Curing Viscosity of HTPB‐Based Binder Embedding Micro‐ and Nano‐Aluminum Particles

Abstract

Aluminum is used as a metal fuel in energetic materials for the improvement of propulsion performance and density. Both nano‐sized and micrometer‐sized activated powders represent valuable options in order to improve metal combustion properties, each possessing advantages and drawbacks. These ingredients bear peculiar properties (namely, higher specific surface, coatings, or surface characteristics) which generate high mixing viscosity once suspended in a polymer as well as altered mechanical properties of the final product. Four different powders dispersed in a polymer binder are taken into consideration and the evolution of viscosity in time during the curing process is investigated. The suspending medium is represented by a mixture of hydroxyl‐terminated polybutadiene (HTPB), isophorone diisocyanate (IPDI) and dioctyl adipate (DOA). Viscosity was measured for 5 h on samples under isothermal curing at 60 °C. Non‐isothermal DSC kinetic analyses were also performed using the Kissinger method. It was found that, for the test conditions, a size reduction of metal particles slowed down the increment rate of curing viscosity while some peculiar coatings, such as fatty acids, introduced opposite trends.

Activated aluminum powders for space propulsion

“…The presence of the activation layer did not interact with curing processes or generated internal bubbling, at the mixing temperature of 36°C. These observations are in line with binder-fuel viscosity analyses recently published by the same research group [41]. For combustion tests, an increase of burning rate in the order of about + 20 %, with respect to the original non-activated powders, was observed.…”

Progress in Additive Manufacturing of Energetic Materials: Creating the Reactive Microstructures with High Potential of Applications

“…The most prominent result observed was the decrease in the ignition time and increase in the burning rate for compositions containing nano-Al [38,155,156]. However, the wide utilization of nanometals is limited by several factors, i. e., (i) the reduced metal content and associated performance losses [160] (note the surprising positive effect of the oxide layer [165]), (ii) stability issues, e. g., oxidation during storage [166], (iii) coalescence prior to reaction, diminishing the effects of nanosize [167,168], (iv) the gradual increase in viscosity for compositions with a binder [169], and (v) the difficulty of obtaining a uniform composite mixture with nanocomponents [156,170].…”

Tailoring of Mechanical Properties of Highly Filled Nano‐Aluminized Propellants by Modifying Binder Polymer Microstructure

“…A higher dampening was observed with powders having large specific surface area. The slowest viscosity build-up was reported from propellants with uncoated nano aluminium powders [22][23].…”