Jewellery Alloys Research Articles

Jewellery-Related Properties Of Platinum

The performance of precious metal alloys can be usefully compared by the application of engineering design theory and heat flow properties on the small scale that is required for jewellery production. Some of the physical and mechanical properties of Platinum jewellery alloys differ sufficiently from typical gold and silver alloys to require modifications in the processing techniques, but these properties may allow for stronger slender designs. The thermal diffusivity of Platinum jewellery alloys is significantly lower than that of other precious metal jewellery alloys. This explains why laser welding is so efficient when used in making platinum jewellery and why it also allows most of the cold work hardening to be retained in components.

Silicon microsegregation in 14K yellow gold yellow gold

Phase equilibria have been used to construct a simplified model of 14 karat (14K) yellow jewelry alloys. In this model, silicon has a reduced solubility in solid 14K (Au-Cu-Ag-Zn) alloys compared to its solubility in pure copper. This reduced solubility results in low values of the partition coefficient for silicon in these alloys. The microsegregation of silicon in 14K yellow gold jewelry casting alloys was evaluated based on the principles of non-equilibrium solidification. The dynamics of non-equilibrium freezing described by the Gulliver-Scheil equation predict the build-up of silicon in the liquid phase to such an extent that unexpected, silicon-rich phases and compounds may appear in the solidification structure. These phases can have deleterious effects on mechanical properties and limit the use of certain types of grain refiners in (Au-Cu-Ag-Zn) families of alloys. The practical limits of silicon levels in 14K yellow gold alloys which do not allow the formation of Cu-Si intermetallics are estimated.

Properties of melt and thermal processes during solidification in jewellery casting

A survey is made of the significant thermal properties pertaining to liquid and solidifying jewellery alloys, and some properties of the investment are also considered. Values found in the literature, or measured in our own investigations are used together with estimates. A relatively simple model for solidification is presented. Some parameters such as volume/surface area ratio, superheat and solidification temperature are discussed. The solidification behaviour of a simplified ring is investigated in more detail using the model. In addition, some observations were made whilst casting spirals.

Metal release from gold-containing jewelry materials: no gold release detected.

Metal release from 13 different gold-containing jewelry alloys stored for 1 and 3 weeks in artificial sweat was analysed. For chemical analysis, inductively-coupled plasma detection (ICP) and atomic absorption spectrophotometry (AA), with flame and with furnace, were used. No release of gold was detected. It is unlikely that skin contact with gold-containing metallic items such as jewelry is responsible for inducing contact allergy to gold or allergic contact dermatitis due to the gold. The patch-test reactivity to gold sodium thiosulfate needs to be explained by some other mechanism(s).

Gold and gold alloy reference materials for XRF analysis

A method for the production of a series of certified gold reference materials is presented. These reference materials are intended for use in the analysis of the elemental composiortion of gold alloys using a nondestructive X-Ray Florescence (XRF) spectrometry method. The chemical composition of the reference materials covers the complete range of conventional coloured and white carat gold jewellery alloys. The XRF method based on this series of reference materials produces analytical results which are comparable with those obtained when using traditional chemical methods of analysis.

Thermal and microchemical characterisations of CaSO 4–SiO 2 investment materials for casting jewellery alloys

Differential thermal analysis (DTA) and thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were used to study the thermal decomposition of calcium sulphate in the CaSO 4 (25 wt%)-bonded silica investment which is the commonly used material for casting jewellery gold-based alloys. The thermal decomposition of CaSO 4 generates sulphur dioxide, leads to gas porosity in the molten gold-based alloys and therefore, defective jewellery products. This latter reaction was studied as a function of the temperature and atmosphere (air, argon and argon-5% hydrogen), in order to simulate, as for as possible, different casting conditions used by the jewellery industry. Furthermore, special attention was given to the effect of the presence of ZnO, Cu 2O, CuO and Ag 2O on the thermal decomposition of CaSO 4. DTG-TG results confirmed that the temperature of the thermal decomposition of CaSO 4 bonded with silica was lower with respect to the nearly pure CaSO 4. Unfortunately, it was very close to the casting temperature of some typical gold alloys. In addition, the temperature of the decomposition was further lowered when inert and reducing atmospheres are used, as well as in the presence of ZnO, Cu 2O, CuO and Ag 2O.

Precise coulometric titration of precious metals III. Determination of gold (III) with electrogenerated chlorocuprous ion in KCl-Cu-EDTA buffer medium

A method for the precise coulometric titration of gold (III) with electrogenerated chlorocuprous ion in KCl-Cu-EDTA buffer medium is described. 7.45–16.8 mg of gold can be determined with potentiometric end-point detection (RSD = 0.04%). The method is applied to precise analysis of gold in pure gold, jewellery and gold alloys with good selectivity. The mechanism of electron exchange at the gold-plated platinum cathode-electrolyte interface during the process of titration and the reversibility of the electrode in the proposed electrolyte are discussed.

Robotized ICP—Laboratory for the analysis of precious metals

A highly automated system, based on inductively coupled plasma (ICP) optical emission spectrometry of aqueous solutions, has been developed for the analysis of precious metals. The system, designated ICP-SIM-ROB, is designed around an ICP simultaneous spectrometer, supported by auxiliary equipment ranging from robot units for the preparation and handling of the sample and reference solutions to a facility for producing machine-readable labels. Under the control of its main computer, the system can be set up for unattended operation and it is even possible for analysis to be initiated on a ‘self-service’ basis by users not familiar with the detailed operation of the equipment. The modular design enables hardware and software components of the system to be added to or updated in line with evolving requirements and progress in technology. The system is capable of determining the fineness of gold jewellery alloys with the same precision as the manual ISO standard method.

Spangold: a new aura for intermetallics

Abstract Intermetallic compounds with unusual properties form the basis of a novel family of jewellery alloys. Drawing on fields in materials science as diverse as the study of solid state transformations, colour in metals and shape memory, Spangold represents an innovative departure from classical design materials, and gives impetus to the wider exploitation of intermetallic compounds as functional materials.

Diffusion soldering

Diffusion soldering is a hybrid of diffusion bonding and soldering. The principle of the process is to run a minute volume of solder into a joint between components that are pressed together and to solidify the solder by conversion to high melting point phases through isothermal reaction with the substrates. Thereafter the joint will not remelt unless heated to the temperature at which the high melting point phases melt. Tin can be used to make diffusion soldered joints between components of pure gold.The objctive of the present study was to evaluate tin as a diffusion solder for joining items of 18 carat golds, representative of alloys widely used in the fabrication of jewellery. The permissible range of the process parameters have been identified and a process specification has been developed. Joints can be made by heating to 450°C, which is substantially lower than the temperature needed for brazing of jewellery using conventional carat filler alloys. The resulting joints are colour matched and have mechanical properties that are likely to be adequate for jewellery applications. Diffusion soldering with tin has also been applied successfully to join 22 carat jewellery and the new jewellery alloy of 990 gold.

Determination of gold in gold jewellery alloys by ICP spectrometry

As a result of recent research and development work supported by World Gold Council, Inductively Coupled Plasma Spectrometry (ICP) is rapidly emerging as a serious and viable alternative to the centuries-old cupellation or fire assay method for the determination of gold in gold jewellery alloys.

Potentiometric determination of silver(I), palladium(II) and gold(III) in mixtures by use of an iodide-selective electrode

Two procedures are proposed for the potentiometric determination of Ag(I), Pd(II) and Au(III) in binary mixtures, by titration with potassium iodide solution, and use of a commercial iodide electrode as sensor. In the first procedure, two aliquots of the mixture are titrated, at pH 2.0 ± 0.2 and 9.0 ± 0.2, adjusted with dilute sulphuric acid and ammonia solution. At pH 2.0, the titrant reacts with both metals, whereas at pH 9.0, Ag(I) is the only reactant. The second procedure utilizes titration of two aliquots of the mixture in the presence and absence of a selective masking agent. The methods have been applied to the determination of these metals in some jewellery alloys.

The development of 990 gold — titanium: Its production, use and properties

Pure gold with only one per cent of titanium may well be the only significantly different new jewellery and coinage alloy developed in recent times. In this paper, an account is given of the development of a 990 fineness gold alloy with good colour, durability and mechanical properties, and why titanium was chosen as the alloying metal. Methods are described for the alloy’s production, solutionizing and age-hardening. Mechanical properties are given as a function of deformation, age-hardening time and temperature for three different starting states. These properties are compared with those of some standard 14 and 18 carat jewellery alloys and pure gold.

Polishing compound residues in gold jewellery alloys

The assaying of gold jewellery before hallmarking is generally carried out on samples scraped from the surface. But the assay result may not necessarily be representative of the bulk composition. Analyses reported here have shown the presence of polishing compound residues on, and just below, the surface of some of the jewellery tested.

Symposium on Jewellery Manufacturing Technology, Santa Fe, USA

Symposium on Jewellery Manufacturing Technology, Santa Fe, USA

Corrosion behavior of nickel-containing alloys in artificial sweat.

The corrosion resistance of various nickel-containing alloys was measured in artificial sweat (perspiration) using the Tafel extrapolation method. It was found that Ni, CuNi 25 (coin alloy), NiAl (colored intermetallic compounds), WC + Ni (hard metal), white gold (jewelry alloy), FN42 and Nilo Alby K (controlled expansion alloys), and NiP (electroless nickel coating) are in an active state and dissolve readily in oxygenated artificial sweat. By contrast, austenitic stainless steels, TiC + Mo2C + Ni (hard metal), NiTi (shape-memory alloy), Hastelloy X (superalloy), Phydur (precipitation hardening alloy), PdNi and SnNi (nickel-containing coatings) are in a passive state but may pit under certain conditions. Cobalt, Cr, Ti, and some of their alloys were also investigated for the purpose of comparison. Cobalt and its alloys have poor corrosion resistance except for Stellite 20. Chromium and high-chromium ferritic stainless steels have a high pitting potential but the latter are susceptible to crevice corrosion. Ti has a pitting potential greater than 3 V. Comparison between the in vitro measurements of the corrosion rate of nickel-based alloys and the clinical observation of the occurrence of contact dermatitis is discussed.

The wear of precious jewellery

Scratch and polishing tests have been carried out on a series of platinum and 18 carat gold jewellery alloys, and used platinum and 18 carat gold rings were examined. The mechanism by which the aesthetic appearance of precious jewellery items deteriorates in service is considered. It is concluded that from the point of view of maintaining the appearance of highly specularly reflecting surfaces during use, the surface hardness and the behaviour on mechanical polishing of a precious jewellery alloy are important.

Oxidation behaviour of some platinum and gold jewellery alloys at 150°C

Etude experimentale par spectrometrie d'electron Auger de l'oxydation de quatre alliages de platine et de deux alliages d'or chauffes a 150°C pendant 24 h dans une atmosphere a 100% d'oxygene

Prochlorperazine bismethanesulfonate as a new reagent for the spectrophotometric determination of palladium

A simple, rapid, and selective method for the determination of palladium is described. The orange-red palladium(II)-prochlorperazine bismethanesulfonate complex in the presence of hydrochloric acid-sodium acetate buffer exhibits maximum absorbance at 480 nm with a molar absorptivity of 4.32 × 10 3 liters mol −1 cm −1. The sensitivity of the reaction is 24.62 ng cm −2. The system obeys Beer's law over the concentration range 0.4–20 ppm of palladium with an optimum concentration range of 1–19 ppm. The apparent stability constant of the complex is found to be log K = 5.3 ± 0.1 at 27 °C. The effects of pH, time, temperature, order of addition of reactants, reagent concentration, and interferences from various ions are reported. The proposed method offers the opportunity to carry out the determination at room temperature without the need for an extraction step. The method is also found to be suitable for the determination of palladium in jewelry alloy.

Grain-refined recrystallized 14-carat gold alloy

Prevention of excessive grain growth during annealing treatments is important for jewellery applications of gold alloys. The beneficial effects of small amounts of a number of metals of high melting points and low solubilities in gold to dental gold alloys are well known. Some of these elements, and others, have been added singly or in combinations, to a 14-carat gold jewellery alloy and their effects on grain size, on recrystallization, and on the formation of ‘orange peel’ during subsequent cold working have been studied. Possible mechanisms by which grain refining during solidification and annealing is brought about by small additions of certain elements are discussed in the light of the data obtained.