Browsing by Author "Bergin, Sarah"

Now showing 1 - 9 of 9
  • Thumbnail Image
    ItemOpen Access
    Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 1: Design and implementation
    (Nature Publishing Group, 2020-05-26) Lourenço, Célia; Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Staines, Stephen E.; Saffell, John R.; Walton, Christopher; Tatam, Ralph P.
    A novel suite of instrumentation for the characterisation of materials held inside an air-tight tube furnace operated up to 250 °C has been developed. Real-time detection of released gases (volatile organic compounds (VOCs), CO2, NO, NO2, SO2, CO and O2) was achieved combining commercial off-the-shelf (COTS) gas sensors and sorbent tubes for further qualitative and semi-quantitative analysis by gas chromatography-mass spectrometry coupled to thermal desorption (TD-GC-MS). The test system was designed to provide a controlled flow (1000 cm3 min−1) of hydrocarbon free air through the furnace. The furnace temperature ramp was set at a rate of 5 °C min−1 with 10 min dwell points at 70 °C, 150 °C, 200 °C and 250 °C to allow time for stabilisation and further headspace sampling onto sorbent tubes. Experimental design of the instrumentation is described here and an example data set upon exposure to a gas sample is presented.
  • No Thumbnail Available
    ItemOpen Access
    Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 1: Design and implementation
    (Cranfield University, 2020-05-27 20:00) Lourenco, Celia; Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Staines, Stephen E.; Saffell, John R.; Walton, Christopher; Tatam, Ralph
    Data to support manuscript Part 1.
  • No Thumbnail Available
    ItemOpen Access
    Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 2: Analysis of carbon fibre reinforced epoxy composite
    (Cranfield University, 2020-05-27 20:01) Lourenco, Celia; Francis, Daniel; Fowler, Dawn; E. Staines, Stephen; Hodgkinson, Jane; Walton, Christopher; Bergin, Sarah; Tatam, Ralph
    Data to support manuscript Part 2.
  • Thumbnail Image
    ItemOpen Access
    Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 2: Analysis of carbon fibre reinforced epoxy composite
    (Nature Publishing Group, 2020-05-26) Lourenço, Cecilia; Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Staines, Stephen E.; Saffell, John R.; Walton, Christopher; Tatam, Ralph P.
    We have investigated the release of gases and volatile organic compounds (VOCs) from a carbon fibre reinforced epoxy composite matrix used in aircraft structural components. Analysis was performed at several temperatures both up to and above the recommended operating temperature (121 °C) for the material, to a maximum of 250 °C. Gas chromatography-mass spectrometry (GC-MS) combined with thermal desorption (TD-GC-MS) was used to identify and quantify VOCs, and in parallel real-time gas detection with commercial off-the-shelf (COTS) gas sensors. Under hydrocarbon free air, CO, SO2, NO, NO2 and VOCs (mainly aldehydes, ketones and a carboxylic acid) were detected as the gaseous products released during the thermal exposure of the material up to 250 °C, accompanied by increased relative humidity (4%). At temperatures up to 150 °C, gas and volatile emission was limited.
  • Thumbnail Image
    ItemOpen Access
    Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation
    (OSA, 2016-05-10) Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Tatam, Ralph P.
    We present a four beam ratiometric setup for an integrating sphere based gas cell, which can correct for changes in pathlength due to sphere wall contamination. This allows for the gas absorption coefficient to be determined continuously without needing to recalibrate the setup. We demonstrate the technique experimentally, measuring methane gas at 1651nm. For example, contamination covering 1.2% of the sphere wall resulted in an uncompensated error in gas absorption coefficient of ≈41%. With the ratiometric scheme, this error was reduced to ≈2%. Potential limitations of the technique, due to subsequent deviations from mathematical assumptions are discussed, including severe sphere window contamination.
  • No Thumbnail Available
    ItemOpen Access
    Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation
    (Cranfield University, 2016-11-28 13:52) Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Tatam, Ralph
    Data to support the following paper: Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation S Bergin, J Hodgkinson, D Francis and R P Tatam Optics Express 24 (12), 13647 - 13664, 2016 doi:10.1364/OE.24.013647
  • Thumbnail Image
    ItemOpen Access
    Pathlength calibration of integrating sphere based gas cells
    (Cranfield University, 2016) Bergin, Sarah; Hodgkinson, Jane; Tatam, Ralph P.
    Integrating sphere based multipass cells, unlike typical multipass cells, have an optically rough reflective surface, which produces multiple diffuse reflections of varying lengths. This has significant advantages, including negating scattering effects in turbid samples, removing periodicity of waves (often the cause of etalon fringes), and simple cell alignment. However, the achievable pathlength is heavily dependent on the sphere wall reflectivity. This presents a challenge for ongoing in-situ measurements as potential sphere wall contamination will cause a reduction in mean reflectivity and thus a deviation from the calibrated pathlength. With this in mind, two techniques for pathlength calibration of an integrating sphere were investigated. In both techniques contamination was simulated by creating low reflectivity tabs e.g. ≈5x7mm, that could be introduced into the sphere (and removed) in a repeatable manner. For the first technique, a four beam configuration, adapted from a turbidity method used in the water industry, was created using a 5cm diameter sphere with an effective pathlength of 1m. Detection of methane gas was carried out at 1650nm. A mathematical model was derived that corrected for pathlength change due to sphere wall contamination in situ, thus enabling gas measurements to continue to be made. For example, for a concentration of 1500ppm of methane where 1.2% of the sphere wall was contaminated with a low reflectivity material, the absorption measurement error was reduced from 41% to 2% when the model was used. However some scenarios introduced errors into the correction, including contamination of the cell windows which introduced errors of, for example, up to 70% if the particulate contamination size was on the order of millimetres. The second technique used high frequency intensity modulation with phase detection to achieve pathlength calibration. Two types of modulation were tested i.e. sinusoidal modulation and pulsed modulation. The technique was implemented using an integrated circuit board which allowed for generation of modulation signals up to 150MHz with synchronous signal processing. Pathlength calibration was achieved by comparison of iii the phase shift for a known length with the measured phase shift for the integrating sphere with unknown pathlength over a range of frequencies. The results for both modulation schemes showed that, over the range of frequencies detected, 3-48MHz, the resultant phase shift varied as an arctangent function for an integrating sphere. This differed from traditional single passes where frequency and phase have a linear relationship.
  • No Thumbnail Available
    ItemOpen Access
    Ratiometric pathlength calibration of integrating sphere-based absorption cells
    (Cranfield University, 2020-09-02 09:17) Hodgkinson, Jane; Francis, Daniel; Bergin, Sarah; Tatam, Ralph
    Data to support the paper ' Ratiometric pathlength calibration of integrating sphere-based absorption cells' S Bergin, J Hodgkinson, D Francis and R P Tatam Optics Express 28 (13), 19574-19592, 2020.
  • Thumbnail Image
    ItemOpen Access
    Ratiometric pathlength calibration of integrating sphere-based absorption cells
    (Optical Society of America, 2020-06-19) Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Tatam, Ralph P.
    Chemical sensors based on optical absorption require accurate knowledge of the optical pathlength of the sample cell. Integrating spheres offer increased pathlengths compared to single pass cells combined with tolerance to misalignment, making them attractive for use in challenging environments subject to vibration. However, the equivalent optical pathlength can be degraded by dirt and / or condensation on the inner surface of the sphere. We present a new scheme for in-situ calibration that uses a ratiometric two-beam approach. Results are presented for an integrating sphere used in the measurement of methane by tunable diode laser spectroscopy (TDLS) at 1651nm. Reduced sphere reflectivity was simulated by applying small areas of black tape on the inner surface. At methane concentrations of 1500ppm and 3125 ppm, for areas of contamination up to 2.3% of the sphere wall, the technique reduced the error from over 50% to within ±4%. At a concentration of 6250 ppm and the most severe fouling corresponding to 2.9% wall coverage, the technique reduced the error from 55-65% to within ±11%