Al SiO2 Research Articles

Interaction of aluminum projectiles with quartz sand in impact experiments: Formation of khatyrkite (CuAl2) and reduction of SiO2 to Si

We analyzed the interaction of spherical, 6.36-mm-diameter, Cu-bearing aluminum projectiles with quartz sand targets in hypervelocity impact experiments performed at NASA Ames Vertical Gun Range. Impact velocities and inferred peak shock pressures varied between 5.9 and 6.5km/s and ∼41 and 48GPa, respectively. Shocked particles (“impact melt particles”) coated with thin crusts of molten projectile material were recovered from the floors of the ca. 33-cm-diameter craters and the respective ejecta blankets. Through petrographic and chemical (optical microscopy, FE-EMPA, SEM-EDX, and XRF) analysis we show that these particles have a layered structure manifested in distinct layers of decreasing shock metamorphism. These can be characterized by the following physical and chemical reactions and alteration products: (i) complete melting and subsequent recrystallization of the projectile, forming a distinct crystallization texture in the fused metal crust; (ii) projectile–target mixing, involving a redox reaction between Cu-bearing Al alloy und SiO2, leading to formation of khatyrkite (CuAl2), Al2O3 melt, euhedral silicon crystals, and spherical droplets of silicon; (iii) melting of quartz to lechatelierite and formation of planar deformation features in relic quartz grains; and (iv) shock lithification of quartz grains with fracturing of grains, grain-boundary melting, planar deformation features, and complete loss of porosity. To our knowledge, this is the first report of khatyrkite formed experimentally in hypervelocity impact experiments. These results have implications for the understanding of a similar redox reaction between Al–Cu metal and siliceous impact melt recently postulated for the Khatyrka CV3 carbonaceous chondrite. Moreover, these results bear on the processes that lead to layers of regolith on the surfaces of planetary bodies without atmospheres, such as asteroids in the main belt (e.g., 4 Vesta), and on the Moon. Specifically, impacts of mm-sized projectiles at velocities between 4 and 6km/s into regolith-covered, asteroidal surfaces in the main belt should yield similar impact melt particles that feature a continuum of shock effects, i.e., partially to completely molten projectile remnants adhering to impact-melted regolith agglomerates, as well as projectile-contaminated impact melts and local shock melting along grain boundaries.

Wearing resistance of in-situ Al-based composites with different SiO2/C/Al molar ratios fabricated by reaction hot pressing

The in-situ Al-based composites with different SiO2/C/Al molar ratios were fabricated by reaction hot pressing. The dry sliding wear characteristics of the composites were investigated using a pin-on-disc wear tester. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to investigate the surface composition and its morphology. The results show that when the SiO2/C/Al molar ratio is 3:6:9, more in-situ synthesized Al2O3 and SiC along with Si particles are produced, and Al4C3 is prevented completely from the Al–SiO2–C system. Thereby, a significant improvement of wear resistance is obtained. When the sliding velocity increases from 0.4 to 1.6 m/s, the wear loss decreases gradually. With increasing the normal load, the wear loss increases as well. Ploughing, craters and micro-grooving are observed as dominant abrasive wear mechanisms. Whereas, when a high velocity is employed, only the oxidation mechanism controls the wear behavior of the composites.

Si-filled ceramic composite by thermal explosion in the Al–SiO2 system

Si-filled ceramic composite was prepared through thermal explosion in the Al–SiO2 system. The material can be expected to find its application to reprocessing quartz wastes into cermets to be used in microelectronic devices.

Interfacial Structure and Formation Mechanism of Ultrasonic-assisted Brazed Joint of SiC Ceramics with Al[sbnd]12Si Filler Metals in Air

Ultrasonic-assisted brazing of SiC ceramics was performed by filling with an Al 12Si alloy at a low temperature of 620 °C in air. The interfacial characteristics and formation mechanism were investigated. The joint shear strength reached 84–94 MPa using the ultrasonic time of 2–16 s. The fracture morphology showed that the fracture path initiated and propagated in the joint alloy. The thin film of amorphous SiO2 that formed on the SiC surface was non-uniformly decomposed and diffused into the liquid Al 12Si alloy under the cavitation erosion effect of ultrasound. Abnormal isolated blocks of Al2SiO5 compounds formed at the interface between Al 12Si and a thicker SiO2 layer formed during the thermal oxidation treatment of the SiC ceramic. The SiO2 layer on the SiC ceramic did not hinder or impair the wetting and bonding process, and a stronger bond could form between Al 12Si and SiO2 or SiC in ultrasonic-assisted brazing.

High spectral field enhancement and tunability in core–double shell metal–dielectric–metal spherical nanoparticles

Full Mie theory for spherical core–double shell NPs has been developed to study plasmon resonances, optical extinction and spectral field enhancement of a generalized metal–dielectric–metal NPs, reaching an external factor of 33 for Al–SiO2–Au.

Effects of excess boron and B4C addition on combustion synthesis of NbB2/mullite composites

NbB2/mullite composites were fabricated by self-propagating high-temperature synthesis (SHS) involving aluminothermic reduction of Nb2O5. Amorphous boron and B4C were adopted as the source of boron in two reaction systems composed of Nb2O5–B–Al–SiO2 and Nb2O5–B–B4C–Al–SiO2. The effects of excess boron and B4C addition were studied on the combustion characteristics and product compositions. Due to sufficiently high combustion temperatures, the B-adopted samples were subjected to not only aluminothermic but also borothermic reactions. Because the latter caused a considerable loss of boron, the B-adopted sample required excess boron of about 24mol% to convert boride phases into NbB2. Besides providing boron, B4C was found to reduce the combustion exothermicity and then to suppress the borothermic reaction for the B/B4C-containing sample. Consequently, a small amount of excess boron of 2.6mol% was sufficient for the B/B4C-adopted sample to produce NbB2 and mullite with trivial minor phases.

Microstructural and mechanical properties of Al–SiO2 nanocomposite foams produced by an ultrasonic technique

In this study, nanocomposite foams reinforced with different weight percentages of silicon dioxide nanoparticles (0.25, 0.5, 0.75 and 1.0wt%) were fabricated using the ultrasonic and stir casting techniques. For this purpose heat treated TiH2 was used as foaming agent. Microstructural studies were done by optical microscope and scanning electron microscope. Hardness evaluation of precursor nanocomposites showed that the hardness was significantly increased by the addition of SiO2 nanoparticles and Al–0.75wt% SiO2 nanocomposite makes the highest hardness. Evaluation of compressive behavior of Al–SiO2 nanocomposite foams showed that the plateau stress increases more than 3 times as the foam relative density increases from 0.09 to 0.16. Energy absorption of Al–SiO2 nanocomposite foams has been found to be dependent on both relative density and structural properties.

Influences of carbon additions on reaction mechanisms and tensile properties of Al-based composites synthesized in-situ by Al–SiO2 powder system

Abstract The effects of carbon additions on reaction mechanisms and mechanical properties of Al-based composites fabricated in-situ through Al–SiO 2 system were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS). It was found that when the powder of C was added into the Al–SiO 2 system, Al first reacted with SiO 2 to form the α-Al 2 O 3 and Si. Some of the Si then reacted with the C to form the SiC, and the remaining Si dissolved into Al to form the Al–Si alloy. Based on the DSC curves obtained from five different heating rates, the apparent activation energy for the synthesis of the new composites was calculated and found to be 309 kJ/mol, which was larger than that of Al–SiO 2 system that yielded the same reinforcement volume fraction of 30%. As compared with the reference materials prepared from the Al–SiO 2 system, the morphology of Si in the new composites changed from a large block to a needle-like shape. Moreover, the tensile strength and ductility of the new materials increased from 165 MPa and 3.95% to 208 MPa and 4.20%, respectively.

Synthesis and Characterization of In Situ (Al2O3–Si)/Al Composites by Reaction Hot Pressing

In situ (Al2O3–Si)/Al composites with a reinforcement volume fraction of 10% were synthesized from the Al–SiO2 system using low energy ball milling and reaction hot pressing. Differential thermal analysis was used to investigate the reaction mechanisms between SiO2 and Al. X-ray diffraction results revealed that the reaction between Al and SiO2 took place completely at 900 °C with a holding time of 2 h, thereby forming Al2O3 and Si. Scanning electron microscopic, energy dispersive X-ray spectroscopic, and transmission electron microscopic (TEM) results showed that the in situ synthesized Al2O3 and Si particles, whose sizes are less than 2 µm, were polygonal in shape and dispersed uniformly in the matrix. Moreover, Al2O3 particle size showed a tendency to increase from ~2 to ~6 µm when the synthesis temperature was increased. Furthermore, TEM observation showed that the interface between the reinforcements and Al matrix is clean. The yield strength, ultimate tensile strength, and Brinell hardness of the in situ (Al2O3–Si)/Al composite was significantly higher than the aluminum matrix. Mechanisms governing the tensile fracture process are discussed.

Preparation of TaB/TaB2/mullite composites by combustion synthesis involving aluminothermic reduction of oxide precursors

TaB/TaB2/mullite composites were fabricated by self-sustaining combustion involving aluminothermic reduction of two oxide precursors, Ta2O5 and B2O3. Reactant mixtures were formulated by different combinations of Ta2O5–B2O3–Al–SiO2 with or without addition of boron. Exothermic reduction of Ta2O5 and B2O3 by Al provides sufficient heat to sustain the synthesis reaction in the SHS mode. The increase of SiO2 improved the mullite formation, but reduced the combustion temperature and velocity due to the dilution effect of SiO2 and the endothermic mullitization process. The phase of tantalum borides formed depended on the content of Al and the addition of boron. Specifically, the TaB/mullite composite with a small amount of TaB2 was produced from an Al-deficient sample of Ta2O5–2B2O3–6Al–2SiO2. For a boron-added sample of Ta2O5–2B2O3–6Al–2SiO2–3B, it was found that TaB2 prevailed and the resulting product was a TaB2/mullite composite. The SHS-derived mullite grains exhibit a thick whisker shape with a large aspect ratio.

Formation of Aluminum Matrix Composite Material with High-Temperature Reaction of Al–SiO2 System Components

Results are presented for a study of aluminum chemical composition and structure after reaction with silicon dioxide refractory material. It is established that high-temperature reaction of Al–SiO2 system components is accompanied by refractory working surface breakdown and formation of aluminum matrix composite material containing silicon microparticles.

Laminar Nanofluid Flow Over Periodic Two Dimensional Rectangular Baffled Channels

Forced convection of laminar nanofluid flow in a periodic baffled channel is numerically studied. The governing equations of the problem are continuity, momentum and energy equations which are discretized using finite volume method (FVM). The upper and lower walls of the test section are kept at a constant temperature. Two distinct baffle shapes are studied, which are diamond baffle and vertical flat plate baffle. Different half tip angles of the diamond baffle (5°, 10° and 15°) and different block ratios (BR = 0.1 H, 0.3 H and 0.5 H) for both diamond and vertical flat plate baffles are pondered. Four varied types of nanofluids are employed as working fluids which are Al 2O2, CuO, SiO2, and ZnO dispersed in pure water as a base fluid. Different concentrations of nanoparticles (1% to 4%) and different diameters of nanoparticles (30 nm to 80 nm) are used. The range ofReynolds number varied from 100 to 1200. The numerical results state that with the increase in the height and the decrease in the angle of the baffle and also the increase of the volume fraction and the decrease of the nanoparticle diameter, the Nu number increases and so does the friction factor. Among all of the four studied nanofluids, SiO2-water with 4% volume fraction and 30 nm diameter of the nanoparticles shows the highest heat transfer and thermal enhancement of the system.

Reaction mechanism and mechanical properties of an aluminum-based composite fabricated in-situ from Al–SiO2 system

An (α-Al2O3 + Si)/Al composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and SiO2. The synthesis mechanism and resulting microstructure of the composite were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray energy dispersive spectroscopy (EDS). It was found that when the reinforcement volume fraction was 30%, Al reacted with SiO2 at a temperature of around 950 K to form α-Al2O3 and Si, and the corresponding apparent activation energy was 235 kJ mol−1. The apparent activation energy of the reaction decreases with the increase of the reinforcement volume fraction. On the other hand, with increasing heating rate, the reaction time was reduced and the characteristic exothermic peak shifted to a higher temperature. The tensile strength and elongation of the composite having the reinforcement volume fraction of 30% were 165 MPa and 3.95%, respectively. On the tensile fracture surfaces, there were many fine dimples in addition to some fractured blocks. The α-Al2O3 particles were located in the center of the fine dimples. The Si crystal blocks fractured along certain cleavage plane in a brittle manner and are a limiting factor to the tensile property of the newly-developed composite. Therefore, the elimination or replacement of the Si crystals by a tougher phase is an important consideration for future work.

Ceramic Refractory SHS-Coatings Based on the System Al–SiO2

Preparation of refractory coatings by self-propagating high-temperature synthesis (SHS) based on the system Al–SiO2 on aluminum silicate refractories using quartz sand and kaolin from the Belorussian Republic is studied. It is established that use of a mixture of kaolin and quartz sand reduces the probability of crack formation in a coating during drying and firing, and improves its qualitative properties. It is shown that coating refractoriness higher than 1300°C is only achieved using binders not containing sodium salts. Physicochemical and thermal properties of synthesized ceramic SHS-materials and coatings based on them are studied. The effect of additives on these properties is established. High adhesive strength is apparent for coatings containing additions of titanium dioxide and boric acid.

Self-forming Al oxide barrier for nanoscale Cu interconnects created by hybrid atomic layer deposition of Cu–Al alloy

The authors synthesized a Cu–Al alloy by employing alternating atomic layer deposition (ALD) surface reactions using Cu and Al precursors, respectively. By alternating between these two ALD surface chemistries, the authors fabricated ALD Cu–Al alloy. Cu was deposited using bis(1-dimethylamino-2-methyl-2-butoxy) copper as a precursor and H2 plasma, while Al was deposited using trimethylaluminum as the precursor and H2 plasma. The Al atomic percent in the Cu–Al alloy films varied from 0 to 15.6 at. %. Transmission electron microscopy revealed that a uniform Al-based interlayer self-formed at the interface after annealing. To evaluate the barrier properties of the Al-based interlayer and adhesion between the Cu–Al alloy film and SiO2 dielectric, thermal stability and peel-off adhesion tests were performed, respectively. The Al-based interlayer showed similar thermal stability and adhesion to the reference Mn-based interlayer. Our results indicate that Cu–Al alloys formed by alternating ALD are suitable seed layer materials for Cu interconnects.

Al-SiO2-Y2O3-SiO2-poly-Si Thin-Film Transistor Nonvolatile Memory Incorporating a Y2O3 Charge Trapping Layer

In this letter, we investigate the structural properties and electrical characteristics of the Al–SiO2–Y2O3–SiO2–poly-Si (AOYOP) thin-film transistor (TFT) nonvolatile memory device. The composition of Y2O3 charge-trapping layer was analyzed using X-ray photoelectron spectroscopy. The Y2O3 AOYOP TFT memory device exhibited a large memory window of 2.5 V, a long charge retention time of ten years with a minimal charge loss of ∼15%, and a better endurance performance for P/E cycles up to 105. © 2013 The Electrochemical Society. [DOI: 10.1149/2.002310ssl] All rights reserved.

Nanoscale interaction layer at the interface between Al films and SiO2 substrates of Al/AlOx/Al Josephson tunnel junctions

An interaction layer is found at the Al/SiO2 interface in Al/AlOx/Al tunnel junctions grown on SiO2 substrates. The amorphous intermixing layer has an average thickness of about 5 nm. We present the detailed structure of this interfacial layer as determined by transmission electron microscopy. The layer contains alumina with aluminum being octahedrally coordinated according to electron energy loss spectroscopy analysis rather than tetrahedrally coordinated, where the latter coordination is the most common type in amorphous alumina. Depth profiles of the Al-O and Si-O bonding characteristics were also investigated using energy loss near edge structure.

Study of the effect of tunneling through the traps inside the insulator on small-signal admittance of the MOS structure

The effect of tunneling through traps located inside the insulator layer on the small-signal admittance parameters of the MOS tunnel diode is investigated by means of the theoretical model. An influence of geometric and energy positions of the traps is studied. The model and considerations are confirmed by a comparison with measurement data of an experimental Al–SiO2–Si structure.

Early Eocene magmatism in the Sredinnyi Range, Kamchatka: Composition and geodynamic aspects

Migmatization and granite-forming processes were widespread in the southern Sredinnyi Range of the Kamchatka Peninsula in the Early Eocene (at approximately 52 ± 2 Ma). The paper presents data on the composition and genesis of the Early Eocene granitoids. The Malka Rise contains both equigranular peraluminous garnet-bearing granites, on the one hand, and migmatites and tonalites and trondhjemites (TTG), on the other. The petrography and petrochemistry of most granites in the Malka Rise in the Sredinnyi Range (high SiO2 concentrations, the presence of muscovite and garnet, the proportions of their Al saturation index ASI and SiO2, FeOt + MgO + TiO2, and SiO2, Al2O3/TiO2, and CaO/Na2O), and the composition of biotite in these rocks highlight their similarities with S-granites. The character of the REE patterns and the Sr and Y concentrations suggest that the granites and TTG were formed via the melting of sources of two types: metasediments and metabasites. The metasedimentary nature of the protolith of most of the granitoids also follows from similarities between the REE patterns of the granitoids and host metaterrigenous rocks of the Kolpakova and Kamchatka groups. The variations in the Rb/Ba and Rb/Sr ratios of the granites imply that their protoliths could be sedimentary rocks both depleted and enriched in pelite components. The facts that, along with S-granites, some of the granites are TTG, which likely had mafic protoliths, make the Early Eocene granites generally similar to S-granites of the Cordilleran type. The collision of the Achaivayam-Valaginskii ensimatic island arc with the Kamchatka margin of Eurasia started at 55–53 Ma and predated Early Eocene magmatism. In the course of this collision, arc complexes were obducted over continental marginal rocks, and this resulted in their rapid subsidence, crustal heating, magma generation, and the derivation of the granites, tonalites, and trondhjemites at 52 ± 2 Ma at temperatures of 645–815°C. This rapid heating (duirng no more than 3–5 Ma) required an additional heat source, which was likely the mantle. The latter heated the bottom of the crust at the detachment of the slab. The influx of mantle material resulted in intrusions of the norite-cortlandite association, which was coeval with the granites and was accompanied by Cu-Ni sulfide mineralization. The composition of the granitoids and data on the intrusions of the norite-cortlandite association suggest that mantle material was involved in Early Eocene syncollisional magma generation in Kamchatka. Newly obtained U-Pb zircon SHRIMP dates of the granitoids and recently published data on the age of the norite-cortlandite intrusions indicate that they are coeval and make it possible to recognize an Early Eocene phase of magmatic activity in Kamchatka.

Optical constants from 370 nm to 900 nm of Titan tholins produced in a low pressure RF plasma discharge

Determining the optical constants of Titan aerosol analogues, or tholins, has been a major concern for the last three decades because they are essential to constrain the numerical models used to analyze Titan’s observational data (albedo, radiative transfer, haze vertical profile, surface contribution, etc.). Here we present the optical constant characterization of tholins produced with an RF plasma discharge in a (95%N2–5%CH4) gas mixture simulating Titan’s main atmospheric composition, and deposited as a thin film on an Al–SiO2 substrate. The real and imaginary parts, n and k, of the tholin complex refractive index have been determined from 370nm to 900nm wavelength using spectroscopic ellipsometry. The values of n decrease from n=1.64 (at 370nm) to n=1.57 (at 900nm) as well as the values of k which feature two behaviors: an exponential decay from 370nm to 500nm, with k=12.4×e−0.018λ (where λ is expressed in nm), followed by a plateau, with k=(1.8±0.2)×10−3. The trends observed for the PAMPRE tholins optical constants are compared to those determined for other Titan tholins, as well as to the optical constants of Titan’s aerosols retrieved from observational data.