Corrosion can be defined as the chemical reaction of a metallic material with its environment. The products of this reaction can be solid, liquid or gaseous and the physical and chemical natures of the products are important as they often influence the subsequent rate of reaction.
Handbooks and reference charts are available, providing information on the behaviour of metals and other materials in certain well-defined environments. Unfortunately the precise operational environment is, in practice, difficult to predict and can vary considerably, e.g. for reusable space components.
Additionally, the method of fabrication and fastening can affect the susceptibility to, and rate of, corrosion.
Thus to avoid corrosion problems, the factors to be considered by a designer are:
- • The working environment and exposure to it
- • The probable reactivity of the materials involved in fabrication
- • The features of the design that can modify that reactivity
Figure 13-1 shows the types of corrosion that have been identified as most relevant to space applications. The following sections briefly describe the various types of corrosion and some recommendations are given for overcoming corrosion problems.
Figure description:
The image depicts various forms of corrosion through cross-sectional diagrams:
- Original Surface: Indicated by a dashed line at the top level of the metal.
- a General Corrosion: Uniform reduction and unevenness of the entire top surface.
- b Localized Corrosion:
- Local Cell: A broad, shallow depression in the surface.
- Pitting: Small, deep cavities or circular indentations in the surface.
- Crevice: Corrosion occurring in the gap or joint between two overlapping surfaces.
- c Galvanic or Bimetallic Attack: Features two connected materials:
- Anode: The primary metal experiencing surface loss.
- Noble Metal (Cathode: A secondary, hatched material in contact with the anode.
- d Stress Corrosion Cracking: Branching, jagged internal cracks originating within the metal block.
Figure 13-1 - Forms of Corrosion