Abstract: A thermal reactor to carry out a chemical reaction under precise and controlled temperature conditions. In a preferred embodiment, the reactor supplies a carbon-laden atmosphere with a predetermined carbon potential to a heat treatment furnace. The reactor has a sealed chamber, in which a chemical reaction is carried out. The chamber forms an electrical resistance element in order to produce within it the reaction temperature conditions. The chamber further being electrically isolated, having an inlet for supplying reaction products, and an outlet for the products coming from the reaction. Temperature measuring thermocouples are positioned on the chamber to determine, accurately and locally, the temperature required for the reaction. Carbon potential is measured by a probe arranged at the chamber's outlet.