Low-pressure Oxygen Environments Research Articles

Lipoic acid/trometamol assembled hydrogel as injectable bandage for hypoxic wound healing at high altitude

To avoid chronic wound formation caused by hypoxia and cold in high-altitude areas, developing an injectable, strongly adhesive hydrogel bandage with controllable oxygen generation and inflammation regulation functions is of great value. Poly(lipoic acid) (PLA)-based adhesives have been well-developed from polymerization of α-Lipoic acid (LA), showing attractive performances including simple preparation, strong adhesion, anti-inflammatory. However, injection of PLA-based adhesives has not been well-practiced because of its high viscosity and strong adhesion. Herein, LA and trometamol are firstly found to rapidly gel into a supramolecular hydrogel within 5 min at room temperature, exhibiting well-performed injectability. Further presence of Ce3+ significantly accelerates this gelation within 2 min. Meanwhile, dopamine (DA) and g-C3N4 nanosheet synergistically endow the injectable hydrogel with photothermal function, which can convert near-infrared-light (NIR) into heat, triggering LA polymerization and achieving post-injection enhancement. In terms of bandage performance after molding, the introduction of Ce3+, DA, and g-C3N4 contributes to the improvement of mechanical and adhesion properties. The injectable hydrogel bandage not only possesses highly tough and adhesive features, but also produces oxygen under NIR irradiation, effectively alleviating wound hypoxia, creating anti-inflammatory microenvironment, and significantly promoting healing of incision in a low-pressure oxygen environment.

Segregation and Selective Oxidation of Ni Atoms in Pt3Ni(111) in a Low-Pressure Oxygen Environment

Understanding the microscopic mechanism of oxygen interaction with the surfaces of Pt-based alloys is an important issue for applications in various fields such as corrosion and oxygen reaction reduction in fuel cells, for which Pt-based alloys are more efficient catalysts with respect to platinum. Herein, the interaction of oxygen with Pt3Ni(111) has been studied by X-ray photoemission, X-ray absorption, and high-resolution electron energy loss spectroscopies. We have found that the oxidation of Pt3Ni(111) at 600 K leads to the segregation of Ni atoms to the surface region. The presence of Ni atoms at the Pt3Ni(111) surface allows O2 to dissociate to form NiOx surface species. High-resolution electron energy loss spectroscopy measurements performed on Pt(111), Ni(111), and Pt3Ni(111) directly show that, on the Pt3Ni(111) surface, oxygen binds selectively on Ni sites and, moreover, that the O–Ni bond formed on Pt3Ni is weaker than the O–Pt bond formed on Pt(111).

The electrical characterization of a multi-electrode odor detection sensor array based on the single SnO 2 nanowire

The variation of electrical properties of individual SnO 2 wedge-like nanowire along its length was characterized comparatively in a vacuum, low-pressure oxygen environment and in synthetic air mixed with various analytes. For characterization, a vapor–solid grown nanowire was indexed with multiple Pt mesoscopic contacts fabricated by e-beam induced deposition from Pt containing metalorganic precursor. The surface of the selected nanowire segments was functionalized with a catalyst via deposition of Pd nanoparticles. Detailed analysis of the electrical properties of the nanowire shows that the effective diameter of the conducting channel of the nanowire can be substantially modified along its length by the surface functionalization and nanowire width change. These variations of the electrical properties of nanowire segments are sufficient for reliable discrimination of acetone, 2-propanol, CO and hydrogen by this elemental multisensor array.

TGO Growth and Crack Propagation in a Thermal Barrier Coating

In thermal barrier coating (TBC) systems, a continuous alumina layer developed at the ceramic topcoat/bond coat interface helps to protect the metallic bond coat from further oxidation and improve the durability of the TBC system under service conditions. However, other oxides such as spinel and nickel oxide, formed in the oxidizing environment, are believed to be detrimental to TBC durability during service at high temperatures. It was shown that in an air-plasma-sprayed (APS) TBC system, postspraying heat treatments in low-pressure oxygen environments could suppress the formation of the detrimental oxides by promoting the formation of an alumina layer at the ceramic topcoat/bond coat interface, leading to an improved TBC durability. This work presents the influence of postspraying heat treatments in low-pressure oxygen environments on the oxidation behavior and durability of a thermally sprayed TBC system with high-velocity oxy-fuel (HVOF)-produced Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat. Oxidation behavior of the TBCs is evaluated by examining their microstructural evolution, growth kinetics of the thermally grown oxide (TGO) layers, and crack propagation during low-frequency thermal cycling at 1050 °C. The relationship between the TGO growth and crack propagation will also be discussed.

Properties of ITO on plastics and glass by Nd:YAG laser deposition at 355 and 532 nm

Indium tin oxide (ITO) was deposited on polycarbonate (PC), polyethylene terephthalate (PET) and glass substrates at room temperature and in a low-pressure oxygen environment by a pulsed Nd:YAG laser at 355 and 532 nm. The ITO film resistivity varied with the oxygen pressure, which achieved the lowest value of 1.5 × 10 −3 Ω cm from the four-point probe measurements. The highest optical transmittance which depended on the target-to-substrate distance, was determined from UV–vis–NIR spectrophotometer. The highest optical transmission was 94% at 5 cm. The carrier concentration, of the order of 10 19 cm −3 was determined from the Hall-effect measurements. Those films deposited at 355 nm of laser wavelength did show some better properties as compared to 532 nm. Attempts were made to use these ITO-coated plastic substrates for the fabrication of a organic light-emitting device that was based on single-layer, molecularly doped (poly( N-vinyl carbazole)) (PVK) with a mixture of tris(8-hydroxyquinoline) aluminum (III) (Alq 3) and N, N'-bis (3-methylphenyl)- N, N'-bis-(phenyl)-benzidine (TPD) of 1:1 ratio.

Pre-oxidation and TGO growth behaviour of an air-plasma-sprayed thermal barrier coating

In thermal barrier coating (TBC) systems, spinel and nickel oxide formed in an oxidizing environment are believed to be detrimental to TBC durability during service at high temperatures. The present study shows that in an air-plasma-sprayed (APS) TBC with Co–32Ni–21Cr–8Al–0.5Y (wt.%) bond coat, pre-oxidation treatments in low-pressure oxygen environments can suppress the formation of the detrimental oxides by promoting the formation of an Al 2O 3 layer at the ceramic topcoat/bond coat interface. The development of the thermally grown oxide (TGO) layer generally exhibits a three-stage growth phenomenon that resembles high temperature creep. The pre-oxidation treatments reduce the growth rate and extend the steady-state growth stage, leading to an improved durability. Crack propagation in the TBC proceeds via opening and growth of pre-existing discontinuities in the ceramic topcoat, assisted by crack nucleation and growth associated with the TGO. Crack propagation during thermal cycling appeared to be controlled by TGO growth, and the maximum crack length and TGO thickness generally have a power law relationship.

Modification of oxide layer in plasma-sprayed thermal barrier coatings

Formation of Ni(Cr,Al) 2O 4 and NiO in plasma-sprayed thermal barrier coatings (TBCs) is believed to be detrimental to the durability of TBC systems. Therefore, a heat treatment to the as-sprayed TBC in a low-pressure oxygen environment is developed to produce a uniform thin alumina (Al 2O 3) layer at the ceramic/bond coat interface, which suppresses the growth of Ni(Cr,Al) 2O 4 and NiO during later thermal exposure in air.

Tungsten-rhenium filament lifetime variability in low pressure oxygen environments

Accelerated life-testing of tungsten-rhenium filaments in oxygen rich environments has been performed to investigate the longevity of the devices as a function of electron emission intensity and power cycling methodology. The lifetimes of such filaments are found to be independent of the electron emission level over typical operating ranges, but the turn-on/off sequence is found to have important life-span consequences. A gradual turn-on cycle lasting several minutes results in substantially extended lifetimes, ostensibly by reducing the thermal shock associated with more abrupt power cycling.

Nanocrystalline Cr 2O 3–TiO 2 thin films by pulsed laser deposition

In the present work, pulsed laser deposition (PLD) technique was applied to Cr 2O 3–TiO 2 mixed oxide (5–20 at.% TiO 2) gas sensing materials with the aim to find the feasibility and optimal conditions for the growth of nanostructured thin films. The films were deposited by KrF laser ( λ = 248 nm) on Si(1 0 0) substrates in low-pressure oxygen environment, and characterised by X-ray diffraction, X-ray reflection, reflection high-energy electron diffraction and atomic force microscopy. The substrate temperature (450–700 °C), oxygen pressure (10 −3 to 5 × 10 −2 mbar), and laser energy density (1.5–4.5 J/cm 2) were varied for optimising the growth conditions. Structural and morphological analysis showed that the films started to crystallize at oxygen pressures above 10 −2 mbar. At the highest oxygen pressure the first traces of crystallization appeared at raising the temperature over 400 °C (20 at.% of Ti) or 450 °C (at 5 at.% Ti). Smallest particle sizes (10–20 nm) were obtained at 500–550 °C, whereas the best degree of crystallinity of nanostructured films was observed at higher temperature but at lower laser energy densities. When the films were grown or annealed at temperatures over 600 °C the crystallinity further improved but the particle size grew over 100 nm.

Oxidation and crack nucleation/growth in an air-plasma-sprayed thermal barrier coating with NiCrAlY bond coat

The oxidation behavior of an air-plasma-sprayed thermal barrier coating (APS-TBC) system was investigated in both air and low-pressure oxygen environments. It was found that mixed oxides, in the form of (Cr,Al) 2O 3·Ni(Cr,Al) 2O 4·NiO, formed heterogeneously at a very early stage during oxidation in air, and in the meantime, a layer of predominantly Al 2O 3 grew rather uniformly along the rest of the ceramic/bond coat interface. The mixed oxides were practically absent in the TBC system when exposed in the low-pressure oxygen environment, where the TBC had a longer life. Through comparison of the microstructures of the APS-TBC exposed in air and low-pressure oxygen environment, it was concluded that the mixed oxides played a detrimental role in causing crack nucleation and growth, reducing the life of the TBC in air. The crack nucleation and growth mechanism in the air-plasma-sprayed TBC is further elucidated with emphasis on the Ni(Cr,Al) 2O 4 and NiO particles embedded in the chromia.

Reactions of oxygen with VCrTi alloys

Fusion reactors have been proposed with a vanadium alloy as the structural/containment material. However, vanadium has a significant affinity for interstitial contamination that could deleteriously affect its mechanical properties. The effects of oxygen pick-up in air and low pressure oxygen environments were investigated at 400–500°C for two VCrTi alloys. As expected the studies showed that the room temperature tensile ductility is reduced by exposure to air or low pressure oxygen environments. However, the magnitude depends upon processing history and subsequent heat treatment. Possible embrittling mechanisms such as grain boundary weakening or weakening of near-boundary regions are discussed.

Studies of target materials and wavelength for laser ablation-deposition of Ti:sapphire

The laser ablation of crystalline and ceramic Al2O3 and aluminium metal targets in a low pressure oxygen environment has been studied as a first step in the investigation of alternative routes to the ablation-deposition (LAD) of thin film Ti:sapphire. The different targets were ablated using both ultraviolet (193 nm ArF) and infrared (10.6 μm CO2) pulsed lasers with deposition on Si substrates at room and elevated temperatures. Preliminary characterisation of the deposited films indicates that optimisation of the processing parameters is likely to result in successful deposition by these alternative routes.