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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).

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Presentation Transcript
slide1
Slide 1

Fibres and forensics

Text and images by the Centre for Microscopy & Microanalysis, University of Queensland, Australia, August 2007

slide2
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.

slide3
What is scale all about?

Slide 3

Scanning

Electron

Microscope

slide4
Slide 4

Resolution (not magnification!) is the ability to separate two objects optically

Unresolved

Partially resolved

Resolved

slide5
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

slide6
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

slide7
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

slide8
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

slide9
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

slide10
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.

slide12
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.

slide13
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

slide15
Paper

Slide 15

slide17
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

slide18
Natural fibres

(Animal)

(A) Human hair strands at low magnification.

(B) & (C) At higher magnifications showing surface detail (scales).

Slide 18

slide19
Slide 19

Human hair

slide22
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

slide23
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

slide24
Slide 24

Shade cloth

slide26
Slide 26

Velcro

slide28
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

slide29
A

Slide 29

Asbestos – why is it

dangerous to health?

B

How many fibres this wide

would fit across 1 mm ?

C

slide30
Slide 30

Asbestos

slide32
Slide 32

Mystery fibre

slide34
Slide 34

Mystery fibre

slide36
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

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