Phase and orientation effects in X-ray attenuation of carbonaceous epoxy composites

Abstract

Composites made of carbon nanotubes (CNTs) reinforced in an epoxy matrix have already been successfully used as electromagnetic interference shielding materials. Different weight fractions of randomly distributed and vertically aligned multiwall carbon nanotubes (MWCNTs), graphite, and carbon fiber reinforced in the epoxy matrix were used to make these composites. The comparisons of percentage attenuation of different composite materials were studied under both diagnostic or hard (narrow beam geometry) and soft X-rays (monochromatic X-rays beam). It was found that the concentration of CNTs and graphite in epoxy composites affects attenuation. The results also demonstrate that the percentage attenuation for CNTs (as made) epoxy composite is always higher than graphite epoxy and treated CNTs epoxy composite at any concentration at the same thickness and tube voltage. This study also confirmed that the metal catalyst particles present in CNTs contribute to a considerable attenuation of X-rays along with CNTs and also demonstrated that the increase in metal content inside CNTs increases the attenuation. For hard X-rays, the orientation of CNTs in composites affects attenuation, and this effect gradually weakens at higher tube voltages. Vertically aligned carbon nanotubes (VACNT) array epoxy, and the thin composites are not suitable to attenuate diagnostic X-rays coming from high tube potential. For thin samples, VACNT array epoxy composites always perform better on attenuation of soft X-rays than randomly oriented CNTs in composites with any other composition lower than 15 wt %. This study also showed that there is a difference in the attenuation of soft X-rays amongst CNTs, graphite, and carbon fiber epoxy composites, which confirms that the attenuation depends on the geometry of the carbon structures. There is a clear effect of the orientation of CNTs in VACNTs epoxy composite on soft X-ray attenuation, and it shows that the radial direction of CNTs attenuates more X-ray radiation than the tube axis direction.