Experimental Research Of Sound Velocity In Nitrobenzene And Nitromethane Under Variable Temperature And Pressure Conditions

Sound velocity,the speed of sound waves,is an important parameter that is related with many physical and chemical properties of materials.There are multiple ways for measuring sound velocity.The impulsive stimulated light scattering method combines the characteristics of laser ultrasonic and light scattering methods,has the advantages of all-optical non-contact measurement experiment.Sound velocity in energetic materials under high temperature and high pressure conditions is the focus that people pay attention to because it is related with the shock induced chemical reaction processes of energetic materials.This work investigates the temperature and pressure effects on sound velocity of two typical liquid energetic materials nitrobenzene and nitromethane.The applicability and merits of different sound velocity measuring methods were firstly analyzed.The impulsive stimulated light scattering method was used in order to measure the sound velocity of liquid sample under high temperature and high pressure conditions in this work because this is a non-contact measuring method that has smaller diffraction angle,and the confined pressure and temperature devices can be used in the light path.Therefore,this method is suitable for the sound velocity observations under high temperature and high pressure conditions.High sensitivity homodyne detection method was used to magnify the measured signal.IR780 dye was dissolved in nitrobenzene and nitromethane to increase the absorbance of the pump pulse.The original impulsive stimulated light scattering setup was improved to make it adapt to the high temperature and high pressure experiments.The sound velocities in nitrobenzene and nitromethane under ambient conditions were firstly measure.The measured values consist very well with the theoretical values,indicating the validity of the improved setup.Then,sound velocities in nitrobenzene and nitromethane were measured at high temperature & normal pressure and high pressure & room temperature conditions.It can be found from the measured sound velocities that high temperature and high pressure conditions have contrary effects on sound velocities.The sound velocities linearly decrease with the rising temperature,but nonlinearly increase with the rising pressure.Finally,a device that can be used to heating the pressure cell was designed,and the sound velocities of nitrobenzene and nitromethane under high temperature and high pressure coupling effects were measured.The observed sound velocities under different temperature and pressure conditions were simulated based on previous data.The contributions of temperature and pressure to sound velocities can be resolved from this simulation.The simulation results suggest the variations in the sound velocities of nitrobenzene and nitromethane under combined high temperature and pressure condition can be expressed as the liner superposition of high temperature and high pressure effects.This work measured the sound velocities of nitrobenzene and nitromethane under high temperature and high pressure conditions by using of an all-optical non-contact impulsive stimulated light scattering method for the first time.The results of this work provide important information on the shock response behaviors of energetic materials.