Effect of synthesis parameters on structural properties and thermal behavior of Sol-Gel synthesized iron oxide Xerogels

Dinçer Yılmaz, Nil Ezgi
Currently used igniter system compositions are mostly based on the pyrotechnic blends of fuels and oxidizers. In this study, nanostructured metallic xerogels were synthesized by sol-gel method by using various types of proton scavengers and these metallic xerogels were used as oxidizers. In the experiments, Fe(NO3)3·9H2O was used as a precursor and a wide range of proton scavengers (propylene oxide, 1,2 epoxybutane, tetrahydrofuran, tetrahydropyran, 1,4 dioxane and ammonium hydroxide ) were used to start the gelation mechanisms. In order to dry the gels and to obtain xerogel structures, the room temperature drying method was utilized which was followed by low temperature direct drying method. Further, to figure out the effect of drying conditions, sequential solvent exchange (SSE) was applied to obtain xerogel structures. The energetic compositions were prepared by mixing nanostructured Fe2O3 xerogel samples with metal/fuel powders. The fuels used in these energetic compositions were commercially available boron, aluminum, magnesium and 20% magnesium coated boron. The energetic properties of metal/fuel-Fe2O3 composites were determined and the effect vi of proton scavengers, drying conditions, equivalence ratio on the textural properties and thermal behavior of the thermite mixtures were examined. The results showed that the iron oxide xerogels dried with SSE process have exhibited intrinsic properties of aerogels with high surface area, larger than 300 m2/g, mesoporous structure with a size range of 3-4 nm and nano-scale particle sizes with 3-4.nm. It was observed that the surface area of xerogels was strongly dependent on the type of proton scavenger used. The heat output values of the fuel/iron oxide nano thermites were determined from 85 to 3285 J/g depending on the fuel-oxidant ratio, proton scavenger, drying conditions and fuel type based on DSC/TG analysis. It was shown that the type of proton scavenger, drying conditions and fuel-oxidant ratio could be used to modify the combustion performance, thermal behavior and the structural properties of nanothermites and the particle size distribution, surface area and crystallinity of the xerogels synthesized with the sol-gel synthetic route. The structural and morphological properties of the samples were characterized by XRD, FTIR, elemental analysis and SEM. The surface area and particle size distribution of the samples were determined by BET method. The thermal behavior and combustion characteristics were characterized by using TG-DSC Instrument and Parr Bomb Calorimetry. The impact and friction sensitivity of the energetic nanocomposites were evaluated by BAM Impact and Friction Tester.
Citation Formats
N. E. Dinçer Yılmaz, “Effect of synthesis parameters on structural properties and thermal behavior of Sol-Gel synthesized iron oxide Xerogels,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.