Degradable metallic materials

Corrosion is generally taken to be the waste of a metal by the action of corrosive agents. However, a wider definition is the degradation of a material through contact with its environment. Thus, corrosion can include non-metallic materials such as concrete and plastics and mechanisms such as cracking in addition to wastage (i.e. loss of material). This chapter is primarily concerned with metallic corrosion, through a variety of mechanisms. 

Corrosion prevention and protection arrests the degradation of metals/materials and contributes in a significant way to the conservation of resources with minimum damage to the ecosystems. Since materials are prone to corrosion it is useful to know the factors both direct and indirect, which affect the choice of materials and their related corrosion resistance of paramount importance in the design of an engineering structure. 

Shipilov, S.A., Catastrophic Failures Due to Environment-Assisted Cracking of Metals Case Histories, in Proceedings of the International Symposium on Environmental Degradation of Materials and Corrosion Control in Metals, M. Elboujdaini, E. Ghali (eds.), The Conference of Metallurgists, COM, METSOC, pp. 225-242, 1999. 

The miscellaneous materials committees include paint, paper, packaging, rubber textiles, and plastics. The miscellaneous subjects committees include emission spectroscopy, fire standards, appearance of materials, microscopy, and resource recovery. The materials for specific applications committees include electronics, tires, consumer products, and food-service equipment. The corrosion, deterioration, and degradation of materials committees include corrosion of metals, erosion and wear, and durability of nonmetallic materials. 

K. S. Brown, G. M. Gordon in Environmental Degradation of Materials Nuclear Power Systems - Water Reactors, G. J. Theus, J. R. Weeks (eds.). The Metallurgical Society, Metals Park, OH (1988), p. 243. 

The broadest definition of corrosion is the degradation of a material s properties or mass over time because of the effect of the environment. We can think of this in simpler terms by recognizing this process as the tendency for a material to return to its most thermodynamically stable state. For most metallic materials, this means the formation of oxides or sulfides, or other basic metallic compounds generally considered to be ores. For polymeric materials, the end result could be a variety of simple organic compounds. Only in vacuums or under inert atmospheres can corrosion processes be expected to halt entirely. In most cases, these processes are slow enough to afford useful and practical equipment life. 

Sulfate reducing bacteria are anaerobic microorganisms that have become especially important in biotechnological processes (i.e. water treatment) due to its ability to degrade organic material and remove heavy metals [1]. 

The practices of dematerialization and substitution are not only important independently, but are also interrelated in a dynamic way that should be utilized for planning. For example, the less degradable a material is, the more it must be safeguarded and/or dematerialized within the techno-sphere, or industrial systems, particularly if it is relatively scarce in natural systems. For scarce metals the assimilation is slow and occurs as sedimentation and biomineralization. For chemicals that are relatively persistent and foreign to nature, assimilation occurs also as degradation with relatively long half-lifetimes. 

In addition to the chemical factors, implants can also be subjected to abrasion or stress under actual use conditions. Some examples would be replacement joints, tendons, and dental appliances. Essentially all polymeric materials show some chemical and/or mechanical degradation under actual physiological conditions, but often polymeric materials survive better than some ceramic or metallic materials. 

Although atmospheric corrosion degrades most materials, such as calcareous stones, glasses, polymers, or metals, our understanding originates mostly from investigations of metallic objects. Hence, in order to illustrate the most important processes and concepts involved in atmospheric corrosion, this chapter is primarily based on our knowledge of... 

Thermoplastic materials can be repeatedly re-formed by the application of heat, similar to metallic materials. They are long-chain linear molecules that are easily formed by the application of heat and pressure at temperatures above a critical temperature referred to as the glass temperature. Because of this ability to be re-formed by heat, these materials can be recycled. However, thermal aging that results from repeated exposure to the high temperatures required for melting causes eventual degradation of the polymer and limits the number of reheat cycles. 

E. Heitz. Metallic materials. In A Working Party Report on Microbiological Degradation of Materials and Methods of Detection, European Federation of Corrosion Pubhcations, Number 9, The Institute of... 

In the case of metallic materials, one of the main causes of degradation is electrochemical corrosion, and electrochemical corrosion means electric current. The electrochemical corrosion can take place if four factors coexist ... 

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