that you have properly designed the heating element and based on the guidelines
in the watt-loading tables the element you have designed should operate
properly in air (or the normal environment for that specific type of element).
What now happens when you place that oxidation resistant material into
an atmosphere containing no oxygen?
is described in the section Electric Resistance Heating Materials, there
are two types of heating element materials, Oxidation Resistant and Non-Oxidation
Resistant. Each behaves slightly differently in atmospheres containing
Oxidation Resistant Materials rely on a layer of oxide to develop and
protect the element from not only further oxidation, but also from other
types of attack. Because of this it is recommended that if possible these
elements should be run in air at the maximum temperatures expected for
several hours. By forming this initial oxide layer, the element will not
only be better prepared to resist most atmospheres, but it will also proved
an extra level of protection against contaminants that may be present
in the pieces that support the element.
that would prove to be hazardous to the heating element include those
that would disrupt, inhibit, or reduce the oxide that has been formed.
Specifically, most fluxes contain halogens (Chlorine, or Fluorine) which
can very quickly reduce the oxide exposing the heater to further attack.
the Chrome-Oxide forming alloys, the temperatures in
Aluminum-Oxide forming alloys, the temperatures in different environments
Disilicide, forms a Silicon-Oxide. Chlorine and fluorine rapidly attack
vacuum the silica is actually evaporated directly from the element. Dry
Hydrogen being very reducing also pulls the silica from the base material,
leaving nearly pure molybdenum.
Carbide, while being resistant to may chemicals, will also not tolerate
high Chlorine or Fluorine. In Nitrogen the element is limited due to interaction
with the element, forming Silicon Nitride that will appear as a fuzzy
white mass surrounding the heater.
the non-oxidation resistant materials, they cannot form any protective
coating and are therefore directly exposed to the atmospheres they are