Li Fengsheng

One-Step Synthesis of Nanocrytalline Perovskite LaMnO3 Powders via Microwave-Induced Solution Combustion Route

Abstract Perovskite LaMnO 3 powders with an average crystallite size of 12.5 nm were rapidly synthesized via a microwave-induced autocombustion reaction using glycine as a fuel and nitrate as an oxidant. After self-propagating combustion, the desired nanocrystalline perovskite LaMnO 3 was obtained and no further calcination was carried out. The possible processes of combustion reaction were discussed according to the principle of propellant chemistry. The autocombustion and thermal decomposition of the precursor were investigated using the TG-DTA and FT-IR techniques. The influences of glycine-nitrate molar ratio and heat-treatment temperature on the perovskite phase formation and crystallite size of as-burnt powder were studied by XRD. The morphology and size of the as-burnt powder before and after milling were characterized and compared by TEM.

Preparation of CuO Modified SBA-15 and Applications as Catalyst in AP/HTPB Solid State Propellants

Nanometer metal oxides were highly desirable to increase the burning rate of composite solid propellant because of their high catalytic activities. However, poor dispersibility limits their wide applications. In this work, the dispersibility of CuO was enhanced significantly by attachment to the mesoporous silica SBA-15. CuO/SBA-15 composites were prepared by using impregnation method with as-prepared SBA-15 as support, and the occluded template (P123) in SBA-15 promoted the dispersion of CuO on SBA-15. X-ray diffraction (XRD) revealed that no CuO crystalline visible in the composite and N2 adsorption-desorption showed a great amount of CuO dispersion on SBA-15. As the catalyst of propellant, CuO/SBA-15 composite not only enhanced the burning rate of propellant but also decreased the pressure exponent. With the addition of 1 wt% CuO/SBA-15 in the propellant, the burning rate of AP-based propellant increased 9.5%, and pressure exponent decreased 17.3%.

Thermal Reactivity of Nanostructure Al0.8Mg0.2 Alloy Powder Used in Thermites

Abstract Al-Mg alloy, as a kind of promising solid fuel applied in impact-initiated energetic materials, was fabricated by bi-direction rotation ball milling. Structure characterization reveals that the surface of Al0.8Mg0.2 granular particles exhibits a mass of nanostructure with size of 15–30 nm and the crystallite size decreases from more than 100 nm (raw Al) to 22.7 nm (Al0.8Mg0.2) after mechanical alloying. Thermal analysis indicates that Al0.8Mg0.2 presents excellent thermal reactivity. In the air, Al0.8Mg0.2 will be oxidized by O2 distinctly before melting. Moreover, the high temperature reaction of Al0.8Mg0.2-O2 is advanced by 33 °C compared with Al-O2 system. TG traces show that about 69.13% of Al0.8Mg0.2 are oxidized when the temperature increases to 1100 °C, but the value is merely 15.52% for raw Al. Using the alloy in thermites, other than Al-Fe2O3, Al0.8Mg0.2-Fe2O3 system presents a considerable solid-solid reaction. In addition, for Al0.8Mg0.2-Fe2O3, the average active energy of solid-solid reaction is lower by 331.664 kJ·mol−1 than that of the liquid-solid reaction, which means an advantage in ignition.

Ignition and Combustion of Super-Reactive Thermites of AlMg/KMnO4

Abstract Al1-xMgx (x=0.1, 0.2, 0.3, 0.4, 0.5) alloys (designated here after as AlMg alloys) were prepared by mechanical ball milling. The thermites were prepared by sonication dispersion method. AlMg/KMnO4 thermites with different Al/Mg ratios were investigated by differential scanning calorimetry (DSC), ignition and combustion measurements. The results show that the reaction temperatures of AlMg/KMnO4 thermites decrease obviously with the increase of Mg contents, indicating that the thermal reactivity of AlMg/KMnO4 thermites is superior to that of Al/KMnO4. Furthermore, it is found that both the reaction temperatures and the burning velocities of AlMg/KMnO4 thermites decrease from 723 to 493 K, and from 254 to 204 mg/s, respectively, as the content of Mg increases from 0.1 to 0.5, among which the Al0.5Mg0.5/KMnO4 thermite displays the largest flame splash range. It is expected that AlMg/KMnO4 will be the most promising energetic material in ordnance applications.