Spark discharge synthesis of semiconductor nanoparticles for thick-film metal oxide gas sensors

Traditional methods of synthesis of metal-oxide gas sensing materials for semiconductor sensors are based on wet sol-gel processes. However, these processes lead to the formation of hydroxyl groups on the surface of oxide particles being responsible for the strong response of a sensing material to humidity. In this work, we investigated the possibility to synthesize metal-oxide materials with reduced sensitivity to water vapors. Dry synthesis of SnO2 nanoparticles was implemented in the gas phase by spark discharge, which allowed us to produce powder with specific surface area of about 40 m2/g after additional annealing at 610 °C. The drop of sensor resistance does not exceed 20%, when air humidity increases from 40 to 100%, whereas the response to 100 ppm of hydrogen is of a factor of 8 with very short response time of about 1 s

Volumes of polytopes in spaces of constant curvature

We overview the volume calculations for polyhedra in Euclidean, spherical and hyperbolic spaces. We prove the Sforza formula for the volume of an arbitrary tetrahedron in $H^3$ and $S^3$. We also present some results, which provide a solution for Seidel problem on the volume of non-Euclidean tetrahedron. Finally, we consider a convex hyperbolic quadrilateral inscribed in a circle, horocycle or one branch of equidistant curve. This is a natural hyperbolic analog of the cyclic quadrilateral in the Euclidean plane. We find a few versions of the Brahmagupta formula for the area of such quadrilateral. We also present a formula for the area of a hyperbolic trapezoid.Comment: 22 pages, 9 figures, 58 reference

Real time investigation of the initial stages of a-C films growth

a-C films were deposited by rf-PACVD. Their growth rate, thickness, density and roughness were derived during deposition from time dependent X-ray reflectivity (XRR) at a wavelength of 1.54 A and at a fixed incidence angle of 18. It is shown that the film density and surface roughness are not constant at the initial stages of growth. The density increases with increasing film thickness, while the surface roughness depends on the substrate roughness. The evolution of these parameters was measured also while etching the film in oxygen plasma and revealed the smoothing effect brought about by etching to the carbon surfac

Inhibition Performance of Chitosan- graft-Polyacrylamide as an Environmentally Friendly and High-Cloud-Point Inhibitor of Nucleation and Growth of Methane Hydrate

© 2020 American Chemical Society. Gas hydrates are considered a major problem in the oil and gas transportation pipelines, and their crystallization involves nucleation and growth of hydrate crystals. Hence, developing inhibitors that can affect nucleation and growth of hydrates is essential to inhibit their formation. Acrylamide polymers are well-known hydrate inhibitors, but they show a low cloud point, causing precipitation problems for field applications. In this research, we used chitosan to synthesize chitosan-graft-polyacrylamide (CS-g-PAM) as a green and high-cloud-point kinetic hydrate inhibitor (KHIs). The inhibition performance of CS-g-PAM on nucleation and growth of methane hydrate crystals was assessed by a high-pressure autoclave and high-pressure microdifferential scanning calorimeter (HP-μDSC). CS-g-PAM showed no cloud point in both deionized water and 3.5 wt % NaCl solutions, up to 100 °C. Autoclave experiments demonstrated that CS-g-PAM can increase the hydrate nucleation time 13 times (in 1 wt % sample) compared to the pure water system. According to HP-μDSC results, by adding 0.1, 0.5, and 1 wt % CS-g-PAM, the onset methane hydrate formation temperature was decreased from -12.7 °C in the pure water system to -15.8, -17.0, and -19.0 °C, respectively. Also, CS-g-PAM can change the morphology of methane hydrate crystals from solid state into a viscous foam-like slurry. These results show that the modification of acrylamide-based KHIs with natural polymers is an attractive option to improve their deposition point and change the morphology of hydrate crystals

NMR chemical shifts of carbon atoms and characteristic shift ranges in the oil sample

Application of high resolution 13C nuclear magnetic resonance (NMR) spectroscopy to characterize crude oil was demonstrated. The chemical shifts of 13C NMR functional groups that determine the composition of the oil sample were determined. Molar fractions of primary, secondary, quaternary, tertiary, aromatic groups, aromatic factor and average hydrocarbon chain length of aliphatic hydrocarbons of the oil sample according to 13C NMR spectra were determined. Detailed description of the 13C NMR spectra of the oil sample using a single consideration of three NMR spectra: 13C, 13C Attached Proton Test (APT), 13C with Gated Decoupling (GD) was performed. The different contribution of the studied oil sample in the aliphatic (10–75 ppm) and aromatic (115–165 ppm) areas of the 13C NMR spectra was determined. The presence of all major hydrocarbon components in the studied oil sample was established on the quantitative level, the aromaticity factor and the mean length of the hydrocarbon chain were evaluated. Quantitative fractions of aromatic molecules and functional groups constituting oil hydrocarbons were determined. In this work we demonstrate that the attached proton test and gated decoupling 13C NMR spectroscopy can afford all information to complete the chemical shift assignment of an oil sample, especially for determination of long range 1H–13C coupling constants and 13C multiplicity

ТОРАКОСКОПИЧЕСКАЯ САНАЦИЯ ПЛЕВРАЛЬНОЙ ПОЛОСТИ ПРИ ГНОЙНО-ВОСПАЛИТЕЛЬНЫХ ЗАБОЛЕВАНИЯХ ЛЕГКИХ У ДЕТЕЙ

Experience in treatment of pleural complication of destructive pneumonia in children was submitted. Of the 46 children, admitted with pneumonia complicated by the destructive, in 92% cases were typed pleural complications - 35% in the form of pleural empyema, in 30% fibrinothoracs. Delimited pleural empyema and fibrinothoracs found in children, treated for an average of two weeks in district hospitals. In these cases is made thoracoscopic pnevmoliz with resolution adhesions, opening and readjustment cavities, abscesses, removal of fibrin and subsequent drainage of pleural cavity. All 16 operated patients have a positive result, length of stay decreased by 1,5-2 times: 21 days vs 44-68 days with conservative tactics.Представлен опыт лечения плевральных осложнений деструктивной пневмонии у детей. Из 46 детей, поступивших с осложненной деструктивной пневмонией, в 92% случаев наблюдались плевральные осложнения: в 35% в виде эмпиемы плевры, в 30% в виде фибриноторакса. Отграниченная эмпиема плевры и фибриноторакс выявлены у детей, лечившихся в среднем в течение 2-х нед в районных больницах. В этих случаях выполнен торакоскопический пневмолиз с разрушением спаек, вскрытием и санацией полостей, абсцессов, удалением фибрина и последующим дренированием плевральной полости. У всех оперированных 16 пациентов получен положительный результат, продолжительность госпитализации снизилась в 1,5-2 раза: 21 день против 44-68 койко-дней при консервативной тактике

The nature of some Late Bronze Age iron-bearing artefacts of the Ural-Kazakhstan region

The problem of the beginning of iron production in the Late Bronze Age of the Ural-Kazakhstan region is discussed. For this, 13 iron-bearing artefacts from nine settlements that functioned in the 2nd mil. BC were studied using the SEM-EDS and LA-ICP-MS methods: metal objects, metallurgical slags, and a bimetallic droplet. Most of the studied artefacts are not related to the iron metallurgy. High ferric impurities in copper metal products of the Late Bronze Age on the territory of the Southern Trans-Urals are caused by the use of iron-rich ore concentrates. The raw materials for these products were represented by mixed oxidized-sulphide ores from the cementation subzone of the volcanogenic massive sulphide and skarn copper deposits. Iron droplets, frequently found in the Late Bronze Age copper slag in the Ural-Kazakhstan region, are not directly related to iron metallurgy. They are by-products of the copper metallurgy formed in the process of copper extraction from the iron-rich components of the furnace charge or fluxes (brown iron ore, iron sulphides). The only artefacts that indicate direct smelting of metal from iron ore are the slag fragments from the Kent settlement. Presumably, oxidized martitized ore of the Kentobe skarn deposit or its nearby analogues was used to extract iron at the Kent settlement. Rare finds of iron slags from the Late Bronze Age, known only in the territory of Central Kazakhstan, confirm an extremely small scale of iron production. Iron ore had been already deliberately used for these experiments. However, iron metallurgy in the Ural-Kazakhstan region developed into a mature industry much later. The discovery of iron metallurgy based on the smelting of copper-sulphide ores in the Ural-Kazakhstan steppes is doubtful. The use of sulphide ores here is known from the 20th c. BC, and it was widespread. In the meantime, the first iron slags and products appear much later, and their finds are sporadic. The development of iron metallurgy on the basis of experiments with iron ores seems more likely

Sulfonated chitosan as green and high cloud point kinetic methane hydrate and corrosion inhibitor: Experimental and theoretical studies

© 2020 Elsevier Ltd In this work sulfonated chitosan (SCS) was introduced as a promising green kinetic methane hydrate and corrosion inhibitor to overcome the incompatibility problem between inhibitors. Evaluation of hydrate inhibition performance of SCS with high-pressure autoclave and micro-differential scanning calorimeter revealed that hydrate formation was delayed 14.3 ± 0.2 times and amount of hydrate formed was decreased to 30 % compared to water. The weight loss experiments showed that SCS provides corrosion inhibition efficiency of 95.6 ± 0.1 at 5000 ppm concentration. SCS is able to increase polarization resistance and decrease corrosion current density according to electrochemical measurements. Study of surface morphology by SEM-EDX and profilometer showed that SCSs suppress corrosion rate and reduce the surface roughness of carbon steel. Quantum chemical study confirmed that the pendant groups caused by chitosan modification interact with carbon steel surface. The findings of this research can provide new opportunities to develop biodegradable materials as KHIs/CIs for flow assurance in oil and gas pipelines