Paper Title:

Crystallography of Natural and Synthetic Gold Alloy Microstructures

Periodical Materials Science Forum (Volume 753)
Main Theme Recrystallization and Grain Growth V
Chapter Chapter 7: Related Phenomena
Edited by Matthew Barnett
Pages 477-480
DOI 10.4028/www.scientific.net/MSF.753.477
Citation Angela Halfpenny et al., 2013, Materials Science Forum, 753, 477
Online since March 2013
Authors Angela Halfpenny, Robert Hough, Michael Nugus
Keywords Alloy, Broad Ion-Beam Polishing (BIBP), CSL, Electron Backscatter Diffraction (EBSD), Gold, Microstructure, Static Grain Growth, Twin
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To improve our understanding of the mechanisms of gold deposition, a comparison was made of the microstructures of a natural gold sample with a synthetic gold foil of similar alloy composition (approximately Au 90%, Ag 10%). The aim was to identify any similarities between the samples that could help increase our knowledge of how the natural gold microstructures formed and were modified post-mineralisation. The samples were analysed using electron backscatter diffraction to map their microstructure, with the synthetic gold foil then heated to and mapped at 400°C, 500°C, 600°C and 700°C. Both the natural and synthetic sample exhibited a dominance of ∑3 twin boundaries, but these were much less abundant in the synthetic sample prior to heating. The natural sample is dominated by coarse grains exhibiting lattice distortion and low angle grain boundaries, which more closely resemble the synthetic gold foil microstructure after recrystallisation has taken place, than the initial microstructure, implying that the grains have had time to grow. Performing experiments such as these allows direct comparison of gold microstructures where the formation conditions are known and the controlling mechanisms can be determined. This will improve our understanding of the important mechanisms behind gold deposition.