Lin-lin Liu

Ignition and combustion characteristics of compound of magnesium and boron

Compound of magnesium and boron (MB) is promising to be the ideal substitute of amorphous boron which is usually used as the raw material of boron-based fuel-rich propellants. In this study, the physical characteristics of MB and amorphous boron were studied by the scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. The thermal reaction characteristics and the ignition and combustion characteristics were investigated through TG/DSC experiments and laser ignition experiments. The experimental results show that the MB particle is much more regular than amorphous boron, which favors for the preparation of boron-based fuel-rich propellants. Magnesium exists in the form of elementary substance, and boron oxide is produced during the preparation of MB which results in the longer ignition delay time of MB. The content of magnesium and the pressure have effects on the MB combustion performance. Although the combustion of magnesium can provide much heat for the combustion of boron, MB with moderate content of magnesium shows the best combustion performance. On the contrast, the ignition delay time of MB is independent on the content of magnesium and the pressure.

Chemical analysis of primary combustion products of boron-based fuel-rich propellants

A facility was designed to collect the primary combustion products of boron-based fuel-rich propellants under different chamber pressures. The morphology and particle size of condensed-phase products were analyzed using a laser particle size analyzer and a scanning electron microscope (SEM), and chemical analysis of condensed-phase products was carried out by X-ray diffraction (XRD), laser Raman spectrometry, wet chemical analysis and elemental analysis. In addition, organics in condensed-phase products and gaseous products were analyzed by Fourier Transform Infrared Spectrometry (FTIR) and Gas Chromatography (GC), respectively. The results show that the condensed-phase products mainly consist of B, C, B4C (or B12C2), BN, Mg, MgO, MgAl2O4, Al, Al2O3, AlCl3, NH4[Mg(H2O)6]Cl3, NH4Cl and Fe3O4; there are large amounts of boron oxide and boron carbide in the condensed-phase products, which indicates that elemental boron is highly active during the primary combustion process; a higher chamber pressure may be disadvantageous to the secondary combustion efficiency because more inactive boron carbide, graphite and h-BN (especially boron carbide) are produced.

Effect of solid oxidizers on the thermal oxidation and combustion performance of amorphous boron

Amorphous boron is usually employed as the most important fuel of boron-based fuel-rich propellants, and NH4ClO4 (AP), cyclotetramethylenetetranitramine (HMX), KClO4 and KNO3 are the solid oxidizers of most used in solid propellants. The mixtures of boron and different solid oxidizers with mass ratio 1:1 were prepared in this paper, and the effect of these oxidizers on the thermal oxidation and combustion performance of amorphous boron was studied by simultaneous thermogravimetry–differential scanning calorimeter–Fourier transform infrared spectroscopy and CO2 laser ignition experiments. The experimental results show that the main reactions during the heating process of B/AP and B/HMX samples are the decomposition of oxidizers, and the decomposition process of oxidizers rather than the decomposition temperature is affected by amorphous boron; boron could react with KClO4 and KNO3 violently with the release of large amounts of heat, and then both of the oxidizers, especially KClO4, have positive effect on the oxidation and combustion performance of amorphous boron.

Thermal decomposition of HTPB/AP and HTPB/HMX mixtures with low content of oxidizer

In this paper, hydroxyl-terminated polybutadiene (HTPB)/ammonium perchlorate (AP) and HTPB/cyclotetramethylene tetranitramine (HMX) mixtures with low content of oxidizer were prepared, and the thermal decomposition process of these mixtures was investigated with TG-FTIR and Raman spectrum. The experimental results indicated that during the thermal decomposition process under an inert atmosphere, HTPB and the two oxidizers could both decompose into gaseous products completely, while the mixture of HTPB and the two oxidizers produced some solid residue with carbon as the main ingredient; unlike the thermal decomposition of HTPB under argon atmosphere, HTPB cannot decompose completely under air or oxygen atmosphere, and the more the concentration of oxygen, the more the solid residue produced. Decreasing the content of oxidizer reacting with HTPB may improve the combustion performance of fuel-rich propellants by increasing the combustion temperature and the percentage of gaseous products. The results of this paper can provide the useful information for improving the combustion performance of fuel-rich propellants.

Ab Initio Calculations of the N-N Bond Dissociation for the Gas-phase RDX and HMX

NO2 fission is a vital factor for 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) decomposition. In this study, the geometry of the gas-phase RDX and HMX molecules was optimized, and the bond order and the bond dissociation energy of the N-N bonds were examined. Moreover, the rate constants of the gas-phase RDX and HMX conformers, concerning the N-N bond dissociation, were evaluated using the microcanonical variational transition state theory (μVT). The calculation results have shown that HMX is more stable than RDX in terms of the N-N bond dissociation, and the conformers stability parameters were as follows: RDXaaa < RDXaae < HMX I < HMX II. In addition, for the RDX conformers, the N-N bond of the pseudo-equatorial positioning of the nitro group was more stable than the N-N bond of the axial positioning of the nitro group, while the results were opposite in the case of the HMX conformers. Moreover, it has been shown that the dissociation rate constant of the N-N bond is influenced by the temperature significantly, thus the rate constants were much lower (<10−10 s−1) when the temperature was less than 1000 K.

Thermal oxidation reaction of paraffin with O 2 and N 2 O under different pressures

Thermal reaction of paraffin with oxidizers could provide valuable information concerning the regression rate and combustion efficiency of paraffin-based fuels. In this paper, thermogravimetric–differential scanning calorimetry experiments were carried out for paraffin under O2 and N2O atmosphere, and the thermal reaction kinetics of paraffin under different pressures of O2 and N2O was estimated through the non-isothermal measurements and model-free isoconversional methods. The results show that the oxidation of paraffin under O2 and N2O atmosphere represents the multistage reaction process; the obtained activation energy (Ea) is much close by using different model-free isoconversional methods, and paraffin is easier to be oxidized under O2 because of the lower Ea and lower reaction temperature; Pressure plays a positive effect on the oxidation of paraffin, especially under O2 atmosphere.

Factors Affecting the Primary Combustion Products of Boron-Based Fuel-Rich Propellants

Boron-based fuel-rich propellants with different formulation were prepared, and the condensed-phase products under different chamber pressures were collected in this study. The composition of boride (elemental boron, boron oxide, boron carbide, and boron nitride) in the condensed-phase products was measured by chemical analysis and the particle size distribution was determined using a laser particle size analyzer. Moreover, the burning rate and combustion temperature of the propellants were measured using a strand burner. The experimental results show that both the propellant burning rate and combustion temperature played an important role in the production of boride. There might be large amounts of boron carbide in the condensed-phase products which appear to have a negative effect on the combustion efficiency of the propellants studied in this work. The production of boron carbide could be reduced and combustion efficiency was improved by lowering the combustion temperature while increasing the burning ...