Encapsulated graphite heater and process

Abstract

A graphite heater and method of forming a graphite heater comprising a graphite body configured in a spiral or serpentine geometrical shape defining at least one zone of an electrical heating circuit having opposed ends so as to provide an electrical path for each heating zone through the graphite body from the opposed ends with said graphite body having at least one heating surface, a coating of pyrolytic boron nitride or aluminum nitride encapsulating said graphite body and a surface layer of pyrolytic boron nitride or aluminum nitride disposed on said graphite body such that said heating surface is continuous and solid.

What is claimed is:  
     
         1 . A graphite heater comprising a graphite body configured in a spiral or serpentine geometrical shape defining at least one zone of an electrical heating circuit having opposed ends so as to provide an electrical path for each heating zone through the graphite body from the opposed ends with said graphite body having at least one heating surface, a coating of pyrolytic boron nitride or aluminum nitride encapsulating said graphite body and a surface layer of pyrolytic boron nitride or aluminum nitride disposed on said graphite body such that said heating surface is continuous and solid.  
     
     
         2 . A method for forming a graphite heater from a body composed of graphite, comprising the steps of: coating the graphite body in a CVD reactor furnace with a layer of pyrolytic boron nitride or aluminum nitride; machining the coated graphite body from the side opposite said continuous surface to form a spiral or serpentine pattern extending through the graphite body up to said continuous surface such that a solid continuous surface layer of pyrolytic boron nitride or aluminum nitride of predetermined thickness is left intact covering the surface of the machined graphite body, with the spiral pattern formed in said graphite body having opposed ends adapted for connection to an external power supply and encapsulating said machined graphite body in a material composition selected from the group consisting of pyrolytic boron nitride or aluminum nitride to form a thin film shell of such material composition surrounding said heater.