The kinetics of amorphization of silicon as well as the reactivity of mechanically disordered silicon with oxygen and hydrogen were measured under mechanical treatment of silicon in the atmosphere of argon, hydrogen, or oxygen. The mechanical treatment of silicon in an inert atmosphere is accompanied by the formation of two fractions (coarse and fine) of nanoparticles along with the formation of the amorphous phase. The kinetics of grain sizes changing for both fractions wore analyzed. One may conclude that the decrease of grain size below the critical value of about 4 nm is accompanied by transition of the material into the amorphous phase. The amount of amorphous phase for the maximum dose, (D=500 kJ/g) exceeds 40%. The amorphous phase crystallization was accompanied by the exothermic thermal effects at the temperatures of 560-700 degreesC. During the mechanical treatment in the atmosphere of active gases, an irreversible absorption of oxygen and hydrogen is observed. The value of chemisorption of hydrogen is comparable to the number of surface atoms measured by the BET method. It does not prevent the formation of an amorphous phase. Chemisorption of oxygen depends on the gas pressure. At high gas pressure, the number of sorbed oxygen atoms reaches similar to 50% of the total number of silicon atoms and is comparable with the number of atoms in the amorphous phase. One can assume that mostly oxygen forming oxide with the atoms in the amorphous phase.