Structural,morphological and optoelectronic properties of porous silicon combined alumina coating film deposited by PLD

Pulsed laser deposition of Al₂O₃ onto porous silicon (PS) is shown to provide excellent passivation of multi-crystalline silicon surfaces intended for solar cells applications. Surface passivation and reflectivity are investigated before and after the deposition of various nominal thicknesses of Al₂O₃ ranging from isolated nanoparticles to ~80 nm-thick films. The level of surface passivation is determined by techniques based on photoconductance and FTIR. As a result, the effective minority carrier lifetime increase from 1 to 130 μs at a minority carrier density (Δn) of 1?×?10¹³ cm^?3. However, passivation scheme provide a significant decrease in the reflectivity; it’s reduced from 28% to about 5% after Al₂O₃/PS coating.     

Enhanced osteoconduction and angiogenesis of a three dimensional continuously porous Al2O3 implant

A 3-dimensional alumina (Al₂0₃) implant consisting of a continuous porous structure was fabricated using a fibrous monolithic process and its biocompatibility was evaluated through in vitro procedures and in vivo angiogenesis. In vitro experiments were carried out using human osteoblast like cells, MG-63 and osteoclast-like cells, Raw-264.7. Cellular proliferation and growth behavior were examined on the specimen surfaces by SEM. Highly condensed, circular cells with three-dimensional network like growth pattern was observed inside the pore surfaces using MG-63 cells. In contrast, the osteoclast-like Raw 264.7 cells had a multi-layered pebblestone appearance with interconnections. Moreover, the crystalline-like nodules generated by osteoblasts cultured on an Al₂O₃ porous body were shown to have resulted from the in vitro mineralization of calcium-phosphate deposits. To investigate the in vivo angiogenesis, 3-dimensional Al₂O₃ porous bodies were implanted into the subcutaneous tissues of rats. The porous bodies were completely filled with fibroblasts at 4 weeks and the formation of new blood vessels inside the porous body was observed at 6 weeks.     

Controlling fibroblast adhesion and proliferation by 1D Al2 O3 nanostructures

The fibrotic encapsulation, which is mainly accompanied by an excessive proliferation of fibroblasts, is an undesired phenomenon after the implantation of various medical devices. Beside the surface chemistry, the topography plays also a major role in the fibroblast–surface interaction. In the present study, one‐dimensional aluminium oxide (1D Al₂ O₃) nanostructures with different distribution densities were prepared to reveal the response of human fibroblasts to the surface topography. The cell size, the cell number and the ability to form well‐defined actin fibres and focal adhesions were significantly impaired with increasing distribution density of the 1D Al₂ O₃ nanostructures on the substratum.Inspec keywords: biomechanics, adhesion, surface chemistry, biomedical materials, cellular biophysics, surface topography, nanostructured materials, alumina, nanomedicineOther keywords: fibrotic encapsulation, medical devices, surface chemistry, human fibroblasts, surface topography, cell size, cell number, well‐defined actin fibres, focal adhesions, distribution density, fibroblast adhesion, 1D nanostructures, distribution densities, fibroblast proliferation, fibroblast‐surface interaction, one‐dimensional aluminium oxide nanostructures, Al₂ O₃      

Aluminum‐Ion‐Intercalation Supercapacitors with Ultrahigh Areal Capacitance and Highly Enhanced Cycling Stability: Power Supply for Flexible Electrochromic Devices

Electrochemical capacitor systems based on Al ions can offer the possibilities of low cost and high safety, together with a three‐electron redox‐mechanism‐based high capacity, and thus are expected to provide a feasible solution to meet ever‐increasing energy demands. Here, highly efficient Al‐ion intercalation into W₁₈O₄₉ nanowires (W₁₈O₄₉NWs) with wide lattice spacing and layered single‐crystal structure for electrochemical storage is demonstrated. Moreover, a freestanding composite film with a hierarchical porous structure is prepared through vacuum‐assisted filtration of a mixed dispersion containing W₁₈O₄₉NWs and single‐walled carbon nanotubes. The as‐prepared composite electrode exhibits extremely high areal capacitances of 1.11–2.92 F cm^?2 and 459 F cm^?3 at 2 mA cm^?2, enhanced electrochemical stability in the Al³⁺ electrolyte, as well as excellent mechanical properties. An Al‐ion‐based, flexible, asymmetric electrochemical capacitor is assembled that displays a high volumetric energy density of 19.0 mWh cm^?3 at a high power density of 295 mW cm^?3. Finally, the Al‐ion‐based asymmetric supercapacitor is used as the power source for poly(3‐hexylthiophene)‐based electrochromic devices, demonstrating their promising capability in flexible electronic devices.     

In vitro cellular response to titanium electrochemically coated with hydroxyapatite compared to titanium with three different levels of surface roughness

The in vitro response of primary human osteoblast-like (HOB) cells to a novel hydroxyapatite (HA) coated titanium substrate, produced by a low temperature electrochemical method, was compared to three different titanium surfaces: as-machined, Al₂O₃-blasted, plasma-sprayed with titanium particles. HOB cells were cultured on different surfaces for 3, 7 and 14 days at 37 °C. The cell morphology was assessed using scanning electron microscopy (SEM). Cell growth and proliferation were assessed by the measurement of total cellular DNA and tritiated thymidine incorporation. Measurement of alkaline phosphatase (ALP) production was used as an indicator of the phenotype of the cultured HOB cells. After three days incubation, the electrochemically coated HA surface produced the highest level of cell proliferation, and the Al₂O₃-blasted surface the lowest. Interestingly, as the incubation time was increased to 7 days all surfaces produced a large drop in tritiated thymidine incorporation apart from the Al₂O₃-blasted surface, which showed a small increase. Cells cultured on all four surfaces showed an increased expression of ALP with increased incubation time, although there was not a statistically significant difference between surfaces at each time point. Typical osteoblast morphology was observed for cells cultured on all samples. The HA coated sample showed evidence of a deposited phase after three days of incubation, which was not observed on any other surface. Cells incubated on the HA coated substrate appeared to exhibit the highest number of cell processes attaching to the surface, which was indicative of optimal cell attachment. The crystalline HA coating, produced by a low temperature route, appeared to result in a more bioactive surface on the c.p. Ti substrate than was observed for the other three different Ti surfaces.     

Analysis of morphology and microstructure of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> layers

The paper presents the characterization of obtaining Al₂O₃ oxide layers on AlMg₂ aluminum alloy as a result of hard anodizing by the electrolytic method in a three-component electrolyte. The Al₂O₃ layers obtained on the AlMg₂ alloy in the three-component SBS electrolyte were subjected to detailed microstructural investigations (by means of a scanning electron microscope). By using X-ray diffraction, the phase compositions of obtained oxide layers were examined. It was found that the Al₂O₃ oxide layers obtained via hard anodizing in a three-component electrolyte are amorphous. The chemical composition of the Al₂O₃ layers is presented and compared with the results of stechiometric calculations for the Al₂O₃ layer. Surface morphologies of the obtained oxide layers are characterized and discussed in nano- and microscopic scales. The surface morphologies of the layers obtained have a significant influence on their properties, including their susceptibility to further modification (e.g., to incorporation of graphite), their wear resistance, and the capacity for sorption of lubricants.     

Physico-chemistry and cytotoxicity of ceramics

General cytotoxicity was assayed for ceramic (Al₂O₃, ZrO₂/Y₂O₃, AIN, B₄C, BN, SiC, Si₃N₄, TiB₄, TiC, TiN) diamond and graphite powders, using 3T3 Balb/c permanent cell lines. Neutral red test was carried out in order to establish cell viability. Further investigations were undertaken on human differentiated cells (human umbilical venous endothelial cells): cell behaviour (MTT assay, total cell protein content) and differentiation (immunofluorescence) were studied. In both cases, no cytotoxic effect has been noticed. All the impurities contained at low concentration in these powders do not seem to present any effect. The correlation which has been previously observed between cytotoxicity-cell culture response and blood haemolysis for polymers has not been established here for ceramic powders. We conclude that all the ceramic powders tested here and therefore the corresponding bulk ceramics or ceramic coatings do not induce any cytotoxic effect.     

Electro co-deposition of Ni–Al2O3 composite coatings

Nickel–Al₂O₃ composite coatings have been successfully deposited galvanostatically on to stainless steel substrates by electro co-deposition from a Watts bath containing between 50 and 150?g/l of sub-micron or nano- sized alumina particles applying current density of ?10, ?20 and ?32?mA?cm^?2. The alumina distribution in the composite films on the two sides of the substrate was remarkably different due to solution hydrodynamics and electric field effects. The effect of current density, particle concentration in the bath and particle size are studied systematically producing a comprehensive set of data for better understanding the effects of these variables on the amount of particles co-deposited. The amount of Al₂O₃ co-deposited in the films increases with the particle concentration in the bath and strongly depends on the current density and on particle size. The effect of the current density and of the alumina inclusions on the crystallinity of the Ni matrix and on the Ni crystallites grain size has also been studied. The inclusions of nano or sub-micron-Al₂O₃ particles are found to strongly influence the metallic nickel microstructure.     

Mechanical properties and fracture behavior of interfacial alumina scales on plasma-sprayed thermal barrier coatings

Abstract

The mechanical properties and fracture behavior of Y-doped Al₂O₃ scales were investigated by furnace thermal cycling (to 1,150°C) of plasma-sprayed thermal barrier coatings (TBCs) with vacuum plasma-sprayed (VPS) or air plasma-sprayed (APS) Ni–22Cr–10Al–1Y bond coatings. No significant alterations in Al₂O₃ hardness or Young’s modulus (as measured by mechanical properties microprobe) were detected as a function of bond coat type, exposure time, or number of thermal cycles. The interfacial Al₂O₃ scales on VPS NiCrAlY exhibited progressive increases in localized fracture, buckling, and delamination during thermal cycling. The concentration of arrayed lenticular voids in the columnar Al₂O₃ grain boundaries significantly increased during cyclic oxidation (as compared to isothermal oxidation), but only in scales which formed on convex surfaces, suggesting internal void growth was stress-related. The amount and frequency of scale damage was higher on convex surfaces with a relatively large radius of curvature as compared to convex surfaces with a very small radius of curvature. Although the thermo-mechanical fracture resistance of Al₂O₃ scales on APS NiCrAlY was superior to scales on VPS NiCrAlY, TBC lifetimes on VPS NiCrAlY were greater by a factor of 2. Apparently, severe interfacial scale damage did not rapidly degrade the adherence of the ceramic top coatings.     

Synthesis by an ionic liquid-assisted method and optical properties of nanoflower Y2O3

Flower-like Y₂O₃ nano-/microstructured phosphors without metal activators have successfully been fabricated by an ionic liquid (IL)-assisted method involving temperature (600 °C) annealing. In this paper, the effect of IL concentration on the morphology of the product has been investigated. The IL plays a crucial role in the formation of various morphologies of Y₂O₃. The structural and morphological features of the obtained samples have been characterized by means of X-ray powder diffraction (XRD) analysis, photoluminescence spectra (PL), Fourier-transform infrared (FT-IR) spectra and X-ray photoelectron spectra (XPS). The photoluminescence spectra of the products exhibit an intense bluish-white emission (ranging from 405 to 430 nm and centered at 418 nm). The luminescent mechanisms have been ascribed to the carbon impurities in the Y₂O₃ host. The effect of the ILs cation and the counter anions on the Y₂O₃ morphology of these nanostructures was studied experimentally. It was observed that Y₂O₃ morphology and PL of these nanostructures were strongly influenced by the type of cation and anion. As the length of the subsidiary chain of cation section of IL (imidaziole ione) reduces, the thickness of the nano-sheets increases. It is expected that the present method may easily be extended to similar nano-/microstructures of other oxide materials. Such investigations are currently underway.     

Copper Nitride Nanowires Printed Li with Stable Cycling for Li Metal Batteries in Carbonate Electrolytes

The practical implementation of the lithium metal anode is hindered by obstacles such as Li dendrite growth, large volume changes, and poor lifespan. Here, copper nitride nanowires (Cu₃N NWs) printed Li by a facile and low-cost roll-press method is reported, to operate in carbonate electrolytes for high-voltage cathode materials. Through one-step roll pressing, Cu₃N NWs can be conformally printed onto the Li metal surface, and form a Li₃N@Cu NWs layer on the Li metal. The Li₃N@Cu NWs layer can assist homogeneous Li-ion flux with the 3D channel structure, as well as the high Li-ion conductivity of the Li₃N. With those beneficial effects, the Li₃N@Cu NWs layer can guide Li to deposit into a dense and planar structure without Li-dendrite growth. Li metal with Li₃N@Cu NWs protection layer exhibits outstanding cycling performances even at a high current density of 5.0 mA cm⁻² with low overpotentials in Li symmetric cells. Furthermore, the stable cyclability and improved rate capability can be realized in a full cell using LiCoO₂ over 300 cycles. When decoupling the irreversible reactions of the cathode using Li₄T_i5O₁₂, stable cycling performance over 1000 cycles can be achieved at a practical current density of ≈2 mA cm⁻².     

Growth of ZnGa2O4 nanowires on a ZnO buffer layer by carbothermal reduction of Ga2O3 powder

The synthesis of pure ZnGa₂O₄ nanowires (NWs) on the ZnO-coated Si substrates could be achieved by carbothermal reduction of Ga₂O₃ powder. The processing parameters such as the weight of Ga₂O₃ powder, the thickness of ZnO buffer layer, and the substrate temperature were explored. The growth of ZnGa₂O₄ NWs followed the vapor-solid process. Surplus ZnO source favored the growth of ZnGa₂O₄ NWs, while higher substrate temperature promoted the growth of Ga₂O₃ nanobelts. The results indicated a window for the growth of abundant and pure ZnGa₂O₄ NWs. The growth mechanism of ZnGa₂O₄ NWs on the ZnO buffer layer via carbothermal reduction of Ga₂O₃ powder was discussed. The ZnGa₂O₄ NWs showed a photoluminescence band centered at 466-475 nm.     

Compositional dependence of bioactivity of glasses in the system CaO-SiO2-Al2O3: itsin vitro evaluation

In order to investigate fundamentally the effect of Al₂O₃ on the bioactivity of glasses and glass-ceramics, the compositional dependence of bioactivity of glasses in the system CaO-SiO₂-Al₂O₃ was studiedin vitro. It is already known that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body, and that the surface apatite layer can be reproduced even in an acellular simulated body fluid which has almost equal ion concentrations to those of the human blood plasma. In the present study, bioactivity of the glasses was evaluated by examining apatite formation on their surfaces in the simulated body fluid with thin-film X-ray diffraction, Fourier transform infrared reflection spectroscopy and scanning electron microscopic observation. Only CaO-SiO₂-Al₂O₃ glasses containing Al₂O₃ less than 1.5 mol % formed the surface apatite as well as Al₂O₃-free CaO-SiO₂ glasses, but CaO-SiO₂-Al₂O₃ containing Al₂O₃ more than 1.7 mol % did not form it as well as an SiO₂-free CaO-Al₂O₃ glass. This indicates that only a small amount of addition of Al₂O₃ to glass compositions suppresses the bioactivity of glasses and glass-ceramics by suppressing apatite formation on their surfaces in the body.     

Preparing of nanostructured Al2O3–TiO2–ZrO2 composite powders and plasma spraying nanostructured composite coating

Nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders for plasma spraying were prepared by spray drying granulation technology. The effects of processing parameters on the microstructure and properties of composite powders were investigated. The results show that with increasing the slurry solid content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the binder content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the spray drying temperature, the particle size of powders increases, and the bulk density and flowability of powders increases firstly and then decreases. The most appropriate spray drying parameters are the slurry solid content of 40 wt.%, the binder content of 2.0 wt.% and the spray drying temperature of 250 °C. The nanostructured composite coating was successfully prepared by using the as-prepared nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders as feedstocks. The nanostructured coating possessed higher hardness and toughness compared with the conventional microstructured one, which was attributed to the use of the nanostructured composite powders feedstocks.     

Synthesis and investigation of bimetallic Ni-Co/Al2O3 nanocatalysts using the polyol process

ABSTRACT

Ni-Co/Al₂O₃ catalysts with different Ni:Co ratios by weight were prepared using a simple polyol process. The activities of the catalysts were evaluated for the catalytic partial oxidation of methane (CPOM) in the temperature range of 600–800°C. Numerous techniques such as x-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, inductively coupled plasma-mass spectroscopy (ICP-MS), thermogravimetric analysis (TGA), high-resolution transmission electron microscopy analysis (HRTEM), scanning electron microscopy analysis (SEM-EDS) and temperature-programmed oxidation (TPO) were applied to characterize fresh and spent catalysts. The XRD analysis confirmed that the loaded particles were metals and showed possible bimetallic nano-alloy Ni-Co formation for Ni- and Co-containing catalysts. The highest metal dispersion was 15.7% for the Ni_2.8Co_2.6/Al₂O₃ catalyst. The catalytic test results showed no correlation between metal dispersion and the metal particle size, and the activity decreased in the order of Ni_7.7/Al₂O₃ > Ni_2.8Co_2.6/Al₂O₃ ≈ Ni_3.8Co_1.5/Al₂O₃ > Ni_2.0Co_3.8/Al₂O₃ >> Co_6.8/Al₂O₃ under a flow rate of 157,500 L kg^?1 h^?1 with CH₄/O₂ = 2 (using air as an oxidant) at 800°C. The obtained results also showed that when the actual atomic Ni/Co ratio was 1.07 in the Al₂O₃-supported catalyst, the dispersion of the active sites appeared to be promoted by Co addition, and the catalytic activity was stable over a reaction time of 10 h. Among all the tested catalysts, the Ni_2.8Co_2.6/Al₂O₃ catalyst exhibited acceptable activity (75%) without coking.     

Characterization of the interaction between molten titanium alloy and Al2O3

Pure titanium and Ti6Al4V alloys with single-crystal Al₂O₃ rod cores were prepared at 1740 °C and 1.2 atm Ar for 30 min. Aluminium diffusion takes place from Al₂O₃ into the titanium region for both Ti/Al₂O₃ and Ti6Al4V/Al₂O₃ interaction couples and results in the formation of an ordered ₂ phase (Ti3Al) in the titanium region adjacent to interfaces, even though there is no visible interaction product at interfaces.     

Atomic and electronic structures of Cu/α-Al2O3 interfaces prepared by pulsed-laser deposition

Interfacial atomic structures of Cu/Al₂O₃(0001) and Cu/Al₂O₃(11 0) systems prepared by a pulsed-laser deposition technique have been characterized by using high-resolution transmission electron microscopy (HRTEM). It was found that Cu metals were epitaxially oriented to the surface of Al₂O₃ substrates, and the following orientation relationships (ORs) were found to be formed: (111)_Cu//(0001)Al₂O₃, _Cu//[1 00]Al₂O₃ in the Cu/Al₂O₃(0001) interface and (001)_Cu//(11 0)Al₂O₃, [1 0]_Cu//[0001]Al₂O₃ in the Cu/Al₂O₃(11 0) interface. Geometrical coherency of the Cu/Al₂O₃ system has been evaluated by the coincidence of reciprocal lattice points method, and the result showed that the most coherent ORs were (111)_Cu//(0001)Al₂O₃, [11 ]_Cu//[1 00]Al₂O₃ and (1 0)_Cu//(11 0)Al₂O₃, [111]_Cu//[0001]Al₂O₃, which are equivalent to each other. These ORs were not consistent with the experimentally observed ORs, and it was possible that crucial factors to determine the ORs between Cu and Al₂O₃ were not only geometrical coherency, but also other factors such as chemical bonding states. Therefore, to understand the nature of the interface atomic structures, the electronic structures of the Cu/Al₂O₃ interfaces have been investigated by electron energy-loss spectroscopy. It was found that the pre-edge at the lower energy part of the main peak appeared in the O-K edge spectra at the interface region in both the Cu/Al₂O₃(0001) and Cu/Al₂O₃(11 0) systems. This indicates the existence of Cu–O interactions at the interface. In fact, HRTEM simulation images based on O-terminated interface models agreed well with the experimental images, indicating that O-terminated interfaces were formed in both systems. Since the overlapped Cu atomic density in the experimental ORs were larger than that in the most coherent OR, it is considered that the on-top Cu–O bonds stabilize the O-terminated Cu/Al₂O₃ interfaces.     

Experimental investigation on tribological behaviours of PA6, PA6-reinforced Al<Subscript>2</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>3</Subscript> and PA6-reinforced graphite polymer composites

This article reports on the preparation, characterization and experimental investigation of polyamide 6 (PA6) reinforced with alumina oxide (Al₂O₃) and graphite composites. The test specimens were prepared in an injection-moulding machine by varying the weight proportions of Al₂O₃ and graphite particles blended with PA6. The tribological properties of the composites were observed by using pin-on-disc wear test rig under dry sliding conditions. The worn surfaces of the composites were examined using scanning electron microscope. The addition of Al₂O₃ and graphite significantly enhanced the tribological properties of PA6. The PA6 containing 30 wt% Al₂O₃ and 20 wt% graphite revealed the best tribological behaviours due to the stronger interfacial bonding characteristics with improved wear resistance. Further, the thermal stability of Al₂O₃ and graphite particles was studied through thermogravimetric analysis test. It was also found that further addition of Al₂O₃ and graphite in PA6 had no significant improvement in wear resistance, the co-efficient of friction and heat generation.     

Origins of hindrance in densification of Ag/Al2O3 composites

The densification and microstructure development were studied for Ag-matrix composites containing dispersed Al₂O₃ particles to examine the effect of inclusions on the densification of composites. The incorporation of Al₂O₃ particles into Ag matrix hindered densification. Microstructure observation revealed that pores larger than those in the matrix formed around Al₂O₃ particles during sintering. The pore morphology was dependent on the number density of Al₂O₃ particles. When the number density was low, pores remained around an Al₂O₃ particle and coalesced to a large circumferential void at high temperatures. When the number density was intermediate, clusters made of a few Al₂O₃ particles formed and pores within and around clusters remained up to high temperatures. When the number density was high, the distance between clusters became small and the clusters were connected, forming continuous pores (pore channels). The three-dimensional connectivity of Ag was decreased, and the shrinkage between Ag particles resulted in thickening of pore channels. The presence of these large pores was the origin of the hindrance in densification.