Materials corrosion

Choices of alternative materials. Corrosion probes are carefully chosen to be as close as possible to the alloy composition, heat treatment, and stress condition of the material that is being monitored. Care must be taken to ensure that the environment at the probe matches the service environment. Choices of other alloys or heat treatments and other conditions must be made by comparison. Laboratory testing or coupon testing in the process stream can be used to examine alternatives to the current material, but the probes and the monitors can only provide information about the conditions which are present during the test exposure and cannot extrapolate beyond those conditions. 

Aluminium Building materials Corrosion to aluminium sulphate (white)... 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Corrosive, particularly when diluted. Attacks most common metals, including most stainless steels. Excellent solvent for many synthetic resins or rubber Stability During Transport Stable Neutralizing Agents for Acids and Caustics Dilute with water, rinse with sodium bicarbonate solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Environmental composition is one of the most critical factors to consider. It is necessary to simulate as closely as possible all constituents of the service environment in their proper concentrations. Sufficient amounts of corrosive media, as well as contact time, must be provided for test samples to obtain information representative of material properties degradation. If an insufficient volume of corrosive media is exposed to the construction material, corrosion will subside prematurely. 

Building durability, by preventing decay of wood-based materials, corrosion of metals, and spalling of masonry and concrete caused by freeze-thaw cycles... 

Syrett, B. C. and Wing, S S., An Electrochemical Investigation of Fretting Corrosion of Surgical Implant Materials , Corrosion, 34, 379-386 (1978)... 

Norton, J. F. (ed). High Temperature Materials Corrosion in Coal Gasification Atmospheres, Applied Science Publishers, London (1984)... 

Organic materials Corrosive vapours are sometimes emitted by organic materials used either in packaging or in the manufactured article, and may be troublesome in confined spaces. Some woods, particularly unseasoned oak and sweet chestnut, produce acetic acid (see Section 18.10), and certain polymers used in paints, adhesives and plastics may liberate such corrosive vapours as formic acid and hydrogen sulphide . It may be necessary to carry out exposure trials, particularly where materials capable of liberating formaldehyde or formic acid are involved. Most corrosion problems of this kind can be prevented by using desiccants, and in many cases they are confined to imperfectly cured materials. For an excellent review see Reference 9. 

Nitric-hydrofluoric acid test 1 10% HNO3 -1- 3% HF 4 h exptosure to 70° C solution Comparison of ratio of mass loss of laboratory annealed and as-received samples of same material Corrosion potential of 304 steel = -l-O-14 to -I-0-54 1. Chromium-depleted areas 2. Not for 0-phase 3. Used only for Mo-bearing steels... 

From a practical review, perhaps it can be stated that buildings and construction materials are exposed to the most severe environments on earth, particularity when the long time factor is included. The environments include such conditions as temperature, ultraviolet, wind, snow, corrosion, hail, wear and tear, etc. Basically the following inherent potentials continue to be realized in different plastics ease of maintenance, light weight, flexibility of component design, combine with other materials, corrosion/abrasion/weather resistance, variety of colors and decorative appearance, multiplicity of form, ease of fabrication by mass production techniques, and total cost advantages (combinations of base materials, manufacture and installation). 

It has long been recognized that local environmental characteristics influence the rates of material corrosion. After two years of measurements at 39 sites in Europe and North America, significant relationships have been shown between corrosion rates of building materials and atmospheric pollutants( 5). While direction of exposure relative to weather and other factors such as frequency and duration of wetting significantly influence corrosion, Kucera (46) has shown that sulphur oxides are strongly correlated with deterioration of structural materials. 

Hazard Class A series of nine descriptive terms that have been established by the UN Committee of Experts to categorize the hazardous nature of chemical, physical, and biological materials. These categories are flammable liquids, flammable solids, explosives, gases, oxidizers, radioactive materials, corrosives, poisonous and infectious substances, and dangerous substances. 

This book incorporates into many traditional disciplines of science and engineering such as interfacial chemistry, biochemistry, enzyme chemistiy, membrane chemistry, metallurgy, modification of solid interfaces, and materials corrosion. 

---