HT Furnace Insulation

The insulation adjacent to the hot muffle will have to be either carbon or graphite and as the temperature is dropped, it can be replaced by a ceramic form, although many subscribe to the view that it is best to keep all insulation black in order to avoid any possible interaction with the water and Si02 that may be present in the ceramic insulation, or the Na evolved from the product. Three forms of carbon/graphite insulation can be used, namely, board, felt and powder. The use of powder is not recommended, since there are many handling problems, including possible contamination during use with NaCN. 

It is most essential that air is not allowed to enter this furnace when it is hot since severe erosion of the carbon/graphite will occur. All air in the furnace should be displaced with inert gas before start-up. 

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