Characterisation of Electroplated Gold Coatings for Dental Applications: Estimation of Thickness Using Non-Destructive Electron-Probe Microanalysis Related to Plating Time

Objectives: This study aimed to measure non-destructively gold (Au) electrodeposited on a high-gold alloy by modulating coating time and comparing this to sputtering Au to known thicknesses. Methods: Au was electrodeposited (plated) on 11 high-gold alloy plates (A–K) at 2.8V between 20 and 220 min. Seven Au strips were sputter coated on the same alloy to known thicknesses (range 50–500 nm). Energy dispersive X-ray spectroscopy (EDS) was used to measure minimal electron energy (E0) required to penetrate Au coatings and generate x-ray signals of 1% atomic palladium (Pd) from the underlying alloy for test samples and Au strips. % Pd X-ray concentration at maximum 30 kV was also obtained. The obtained signal–thickness relationship of known Au strip thicknesses was used to calculate Au thickness on the A–K samples based on two analytical relations. Energy dispersive X-ray fluorescence spectroscopy (XRF) was used as a complementary method to ensure coating thickness estimations were accurate. Results: EDS values for all reference and unknown thicknesses were obtained and verified with XRF. Correlating these signals with the Data Analysis Software and matching with known plating times allowed estimation of Au thickness of the unknown samples (range 27–425 nm). Estimated thicknesses were shown to have a linear relationship with plating time except for samples C–D, where there was an inverted relationship. Significance: A non-destructive method for measuring electrodeposited thickness of Au on high-gold alloys related to plating time was developed and verified. There is a linear relationship to Au thickness and plating time between 20 and 220 min.

Evaluation of the contributions of gold derived from hypogene, supergene and surficial processes in the formation of placer gold deposits

Placer gold particles have traditionally been considered as either detrital products of weathering or authigenic minerals growing within placers. Recent advances in understanding of gold chemistry/bio-geochemistry demonstrate that gold growth in specific environments is plausible, but opinions differ on the importance of ‘new’ gold in the overall placer inventory. Here we draw upon visual inspection over 40,000 polished gold particle sections from locations worldwide to evaluate the implications of gold alloy composition and particle heterogeneity in determining the contributions of detrital and authigenic gold to fluvial placers. We conclude i. the detrital model of placer gold formation is widespread and demonstrable, ii. supergene gold may be a locally important constituent of fluvial placers, iii. gold-rich rims on placer gold particles comprise two distinct components: a surface micron-scale addition of pure Au and a tens- of- micron- scale inner rim formed by Ag depletion, iv. the importance to placer inventories of gold particle formation and modification by biogenic processes is considerably overstated.

A new kind of invisible gold in pyrite hosted in deformation-related dislocations

Mining of “invisible gold” associated with sulfides in gold ores represents a significant proportion of gold production worldwide. Gold hosted in sulfide minerals has been proposed to be structurally bound in the crystal lattice as a sulfide-gold alloy and/or to occur as discrete metallic nanoparticles. Using a combination of microstructural quantification and nanoscale geochemical analyses on a pyrite crystal from an orogenic gold deposit, we show that dislocations hosted in a deformation low-angle boundary can be enriched in Ni, Cu, As, Pb, Sb, Bi, and Au. The cumulative trace-element enrichment in the dislocations is 3.2 at% higher compared to the bulk crystal. We propose that trace elements were segregated during the migration of the dislocation following the dislocation-impurity pair model. The gold hosted in nanoscale dislocations represents a new style of invisible gold.

Mapping Spatial Distribution of Pores in an Additively Manufactured Gold Alloy Using Neutron Microtomography

A crucial criterion for the quality of the additively manufactured parts is the porosity content for achieving an acceptable final relative density. In addition, for jewelry applications, visible pores are unacceptable at or in the vicinity of the surface. In this study, non-destructive 3D neutron microtomography is applied to map the spatial distribution of pores in additively manufactured red-gold samples. The 3D imaging assessment underlines the high relative density of the printed red-gold sample and indicates residual pore sizes are predominantly below the limit of concern for jewelry applications. The 3D maps of pores within printed samples highlight the effect of the scanning strategy on the final quality and location of pores in the printed samples. These results confirm that neutron microtomography is a novel and precise tool to characterize residual porosity in additively manufactured gold alloys and other higher-Z materials where such investigation using other non-destructive methods (such as X-rays) is challenging due to the limited penetration depth.

Facile synthesis of silver/gold alloy nanoparticles for ultra-sensitive rhodamine B detection

The synthesis of Ag/Au nanoparticles (NPs) in a controlled manner has been a challenge for a long time.