High-temperature oxidation
High-temperature oxidation is a process that involves the rapid oxidation of a material at a high temperature. This can be a simple process involving only oxygen or an oxidation reaction involving other agents such as sulfur dioxide, chlorine, hydrogen peroxide, and nitric oxide. The temperature of an oxidation reaction can range from room temperature to over 1000 ˚C. Oxidation is an exothermic reaction and often generates heat which can accelerate the oxidation process. High-temperature oxidation can be used to process metals, ceramics, and polymers.
High-temperature oxidation is commonly used to form protective oxide layers on the surface of materials. These oxide layers are generally able to resist further oxidation in atmospheric conditions. The process also combines gases with the surface of the material to form volatile oxides that can be removed with air or further heat treatment. This can also be used to form different colorings on the surface of materials.
The rate of oxidation of a material at high temperature depends on the thermodynamic behavior of the system, the reactivity of the material, and the rate of transfer of elements at the reaction surface. Oxidation can occur over the surface of a solid by diffusion, through gas or liquid, or can occur at the grain boundaries. The behavior of the material during oxidation is also determined by the diffusion, thermomechanical, and thermoelectrical properties of the material.
Oxidation of a material at high temperature can cause changes in its structure such as grain growth, phase transformation, or microstructure changes in the material. The presence of oxides can also cause the material to become brittle and restrict its ability to deform or be machined. This can be beneficial as it can improve the properties of the material such as its corrosion resistance. Alternatively, oxidation can cause a loss of strength and creep resistance.
Oxidation of materials is often accelerated and modified by the presence of other agents. Chlorine and sulfur dioxide, for example, can accelerate the oxidation process significantly. Hydrogen peroxide is often used to control the oxidation of a material and allows the user to control the rate of the oxidation reaction.
High-temperature oxidation can be beneficial when used to prevent corrosion damage or to form protective oxide layers on metals, to form ceramic colors or colors on other materials, or when used to remove volatile oxides from the surface of materials. However, it can cause detrimental changes to the properties of materials such as a decrease in strength and creep resistance. It is therefore important to consider the reaction conditions before subjecting a material to high-temperature oxidation.
