Research On The Thermal Hazard Of The Pyrotechnics For Fireworks And Crakers

Due to the increasingly incisive contradiction between the growing demand of pyrotechnics and frequent occurrence of accidents in recent years, the hazard of pyrotechnics used in fireworks and crackers during the process of manufacturing, transportation and storage should be investigated. Among the factors inducing the accidents, the stimulation of the heat is one of the main factors resulted in the accidents. Therefore, it is significant to investigate the thermal hazard in order to guard against unexpected accidents and reduce the economic loss.The typical pyrotechnics used for fireworks and crackers were researched in this dissertation. The thermal hazard of the pyrotechnics were predicted by the maximum heat of decomposition, the difference between the maximum heat of decomposition and the heat of combustion and the oxygen balance which are three evaluation indexes in CHETAH. The DSC experiments were carried out and the kinetic parameters such as activation energy, the pre-exponential factor and the mechanism function were calculated out by Kissinger method, Ozawa method, Starink method, Satava-Sestak method and Friedman method. The results show that the onset temperatures of thermal decomposition are mostly between350℃and450℃. The activation energies obtained by aforementioned four methods are between80and390kJ·mol-1. The activation energies obtained by Friedman method vary with the reaction progress.Based on DSC data, the methods of thermal hazard evaluation were discussed. The onset temperature of thermal decomposition, the heat release and the activation energy were selected to evaluate the thermal hazard in the direct method. The finding is that these three factors must be used as the independent factors to evaluate the thermal hazard. On the strength of the definition’Risk=Possibility×Severity’, a comprehensive criterion of the risk was put forward. The mechanical sensitivity and the onset temperature were used to characterize the possibility and the heat release to severity. The results show that it is appropriate to use this criterion to estimate the risk level. The second method is based on the kinetic process got by Friedman method. The thermal behaviors of pyrotechnics under adiabatic condition were simulated by AKTS-Thermokinetics. And also the accelerating decompositions of the50kg pyrotechnics without any packaging were considered. Two factors, TD24and SADT were chose to assess the thermal hazard. The results are almost the same. Besides, based on the method proposed by Yoshida Tadao’s laboratory, the properties of the propagation of explosion were judged. It turns out that most samples have no explosive properties.The thermal hazard of the RNC was evaluated systematically. There are two advantages if the retired single base propellant (RNC) is applied to the fireworks:Solve the problem of the handling of the RNC; Meet the development tendency of the safe and environmental-friendly fireworks. The heat of formation, bond dissociation energy and detonation property of nitrocellulose monomer were calculated by Gaussian model. The results indicate that the heat of formation is negative and there does appear to a link between the BDE and the activation energy. TG-DSC-FTIR-QMS and ARC were used to study the thermal behavior of RNC. Although there was only one exothermic peak in DSC curve and one weight loss step in TG curve, the process of thermal decomposition can be divided into three steps. The thermal behavior under adiabatic condition shows that once the exothermic signal was detected in ARC, the rate of heat release is very violent. Based on the ARC data, the time to maximum rate (TMR) was obtained by three methods:the extrapolation of the raw data, approximate solution of TMR supposed by Townsend and Tou and another empirical formula. The results were compared with the results obtained by AKTS based on DSC data. It is stated that the values of TD24are different by these four methods. It must be better to keep an eye on the real situation when it is used in practice. Besides, the characterization methods of autocatalytic reaction were discussed. An identification method based on a numerical simulation technique from the Swiss Institute for the Promotion of Safety and Security was used to determine the characteristic parameters of the decomposition reaction, revealing that the decomposition of RNC is potentially autocatalytic. This type of reaction must be paid more attention in use and storage.The thermal hazards of the mixtures of RNC were studied in term of DSC-TG The kinetic were carried out by three methods. The results indicate that the adding of potassium perchlorate and ammonium perchlorate has no influence on the decomposition of RNC and titanium catalyzes the reaction and makes the thermal hazard increase. The research on the thermal hazard of RNC and the mixtures with other oxidant or fuel has important guiding significance on safe reuse.