A finite-element model of the propagation of corrosion crevices and pits

One of the most destructive modes of corrosion of metals is localized corrosion. This can take many forms depending on the chemical and electrochemical environment of the metal. These include pitting corrosion which is characterized by isolated cavities on the metal surface, and crevice corrosion, which occurs where two or more surfaces in close proximity lead to the creation of a locally occluded region. The aim of this paper is to develop a mechanistic model of the propagation stage of an established pit or crevice, based on a mathematical representation of the physical mechanisms controlling process. The model considers the time evolution of the solution chemistry and electrochemistry within an active cavity, and uses the method of finite elements to solve the complex set of mass-conservation equations describing the system. It is applied to pitting and crevice corrosion in carbon steel and is demonstrated by testing various predictions against experimental data

A New Tool for Cellulose Degradation Studies

AbstractWe describe a new technique for studying thermally-induced chemical transformations in cellulose. The apparatus consists of a carbon dioxide laser for heating, an infrared thermometer, and an optical reflectance spectrometer. To illustrate the technique, we present measurements from a single piece of sample linen along five isotherms in the range 200–290°C. The results are discussed in terms of first-order chemical rate theory and a fourstep model. From the measurements we derive the activation energies, Arrhenius constants, and reflectivities of the chromophoric states.</jats:p