Intermediate Al2O3 Layer Research Articles

Optimizing feed modulation for coupled methane and NOx conversion over Pd-Pt/Mn0.5Fe2.5O4/Al2O3 monolith catalyst

The impacts of feed modulation (frequency, amplitude) and catalyst design (composition and architecture) parameters are reported for the conversion of methane and NOx over a dual-layer Pt+Pd/Al2O3 + Mn0.5Fe2.5O4/Al2O3 monolith. CH4 and NOx conversion data show that the dual-layer catalyst outperforms single-layer samples having the same catalyst loadings, with and without spinel. Close proximity of the PGM and MFO functions in the mixed-layer catalyst lowers the CH4 conversion at high temperature while separating the PGM and spinel layers with an intermediate Al2O3 layer does not. Methane conversion enhancement is linked to its nonmonotonic dependence on O2. The performance gains are tied to a transient activity spike that occurs during the lean-to-rich feed transition when water is present in the feed. The transient spike is attributed to the removal of CO and H2 products via reactions with stored O2 in the spinel, eliminating inhibition of methane steam reforming.

Investigation of an atomic‐layer‐deposited Al2O3 diffusion barrier between Pt and Si for the use in atomic scale atom probe tomography studies on a combinatorial processing platform

In order to enable the application of atomic probe tomography combinatorial processing platforms for atomic‐scale investigations of phase evolution at elevated temperatures, the pre‐sharpened Si tip of 10–20 nm in diameter must be protected against interdiffusion and reaction of the reactive Si with a film of interest by a conformal coating on the Si tip. It is shown that unwanted reactions can be suppressed by introducing a 20‐nm‐thick intermediate Al2O3 layer grown by atomic layer deposition (ALD). As a representative case, Pt is chosen as a film of interest, as it easily forms silicides. Whereas without the ALD coating diffusion/reactions occur, with the protective film, this is prevented for temperatures up to at least 600°C. The effectiveness of the Al2O3 layer serving as a diffusion barrier is not limited to a sharpened Si tip but works generally for all cases where a Si substrate is used.

Influence of the Rear Interface on Composition and Photoluminescence Yield of CZTSSe Absorbers: A Case for an Al2O3 Intermediate Layer.

The rear interface of kesterite absorbers with Mo back contact represents one of the possible sources of nonradiative voltage losses (ΔVoc,nrad) because of the reported decomposition reactions, an uncontrolled growth of MoSe2, or a nonoptimal electrical contact with high recombination. Several intermediate layers (IL), such as MoO3, TiN, and ZnO, have been tested to mitigate these issues, and efficiency improvements have been reported. However, the introduction of IL also triggers other effects such as changes in alkali diffusion, altered morphology, and modifications in the absorber composition, all factors that can also influence ΔVoc,nrad. In this study, the different effects are decoupled by designing a special sample that directly compares four rear structures (SLG, SLG/Mo, SLG/Al2O3, and SLG/Mo/Al2O3) with a Na-doped kesterite absorber optimized for a device efficiency >10%. The IL of choice is Al2O3 because of its reported beneficial effect to reduce the surface recombination velocity at the rear interface of solar cell absorbers. Identical annealing conditions and alkali distribution in the kesterite absorber are preserved, as measured by time-of-flight secondary ion mass spectrometry and energy-dispersive X-ray spectroscopy. The lowest ΔVoc,nrad of 290 mV is measured for kesterite grown on Mo, whereas the kesterite absorber on Al2O3 exhibits higher nonradiative losses up to 350 mV. The anticipated field-effect passivation from Al2O3 at the rear interface could not be observed for the kesterite absorbers prepared by the two-step process, further confirmed by an additional experiment with air annealing. Our results suggest that Mo with an in situ formed MoSe2 remains a suitable back contact for high-efficiency kesterite devices.

Investigation of Cyclic Oxidation Behavior of (Cr, Mo, Si)-Containing (α2 + γ) TiAl-Based Alloys Synthesized by ECAS Sintering

Ti–48Al–2Cr–2Mo–(0 and 0.5 at %) Si intermetallic alloys were synthesized by electric current- assisted sintering (ECAS). Microstructures of the alloys were characterized using scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS), and X-ray diffraction (XRD) methods of analysis. It was found that the microstructures of the produced alloys consist of α2-Ti3Al and γ-TiAl phases. The cycle oxidation behaviors of the alloys were carried out between 700 and 900°C temperatures for 180 h in air. The oxide scale has comprised the TiO2 and Al2O3 mixture layer, intermediate Al2O3 layer, and outermost TiO2 layer. The oxidation rate constants and activation energies of the alloys were calculated.

Self-Alignment of Bottom CZTSSe by Patterning of an Al2O3 Intermediate Layer.

When CZTSSe is synthesized using a metal precursor, large voids of nonuniform size form at Mo back contact side. Herein, we demonstrate that the voids and CZTSSe in the lower part of the CZTSSe double layer can be controlled by using an Al2O3-patterned Mo substrate. The CZTSSe in the lower part self-aligns on the Mo-exposed area, while the voids self-align on the Al2O3-coated area. The origin of the self-alignment is expected to be the difference in bonding characteristics between liquid Sn and the metal or oxide surface, e.g., Al2O3. Good wettability generally forms between nonreactive liquid metals and metal surfaces due to the strong metallic bonding. By contrast, poor wettability generally forms between nonreactive liquid metals and oxide surfaces due to the weak van der Waals bonding between the liquid metal and the oxide layer. When the patterning was added, the device efficiency tended to decrease from 8.6% to 10.5%.

Preparation and characterization of Al3+-doped TiO2 tight ultrafiltration membrane for efficient dye removal

Al3+-doped TiO2 (AT) tight ultrafiltration membrane with stable anatase phase was prepared by a modified sol-gel process using butyl titanate and aluminum chloride as the precursor and aluminum source respectively. The removal of Alizarin red-S was investigated by filtration experiment. A dip-coating process on homemade flat Al2O3 intermediate layer by TiO2 sol followed by heat treatment was adopted to obtain the desired AT membrane. The addition of Al3+ inhibits the phase transformation of nanosized TiO2 from anatase to rutile and restrains the growth of crystallite, resulting in the pore size of the separation layer reducing to 3.5 nm. The prepared AT1-500 membrane exhibits enhanced hydrophilicity with no cracks or pinholes, and shows a water permeability of 9.6 L m-2 h−1 bar−1 and cut-off molecular weight (MWCO) of 4650 Da. The membrane demonstrated a retention rate of 96.9% for Alizarin Red-S (250 ppm) and maintained almost constant under repeated using.

High-Temperature Corrosion of Ti–46Al–6Nb–0.5W–0.5Cr–0.3Si–0.1C Alloy in N2/0.1%H2S Gas

Ti–46Al–6Nb–0.5W–0.5Cr–0.3Si–0.1C alloy was corroded at 800–1100 °C for 200 h in N2/0.1%H2S gas to characterize its corrosion behavior in an aggressive H2S-containing environment. The alloy displayed superior corrosion resistance because Ti and Al preferentially reacted with impurity oxygen in the gas to form TiO2 and Al2O3. It corroded primarily by outward diffusion of Ti, Al, W, and Cr in addition to inward transport of sulfur, nitrogen, and oxygen. Scales were adherent and consisted of an outer TiO2 layer, an intermediate Al2O3 layer, and an inner (TiO2, Al2O3)-mixed layer. TiN and Ti2AlN formed at the scale/matrix interface where sulfur, Nb, W, and Cr segregated.

Beyond 8% ultrathin kesterite Cu2ZnSnS4 solar cells by interface reaction route controlling and self-organized nanopattern at the back contact

Highly efficient, ultrathin (~400 nm) pure sulfide kesterite Cu2ZnSnS4 (CZTS) solar cells have been realized by interface reaction route controlling and self-organized nano-pattern at the back contact. The Al2O3 intermediate layer introduced at the Mo/CZTS interface can effectively inhibit the detrimental interfacial reaction between CZTS and Mo in the initial stage of sulfurization, and then turns into a self-organized nanopattern yielding a nanoscale opening for electrical contact. With this interface modification, the traditional issues of phase segregation (secondary phases) and voids at the back contact region can be well addressed, which greatly improves uniformity and reduces back contact recombination. As a result, this interface modification not only leads to beyond 8% ultrathin CZTS solar cells but also yields two certificated world record efficiencies: 9.26% for 0.237 cm2 small area and 7.61% for 1 cm2 standard kesterite CZTS solar cells (normal thickness).

Carbon Membranes Prepared from a Polymer Blend of Polyethylene Glycol and Polyetherimide

AbstractThrough a dip‐coating technique, carbon membranes were produced from a polymer blend consisting of the thermally stable polymer polyetherimide (PEI) and the thermally labile polymer polyethylene glycol (PEG). The PEG/PEI carbon membranes were synthesized on an alumina support coated with an Al2O3 intermediate layer. The polymer blend ratio and carbonization temperature influenced the structure and permeation performance of the derived carbon membranes. The porosity of the PEG/PEI carbon membranes increased with higher PEG content in the blends. However, the derived carbon membranes tended to lose gas permeability with raising the carbonization temperatures. The carbon membranes were successfully optimized in order to achieve the highest CO2/CH4 and CO2/N2 selectivities.

Role of Al2O3 intermediate layer for improving the quality of polycrystalline-silicon film in inverted aluminum-induced layer exchange

A thin Al2O3 intermediate layer prepared by atomic layer deposition was introduced into inverted aluminum-induced layer exchange (inverted-ALILE) to form high-quality polycrystalline silicon (poly-Si) thin layer. It was demonstrated that the continuity and quality of poly-Si were obviously improved by the Al2O3 layer. The fraction of (100)-oriented crystals reached 93%, and the average grain size of 28μm with uniform surface morphology and low defect density were achieved at the optimal Al2O3 thickness of 4nm. It was also found that an a-AlOx layer always existed at the poly-Si/Al interface after inverted-ALILE process, which is independent on the original surface states. The results suggested that the thin poly-Si layer would be a promising epitaxial template for Si based thin film solar cells.

Cutting temperature effect on PCBN and CVD coated carbide tools in hard turning of D2 tool steel

This study compares the performance of CVD coated tungsten-carbide tools having an intermediate Al2O3 layer to low content PCBN tools in hard turning of D2 tool steel (52HRC). Results revealed that the coated carbide tool can outperform PCBN in machining the selected workpiece material within a certain range of cutting speeds (cutting temperature range). This is associated with tribo-film formation on the coated carbide tool surface. SEM and EDS were used to study the wear patterns of the used cutting tools. The tribo-films were investigated using the X-ray photoelectron method (XPS). The cutting temperature was measured using tool-workpiece thermocouple technique. The formation of the tribo-films was found to be highly-dependent on the cutting temperature and friction kinetics control at the tool–chip interface. Lubricious Cr–O tribo-films formed on the surface of the coated carbide tool, improving tool life at cutting speeds up to 100m/min, which relates to an average tool–chip interface temperature up to 930°C.

A simple method for growing hexaaluminate on the surface of FeCrAl alloy

In situ synthesis of LaMnAl11O19 hexaaluminate in Al2O3 layer coated on the surface of FeCrAl alloy foil is explored in this work. The synthesized plate-like hexaaluminate grains display two morphologies of vertically embedded in and horizontally covered on Al2O3 intermediate layer and the prepared composite hexaaluminate-Al2O3 intermediate layer effectively improved the adhesion stability of the metallic monolithic catalyst. The resulting samples were characterized by XRD, TEM–EDX, SEM, and the formation and the adhesion mechanisms of hexaaluminate were proposed. The adhesion stability and catalytic activity were also evaluated. The behavior indicated that the introduction of hexaaluminate can maintain the high catalytic activity as well as improve the adhesion stability. This preparation strategy can be potentially extended to synthesize other supported catalysts with the same metal source between support and other components.

Magnetic Core–Shell Nano-TiO<SUB>2</SUB>/Al<SUB>2</SUB>O<SUB>3</SUB>/NiFe<SUB>2</SUB>O<SUB>4</SUB> Microparticles with Enhanced Photocatalytic Activity

The core-shell nano-TiO2/Al2O3/NiFe2O4 microparticles of 5-8 microm were prepared by the heterogeneous precipitation followed by calcination treatment. The morphologies, structure, crystalline phase, and magnetic property were characterized by optical biomicroscopy (OBM), scanning electron microscopy (SEM), X-ray diffractometry (XRD) and vibrating sample magnetometer (VSM) respectively. The photocatalytic activity was evaluated by degrading methyl orange solution either under UV light and sunlight. The results indicate that the nano-TiO2 layer consists of needle-like nanoparticles and the intermediate layer of Al2O3 avoids the nano-TiO2 agglomeration, shedding and uneven loading. The nano-TiO2/Al2O3/NiFe2O4 composite particles show high magnetization of 31.5 emu/g and enhanced photocatalytic activity to completely degrade 50 mg/L methyl orange solution either under UV light and sun light. The enhanced activity of the composite is attributed to the unique structure, insulation effect of Al2O3 intermediate layer and the hybrid effect of anatase TiO2 and NiFe2O4. The obtained catalyst may be magnetically separable and useful for many practical applications due to the improved photocatalytic properties under sunlight.

Free-standing highly ordered mesoporous carbon–silica composite thin films

Free-standing mesoporous carbon–silica composite films with different silica contents are successfully prepared with a crack-free morphology, square centimeter size, and a highly ordered mesostructure. The films are first synthesized on Al2O3-coated Si substrates by spin-coating of a tri-constituent solution, in which triblock copolymer Pluronic F127, resin and tetraethoxylsilane (TEOS) are used as the template, carbon and silica precursors, respectively. After the organic–inorganic assembly, calcination, and etching of the intermediate Al2O3 layer, the free-standing mesoporous carbon–silica composite films are obtained. The mechanical property, water wettability and electrical conductivity are well adjusted with different carbon–silica ratios. Furthermore, the free-standing carbon or silica films are also prepared by hydrofluoric acid etching of the carbon–silica composite film or calcination in air, owing to the three-dimensional (3D) interpenetrated frameworks of their parental carbon–silica composite films. The surface area of the obtained free-standing carbon film is extremely high up to ∼2030 m2 g−1, which is ∼4 times larger than that of its parental carbon–silica composite thin film.

Vertical and in-situ growth of hexaaluminate embedded in alumina intermediate layer with high stability

Hexaaluminate (HA) has been in-situ prepared by sharing the aluminum ions from Al2O3 intermediate layer (IML) supported on the FeCrAl alloy foil. The results show that the HA is vertically embedded in Al2O3 IML, and compared with Al2O3 IML, the obtained HA-Al2O3 composite IML shows better adhesion stability.

Propagation Properties of Symmetric Surface Plasmon Polaritons Mode in ${\rm Au}/{\rm Al}_{2}{\rm O}_{3}/{\rm Au}$ Waveguide

Propagation properties of symmetric surface plasmon polariton (SPP) mode excited through a dipole embedded in Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer in Au/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Au waveguide have been investigated. The skin effect of symmetric SPP mode vertical to Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Au interface is presented. The skin depths in the Au layer and in the intermediate Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer are 12 and 24 nm, respectively. Moreover, the propagation properties of symmetric SPP mode along Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Au interface are also analyzed. The propagation lengths of electric and magnetic field component are 0.4 and 0.8 μm, respectively. It is expected that this study will provide additional understanding to the coupling between SPP sources and plasmonic waveguides.

Isothermal oxidation behaviour of beta gamma powder metallurgy TiAl–4Nb–3Mn alloys

A new TiAl–4Nb–3Mn beta gamma alloy was synthesised by a powder metallurgy process. HIPed and vacuum heat treated specimens were isothermally oxidised at 800 and 900°C in air up to 500 h. The TiAl–4Nb–3Mn alloys oxidised parabolically up to 500 h at both 800 and 900°C. The oxides consisted of outer TiO2 layer, intermediate Al2O3 layer and inner TiO2 rich mixed layer and the oxidation mechanisms of the alloy were identical at both temperatures. During oxidation, the degradation of α2 lamellae in the vicinity of the interface forms a diffusion zone (lamellar depleted zone) leading to the formation of Nb and Mn rich white layers just below the interface by outward diffusion of Nb and Mn which are released from breakdown of α2 lamellae. As exposure time increases, Nb begins to diffuse earlier than Mn and diffuses more actively at higher temperature. The activation energy for oxidation of TiAl–4Nb–3Mn alloy was lower than that of Ti–48Al alloy and was higher than those of Ti–48Al–2Nb–2Cr and Ti–48Al–2Nb–2Cr–W alloys.On a synthétisé un nouvel alliage TiAl–4Nb–3Mn de type bêta gamma par un procédé de métallurgie des poudres. On a oxydé en isotherme à 800 et à 900°C à l’air, jusqu’à une durée de 500 heures, les spécimens pressés par HIP et traités thermiquement sous vide. Les alliages de TiAl-4Nb-3Mn s’oxydaient paraboliquement jusqu’à 500 heures tant à 800°C qu’à 900°C. Les oxydes consistaient en une couche externe de TiO2, en une couche intermédiaire d’Al2O3 et en une couche interne mixe riche en TiO2 et les mécanismes d’oxydations de l’alliage étaient identiques aux deux températures. Lors de l’oxydation, la dégradation de lamelles d’α2 dans le voisinage de l’interface forme une zone de diffusion (zone lamellaire appauvrie) menant à la formation de couches blanches riches en Nb et en Mn juste au-dessous de l’interface par diffusion vers l’extérieur du Nb et du Mn, qui sont relâchés par la dégradation des lamelles d’α2. À mesure que la durée de l’exposition augmente, le Nb commence à se diffuser plus tôt que le Mn et se diffuse plus activement à une température plus élevée. L’énergie d’activation pour l’oxydation de l’alliage de TiAl–4Nb–3Mn était plus basse que celle de l’alliage de Ti–48Al et était plus élevée que celle des alliages de Ti–48Al–2Nb–2Cr et de Ti–48Al–2Nb–2Cr–W.

Isothermal oxidation behavior of powder metallurgy beta gamma TiAl–2Nb–2Mo alloy

A new TiAl–2Nb–2Mo beta gamma alloy was synthesized by powder metallurgy process. HIP’ed and vacuum heat treated specimens were isothermally oxidized at 800 °C and 900 °C in air up to 500 h. The TiAl–2Nb–2Mo alloy oxidized parabolically up to 500 h at both 800 °C and 900 °C. The oxides consisted of outer TiO2 layer, intermediate Al2O3 layer, and inner TiO2 rich mixed layer and the oxidation mechanisms of the alloy were identical at both temperatures. During oxidation, the degradation of lamellar colonies formed a diffusion zone just below the oxide/substrate interface consisting of γ-TiAl matrix and dispersed beta phases which contained high concentration of Nb and Mo. The oxidation rate of the TiAl–2Nb–2Mo alloy is more sensitive to temperature than those of the Ti–48Al–2Nb–2Cr and Ti–48Al–2Nb–2Cr–W alloys.

High-temperature oxidation behavior of Al2O3/TiAl matrix composite in air

The oxidation behavior of Al2O3/TiAl in situ composites fabricated by hot-pressing technology was investigated at 900° in static air. The results indicate that the mass gains of the composites samples decrease gradually with increasing Nb2O5 content and the inert Al2O3 dispersoids effectively increase the oxidation resistance of the composites. The higher the Al2O3 dispersoids content, the more pronounced the effect. The primary oxidation precesses obey approximately the linear laws, and the cyclic oxidation precesses follow the parabolic laws. The oxidized sample containing Ti2AlN and TiAl phases in the scales exhibits excellent oxidation resistance. The oxide scale formed after exposure at 900°C for 120 h is multiple-layered, consisting mainly of an outer TiO2 layer, an intermediate Al2O3 layer, and an inner TiO2+Al2O3 mixed layer. From the outer layer to the inner layer, TiO2+Al2O3 mixed layer presents the transit of Al-rich oxide to Ti-rich oxide mixed layer. Near the substrate, cross-section micrograph shows a relatively loose layer, and micro- and macro-pores remain on this layer, which is a transition layer and transferres from Al2O3+TiO2 scale to substrate. The thickness of oxide layer is about 20 μm. It is also found that continuous protective alumina scales can not be observed on the surface of oxidation scales. Ti ions diffuse outwardly to form the outer TiO2 layer, while oxygen ions transport inwardly to form the inner TiO2+Al2O3 mixed layer. Under long-time intensive oxidation exposure, the internal Al2O3 scale has a good adhesiveness with the outer TiO2 scale. No obvious spallation of the oxide scales occurs. The increased oxidation resistance by the presence of in situ Al2O3 particulates is attributed to the enhanced alumina-forming tendency and thin and dense scale formation. Al2O3 particulates enhance the potential barrier of Ti ions from M/MO interface to O/MO interface, thereby the TiO2 growth rate decreases, which is also beneficial to improve the oxidation resistance. Moreover, the multi-structure of the TiO2+Al2O3 mixed layer decreases the indiffusion of oxygen ions and also avails to improve the high temperature oxidation resistance of the as-sintered composites.

High‐temperature oxidation of Ti3Al0.7Si0.3C2compound at 900 and 1000 °C in air

The compound, Ti3Al0.7Si0.3C2, was synthesized by hot pressing a powder mixture of TiCX (x = 0.6), Al and Si. Its oxidation at 900 and 1000 °C in air for up to 50 h resulted in the formation of rutile-TiO2, α-Al2O3 and amorphous SiO2. The oxide scales formed consisted of triple layers, viz, an outer TiO2 layer containing Al2O3 particles, an intermediate Al2O3 layer, and an inner mixed layer that was rich in TiO2, but deficient in Al2O3 and SiO2. During oxidation, Ti diffused outwards to form the outer TiO2 layer, and oxygen was transported inwards to form the inner mixed layer. At the same time, carbon was liberated from Ti3Al0.7Si0.3C2. Ti3Al0.7Si0.3C2 oxidized slower than the TiO2-forming kinetics, but faster than the (α-Al2O3 or SiO2)-forming kinetics.