Mechanochemical activation of aluminum: 3. Kinetics of interaction between aluminum and water

Two regimes of oxidation by water are revealed for nanocrystalline aluminum prepared by the mechanical activation of its mixture with graphite and distributed in the matrix of amorphous carbon. At the temperatures 50 degrees C < T < 90 degrees C, nanosized aluminum particles interact with water under quasi-isothermal conditions. The main products are hydrogen and pseudoboehmite AlOOH; a low content of bayerite Al(OH)(3) is also formed. After the induction period, the kinetics of interaction can be satisfactorily described by the law of a diminishing sphere. The effective activation energy of the reaction is equal to 61 +/- 10 kJ/mol and is identical for the samples of submicron aluminum prepared by different procedures. At temperatures above 90-95 degrees C, the oxidation of mechanically activated aluminum by water is transformed into a thermally self-accelerated explosion process. Under these conditions, the oxidation of aluminum to alpha-Al2O3 is accompanied by an exothermal reaction between the metal and the carbon matrix during which aluminum carbide Al4C3 is formed.