Aluminum Water Reaction Research Articles

Calorimetric investigation of the aluminum–water reaction

The aluminum–water split reaction is characterized experimentally using microcalorimetry. The rates of heat release during the reaction at two fixed temperatures, 303 and 313 K were measured for spherical aluminum powders placed in liquid water. Fully and partially reacted powders were characterized using electron microscopy and x-ray diffraction. Experiments were performed with three commercial powders with nominal sizes of 3–4.5, 10–14, and 17–30 μm. The only crystalline reaction product detected was bayerite. Initially, particles grow bayerite layers which later sinter together forming continuous aluminum–bayerite composites. The observed reaction could be broken down into several parts, including an induction time, two stages of relatively rapid reaction, and reaction termination. The significance of the first of the rapid reaction stages increased for experiments at the higher temperature. The finer powders exhibited faster and more complete reaction. The reproducibility of the heat flow patterns for experiments under identical conditions was surprisingly poor, especially in terms of the induction time. Experimental data were processed using a simplified kinetic model reported in the literature to assess the diffusion coefficient describing the reaction rate-limiting process: transport of hydroxo complexes of aluminum through a growing porous layer of bayerite. The calculated diffusion coefficient was in the range expected for the experimental temperatures; however, its changes as a function of the powder particle size and as a function of the reaction time indicate that the current model is inadequate for describing the present experiments.

Activation Energy for the Corrosion of Aluminum Powders in Water

The self passivation of aluminum in water generally prevents the generation of hydrogen from an aluminum-water reaction in conditions preferred for portable systems. However the potential for corroding aluminum to produce quantities of hydrogen at a lower total system mass compared to compressed storage tanks is spurring research into accelerating aluminum corrosion by ball milling and mixing with other powders. This allows commercially useful amounts of hydrogen to be generated at moderate temperatures and neutral pH regions. To further study the mechanism behind the increased rate the activation energies were calculated for hydrogen evolution from pure aluminum, aluminum that had been ball milled, and aluminum mixed with alumina powder. Overall, aluminum that is in contact with higher amounts of aluminum hydroxide, either grown or added, showed a drop in activation energy from approximately 80 kJ/mole down to 24 kJ/mole.

Feasibility Study and Demonstration of an Aluminum and Ice Solid Propellant

Aluminum-water reactions have been proposed and studied for several decades for underwater propulsion systems and applications requiring hydrogen generation. Aluminum and water have also been proposed as a frozen propellant, and there have been proposals for other refrigerated propellants that could be mixed, frozen in situ, and used as solid propellants. However, little work has been done to determine the feasibility of these concepts. With the recent availability of nanoscale aluminum, a simple binary formulation with water is now feasible. Nanosized aluminum has a lower ignition temperature than micron-sized aluminum particles, partly due to its high surface area, and burning times are much faster than micron aluminum. Frozen nanoscale aluminum and water mixtures are stable, as well as insensitive to electrostatic discharge, impact, and shock. Here we report a study of the feasibility of an nAl-ice propellant in small-scale rocket experiments. The focus here is not to develop an optimized propellant; however improved formulations are possible. Several static motor experiments have been conducted, including using a flight-weight casing. The flight weight casing was used in the first sounding rocket test of an aluminum-ice propellant, establishing a proof of concept for simple propellant mixtures making use of nanoscale particles.

Advancement of Aluminum-Water Reaction and Application

The technology of applying aluminum-water reaction to underwater vehicle is analyzed combining with the energy identity of metal fuel and different aluminum powders. The present research situation and development foreground are studied.

Passivation Rates for Small Particulate Aluminum in Contact with Oxide and Nitride Powders

The self passivation of aluminum in water generally prevents the generation of hydrogen from an aluminum-water reaction in conditions preferred for portable systems. However the corrosion rate of aluminum powders is seen to greatly increase when in contact with alumina powder. This allows commercially useful amounts of hydrogen to be generated at moderate temperatures and neutral pH regions. Scratch tests were run on aluminum disks covered with oxide and nitride powders to look at repassivation rates after the surface film was disturbed and a decrease in the repassivation time observed. Small pellets of aluminum powder mixed with oxide or nitride powders were also studied with scratch events showing far lower current perturbation than seen for pure aluminum.

Molecular dynamic simulation of aluminum–water reactions using the ReaxFF reactive force field

In this study we employed the ReaxFF reactive force field to examine the dynamics associated with the dissociation of adsorbed water molecules on an aluminum nanocluster surface. We have investigated several different concentrations of water on an Al 100 cluster to elucidate the dynamics of the dissociation phenomena. Our results indicate that the dissociation of an isolated water molecule on the surface requires significant activation energy, and that an assisted dissociation by a neighboring, non-adsorbed, water molecule is more energetically favorable. The dynamics of this reaction pathway are discussed and compared to recent quantum studies along with a further investigation of the role inert gases and oxide layers have on these processes. Our results shed light on this atomic scale behavior and increase the potential for reactive metal/water systems to be used as lightweight, portable, and on-demand energy sources via fast hydrogen gas production.

Operating maps of a combined hydrogen production and power generation system based on aluminum combustion with water

The performance of a novel hydrogen production and energy conversion system based on the aluminum–water reaction is addressed by means of a lumped and distributed parameter numerical approach. The interest on this type of technology arises because of the possibility of obtaining at the same time different secondary energy sources, such as hydrogen and heat and mechanical work, with very low pollutant and greenhouse gas emissions. In this paper the numerical models of the main components adopted in the system are developed, including the combustion chamber, the steam/hydrogen turbine and the heat exchangers. The behavior of the whole system is investigated for different configurations and energy conversion cycles, i.e. electric energy production only and combined heat and power production, in order to determine the operating maps in terms of efficiency, power output, pressure and temperature in the main sections, mass flow rates and the hydrogen yield. The numerical analysis of the thermo-dynamic behavior of the power unit is aimed at assessing the guidelines that will lead to the construction of a first prototype of this system. Finally, the use of a cogeneration system based on the aluminum combustion with water system for on-site small scale hydrogen production for feeding a hydrogen refueling station is explored. The proposed system is compared with other technologies as well as the case of large scale hydrogen production and delivery.

The Role of Alumina in Aluminum Corrosion and Passivation

The self passivation of aluminum in water generally prevents the generation of hydrogen from an aluminum-water reaction in conditions preferred for portable systems. However the corrosion rate of aluminum powders and thin foils is seen to greatly increase when in contact with alumina powder. This allows commercially useful amounts of hydrogen to be generated at moderate temperatures and neutral pH regions. Data is presented to support the claim that proton availability from the alumina surface is responsible for the increased hydrogen evolution rates, and hydrogen capture tests show passivation no longer stops the corrosion reaction.

Application of activated aluminum powder for generation of hydrogen from water

This work presents a parametric investigation of aluminum–water reaction to generate hydrogen, using a novel activated aluminum powder. An original thermo-chemical process involving a small fraction of a lithium-based activator enables a spontaneous reaction of the activated aluminum particles with water, which otherwise would not react due to the existence of an oxide or hydroxide surface layer. Experiments have shown that a fast, self sustained reaction of activated aluminum with water takes place even at room temperature and, for appropriate operating conditions, results in a practically 100% yield of hydrogen generation. The reaction rate may be controlled by the aluminum particle size, water temperature, metal activation conditions and metal/water mass ratio. The method demonstrates safe and compact hydrogen storage (11 wt% compared to the aluminum). Among its potential applications may be fuel cells, as well as automotive and marine propulsion.

Enhancement of hydrogen generation rate in reaction of aluminum with water

The aim of this investigation is to enhance hydrogen generation rate in aluminum–water reaction by improving the activity of aluminum particles and using the heat released during the reaction. This was accomplished by developing fresh surfaces by milling aluminum particles together with salt. Salt particles not only serve as nano-millers, but also surround activated particles and prevent re-oxidation of bare surfaces in the air. Therefore, the activated powder can be easily stored for a long time. Immersing the powder in warm water, the salt covers are washed away and hydrogen begins to release at a high rate until efficiency of 100% is achieved. The rate of reaction depends crucially on initial temperature of water. Hence, the mass of water was reduced to employ released energy to increase water temperature and, consequently, to increase hydrogen production rate. The optimum value of salt-to-aluminum mole ratio for achieving high activation, air-storage capability and 100% efficiency was obtained to be 2. When immersed in water, at initial temperatures of 55 and 70 °C, the powder lead to average hydrogen generation rate of ∼101 and ∼210 ml/min per 1 g of Al, respectively. To increase the rate of corrosion, three different alloys/composites of aluminum were prepared by mechanical alloying and activated with optimum salt-to-aluminum mole ratio. The alloys/composites formed galvanic cells after being immersed in water. In the case of aluminum–bismuth alloy, the average hydrogen generation rate increased to ∼287 and ∼713 ml/min per 1 g of Al, respectively.

Spontaneous Hydrogen Generation from Organic-Capped Al Nanoparticles and Water

The development of technologies that would lead toward the adoption of a hydrogen economy requires readily available, safe, and environmentally friendly access to hydrogen. This can be achieved using the aluminum-water reaction; however, the protective nature and stability of aluminum oxide is a clear detriment to its application. Here, we demonstrate the spontaneous generation of hydrogen gas from ordinary room-temperature tap water when combined with aluminum-oleic acid core-shell nanoparticles obtained via sonochemistry. The reaction is found to be near-complete (>95% yield hydrogen) with a tunable rate from 6.4x10(-4) to 0.01 g of H2/s/g of Al and to yield an environmentally benign byproduct. The potential of these nanoparticles as a source of hydrogen gas for power generation is demonstrated using a simple fuel cell with an applied load.

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In this work, the aluminum–water reaction induced by Fe–B, Co–B and Ni–B particles was studied. The catalysts were mixtures of the metal boride and metallic particles. The chainlike Fe–B catalyst forms a network structure under the influence of an external magnetic field and has a large specific surface area. Aggregated particles of Co–B and Ni–B catalyst have small specific surface area. Catalytic activity in the initial corrosion of aluminum increases with increasing Fe–B content because of the large specific surface area and the formation of a micro galvanic cell. However, the amount of hydrogen generated slowly decreases with increasing amount of Co–B and Ni–B. The activity of Fe–B, Co–B and Ni–B in the initial Al/H2O reaction decreases in the order Fe–B > Ni–B > Co–B. The calculated apparent activation energies in the presence of Fe–B, Co–B and Ni catalysts are 38.2, 39 and 29.6 kJ mol−1, respectively. Aluminum is rapidly and completely corroded in a weakly alkaline solution (pH < 10) after consecutive additions of Al batches because of high concentrations of OH− in the local domain and an increase in the amount of Al(OH)3 precipitate.

Tendência à hidratação do pó de alumínio em concretos refratários contendo elevado teor de carbono

Os benefícios proporcionados pela adição de carbono em concretos refratários têm ampliado a utilização desses materiais em aplicações siderúrgicas. Contudo, um problema inerente à utilização de carbono em refratários é a sua susceptibilidade à oxidação a temperaturas superiores a 600 °C. Uma das alternativas empregada na tentativa de controlar a oxidação do carbono é o uso de antioxidantes. Dentre eles, o pó de alumínio tem mostrado bons resultados em tijolos refratários contendo carbono. Porém, sua aplicação em concretos refratários é limitada pela forte tendência que o pó de alumínio apresenta em se hidratar. Algumas técnicas de recobrimento baseadas no processo Sol-Gel têm sido empregadas como forma de impedir a reação de hidratação do pó de alumínio quando em água. Entretanto, a eficiência destes recobrimentos ainda não foi avaliada em concretos refratários. O presente trabalho se propõe a avaliar a eficiência de recobrimentos à base de SiO2 ou TiO2 em inibir a reação de hidratação do pó de alumínio em condições reais de aplicação. Estes recobrimentos foram obtidos a partir de alcóxidos metálicos e um polímero reativo fazendo uso do método Sol-Gel.

Radiant emission from the aluminum-water reaction

The exploding wire technique was used in connection with spectropic measurements to investigate the nature of the radiation emitted from the Al-H 2O combustion process. The absolute spectral intensity emitted from the Al-H 2O reaction throughout the 300–800 nm spectral region has been determined experimentally with a resolution of 4nm at various pressures. Higher resolution (0.57 nm resolution) spectroscopic measurements were also made in several regions of interest in the 300–800 nm spectral region. The spectra measured in this study were dominated by line and band emission, but a low-level continuum was also present. A simplified analysis showed that the observed continuum could be plausibly attributed to emission from small (∼0.01 μm) Al 2O 3(1) particles.

Underwater Power From Aluminum

A thermochemical power system having the highest theoretical performance (hp-hr/cu ft propellants) and particularly suited for underwater applications (power, heat, and propulsion) is described. In this system aluminum is reacted exothermally with sea-water to produce gaseous exhaust products, hydrogen-and steam. The exhaust products are expanded through a prime mover to produce shaft horsepower, or a combustion process can be added before the prime mover to convert the hydrogen to steam for applications that require condensable exhaust products. Open cycle (shallow depth operation) and closed cycle (deep depth operation) systems are described. The technique for reacting aluminum and water at low temperatures is discussed and aluminum-water reaction test data are presented. Design concepts of practical systems are shown, and typical power systems are compared relative to total energy, volume, and weight.

A study of aluminum-water reactions by laser heating

An investigation has been carried out of reactions between water and small aluminum particles that were heated by a focused ruby laser beam. This rapid heating simulated rapid contacting with water of heated, dispersed aluminum which is of significance in hypothetical excursions of nuclear reactors. Complete reaction was not found at 0.03 atm water pressure, but was observed at 1 and 10 atm water pressure when a critical laser output energy was reached. It is believed that particle ignition and complete reaction can occur only when the energy imput is sufficient for the particle temperature to reach the melting point of Al 2O 3. Above this temperature reaction is controlled by the rate of diffusion of water through a hydrogen film surrounding the particle. In contrast to the 1 and 10 atm cases, the boiling point of aluminum at a pressure of 0.03 atm is lower than the melting point of the oxide; hence oxide melting and particle ignition do not occur. Diffusion and heat transfer calculations were carried out and found to support this mechanism.