Imaging Techniques and Scanning Electron Microscopy as Tools for Characterizing a Si-Based Material Used in Air Monitoring Applications.

Marañón Elena,Castrillón Leonor,Megido Laura,Fernández-Nava Yolanda,Negral Luis,Suárez-Peña Beatriz

doi:10.3390/ma9020109

Abstract

This paper presents a study of the quartz fibrous filters used as a substrate for capturing the particulate matter (PM) present in the air. Although these substrates are widely used in environmental applications, their microstructure has been barely studied. The behavior of these devices during the filtration process was investigated in terms of their microstructure and the quartz fibers. Surface and cross sections were monitored. Scanning electronic microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), imaging and stereology techniques were used as tools for this purpose. The results show that most of the quartz filter fibers have sizes that allow them to be classified as nanofibers. It was also observed that, while the mechanisms of the mechanical capture of particles via impaction, interception and diffusion operate simultaneously in the outer zones of the filter cross section, the mechanism of capture by impaction is virtually non-existent in the innermost zones. Particles between 0.1 and 0.5 μm are known to be the most difficult to have captured by means of fibrous substrates. The fibers in inner zones were highly efficient in capturing this type of particle.

Highlights

Fibrous filters are simple and economical devices capable of effectively capturing the submicrometric particles that are dragged by gas streams
The efficiency of the filters employed in this study is based on the use of quartz fibers with different diameters that intertwine at random forming a structure of heterogeneous porosity
Quartz fibrous filters are essentially collections of individual quartz fibers intertwined with one another giving rise to more or less integrated structures

Summary

Introduction

Fibrous filters are simple and economical devices capable of effectively capturing the submicrometric particles that are dragged by gas streams. The fibers used in filters of this kind can be made from a wide range of materials such as cellulose, glass, plastic, ceramics, and metals. This diversity allows their use in fields as varied as the manufacture of disposable respirators, the manufacture of industrial air cleaning equipment, the construction of air purification systems, the manufacture of air filtration systems for the automotive industry, and so on [1]. Happel [8], Kuwabara [9] and Spielman et al [10] assumed in their

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