Materials Chemistry最新文献

The screening effects of some insulating materials like Nylon 66, PTFE and PVC had been tested in corrosion processes of carbon steels with different carbon contents and of ARMCO Iron in deaerated acid solutions showing that all the types of screen in all the experimental conditions induce a fast process of localized corrosion at the three phases contact metal-screen-solution and that the attack morphology depends on geometry contact.

Also the varnishes up to now tested on ARMCO Iron, exhibit the same behaviour except a glycerophtalic Pb₃O₄ charged resin. The generality of this phenomenon has led to formulate the hypothesys that the activation of the localized corrosion process may be due to the interaction of double layers generated in the solution by the metal and by the insulating material. The electrochemical experiments have shown a correlation among the ratio of the coated surface perimeter to the exposed surface area and the electrode potential, the current density and the polarization resistance.

The effect of 1,2-diphenyl, 2,2-dimethoxy, ethanone as photoinitiator in some ultraviolet radiation-cured acrylated acrylic formulations on steel was studied. Correlation between corrosion rates, measured with ASTM D610 standardized method, and electrolyte permeation through coatings, measured with ³⁶Cl-labelled 0.25 M NaCl solutions at 25°C, was systematically investigated. The length of time necessary for the complete failure of the coatings, as observed by the extension of corrosion products over the entire surface, was evaluated by visual inspection of corrosion or by the breakthrough curve of permeation, and found to be a function of photoinitiator concentration. The slight difference between failure time obtained by the two methods may well be due to a time lag between the activation of corrosion cells over the whole surface and onset of visible corrosion products everywhere. This time lag may be correlated to the protective value of the coating, and to its permeation properties, particularly.

Many Engineers who after their period of University training, work in design offices have had little, or no experience of corrosion and its prevention. The need to provide information of this type in order to ensure an adequate life for the structures designed, arises because of the very large cost of corrosion, the order of 5% of the GNP in developed countries, and the possibility of saving about 1% of GNP by proper application of known techniques.

Several international bodies are sponsoring programmes of awareness and scientific research including the European Economic Community, the European Federation of Corrosion, and the International Corrosion Council. National bodies also are contributing to this activity various governmental organisations, and research groups. The impact of this activity which has grown very rapidly over the last ten years will only be fully assessed when it is seen to what extent the life expectancy of structures has been improved. However, an increased awareness of corrosion and a means for its prevention amongst Engineers, and among the general public, should be beneficial.

A method based on faradaic distortion was elaborated for measuring the rate of corrosion taking place under primers. Several primers used in practice were investigated in order to show the applicability of the method.

In the last years the development of more and more sophisticated planning techniques, expecially in advanced sectors such as astronautics and nuclear plants, brought about more and more complex and efficient quality control procedures.

However if certificates and checking have reached an exceptional reliability level in mechanics and electrotecnics, the control of the applied coatings (expecially those based on paint product) is still based on traditional techniques at least in the sector of the industrial plants.

These techniques give some indications of the coating quality, they do not allow yet a particular significant checking.

In this paper has been pointed out some situation that could be advantaged by the electrochemical methods to improve the inspection provided in the specifications of the Engineering Companies.

The exposition of the type of single measurement methods is left to the expert of laboratory, whereas we shall value from now the possibility of updating our specifications on the basis of the actual suitability and conformity of the electrochemical control methods with our needs.