Oxygen sensing with individual ZnO:Sb micro-wires: effects of temperature and light exposure on the sensitivity and stability

Nanostructured ZnO has been widely investigated as a gas sensing material. Antimony is an important dopant for ZnO that catalyses its surface reactivity and thus strengthens its gas sensing capability. However, there are not enough studies on the gas sensing of antimony-doped ZnO single wires. We fabricated and characterized ZnO/ZnO:Sb core–shell micro-wires and demonstrated that individual wires are sensitive to oxygen gas flow. Temperature and light illumination strongly affect the oxygen gas sensitivity and stability of these individual wires. It was found that these micro- and nano-wire oxygen sensors at 200°C give the highest response to oxygen, yet a vanishingly small effect of light and temperature variations. The underlying physics and the interplay between these effects are discussed in terms of surface-adsorbed oxygen, oxygen vacancies and hydrogen doping.

Tantalum-Titanium Oxynitride Thin Films Deposited by DC Reactive Magnetron Co-Sputtering: Mechanical, Optical, and Electrical Characterization

The possibility to tune the elemental composition and structure of binary Me oxynitride-type compounds (Me1Me2ON) could lead to attractive properties for several applications. For this work, tantalum-titanium oxynitride (TaTiON) thin films were deposited by DC reactive magnetron co-sputtering, with a –50 V bias voltage applied to the substrate holder and a constant substrate temperature of 100 °C. To increase or to decrease in a controlled manner, the Ti and Ta content in the co-sputtered films, the Ti and Ta target currents were varied between 0.00 and 1.00 A, in 0.25 A steps, while keeping the sum of the currents applied to the two targets at 1.00 A. The reactive gases flow, consisting of a nitrogen and oxygen gas mixture with a constant N2/O2 ratio (85%/15%), was also kept constant. The single-metal oxynitrides (TaON and TiON) showed a low degree of crystallinity, while all the other co-sputtered films revealed themselves to be essentially amorphous. These two films also exhibited higher adhesion to the metallic substrate. The TaON film showed the highest hardness value (14.8 GPa) and the TiON film a much lower one (8.8 GPa), while the co-sputtered coatings exhibited intermediary values. One of the most interesting findings was the significant increase in the O content when the Ti concentration surpassed the Ta one. This significantly influenced the optical characteristic of the films, but also their electrical properties. The sheet resistivity of the co-sputtered films is strongly dependent on the O/(Ta + Ti) atomic ratio.

The effects of cellulose nanofibers compounded in water-based undercoat paint on the discoloration and deterioration of painted wood products

Cellulose nanofibers (CNFs) have many potentials as filler to improve the properties of the other materials. We have developed the novel paints containing CNFs, and which controlled the discoloration of wood products. To clarify the discoloration mechanism of wood panels using an undercoat paint containing CNFs, prepared by an integrated process from Cryptomeria japonica, the composites and films made of CNFs and acryl resin that was a raw material for the paints were prepared. Observation of the surface of the CNFs/acryl resin composite film by atomic force microscopy showed that the fibers and the resin were uniformly mixed. The composite film prevented light transmittance in the ultraviolet (UV) light region, as well as oxygen gas permeation. The permeability coefficient of the oxygen gas decreased to 60% with the addition of 1.5 wt% of CNFs to the acryl resin. The addition of CNFs also increased the breaking stress by approximately 1.5 times compared with the acryl resin film. Electron spin resonance (ESR) analysis after UV irradiation resulted in the lowest radical formation of a piece of wood wrapped in the CNFs/acryl resin composite compared with the acryl-coated specimen and the wood as it was. Therefore, the CNFs composite film shielded the UV rays and oxygen more effectively than the original acryl resin, making it difficult for these factors to reach the wood’s surface, and thus, perhaps suppressing the generation of radicals from the wood. These actions would suppress the production of coloring substances caused by the radicals, resulting in the suppression of discoloration. Furthermore, the increase in the film’s strength by the addition of CNFs would have enhanced the stability of overall the paints with a CNF-containing undercoat. These effects might have contributed not only to the prevention of discoloration but also to the prevention of the occurrence of minute cracks caused by various weather deterioration factors.

Gas mixture explosion as a tool for generating impulsive disturbances

The work is devoted to the development of a device for generating impulsive perturbations in soil massifs. It is proposed to use the explosion energy of a high-pressure acetylene-oxygen gas mixture as a source of impulse perturbations. Applying the standard method of measuring mechanical stresses and using piezoelectric sensors, it is obtained the stress fields occurring in the soils when an explosion of the gas mixture takes place. It is revealed that the dependences of the maximal stresses in the soil massif on the relative distance to the source, when the gas charge under high pressure acts, are the power functions. The exponents of power functions approximating these experimental dependences are obtained. The attenuation of the maximal radial stresses with the distance is considered for the two cases when the charges filled with gas mixture under low and high pressure act. The comparison of these cases indicates their similarity. In the paper it is also performed the analysis of modern methods of using explosive and non-explosive sources for seismic wave generation during investigations in the search geophysics. The existing structural sources of seismic waves used in the seismic exploration are analyzed in detail. The disadvantages and advantages of explosive and non-explosive impulsive sources of seismic waves are indicated. Among the advantages of the proposed wave sources it is worth noting their low price and mobility. There is no need to obtain special permits for their use. The obtained results allow one to expand the field of gas detonation application. In particular, it can be used as an alternative source of seismic waves. The proposed method is promising for training in search geophysics and in the study of properties of soil massifs.

Influence of the Sputtering Technique and Thermal Annealing on YSZ Thin Films for Oxygen Sensing Applications

Yttria-stabilized zirconia (YSZ) thin films were deposited using direct current (reactive and metallic) and radio frequency magnetron sputtering. The effect of the deposition technique and annealing treatment on the microstructure and crystallinity of the thin films was assessed. Using the films produced in this work, oxygen gas sensors were built and their performance under vacuum conditions was evaluated. All the films exhibited a cubic crystalline structure after a post-deposition thermal treatment, regardless of the sputtering technique. When the annealing treatment surpassed 1000 °C, impurities were detected on the thin film surface. The oxygen gas sensors employing the reactive and oxide-sputtered YSZ thin films displayed a proportional increase in the sensor current as the oxygen partial pressure was increased in the evaluated pressure range (5 × 10−6 to 2 × 10−3 mbar). The sensors which employed the metallic-deposited YSZ films suffered from electronic conductivity at low partial pressures.

Investigations of regularities in the accumulation of hydrogen-reduced slags in circulation circuits with lead-containing coolants

The paper presents a computational analysis of regularities in the accumulation of slags during the interaction of lead and lead-bismuth coolants with oxygen gas. Oxidation of lead-containing coolants will cause the formation of lead oxide, while the formation of bismuth oxide is unlikely. Dosed supply of oxidizing gas to lead-containing coolants makes it possible to oxidize, selectively, chromium and nickel to their oxides without the slag formation from solid lead oxide. Regularities were studied which are involved in the lead oxide formation during the interaction of lead-containing coolants with oxygen gas. It has been found that, in the process of interacting with oxygen gas, a lead-bismuth alloy is oxidized 1.7 times as intensively as lead, this being explained by the presence of bismuth in the alloy. Bismuth is oxidized more intensively than both lead and the lead-bismuth alloy. The inert gas overpressure during depressurization does not prevent air oxygen from entering the circuit, and the dependence of the nitrogen and oxygen flow into the circuit on the argon flow out of the loop is close to linear regardless of the circuit state (cold, without coolant; heated, without coolant; heated, with circulating coolant). Oxygen is a chemically active impurity and is absorbed by the circuit; it is therefore important to control nitrogen in the gas spaces of the reactor and research plant circuits with lead-containing coolants. This will make it possible to signal, in a timely manner, the ingress of oxygen into the circuit and to take measures required to avoid or reduce the scale of the slag formation from lead oxides.