AlO2 Al2O2, and atomic oxygen. The participation of aluminum suboxides has been found to accelerate the combustion of aluminum. Besides, it increases the depth of aluminum burning and rises the final temperature of the process. The changes of temperature, phase composition, and concentrations of gaseous and adsorbed components during the combustion are reported. The mechanism of combustion and c-phase formation is detailed, and the mutual influence of reactions in the gas phase, heterogeneous reactions and the process of aerosol particle formation during combustion are analyzed.

On the interplay of chemical and physical processes during the combustion of aluminum in water vapor

A model is considered, and the results of numerical calculations of the dynamics of the combustion of pre-prepared gas mixtures of Al and H2O under adiabatic conditions are presented. The formation of the condensed phase is modeled taking into account the homogeneous nucleation of Al2O3 molecules and the processes of condensation, evaporation, and coagulation. The time dependences of the gas composition of the system, the concentration of aerosol particles, and their size distribution during the process are simulated. Details of the mechanism of the interplay of the gas-phase reactions and the formation of aerosol particles during aluminum combustion are discussed.

The role of new functional groups in the surface layer of LDPE during its high-voltage contact polarization

New functional groups containing Al-C bonds and Al2O3 molecules are formed in the surface layer of the polymer during depositing of aluminum on polyethylene films. This effect is absent when Au is deposited on the films. For capacitors with Al and Au electrodes, processes of high-voltage contact polarization and conductivity are studied at various configurations of the external electric field. If Al-C organometallic bonds and Al2O3 or, for example, Al-O-C bonds are formed in the surface layer during application of high electric fields, a number of dielectric “anomalies” are observed. They manifest themselves as the fact that an increase in the amount of cycles of a bipolar saw-tooth voltage is accompanied by a marked increase in the residual surface charge density. At such a configuration of the external field, a decrease in its frequency (for region, where dE/dt > 0) leads to a marked reduction in high-voltage dielectric permittivity to negative values. This phenomenon is explained by the fact that, along with the external field, an internal field appears owing to formation of the space charge near metal/polymer boundaries.

Accurate theoretical IR and Raman spectrum of Al2O2 and Al2O3 molecules

The accurate harmonic vibration frequencies together with the infrared (IR) and Raman intensities of the most stable conformers of Al2O2 and Al2O3 molecules have been calculated by the density functional theory (DFT) method with B3LYP exchange–correlation potential and using a set of the augmented correlated consistent basis sets up to quintuple order. The anharmonic vibration frequencies of the non-linear Al2O2 molecule have also been calculated. The obtained equilibrium geometrical parameters, harmonic and anharmonic vibration frequencies along with the IR and Raman intensities good converge to their limits with increasing the size of the used basis set. A comparison of the calculated harmonic and anharmonic vibrational frequencies with the available experimental ones points out that the small differences between the calculated harmonic and experimental frequencies can be further substantially reduced when calculations of the anharmonic vibrational frequencies will be available for all types of molecular geometries.

Properties of an Al2O3/Si interface

The phase chemical composition of an Al2O3/Si interface formed upon molecular deposition of a 100-nm-thick Al2O3 layer on the Si(100) (c-Si) surface is investigated by depth-resolved ultrasoft x-ray emission spectroscopy. Analysis is performed using Al and Si L 2, 3 emission bands. It is found that the thickness of the interface separating the c-Si substrate and the Al2O3 layer is approximately equal to 60 nm and the interface has a complex structure. The upper layer of the interface contains Al2O3 molecules and Al atoms, whose coordination is characteristic of metallic aluminum (most likely, these atoms form sufficiently large-sized Al clusters). The shape of the Si bands indicates that the interface layer (no more than 10-nm thick) adjacent to the substrate involves Si atoms in an unusual chemical state. This state is not typical of amorphous Si, c-Si, SiO2, or SiOx (it is assumed that these Si atoms form small-sized Si clusters). It is revealed that SiO2 is contained in the vicinity of the substrate. The properties of thicker coatings are similar to those of the 100-nm-thick Al2O3 layer and differ significantly from the properties of the interfaces of Al2O3 thin layers.

Thin Films of Silicon Nanoparticles Embedded in Al2O3 Matrices

Silicon nanoparticles embedded in a host matrix of Al2O3 thin film about 260 nm thick were prepared by using the pulsed laser deposition method. The laser target consisted of a small silicon wafer glued onto the surface of a circular Al2O3 plate, which was set to rotate uniformly when laser-ablating. TEM and EDS results showed that the films consisted of silicon nanoparticles in the form of nanocrystals with diameters of less than 6 nm dispersed in the amorphous Al2O3 matrices. Strong PL from the as-prepared and the annealed samples was observed. The SIMS depth profile of the silicon content of the film indicated that the silicon nanoparticles in the Al2O3 matrices were arranged in fairly well demarcated thin layers sandwiched between layers of the host material. FTIR results evidently suggested that the encapsulating amorphous Al2O3 material forms a good host for the prevention of atmospheric oxidation of the silicon nanoparticles. However, prolonged annealing can cause the silicon nanoparticle surface interfacing the host material to be oxidized by the oxygen mostly from the Al2O3 molecules and be bonded to the Al or O–Al bonds.

Sandwich-structured thin film of silicon nanoparticles embedded in Al2O3 matrices

Silicon nanoparticles embedded in the host matrix of anAl2O3 thin film, with a thickness of about 260 nm, were prepared byusing the pulsed laser deposition method. The laser target consisted of asmall silicon wafer glued onto the surface of a circular Al2O3plate, which was set to rotate uniformly when laser-ablating. TEM and EDSresults showed that the films consisted of silicon nanoparticles in theform of nanocrystals with diameters of less than 6 nm dispersed in theamorphous Al2O3 matrices. A secondary ion mass spectroscopy depthprofile of the silicon content of the film indicated that the siliconnanoparticles in the Al2O3 matrices were arranged in fairly welldemarcated thin layers sandwiched between layers of the host material.FTIR results evidently suggested that the encapsulating amorphousAl2O3 material forms a good host for the prevention of atmosphericoxidation of the silicon nanoparticles. However, prolonged annealing cancause the silicon nanoparticle surface interfacing the host material to beoxidized by the oxygen mostly from the Al2O3 molecules and to bebonded to the Al or O-Al bonds.