Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application...

13
Chapter 12 Additional Analytical Methods

Transcript of Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application...

Page 1: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Chapter 12

Additional Analytical Methods

Page 2: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Analytical MethodsTechnique

TypeTechnique application

SubdivisionsSpecific

applicationDescription Destruction

Light microscopyGeneral surveys

Features larger than 1μm

TransmittedTransparent

mineralsPetrographic microscope –

light from below sampleNon

Reflected Opaque minerals (ore minerals)

Petrographic microscope – light from above sample

Non

DiffractionFurther identification,

lattice parameters and crystal structure

X-RayPowders of single

minerals or mixtures (heavy atom

position)

X-Ray beam scattered at differing intensities at different

anglesSemi

NeutronPowders of single

minerals or mixtures (light atom position)

Neutron beam scattered at differing intensities at different

anglesSemi

Particle Microscopy

High resolution imagingFeatures smaller than

1μm

Transmission Electron Microscopy

Images of structural defects: dislocations,

twin and phase boundaries

Accelerated (high voltage)electron beam deeply penetrates small area

Non

Scanning Electron Microscopy

Image sample morphology and

determine compositional

variations

Accelerated (low voltage)electron beam shallowly

penetrates large areaNon

Atomic Force Microscopy

Image arrangement of individual atoms in

surface of crystals

Measure electrostatic repulsion intensity of atoms in sample in close contact with atoms of a

crystal tip

Non

Page 3: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Analytical Methods

Technique Type

Technique application

SubdivisionsSpecific

applicationDescription Destruction

Chemical AnalysisAccurate chemical

compositions of minerals

Microprobe

Quantitative point analyses in polished sections; mostly only

Na and higher

Accelerated electron beam with two detectors: energy

dispersion and x-ray detector compared with standard

Non

X-Ray Fluorescence

Quantitative analyses of rock in

powder; gives chemical elements –

major and trace

High-energy polychromatic X-ray beam produces secondary fluorescent X-rays which are analysed for wavelength and

energy

Semi

Optical emission & absorption

Mostly for liquid sample quantitative chemical analyses

Light beam excite or absorb valence electrons from sample;

secondary beams dispersed into separate wavelengths of

measurable intensities

Complete

Mass spectrometry

Measure amounts of different isotopes - mainly radiometric

dating and determination of stable isotopes

Ionization of atoms, ions accelerated and into magnetic

field which deflects ions – degree of deflection dependant

on ion mass and charge

Complete

Page 4: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Analytical MethodsTechnique

TypeTechnique application

Subdivisions

Specific application

DescriptionDestructi

on

Spectroscopy Investigate structural

environments

Infrared & Raman

Information on symmetry, bond

lengths and angles,

coordination polyhedra

IR radiation or laser beam passed through sample

and intensity of light measured. Absorption of

light corresponds to energy differences of

vibrational levels in the crystal

Non

X-Ray absorption

Compositional edges in mineral

grains

Measure the difference in absorption of X-rays

relative to the intensity of the rays

Non

Nuclear magnetic resonance

Determine the occupancy of an

element in different

structural sites

Nuclei of atoms in mineral spin to cause magnetic

field which is placed inside a large magnetic field.

Magnetic resonance when applied field = energy

difference in spin levels. Specific for different

chemical and crystallographic environments

Non

Page 5: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Chapter 13

Mechanical properties and deformation

Page 6: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Stress-strain Mechanical properties – expression of history of crystal Definitions:

• Stress (σ) Force per surface area

• Strain (ε) Deformation resulting from the stress

• Deformation Elastic

• When stress removed strain returns to original value Plastic or ductile

• Active dislocations cause permanent changes in structure and shape, but material stays in tact

Work-hardening• Stress needed for creating increasing strain increase rapidly as

multiplying dislocations interfere with each other Brittle (Failing)

• Material has reach its ultimate strength and fractures completely

Page 7: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Deformation

Stress applied to crystal Deforms crystal on crystallographic

slip planes (hkl) with displacements along crystallographic slip directions [uvw]

Slip is not instantaneous but propagate along this slip plane, breaking one bond at a time but resulting in a complete displacement of the two parts of the crystal

Page 8: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Deformation

Fig 13.2; 13.3; 13.4

Page 9: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Dislocation microstructures

Present in most crystals even at ideal growth conditions

Number of dislocations generally increase with deformation

Development and propagation of dislocations are influenced by each other or other obstacles such as inclusions

Loops, diffusion of vacancies (climb)

Page 10: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Dislocation microstructures

Loops Fig. 13.6, 13.7

Page 11: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Dislocation microstructures

►Diffusion of vacancies (climb)

►Fig. 13.8, 13.9

Page 12: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Mechanical twinning

A mechanical stress cause part of crystal to flip into new orientation about a plane

New orientation related to old orientation by mirror plane

Thus: Geometric twinning relationship

Fixed small sized deformation unlike slip which is a continuous arbitrary deformation and can be large

Page 13: Chapter 12 Additional Analytical Methods. Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction.

Mechanical twinning

Fig 13.10, 13.11