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.

Cement-free refractory concretes. Part 10. Rheological aspect of technology

The features of the rheological behavior of CFRC matrix systems are considered as highly concentrated dispersed systems. They are characterized by a dilatative, thixotropic and thixotropic-dilatant nature of the flow, depending on the composition, concentration, dispersion, and a number of other factors. The equation of the concentration dependence of the viscosity of suspensions (Pivinskii equation) is proposed. It is shown that the determining factor is the content of a kinetically free dispersion medium in them. The effect of the content of grain aggregate on the rheological properties of foundry systems is characterized. The significant effect of polydispersity of the particles of the solid phase and the temperature on the rheological properties of the HCBS with the dilatant nature of the flow is shown. The data on the effect of defloculation and stabilization of matrix systems on their rheological properties, which determine the reeterological properties of molding systems to obtain CFRC. Ill. 13. Ref. 50.

Pentamethinium Salts Nanocomposite for Electrochemical Detection of Heparin

This study presents a simple route to heparin detection and develops a voltammetric approach using supramolecular principles and nanomaterials. Nanocomposites, including gold nanoparticles (AuNPs) and γ-substituted pentamethinium salts (PMS) deposited on a glass carbon (GC) electrode surface (GC/AuNPs/PMS) and covered by a plasticized poly(vinyl chloride) (PVC) membrane, are proposed for heparin detection. The conductivity of the nonconducting PVC-plasticized membrane is guaranteed by AuNPs, and the selectivity is provided by the interaction between γ-substituted PMS and anionic analytes. In order to extend the linear range, it is necessary to apply a solvent compatible with PVC-plasticized membrane, namely tetrahydrofuran. The proposed voltammetric sensor showed a concentration dependence from 1.72 up to 45.02 IU mL−1 heparin and was used for heparin detection in saline and biological samples with recovery of 95.1–100.9%.