Influence of hygrothermal environment on thermal and mechanical properties of carbon fiber/fiberglass reinforced matrix composite materials
The absorption and diffusion of water in a carbon fiber/glass fiber hybrid composite was investigated. Water-sorption experiments, mechanical property tests and dynamic mechanical analysis (DMA) were performed after immersion in water at different temperatures for up to 32 weeks. The moisture uptake mechanism exhibited by the hybrid fiber system was determined to be more complex than the single fiber type. Weight-change profiles for the composites fitted the theoretical Fickian diffusion curve during the initial immersion time, but diverged substantially as time progressed. The shear properties and the glass transition temperature (Tg) were sensitive to the effects of hygrothermal environment, and values for both decreased with increasing water uptake. Microscopic inspection of water-soaked samples showed no cracking when the absorption was less than saturation. The thermal and mechanical properties were mostly retained (after drying), provided
Tortuosity factors for diffusion in catalyst pellets
The dynamic pulse-response technique was used to measure effective diffusivities under nonreacting conditions in two, unsulfided, extrudate-type, hydrodesulfurization catalyst pellets of different porosities. Pore-volume distribution data showed a bidisperse pore structure with a broad pore-size range (100 μm to 3 nm). 
 
The main purpose of the study was to evaluate various methods for calculating the tortuosity factor, τ. For this particular catalyst, the most constant and unreasonable values of τ were obtained by supposing that diffusion occurred in all the pore volume (micro and macropores) and by summing the combined Knudsen and bulk contributions over each increment of pore volume.
Moisture Sorption Effects on Carbon Fiber-Reinforced Pheny L Ethnyl-Terminated UltemTM Composites
High-performance aerospace applications require materials that are able to withstand exposure to extreme temperatures, high relative humidities, solvents, and other chemicals. Due to their high-performance thermal and mechanical characteristics, poly(etherimide)s are being implemented in such applications. Prior to such use, environmental effects on material performance must be understood. In this study, the effects of moisture sorption on the mechanical properties of carbon-fiber-reinforced phenylethynyl-terminated poly(etherimide) matrix composites were investigated. The through-the-thickness moisture diffusion coefficient and the maximum moisture equilibrium content were determined for the unidirectional composites for exposure to 90'C and 85% relative humidity. In addition, the composites were tested for retention of transverse flexural strength and apparent interlaminar shear strength at maximum moisture equilibrium content. The same properties were tested for property retention following desorption of moisture to a 90'C, 2% relative humidity moisture content. The composite showed high mechanical property retention with recoverable matrix plasticization being the source of property reductions.