The influence of the structure of a nanocrystalline solid (sandstone) on the dynamics of microcrack accumulation on friction

Abstract

On friction of a heterogeneous material: sandstone, flashes of triboluminescence are observed. Triboluminescence arises on the relaxation of excitation of free radicals ≡Si–O^–. These radicals form on disruptions of Si–O–Si bonds and are located at microcrack edges. Microcracks form at the boundaries of feldspar and quartz microcrystals. Their sizes range from ~0.4 to ~7 μm. The microcrack formation on friction leads to the spalling of feldspar and quartz microcrystals from a sample.