The Role of the Surface of Glass Reinforcement Fibers on Their Physical Properties and Performance in Composites
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THE ROLE OF THE SURFACE OF GLASS REINFORCEMENT FIBERS ON THEIR PHYSICAL PROPERTIES AND PERFORMANCE INCOMPOSITES
ALBERT A. KRUGER Department of Physics, Brooklyn College of the City University of New York, Brooklyn, NY 11210
ABSTRACT The widely held explanation for mechanical failure of silicate and silica glasses rests upon the existence of Griffith-flaw and associated free ion diffusion concepts used to model crack growth. However, this theory has consistently failed to provide complete agreement with the experimental results. This dilemma coupled with the reports of single-valued strengths in fibers cannot be rationalized by the modification of the intrinsic Griffith-flaw distribution to essentially a delta function. It is for these reasons that the field-enhanced ion diffusion model has been introduced. The inclusion of a term for the electrostatic potential in the thin-film solution of Fick's second law has been shown to be consistent with the experimental results. Therefore, the effects on alkali ion migration as a consequence of the local variations in charge density that occur on the solution side of the glass/water interface play a direct role on the chemical corrosion mechanism. Thus chemistry which can modify the surface potential can alter the rate of aging of glass. Ithas been found that the chemistry which has been used to modify the corrosion behavior of glass fibers can also alter composite properties. These modifications no doubt arise from changes in the interphase region. We report on the effects of treatments on initial fiber strengths, aging resistance, and preliminary results of composite properties (made from our treated fibers). GLASS PASSIVATION From a search of the literature1 it becomes obvious that aqueous attack of glasses can be divided into two very general stages. The first is the selective leaching of mobile ions (e.g., Na+, Ca 2 +)from the bulk of the solid through the surface and interface, where the pH remains below that necessary to cause the dissolution of the silica network. The second is a process of hydrolytic depolymerization in solutions containing a high concentration of OH ions (i.e., pH>9.5). However, a silicate glass exposed to an aqueous solution of pH
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