Al2O3 Compounds Research Articles

Inclusions, microstructure and properties of flux copper backing submerged arc weld metal

This paper investigates the effect of Ce on inclusions, microstructure and mechanical properties of the weld metal in flux copper backing submerged arc welding. The results show, with the addition of Ce in weld metal, the inclusions are mainly composed of Al2O3, MnO, SiO2, TiO, Ce2S3, CeS and Ce2O2S compound, and the proportion of the inclusions of < 1.0 μm in size increased. In competitive nucleation, acicular ferrite nucleates on the oxysulphides of Ce and inhibits the formation of proentectoid ferrite and ferrite side plate. This led to a high proportion of acicular ferrite, good mechanical properties of weld metal. A small lattice disregistry between CeS, Ce3S4, Ce2O2S and acicular ferrite contributed to low energy for nucleation of acicular ferrite.

THERMODYNAMICS OF OXYGEN SOLUTIONS AT COMPLEX DEOXIDATION OF THE Fe-Co MELTS

A method for thermodynamic analysis of complex deoxidation process of metallic melts is proposed. This method allows to determine the effect of a weaker element-deoxidizer on increasing deoxidizing ability of a stronger element-deoxidizer. Oxygen solubility curves pass through a minimum. Analysis of the equation of dependence of the concentration of oxygen in the melt on the elements-deoxidizers contents for the presence of extremum possible to obtain an equation for determining the content of a stronger element-deoxidizer, wherein the oxygen concentration is the lowest. A thermodynamic analysis of the joint infl uence of aluminum and silicon on the solubility of oxygen in the melts of Fe – Co system has been performed. Deoxidation reaction products may be formed as mullite (3Al2O3·2SiO2 ) and kyanite (Al2O3·SiO2 ). The presence of silicon in the melt enhances the deoxidizing ability of aluminum: insignificantly in the case of formation of compound 3Al2O3·2SiO2 and significantly in the case of formation of compound Al2O3·SiO2 . Oxygen solubility curves in the case of formation of compound Al2O3·SiO2 pass through a minimum, the position of which depends on the content of aluminum in the melt and is not dependent on the silicon content. The aluminum content in the minimum points is insignificantly reduced from iron to cobalt as in the case of melts of Fe – Co – Al. Further additives are aluminum leads to an increase in oxygen concentration. Areas of compounds Al2O3 , 3Al2O3·2SiO2 , Al2O3·SiO2 and SiO2 depending on aluminum and silicon contents in the melt are determined.

Reconfigurable Digital Circuits Based on Chip Expander with Integrated Temperature Regulation

This article is dealing with a development of custom chip expander platform with the possibility of accurate temperature control and integration of additional silicon-based features. Such platform may serve as a useful tool which facilitates the burdens connected with measurement and analysis tasks of experimental semiconductor structures. The devised solution provides the functionality of carrier substrate (Al2O3 compound) with CTE compatibility to the experimental silicon chip and is fully customizable with respect to a particular chip. It also allows achieving an easy fan-out of small-diameter chip terminals into a larger, more convenient area and placement of chip specimens conveniently into space-constrained chamber of the AFM microscopes, probe stations, etc. Real application of the developed chip expander platform is demonstrated in context of digital reconfigurable circuits based on polymorphic electronics. In this case the chip expander with attached polymorphic chip REPOMO is thermally stabilized at an ambient temperature level up to approximately 135。C and its sensitivity to this phenomenon is demonstrated.

Thermodynamic modeling of the CaO–CaF2–Al2O3 system aided by first-principles calculations

The CaO–CaF2, Al2O3–CaF2, and CaO–CaF2–Al2O3 systems are modeled using the CALculation of PHAse Diagram (CALPHAD) approach. The liquid phase is described by a two-sublattice ionic model (Al+3, Ca+2)p(F−, O−2, AlO3/2)q. The compounds Al2O3, CaF2, and CaO are treated as stoichiometric phases. The Gibbs energy of formation of (CaO)11(Al2O3)7(CaF2) is predicted by means of first-principles calculations. Phase diagrams of the CaO–CaF2 and Al2O3–CaF2 quasibinaries as well as the isothermal and vertical sections and the liquid surface projection of the CaO–CaF2–Al2O3 system are calculated, showing favorable accord with available experiments in the literature.

Low-Temperature Densification Sintering and Properties of Monoclinic-SrAl2Si2O8 Ceramics

The dense monoclinic-SrAl2Si2O8 ceramics have been prepared by a two-step sintering process at a sintering temperature of 1173 K (900 °C). Firstly, the pre-sintered monoclinic-SrAl2Si2O8 powders containing small SiO2·Al2O3 crystal phases were obtained by continuously sintering a powder mixture of SrCO3 and kaolin at 1223 K (950 °C) for 6 hours and 1673 K (1400 °C) for 4 hours, respectively. Subsequently, by the combination of the pre-sintered ceramic powders with the composite flux agents, which are composed of a SrO·3B2O3 flux agent and α-Al2O3, the low-temperature densification sintering of the monoclinic-SrAl2Si2O8 ceramics was accomplished at 1173 K (900 °C). The low-temperature sintering behavior and microstructure evolvement of the monoclinic-SrAl2Si2O8 ceramics have been investigated in terms of Al2O3 in addition to the composite flux agents. It shows that due to the low-meting characteristics, the SrO·3B2O3 flux agent can urge the dense microstructure formation of the monoclinic-SrAl2Si2O8 ceramics and the re-crystallization of the grains via a liquid-phase sintering. The introduction of α-Al2O3 to the SrO·3B2O3 flux agent can apparently lead to more dense microstructures for the monoclinic-SrAl2Si2O8 ceramics but also cause the re-precipitation of SiO2·Al2O3 compounds because of an excessive Al2O3 content in the SrO·3B2O3 flux agent.

Thermodynamics of oxygen solutions in the complex reduction of Fe-Co melts

Thermodynamic analysis of the complex reduction of metal melts is considered. The proposed analytical method identifies the influence of the weaker reducing agent in amplifying the effect of the stronger reagent. The curves of oxygen solubility pass through a minimum. Analysis of the extremal curves of oxygen concentration in the melt as a function of the content of reducing agents yields a formula for the content of the stronger reducing agent such that the oxygen concentration is minimal. Thermodynamic analysis of the combined influence of aluminum and silicon on the oxygen solubility in Fe-Co melts indicates that the reaction products may contain both mullite (3Al2O3 · 2SiO2) and kyanite (Al2O3 · SiO2). The presence of silicon in the melt intensifies the reducing action of aluminum: slightly when mullite is formed and significantly when kyanite is formed. When kyanite is formed, the curves of oxygen solubility pass through a minimum, whose position depends on the aluminum content in the melt but not on the silicon content. The aluminum content at the minimum declines slightly from iron to cobalt, as for Fe-Co-Al systems. Further addition of aluminum elevates the oxygen concentration. The formation of the compounds Al2O3, 3Al2O3 · 2SiO2, Al2O3 · SiO2, and SiO2 is investigated as a function of the Al and Si content in the melt.

English

In this paper, thirty-nine phases in the Ti-Al-O system at high temperatures have been analyzed through thermodynamic calculations. A Ti-Al-O isothermal stability diagram was obtained from the thermochemical data. The diagrams described the equations for Ti/Al intermetallic compounds at Al2O3/TixAly and Al2O3/TiAl2O5 interfaces, and their corresponding regions. Four univariant equilibria points and ten bivariant equilibria lines at 1000 K were obtained. The equations for the coexistence points and interface lines were also obtained. A three-domain diagram of Ti-Al-O phase arrangement at temperatures between 1000 K and 1200 K was shown. Thermodynamic calculations confirmed that the formation of titanium aluminate spinel (TiAl2O5) requires a threshold TiO2 activity and a partial pressure of oxygen. In the Ti-Al-O system, when aTiO2 &lt; 0.121 and log PO2 &lt; –47.2 atm, TiAl2O5, TiO2, and Al2O3 compounds are not formed at 1000 K; while at the Ti/Al interfaces, compounds are formed in the order of Ti3Al(s) → TiAl(s) → TiAl2(s) → TiAl3(s).

Shock Induced Reaction of Ni/Al Nanopowder Mixture

Nanopowder Ni/Al mixture (mixed in Al:Ni = 2:1 stoichiometry) was shock compressed by employing single and two-stage light gas gun. The particle size of Al and Ni are 100-200 nm and 50-70 nm respectively, morphologies of Al and Ni are sphere like either. Recovered product was characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. According to the XRD spectrum, the mixed powder undergo complete reaction under shock compression, reaction product consist of Ni2Al3, NiAl and corundum structure Al2O3 compound. Grain size of Ni-Al compound is less than 100 nm. With the shock pressure increasing, the ratio of Ni2Al3 decreased obviously. The corundum crystal size is 400-500 nm according to the SEM observation. The results of shock recovery experiments and analysis show that the threshold pressure for reaction of nano size powder Ni/Al mixture is much less than that of micro size powder.

Physico-chemical processes occurring during polymerization of liquid polydimethylsiloxane films on metal substrates under atmospheric pressure air corona discharges

In this paper we investigated by different complementary methods the processes occurring in the polymer layers bulk and at the polymer/substrate interface during the polymerization of liquid films of polydimethylsiloxane lying on the surface of a solid aluminum respectively titanium substrate under atmospheric pressure air corona discharges.The infrared spectroscopy, Glow Discharge Optical Emission Spectrometry and Plasma Profiling Time of Flight Mass Spectrometry investigations show the presence of Al2O3 and aluminosilicates type compounds at the polymer-substrate/interface and their linkage to the polymers chains by SiOAl bonds. By coupling the spectral results with those obtained by Scanning Electron Microscopy investigations we evidenced the formation of silicon oxide structures preponderantly on the free surface of the polydimethylsiloxane layers but also in the polymer bulk deposited on aluminum respectively titanium substrates.

Laser hole cutting in aluminum foam: Influence of hole diameter on thermal stress

Laser cutting of aluminum foams avoids structural damages, which can be observed during mechanical cutting process. High thermal stresses can be formed in the laser cut sections due to high temperature gradients while limiting the practical applications of parts. In the present study, laser cutting of 2mm and 8mm diameter holes into aluminum foam is carried out. Geometrical changes in the cut section are examined using optical and scanning electron microscopes and oxide compounds formed at the kerf surface are identified by X-ray diffraction. Temperature and stress fields are predicted numerically in the cut section in the line with the experimental conditions. It is found that defect free cutting of small diameter holes is possible in 8mm thick aluminum foam. Air trapped in the pores prior to laser cutting undergoes oxidation reactions with molten material while resulting in forming of Al2O3 and AlO compounds at the cut surfaces. von Mises stress predicted for 2mm diameter hole is almost 3 times higher than that corresponding to 8m diameter hole.

Mechanochemical Behavior of NiO-Al-Fe Powder Mixtures to Produce (Ni, Fe)3Al-Al2O3 Nanocomposite Powder

Mechanical treatment of Fe2O3, Al and Fe powder mixtures was carried out in a high energy ball mill to synthesize Fe3Al–Al2O3 intermetallic matrix nanocomposite. Different compositions including 3Fe + Al, Fe2O3 + 2Al, 3Fe2O3 + 8Al and Fe2O3 + 3Al+Fe were chosen in this study. Phase development and structural changes occurring during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during MA, Fe2O3, Al, and Fe react to give a nanocrystalline Fe3Al intermetallic compound matrix. The presence of pure Fe in initial powder mixture changed the modality of mechanochemical process from sudden to gradual reaction. The Fe3Al–Al2O3 compound had a finer microstructure and particles size compared to the Fe3Al compound.

Structural and mechanical properties of Au alloyed Al[sbnd]O sputter deposited coatings

This paper is focused on the sputtering process and on the structure, chemical composition and mechanical properties of coatings consisting of AlO dielectric matrix incorporated with increasing Au contents. The maximum Au content incorporated in the coatings was 9at.%. Al was in deficient values in relation to the Al2O3 compound. AlO matrix is amorphous irrespectively of the annealing temperature and no signs of Au crystals were detected in the as-deposited films. Segregation of small Au clusters was found in the high Au content coatings after annealing at increasing temperatures. Hardness values were in the range 11–13GPa irrespectively of the Au content and the annealing treatments. Au clustering in the dielectric matrix, which could be able to promote surface plasmon resonance effect, associated with good mechanical properties of the AlO matrix, make envisaging the application of these coatings in decorative fields.

Properties of concrete incorporating bed ash from circulating fluidized bed combustion and ground granulates blast-furnace slag

The properties of concrete incorporating circulating fluidized bed combustion (CFBC) bed ash and ground granulates blast-furnace slag (GGBS) were studied. Compressive strength, drying shrinkage, mercury intrusion porosimetry (MIP), scanning electronic microscopy (SEM), and X-ray diffraction (XRD) of concrete samples containing CFBC bed ash and GGBS were used. This work used initial surface absorption test (ISAT) and rapid chloride penetration test (RCPT) on concrete to measure the absorption and the ability of concrete to resist chloride ion characteristics for different concrete samples containing CFBC bed ash and GGBS. Open circuit potential (OCP), direct current polarization resistance were obtained to evaluate rebar corrosion. The CFBC bed ash was X-ray amorphous and consist of SiO2, Al2O3 and CaO compounds. As the replacement of CFBC for sand increases, the rate of initial surface absorption (ISA) increases but compressive strength decreases. When the content of CFBC bed ash replacement for sand maintains constant, the replacement of GGBS for cement increases, compressive strength increases but the rate of ISA decreases. Chloride and corrosion resistance of rebar significantly improve by utilizing a proper amount of CFBC bed ash and GGBS in concrete.

An Examination of the Effects of Aerosol ChemicalComposition and Size on Radiative Properties of Multi-Component Aerosols

The sensitivity of aerosol radiative properties (i.e., scattering coefficient, extinction coefficient, single scatter albedo, and asymmetry factor) and radiation transmission to aerosol composition, size distributions, and relative humidity (RH) is examined in this paper. Mie calculations and radiation calculations using a tropospheric visible radiation model are performed. The aerosol systems considered include inorganic and organic ions (e.g., Cl－, Br－, , , Na+, , K+, Ca2+, Mg2+, HCOO－, CH3COO－, CH3CH2COO－, CH3COCOO－, OOCCOO2－, MSA1－), and (2) water-insoluble inorganic and organic compounds e.g., (black carbon, n-alkanes, SiO2, Al2O3, Fe2O3 and other organic compounds). The partial molar refraction method and the volume-average method are used to calculate the real and imaginary parts of refractive index of real aerosols, respectively. The sensitivity simulations show that extinction coefficient increases by 70% when RH varies from 0 to 80%. Both extinction coefficient and asymmetry factor increase by ~48% when real part varies from 1.40 to 1.65. Scattering coefficient and single scattering albedo decrease by 18% and 24%, respectively, when the imaginary part varies from –0.005 to –0.1. Scattering and extinction coefficients increase by factors of 118 and 123, respectively, when the geometric mean radius varies from 0.05 to 0.3 ?m. Scattering and extinction coefficients and asymmetry factor increase by factors of 389, 334, and 5.4, respectively, when geometric standard deviation varies from 1.2 to 3.0. The sensitivity simulations using a tropospheric visible radiation model show that the radiation transmission is very sensitive to the change in geometric mean radius and standard deviation; other factors are insignificant.

Interaction of refractory compound nanoparticles with a surfactant in a nickel melt: I. Heterophase interaction

The interaction of nanoparticles of refractory compounds Al2O3 and TiN with a model nickel melt containing a surfactant (sulfur) is studied. The choice of the type of nanoparticles for their interaction with the metal at 1873 K and possible versions of sulfur removal from the melt in the form of S2, SO2, and H2S are grounded. A technique for the preparation of an Ni-Al2O3 (TiN) compact and its introduction into the melt is developed. The character of the change in the sulfur content in the metal after introducing the compact is determined, and the effect of the isothermal holding time of the melt on sulfur removal is revealed.

Computer simulation study of amorphous compounds: structural and vibrational properties

Molecular dynamic (MD) simulations, both classical and ab initio, of amorphous GeO2 (germania), Al2O3 (alumina), and CdTeO compounds are presented. We focus our attention on the structural and vibrational properties, giving an atomic description of the short- and intermediate-range order. Amorphous germanium oxide under pressure was studied by means of classical MD simulations. At normal density, the analysis of the interatomic distances reveals that in the amorphous state there is a short-range order dominated by a slightly distorted (GeO4) tetrahedron. Beyond that, there is an intermediate-range order composed by vertex-sharing tetrahedra. As density increases, there is a structural transformation, from a short-range order defined by the basic tetrahedron to a basic octahedron. Consistent with this picture, the vibrational density of states also presents big changes, where the low frequency band shrinks, and the high frequency becomes wider and flatter. In the case of alumina, both classical and first principles MD calculations of amorphous Al2O3 are reported, comparing both methodologies. Interatomic correlations allow us to conclude that the short-range order is mainly composed by AlO4 tetrahedra, but in contrast to classical MD results, also an important number of AlO5 unit is present. The vibrational density of states presents two main bands, a low frequency one related to the inter-tetrahedron vibration and a high frequency band related to the intra-tetrahedron vibration. Finally, we present an ab initio MD calculation for the complex ternary material CdTeO3. According our calculations, the short-range order of this compound consists of a number of basic building blocks, greater than in the case of its crystalline counterpart. The compound is characterized using pair and angular distribution functions, coordination numbers, and a description of the molecular units of the compound. For example, Cd is coordinated by either six or five atoms. In the case of Te, the chemical unit is TeO3. The most frequent clusters are CdO6, CdO5, TeO3, and TeO4.

XPS and EIS studies of sputtered Al–Ce films formed on AA6061 aluminum alloy in 3.5% NaCl solution

X-ray photoelectron spectroscopy (XPS) was used to analyze the composition of films at different deposition parameters of sputtered Al-Ce coatings on AA6061 aluminum alloys. By means of electrochemical impedance spectroscopy (EIS) measurements, the protective character of these coatings was studied for 21 days of exposure in a 3.5 wt% NaCl solution and an attempt was made to establish the relationship between film thickness and chemical composition (Al/Ce, Ce3/Ce4+ ratios) of the surface before and after the electrochemical characterization. XPS studies revealed the presence of the Alo, Al2O3, CeO2 and Ce2O3 compounds, confirming that the sputtered Al-Ce films were deposited in the metallic form and thereafter were superficially oxidized under ambient conditions. The Al–Ce bonds were overlapped with the signal of cerium oxides. The transport phenomena in the oxide film or controlled diffusion process are strongly dependent on the deposition parameters and exposure time in the aggressive medium. It was also found that in the deposited samples at p4P200t300, the film was still present after 21 days of exposure, although with visible cracks and erosion areas; however, the Ce3/Ce4+ ratio almost remained constant before and after the electrochemical characterization, which explained the barrier properties of these samples as compared with others at different deposition parameters.

Corrosion Properties and Morphology of Laser Melted Aluminum Alloy 8022 Surface

Laser surface melting of aluminum alloy 8022 is considered and electrochemical studies of the laser-melted and as-received alloy surface are carried out. The surface morphology and metallurgical changes in the laser-melted region are examined using optical microscopy, electron scanning microscopy (SEM), and atomic force microscopy (AFM). Elemental changes in the specimens after the laser-melting process are examined using energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD) is used for assessment of the compound formed after the laser-treatment process. Nitrogen is used as an assisting gas during the laser-melting process to prevent high-temperature oxidation reactions. It is found that the laser-melted surfaces is free from cracks and deep cavities. The oxygen diffusion in the surface region of the melt layer forms Al2O3 compound in the surface vicinity. The corrosion current increases significantly for the laser-melted specimens due to the irregular surface structure. AC impedance results showed a decrease in pores resistant and an increase in pores capacitance. In addition, the surface morphology resulting from the laser melting gives rise to pitting sites at the surface.

Ti-Al-C MAX phases by aluminothermic reduction process

A new approach to synthesis of Ti2AlC-Ti3AlC2/Al2O3 compounds is developed based on thermite reaction in the TiO2-Al-C system. The effect of Al excess is also discussed. XRD analysis has proved that this parameter can be used to improve the product purity, i.e., the amount of TiC in the final product. It has also been shown that, with increasing Al excess, the composition of a major MAX phase undergoes a change from Ti2AlC to Ti3AlC2.

Mechanochemical behavior of Fe2O3–Al–Fe powder mixtures to produce Fe3Al–Al2O3 nanocomposite powder

Mechanical treatment of Fe2O3, Al and Fe powder mixtures was carried out in a high energy ball mill to synthesize Fe3Al–Al2O3 intermetallic matrix nanocomposite. Different compositions including 3Fe + Al, Fe2O3 + 2Al, 3Fe2O3 + 8Al and Fe2O3 + 3Al+Fe were chosen in this study. Phase development and structural changes occurring during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during MA, Fe2O3, Al, and Fe react to give a nanocrystalline Fe3Al intermetallic compound matrix. The presence of pure Fe in initial powder mixture changed the modality of mechanochemical process from sudden to gradual reaction. The Fe3Al–Al2O3 compound had a finer microstructure and particles size compared to the Fe3Al compound.