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In the study of a corrosion phenomenon, corrosion product analysis can only be regarded as a part, albeit essential, of the whole investigation. The content to which any corrosion process, and its manifestations, is studied is governed by several factors, which include the information required, the motive behind the investigation (research or industrial), the relevance of laboratory tests with respect to service conditions and the cost of the work. The ad hoc solutions of a plant engineer are often satisfactory over an indefinite period but they can only rarely be regarded as the complete answer to a particular corrosion problem although they will permit the plant to carry on in operation. The corrosion engineer must be able to justify his proposed research or fundamental investigations into a corrosion process from a cost and time standpoint.

Although the first part of this article (published in the November issue) is highly relevant to grid corrosion, certain other considerations are also very important, namely, stresses within the grid and grid growth.

THE variation in weight gains of the binary (and ternary) iron alloys with change in the atmosphere composition clearly demonstrates the sensitivity of oxidation behaviour to conditions. In particular it can be seen from Figs. 3 and 4 that the presence of atmospheric pollutants (sulphur and nitrogen oxides, water vapour) markedly increases the oxidation rate in air. This is supported by the further marked increase in oxidation in flue gases produced by the presence of sulphur oxides. Oxidation in flue gases at 700°C is far greater than in air, Figs. 7 and 10 and Table 3. This is due to the formation of wustite which was not present in air‐formed oxide scales.

Introduction Organic surface coatings are the most familiar, and perhaps the most economical, method used for providing corrosion protection to metallic structures. If appropriate control of the metal preparation and pre‐treatment procedures and specified coating application is followed, the paints will afford protection by one, or more of the following mechanisms:

When tooth substance has been lost either by decay or accidental trauma it should be restored aesthetically and functionally to maintain the patient's oral health. Restorative procedures involve removing caries (decayed tooth substance) of the hard outer enamel and softer inner dentine layer. This is achieved by means of burrs and other dental cutting instruments. The shape of the cavity produced must provide retention for the restorative material and prevent further weakening of the tooth leading to possible cuspal fractures. Materials in common use include porcelain, gold, silver‐tin amalgam and various polymers. The decision as to which material to use in any given situation depends on several factors:

THE oxidation behaviour of low binary iron alloys with aluminium, chromium and silicon in air has been discussed at length. Rather less work has been performed on the ternary systems, Fe‐Cr‐Al and Fe‐Cr‐Si, and very little on Fe‐Al‐Si alloys.

The corrosion behaviour of lead and its alloys in sea‐water is of great commercial interest in view of the considerable use of submerged telecommunications cables and the growing use of lead anodes for cathodic protection of marine structures. This article is concerned with the corrosion of lead in sea‐water and saline solutions and with the anodic behaviour of lead in chloride solutions.

A general survey is made of the techniques currently employed in corrosion studies. The application of both physical‐chemical and physical techniques is discussed. The majority of the techniques described could be used at some time or other by any corrosion laboratory either directly or indirectly. It is only by making such a wide coverage that a detailed picture of a corrosion process can be understood and the significance of alloying and corroding media (be it gas or liquid) appreciated.

In view of the increasing use of the potentiostat, both as a research tool and for accelerated testing of materials, it is felt that a guide along the lines of ‘Have potentiostat, will corrode’ would be useful to both new workers in this field as well as to established corrosion engineers. The magnitude of the subject precludes a detailed discussion and therefore this article is intended to be an introduction rather than a critical appraisal. The current developments in potentiostatic techniques and instrumentation were recently discussed at a Corrosion and Protection Association symposium. (The present article is based on one of the papers.)

Cathodic protection by galvanic or impressed current techniques is probably the most favoured method of obviating the corrosion of buried and immersed metals. The theoretical principles and the economics involved in such protection are well established now and have been the subject of numerous papers, monographs and reviews. Cathodic protection is, however, still far from being an infallible method of corrosion prevention primarily because (a) the cathodic protection conditions necessarily change with the environment, (b) complete corrosion protection is rarely achieved in practice (see below), and (c) corrosion of an apparently protected structure may occur through the presence of stray currents