Reactions of Nonaluminum with Ice: Theoretical and Experimental Study

Abstract

The paper considers the oxidation reactions of nanodispersed aluminum powder with water at room temperature in a reactor without stirring, heating, or other activation methods using a homogeneous mixture of powder with ice prepared in advance. The process is considered theoretically resorting to previously obtained data on the macrokinetics of reactions of dispersed aluminum with water, taking into account the melting of the ice mixture and warming-up to room temperature. An experiment confirming the obtained theoretical results is conducted. The solution to the problem of searching for controlled hydrogen generation modes in the reaction of nanoaluminum with water is relevant in connection with the development of hydrogen sources for fuel cells. The problem of optimizing the hydrogen generation modes in the aluminum reaction with water arises because the dynamics of the reaction of highly dispersed aluminum with water is accompanied by a sharp increase and sharp drop of the hydrogen pressure and begins even at room temperature, which complicates the preparation of the mixture under these conditions. Meanwhile, technologies using hydrogen as fuel require a uniform supply of the gas to the fuel cell. The paper describes the preparation of a homogeneous mixture of nanoaluminum powder with ice at a temperature below 273 K, when the reaction does not occur. Then the mixture is placed in a reactor at room temperature (290–298 K); the reaction begins gradually as the mixture is heated in a gradual mode without adverse abrupt self-heating effects. The temperature of the mixture, the degree of aluminum conversion, and the rate of hydrogen formation are measured as functions of time. The calculations were performed using the kinetic parameters for the Alex brand powder; it is considered that the mass of ice (water) significantly exceeds the stoichiometric one. Solution of the problem in the dimensionless form and the calculations resulted in interpolation equations for the time of complete aluminum conversion depending on the process control parameters. It is shown theoretically and experimentally that hydrogen is completely released in these process in a controlled mode within several hours, without thermal explosion caused by the exothermic reaction. The found patterns of the reaction can be further used to calculate the engineeting parameters of hydrogen generation systems using a pre-prepared mixture of nanoaluminum with ice.