Effects of Mg/PTFE pyrotechnic compositions on reignition characteristics of base bleed propellants and heating mechanism

The effects of magnesium/polytetrafluoroethylene(Mg/PTFE)pyrotechnic compositions on the coupled flow field and reignition mechanism are important aspects governing the perfommance and range of base bleed projectiles(BBPs).Owing to a decrease in pressure and temperature when the BBP leaves the muzzle,rapid depressurization occurs,which extinguishes the base bleed propellant.The Mg/PTFE py-rotechnic composition pressed in the igniter of the base bleed unit(BBU)provides additional energy to the BBU via a chemical reaction.Thus,the extinguished base bleed propellant is reignited under the effect of high-temperature combustion gas jets from the igniter.In this study,a numerical analysis is conducted to evaluate the effects of PTFE and Mg granularity as well as Mg/PTFE pyrotechnic compo-sitions.Owing to the rapid depressurization,the temperature and pressure was found to decrease fordifferent Mg/PIFE pyrotechnic compositions.However,the depressurization time increased as the PTFE granularity increased,the Mg granularity decreased,and the Mg content increased.When the pressure in the combustion chamber of the BBU decreased to the atmospheric pressure,the combustion gas jets from the igniter expand upstream(rather than downstream).However,these combustion gas jets exhibit different axial and radial expansion characteristics depending on the pyrotechnic compositions used,The results show that the reignition delay time,ta,of the base bleed propellant was 377.608,94.27,387.243,523.966,and 221.094 ms for cases A-E,respectively.Therefore,it was concluded that the Mg/PTFE pyrotechnic composition of case B was the most beneficial for the reignition of the base bleed propellant,with the earliest addition of energy and mass to the BBP.

Determination of potassium content as principal components in pyrotechnic compositions used for fireworks and firecrackers based on inductively coupled plasma optical emission spectrometric approach （ICP-OES）

Inductively coupled plasma optical emission spectrometric approach（1CP-OES） is used to determine the potassium content as principal component in pyrotechnic compositions used for fireworks and firecrackers. Element of potassium is conunonly found in potassium nitrate and potassium perchlorate in pyrotechnic compositions in fireworks and firecrackers. Statistical analysis shows that potassium nitrate content in pyrotechnics is between 10% to 60% and the potassium perchlorate content is between 20% to 70%,which counted in the content of potassium element is between 4% to 23%. Concept of this method： considering the weight of the sample is 400rag,constant volume is 1L and the concentration of potassium is between 10 mg/L to 90 mg/L in sample solution, the determination scope of the method for the potassium content would be between 1% to 23%.Further experiments proved that the fitting correlation coefficient of potassium calibration curve is 0.9997 or higher, recovery is 89.15%-100.23%.The allowable differential value is 0.4% between two single tests under repeatable conditions. This method can completely satisfy the requirements of the fireworks and firecrackers industry with high accuracy and good precision.

Determination of magnesium and aluminum content as principal components in pyrotechnic compositions used for fireworks and firecrackers based on inductively coupled plasma optical emission spectrometric approach （ICP-OES）

Inductively coupled plasma optical emission spectrometric approach（ICP-OES）is used to determine the magnesium and aluminum content as principal components in pyrotechnic compositions used for fireworks and firecrackers. Elements of magnesium and aluminum are commonly found in aluminum powder or magnesium-aluminum alloy powder in pyrotechnic compositions in fireworks and firecrackers. Statistical analysis shows that the magnesium content in pyrotechnics is between 8% to 30% and the aluminum content is between 8% to 35%（roughly）.Concept of this method： suppose the weight of the sample is 400rag,constant volume is IL and the concentlation of magnesium and aluminum is between 12mg/L to 160mg/L in sample solution, the determination scope of the method for magnesium and aluminum content would be between 3% to 40%.Further experiments proved that the fitting correlation coefficient of the magnesium calibration curve is 0.9999 or higher, recovery is 101.01% -101.96%.The fitting correlation coefficient of the aluminum calibration curve is 0.9999 or higher, recovery is 99.36%-103.07%. The allowable differential value is 0.4% between two single tests under repeatable conditions. This method can completely satisfy the requirements of the fireworks and firecrackers industry with high accuracy and good precision.

Flash Lamps as Ignition and Initiation Sources of the VS-2 Pyrotechnic Composition

In the present work it is found that the pyrotechnic composition VS⁃2 can be initiated with flash lamps IFC⁃500 and EVIS.VS⁃2 pyrotechnic composition contains 90%of mercury(Ⅱ)5⁃hydrazinotetrazolate perchlorate and 10%of optically trans⁃parent copolymer of 2⁃methyl⁃5⁃vinyltetrazole and methacrylic acid(PVMT).We have found that the flash lamps make it possi⁃ble to initiate combustion of VS⁃2 composition with its transition to detonation both in cylindrical charges placed in brass caps of 5 mm diameter and 2 mm high,and film charges with 10 mm×80 mm in size and surface weights of 60 mg·cm^(-2)and 90 mg·cm^(-2),showing ignition delay times 10μs and 3μs,respectively.We also measured detonation velocities for VS⁃2 composition film charges,which were 4375-4505 m·s^(-1)(of the charge being surface mass 60 mg·cm^(-2))and 4221-4281 m·s^(-1)(of the charge be⁃ing surface mass 90 mg·cm^(-2))and their blasting action on the aluminum plate.The depths of the normal shock wave imprints at the charge⁃barrier interface were 0.6-0.7 mm(for surface mass of the film charges 60 mg·cm^(-2))and 1.2-1.3 mm(for surface mass of the film charges 90 mg·cm^(-2))

Role of binders in reactive composites: A case study with spherical B/Pb_(3)O_(4) particles

The strategic selection of appropriate preparation methods and binder strategies is crucial for enhancing the particle and combustion performance of pyrotechnic delay compositions(PDCs).This study,utilizing droplet microfluidics technology(DMT)and micron-scale raw materials,prepared spherical B/Pb_(3)O_(4) composite particles with varying concentrations of fluorine rubber(F_(2604)).The morphology,specific surface area,bulk density,flowability,friction sensitivity,thermal decomposition,and combustion performance of these microspheres were characterized.The results indicate that as the binder content increases,the particle size of the microspheres first decreases and then increases,the specific surface area decreases,and the bulk density increases,correlating with tighter binding of the reactant powders by the binder.Furthermore,tighter powder-to-powder binding results in a progressive decrease in the thermal decomposition peak temperature of the samples(from 404.2℃ to 346.4℃).Additionally,increased binder content reduces the friction sensitivity and combustion rate of the samples,which is attributed to the energy absorption properties of the binder.Compared to the control group,the microsphere samples exhibit significantly enhanced bulk density,flowability,friction safety,and combustion delay precision,potentially improving the reliability of PDCs in ignition sequences.

Reaction mechanism,insensitivity and mechanical property of PTFE-Mg-W composites with magnesium particles surface modification

This paper aims at enhancing impact insensitivity of polytetrafluoroethylene(PTFE)-Mg-W without sacrificing bulk of energy released in the reaction and optimizing mechanical properties of PTFE-Mg-W by magnesium surface treatment.The reaction energy results indicate that the reaction energy of PTFE-Mg-W(modified 1 min)in oxygen decreases slightly to 7905 J·g^(-1)compared with that of PTFE-Mg-W(unmodified)which is8533 J·g^(-1).Under impact condition(impact velocity between 16.232 and 17.726 m·s^(-1)),compared with PTFEMg-W(unmodified),the initiation time before ignition of PTFE-Mg-W(modified 1 min)delays 50μs;the absorbed energy needed for ignition of PTFE-Mg-W(modified1 min)increases by 67.9%.This increase in impact insensitivity of PTFE-Mg-W can be contributed to the formation of passivated layers of magnesium particles after modification which effectively weakens the total interface area among reactive components and partly contributes to the loss of released energy of PTFE-Mg-W after magnesium modification.The quasi-static and dynamic compression results show that PTFE-Mg-W(modified 1 min)possess the highest strength and the best ductility.