Browsing by Author "Fang, Xiao"

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    Elemental analysis in environmental land samples by stand-off laser-induced breakdown spectroscopy
    (Elsevier, 2013-09-07) Fang, Xiao; Ahmad, Sheikh R.
    The stand-off detection and analysis of environmental land samples have been demonstrated using laser-induced breakdown spectrometry. The samples of interest have included soils and vegetation powder. Elements Hg, As, Pb, Zn, Cd and Cr have been spectrally analysed with a focus on Hg as a trace contaminant in the samples. It is found that element Fe, usually contained in land samples, is a main source of spectral interference for Hg detection due to its ever present iron emission line at 253.68 nm that is closely adjacent to the strongest Hg emission line at 253.65 nm, and hence, a high resolution of spectral detection is necessary. The strong spectral signals from Bremsstrahlung emission in laser-induced plasma and atomic emission of Fe of high concentration caused a significant reduction in detection resolution in the use of image intensifier of an ICCD. The limit of detection at ~8 ppm for Hg detection in soil samples with iron as a minor constituent has been achieved, using an optical chopper and a CCD detector for laser-induced breakdown spectroscopy (LIBS) signal detection. Such detection method in LIBS system has shown a great advantage in determining trace elements from interfering elemental constituents in land sample matrixes.
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    Laser ignitability of insensitive propellants
    (OAT, 2018-04-26) Fang, Xiao; Ahmad, Sheikh R.
    Laser ignition tests were conducted on insensitive propellants formulated with an insensitive filler (1,1‑diamino-2,2-dinitroethylene, commercially known as FOX-7) and with either energetic or non-energetic binders: poly3-nitromethyl-3-methyloxetane (PolyNIMMO) and hydroxyl-terminated polybutadiene (HTPB), respectively. The tests were conducted in an unconfined environment using both visible (514 nm) and near infrared (808 nm) lasers. The non-energetic binder rendered the formulated ammunition more susceptible to initiation by the visible laser. The graph of ignition delay times versus laser power density followed the expected asymptotic trend. However, the shape of the ignition map was greatly affected by the beam area on the target. The results of the unconfined laser ignition tests were analysed to determine the feasibility of using lasers as cost-effective and safe igniters for future weapons and rocket motor systems.
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    Laser ignitibility of energetic crystals doped with gold nanoparticles
    (Elsevier, 2019-01-04) Churchyard, Sam; Fang, Xiao; Vrcelj, Ranko
    Laser ignition mechanism enhances the safety of explosive applications. However, optical sensitisation of the energetic materials is required for their optical absorption. In this research, explosive Cyclotrimethylene Trinitramine (RDX) was doped with gold nanoparticles during recrystallisation to provide a suitable optical sensitisation method. The relationship between the precipitation rate used during RDX recrystallisation and the subsequent laser ignition properties using an 808-nm continuous wave diode laser was studied. Faster initial precipitation was found to reduce the laser ignition delay times and smaller nanoparticle size reduced ignition thresholds. It was shown that recrystallized RDX particle size, which is determined by both nanoparticle induced nucleation and precipitation rate, affects the ignition delay time and quality of the crystals. The largest crystals in each batch were investigated using both high-speed photography and microscopic etching, revealing that in contrast to the bulk sample (which was generally a powder), a slower precipitation seems to achieve better doping. The largest crystals in each sample therefore do not represent the bulk sample, a useful indication as such large crystals are easier to handle and therefore tend to be selected for detailed characterisation work.
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    Laser ignitibility of insensitive secondary explosive 1,1-diamino-2,2-dinitroethene (FOX-7)
    (Elsevier, 2014-12-15) Fang, Xiao; McLuckie, Warren G.
    An experimental investigation into laser ignitibility of insensitive secondary explosives, 1,1-diamino-2,2-dinitroethene (FOX-7) has been carried out, using a diode laser of continuous wave at the laser wavelength of 974 nm. The direct optical ignition of an insensitive explosive will add more safety features to insensitive munitions (IM) or explosive devices. In this study, effects of laser parameters on the ignitibility were analysed in terms of laser ignition threshold, the times to initiate the ignition and full combustion, and burning sustainability. The results have shown that carbon black (CB) as an optical sensitizer is compatible with FOX-7, and significantly enhances laser ignitibility of the explosive when a small amount of CB is uniformly doped in FOX-7. The delay times for ignition and subsequent development of sustainable burning of the material are mainly determined by ignition laser power, although the other laser parameters have effects. The minimum laser power required to ignite the optically sensitized FOX-7 was found below 10 W and a fast ignition was initiated in as short as 70 μs by a laser power of 40 W. Also the effect of the mixture uniformity of FOX-7/CB on laser ignition performance was evaluated in this study.
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    Laser ignition of an optically sensitised secondary explosive by a diode laser
    (Institute of Industrial Organic Chemistry, Poland, 2016-01) Fang, Xiao; Ahmad, Sheikh R.
    As a green technology, laser ignition of a relatively insensitive secondary explosive has been experimentally investigated. The explosive, hexanitrostilbene (HNS), was doped with one of two optical sensitizers, carbon black or a laser absorbing dye, and a continuous-wave (CW) infrared diode laser was used as the igniting source. The ignition sensitivities of HNS with each of the two optical sensitizers were analysed and compared in terms of: optical power threshold for ignition, ignition delay and full burn delay at various laser powers. The results have shown that both the chemical dye and carbon black optically sensitize the explosive with similar efficiencies. In contrast to the carbon black, the dye provides wavelength specificity and selectivity in the laser ignition process and its solubility in some specific solvents improves the coating of the explosive material. It was therefore concluded that the laser absorbing dye is a better candidate for optical sensitization in laser ignition than the commonly used carbon black. The combination of laser ignition sensitivity with wavelength selectivity potentially offers higher reliability and safety at a low optical power for future ignitors of secondary explosives.
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    Laser ignition of elastomer-modified cast double-base (EMCDB) propellant using a diode laser
    (Elsevier, 2016-10-06) Herreros, Dulcie N.; Fang, Xiao
    An experimental study was conducted to investigate laser ignition using a diode laser for elastomer-modified cast double-base (EMCDB) propellant in order to develop more liable and greener laser ignitors for direct initiation of the propellant. Samples of the propellant were ignited using a 974 nm near-infrared diode laser. Laser beam parameters including laser power, beam width and pulse width were investigated to determine their effects on the ignition performance in terms of delay time, rise time and burn time of the propellant which was arranged in several different configurations. The results have shown that the smaller beam widths, longer pulse widths and higher laser powers resulted in shorter ignition delay times and overall burn times, however, there came a point at which increasing the amount of laser energy transferred to the material resulted in no significant reduction in either delay time or overall burn time. The propellant tested responded well to laser ignition, a discovery which supports continued research into the development of laser-based propellant ignitors.
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    Optical sensitisation of energetic crystals with gold nanoparticles for laser ignition
    (Elsevier, 2017-05-18) Fang, Xiao; Sharma, Mishminder; Stennett, Christopher; Gill, Philip P.
    The laser ignition of explosives is safer and more environmentally beneficial than electric ignition systems, but optical sensitisers must be present to facilitate heating by optical absorption. We investigated, for the first time, the optical sensitisation of cyclotrimethylenetrinitramine (RDX) crystals by doping them with gold nanoparticles to enhance laser ignitibility using a near-infrared diode laser. RDX crystals physically coated with gold nanoparticles or recrystallised from a solution containing gold nanoparticles were tested for optical sensitisation by micro-imaging with a scanning electron microscope, and high-speed video was used to experimentally observe the enhanced laser ignitibility. The gold nanoparticles achieved effective optical sensitisation and significantly enhanced the laser ignitibility of RDX, reducing the laser ignition threshold power from more than 45 W to as little as 1 W. Our results show that gold nanoparticles are effective as optical sensitisers for the ignition of energetic materials using a small, low-power diode laser.
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    Optical sensitising of insensitive energetic material for laser ignition
    (Elsevier, 2022-10-21) Fang, Xiao; Walton, Alexander J.
    An experimental investigation into optical sensitisation for laser ignition of an insensitive explosive 1,1-Diamino-2,2-dinitroethene (FOX-7) has been carried out, by using a near-infrared diode laser at a wavelength of 808 nm. In this study carbon black as the optical sensitiser was mixed at 5 wt.% with the explosive using two different mixing techniques, tumble mix and ground mix. The mixture samples were characterised by microscopy to examine the dispersion of carbon black within the mixtures and analyse effects of the mixing techniques on their laser ignitability. Laser ignition maps were developed for both mixing techniques and varying sample densities also examined to determine the density effect on laser ignition with various laser parameters of beam width, laser duration and laser power. The results have shown that ground mixing method provides more uniform dispersion of carbon black in the mixture samples, and therefore allows a lower laser ignition threshold than that of tumble mixing method.