380 likes | 517 Views
Slide 1. Fibres and forensics. Text and images by the Centre for Microscopy & Microanalysis, University of Queensland, Australia, August 2007. Slide 2. Fibres: Natural [animal & mineral] Synthetic [human –made] What we will cover: 1) Scanning Electron Microscopy (SEM).
E N D
Slide 1 Fibres and forensics Text and images by the Centre for Microscopy & Microanalysis, University of Queensland, Australia, August 2007
Slide 2 Fibres: Natural [animal & mineral] Synthetic [human –made] What we will cover: 1) Scanning Electron Microscopy (SEM). 2) How to identify fibres using the SEM. 3) The identification of a mystery fibre.
What is scale all about? Slide 3 Scanning Electron Microscope
Slide 4 Resolution (not magnification!) is the ability to separate two objects optically Unresolved Partially resolved Resolved
Slide 5 With enough resolution we can magnify an object many millions of times and still see new detail This is why we use electron microscopes If you magnified your thumb nail just 10,000 times it would be about the size of a football pitch. For example think of the size of Suncorp Stadium in Brisbane
Slide 6 Electron beam produced here Beam passes down the microscope column Electron beam now tends to diverge But is converged by electromagnetic lenses Cross section of electromagnetic lenses Sample Diagram of Scanning Electron Microscope or SEM in cross section - the electrons are in green
Slide 7 - + Using X-rays and the scanning electron microscope e Electron falls back again to inner ring [lower energy state or valence] & burst of X-ray energy given off that equals this = Characteristic packet of energy
What the X-rays tell us Slide 8 Quantity of packets Characteristic oxygen peak Energy of packets in thousands of electron volts come off atoms Characteristic carbon peak Characteristic chlorine peak
Some definitions of fibre Any slender, elongated, threadlike object or structure. A natural (e.g. plant, animal or mineral) or synthetic filament, capable of being spun into yarn. Commonly also used in: Botany: One of the elongated, thick-walled cells that give strength and support to plant tissue. Anatomy: Any of the filaments constituting the extracellular matrix of connective tissue. Any of various elongated cells or threadlike structures, especially a muscle fiber or a nerve fiber. Slide 9
Sample preparation for SEM Slide 10 Sample Adhesive tape Sample mount 12mm wide Fibre samples are dried then mounted on 12mm metal stubs and coated with platinum.
Slide 12 The following images are of various natural (plant and animal) fibres and synthetic fibres imaged using a scanning electron microscope Note: electrons provide monochrome images.
A Slide 13 Natural Fibres (Plant) (A) Tissue paper at low magnification. (B) Same tissue paper at higher magnification showing individual fibres. How wide are these fibres? B
Paper Slide 15
Not all hair is the same! Rabbit hair (A) looks different from human hair (B) under the SEM. What are the differences? Slide 17 A B
Natural fibres (Animal) (A) Human hair strands at low magnification. (B) & (C) At higher magnifications showing surface detail (scales). Slide 18
Slide 19 Human hair
Slide 20 Wool
Fibres can be natural or synthetic. But how can we tell them apart quickly and easily? Coconut fibres (coir) Shade cloth woven plastic fibres We can use an SEM to examine the size, shape, surface detail and elemental composition Slide 22
A Slide 23 • Synthetic fibres • Plastic shade • cloth at • low magnification. • (B) Plastic shade • cloth at higher • magnification • showing smooth • individual fibres • and extrusion grooves. B
Slide 24 Shade cloth
Synthetic fibre: velcro Slide 25
Slide 26 Velcro
A Synthetic fibres (A) Fibre glass at low magnification. (B) & (C) Fibre glass at progressively higher magnifications showing individual fibres. B Note smooth fibre surfaces B C Slide 28
A Slide 29 Asbestos – why is it dangerous to health? B How many fibres this wide would fit across 1 mm ? C
Slide 30 Asbestos
Slide 32 Mystery fibre
Slide 34 Mystery fibre
Some fibres have very characteristic features that are seen easily with the SEM. As seen by a light microscope 6 mm As seen by an SEM ! Slide 36