SUPPRESSING HYDROGEN EVOLUTION BY AQUEOUS SILICON POWDER DISPERSIONS THROUGH THE INTRODUCTION OF AN ADDITIONAL CATHODIC REACTION

Abstract

Silicon powder reacts with water, liberating hydrogen gas, which poses an explosion risk. Adding metal ions with a high reduction potential suppresses hydrogen generation. Copper (II) ions are particularly effective in this regard. In their presence the reaction features three distinct stages. In the initial phase copper is deposited on the silicon surface concomitant with a rapid drop in the solution pH. Most of the hydrogen evolves during a second active stage with the pH showing a slight upward drift. Finally, in the third stage, the silicon surface passivates and hydrogen evolution comes to a halt. A comparison of this method and two other methods previously reported, i.e., controlled air oxidation of the silicon powder before slurrying and adding organic corrosion inhibitors, shows that silane surface modification of silicon is the most effective method in terms of decreasing the greatest amount of hydrogen released and increasing silicon reactivity in a typical pyrotechnic composition.

Keywords:

• Copper
• Hydrogen
• Pyrotechnics
• Silicon

Acknowledgments

Financial support from the THRIP programme of the Department of Trade and Industry and the National Research Foundation as well as AEL Mining Services is gratefully acknowledged.

Notes

^a Amount of Cu deposition on Si after immersion in 0.1 M Cu²⁺salt solutions.

I = ignites and propagates; X = difficult to ignite and propagates; D = difficult to ignite and does not propagate.