Crystal, habit Subject

When suspensions are formulated to provide a stable system, the particle size becomes critical. Flocculated suspensions also require careful particle size control either in the process of manufacturing or in the starting material. Equally important is the crystal habit — the outward appearance of an agglomeration of crystals. Crystal structure can be altered during the manufacturing process, particularly if the product is subject to temperature cycling, and this can alter the stability of suspensions. 

In a eutectic system, the whole composition or just the excipient may be subject to crystallisation, but this process takes time to reach completion. It may be much longer than the time taken to freeze the product to the desired temperature (Tg). After primary drying (ice sublimation), only solid solutes remain. The mixture may then be carefully warmed to its final storage temperature. The residual solid will not necessarily be anhydrous and may, for example, contain water of crystallisation. In addition, as the temperature is raised, the crystalline product may undergo solid-solid transitions, i.e. over a period of time, a different polymorph may become the preferred crystal habit. In a completely crystalline preparation, the maximum safe storage temperature will be governed by the component with the lowest melting point. 

The surface of ice shows structural transitions, such as surface roughening and surface melting, at temperature, T, below T. The occurrence of structural transitions at the surface of ice causes alterations in the dynamic, mechanical, elastic, and electric properties of the surface. Moreover, anisotropy in structural transitions among several crystallographic plane surfaces of ice is vital for understanding habit changes of snow crystals [9]. Thus, the surface ofice near is an important subject... 

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