Nitrogen Carrier Gas Research Articles

Ultrafast Gas Chromatography-Tandem Differential Mobility Spectrometry: Toward A New Generation of On-Site, Real-Time Trace-Explosives Detection.

In the defense and security sector, rapid detection of trace quantities of threat materials is paramount. Traditional instrumentation typically relies on standalone ion mobility techniques due to being inexpensive, portable, and highly sensitive. However, these techniques face limitations when handling complex samples, suffering from low resolving power (often less than 100) and ion-suppression effects, which can lead to false-positive and false-negative results. Here, we present a foundation to the solution through the hyphenation of the flow field thermal gradient gas chromatograph (FF-TG-GC) developed by HyperChrom with a tandem differential ion mobility spectrometer (DMS-DMS) developed in-house at New Mexico State University. The FF-TG-GC demonstrates the ability to separate a variety of nitroaromatic compounds of explosive significance in 20 s using a nitrogen carrier gas, highlighting the potential to offer selectivity advantages without substantially compromising high-throughput demands. These selectivity advantages are illustrated by the successful application of the FF-TG-GC-DMS-DMS to the detection and identification of single-nanogram loadings of 18 explosives and related substances in the presence of interfering materials, such as lactic acid, musk, and diesel. Furthermore, the system is capable of mitigating in-source ion-suppression effects by chromatographic separation of target analytes from background interference prior to ionization.

Quantitative estimation of ethanol content in eribulin mesylate injection using headspace gas chromatographic with flame ionization detector [HS-GC-FID

A specific HS-GC method has been developed, optimized, and validated for the quantitative estimation of ethanol content in eribulin mesylate injection. Chromatographic separation was achieved on DB-624 column (30 m x 0.32 mm, 1.8 μm), consisting of 6% cyanopropyl and 94% polydimethylsiloxane as stationary phase and passing nitrogen carrier gas. The performance of the method was assessed by evaluating the specificity, linearity, precision, and accuracy of experiments. The correlation coefficient value of the linearity experiment was 0.9999. The average recoveries for the accuracy were in the range of 98.7 to 102.4%. The results proved that the method is suitable for the quantitative estimation of ethanol content in eribulin mesylate injection.

A method for generating quantitative vapor-phase infrared spectra of solids: results for phenol, camphor, menthol, syringol, dicyclopentadiene and naphthalene

A method is presented to generate quantitative vapor-phase infrared spectra from substances that naturally occur as solids with moderate volatility. The solid is gravimetrically dissolved into a solvent that has few infrared spectral features, typically CS2 and CCl4 separately. The solution is flowed at a constant rate from a linearly pumped syringe into a metered stream of nitrogen carrier gas regulated by a mass flow controller. The analyte/solvent mix is flash vaporized by volatilizing the solution across a heated stainless-steel surface as it emanates from the syringe tip. The N2 gas-solution mixture is flowed into a long-path White cell thermostatted at a desired temperature, the long optical path compensating for the modest analyte mixing ratio. A composite spectrum is generated from typically ten or more 760-Torr pressure-broadened spectra over the 600 to 6500 cm−1 spectral range at 0.1 cm−1 spectral resolution. The solid analytes reported here using this novel technique include dicyclopentadiene, menthol, syringol, phenol, camphor, and naphthalene.

Comparison of carrier gases for the separation and quantification of mineral oil hydrocarbon (MOH) fractions using online coupled high performance liquid chromatography-gas chromatography-flame ionisation detection

On-line coupled high performance liquid chromatography-gas chromatography-flame ionisation detection (HPLC-GC-FID) was used to compare the effect of hydrogen, helium and nitrogen as carrier gases on the chromatographic characteristics for the quantification of mineral oil hydrocarbon (MOH) traces in food related matrices. After optimisation of chromatographic parameters nitrogen carrier gas exhibited characteristics equivalent to hydrogen and helium regarding requirements set by current guidelines and standardisation such as linear range, quantification limit and carry over. Though nitrogen expectedly led to greater peak widths, all required separations of standard compounds were sufficient and humps of saturated mineral oil hydrocarbons (MOSH) and aromatic mineral oil hydrocarbons (MOAH) were appropriate to enable quantitation similar to situations where hydrogen or helium had been used. Slightly increased peak widths of individual hump components did not affect shapes and widths of the MOSH and MOAH humps were not significantly affected by the use of nitrogen as carrier gas. Notably, nitrogen carrier gas led to less solvent peak tailing and smaller baseline offset. Overall, nitrogen may be regarded as viable alternative to hydrogen or helium and may even extend the range of quantifiable compounds to highly volatile hydrocarbon eluting directly after the solvent peak.

A new gas chromatographic method for quantification of Metformin hydrochloride and Vildagliptin in bulk and pharmaceutical dosage form: development and validation

BackgroundMetformin, an antidiabetic drug, assists in reducing the creation of glucose inside the liver. Vildagliptin, a DPP-4 inhibitor, enhances insulin release from the pancreas and reduces the hormones that elevate blood sugar levels. The combined medications work synergistically to lower blood sugar levels. This study was designed to develop and validate a reliable method of simultaneous assessment of Metformin and Vildagliptin in bulk and pharmaceutical dosage forms. For the chromatographic separation, a Gs-Tek INNOWAX column was utilized. This column has a length of 30 m, an internal diameter of 0.25 mm, and a 1.8 µm film thickness. For the detection, a Flame Ionization Detector was utilized. The ideal conditions included an injection volume of 1 µL with a split mode of 10 to 1 ratio, a flow rate of 1 mL/minute for the nitrogen carrier gas, an injector temperature of 300 °C, a detector temperature of 250 °C, an initial oven temperature of 100 °C that was maintained for seven minutes and then programmed to climb at a rate of 10 °C per minute up to a temperature of 300 °C.ResultsA gas chromatographic method that is simple, precise, accurate, robust, and reliable has been developed and implemented for the simultaneous estimation of Metformin and Vildagliptin in the tablet dosage form. The retention time for Metformin and Vildagliptin was 10.203 and 22.021 min. respectively. Validation studies were performed on the method’s Linearity, detection limit (LOD), and quantitation limit (LOQ), as well as its accuracy, precision, system suitability, and robustness, using the norms established by the International Conference on Harmonization (ICH). The mean recovery value for Metformin and Vildagliptin was 100.31% (% R.S.D. = 0.6743%) and 100.33% (% R.S.D. = 0.6900%). All the results are within the acceptable range.ConclusionValidation of the developed method revealed that all the results were within an acceptable range, and techniques can be employed to analyze these two medications in combined dosage forms. It is the first method used for simultaneous estimation of these two drugs.Graphical abstract

Pyrolytic decomposition of methanol, ethanol, and butanol at various temperatures and residence times in a high-temperature flow reactor

The potential use of low-carbon renewable fuel molecules, such as short chain alcohols, as a substitute or extender for fossil fuels, offers an opportunity to address pollutant emissions from transport and the sustainability of energy sources. Moreover, it may help reduce pollutants detrimental to air quality and human health, of which particulate matter (PM) is a significant contributor. To this end, the pyrolysis of three renewable alcohol fuels, methanol, ethanol, and butanol, has been studied in a laminar flow reactor at a sample inlet temperature range of 869 0C to 1120 0C. All the tested fuels were injected into a nitrogen carrier gas stream at a fixed concentration of 10,000 ppm on a carbon atom basis. A range of pyrolysis temperatures and residence times were selected so as to gain insight into the pyrolytic decomposition of short chain alcohol fuels to intermediate species important to the subsequent formation of benzene rings, larger polycyclic aromatic hydrocarbons (PAH), and particulate matter. In this paper, the presence of ten intermediary species that may aid in the formation of benzene rings and the growth of PAHs were quantified, with an emphasis on probable routes of first ring formation from the alcohols of varying chain length. Gaseous samples were collected from the pyrolyser at different temperatures and residence times using a novel high-temperature air-cooled ceramic sampling probe. The identification and quantification of intermediate gaseous species were undertaken by Gas Chromatography-Flame Ionization Detection (GC-FID). During methanol pyrolysis, only a tenth of the supplied carbon was detected as hydrocarbon gaseous species (mainly methane), with no benzene found, highlighting that methanol pyrolysis does not readily result in polyaromatic hydrocarbons and soot. Ethanol and butanol pyrolysis produced substantial amounts of ethylene and acetylene, suggesting a role in benzene and soot formation. Uniquely, pyrolysis of the longest chain alcohol, butanol, produced appreciable levels of C3 and C4 hydrocarbons, in addition to C1 and C2 hydrocarbons, suggesting additional reaction pathways for benzene formation and growth in comparison with ethanol.

Cu2O films without impurities fabricated via the mist spin spray technique using a mixed alkaline solution for flexible glucose sensors

The mist spin spray (MSS) technique was used to fabricate crystalline Cu2O thin films on seed-free glass substrates and a flexible indium tin oxide (ITO)/polyethylene terephthalate (PET) substrate. In this technique, a solution containing Cu+ ions and a mixed alkaline solution of NH3 and NaOH were separately atomized by ultrasonication to generate mists. These mists were sprayed with a nitrogen carrier gas onto the substrates heated to 90°C on a rotating table under atmospheric pressure. This led to nanoscale-thick, dense, and high-purity Cu2O films with good adhesion to the substrates. The NaOH concentrations of the initial solution affected the film morphology, and the specimen films prepared with a NaOH concentration higher than 0.2 mol/L exhibited rough surfaces, whereas those prepared with a NaOH concentration of 0.1 mol/L and lower had dense and flat surfaces. The crystallized Cu2O film with nano-sized structure was fabricated directly on the ITO/PET substrate at 90°C to produce a flexible glucose sensor and exhibited good validity with a sensitivity of 561.6 µA cm−2 per concentration of mmol L−1.

Development and Validation of Headspace-Gas Chromatography (HS-GC) Method for the Determination of Potential Genotoxic Impurities in Meloxicam

The development and validation of a specific Headspace-Gas Chromatography (HS-GC) method for the determination of genotoxic impurities (isopropyl chloride, propionaldehyde, 2-chloropropanol, and chloromethane) in Meloxicam. The chromatographic separation of these impurities was accomplished using a nitrogen carrier gas on a DB-624 (6% cyanopropyl phenyl + 94% dimethyl polysiloxane fused silica) (75 m x 0.53 mm, 3.0 µ) GC analytical column. The Flame Ionization Detector (FID) served as the detector with optimized temperatures set at 260°C for the detector and 240°C for the injector port. Additionally, an injection volume of 1.0 mL with a split ratio mode was employed. The performance of this method was assessed through parameters, including system suitability, specificity, linearity, range, accuracy, limit of detection (LOD), limit of quantification (LOQ) and precision. The limit of detection and limit of quantification for isopropyl chloride, propionaldehyde, 2-chloropropanol, and chloromethane were determined to be 2 and 4 ppm, respectively, and for chloromethane 0.8 and 1.6 respectively. The correlation coefficient of the linearity experiment was 0.999 for propionaldehyde, 2-chloropropanol, chloromethane and 1 for isopropyl chloride compounds. Furthermore, the accuracy assessment involved spiking the genotoxic impurities at various levels, demonstrating favourable recovery percentages well within the acceptable range of 80–120% of the limit level. These compelling results substantiate the suitability of the proposed HS-GC method for the accurate determination of isopropyl chloride, propionaldehyde, 2-chloropropanol, and chloromethane in Meloxicam.

Adsorption of radon on silver exchanged zeolites at ambient temperatures

Since more than 100 years, the adsorption of the radioactive noble gas radon (222Rn) is performed on activated charcoal at cryogenic temperatures. There is little—if any—progress in the field of radon adsorption at ambient conditions to facilitate the development of simple and compact radon adsorption systems. We report here on the truly remarkable property of the synthetic silver-exchanged zeolites Ag-ETS-10 and Ag-ZSM-5 to strongly adsorb radon gas at room temperature. 222Rn breakthrough experiments in nitrogen carrier gas have shown that these materials exhibit radon adsorption coefficients exceeding 3000 m3/kg at 293 K, more than two orders of magnitude larger than any noble gas adsorbent known to date. Water vapor and carrier gas type were found to strongly influence radon adsorption, practically qualifying these silver exchanged materials as a new class of radon adsorbents. Our results demonstrate that Ag-ETS-10 and Ag-ZSM-5 are materials that show high affinity towards radon gas at ambient temperatures making them candidate materials for environmental and industrial 222Rn mitigation applications. Adsorption systems based on silver loaded zeolites have the potential to replace activated charcoal as material of choice in many radon related research areas by avoiding the necessity of cryogenic cooling.

Sampling of Gas-Phase Intermediate Pyrolytic Species at Various Temperatures and Residence Times during Pyrolysis of Methane, Ethane, and Butane in a High-Temperature Flow Reactor

Air pollution in many major cities is endangering public health and is causing deterioration of the environment. Particulate emissions (PM) contribute to air pollution as they carry toxic polyaromatic hydrocarbons (PAHs) on their surface. Abatement of PM requires continuous strict emission regulation and, in parallel, the development of fuels with reduced formation of PM. Key processes in the formation of PM are the decomposition of hydrocarbon fuels and the synthesis of potential precursors that lead to the formation of benzene rings and thereafter growth to PAHs and eventually PM. Methane, ethane and butane are important components of natural gas and liquefied petroleum gas, and are also widely used in transportation, industrial processes and power generation. This paper reports on a quantitative investigation of the intermediate gaseous species present during pyrolysis of methane, ethane and butane in a laminar flow reactor. The investigation aimed to further the understanding of the decomposition process of these fuels and the subsequent formation of aromatic rings. The pyrolysis of methane, ethane and butane were carried out in a tube reactor under laminar flow conditions and within a temperature range of 869–1213 °C. The fuels were premixed in nitrogen carrier gas at a fixed carbon atom concentration of 10,000 ppm, and were pyrolysed under oxygen-free conditions. Intermediate gaseous species were collected from within the tube reactor at different residence times using a specially designed high-temperature ceramic sampling probe with arrangements to quench and freeze the reactions at entry to the probe. Identification and quantification of intermediate species were carried out using a gas chromatography-flame ionization detector (GC-FID). During methane pyrolysis, it was observed that as the concentration of acetylene increased, the concentration of benzene also increased, suggesting that the benzene ring is formed via the cyclo trimerisation of acetylene. With all three fuels, all intermediate species disappeared at higher temperatures and residence times, suggesting that those species converted into species higher than benzene, for example naphthalene. It was observed that increasing carbon chain length lowered the temperature at which fuel breakdown occurred and also affected the relative abundance of intermediate species.

Investigation of high-density polyethylene pyrolyzed wax for asphalt binder modification: Mechanism, thermal properties, and ageing performance

The thermal pyrolysis of high-density polyethylene in a fixed bed reactor has been studied in the temperature range of 450–550 °C with two different nitrogen carrier gas flowrates, 2 and 4nullLnullmin−1, to study the effect of these process parameters as well as the resultant vapour residence times on the formation of wax and its chemical and thermal properties. The technology had a high selectivity to waxes, with a yield of up to 91.87% wax from high-density polyethylene at 500 °C using a nitrogen carrier gas flowrate of 4nullLnullmin−1 and subsequent 1.76 second vapour residence time, calculated using the ideal gas law. The waxes were characterised using techniques including gas-chromatography-mass spectroscopy (GC-MS), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The process operating temperature especially and its subsequent effect on vapour residence times within the reactor had a considerable impact on both the chemical and thermal properties of the waxes. Higher operating temperatures yielded more olefinic waxes due to the promotion of degradation radical mechanisms such as β-scission. They were observed to have higher melting points and thermal stability. An investigation was conducted to assess the thermal properties and ageing performance of the waxes. Thermal conditioning in an ashing oven at 170 °C for 0–6 hours was conducted with a detailed analysis of GC-MS and FTIR at each stage of thermal exposure to further support thermal characterisation results. The changes in chemical composition were attributed mainly to oxidation and polymerization ageing reactions and were seen to be more prominent in the more unsaturated waxes produced at higher pyrolysis temperatures. The wax produced at 550 °C was determined the optimal wax for binder modification in hot-mix asphalt pavement design due to lower volatile/mass loss. A lower temperature range was suggested for optimal blending conditions to further reduce loss of volatiles with initial blending and storage.

Development and validation of determination of genotoxic impurity Bromoethane in Vigabatrin drug substance using head space gas chromatographic method [HS-GC

A specific HS-GC method has been developed, optimized, and validated for the determination of genotoxic impurity Bromoethane in Vigabatrin (VGB) drug substance. Chromatographic separation of genotoxic Bromoethane impurity was achieved on DB-1 column (30 m × 0.53 mm, 5.0 μm), consists of 100% dimethyl polysiloxane as stationary phase and passing nitrogen carrier gas. The performance of the method was assessed by evaluating the specificity, linearity, sensitivity, precision, and accuracy experiments. The established limit of detection and limit of quantification values for the genotoxic impurity was in the range of 3.57–10.80 μg/mL. The correlation coefficient value of the linearity experiment was 0.9880. The average recoveries for the accuracy were in the range of 95.3–106.8%. The results proved that the method is suitable for the determination of Bromoethane content in Vigabatrin.

Recent developments and applications of selected ion flow tube mass spectrometry(SIFT-MS).

Selected ion flow tube mass spectrometry(SIFT-MS) is now recognized as the most versatile analytical technique for the identification and quantification of trace gases down to the parts-per-trillion by volume, pptv, range. This statement is supported by the wide reach of its applications, from real-time analysis, obviating sample collection of very humid exhaled breath, to its adoption in industrial scenarios for air quality monitoring. This review touches on the recent extensions to the underpinning ion chemistry kinetics library and the alternative challenge of using nitrogen carrier gas instead of helium. The addition of reagent anions in the Voice200 series of SIFT-MS instruments has enhanced the analytical capability, thus allowing analyses of volatile trace compounds in humid air that cannot be analyzed using reagent cations alone, as clarified by outlining the anion chemistry involved. Case studies are reviewed of breath analysis and bacterial culture volatile organic compound(VOC), emissions, environmental applications such as air, water, and soil analysis, workplace safety such as transport container fumigants, airborne contamination in semiconductor fabrication, food flavor and spoilage, drugs contamination and VOC emissions from packaging to demonstrate the stated qualities and uniqueness of the new generation SIFT-MS instrumentation. Finally, some advancements that can be made to improve the analytical capability and reach of SIFT-MS are mentioned.

Nitrogen carrier gas for the separation of trace explosives on CI-GC/MS.

Fluctuations in ultra high purity (UHP) helium supply has the potential to negatively impact critical research efforts. Disruptions have increased significantly with suppliers prioritizing delivery to medical facilities. Due to the greater demand for helium, supply issues are likely to continue through the coming years. Many gas chromatography (GC)-based analytical methods rely on the supply of UHP helium, including those developed for the quantification of trace explosives. Vapor validation is critical in establishing sensor performance, limits of detection, and instrument performance. An alternate carrier gas must be established to maintain these critical functionalities. To circumvent the UHP helium disruptions, UHP nitrogen was explored as a replacement carrier gas in negative mode chemical ionization-gas chromatography/mass spectrometry (CI-GC/MS). Although, hydrogen is considered an acceptable alternative to helium in most GC-based separations, its' use as a replacement was omitted due to reactivity resulting in degradation of the CI-MS detector and incompatibility with the programmable temperature vaporization inlet on the GC used in this work. Herein discusses the method development of nitrogen carrier gas in the separation of an explosives mixture. Adjustments in flow rate, initial oven temperature, and ramp rate were made to achieve comparable analysis to that of helium. By lowering the flow rate and initial oven temperature peak resolution and sensitivity increased when using nitrogen carrier gas. Development of this method allows for continual laboratory output in times of helium scarcity.

Study of Catalytic Properties of the HoxMg1-xAl2O4 Modified HZSM-5 Zeolite in Conversion of Methanol to C2-C4 Alkenes and p-Xylene

Selective conversion of methanol to C2-C4 alkenes and p-xylene is one of the appealing chemical routes. Currently, there are no effective catalysts for the co-production of C2-C4 alkenes and p-xylene from methanol. To date, modified medium-pore ZSM-5 zeolites are considered one of the excellent candidates for the development of selective catalysts for the conversion of methanol to lower alkenes and aromatic hydrocarbons. In this paper, nanosized (30-33nm) powders of HoхMg1-хAl2O4 spinel structure were obtained by the method of combustion of nitrate solutions of aluminium, magnesium, holmium, diethylmalonate and hydrazine monohydrate with the further calcination of nanopowders at 1000 °C. Obtained nanopowders used in the preparation of a solid-phase catalytic composition of HoхMg1-хAl2O4-HZSM-5. Various physico-chemical properties of the catalytic composition were investigated using X-ray diffraction (XRD), pyridine adsorption (BİO-RAD FTS 3000 MX) and low-temperature nitrogen adsorption (BET) techniques. The textural properties and acidity of the catalysts were altered by adjusting the nanopowder concentration (1.0-5.0 wt.%) in the catalytic composition. The conversion of methanol in the presence of the catalytic compositions was carried out in flow-type fixed-bed catalytic reactor at 400 °C, in the presence of nitrogen carrier gas with 1.0 h-1 flow rate. A correlation between the selectivity to C2-C4 alkenes and p-xylene with a ratio of Lewis (L) and Brønsted (B) acid sites and the volume of the catalyst pore, the amount of the modifier in the catalytic system has been established. As the amount of HoхMg1-хAl2O4 nanopowder increases, the ratio of B/L acid sites and the volume of the catalyst pore decrease, which play a significant role in the increase of the selectivity to C2-C4 alkenes and p-xylene. Maximum yield of C2-C4 alkenes (31.6%) and selectivity to p-xylene (80.5%) is achieved on a catalytic composition containing 5.0 wt.% HoxMg1-xAl2O4. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

STRAIGHT PYROLYSIS OF COCONUT HUSK IN A ROTATING CYLINDER REACTOR AND PRODUCT CHARACTERIZATION

The objective of this work is to produce and characterize bio-oil, char, and gases obtained from the pyrolysis of coconut husk using a laboratory reactor. In the experiments, the reactor rotated at 33.7 rpm, the reaction time was usually 30 min, and the biomass flow rate was 540 g h-1. A mass balance showed that the maximum yields of the phases were: bio-oil (18.1%), char (21.7%), gas (37.6%), obtained at 500 °C and 100 cm3 min-1 of the nitrogen carrier gas. The bio-oil was characterized for density, viscosity at 40 °C, pH, higher heating value, solid contents, and composition. The char was characterized for the contents of ash, moisture, volatiles, fixed carbon, higher heating value, elemental analysis, and FTIR. The gases were analyzed by chromatography and consisted mostly of CO2 (39.45%), CO (30.64%), and H2 (24.07 v/v%).

The effects of methanol clustering on methanol-water nucleation.

The formation of subcritical methanol clusters in the vapor phase is known to complicate the analysis of nucleation measurements. Here, we investigate how this process affects the onset of binary nucleation as dilute water-methanol mixtures in nitrogen carrier gas expand in a supersonic nozzle. These are the first reported data for water-methanol nucleation in an expansion device. We start by extending an older monomer-dimer-tetramer equilibrium model to include larger clusters, relying on Helmholtz free energy differences derived from Monte Carlo simulations. The model is validated against the pressure/temperature measurements of Laksmono et al. [Phys. Chem. Chem. Phys. 13, 5855 (2011)] for dilute methanol-nitrogen mixtures expanding in a supersonic flow prior to the appearance of liquid droplets. These data are well fit when the maximum cluster size imax is 6-12. The extended equilibrium model is then used to analyze the current data. On the addition of small amounts of water, heat release prior to particle formation is essentially unchanged from that for pure methanol, but liquid formation proceeds at much higher temperatures. Once water comprises more than ∼24 mol% of the condensable vapor, droplet formation begins at temperatures too high for heat release from subcritical cluster formation to perturb the flow. Comparing the experimental results to binary nucleation theory is challenged by the need to extrapolate data to the subcooled region and by the inapplicability of explicit cluster models that require a minimum of 12 molecules in the critical cluster.

Wurtzite Al[formula omitted]Ga[formula omitted]P[formula omitted]N[formula omitted] barrier layer growth for high electron mobility transistors

Wurtzite AlPyN1−y and Al1−xGaxPyN1−y was grown on GaN using Metal-Organic Vapour Phase Epitaxy using tertiary-butylphosphine (tBP). To incorporate more than 5% P, the temperature needs to be higher than 1100 °C and the tBP/(tBP+NH3) ratio must exceed 0.2 at 20 kPa and 0.3 at 5 kPa reactor pressure. This limits the V/III ratio to less than 20, which can result in high unintentional Ga incorporation due to the decomposition of the initial GaN surface. Thus, pure AlPyN1−y is preferably grown with nitrogen carrier gas and fast growth rates. Since P can also incorporate on the Al sub-lattice, tensile stain through coherent growth on GaN is mandatory. Too high P/N ratios or too thick layers lead to relaxation and subsequent non-stoichiometric AlxPx+yN1−y growth. A coherent 5 nm thin layer of nominal AlP0.07N0.93 showed a two-dimensional electron gas with sheet carrier densities above 1013cm−2 at 30K.

Kinetics driving thin-film deposition in dielectric barrier discharges using a direct liquid injector operated in a pulsed regime

This work investigates the effects of process parameters on thin-film deposition by direct liquid injection in a low-frequency dielectric barrier discharge. The precursor, hexamethyldisiloxane, is introduced as micrometer-size liquid droplets with nitrogen carrier gas in a pulsed mode and the discharge is produced at atmospheric pressure in a pulsed regime. No significant deposit is observed during plasma-off time and outside the discharge region. Despite the pulsed injection, this reveals that the precursor content in the plasma zone remains constant over much longer time scales and that thin-film deposition results from droplets charging and their transport towards the dielectrics by the low-frequency electric field. Over the range of experimental conditions investigated, it is found that pulsed, aerosol-assisted plasma deposition is limited by the amount of energy provided to precursor droplets, and not by precursor insufficiency.

Fire extinguishing and explosion suppression characteristics of explosion suppression system with N2/APP after methane/coal dust explosion

The study aims to examine the suppression performance of an inhibitor after a methane/coal dust explosion. The design of an explosion suppression system included the carrier gas of nitrogen (N2) with an inhibitor of ammonium polyphosphate (APP). The study investigated fire extinguishing and explosion suppression of methane/coal dust by N2/APP in a vertical pipe. Flame propagation characteristics were measured by a high-speed camera, micro-thermocouple, and pressure sensor. The residues after the explosion were characterized chemically by X-ray photoelectron spectroscopy, and the thermal decomposition characteristics of coal dust and APP in the N2 atmosphere were analyzed by synchronous thermal analysis. Experimental results show that the explosion suppression system can effectively hinder the flame propagation of methane/coal dust explosion. The flame height, bottom velocity, and temperature were all weakened significantly. The optimum level of suppressant minimizes the explosion pressure and suppresses the flame significantly. In addition, the fire extinguishing and explosion suppression mechanisms of N2/APP were summarized. The suppression method used in this study blocks the explosion after it occurs rather than preventing it through premixed inerting.