Editorial for Special Issue “Mineral Fibres”

Fiber Selection for Reinforced Additive Manufacturing

The purpose of this review is to survey, categorize, and compare the mechanical and thermal characteristics of fibers in order to assist designers with the selection of fibers for inclusion as reinforcing materials in the additive manufacturing process. The vast “family of fibers” is described with a Venn diagram to highlight natural, synthetic, organic, ceramic, and mineral categories. This review explores the history and practical uses of particular fiber types and explains fiber production methods in general terms. The focus is on short-cut fibers including staple fibers, chopped strands, and whiskers added to polymeric matrix resins to influence the bulk properties of the resulting printed materials. This review discusses common measurements for specific strength and tenacity in the textile and construction industries, including denier and tex, and discusses the proposed “yuri” measurement unit. Individual fibers are selected from subcategories and compared in terms of their mechanical and thermal properties, i.e., density, tensile strength, tensile stiffness, flexural rigidity, moisture regain, decomposition temperature, thermal expansion, and thermal conductivity. This review concludes with an example of the successful 3D printing of a large boat at the University of Maine and describes considerations for the selection of specific individual fibers used in the additive manufacturing process.

X-ray synchrotron microtomography: a new technique for characterizing chrysotile asbestos

Over the last decades, many studies have been conducted on rocks containing Naturally Occurring Asbestos (NOA) to determine the potential health risks to exposed neighboring populations. It is difficult to accurately characterize the asbestos fibres contained within the rocks as conventional techniques are not effective and have drawbacks associated with the disturbance of the sample under study. X-ray synchrotron microtomography (SR-μCT) supplemented with polarized light microscope (PLM), scanning electron microscopy analysis combined with energy dispersive spectrometry (SEM/EDS), electron probe micro-analysis (EPMA) were used for identifying asbestos fibres in a mineral matrix. As a case study, we analyzed a representative set of veins and fibrous chrysotile that fills the veins, taken from massive serpentinite outcrops (Southern-Italy). We were able to identify respirable chrysotile fibres (regulated asbestos) within the serpentinite matrix. SR-μCT of NOA veins achieved the resolution and reconstructed 3D structures of infill chrysotile asbestos fibres and other phase structures that were not resolvable with PLM, SEM or EPMA. Moreover, due to differences in chemical composition between veins and matrix, the data obtained enabled us to evaluate the vein shapes present in the massive serpentinite matrix. In particular, iron and aluminum distribution variations between veins and matrix induce different radiation absorption patterns thus permitting a detailed image-based 3D geometric reconstruction. The advantages of the SR-μCT technique as well as limitation of conventional methods are also discussed. These analytical approaches will be used for conducting future research on NOA of other minerals, which exhibit asbestiform and non-asbestiform habits within veins, including asbestos amphiboles.