In situ observation of subcritical crystalline particles and their behavior on growth of KDP crystals from aqueous solut
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Lu Taijing Institute of Physical and Chemical Research (RIKEN), Hirosawa 2-1, Wako-shi, Saitama, 351-01 Japan
Kazufumi Sakai and Tomoya Ogawa Department of Physics, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo, 171 Japan (Received 1 April 1992; accepted 16 June 1992)
By the 90° laser light-scattering technique, it was possible to visualize ultraflne crystalline particles and to investigate their behavior in relation to the growth of KDP crystals in an aqueous solution. It was found that the scattered microparticles move randomly and exist inhomogeneously in the solution. The density of microparticles increases with increasing supersaturation. Whereas in the bulk solution, the movements of the particles are slow, as soon as they approach the crystal, they are rapidly sucked into the surface to within a certain distance, corresponding to the thickness of the diffusion boundary layer. On the growing surface, they move or shake themselves for a while, and eventually become invisible. The crystal growth rate increases proportionally with increasing the density of the microparticles and the supersaturation. The results suggest that they are subcritical crystalline particles which are formed in the KDP solution, and contribute to the crystallization of KDP from the aqueous solution.
I. INTRODUCTION All existing models or theories of crystal growth mechanism assume atomic, ionic, or molecular entities as growth units.1"3 Such theories are questioned by some experimentalists, particularly those concerned with crystal growth from aqueous solutions, who believe that larger growth units than the above exist and play an important role. An international symposium was held on this topic 4 ; however, so far no confirmational data to suggest the presence of such large growth units have been presented. To this end, it is necessary to investigate the properties and behaviors of the microparticles in relation to crystal growth from aqueous solutions, one of the most fundamental problems in crystal growth. Light-scattering techniques (LST) have been developed and widely used to detect and characterize lattice defects in crystals.5"8 One of the merits of LST, which is based on the principles of Rayleigh scattering and darkfield microscopy,6-9"11 is that it has a higher resolution than ordinary optical microscopy. In the case of silicon crystals, the microprecipitates of oxygen with the size of about 100 nm or less can easily and clearly be detected by the LST using a high resolution TV camera as a detector.6'8 A second advantage of LST is that it prevents contact and thus allows nondestructive observation of J. Mater. Res., Vol. 7, No. 12, Dec 1992 http://journals.cambridge.org
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microparticles. In other words, LST is suitable for in situ observation of microparticles which cannot usually be detected by ordinary optical microscopy. In this paper, we mainly report on an in situ observation method using light-scattering techniques and preliminary results on the behavior of microparticles in relation to
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