Аннотация:Wetting of grain boundaries in polycrystalline materials leads to
considerable changes in their physicochemical and mechanical properties.
Under a constant compressive load, internally wetted materials display
an enhanced deformability; creep rate increases sometimes by several
orders of magnitude. The dominant creep mechanism is known as
dissolution-precipitation or pressure solution; a stress-induced
excessive chemical potential provides a driving force for dissolution of
material within grain contacts, diffusion through the grain boundary
solution film and re-precipitation elsewhere. Sensitivity of pressure
solution rate to the chemical composition of the intergranular liquid
was reported earlier, but the underlying mechanisms were poorly
understood. In the present work, the creep experiments were carried out
on poly- or monocrystalline sodium chloride in the presence of NaCl
aqueous solution (pure or containing additives such as copper, magnesium
and lead chlorides, K4Fe(CN)(6) and urea). In all cases, pressure
solution has been shown to be the main deformation mechanism. Creep rate
decreases in the presence of additives which are known to affect the
dissolution and growth processes of sodium chloride or its concentration
in the brine. Rate-limiting stage (dissolution or diffusion) in various
environments has been identified.