Particle aluminum

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

Lead alloys containing 0.09—0.15 wt % calcium and 0.015—0.03 wt % aluminum are used for the negative battery grids of virtually all lead—acid batteries in the United States and are also used in Japan, Canada, and Europe. If the molten alloy is held at too low a temperature, the aluminum precipitates from solution, rises to the surface of the molten alloy as finely divided aluminum particles, and enters the dross layer atop the melt. 

If the temperature of a molten lead—calcium (tin)—aluminum ahoy is not kept sufficiently high, finely divided aluminum particles may precipitate and float to the top of the melt. These may become mixed with oxides of lead in the dross. The finely divided aluminum particles can react violently with the oxides in the dross if ignited. Ignition can occur if attempts are made to melt or bum the dross away from areas of buildup with a torch. The oxides in the dross can supply oxygen for the combustion of aluminum once ignited. 

The strong influence of morphology and mixing is well illustrated with the composite particle investigation. These particles were composed of a nickel shell coated on spherical aluminum particles by hydrogen reduction in aqueous metal salt solution. The overall ratio of material in a particle was about 80 wt% Ni and 20 wt% aluminum. With these particles, the ratio of reactants was approximately the same as in the mixed powders, but the morphology of the reactants is radically different. 

Most theoretical studies have concentrated on the analysis of the combustion zone of nonaluminized propellant systems. In actual practice, propellants containing aluminum are used in many applications. One study in which aluminum has been included has recently been published by Dunlop and Crowe (D2). In this study, the combustion zone is idealized to consist of four regions, as shown in Fig. 21. The results of these simplified one-dimensional analyses suggest that the combustion of aluminum particles in the gas... 

Similar phenomena have also been observed in the combustion of composite propellants. Eisel (El) has observed that there is a unique frequency-pressure relation in a low-pressure region where nonacoustic instability results. He speculates that this preferred frequency is related to the periodic appearance and depletion of the aluminum particles on the propellant surface. High-speed pictures confirm the periodic sluffing of aluminum, but its relation to the preferred frequency is still not clear. 

Liao P.F., Stem M.B., Surface-enhanced Raman-scattering on gold and aluminum particle arrays, Opt. Lett. 1982 7 483-185. 

See also Alumina hydroxides classification, 2 422 Aluminum particle size, 10 22-23 Aluminum perchlorate, 18 278 Aluminum phosphide, 2 284 19 58 Aluminum-polyphenylenevinylene-ITO, in photovoltaic devices, 22 221 Aluminum production, 9 639-640 Aluminum recycling, 2 305 21 371-372 economic aspects of, 21 402 remelting, 2 333-334 Aluminum reduction, of ferrovanadium, 25 518... 

Cho (C2) has calculated charging by contact potentials essentially on the basis described above, assuming a contact potential of 1 V for the case of an aluminum particle in contact with a steel plate. Arabadzhi (Al) reports a contact potential between ice and water of 0.15 V, although the abstract for another article by Arabadzhi (A2) reports this value as 1.5 V. 

Fig. 4.43. Visualization of ion motion in the ion trap, (a) Mechanical analogue of the QIT. (b) Photograph of ion trajectories of charged aluminum particles in a quadrupole ion trap.

Activation by Thermal Decomposition of Metallic Oxides. The surface of alumina, AI2O3, may be activated by employing laser or ultraviolet irradiation to decompose AI2O3 (68). Decomposition of AI2O3 results in the generation of aluminum particles that are catalytic for electroless deposition of Cu (the first reaction probably is displacement deposition). 

Combustion of aluminum particle as fuel, and oxygen, air, or steam as oxidant provides an attractive propulsion strategy. In addition to hydrocarbon fuel combustion, research is focussed on determining the particle size and distribution and other relevant parameters for effectively combusting aluminum/oxygen and aluminum/steam in a laboratory-scale atmospheric dump combustor by John Foote at Engineering Research and Consulting, Inc. (Chapter 8). A Monte-Carlo numerical scheme was utilized to estimate the radiant heat loss rates from the combustion products, based on the measured radiation intensities and combustion temperatures. These results provide some of the basic information needed for realistic aluminum combustor development for underwater propulsion. 

Olsen, S.E., and M. W. Beckstead. 1995. Burn time measurements of single aluminum particle in stream and carbon dioxide mixtures. AIAA Paper No. 95-2715. 

Results of an experimental program in which aluminum particles were burned with steam and mixtures of oxygen and argon in small-scale atmospheric dump combustor are presented. Measurements of combustion temperature, radiation intensity in the wavelength interval from 400 to 800 nm, and combustion products particle size distribution and composition were made. A combustion temperature of about 2900 K was measured for combustion of aluminum particles with a mixture of 20%(wt.) O2 and 80%(wt.) Ar, while a combustion temperature of about 2500 K was measured for combustion of aluminum particles with steam. Combustion efficiency for aluminum particles with a mean size of 17 yum burned in steam with O/F) / 0/F)st 1-10 and with residence time after ignition estimated at 22 ms was about 95%. A Monte Carlo numerical method was used to estimate the radiant heat loss rates from the combustion products, based on the measured radiation intensities and combustion temperatures. A peak heat loss rate of 9.5 W/cm was calculated for the 02/Ar oxidizer case, while a peak heat loss rate of 4.8 W/cm was calculated for the H2O oxidizer case. 

The size distribution for the large diameter fraction of the H2O oxidizer combustion products is shown in Fig. 8.8, along with the size distribution of the aluminum powder fuel. The mean particle size of the unburned fuel fraction in the combustion products is about 10.7 pm, while the mean size of the fuel particles is 17.4 pm. Most sources report that burning aluminum particles follow a rate law of the form d = do" — Pt, where / is a constant and the exponent n is between 1.5 and 2.0. In that case, the size distribution of the unburned fraction of the combustion products would be expected to be larger than that of the fuel. A size distribution of unburned aluminum smaller than that of the parent fuel is more consistent with particles that never ignited, since the larger particles would probably be undersampled. On the other hand, it seems unlikely that any particle could... 

In this study, measurements of the combustion temperature, radiation intensity, combustion products particle size distribution, and combustion efficiency have been made for combustion of aluminum particles with steam in a small-scale atmospheric dump combustor. This data will be useful for designers of combustion chambers for burning of aluminum powder with steam. 

Friedman, R., and A. Macek. 1962. Ignition and combustion of aluminum particles in hot ambient gases. Combustion Flame. 6. 

Keshavan, R., and T. A. Brzustowski. 1972. Ignition of aluminum particle streams. Combustion Science Technology 6 203-9. 

Wilson, R. P., Jr. 1970. Combustion of aluminum particles in 02/Ar. Doctoral Dissertation. San Diego University of California. 

Marion, M., et al. 1995. Studies on the ignition and burning of aluminum particles. Paper No. 95S-060, Joint Technical Meeting of Central and Western States Sections and Mexican National Section of The Combustion Institute and American Flame Research Committee, San Antonio, TX. April 23-26. 

Bucher, P., et al. 1996. Observations on aluminum particles burning in various oxidizers. 33rd JANNAF Combustion Subcommittee Meeting. 

When aluminized AP composite propellant burns, a high mole fraction of aluminum oxide is produced as a combustion product, which generates visible smoke. If smoke has to be avoided, e. g. for miUtary purposes or a fireworks display, aluminum particles cannot be added as a component of an AP composite propellant In addition, a large amount of white smoke is produced even when non-aluminized AP composite propellants bum. This is because the combustion product HCl acts as a nucleus for moisture in the atmosphere and relatively large-sized water drops are formed as a fog or mist This physical process only occurs when the relative humidity in the atmosphere is above about 60%. If, however, the atmospheric temperature is below 260 K, white smoke is again formed because of the condensation of water vapor with HCl produced as combustion products. If the HCl smoke generated by AP combustion cannot be tolerated, the propellant should be replaced with a double-base propellant or the AP particles should be replaced with another... 

Azide polymers such as GAP and BAMO are also used to formulate AP composite propellants in order to give improved specific impulses compared with those of the above-mentioned AP-HTPB propellants. Since azide polymers are energetic materials that burn by themselves, the use of azide polymers as binders of AP particles, with or without aluminum particles, increases the specific impulse compared to those of AP-HTPB propellants. As shown in Fig. 4.15, the maximum of 260 s is obtained at (AP) = 0.80 and is approximately 12 % higher than that of an AP-HTPB propellant because the maximum loading density of AP particles is obtained at about (AP) = 0.86 in the formulation of AP composite propellants. Since the molecular mass of the combustion products. Mg, remains relatively unchanged in the region above (AP) = 0.8, decreases rapidly as (AP) increases. 

When HNF or ADN particles are mixed with a GAP copolymer containing aluminum particles, HNF-GAP and ADN-GAP composite propellants are formed, respectively. A higher theoretical specific impulse is obtained as compared to those of aluminized AP-HTPB composite propellants.However, the ballistic properties of ADN, HNIW, and HNF composite propellants, such as pressure exponent, temperature sensitivity, combustion instability, and mechanical properties, still need to be improved if they are to be used as rocket propellants. 

The AI-H2O reaction increases the temperature and the number of moles of gas in the bubble by the production of H2 molecules. The pressure in the bubble is thereby increased. As a result, the bubble energy and shock wave energy are increased. It must be understood that the oxidation of aluminum powder is not like that of gaseous reactants. Reaction occurs at the surface of each aluminum particle and leads to the formahon of an aluminum oxide layer that coats the particle. The oxidized layer prevents the oxidation of the interior particle. The combustion efficiency of aluminum parhcles increases with decreasing particle size.l =l The shock wave energy and bubble energy are increased by the use of nano-sized aluminum powders. 

Fig. 11.17 shows burning rate augmentation, Eb, as a function of the adiabatic flame temperatures of B-AP and Al-AP pyrolants. The incorporahon of aluminum particles into a base matrix composed of AP-CTPB pyrolant increases Ej. However, the effect of the addihon becomes saturated for adiabahc flame temperatures higher than about 2500 K. On the other hand, the incorporahon of boron particles into the same base matrix increases Eg more effectively, even though the adiabahc... 

When fine aluminum particles are incorporated into AP pyrolants, aluminum oxide (AI2O3) particles are formed when they bum. Dispersal of these aluminum oxide particles in the atmosphere generates white smoke even when the atmosphere is dry. The mass fraction of aluminum particles added is approximately 0.2 for the complete combustion of AP pyrolants. Though an excess of aluminum... 

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