AN INSTRUMENT FOR IN-SITU GROWTH-RATE CHARACTERIZATION OF MECHANICALLY STRAINED CRYSTALS

The crystal growth and dissolution characteristics of a certain materi al can be considerably influenced by the strain present in a growing ( dissolving) crystal. Strain can be induced in various ways. One of the most common and always present in industrial processes, where attriti on processes are always accompanied by generation of mechanical strain in a newly formed small crystal fragments, is mechanical stressing, i n situ, during preparation and handling. To gain deeper insights into some aspects of this phenomenon, a sophisticated equipment is needed f or in situ controlled stressing of extremely brittle and fragile cryst als. For this purpose, we have developed an apparatus which comprises a specially designed straining cell coupled with a laser Michelson int erferometer for growth rate measurements. The straining cell is design ed to accommodate crystals that undergo. fracture below 200 microstrai ns. The stress imposed on a crystal is computer controlled with a prec ision of approximately 5%. Details of the instrument are given togethe r with two examples of straining in situ brittle paracetamol and plast ic sodium nitrate crystals. The measured changes in growth rate of a p aracetamol crystal, in the quasi linear region 0-70 kPa are estimated to be (-9.4+/-0.1) X 10(-11) m/s/kPa. (C) 1998 American Institute of P hysics. [S0034-6748(98)05606-8]