Formation of primary fluid inclusions under influence of the hydrodynamic environment

When crystals grow under convection conditions, the hydrodynamic environment can promote the formation of inclusions in the rear side of the crystals, downstream in relation to the fluid flow. An experimental study of this mechanism of fluid trapping is presented, and the conditions under which hydrodynamics influences growth behaviour are discussed. Crystal growth experiments have been carried out with aqueous solutions in a convection system under controlled conditions of temperature, solution velocity V (sub s) and supersaturation sigma (sub infinity) . Growth rates of {011} faces of ADP crystals have been measured for different orientations, in relation to the solution flow and for different values of sigma (sub infinity) and V (sub s) . It is concluded that hydrodynamics can produce an anisotropy in the contribution of material to crystallographically equivalent faces. At low solution velocities and moderate supersaturation, the growth rate depends on the flow "impact" angle. In contrast, at high solution velocities (V (sub s) > 3 cm.s (super -1) for sigma (sub infinity) = 2.45 %) the hydrodynamic configuration has no influence on the growth kinetics. Hydrodynamics can also play an important role in the formation of fluid inclusions during crystal growth. However, this effect only occurs at low solution velocities, when the growth kinetics is controlled by the hydrodynamic configuration. Crystals grown at low solution velocities (V (sub s) < 3 cm.s (super -1) for sigma (sub infinity) = 2.45 %) show large fluid inclusions in the rear zone. At high solution velocities the mass-transfer is high enough to avoid the hydrodynamic control of growth, and no inclusions are generated by this mechanism.