Aluminum Oxygen Research Articles

Characterization of the E1′ center in quartz: Role of aluminum hole centers and oxygen vacancies

The growth of E1′ centers in a variety of natural and synthetic quartz crystals has been investigated by employing the electron spin resonance technique. It has been reported that the growth of E1′ centers, formed by irradiation and subsequent annealing at 300 °C for 15 min, scale with the concentration of the aluminum hole center, [AlO4]0, till a limit. Later, the E1′ centers show saturation even when the [AlO4]0-center continues to grow. For quartz with low efficiency of the formation of [AlO4]0-center or irradiated with low accumulated doses, the intensity of E1′ center was small where not all oxygen vacancies are converted to the E1′ center. Thus, besides the availability of a number of oxygen vacancy sites, the number of holes released from the [AlO4]0-center plays an important role in the formation of E1′ centers in quartz.

A molecular dynamics simulation interpretation of neutron and x-ray diffraction measurements on singlephase Y2O3–Al2O3 glasses

Molecular dynamics simulations and complementary neutron and x-ray diffractionstudies have been carried out within the single phase glass forming range of(Y2O3)x(Al2O3)(100−x), forx = 27 and 30.For x = 27, the experimental Al–O and Y–O coordination numbers are found to be4.9 ± 0.2 and6.9 ± 0.4 respectively, compared to 4.4 and 6.8 obtained from the simulation. Similar results were found forx = 30.An R-factor analysis showed that the simulation models agreed to within∼6% of the diffraction data in both cases. The Al–O polyhedra are dominated by fourfoldand fivefold species and the Y–O local coordinations are dominated by sixfold,sevenfold and eightfold polyhedra. Analysis of the oxygen environments reveals alarge number of combinations, which explains the high entropy of single phaseyttrium aluminate glasses and melts. Of these, the largest variation betweenx = 27 and 30 is found in the number of aluminum oxygen triclusters (oxygens bonded to three Al) andoxygens surrounded by three Y and a single Al. The most abundant connections are between theAlOx andYOy polyhedra of which 30% are edge shared. The majority ofAlOx–AlOx connections were found to be corner shared.

Investigation of anti-corrosion behavior of waterborne organosilane–polyester coatings for AA6011 aluminum alloy

Thermal-cured, sol–gel derived, waterborne organosilane–polyester coatings (SiE) have been developed using methyltrimethoxysilane, 3-glycidoxytrimethoxysilane and polyester resin for corrosion protection of aluminum AA6011. The structural and morphological features of the coatings were analyzed by Fourier transform infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). Results show that the coatings on aluminum were smooth, continuous and defect-free. Performance of the SiE coatings were investigated and compared with pure organosilane coating and polyester coating using potentiodynamic polarization studies, contact angle measurement and pencil hardness test. Results from polarization studies have shown that the SiE coated substrate (4.6–13.1×10−7A/cm2) provided a better corrosion protection than the polyester coated substrate (7.8×10−6A/cm2) due formation of aluminum–oxygen–silicon covalent bond at aluminum-coating interface. Furthermore, SiE coatings provided better hydrophobicity and hardness than the polyester coating.

Effect of pressure on the refractive index and relative density of the CaO·Al2O3·6SiO2 glass

The refractive index for glass of the CaO · Al2O3 · хSiO2 system with х = 6 in the range of pressures up to 6.0 GPa was measured using a polarization-interference microscope and an apparatus with diamond anvils. The changes in the relative density characterizing the compressibility of glass were estimated from the measured refractive indices within the framework of the theory of photoelasticity. The data were compared with the previous data for glasses of the same system with х = 2 and 4. The most compressible of the three glasses in the range 2.0–6.0 GPa was the CaO · Al2O3 · 6SiO2 glass. For glasses with х = 2, 4 and 6 we calculated the degrees of polymerization of silicon–aluminum–oxygen network, NBO/T (NBO – non-bridging oxygen), which are determined as the ratio of the number of gram-ions of non-bridging oxygen atoms to the total number of gram-ions of network formers. The structure–chemical parameter NBO/T was calculated with due regard for the formation of triclusters and highly coordinated aluminum. The degree of polymerization of the CaO · Al2O3 · хSiO2 glasses increases with increasing х, which agrees with the change of their relative density under pressure.

Atmospheric pressure chemical vapor deposition mechanism of Al 2O 3 film from AlCl 3 and O 2

Aluminum oxide (Al 2O 3) films were deposited by atmospheric pressure chemical vapor deposition (AP-CVD) method from aluminum trichloride (AlCl 3), argon, and oxygen gas mixtures at temperatures ranging from 800 to 1000 °C. Alumina films with crystalline phases of γ- or θ-, and α-alumina were obtained starting at 800 °C. Increase in the relative amount of the α-phase as well as improvement in crystallinity is observed as temperature is increased to 1000 °C. The films have low chlorine content, which continued to decrease with increasing temperature. Analysis of the film growth rate on tubular substrates of varying diameters revealed a diffusion-limited growth from 800 to 950 °C and gas-phase reaction-limited growth at 1000 °C. The growth species is a cluster with size 1.2 nm at 800 °C and 0.9 nm at 950 °C. The gas-phase reaction constant at 1000 °C is 1.1/s.

Free oxygen ions and cage deformation in the nanoporous material 12CaO·7Al 2O 3: A temperature-dependent neutron powder diffraction study

Neutron powder diffraction was used to investigate the detailed structure of the novel nanoporous oxide 12CaO·7Al 2O 3 (C12A7) over a wide temperature range. The position of the free oxygen ion captured in the cage structure of C12A7 was confirmed to be displaced from the center of the cage as well as from the S 4 axis running through the two calcium ions at the top and the bottom of the cage. The calcium ions were also found to move off of the S 4 axis and shift toward the center of the cage when the free oxygen ion is present inside the cage. Examination of the structure revealed three types of aluminum–oxygen bonds which are characterized as short, medium and long. The distance between the free oxygen ion and the oxygen ion forming the longest bond with an aluminum ion becomes shorter as the temperature increases, suggesting promotion of exchange of the oxygen ions between the two sites. A possible migration path of the oxygen ion is examined from the obtained structural configuration.

Cellular detonations in bidispersed gas-particle mixtures

Formation of cellular detonation in bi-fractional stoichiometric mixtures of aluminum particles and oxygen is investigated numerically. The detonation cell size depends on the particle diameters and relative concentration of the fractions. Certain degeneration of cellular detonation is obtained when compared to the monodisperse mixtures. It is characterized by maximal pressure decrease, transverse wave relaxation and detonation front rectification. Complete degeneration of cellular detonations and stable propagation of a plane detonation front is found in some bi-fractional mixtures. The numerical results are confirmed by acoustic analysis of the detonation structures.

Spin Accommodation and Reactivity of Aluminum Based Clusters with O2

It is shown that spin accommodation plays a determining role in the reactivity of aluminum based anion clusters with oxygen. Experimental reactivity studies on aluminum and aluminum-hydrogen clusters show variable reactivity in even electron systems and rapid etching in odd electron systems. The reactivity of even electron clusters is governed by a spin transfer to the singlet cluster through filling of the spin down antibonding orbitals on triplet oxygen. Theoretical investigations show that when the spin transfer cannot occur, the species is unreactive. When spin accommodation is possible, more subtle effects appear, such as the required spin excitation energy, which raises the total energy of the system, and the filling of the antibonding levels of the O2 molecule, which is stabilized by becoming an aluminum oxygen pi bond. This explanation is consistent with observed behavior in oxygen etching reactions with a variety of clusters including AlnHm-, Aln-, AlnIm-, and AlnC-. The proposed reaction mechanism lends a physical interpretation as to why the HOMO-LUMO gap successfully predicts oxygen etching behavior of the considered systems.

Structure and chemical analysis of aluminum wear debris: Experiments and ab initio simulations

Sliding can produce severe plastic deformation and drive material far from equilibrium. Commonly, it also involves material transfer, mechanical mixing and formation of tribomaterial that influences both friction and wear. This paper describes aluminum wear debris generated by sliding in different environments. One portion of the debris is highly strained and another portion contains a large amount of oxygen, but not in the form of a simple oxide such as α-alumina. Annealing the debris allows strain relaxation, weight loss and changed electrical conduction characteristics. Characterization of debris before and after annealing suggests that the tribomaterial and the debris consist partly of an aluminum–oxygen solid solution and partly of hydroxylated material. These constituents are not normally formed in the absence of external forces. Quantum mechanical ab initio simulations were performed to complement the experiments. The simulations indicate that tetrahedral sites in aluminum are favored for oxygen in solid solution.

Molecular Modeling of Interactions between Ionic Liquids and Metal Surfaces

The interactions between metal surfaces and selected ionic liquids is examined in this report. The ionic liquids include a series of seven cationic imidazolium derivatives with PF6 as the anion. The tribological properties of these ionic liquids and their interactions with aluminum and steel are modeled using a smooth aluminum oxygen surface. The ionic liquids are placed above the aluminum oxygen surface and allowed to form a complex with this surface. Enthalpies of complex formation correlate with the tribological properties of the seven ionic liquids.

Combined experimental and theoretical study of small aluminum oxygen clusters

We report a combined experimental and computational investigation of small AlnOm species (n ≤20, m ≤ 12), produced in a laser vaporization cluster source. The oxygen content in the clusters was tuned by varying the oxygen concentration in the carrier gas. Ionization energies are bracketed using different ionizing photon energies in the energy range between 5.37 and 7.89 eV. Among the singly doped AlnO species, Al3O and Al15O are found to have relatively low ionization energies, which can be related to the magic character of the corresponding cations. Peculiarly low ionization energies also are observed for specific oxygen rich species (m > 1), suggesting the formation of ionically bound subunits. The structures and ionization energies of singly doped AlnO0,+ (n = 1 - 7) clusters were determined using density functional theory (B3LYP/6-311+G(d)).

Prediction of Al(OH) 3 fluidized roasting temperature based on wavelet neural network

The recycle fluidization roasting in alumina production was studied and a temperature forecast model was established based on wavelet neural network that had a momentum item and an adjustable learning rate. By analyzing the roasting process, coal gas flux, aluminium hydroxide feeding and oxygen content were ascertained as the main parameters for the forecast model. The order and delay time of each parameter in the model were deduced by F test method. With 400 groups of sample data (sampled with the period of 1.5 min) for its training, a wavelet neural network model was acquired that had a structure of ▪, i.e., seven nodes in the input layer, twenty-one nodes in the hidden layer and one node in the output layer. Testing on the prediction accuracy of the model shows that as the absolute error ±5.0 °C is adopted, the single-step prediction accuracy can achieve 90% and within 6 steps the multi-step forecast result of model for temperature is receivable.

Molecular modeling of ionic liquid tribology: Semi-empirical bonding and molecular structure

The interactions between selected ionic liquids and either an aluminum oxide or a silicon nitride surface are modeled in this report using semi-empirical methods. The ionic liquids include a series of seven cationic imidazolium derivatives with PF 6 − as the anion. The tribological properties of these ionic liquids and their interactions with aluminum and Al–steel alloys are modeled using a smooth aluminum oxygen surface. The ionic liquids are allowed to form a complex with this surface and the enthalpies of complex formation are seen to correlate with the tribological properties of the seven ionic liquids. The seven ionic liquids are also complexed with a hexagonal silicon nitride surface and their tribological properties are predicted on the basis of complex formation enthalpies.

Composition of alumina films grown on Si at low temperature with catalytic CVD

The X-ray photoelectron spectroscopy (XPS) measurements have been used to reveal the compositions of alumina (Al 2O 3) films formed on Si wafers using tri-methyl aluminium (TMA) and molecular oxygen (O 2) with catalytic chemical vapour deposition (Cat-CVD). The atomic ratio (O/Al) for Al 2O 3 samples formed at substrate temperature of 200–400 °C has been obtained to be 1.4 which is close to stoichiometry. The increase of growth rate at substrate temperatures below 200 °C and above 400 °C can be attributed to formation of aluminum oxides with non-stoichiometry and metallic aluminum incorporated in the films resulting from deficient oxygen. Angle resolved XPS measurements have revealed that the alumina/Si interface with no SiO 2 film has been obtained at substrate temperatures below 200 °C.

Electrical properties of alumina films grown on Si at low temperature using catalytic CVD

The electrical properties of alumina films formed at substrate temperatures as low as 27 °C using tri-methyl aluminum (TMA) and molecular oxygen (O 2) by catalytic chemical vapor deposition (Cat-CVD) have been investigated by capacitance–voltage ( C– V), current–voltage ( I– V) measurements and X-ray photoelectron spectroscopy (XPS). Substrate temperature dependence of dielectric constant and leakage current of the films has been explained on the basis of deficiency in oxygen. Interface trapping density of the order of 10 9 ev − 1 cm − 2 has been obtained. Angle resolved XPS measurements have revealed that the direct bonding of alumina and Si was realized with very small interface trapping density.

Coupling a PEM fuel cell and the hydrogen generation from aluminum waste cans

High purity hydrogen was generated from the chemical reaction of aluminum and sodium hydroxide. The aluminum used in this study was obtained from empty soft drink cans and treated with concentrated sulfuric acid to remove the paint and plastic film. One gram of aluminum was reacted with a solution of 2 mol dm - 3 of sodium hydroxide to produce hydrogen. The hydrogen produced from aluminum cans and oxygen obtained from a proton exchange membrane electrolyzer or air, was fed to a proton exchange membrane (PEM) fuel cell to produce electricity. Yields of 44 mmol of hydrogen contained in a volume of 1.760 dm 3 were produced from one gram of aluminum in a time period of 20 min.

Identification of tobacco genes encoding proteins possessing removal activity of 5-methylcytosines from intact tobacco DNA

Cytosines in eukaryotic DNA is often methylated to yield 5-methylcytosines (m 5 C), which play an important role in controlling gene expression. This is referred as DNA methylation, and its status dynamically changes during plant growth by active methylation and demethylation. DNA glycosylases have been known to possess base excision DNA repair activity, and an Arabidopsis enzyme, ROS1 (Repressor of Silencing 1), was recently shown to exhibit m 5 C DNA glycosylase activity. We isolated and characterized four genes encoding ROS1-like proteins from tobacco plants (Nicotiana tabacum), and designated as NtROS1, NtROS2a, NtROS2b and NtROS3, each respectively encoding a polypeptide with 1796, 1673, 1673 and 1662 amino acids. Purified NtROS1 and NtROS2a proteins expressed in Sf9 insect cells clearly exhibited activity of m 5 C removal from tobacco genomic DNA in vitro. GFP fusion assay showed that NtROS1 and NtROS2a were localized in nucleus. Transcripts of NtROS1, NtROS2a and NtROS3 were induced by abiotic stresses, including aluminium, salt and reactive oxygen species. These observations suggested that NtROS proteins function in demethylating process of genomic DNA during plant stress response, thereby maintaining the balance of gene expression in combination with DNA methyltransferases.

A diffusion-controlled mullite formation reaction model based on tracer diffusivity data for aluminium, silicon and oxygen

This paper compiles all the data from our tracer diffusivity studies in single crystalline 2/1-mullite. As tracers we used the rare stable isotopes 18O and 30Si and the artificial pseudo-stable isotope 26Al. Secondary-ion mass spectrometry was applied to analyze the depth distribution of the tracer isotopes after the diffusion annealing. An essential result of our tracer diffusivity studies was the very low diffusivity of 30Si compared to the diffusivities of 26Al and 18O, which are almost equal. Based on this observation, we propose a reaction model for the diffusion-controlled formation of mullite in the solid state, which assumes that the growth kinetics of a mullite layer is mainly controlled by the diffusion of aluminium ions and oxygen ions.

Organometallic vapour deposition of crystalline aluminium oxide films on stainless steel substrates

The organometallic vapour deposition of aluminium oxide films in a cold wall reactor was studied at temperatures between 773 and 1273 K and the pressure range of 55–1000 hPa. Aluminium acetylacetonate and oxygen were used as precursors. All films were characterized by scanning electron microscopy, electron dispersive X-ray spectroscopy and X-ray diffraction. Film growth at low pressure (55 hPa) was analyzed as a function of the deposition temperature: It is mainly surface kinetically controlled, and films grown at low temperatures (< 1073 K) are amorphous and transparent, while those grown at 1273 K are dark and crystalline. Thereby the latter ones consist of different phases: γ-Al 2O 3, θ-Al 2O 3, and α-Al 2O 3. These crystalline films are spalling. In addition, the influence of the total pressure on the deposition was studied for high deposition temperatures (1273 K): Film growth was significantly faster at pressures below 300 hPa. Additionally, a phase change is observed with increasing pressure: Films deposited at 55 hPa consist of three phases, γ-Al 2O 3, θ-Al 2O 3, and α-Al 2O 3, whereas above 200 hPa mainly the latter two phases are observed. Films grown at high pressures above 200 hPa are better adhering.

Calculation of the relative stability of molecular alumoxanes

Calculations have been performed on a series of alumoxane rings and cages having the formula [HAlO] n ( n = 2–10). Results from these calculations are in excellent agreement with previous calculations on methyl alumoxane rings and cages and experimental structures of organic alumoxane rings and cages. Optimized aluminum–oxygen bond lengths of both rings and cages were found to increase with decreasing stability of these compounds. Comparison of the calculated IR spectra for all of these cages with the experimental spectra of methyl alumoxane (MAO) catalyst suggests that the structure of MAO is composed of large cages containing both four- and six-membered rings.