Drawing of a 10R vial containing a frozen solution undergoing the process of ice sublimation, during the primary drying stage of a freeze-drying cycle.

The image was created as part of a library of images (hosted on Figshare) to be used by myself and the academic and industrial communities who re working of the process of pharmaceutical freeze-drying. I hope that they are particularly useful to under-graduate and post-graduate students who require such images for reports, dissertations and presentations.

This particular image is intended to show how the ice mass sublimes from the top of the frozen mass to reveal a layer of 'dried solid'.

The sublimation process can be described as follows: At the start of primary drying, the vial has a frozen mass comprising ice crystals interspersed within a matrix of the concentrated solution which formed when water was removed from the solution. As sublimation proceeds, with ice being removed from the top of the frozen mass, then the so-called “dry layer” develops which comprises a series of inter-connected pores. The porous layer creates a barrier to vapour flux and hence becomes on the of factors that controls the rate of sublimation and hence rate of drying.