Nature Of Carrier Gas Research Articles

Behavior of micro pillar array column in high pressure gas chromatography

Micro pillar array column with interpillar distance of 2.5 µm for pillars diameter of 5 µm has been introduced in high pressure gas chromatographic systems for online industrial analysis. Separation of gas mixtures have been performed under carrier gas pressure as high as 60 bar using rotating valve for gas injection without sample decompression stage prior to injection. A very low intrinsic height equivalent to a theoretical plate value of 14 µm has been obtained in few seconds. Instead of conventional gas chromatography, carrier gas nature such as helium, argon and carbon dioxide and pressure can be used to tune the selectivity. Liquid hydrocarbon samples have been successfully introduced in the column using a septum based split/splitless injector modified to work up to 40 bar. Separations of VOCs and gasoline samples have been successfully performed.

A spark discharge generator for scalable aerosol CVD synthesis of single-walled carbon nanotubes with tailored characteristics

We have designed and built an exhaust-free spark discharge generator for robust aerosol CVD synthesis of single-walled carbon nanotubes. The systematic study has shown the generator to provide a facile and repeatable route to precisely control the size of the catalyst particle and, therefore, carbon nanotube growth. Using a comprehensive set of methods (the analysis of differential mobility of the aerosol particles, optical spectroscopy, scanning and transmission electron microscopy, Raman spectroscopy, and atomic force microscopy) we have revealed the relation between the defectiveness, length, diameter distribution of carbon nanotubes and specific features of a generator such as electrode characteristics (breakdown voltage, composition, and current) as well as the nature of the surrounding media (carrier gas nature, flow rate). The design used has resulted in separation of the nanoparticle formation and carbon nanotube nucleation processes. This provides a mutual independence of the growth parameters and the diameter distribution of the single-walled carbon nanotubes enhancing the scalability of the process. For instance, the breakdown voltage has been shown to have nearly zero effect on diameter and length distribution of carbon nanotubes produced while strictly governing the yield. We focus here on producing specifically short carbon nanotubes (l < 500 nm) of pronounced defectiveness for drug delivery and transistor applications.

Structure and Properties of Coatings Formed by Detonation Spraying of Titanium Powder

Structure and properties of the coatings formed by detonation spraying of titanium powder have been studied at varying the deposition parameters (nature of carrier gas, spraying distance, O2/C2H2 ratio, and the volume of explosive mixture). It is shown that when air is used as the carrier gas the primary strengthening by the titanium oxide phases is realized. When nitrogen is introduced into the explosive mixture, a more complicated mechanism of hardening is realized due to the formation of titanium oxides, carbides, oxynitrides and carbonitrides. The aspects of employing the revealed “rational” modes of the detonation spraying for formation of protective composite coatings based on titanium possessing a complex of improved physical and mechanical properties are discussed.

Behavior of macroporous vinyl silica and silica monolithic columns in high pressure gas chromatography

80% vinyltrimethoxysilane-based hybrid silica monoliths (80-VTMS), which have been initially developed for separation in reversed-phase liquid chromatography, have been investigated in high pressure gas chromatography separations (carrier gas pressure up to 60bar) and compared to silica monolithic columns. The behavior of both silica and 80-VTMS monolithic columns was investigated using helium, nitrogen and carbon dioxide as carrier gas. The efficiency of 80-VTMS monolithic columns was shown to vary differently than silica monolithic columns according to the temperature and the carrier gas used. Carrier gas nature was a significant parameter on the retention for both silica and vinyl columns in relation to its adsorption onto the stationary phase in such high pressure conditions. The comparison of retention and selectivity between 80-VTMS monoliths and silica was performed under helium using the logarithm of the retention factor according to the number of carbon atoms combined to Kovats indexes. The very good performances of these columns were demonstrated, allowing the separation of 8 compounds in less than 1min.

(Invited) Ultrasonic Spray Coating of Electrochromic Nanomaterials

Ultrasonic spray deposition is a promising and versatile method for both fundamental and industrial researches and applications. It leads to the formation of uniform thin films on large area substrates at atmospheric pressure, with a fine control of the resulting morphology and thickness by adjustment of the practical spray conditions (substrate temperature, nozzle-to-substrate distance, deposition pattern, solution flow rate, carrier gas nature and pressure…). The ultrasonic atomization of the injected precursor solution/suspension is also particularly advantageous as it reduces overspray and energy consumption [1-2]. In our recent works [3-7], we are considering the spray deposition of thin films of electrochromic oxides such as WO3and NiO, which are exploited as nanomaterials for various optical-related devices, notably “smart windows” for energy-efficient fenestration in glass buildings [8-9]. A specific attention is thus paid to the composition of the sprayed solution/suspension (precursor type and concentration, solvent…) as it has a significant influence on film deposition mechanisms and properties. Substrate nature (morphology, crystallinity, conductivity…) is of particular importance too, and different types of transparent conductive oxide (TCO) coated glass are therefore investigated. Incorporation of selected surfactants is also acknowledged for influencing wettability, nucleation and growth processes, and resulting functionality. Consequent characterizations analyze crystallinity, microstructure and porosity, ionic reversibility and diffusion, cycling response, optical modulation, coloration/bleaching kinetics, tint and haze.

Competition between inter- and intra-molecular hydrogen bonding: An infrared spectroscopic study of jet-cooled amino-ethanol and its dimer.

The Fourier transform IR vibrational spectra of amino-ethanol (AE) and its dimer have been recorded at room temperature and under jet-cooled conditions over the far and mid infrared ranges (50-4000 cm-1) using the White-type cell and the supersonic jet of the Jet-AILES apparatus at the synchrotron facility SOLEIL. Assignment of the monomer experimental frequencies has been derived from anharmonic frequencies calculated at a hybrid CCSD(T)-F12/MP2 level. Various thermodynamical effects in the supersonic expansion conditions including molar dilution of AE and nature of carrier gas have been used to promote or not the formation of dimers. Four vibrational modes of the observed dimer have been unambiguously assigned using mode-specific scaling factors deduced from the ratio between experimental and computed frequencies for the monomer. The most stable g'Gg' monomer undergoes strong deformation upon dimerization, leading to a homochiral head to head dimer involving two strong hydrogen bonds.

Behavior of short silica monolithic columns in high pressure gas chromatography

In order to analyze light hydrocarbons mixtures with silica monolithic columns, a conventional gas chromatograph was modified to work with carrier gas pressure as high as 60bar. To understand hydrodynamic flow and retention with short columns (less than 30cm), special attention was required due to the temperature difference between the oven area and the FID detector which contain a significant length of the column. Efficiency and selectivity using various carrier gases (helium, nitrogen and carbon dioxide) at different inlet pressure for different oven temperature were studied. Carrier gas nature was a very significant parameter: on one side, linked to adsorption mechanism for gases like nitrogen and carbon dioxide onto the stationary phase modifying retention and selectivity, on the other side in relation to the minimum theoretical plate height which was as low as 15μm (66 000 platem−1) using carbon dioxide as carrier gas. The chromatographic system was then used to separate methane, ethane, ethylene, acetylene, propane, cyclopropane, and butane in less than 30s.

Optimization of VLS Growth Process for 4H-SiC P/N Junctions

P/N junctions have been fabricated with N+ commercial 4H-SiC substrate on which Vapor-Liquid-Solid (VLS) selective epitaxy was used to create a localized p-type doping. The influence of the carrier gas nature (argon or hydrogen) has been investigated in terms of quality of the growth morphology, deposit thickness and electrical behavior of the P/N junction. Distinct results have been observed with a clear improvement when using VLS selective epitaxy under hydrogen.

Kinetic efficiency of polar monolithic capillary columns in high-pressure gas chromatography

Poppe plots were used for analysis of kinetic efficiency of monolithic sorbents synthesized in quartz capillaries for utilization in high-pressure gas chromatography. Values of theoretical plate time and maximum number of theoretical plates occurred to depend significantly on synthetic parameters such as relative amount of monomer in the initial polymerization mixture, temperature and polymerization time. Poppe plots let one to find synthesis conditions suitable either for high-speed separations or for maximal efficiency. It is shown that construction of kinetic Poppe curves using potential Van Deemter data demands compressibility of mobile phase to be taken into consideration in the case of gas chromatography. Model mixture of light hydrocarbons C1 to C4 was then used for investigation of influence of carrier gas nature on kinetic efficiency of polymeric monolithic columns. Minimal values of theoretical plate times were found for CO2 and N2O carrier gases.

Metal organic chemical vapor deposition growth and luminescence of ZnO micro- and nanowires

One dimensional (1D) ZnO heterostructures were deposited on C-plane sapphire using metal organic chemical vapor deposition at atmospheric pressure. Both catalyst-assisted and catalyst-free processes were investigated. In this latter case, growth parameters such as the substrate temperature, the oxygen/zinc ratio, or the carrier gas nature were varied in order to observe the modification of the film morphology. Different 1D shapes were produced, including rods, tubes, and needles, and were observed by scanning electron microscopy. Photoluminescence spectra reveal sharp excitonic transitions, and cathodoluminescence signals recorded along a ZnO conical needle exhibit a blueshift from the base to the top. The vapor-liquid-solid growth of ZnO nanowires using gold droplets was also successful.

Microcalorimetric study of sorption of water and ethanol in zeolites 3A and 5A

Sorption of water and ethanol in zeolites 3A and 5A was investigated using gas flow-through microcalorimetry in view of finding differences in these materials performance as potential sorbents in the process of drying of ethanol. In microcalorimetric experiments, both zeolites show comparable properties for the sorption of water, but they differ profoundly in their sorption of ethanol, which was negligible small in zeolite 3A compared to zeolite 5A, in spite of the much larger enthalpy of sorption of ethanol in zeolite 3A. The difference can be explained in terms of a steric hindrance preventing the ethanol molecules from entering the narrow pores of the 3A structure, with the 5A structure remaining easily accessible for both the water and ethanol molecules alike. We propose to use a size selectivity index, defined as the ratio of sorption capacity of water and ethanol, to characterise the applicability of a zeolite as sorbent for drying of ethanol. The thermal effects of sorption of water in zeolite 3A was found to be a function of the nature of carrier gas, He or N 2, used in microcalorimetric measurements.

Heat and mass transfer and condensation interference in a laminar flow diffusion chamber

New mathematical model of laminar flow diffusion chamber (LFDC) performance is proposed, which includes mutial influence of homogeneous (heterogeneous) nucleation and droplets growth on heat and mass transfer processes. Qualitative investigation of heat and mass transfer processes and their influence on droplets growth is made. The limits of applicability of earlier mathematical model of LFDC are established. The numerical simulation of new mathematical model of the performance LFDC is presented. It is discovered that the nature of carrier gas substantially affects on the volume of nucleation zone in LFDC. In particular, for argon as the carrier gas the volume of nucleation zone is on the order above then for helium as the carrier gas. Effects of local structure of supersaturation field near growing droplets are discussed. Their application for interpretation of experimental data is proposed.

Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Thin Films by the Spray Pyrolysis Technique

This paper deals with the preparation and characterization of iron oxide thin films by the spray pyrolysis method at atmospheric pressure. Inorganic salts were employed as precursors instead of coordination complexes, reducing the cost of the starting material for the preparation of iron oxides with possible applications in the detection of toxic and contaminant gases field. The so obtained films, characterized by X-Ray Diffraction and Scanning Electron Microscopy, showed good quality and homogeneity. The carrier gas nature resulted a critic parameter: thin films obtained in an argon atmosphere could be identified as α-Fe 2 O 3 with a preferred orientation along the [110] direction which increases with the temperature, while in an air stream, the orientation along [110] is accompanied by the appearance of the β-Fe 2 O 3 phase with a [100] preferred orientation at high temperatures.

Dependence of the relative retention of organic compounds on the nature and pressure of the carrier gas and on the thickness of the PEG-20M film in the capillary column

The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases: helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention.

The reverse Wilson chamber method as a tool for heterogeneous nucleation studies

On the basis of the Richarz-Powell equation the effect of different factors (temperature, the nature of carrier gas and condensing liquid etc.) has been investigated in detail. The simple theory of the RWC method proposed in this paper is generalized for the more complicated case of binary (multicomponent) heterogeneous nucleation.

Reproducibility of filament pyrolysers: Influence of sample deposition and other factors

The reproducibility and reliability of results obtained from kinetic studies of pyrolysis depend on many factors. In the case of filament pyrolysers, those factors which pertain specifically to the sample are identified and discussed in this paper. These factors are: method of sample deposition, region of sample deposition, sample thickness, catalytic effects, sample-to-filament contact, nature of carrier gas, flow rate, pyrolysis chamber temperature and purity of solvents used in sample deposition.

Modelling of polyethylene terephthalate reactors—X. A comprehensive model for solid-state polycondensation process

A new comprehensive model for solid-state polycondensation (SSP) of polyethylene terephthalate (PET) has been developed, which interprets a number of hitherto unexplained observations. Degradation and other side reactions which were neglected in the earlier models for SSP process of PET are included. The diffusivity changes due to crystallisation of PET, the true influence of nature of carrier gas and the increase in the reactive chain end group mobility due to the change in the free volume in the presence of an inert gas have been considered. The model predictions have been validated with experimental data reported in the literature. The model can be used for a quantitative prediction of the influence of a variety of parameters on the degree of polymerisation as well as side products formation. The model correctly brings out the true influence of the carrier gas which had remained unexplained so far. It also suggests additional directions for improving the SSP process.

Experimental study of aerosol production by laser ablation

The characterization of ultrafine particles produced by laser ablation are presented: numerical concentration and volumic mean particle diameter versus different parameters, i.e. power and frequency of the laser pulses, carrier gas nature and flow rate.

Determination of melissyl alcohol by capillary column gas chromatography

For accurate determination of polar, high-boiling melissyl alcohol in mixtures containing also low-boiling components by capillary column gas chromatography with hot split injection, all experimental paramenters, such as the injection procedure, insert size and design, injector temperature, sample size, solvent and carrier gas nature, etc. must be optimized. Of the factors affecting the quantitation the nature of the insert packing material is of the greatest importance. With the commonly used packing material, quartz wool, in the insert, a much lower than true melissyl alcohol concentration was obtained. Accurate quantitation was only possible when stop-flow injection, together with an insert packed with glass beads was used.

Selective layers of TiSi2 deposited without substrate consumption in a cold wall LPCVD reactor

Abstract Selectively deposited layers of TiSi2 have been obtained without silicon substrate consumption using the TiCl4/SiH4 system diluted in H2. For a given set of parameters, at 800°C, we show that TiSi2 formation uses Si from the substrate or from the gas phase. The important parameters are the reacting gas ratio, carrier gas nature and process time. We present some possible mechanisms which include surface reactions as well as mass-transfer as the limiting phenomena. We propose a model, involving gas mass transport of TiCl4 as the rate limiting step and assuming independence of the SiH4 chemistry, which agrees well with the experimental results.