RECOGNITION OF GAS-AIR MIXTURES BY A SINGLE GAS SENSOR BASED ON TIN DIOXIDE NANOWHISKERS

Нитевидные нанокристаллы диоксида олова были выращены методом физического осаждения из паровой фазы и перенесены на контактную систему методом замороженной капли. Полученные сенсоры обладают газочувствительностью, воздействие паров газов-восстановителей приводит к увеличению их проводимости. Показано, что существует долговременный дрейф проводимости сенсора при воздействии пробы. Исследована концентрационная зависимость чувствительности сенсора к парам этанола, ацетона и пропанол-2 при температуре 300 °С. На основе анализа концентрационных зависимостей проводимости рассчитаны энергии десорбции частиц, а также положения донорных уровней, индуцированных при адсорбции газов-восстановителей, относительно акцепторного уровня кислорода. Показано, что рассчитанные параметры имеют существенно меньший по сравнению с проводимостью временной дрейф. Использование указанных параметров позволяет распознавать газовоздушные смеси, т.е. однозначно отнести одну из трех исследованных проб к её классу. Tin dioxide nanowhiskers were grown by physical vapor deposition and transferred to the contact system by the frozen drop method. The sensors demonstrate gas-sensitivity. Exposing sensors to the atmosphere contained vapors of reducing-gases leads to an increasing of their conductivity. A long-term drift of the sensor conductivity during reducing-gas exposition was shown. A sensitivity response vs concentration for ethanol, acetone, and propanol-2 vapors at temperature 300 °C was investigated. Desorption energies of the particles and the positions of the donor levels induced by adsorption of reducing gases particles were calculated by analysis of the conductivity vs concentration dependence. The calculated parameters had a significantly smaller time drift in comparison with the conductivity. Using of these parameters makes possible to recognize gas-air mixtures: classify the each of three studied samples to one of classes.

Effect of Composition and Structure of Metal Oxide Composites Nanostructured on Their Conductive and Sensory Properties

The relationship between the structure and properties of nanoscale conductometric sensors based on binary mixtures of metal oxides in the detection of reducing gases in the environment is considered. The sensory effect in such systems is determined by the chemisorption of oxygen molecules and the detected gas on the surface of metal oxide catalytically active particles, the transfer of the reaction products to electron-rich nanoparticles, and subsequent reactions. Particular attention is paid to the doping of nanoparticles of the sensitive layer. In particular, the effect of doping on the concentration of oxygen vacancies, the activity of oxygen centers, and the adsorption properties of nanoparticles is discussed. In addition, the role of heterogeneous contacts is analyzed.

Humidity Dependence of Commercial Thick and Thin-Film MOX Gas Sensors under UV Illumination

Enhancing the performance of a chemo-resistive gas sensor is often challenging due to environmental humidity influencing its sensitivity and baseline resistance. One of the most promising ways of overcoming this challenge is through ultraviolet (UV) illumination of the sensing material. Most research has focused on using UV with in-house developed sensors, which has limited their widespread use. In this work, we have evaluated if UV can enhance the performance of commercially available MOX-based gas sensors. The performance of five different MOX sensors has been evaluated, specifically SGX Microtech MiCS6814 (thin-film triple sensor), FIGARO TGS2620 (n-type thick film), and Alphasense VOC sensor (p-type thick film). These sensors were tested towards isobutylene gas under UV light at different wavelengths (UV-278 nm and UV-365 nm) to investigate its effect on humidity, sensitivity, baseline drift, and recovery time of each sensor. We found the response time of thin-film sensors for reducing gases was improved by 70 s under UV- 365 nm at normal operating temperatures. In addition, all the sensors were left in a dirty environment and the humid-gas testing was repeated. However, due to their robust design, the sensitivity and baseline drift of all the sensors remained the same. This indicates that UV has only limited uses with commercial gas sensors.

Effect of Al and Mg Doping on Reducing Gases Detection of ZnO Nanoparticles

In this work, the main objective is to enhance the gas sensing capability through investigating the effect of Al and Mg doping on ZnO based sensors. ZnO, Mg1% doped ZnO, Al5% doped ZnO and (Al5%, Mg1%) co-doped ZnO nanoparticles (NPs) were synthesized by a modified sol-gel method. The structural characterization showed the hexagonal crystalline structure of the prepared samples. Morphological characterizations confirmed the nanometric sizes of the NPs (27–57 nm) and elemental composition investigation proved the existence of Al and Mg with low concentrations. The optical characterization showed the high absorbance of the synthesized samples in the UV range. The gas sensing performances of the synthesized samples, prepared in the form of thick films, were investigated. Sensing tests demonstrated the high influence of the Al and Mg on the sensing performances towards H2 and CO gas, respectively. The 5A1MZO-based sensor exhibits high sensitivity and low detection limits to H2 (<2 ppm) and CO (<1 ppm). It showed a response around 70 (at 250 °C) towards 2000 ppm H2 and 2 (at 250 °C) towards CO.

Structural Characterization and Gas Sensing Properties of Nano-Sized Tin Dioxide Material Synthesized from Tin(II) Sulfate

Structural features, surface condition, and gas-sensing properties of the nanocrystalline SnO2 powders synthesized from SnSO4 precursor by different methods have been studied. XRD, TEM, BET, and FTIR methods were used for the samples characterization. The gas sensors were fabricated by the thick-film technology from the synthesized SnO2 powders. The responses of the sensors toward CO and CH4 gases are measured. It is revealed that the preoxidation of SnSO4 powder with concentrated sulfuric acid before the hydrolysis results in the lower particle size, higher surface area, improved adsorption activity, and higher sensitivity to reducing gases (CO, CH4) of the synthesized SnO2 materials, than in the case of the SnO2 materials obtained without the preoxidation stage.

Processing of industrial waste by plasma-chemical method

In this paper, the results of the processing of magnesium fluoride by plasma-chemical method to obtain periclase and a solution of hydrogen fluoride (hydrofluoric acid) were presented. For the industrial implementation of plasma technologies, it is necessary to study the main parameters of plasma processes for obtaining reducing gases and processing metal oxides with them, to solve the issues of their hardware design, to increase the service life of plasma torches for their use in continuous metallurgical processes. The purpose of this work was to determine the conditions for the plasma-chemical process of processing magnesium fluoride. Thermal analysis of magnesium fluoride on a TGA/DSC2 thermogravimetric analyzer was performed. Thermogravimetric analysis showed that in the temperature range under consideration the process is endothermic, and at a temperature of ~1280°C a phase transition of the 1st kind is observed due to the melting of magnesium fluoride. The fractional composition of MgF2 and MgO powders was studied using the Analysette-22 Nanotech laser diffraction analyzer. The results of the evaluation of the fractional composition of powders have a significant difference. At the same time, the convergence of the data obtained using laser diffraction and electron microscopy methods was found.

Atomistic Descriptions of Gas–Surface Interactions on Tin Dioxide

Historically, in gas sensing literature, the focus on “mechanisms” has been on oxygen species chemisorbed (ionosorbed) from the ambient atmosphere, but what these species actually represent and the location of the adsorption site on the surface of the solid are typically not well described. Recent advances in computational modelling and experimental surface science provide insights on the likely mechanism by which oxygen and other species interact with the surface of SnO2, providing insight into future directions for materials design and optimisation. This article reviews the proposed models of adsorption and reaction of oxygen on SnO2, including a summary of conventional evidence for oxygen ionosorption and recent operando spectroscopy studies of the atomistic interactions on the surface. The analysis is extended to include common target and interfering reducing gases, such as CO and H2, cross-interactions with H2O vapour, and NO2 as an example of an oxidising gas. We emphasise the importance of the surface oxygen vacancies as both the preferred adsorption site of many gases and in the self-doping mechanism of SnO2.

In Situ Reduced Multi-Core Yolk–Shell Co@C Nanospheres for Broadband Microwave Absorption

The preparation of yolk–shell microwave absorption materials with low density and excellent microwave absorption property requires reasonable design and economical manufacture. In this study, an efficient strategy without any templates or reducing gases has been designed to fabricate multi-core yolk–shell Co@C nanospheres by high temperature carbonization. The results showed that Co3O4 was completely reduced by the carbon shell to metal cobalt at temperatures above 750 °C. This unique multi-core yolk–shell structure with shell of 600 nm and multiple cores of tens of nanometers can provide sufficient interface and space to reflect and scatter electromagnetic waves. At the same time, the metal cobalt layer and carbon layer provide magnetic loss ability and dielectric loss ability, respectively, making the composite show good wave absorption performance. The minimal RL value of samples carbonized at 750 °C reaches −40 dB and the efficient absorption band reaches 9 GHz with the thickness ranges from 2–9 mm. Therefore, this is a facile, effective and economical strategy to prepare yolk–shell structure, which provides a new idea for the preparation of microwave absorption materials.