Selective control of oxidation atmospheres in carbon fiber production

A method for making carbon fiber from a precursor fiber wherein the precursor fiber is subjected to an oxidation treatment in a plurality of oxidation ovens to form an oxidized fiber, said oxidized fiber then being subjected to a carbonization treatment to form said carbon fiber, said plurality of oxidation ovens being surrounded by ambient air which has an ambient air humidity of from 2 to 10 grams of water per kilogram of air and wherein said oxidation treatment comprises the steps of:

• providing at least a first oxidation oven that defines a first oxidation zone having a first oxidation zone atmosphere comprising first oxidation air which enters said first oxidation zone via one or more first oxidation air entrances, said first oxidation zone atmosphere having a first oxidation atmosphere, humidity wherein said first oxidation air comprises dehumidified ambient air such that said first oxidation atmosphere humidity is from 1 to 3 grams of water per kilogram of air and wherein said first oxidation atmosphere humidity is at least 1 gram of water per kilogram of air less than said ambient air humidity and wherein the temperature or temperatures within said first oxidation zone fall within a first oxidation zone temperature range;
• passing said precursor fiber through said first oxidation zone to form a partially oxidized fiber;
• providing a final oxidation oven that defines a final oxidation zone having a final oxidation zone atmosphere comprising said ambient air which enters said final oxidation zone via one or more ambient air entrances wherein the temperature or temperatures within said final oxidation zone fall within a final oxidation zone temperature range which is higher than said first oxidation zone temperature range;
• passing said partially oxidized fiber through said final oxidation zone to form said oxidized fiber.