Operating the MiniZone Refiner

A sample is prepared for purification by loading about .5 g of sample into a 180 mm long X 3 mm diameter tube.  Other diameter tubes are also available that allow sample sizes down to about 25 milligrams to be loaded.    Loading is easily performed by melting the sample and then pulling the sample into the tube using a small syringe attached to the end of the tubing.

The thin walls of this tubing and the small diameter allows the transfer of heat into and out of the sample much faster than the traditional glass tube design.  This, in turn, allows the molten zones to be closer together and to be moved faster through the sample. Recrystallization speed is at least an order of magnitude faster than earlier designs.

After loading the sample into the tubing, the tube (or tubes) ends are locked into the slots of the transport mechanism.   The melt and freeze temperatures are then selected on the front panel.  These temperatures are usually selected as the melting point of the sample + and - 5 to 15 degrees C respectively.  The Zone Rate is then selected (usually between .1 and 10 cm/hour) and the zone refining begins.

The molten and crystalline zones are clearly visible when the unit is operating.

Electronically regulated heaters and coolers alternately melt and freeze the sample. At the same time, the tube(s) is/are moved slowly toward the front of the unit.  When the movement is equal to the spacing between one hot and one cold zone (2 centimeters), the tray is rapidly returned to the original position and the process is repeated.  The net result of this action is that four molten and four frozen (crystalline) zones move continuously and smoothly up toward the rear of the unit.

After the sample has recrystallized sufficiently, the sample is allowed to cool and completely solidify.  (Typically this takes between 8 to 12 hours.)  The tube is removed from the instrument and the sample recovered from the tubing by cutting the tube at the appropriate position.

The major portion of the impurities are concentrated in a band on one end of the tube.