Abstract

Filamentary growths have been found on metal surfaces of some of the parts used in telephone communications equipment, particularly on parts shielded from free circulation of air. The growths are of the same character as those known as “whiskers” and which developed between the leaves of cadmium plated variable air condensers, causing considerable trouble in military equipment during the early part of World War II. An investigation has been under way in an attempt to determine the mechanism of growth of the whiskers, found not only on cadmium plated parts but also on other metals. This paper summarizes the findings to date as revealed by the study of approximately one thousand test specimens of different metals, solid and plated, exposed under various environmental conditions. The study is being extended in the light of the findings which have developed during the course of the work. While the whiskers normally are not found on parts such as condenser leaves for some time, often months, after being electroplated, it is possible, by increasing the ambient temperature, to so accelerate their growth that they will develop in a matter of weeks. So as to avoid the introduction of additional variables which so often attend accelerated methods of test, the greater part of the present work is being carried out at temperatures attained by equipment operating under normal exposure conditions. The effects of humidity and the presence of various organic materials, different film thicknesses and methods of application, surface preparation and supplementary treatments, chemical and physical properties and X-ray studies of structure are discussed in the paper.