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Several aluminum nanopowders were examined and compared with the final goal to evaluate their application in solid rocket propulsion. A detailed investigation of pre-burning properties by the Brunauer-Emmet-Teller method, electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy was carried out. Ballistic properties and the combustion mechanism of several aluminized propellant formulations were investigated. In particular, aggregation and agglomeration of metal particles at and near the burning surface were analyzed by high-speed high-resolution color digital video recordings. All tested nano-powders are of Russian production; their physical characterization was carried out at the Istituto Donegani (Novara, Italy); ballistic studies were performed at the Solid Propulsion Laboratory (Milano, Italy) using laboratory and, for comparison, industrial composite propellants based on ammonium perchlorate as an oxidizer. Results obtained under a fair variety of operating conditions typical of rocket propulsion indicate, for increasing nano-Al mass fraction or decreasing nano-Al size, larger steady burning rates with essentially the same pressure sensitivity. While aggregation and agglomeration phenomena still occur, their significance may be reduced by using nano-Al instead of micro-Al.

Experiments concerning the ballistic characterization of several nanoaluminum (nAl) powders are reported. Most studies were performed with laboratory composite solid rocket propellants based on ammonium perchlorate as oxidizer and hydroxyl-terminated polybutadiene as inert binder. The ultimate objective is to understand the flame structure of differently metallized formulations and improve their specific impulse efficiency by mitigating the twophase losses. Ballistic results confirm, for increasing nAl mass fraction or decreasing nAl size, higher steady burning rates with essentially the same pressure sensitivity and reduced average size of condensed combustion products. However, aggregation and agglomeration phenomena near the burning surface appear noticeably different for microaluminum ( Al) and nAl powders. By contrasting the associated flame structures, a particle-laden flame zone with a sensibly reduced particle size is disclosed in the case of nAl. Propellant microstructure is considered the main controlling factor. A way to predict the incipient agglomerate size for Al propellants is proposed and verified by testing several additional ammonium perchlorate/hydroxyl-terminated polybutadiene/aluminum formulations of industrial manufacture

Experimental studies on the burning of nanoaluminum-based solid rocket propellants are carried out. Data on the properties of condensed combustion products, mechanisms of their formation, and burning-rate law are obtained.\ud Based on these data, a physical picture is developed of the considered burning-propellant classes. Mathematical modeling of burning nanoaluminum in composite solid rocket propellants is carried out. The influence of nanoaluminum on ignition temperature of the metal fuel and burning-rate law is shown. The results of this study allow carrying out the analysis and selection of good-quality propellants using nanoaluminum

This paper reports results obtained from an experimental study of the combustion mechanism of aluminized propellants based on an energetic binder. The techniques used in this investigation include: * Quench-collection of condensed combustion products in the gas phase zone above the burning surface and study of the products including mass, chemical, and structural analyses and particle size measurements * Measurement of propellant burning rate * Study of combustion residues collected using special plates On the basis of the experimental data obtained, a general physical picture of combustion of aluminized propellants based on energetic binders was developed. The results of this study allowed us to refine the general understanding of metallized propellant combustion, to identify problems related to the use of such propellants, and to suggest methods for the optimization of high-energy solid rocket propellants.* Quench-collection of condensed combustion products in the gas phase zone above the burning surface and direct study of the products, including mass, chemical, and structural analyses and particle size measurements * Measurement of the propellant burning rate * Study of combustion residues obtained using special collecting platesThe techniques and equipment used are described in [1] and [2]. For a quantitative description of the process the following parameters are used: * f m (D) -mass-median probability density of size of agglomerates * f m (d) -mass-median probability density of size of smoke oxide particles * Z m -fraction of unburned metal in agglomerates relative to initial metal content in propellant * Z ox m -fraction of initial metal content in propellant used to form oxide in agglomerates * Z a m -fraction of initial metal content in propellant used to form agglomerates * h -mass fraction of oxide in agglomerate * D 43 -mass-median diameter of agglomerates, mm

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An experimental study of aluminized solid rocket propellant combustion was conducted in order to determine the influence of various propellant formulation factors on metal agglomeration. The results allowed us to determine the dependencies of the agglomeration process characteristics on the physical and mechanical properties of the propellant binder, the particle size of the metal fuel, the type of film covering the original metal particles, and the type of oxidizer in the propellant. These results, combined with earlier data, were used to develop a physical picture of the agglomeration process. which may serve as the basis for conducting analysis of the influence of various propellant formulation factors on agglomeration.

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