Burning Rate Characterization of Ammonium Perchlorate Pellets Containing Micro- and Nano-Catalytic Additives
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abstract
Ammonium perchlorate (AP) is an extensively used oxidizer in solid composite propellants, and its combustion behavior can be tailored by the presence of catalytic additives such as metal oxides. Nano-sized metal oxide catalysts have been utilized in place of their micro-sized counterparts to tailor burning rates of composite Ammonium Perchlorate (AP)/Hydroxyl-terminate Polybutadiene (HTPB) propellants. The effects of micro- and nano-sized metal oxide catalysts on the combustion of AP were investigated and thoroughly characterized herein. AP pellets were manufactured with micro- and nano-iron oxide (FeO) and micro- and nano-titanium oxide (TiO) at several mass loadings (0-3% by mass) and were burned from 3.45-34.5 MPa (500-5,000 psi) in a constant-volume strand bomb. Intimate contact between the AP and micro- or nano-catalysts was ensured using a Resonant Acoustic Mixer (RAM). The homogenous mixture of AP and catalyst was pressed into pellets using a Carver hydraulic press. The sides of the pellets were inhibited prior to burning to discourage side-wall burning. The incorporation of 1% FeO yielded the highest burning rate among all formulations herein within the investigated pressure range. The incorporation of nTiO and nFeO yielded burning rates which were independent of mass loading within the range of evaluated conditions (0.25-1%). All micro-formulations investigated increase the burning rate at pressures ranging from roughly 13.45- 17.24 MPa (1,950-2,500 psi) and 4.50-8.60 MPa (650-1,250 psi) and for TiO and FeO, respectively; and these effects were dependent on the catalyst mass loading. The nano-formulations increased the burning rate at pressures greater than 11.27 (1,620 psi) and 8.27 MPa (1,200 psi) for nTiO and nFeO, respectively. The low-pressure deflagration limit (LPDL) is observed at higher pressures for samples containing the nano-additives in comparison to samples containing micro-additives. The occurrence of a LPDL was attributed to radiative heat transfer losses. Future testing efforts will be geared towards the characterization of AP pellets with energetic additives such as aluminum, boron, and zirconium.
