Today transport is made of metals and consumes hydrocarbons as fuel. Environmentally friendly transport may represent the opposite: hydrocarbons will be used as a constructional material, and metals will be used as fuel.
Metals have a high energy density, and the combustion of the metal produces a solid oxide that can be returned back to the metal production process. Thus, a closedcycle is obtained. If metal is produceddue to cheap and clean electricity from nuclear power plants, hydroelectric power stations or renewable energy sources, then the entire cycle of using metal as fuel is “green” and competitive with traditional fuels. Metals can be delivered anywhere as simple as coal transportation.
One of the promising metallic fuels is aluminum. Its energy density is one of the highest and almost twice as high as that of gasoline.
It is well known that aluminum on its surface is coated with a thin and strong oxide film, which prevents its further oxidation. Therefore, one of the key problems in creating energy plants using aluminum as a fuel is the organization of the process of its oxidation (burning).
One of the possible ways to extract useful energy from aluminum is to oxidize it in water to produce hydrogen and energy. In this area, in recent years, a large number of studies have been carried out, which were mainly devoted to various methods of activating the aluminum oxidation. In order to oxidize aluminum in water, various chemical additives were used either to water or to aluminum, or aluminum was used in the form of a very fine powder. All this complicated and increased the cost of aluminum oxidation.
Scientists from Joint Institute for High Temperatures of the Russian Academy of Sciences discovered and described a method for burning aluminum of almost any size in water without any additional chemicals. To do this, a piece of aluminum must be placed in usual water, slightly heated and a little magicshould be applied.
“Imagine a closed vessel half-filled with water,” explains the head of the project Dr. Mikhail Vlaskin, “If you heat this vessel to a temperature of, for example, 250 °C, there will be liquid water in the bottom in the vessel, and gaseous water vapor will be on top. So if an aluminum particle, no matter what size, is placed in gaseous water vapor, then it will burn until it completely oxidizes, the oxide film in this case will not be a problem, but if the aluminum particle is placed in a volume with liquid water, then the aluminum oxidation reaction will quickly stop, in which case the reaction will penetrate deep into the metal by only a few microns.”
Russian scientists conducted a study with aluminum granules of about 1 cm in size at temperatures from 250 to 400 °C and found that under such conditions, aluminum burns in water at a rate of about 1 cm/hour deep into the metal. The results of this study have been published in the International Journal of Energy Research (Article DOI: 10.1002 / er.5561).
“Any water may be suitable for burning aluminum. It can be distilled water, tap water or water from a drinking bottle,” emphasizes Mikhail Vlaskin, “Temperatures of 250-300 °C are not so high temperatures. We encounter such temperatures, for example, in the kitchen oven.”
When aluminum is burned in water, hydrogen gas and solid aluminum oxideare formed, and thermal energy is released. The authors believe that their method can be already used to produce high-purity hydrogen and various functional materials based on aluminum oxide.
The main roadblock to energy production remains the transformation of the enthalpy of aluminum oxidation into usable energy. External combustion engines could use the enthalpy of aluminum oxidation. Depending on the power, for these purposes both turbine engines and piston engines, which are widely usedin energy, could be used.Hydrogen could be utilized also in internal combustion engine or fuel cells.
Authors believe that the results of their work made a significant contribution to understanding the combustion mechanism of metals and open up the road of creating CO2-free power plants using metals as fuel. Such power plants, according to the author’s opinion, can be used, for example, in transport instead of power plants fueled byhydrocarbon fuels.