FORMATION OF PRIMARY FLUID INCLUSIONS UNDER INFLUENCE OF THE HYDRODYNAMIC ENVIRONMENT

When crystals grow under convection conditions, the hydrodynamic envir onment can promote the formation of inclusions in the rear side of the crystals, downstream in relation to the fluid flow. An experimental s tudy of this mechanism of fluid trapping is presented, and the conditi ons under which hydrodynamics influences growth behaviour are discusse d. Crystal growth experiments have been carried out with aqueous solut ions in a convection system under controlled conditions of temperature , solution velocity V-s and supersaturation sigma infinity. Growth rat es of {011} faces of ADP crystals have been measured for different ori entations, in relation to the solution flow and for different values o f sigma infinity and V-s. It is concluded that hydrodynamics can produ ce an anisotropy in the contribution of material to crystallographical ly equivalent faces. At low solution velocities and moderate supersatu ration, the growth rate depends on the flow ''impact'' angle. In contr ast, at high solution velocities (V-s > 3 cm.s(-1) for sigma infinity = 2.45 %) the hydrodynamic configuration has no influence on the growt h kinetics. Hydrodynamics can also play an important role in the forma tion of fluid inclusions during crystal growth. However, this effect o nly occurs at low solution velocities, when the growth kinetics is con trolled by the hydrodynamic configuration. Crystals grown at low solut ion velocities (Vs < 3 cm.s(-1) for sigma infinity = 2.45 %) show larg e fluid inclusions in the rear zone. At high solution velocities the m ass-transfer is high enough to avoid the hydrodynamic control of growt h, and no inclusions are generated by this mechanism.