Chapter 12 Additional Analytical Methods

Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction Light microscopy General surveys Features larger than 1μm Transmitted Transparent minerals Petrographic microscope – light from below sample Non ReflectedOpaque minerals (ore minerals) Petrographic microscope – light from above sample Non Diffraction Further identification, lattice parameters and crystal structure X-Ray Powders of single minerals or mixtures (heavy atom position) X-Ray beam scattered at differing intensities at different angles Semi Neutron Powders of single minerals or mixtures (light atom position) Neutron beam scattered at differing intensities at different angles Semi Particle Microscopy High resolution imaging Features 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 area Non 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

Analytical Methods Technique Type Technique application Subdivisions Specific application DescriptionDestruction Chemical Analysis Accurate 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

Analytical Methods Technique Type Technique application Subdivision s Specific application Description Destructi 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

Chapter 13 Mechanical properties and deformation

Stress-strain Mechanical properties – expression of history of crystal Mechanical properties – expression of history of crystal Definitions: Definitions: Stress (σ)Stress (σ) Force per surface area Force per surface area Strain (ε)Strain (ε) Deformation resulting from the stress Deformation resulting from the stress DeformationDeformation Elastic Elastic When stress removed strain returns to original valueWhen stress removed strain returns to original value Plastic or ductile Plastic or ductile Active dislocations cause permanent changes in structure and shape, but material stays in tactActive dislocations cause permanent changes in structure and shape, but material stays in tact Work-hardening Work-hardening Stress needed for creating increasing strain increase rapidly as multiplying dislocations interfere with each otherStress needed for creating increasing strain increase rapidly as multiplying dislocations interfere with each other Brittle (Failing) Brittle (Failing) Material has reach its ultimate strength and fractures completelyMaterial has reach its ultimate strength and fractures completely

Deformation Stress applied to crystal Stress applied to crystal Deforms crystal on crystallographic slip planes (hkl) with displacements along crystallographic slip directions [uvw] 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 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

Deformation Fig 13.2; 13.3; 13.4 Fig 13.2; 13.3; 13.4

Dislocation microstructures Present in most crystals even at ideal growth conditions Present in most crystals even at ideal growth conditions Number of dislocations generally increase with deformation Number of dislocations generally increase with deformation Development and propagation of dislocations are influenced by each other or other obstacles such as inclusions Development and propagation of dislocations are influenced by each other or other obstacles such as inclusions Loops, diffusion of vacancies (climb) Loops, diffusion of vacancies (climb)

Dislocation microstructures Loops Loops Fig. 13.6, 13.7 Fig. 13.6, 13.7

Dislocation microstructures Diffusion of vacancies (climb) Diffusion of vacancies (climb) Fig. 13.8, 13.9 Fig. 13.8, 13.9

Mechanical twinning A mechanical stress cause part of crystal to flip into new orientation about a plane A mechanical stress cause part of crystal to flip into new orientation about a plane New orientation related to old orientation by mirror plane New orientation related to old orientation by mirror plane Thus: Geometric twinning relationship Thus: Geometric twinning relationship Fixed small sized deformation unlike slip which is a continuous arbitrary deformation and can be large Fixed small sized deformation unlike slip which is a continuous arbitrary deformation and can be large

Mechanical twinning Fig 13.10, Fig 13.10, 13.11