Reagent Gas Research Articles

SYSTEM FOR CONTROLLING MASS BALANCE OF GASES AND REAGENTS DURING FORMATION OF ION-PLASMA COATINGS

Providing an increase in the working capacity of a metal-cutting tool, it is possible to significantly increase the productivity of mechanized labor, thereby reducing the cost of purchasing a new tool and saving on other accompanying technological components. During the operation of the cutting tool, the main load is transferred to its working part, this, as a rule, leads to partial wear or complete destruction of the planes and cutting edges. There are a number of technologies for processing working surfaces, which provides them with additional strengthening, the most effective of which is the method of applying special coatings to the surface of the cutting tool. Taking into account the specifics of the processes of formation of coatings, they can be divided into three main groups [1]. The first group includes methods in which the formation of coatings is carried out mainly due to diffusion reactions between saturating elements and structures of the instrumental material. The second group includes methods of forming coatings by a complex mechanism. The third group includes methods of forming coatings due to chemical and plasma-chemical reactions of particle flux simultaneously in volumes of space immediately adjacent to the saturable surfaces of the instrumental base. One such technology is the CIB (condensation and ion bombardment) method, which is a physical deposition of coatings. The most characteristic feature of coatings produced by this method is the absence of a transition zone between the coating and the tool material. This makes it possible to obtain a complex of properties on the working surfaces of the tool without deteriorating its original properties. The article is devoted to the issues of increasing the efficiency of ion-plasma technologies through the development and implementation of an automated system for analyzing and controlling the mass balance of reagent gases under conditions of several gases supply. Thus, the improvement of the technology of coating the working surfaces of the cutting tool, namely, the effective control of the process of applying ion-plasma coatings with the introduction of an automated system for analyzing and controlling the mass balance of reagent gases under conditions of supplying several gases is an urgent task.

Gas‐solid displacement reactions in the Ti–W–C system

AbstractDisplacement reactions between binary and ternary ceramics in the Ti–W–C system and reactive gaseous atmospheres are investigated in this work. Specifically, WC and 50:50 wt% TiC:WC solid solution powders were exposed to flowing hydrogen gas, or equilibrated against an excess of titanium in the presence of iodine, to form metallic tungsten and TiC solid products. In the case of pure WC reacting with hydrogen, transformation to metallic tungsten occurred as a result of removal of chemically bound carbon as gaseous hydrocarbons. In the case of pure WC reacting with titanium iodide vapors, transformation was accompanied by the appearance of TiC as a solid product formed at the gas‐solid interface. In the case of 50:50 wt% TiC:WC solid solution powders, hydrogen was generally found to be an ineffective displacing reagent, whereas reaction with titanium iodide vapors was observed to proceed virtually to completion, resulting in a two phase product mixture comprising metallic tungsten and TiC. For the latter case, a variety of microstructures could be observed within a given batch, including tungsten platelets and/or lamellae in a TiC matrix, or coarse tungsten grains interspersed with TiC grains. These morphological variations are speculated to arise from compositional variation in the starting material and the occurrence of local rapid coarsening along fast diffusion pathways within reacting agglomerates and polycrystalline primary particles. The observed reaction products and relative efficacy of gaseous reagents to promote displacement reactions in the Ti–W–C system are rationalized on the basis of thermodynamic predictions. The reaction between 50:50 wt% TiC:WC solid solution powders and titanium iodide vapors constitutes the first known report of an internal displacement reaction proceeding via gaseous intermediates in a nonoxide ceramic system.

New fully automated gas chromatographic analysis of urinary S-phenylmercapturic acid in isotopic dilution using negative chemical ionization with isobutane as reagent gas.

The determination of urinary S-phenylmercapturic acid (S-PMA) represents the most reliable biomarker to monitor the intake risk of airborne benzene. Recently, the European Chemical Agency deliberated new occupational exposure limits for benzene and recommended an S-PMA biological limit value of 2-μg/g creatinine. This limit is an order of magnitude lower than the previous one, and its determination constitutes a challenge in the analytical field. We developed and validated a method that allows the fully automated and sensitive determination of S-PMA by the use of gas-chromatography negative chemical ionization tandem mass spectrometry in isotopic dilution. For negative chemical ionization, we selected a mixture of 1% isobutane in argon as reactive gas, by studying its chemical ionization mechanism and optimal parameters compared with pure isobutane or pure methane. This gas mixture produces a more abundant signal of the target analyte than isobutane or methane, and it extended the operative lifetime of the ion source, enabling us to start a high-throughput approach of the S-PMA analysis. Moreover, energy-resolved mass spectrometry experiments were carried out to refine the MS/MS analysis conditions, testing nitrogen and argon as collision gases. The method optimization was pursued by a chemometric model by using the experimental design. The quantification limit for S-PMA was 0.10 μg/L. Accuracy (between 98.3% and 99.6%) and precision (ranging from 1.6% to 6.4%) were also evaluated. In conclusion, the newly developed assay represents a powerful tool for the robust, reliable, and sensitive quantification of urinary S-PMA, and because of its automation, it is well suited for application in large environmental and biological monitoring.

Probability Langmuir-Hinshelwood based CO2 photoreduction kinetic models

For engineering solutions, scaling photoreactors and processes, kinetic models that describe the impact of process conditions on CO2 photoreduction are critical to driving this technology forward. Probability Langmuir-Hinshelwood based CO2 photoreduction kinetic models were developed after several criteria that included: a high purity photodifferential photoreactor with a high ratio of reagent gas volume to irradiated photocatalyst surface area and automated robust data collection and kinetic modelling using a MATLAB program. Product distribution profiles indicated the dynamic changes occurring over the photocatalyst with an initial increase in H2 product distribution, followed by an increase in CH4 and finally CO product distribution, possibly due to the photocatalytic degradation of CH2O and CH2O2 intermediates. Production of H2 increased with a decrease in CH4 when the partial pressure of H2O was increased. Using the glyoxal mechanism, this is possibly explained via the formation of CH3CO2H from H2O reacting with CH3CHO that prevents the full conversion of CH3CHO to CH4. To account for deactivation, probability Langmuir–Hinshelwood based kinetic models were used to fit CO2 photoreduction kinetic data for CH4, CO and H2 with low average standard errors of 3.44×10-4,1.54×10-4 and 1.36×10-4, respectively. The probability LH based kinetic model coefficients were estimated with low standard deviations, using a robust and repeatable numerical method using a trust-region and multi-start algorithm. The models were used to predict optimised selectivity of CH4, CO and H2.

Transition of the Combustion Wave of a Heterogeneous System through a Shaped Obstacle

The transition of the combustion wave of a titanium powder layer in air through an inert shaped obstacle has been experimentally studied. It has been shown that an inhomogeneous wave-like structure of the combustion front can form due to the limited supply of gaseous reagents and the thermal instability of combustion of the titanium powder layer. Conditions of the optimal transient combustion mode in the presence of gaseous impurities affecting gas exchange in the reaction zone and the stability of the front in the layered system are obtained. It is shown that there exists a phenomenological criterion for assessing the nature of the transient combustion mode of titanium powder depending on the shape of the inert obstacle and the combustion front.

Conversion of liquid combustible wastes in the filtration regime to syngas by partial oxidation

A new method of combustion/conversion of liquid combustible wastes is proposed in the filtration mode when one of the reagents (liquid fuel or oxidizer gas) is supplied from the end of the reactor filled with a porous incombustible backfill (inert) and the other into the middle part. In this case, the inert, charged to the upper part of the reactor at room temperature, is heated in countercurrent combustion products. At discharging of inert from the lower part of the reactor (and the equal volume is simultaneously added to the upper part, so that the bed in the reactor is kept constant), the inert heated in the upper part enters the lower part, where it gives heat to the gaseous reagent supplied from below. This method can be carried out both with an excess of the oxidant with the combustion of combustible liquids to CO2 and H2O, and with a lack of oxidizer, when the conversion of the initial fuel to the synthesis of a gas predominantly containing CO and H2 takes place. On the example of a model fuel (isopropyl alcohol), the regularities of filtration combustion at different oxidant to fuel ratios have been experimentally studied.

Polymers of Intrinsic Microporosity in Triphasic Electrochemistry: Perspectives

AbstractPolymers of intrinsic microporosity (PIMs) as molecularly rigid polymers have emerged as a new class of gas‐permeable glassy materials. They offer excellent processability and a range of potential applications also in electrochemical processes. Particularly interesting is the ability of some PIM films to remain gas‐permeable/binding even in the presence of (aqueous) liquid electrolyte to give triphasic interfacial reactivity. Gaseous reagents or products (such as hydrogen or oxygen) are bound probably into hydrophobic regions in the wet PIM film to avoid macroscopic bubble formation and to enhance both the surface reactivity and the apparent activity of the gas solute close to the electrode/catalyst surface. The photoelectrochemical formation of hydrogen gas close to a platinum electrode is enhanced by PIM‐1, which is presented as an example of energy harvesting through molecular H2 “energy carrier” transport.

Theoretical and experimental study of cellular structures in restricted filtration combustion of porous media

Infiltration-mediated combustion of a thin porous cylinder in reactive gas was studied by mathematical modeling. Gas reagent is infiltrated through an annular gap left of the side surface. In conditions of instability, the self-sustained propagation of individual cellular spots of exothermic combustion was observed. The structure of cellular waves, their dynamics, and travel direction are defined by such factors as temperature profile, pressure gradients, heat release rate, porous structure, and heat losses. Cellular combustion of Ti powder in dish was also explored experimentally and the results were compared with theoretical predictions.

Synthetic Small Molecule Characterization and Isomer Discrimination Using Gas-Phase Hydrogen–Deuterium Exchange IMS-MS

Ion mobility spectrometry-mass spectrometry (IMS-MS) combined with gas-phase hydrogen-deuterium exchange has been used to characterize novel psychoactive substances (NPSs) which are small synthetic compounds designed to mimic the effects of other illicit substances. Here, NPSs containing labile heteroatom hydrogens were evaluated for HDX reactivity in the presence of either deuterated water (D2O) or ammonia (ND3) within the drift tube. An initial evaluation of exchange propensity was performed for six NPSs. Five compounds exchanged in the presence of ND3 while only one NPS (benzyl piperazine) exchanged with D2O. The exchange mechanism of D2O requires stabilization with a nearby charged site; the diamine ring of benzyl piperazine provided this charge site at a fixed length. Three disubstituted benzene isomers ( o-, m-, and p-fluorophenyl piperazine) containing the diamine ring structure and a fluorine atom were subsequently analyzed. Having identical isotopic composition and nearly identical drift time distributions, these isomers could not be distinguished by IMS-MS alone. However, upon undergoing HDX in the drift tube, a t test of means (α = 0.05) showed that discrimination was possible if the exchange data from both reagent gases were included. Molecular dynamics simulations show that the proximity of the fluorine to the diamine ring hinders the dihedral angle rotation between the benzene and the diamine ring; this may partially account for the observed exchange differences.

Synthesis of AlN nanopowder coated with a thin layer of C, using a thermal plasma reactor

High-purity nanocrystalline aluminum nitride powders were synthesized by using a 12 kW non-transferred arc plasma. The synthesis was conducted in a versatile, new designed, one-chamber thermal plasma reactor (TPR). The novel experimental assembly incorporated better working conditions like: high temperature gradient between the crucible and reactor's wall, and high super-saturation of the system by nitrogen and carbon. Thermodynamic modelling of the synthesis was conducted in order to achieve the best conditions for AlN formation. In this study, aluminum discs of Al 1100 were used as precursor material and pure nitrogen was the only gas used as reagent and plasmogenic gas. Nanopowders collected from reactor's wall were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-Ray diffraction (XRD). Synthesized h-AlN nano-powders were found to be free of oxides and aluminum metal. A thin carbon-layer around the particles was detected. TEM results indicated that the carbon-layer was around 5 and 10 nm. This outcome could make a significant difference with other synthesis reported in the literature since the occurrence of the carbon-layer, could delay AlN oxidation, prevent hydration, and could avoid the agglomeration of the particles.

Forensic drug analysis of chloro-N,N-dimethylcathinone (CDC) and chloroethcathinone (CEC): Identification of 4-CDC and 4-CEC in drug seizures and differentiation from their ring-substituted positional isomers

We report our findings for the determination of 4-chloro-N,N-dimethylcathinone (4-CDC), a newly encountered NPS in drug seizures examined in our laboratory, and its differentiation from 4-chloroethcathinone (4-CEC), one of the most common cathinones examined locally, and their respective regioisomers, namely 2-CDC and 3-CDC, as well as 2-CEC and 3-CEC in routine drug analysis.As CDCs and CECs have the same molecular mass of 211 with similar and non-characteristic spectra when analysed by gas chromatography-electron ionization-mass spectrometer (GC–EI-MS), it is imperative to establish methods easily amendable for forensic laboratories to differentiate these substances unambiguously. To confirm the identity of the solid, reference standards of all regioisomers of CDC (i.e., 2-CDC, 3-CDC and 4-CDC) and CEC (i.e., 2-CEC, 3-CEC and 4-CEC) were acquired and analysed using GC–EI-MS, liquid chromatography-diode array detector (LC–DAD) and Fourier Transform Infrared Spectrophotometer (FTIR) commonly used in routine forensic drug analysis. In addition, drug analysis with gas chromatography-chemical ionization-mass spectrometer (GC–CI-MS) using methane as the reagent gas operated in positive mode was also explored. It is found that using GC–EI-MS, all isomers of CDCs and CECs eluted with close but different retention times. However, the mass spectra between respective regioisomers were similar and difficult to distinguish. Using LC–DAD, the retention times of all studied cathinones were again different although there were partial overlap between 3-CDC and 4-CDC as well as between 3-CEC and 4-CEC but they all have distinguishable UV spectra. Apart from the detection of quasimolecular ion as the most prominent ion for each cathinone, GC–CI-MS is considered a superior technique to determine all six cathinones where each cathinone showed a unique fragmentation pattern for ease of identification. The analytical techniques have been applied for the examination of drug seizures where 4-CDC and 4-CEC were unambiguously identified either as a single component or mixed components in the seized materials.While FTIR is capable of providing confirmative structural information for the cathinones with each regioisomer exhibits a distinctive pattern but requiring high drug purity, LC–DAD and GC–CI-MS are demonstrated to be useful techniques that can readily differentiate structurally similar synthetic cathinones (even in mixtures) for routine forensic drug analysis.

Sol–gel–xerogel transformations in the thin layer at the salt solution–gaseous reagent interface and the synthesis of new materials with microtubular morphology

In this report, we consider the peculiarities of sol–gel–xerogel transformations, which occurs in the thin layer at the FeCl2/FeCl3 water solution and gaseous NH3 interface. A thin layer consisting of nanoparticles of Fe(OH)3 and Fe3O4 is formed as a result of interfacial reaction. Depending on the time of treatment with gaseous ammonia, it was possible to obtain either a freestanding layer with a thickness of 1 μm or microtubular structures (scrolls). Synthetic conditions, under which a large number of preferentially oriented microtubes are formed with diameters of about 10 and up to 200-μm long, were determined. The synthesized structures consisted of crystalline Fe3O4 nanoparticles with an average diameter of about 5–10 nm incorporated in an amorphous matrix. Layers and tubes were characterized by X-ray diffraction analysis, scanning and transmission electron microscopy (SEM and TEM), and X-ray photoelectron spectroscopy. The model, concerning sol–gel–xerogel transformations in the thin layer, formed after interaction at the salt solution–gaseous reagent interface, was suggested. The magnetic properties of the products were studied.

Two-Stage Conversion of Silicon to Nanostructured Carbon by the Method of Coordinated Atomic Substitution

A fundamentally new method of obtaining epitaxial layers of nanostructured carbon on silicon substrates has been considered. Epitaxial growth in the case of seemingly incompatible lattices has been achieved by converting the crystal by the method of coordinated substitution of atoms, in which the overall structure of the bonds between the atoms is not destroyed. In the first stage of conversion, the first half of the silicon atoms are concertedly replaced by the carbon atoms due to the reaction of silicon with CO gas, during which an epitaxial layer of SiC–3C cubic silicon carbide is obtained. In the second stage of conversion, the remaining half of silicon atoms is concertedly replaced by carbon atoms due to the reaction of SiC with CF4 gas. Carbon structures with different properties from nanodiamonds to nanotubes and carbon nanoonions have been obtained depending on the orientation of the silicon surface, pressure of the reagent gas, and temperature and growth time. A key feature of this method is that the substrate orders the resulting structures using the original chemical bonds between the atoms in silicon. The term “concertedly” means that new chemical bonds are formed simultaneously and concertedly with the destruction of old bonds. Data on electron diffraction and analysis of Raman and ellipsometric spectra of the obtained samples of nanostructured carbon on silicon substrates have been presented. Two competing growth mechanisms have been discussed.

Making the SF5 Group More Accessible: A Gas-Reagent-Free Approach to Aryl Tetrafluoro-λ6 -sulfanyl Chlorides.

Modern pentafluorosulfanyl (SF5 ) chemistry has an Achilles heel: synthetic accessibility. Herein, we present the first approach to aryl-SF4 Cl compounds (key intermediates in state-of-the-art aryl-SF5 synthesis) that overcomes the reliance on hazardous fluorinating reagents and/or gas reagents (e.g. Cl2 ) by employing easy-to-handle trichloroisocyanuric acid, potassium fluoride, and catalytic amounts of acid. These simple, mild conditions allow direct access to aryl-SF4 Cl intermediates that either have not been or cannot be demonstrated using previous methods. Furthermore, the same approach provides access to aryl-SF3 and aryl-SeF3 compounds, which extend the applications of this chemistry beyond arene SF5 -functionalization, and demonstrate its ability to address a more general oxidative fluorination problem.

Mechanochemistry of Gaseous Reactants.

In recent years, the application of mechanical energy to chemical systems has repeatedly proven beneficial to facilitate chemical transformations in various areas in chemistry. Today, a systematic body of evidence indicates that mechanochemistry holds great promise to become a game-changer in chemical synthesis. Not only does mechanochemistry permit access to products that are inaccessible by established means (e.g. purely thermal activation), mechanochemical reactions often outperform their solution-based counterparts in terms of sustainability. Most mechanochemical reactions carried out by ball milling techniques involve transformations of solids and liquids, but the number of mechanochemical reactions with gaseous reactants is increasing. The aim of this Minireview is to provide an overview of recent chemical reactions involving gaseous samples by ball milling techniques and to highlight advances in ball milling technology for the safe handling of gaseous reagents. Examples of reactions proceeding at the interface of solid-/liquid-/gas-gas systems that led to significant improvements in reactivity or selectivity will also be highlighted.

Thermochemical investigation of perspective MOCVD precursor of MgO functional layers

This paper presents a reliable and useful thermochemical information on a mixed-ligand magnesium complex with trifluoroacetylacetonate (tfac) and N,N,N′,N′-tetramethylethylenediamine (tmeda), Mg(tmeda)(tfac)2, as low melting and highly volatile precursor for metal–organic chemical vapor deposition. New vapor pressure data for sublimation and vaporization processes were obtained by Knudsen effusion and transpiration methods, respectively, giving the corresponding molar enthalpies and entropies: ∆subH328.0 = 106.2 ± 3.1 kJ mol−1 and ∆subS°328.0 = 224.8 ± 9.6 J K−1 mol−1, ∆vapH385.5 = 71.5 ± 1.4 kJ mol−1 and ∆vapS°385.5 = 131.6 ± 3.8 J K−1 mol−1. Based upon these new results, the sublimation data obtained previously by transpiration method were re-treated giving the following thermodynamic characteristics of sublimation: ∆subH345.5 = 106.4 ± 1.0 kJ mol−1 and ∆subS°345.5 = 227.4 ± 2.8 J K−1 mol−1. The thermal behavior of the precursor vapor on the heated surface in vacuum was investigated by in situ mass spectrometry in the temperature range (353–773) K. A two-step dissociation of the complex molecule was established, while no complete decomposition to form the inorganic phase was observed without reagent gases. Thermodynamic simulation of the solid phase formation from the gaseous mixture of the precursor and oxygen or water as co-reagents in Mg–O–F–C–N–H system was carried out within wide range of the deposition temperature, total pressure and reagent molar ratio in order to determine the conditions of obtaining pure MgO films.

Investigations of the generality of quaternary ammonium salts as alkylating agents in direct C-H alkylation reactions: solid alternatives for gaseous olefins.

C-H alkylation reactions using short chain olefins as alkylating agents could be operationally simplified on the lab scale by using quaternary ammonium salts as precursors for these gaseous reagents: Hofmann elimination delivers in situ the desired alkenes with the advantage that the alkene concentration in the liquid phase is high. In case a catalytic system did not tolerate the conditions for Hofmann elimination, a very simple spatial separation of both reactions, Hofmann elimination and direct alkylation, was achieved to circumvent possible side reactions or catalyst deactivation. Additionally, the truly catalytically active species of a rhodium(i) mediated alkylation reaction could be identified by using this approach.

Двухстадийная конверсия кремния в наноструктурированный углерод методом согласованного замещения атомов

Abstract—A fundamentally new method of obtaining epitaxial layers of nanostructured carbon on silicon substrates has been considered. Epitaxial growth in the case of seemingly incompatible lattices has been achieved by converting the crystal by the method of coordinated substitution of atoms, in which the overall structure of the bonds between the atoms is not destroyed. In the first stage of conversion, the first half of the silicon atoms are concertedly replaced by the carbon atoms due to the reaction of silicon with CO gas, during which an epitaxial layer of SiC–3C cubic silicon carbide is obtained. In the second stage of conversion, the remaining half of silicon atoms is concertedly replaced by carbon atoms due to the reaction of SiC with CF_4 gas. Carbon structures with different properties from nanodiamonds to nanotubes and carbon nanoonions have been obtained depending on the orientation of the silicon surface, pressure of the reagent gas, and temperature and growth time. A key feature of this method is that the substrate orders the resulting structures using the original chemical bonds between the atoms in silicon. The term “concertedly” means that new chemical bonds are formed simultaneously and concertedly with the destruction of old bonds. Data on electron diffraction and analysis of Raman and ellipsometric spectra of the obtained samples of nanostructured carbon on silicon substrates have been presented. Two competing growth mechanisms have been discussed.

Theoretical and Experimental Study of Cellular Modes of Filtration Combustion of Cylindrical Systems

Experimentally and theoretically (using mathematical modeling) the combustion of the undeformed porous matrix of cylindrically symmetric forms, in which the active gas reagent is fed from outside through the permeable surface part owing to difference between outside and inside pore pressure in the reaction zone, has been studied. It has been shown that under conditions of the instability of many-dimensional filtration combustion separate cells of exothermic chemical combustion form, which propagated in self-sustained mode. Structure of cellular waves, distribution dynamics and moving direction are determined by totality of factors: temperature field, gas pressure gradients, intensity of exothermic heat release, geometric parameters of porous layer, and heat loss value. The cellular combustion modes of the titanium powder layer were experimentally studied in the circular bath as the flat dish. The comparative analysis of theoretic and experimental results of combustion dynamics of cylindrical sample under cellular mode is given.

Monitoring of the Operating Parameters a Low-Temperature Fuel-Cell Stack for Applications in Unmanned Aerial Vehicles: Part I

The paper presents a brief analysis of the potential use of hydrogen-oxygen low-temperature fuel cells with proton-exchange membrane fuel-cell stacks as power sources for the construction of drive units powering unmanned aerial vehicles. Hydrogen storage methods are discussed. Characteristics of selected aspects of monitoring the electrical and non-electrical operating parameters of a drive unit with fuel cells were investigated, with respect to the fuel cell, fuel-cell cooling system, and gas reagent supplying the system with hydrogen and air. Hydrogen fuel consumption for the production of electricity and purification, or so-called purge, was analysed. Based on the results of laboratory tests of the parameters of a generator with fuel cells, an exemplary method of monitoring operating parameters and controlling power sources involving fuel cells is proposed.