Study On Reactivity Photoacoustic Characteristics Of Energetic Materials

The reactivity photoacoustic spectroscopy is the complex photoacoustic spectroscopy of photothermal photoacoustic and chemical reaction heat sound. The key point of this technology is to detect the dynamic reactivity photoacoustic spectroscopy with high sensitivity and high signal to noise ratio. The scientific problems are to separate the traditional photoacoustic spectroscopy and the chemical reaction sound spectroscopy from the photoacoustic spectroscopy, and to carry out the chemical dynamics calculation. The present two issues have unresolved yet. In order to get a better understanding of the correlation between the chemical reaction kinetics and photoacoustic spectroscopy, some researches were carried out on energetic materials with different reactivity and thermal effects to reveal reactivity photoacoustic characteristics and laws. The results might throw some light on the quantitative analysis of photoacoustic technique. In this paper, pulsed laser induced reactivity photoacoustic experimental techniques, optical reflectance analysis, TG-DSC thermal analysis techniques, radiation spectroscopy, confocal microscopy analysis techniques and high-speed image analysis technology and other advanced analytical techniques, combined with numerical simulation, optical properties, thermo-chemical reaction characteristics, laser ablation and ignition characteristics and reactivity photoacoustic characteristics of several typical energetic materials, such as, potassium nitrate (KNO3)/graphite (C), carbon nanotubes (CNTs) and carbon black (CB) doped RDX, HMX, PETN and HNS were studied. Combined with the results of theoretical modeling and numerical simulation, the intrinsic relationship between the chemical reactivity and the reactivity photoacoustic characteristics, and the excitation mechanism of the reactivity photoacoustic spectroscopy of energetic materials was revealed. The following progresses were made:(1) The reaction of KNO3/C is a solid phase reaction, when the content of KNO3was between75%and80%, the reaction completed relatively. Three or more chemical reaction existed in the dynamic process. The interaction of the pulsed laser with KNO3/C could lead to ablation and chemical reaction, and the corresponding reactivity light waves and radiation were excited. The reactivity photoacoustic intensity of KNO3/C samples was mainly determined by the thermochemical reaction characteristics of KNO3/C system. The photoacoustic signal intensity was proportional to the incident laser intensity, this was similar to the ordinary photoacoustic signal, the new result was that the chemical reactivity and the increase of heat release could enhance the intensity of the photoacoustic signals. The peak of the reactivity photoacoustic signal lagged behind the laser pulse duration in the time domain, indicating that the thermal chemical reaction of the reactive material enhanced the intensity of the photoacoustic signals. The chemical reaction and the gaseous product of ablation and dissociation on strengthening the intensity of photoacoustic signal were more significant. The radiation spectra of KNO3/C had the feature of linear spectrum characteristics under laser irradiation. These were mainly composed of atomic spectra and ion spectra of N, O, C and K. The spectral wavelength mainly distributed in300nm～600nm. The spectral information of KNO3/C under different laser energy showed that, at higher incident laser energy, atomic spectra ablation products were mainly N,O, K and C elements, the ion spectra were mainly NⅡ, OⅡ, OⅤ, K I and CⅤ. The chemical reaction was between KNO3and C. At lower laser energy, spectral lines were mainly OⅡ and K Ⅰ, the main reaction was the decomposition of KNO, the excess heat was from the endothermic heat of C.(2) The light reflectance analysis of carbon black and carbon nanotubes showed that the light reflectance of carbon nanotubes was30%smaller than carbon black. The reflectivity of pure explosives was great, and the photoacoustic signal was very weak, the intensity of photoacoustic signal was proportional to the incident laser energy. When the explosives were doped with carbon nanotubes and carbon black, the optical absorption coefficient rate increased. For the same explosives and under the same doping amount, the CNTs doped photoacoustic signal was greater than the CB doped signal. For the same sample and under the same dopant, the greater the amount of doping, the stronger the photoacoustic signal. There was optimum ignition energy for the doped system. For the above explosives, the relationship between the laser energy (E) and peak time (τ) was hyperbolic. But for the KNO3/C system, the relationship was parabola. As the laser energy increased, the lag τ first increased and then decreased. But photoacoustic signal intensity was proportional to the incident laser energy. The results indicated that the dynamic characteristics of the KNO3/C system were obviously different to those of the explosive system under laser irradiation.(3) The reactivity photoacoustic model considering of the photothermal effect, condensed phase chemical reactions and gasification phase transitions and other factors was established, the numerical simulation results of the influence of photoacoustic signal characteristics and related factors were agreed with the experimental results. The numerical results showed that the photoacoustic signal intensity of the incident laser energy and gas products, the heat of reaction of the sample was closely related to the intensity of the photoacoustic signal. The effect of laser energy was the most significant, followed by gas products of chemical reactions or ablation, and then was the heat of reaction of the chemical reaction. This thesis has innovation and breakthrough in the following aspects:(1) The optical properties, thermochemical properties, pulse laser induced reactivity photoacoustic characteristics and pulse laser ablation properties of KNO3/C and carbon black and carbon nanotubes doped RDX, HMX, PETN and HNS were obtained systematically. The correlation between these characteristics was determined.(2) The relationship of chemical reaction and photoacoustic characteristics was revealed and the solid photoacoustic model with the chemical reaction and gasification was established. The excitation mechanism of the reaction heat of the reactivity photoacoustic process and the phase transition, the quantitative relationship of the heat effect of the chemical reaction and the gaseous products with the reactivity photoacoustic characteristics were also revealed.