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In this work, the effects of two TiO2 polymorphs on the decomposition of ammonium perchlorate (NH4ClO4) were studied experimentally and theoretically. The interactions between AP and various surfaces of TiO2 were modeled using density functional theory (DFT) calculations. Specifically, the adsorption of AP on three rutile surfaces (1 1 0), (1 0 0), and (0 0 1), as well as two anatase surfaces (1 0 1), and (0 0 1) were modeled using cluster models, along with the decomposition of adsorbed AP into small molecules. The optimized complexes of the AP molecule on TiO2 surfaces were very stable, indicating strong covalent and hydrogen bonding interactions, leading to highly energetic adsorption reactions. The calculated energy of adsorption (ΔEads) ranged from −120.23 to −301.98 kJ/mol, with highly exergonic calculated Gibbs free energy (ΔGads) of reaction, and highly exothermic enthalpy of reaction (ΔHads). The decomposition of adsorbed AP was also found to have very negative ΔEdec values between −199.08 and −380.73 kJ/mol. The values of ΔGdec and ΔHdec reveal exergonic and exothermic reactions. The adsorption of AP on TiO2 surfaces anticipates the heat release of decomposition, in agreement with experimental results. The most common anatase surface, (1 0 1), was predicted to be more reactive for AP decomposition than the most stable rutile surface, (1 1 0), which was confirmed by experiments. DFT calculations show the mechanism for activation of the two TiO2 polymorphs is entropy driven. [ABSTRACT FROM AUTHOR]

Understanding the melt layer of composite solid propellants is crucial to theoretically model the combustion mechanism. Numerous studies on the melt layer flow have determined that the melting temperatures of the binder govern the burning rate dependence on pressure. Previous investigations discovered that using curatives and using different binders alter the binder melting temperature. The authors have developed a process to tailor the melting temperature through a functionalization process on the hydroxyl-terminated polybutadiene (HTPB) polymer. This study presents the analysis on the impacts of the melt layer dynamics of an ammonium perchlorate (AP)/HTPB-based propellant with tailorable melting temperatures. Pyrolysis measurements observed increased binder melt layer flow, resulting in lower pyrolysis rates. Propellants made with similar melting temperatures to the traditional R45M had similar burning rates but introduced more scatter due to the hardness of the propellant. Additional propellant samples containing 17 wt% aluminum (Al) and 70 wt% AP were made with a range of melting temperatures to study the impact of melting temperature on the melt layer. A rheological study on the cured propellant mixtures with tailored melting properties identified the melting temperatures for the level of HTPB functionalization. Those mixtures were burned, and the burning rates varied based on the melting temperature. The results suggested that a lower melting temperature produces a plateau propellant. [ABSTRACT FROM AUTHOR]

This study presents a comparison of commercially available titania nano-particles produced using electric wire explosion with nano-particles manufactured by the authors using a sol-gel synthesis process. For the present study, 20-nm titania was purchased off-the-shelf. It was determined to be rough spheres of 20 nm forming large, micron-sized agglomerates, whereas particles synthesized using the sol-gel process were found to be fundamentally 10 nm but with sub-micron agglomerations thereof. The nano-titania was added to 80% AP monomodal propellants at 0.3% and 1.0% by mass. Additional, 85% bimodal-AP mixtures were made, comparing commercial titania to the laboratory-synthesized particles at 1.0% by mass. Another set of samples compared a method of pre-mixing the synthesized additives directly into the binder material at 0.3% by mass of laboratory titania; two additional pre-mixed titania batches at 0.5% by mass were doped with either Fe or Cu into the nanocrystals. All propellants were tested up to 13.8 MPa at 3.8 MPa increments. Dry powder laboratory additives show a 60-to-100% increase in burning rate over the baseline samples with no catalyst and a 20-to-30% increase over the commercial nano-particles. Pre-mixed additives were found to produce similar burning rate increases but with lower concentrations required. This latest generation of particle synthesis techniques was further demonstrated in this study to have great potential for future propellant catalyst development. [ABSTRACT FROM AUTHOR]