Mechanism of Formation of the Condensed Phase in Aluminum Combustion in Carbon Dioxide

Abstract

Aluminum powders are widely used in mixed energy-rich materials (rocket propellants, explosives, pyrotechnics) for improving their energy characteristics. Carbon dioxide is a typical component of the oxidizing gas medium in the combustion of aluminum particles in energy-rich materials. The efficiency of using aluminum in energy-rich materials is often decreased because of an increase in the mass fraction of the condensed phase in the combustion products. For example, in metallized rocket propellants, this leads to so-called two-phase losses in the specific impulse of the propellant. Knowledge of the law and mechanism of formation of the condensed phase in the combustion of the Al-CO 2 system favors the solution of the problem of two-phase losses.Of special interest has recently been the use of this process for producing promising composites, including nanocomposites. The directed gas-phase synthesis of such materials and the determination of the optimal synthesis conditions require a detailed investigation of the mechanism of aluminum combustion in a medium containing carbon oxides. In addition, the results of such investigations can be applied to obtain useful products by utilizing metallized energy-rich materials.Although the formation of the condensed phase is of great importance to many applications of aluminum combustion (from the production of ceramic materials to the formation of cosmic dust), there is no universally accepted theory of this process [1,2]. This is primarily because of difficulties in experimental investigation, which are caused by high temperature and concentration gradients around a burning particle and complicate the monitoring of chemical reactions in the combustion of the particle. Additional difficulties are related to the free and forced convection, because of which the temperature and concentration fields around the burning particle are much more complex. To overcome these difficulties, in this work, specially designed experimental setups and procedures [3,4] were used that enabled us to determine the thermal structure of reaction zones and also the morphology and composition of the combustion products in various periods of ignition, combustion, and extinction of the particle. This work continues and develops investigations of the combustion of aluminum particles in simple oxidizing gaseous media ( O 2 , CO 2 , H 2 O, and their mixtures with inert gases) begun in [3] with study of the combustion of single aluminum particles in oxygen mixtures with inert gases. EXPERIMENTALThe combustion of a cloud of free aluminum particles was analyzed using an original setup, which allowed us to create particles directly in a combustion chamber by breaking aluminum foil by an electric discharge [4] (Fig. 1). The main part of this setup was extended combustion chamber 1 , capable of holding the gas pressure in the range of vacuum to 150 atm. Inside the chamber was special assembly 2 -5 , generating a short jet (small cloud) of aluminum drops of different diameters heated to the ignition temperature....

Nano Aluminum Powders Oxidation in CO₂ and O₂ Environments

“…So the sample weight decreased. The previous energy dispersion X-ray spectrometry also showed the amount of C increased between 600 and 1000 ℃ and then decreased to the minimum at 1200 ℃ [13].…”

“…The earlier papers has also reported that other forms of aluminum oxides may formed [9,13], such as Al 4 C 3 , Al 2 OC and Al 4 O 4 C. But this can not explain the weigh loss, because if any of these aluminum oxides decompose into Al, then it can continue to react with CO 2 to formed Al 2 O 3 , then the weight would increase. So the most possibly reason is Al can react with CO to produce C. In low pressure, C can react with CO 2 to produce CO at 800-1200 ℃.…”

Spectral investigations of the combustion of pseudo-nanoaluminized micro-cyclic-[CH2N(NO2)]3in a shock wave

“…None of the aluminium oxycarbides were detected in the experiment of combustion of aluminium in CO 2 performed by Rossi [35]. Similarly, Assovskii et al [36] have also reported Al 3 C 4 emerging in the temperature range 1800-2300 K, and that any carbon phase is unexpectedly absent when combustion of millimetre-sized aluminium was conducted in a CO 2 atmosphere under 20 MPa. In hot ambient gases, aluminium oxycarbide can be melted, which promotes direct surface reactions.…”

“…Sarou-Kanian et al [37] observed Al 3 C 4 in residua, and that aluminium oxycarbide and carbon are intermediate products as surface reactions in the initial reactions stage. The result of the quantitative analysis by Assovskii et al [36] showed the concentration of α-Al 2 O 3 is less than 30%, and the γ -Al 2 O 3 is in larger proportion in the condensed sample. The discrepancy proves that combustion of aluminium is intensive in our experiments.…”