AN IMPROVED MICROSCOPE STAGE FOR DIRECT OBSERVATION OF FREEZING AND FREEZE-DRYING

A microscope stage for observation of freezing and freeze drying is de scribed. The stage uses thermoelectric (Peltier) heaters configured in two stages, with circulating fluid as a heat sink on the high tempera ture side. Lowest attainable sample temperature is about -47 degrees C . Principal advantages of this system are closed-loop control of stage temperature, rapid response to changes in temperature set point, and improved documentation of experiments by use of a video recorder syste m with a character generator which allows display of sample identity a nd temperature. Accuracy of measuring the sample temperature in the fi eld of view was validated by comparing observed values of eutectic mel ting with published values for a series of solutes with eutectic tempe ratures in the range from -2 degrees C to -32 degrees C. Good agreemen t was obtained throughout this range.