Showing papers on "Vapours published in 2001"

A rapidly-responding sensor for benzene, methanol and ethanol vapours based on films of titanium dioxide dispersed in a polymer operating at room temperature

Abstract: Thin films of titanium dioxide (TiO 2 ) powder, dispersed in poly(vinylidenfluoride) and deposited on glass slides containing gold electrodes, are used as sensors for benzene, ethanol and methanol vapours at room temperature. The resistance of the films at a potential difference of 1.5 V is determined when the films are exposed to atmospheres containing these vapours with concentrations over the range 150–350 ppm. The relative resistance, Δ R , of the films increases linearly with increasing concentrations of the vapours (regression coefficients, r =0.90, 0.98 and 0.97 for benzene, methanol and ethanol, respectively). The findings are consistent with the TiO 2 films having p-type semiconductor characteristics. The responses of the films are reversible with changes in Δ R of 0.042, 0.1 and 0.122% ppm −1 for benzene, ethanol and methanol, respectively. The response times to increasing concentrations of the vapours are about 1, 2 and 2 min for benzene, ethanol and methanol, respectively, and the corresponding values for decreasing concentrations 5, 6 and 6 min, respectively. The limit of detection for the vapours is about 10 ppm. With improvements in the sensitivity, selectivity and stability, the films could form the basis of a handheld instrument for the atmospheric monitoring of benzene.

A novel porous silicon sensor for detection of sub-ppm NO2 concentrations

Abstract: We developed a new technique for the deposition of free-standing porous silicon (PS) on alumina substrate with interdigital contacts (Italian Patent ENEA-INFM), thus removing the silicon substrate, that is inactive in gas detection and is much more conductive than PS. The dc and ac electrical measurements in a controlled atmosphere were performed to test the sensor response towards NO 2 (0.1–10 ppm), O 3 (200 ppb), CO (1000 ppm), benzene (20 ppm), organic vapours and humidity. The device was able to detect very low concentrations of nitrogen dioxide (100 ppb) with no interference from ozone, benzene, CO and organic vapours. Indeed humidity interferes with nitrogen dioxide detection and must be kept under control. Since PS showed great response to NO 2 at room temperature (RT), no heating of the sensor is required.

Organic vapour sensing by current response of porous silicon layer

Abstract: In this paper, a porous silicon (PS) layer is investigated as a sensing material to detect organic vapours with low concentration. To do this, PS sensors with membrane structure were designed and fabricated. The sensors were made by applying the technologies of membrane formation by anisotropic etching of silicon and PS formation by anodization in HF solution. From fabricated sensors, current-voltage (I-V) curves were measured for ethanol (called alcohol), methanol and acetone gases evaporated from 0.1-0.5% solution concentrations at 36°C. As a result, all curves showed rectifying behaviour due to a diode structure between Si and the PS layer. The conductance of our sensors mostly increased along with the organic solution concentration at a high voltage of 5 V, but the built-in potential on the measured I-V curve was lowered with it by the adsorption effect of the organic vapours with high dipole moment.

Transport of Gases and Organic Vapours Through Membranes Made of Poly(amide-imide)s Crosslinked with Poly(ethylene adipate)

Abstract: Transport of permanent gases (N 2 , O 2 , CO 2 ) and of saturated organic vapours of benzene, toluene and methanol through membranes based on poly(ethylene adipate)-crosslinked poly(amide-imide)s was studied. The membranes containing more than 50 wt.% of non-polyimides showed higher permeability coefficients (by 2-3 orders) for the organic vapours than for the gases.

Process for the adsorption of organic vapours from gas mixtures containing them

Abstract: The invention is directed to a process for the adsorption of organic vapours from gas mixtures containing them onto activated carbon, said process comprising passing the gas mixture consecutively through at least a first and a second adsorption system, the first system consisting of activated carbon having a first adsorption rate for the said organic vapours and the second system consisting of an adsorbent having a second adsorption rate for the said organic vapours, the said second adsorption rate being higher than the said first adsorption rate, more in particular to such process when used in the operation of vehicle internal combustion engines.

Spherical high-performance adsorbents with microstructure

Abstract: Spherical high-performance adsorbents, which are manufactured from polymer resin by water vapour activation with an activation time of at least 6 hours. The adsorbents have a pronounced microstructure in the range of 0 to 40 Å pore diameter and an overall micropore volume of at least 0.6 cm 3 /g. A substantial increase in the adsorption capacity for gases and vapours is achieved which is also represented by the very favourable ratio of weight capacity to volume capacity of upto 2 to 1. The spherical high-performance adsorbents with microstructure can be used for many purposes, in particular, textile fabrics for the adsorption of chemical warfare agents and toxic gases and vapours, in adsorption refrigerating plants in combination with the refrigerating agent methanol, in motor vehicle filters and biofilters.

A passive tube-type sampler for the determination of formaldehyde vapours in museum enclosures

Abstract: A tube-type passive sampling method has been developed and assessed for the quantification of formaldehyde (methanol) vapours in indoor air. The sampler was designed for use in museums where test sites often include small enclosures with low air movement. The procedure involves collection of formaldehyde vapours in a Palmer diffusion tube containing a paper support impregnated with an acidified solution of 2,4-dinitrophenylhydrazine (2,4-DNPH). After sampling, quantification of the trapped F-DNPH is achieved by high performance liquid chromatography (HPLC) analysis with UV detection at 350mm. To validate the procedure, permeation devices were used to generate formaldehyde-containing atmospheres., 81-2975pph, in a 20dm(3) chamber so that experimentally derived sampling rates could be calculated and compared with the theoretical value. Three 2,4-DHPH solutions were investigated to obtain an efficient and stable trapping solution. Best results were achieved with a 27mg.ml(-2) solution of 2,4-DNPH which contained 4(3.)6ml.min(-1). The passive sampling method was repeatable and reproducible with RSD (relative standard deviation) values below 7% for long-term exposures at low air velocities.

Adsorption from pure and mixed vapours of n-hexane and n-perfluorohexane

Abstract: We have used a modified surface force apparatus (SFA) to study adsorption onto mica surfaces from near-saturated vapours of n-hexane and n-perfluorohexane, and mixtures thereof. For relative vapour pressures in the range 0.9-0.998 the films adsorbed from vapours of the pure liquids range in thickness from 1 to 4 nm, in crude agreement with the predictions of non-retarded van der Waals-Lifshitz theory. The observed deviations from theory show a qualitative difference between the two liquids, which may reflect differences in the significance of structural contributions to the disjoining pressure. Under the same experimental conditions, adsorption from vapours of (one-phase) liquid mixtures gives rise to films which are significantly thicker, over a broad range of intermediate compositions, than those adsorbed from the pure vapours, with a broad maximum in thickness observed near the critical composition of the bulk liquid mixture.

Condensation characteristics during supersonic flow of organic vapours

Abstract: Condensation of some organic vapours including ammonia, ethanol and fieon-1 1 by homogeneous nucleation of liquid droplets has been studied here during supersonic flow through convergent-divergent nozzles. Theoretical model of the present work is based upon three groups of equations namely: gasdynamic equations, equations of condensation kinetics and droplets growth equations. Modified equations for the classical nucleation rate, droplets surface tension and the thermodynamic properties of the condensing vapour are used in the present theoretical model. Generally, present model predictions show that condensation characteristics of the tested organic vapours are qualitatively similar to those of steam condensation. Also, the present study indicates that the condensation characteristics of the tested organic vapours are affected with the operating parameters such as the vapour temperature and its mass fraction. The theoretical predictions of the pressure variation along the divergent sections of such supersonic nozzles are in good agreement with the published experimental measurements of these organic vapours.

System for conveying the venting vapours in fuel distributors

Abstract: A system for conveying the venting vapours in the columns (10) of fuel distributors includes a pipe (40), which connects the fuel pumping unit (13) to the pipe (28) for delivery of the vapours from the vapour recovery system to the storage tank, and which comprises at least one device (41) for stopping the liquid fuel, and at least one non-return valve (42).

Synthesis,characterisation and humidity sensing of metallophtha!ocyanines

Abstract: Metallophthalocyanines synthesized for different metals such as Ni, Cr, Ag, Mg, Cu, Cd, Al, etc by chemical methods were characterized with FTIR, TGA etc. Sensing of humidity and different gases such as NOx, H 2 , O 2 , CO 2 , N 2 , ammonia, alcohol vapours etc were checked with 2-probe technique with monitoring change in resistance change. These samples have excellent stability against heat, light, air, and hence it has considerable attention for environmentally stable gas sensor. The electrical property of these samples were investigated at room temperature and at normal atmospheric pressure from low to 98% relative Humidity. It was observed that these samples shows good response and recovery for humidity sensing.