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Texture and Chemical Resistance of Materials


    DR. C. H. DESCH delivered a public lecture on October 26 before the Institution of Chemical Engineers on “Texture and Chemical Resistance”. Dr. Desch pointed out that the resistance of materials of construction to attack by chemical agents depends not only on their composition, both ultimate and proximate, but also on their texture. This is illus trated by the differences between the behaviour of wrought iron and mild steel, the attack of sulphates on limestone, and the action of hard and soft waters on concrete dams. On a finer scale, the resistance of metals and alloys to chemical attack is affected by the grain size, the presence of cold-worked regions, the smoothness of the surface, and the directional effects of rolling and drawing. In steels, the distribu-tion of the carbides and the size of their particles influence the rate of attack by acids. The texture of the resisting or ‘stainles's steels to steam at high temperatures depends on the distribution of the compounds precipitated from the solid during heat ing. Oxidising agents produce a thin skin on the surface of many metals, and this protects against further action, or fails to protect, according to the texture of the oxide so formed. On a yet finer scale, certain classes of solids containing ‘giant molecule's have their chemical properties determined by the shape of those molecules, whether forming thin sheets, fibres, or a loose network. Examples are graphite and other forms of carbon, textile fibres and the zeolites. The study of texture, usually by means of the microscope but also making use of many physical methods, is therefore an essential part of the study of chemically resistant materials.

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