Showing papers on "Vapours published in 2012"

Application of metal organic framework crystals for sensing of volatile organic gases

Abstract: In this work, metal organic frameworks are used for the first time to detect volatile organic compounds. A sensitive nanoporous metal organic framework layer was deposited using a custom electrospraying system onto the surface of quartz resonators to build a gravimetric sensor. The response of sensors made using the electrosprayed film is compared against those prepared with the more common technique of drop-casting. It is demonstrated that our electrospraying technique resulted in a significantly higher quality factor for the quartz resonators which leads to improved sensor resolution and stability. The experimental set-up is presented and the response of the system to various concentrations of the vapours of three ubiquitous solvents, i.e., acetone, tetrahydrofuran, and isopropyl alcohol, is investigated. The minimum detectable concentrations of these organic vapours are 50 ppm, 10 ppm, and 2 ppm, respectively.

Room temperature detection of amine vapours using copper phthalocyanine based thin films

Abstract: In this paper, we report the preparation and characterization of 50 nm thin film of non-peripherally substituted copper(II)1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (nCuPc(OBu)8) using spin coating technique for room temperature sensing of different primary amines namely methylamine, butylamine and octylamine, respectively. AFM studies of film reveal that film is porous, uniform and crack free. The rms roughness and average pore size of film is found to be 24 and 430 nm, respectively. The adsorption of analytes on film surface is consistent with Elovich equation. The response of the film towards different amines is related to the vapour temperature and chain length of amine molecules. The film shows better response for methylamine vapours at room temperature 25 °C.

Nano-porous indium oxide transistor sensor for the detection of ethanol vapours at room temperature

Abstract: Porous indium oxide thin film prepared by the dip coating technique has been used in the construction of a field effect transistor. The coating solution was prepared from indium chloride precursor. The average particle size of the dip coated thin film was found to be 25 nm. Scanning electron microscopic images show the porous nature of the film, and the root mean square roughness of the film calculated using atomic force microscope was 24 nm. A transistor has been constructed by evaporating metal Aluminium as source and drain electrodes on the indium oxide active layer and employing the silicon substrate itself as a gate. The sensor response of the constructed transistor was tested with ethanol, ammonia and acetone vapours. The sensor showed good response to ethanol vapours even at 5-ppm level, and the time for response and recovery of the gas was nearly 1 min. Response to ammonia and acetone was comparatively poor. When the gate voltage was increased from 0 to 300 mV, a considerable increase in the source-drain current was observed. As the temperature of the sensing element increased, response to ethanol vapours also increased. There was nearly a linear variation in the transistor response for 100 ppm of ethanol vapours when the gate voltage was swept from 0 to 300 mV. The sensor response of the transistor increases with the gas concentration. The constructed transistor was found to be selectively sensitive to ethanol; therefore it can be implemented to work as a breath alcohol checker.

Ionic Liquid/Styrene-Acrylonitrile Copolymer Nanofibers as Chemiresistor for Alcohol Vapours

Abstract: SAN/ nanofibers were fabricated by an electrospinning process and used as chemiresistors for sensing alcohol vapours. A hydrophobic and air-stable ionic liquid, , was used to impart electrical conductivity to insulating SAN nanofibers. The effects of addition on the morphology of the nanofibers were explained in terms of surface tension, viscosity and conductivity. After exposing the SAN/ nanofibers collected on an interdigitated electrode to alcohol vapours (ethanol, 1-propanol and 1-butanol), the resistance of the nanofibers decreased due to adsorption of alcohol molecules. The electrospun SAN/ nanofibers sensor exhibited good sensitivity and reproducibility.

Microelectrode sensor utilising nitro-sensitive polymers for application in explosives detection

Abstract: This Letter describes a fabrication of a microsensor incorporating a novel customised nitro-sensitive polymer derived from the propylenedioxythiophene family. Electrochemical polymerisation was used to selectively grow different types of localised polymer films on interdigitated electrode arrays, thereby fabricating miniature sensors that exhibited a highly selective and reversible response to chemical vapours containing ‘nitro’ (NO2) groups. Such nitro-bearing vapours are also present in trace quantities in the atmosphere in the presence of explosives. Vapours of nitropropane and nitrobenzene, serving as model analytes for explosives, were used for sensor testing. The sensors were demonstrated to have up to three orders of magnitude higher signal response to vapours from nitro compounds compared to other vapours commonly found in the atmosphere. The authors believe this is the highest selectivity to nitro compounds reported from a polymer-based chemicapacitor sensor.

Vapour breakthrough behaviour of carbon tetrachloride - a simulant for chemical warfare agent on ASZMT carbon

Abstract: ASZMT (Cu, Ag, Zn, Mo, TEDA impregnated) carbon was prepared by impregnation of active carbon with ammonical salts of Cu (II), Ag (I), Zn (II), Mo (VI) and TEDA using incipient wetness technique. Thereafter, ASZMT carbon was characterized using scanning electron microscopy, atomic absorption spectroscopy, thermogravimetry and surface characterization techniques. The ASZMT carbon was evaluated under dynamic conditions against carbon tetrachloride vapour that was used as a simulant for the persistent chemical warfare agents for testing breakthrough times of filter cartridges and canisters of gas masks in the National Approval Test of Respirators. The effect of carbon tetrachloride concentration, test flow rate, temperature and relative humidity on the breakthrough behaviour of the ASZMT carbon for CCl4 vapour has also been studied. The study clearly indicated that the ASZMT carbon provided adequate protection against carbon tetrachloride vapours. The breakthrough time decreased with the increase of the carbon tetrachloride concentration and flow rate. The variation in temperature and relative humidity did not significantly affect the breakthrough behaviour of ASZMT carbon at high vapour concentration of carbon tetrachloride whereas breakthrough time of ASZMT carbon reduced by an increase of relative humidity at low carbon tetrachloride vapour concentration.

Method of cleaning water from ammonium vapours

Abstract: FIELD: process engineering. ^ SUBSTANCE: invention relates to cleaning air from toxic volatile substances and may be used in medicine, veterinary medicine, at chemical and woodworking fabrics, etc. Proposed method consists in neutralisation of ammonium vapours by water solution of 20%-cutric acid at 2 atm for 2 minutes, successively 6 to 8 times every 15 minutes. ^ EFFECT: efficient, non-polluting method. ^ 5 dwg, 16 tbl

Manifold sensitivity improvement of hydrocarbon odour sensors

Abstract: We show that the sensitivity of swelling- based gold core- shell nanoparticle (Au CSNP) chemiresistors for vapour sensing can be enhanced considerably by cooling such sensors with respect to ambient temperature. We explain this by the increased swelling of the ligand shell at lower temperature due to the reduced volatility of the analyte. This interpretation is supported quantitatively by measurement and analysis of sensitivity at different temperatures, and to different vapours. Sensitivity to a particular vapour scales with temperature in the same way as that vapour's saturated vapour pressure. That allows quantitative prediction of sensitivity enhancement for vapours not yet tested, as long as their enthalpy of vaporisation is known. We believe our conclusions apply to all sensors that work by swelling in analyte vapour.

Cross-sensitivity of humidity sensor layers based on organic materials

Abstract: This article deals with the research of an impact of various gases and vapours on electrical parameters of phthalocyanine. Cross-sensitivity was researched in order to exclude a negative impact of organic vapours on humidity sensor. Thin layer of phthalocyanine was exposed to various vapours, and then responses of its electrical characteristics were measured. This suitable material for humidity sensors, was deposited from the liquid phase on a substrate with interdigital electrodes and than exposed to the effect of analytes. Subsequently, the impedance characteristic of this thin film layer was measured. The comparison of responses to various gases and vapours is discussed in more detail as well.

Simulating condensation of ammonium fluoride during fluorination of yttria

Abstract: The preparation of yttrium fluoride (YF3) by fluorination of yttria with ammonium bifluoride is an established process. During fluorination, large amounts of ammonium fluoride (NH4F) vapours are generated in the reaction zone. In order to prevent back reaction, the vapours must be suitably removed from the reaction zone. In usual practice, gas purging (argon or dry air), at fairly high flowrate, removes the vapours suitably. The high flowrates have a considerable effect on the temperature inside the reactor. The ammonium fluoride vapours, transported with the inert gas, condense on the cooler regions of the reactor. The condensed vapours being highly corrosive attack the reactor wall. The present study attempts to address the above issue. A three-dimensional numerical heat transfer model has been developed for the fluorination reactor using a commercial software – Fluent 6·1. The simulations were attempted with varying argon flow velocities, to identify the heat taken away by argon during the reac...

Production of silicon with the use of aluminium subchloride

Abstract: FIELD: metallurgy. SUBSTANCE: proposed method comprises reduction of silicon from vapours of silicon compounds with chlorine or silicon with chlorine and hydrogen at mixing of said vapours with vapours of lower aluminium chlorides at 1000-1250°C in transfer gas flow. Said gas represents the mix of hydrogen with argon or the mix of hydrogen with helium containing 2-20 molar parts of hydrogen per one part of silicon compounds vapours. Note here that aluminium lower chlorides of required purity are produced from aluminium metal of 99.0-99.8% purity and gaseous aluminium trichloride or hydrogen chloride or chlorine by multiple reiteration of sublimation and decomposition of formed lower aluminium chlorides. Note also that precipitated silicon crystals are subjected to heat treatment at above 577°C and less than 1400°C, processed by hydrochloric acid and subjected to refining remelting. EFFECT: higher purity of silicon, lower production costs. 2 dwg, 4 ex