• Resources Recycling
• /
• v.10 no.1
• /
• pp.42-48
• /
• 2001

The dissolution behavior of gold and silver from gold-silver alloys in aerated cyanide solutions has been investigated by an electrochemical means as well as a direct measurement of gold and silver ions reported in the bulk solution as a function of time using rotating disc electrodes. The variables studied included oxygen partial pressure, rotating speed of the disc, concentration of cyanide, temperature and composition of the allyos. The dissolution potential and the rate of dissolution were obtained in view of the anodic and cathodic current-potential relationships. The results were discussed in terms of the mixed potential theory. The results showed that the dissolution rate of gold and silver from the alloys was controlled partially by chemical reaction. but largely by transport of either oxygen or cyanide, depending on their relative concentration under the experimental conditions employed in this study.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.5
• /
• pp.1547-1551
• /
• 2010

We newly propose the silver alloys of Ag-5wt%Ge-2.5wt%Cu(Ge1) and Ag-5wt%In-2.5wt%(In1) to overcome the tarnish and mechanically weak problems of the conventional sterling silver Ag-7.5wt%Cu (Cu1). We check the castability, surface color stability during process and wearing, and work hardening with plastic deformation of all three silver alloys. Our newly proposed silver alloys of Ge1 and In1 showed improved castability, anti-tarnish stability, and work hardening property compared to the conventional sterling silver, which implied that these alloys might be more appropriate for the high-end silver jewelry.

• The Journal of Korean Academy of Prosthodontics
• /
• v.21 no.1
• /
• pp.9-26
• /
• 1983

In order to investigate the biocompatibility of silver-palladium alloys, gingival fibroblast was obtained from a healthy human gingival and cultured in MEM medium with the addition of silverpalladium alloys. Four different mixture of silver-palladium alloys comprising of Ag-Pd-Au, Ag-Pd-In and Ag-Sn were tested. Results were assessed by calculating the cell multiplication rate per millimeter of medium and morphological changes in cells were also observed and noted.The obtained results were as follows; 1. Ag-Pd-Au alloy was indicated to be most biocompatible with gingival fibroblast. Also there was a decrease in cytotoxicity of the alloy as the concentration of gold increased. 2. Ag-Pd alloy showed a decrease in cell multiplication rate as compared to Ag-Pd~Au alloy. 3. Silver-palladium alloy supplemented with Indium increased the cell multiplication rate. 4. Among the alloys tested, Ag-Sn alloy was indicated to be the most cytotoxic and the least biocompatible with human gingival fibroblast.

• Korean Journal of Materials Research
• /
• v.25 no.2
• /
• pp.90-94
• /
• 2015

We prepared 8 samples of non-silver and silver-added master alloys containing silicon to confirm the existence of nickel-silicides. We then prepared products made of 14K and 18K white gold by using the prepared master alloys containing 0.25, 0.35, and 0.50 wt% silicon to check for nickel release. We then employed the EN 1811 testing standard to investigate the nickel release of the white gold products, and we also confirmed the color of the white gold products with an UV-VIS-NIR-color meter. We observed $NiSi_x$ residue in all master alloys containing more than 0.50 wt% Si with EDS-nitric acid etching. For the white gold products, we could not confirm the existence of $NiSi_x$ through XRD after aqua-regia etching. In the EN 1811 test, only the white gold products with 0.25 wt% silicon master alloys successfully passed the nickel release regulations. Moreover, we confirmed that our white gold products showed excellent Lab indices as compared to those of commercial white gold ones, and the silver-added master alloys offered a larger L index. Our results indicate that employing 0.25 wt% silicon master alloys might be suitable for white gold products without nickel-silicide defects and nickel release problems.

• Journal of the Korean Society for Heat Treatment
• /
• v.24 no.5
• /
• pp.243-250
• /
• 2011

When alloys are vacuum-deposited on cooled substrates, super-rapidly cooled alloy films in the unequilibrium state can be obtained. As an application of this method, Ag-Cu, Ag-Ni and Ag-C alloys were successfully produced, and their mechanical properties with tempering temperature were investigated. The following results were obtained : (1) In case of Ag-Cu alloys, the solid solution was hardened by tempering at $150^{\circ}C$. The hardening is considered to occur when the solid solution begins to decompose into ${\alpha}$ and ${\beta}$ phases. The Knoop hardness number of a 40 at.%Ag-Cu alloy film deposited on a cooled glass substrate was 390 $kg/mm^2$. The as-deposited films were generally very hard but fractured under stresses below their elastic limits. (2) In case of Ag-Ni and Ag-C alloys, after the tempering of 4 at.%Ni-Ag alloy at $400^{\circ}C$ and of 1 and 2 at.%C-Ag alloys at $200^{\circ}C$, they were hardened by the precipitation of fine nickel and carbon particles. The linear relationship between proof stress vs. $(grain\;diameter)^{-l/2}$ for bulk silver polycrystals can be applied to vacuum-deposited films up to about 0.1 ${\mu}m$ grain diameter, but the proof stress of ultra-fine grained silver with grain diameters of less than 0.1 ${\mu}m$ was smaller than the value expected from the Petch's relation.

• Bulletin of the Korean Chemical Society
• /
• v.16 no.4
• /
• pp.321-325
• /
• 1995

Adsorption mechanisms of diisobutyl dithiophosphinate (DIBDTPI) and diisobutyl monothiophosphinate (DIBMTPI) on gold and gold-silver alloys (80:20 and 50:50) have been studied. The adsorption mechanisms on gold-silver alloys can be explained by the EC mechanism involving an electron transfer step and a chemical reaction step. Thus, the adsorption should be controlled by the E of the electrochemical oxidation of the electrode involved and the pK of the metal collector complex. Both di- and mono- thiophosphinate adsorb on 50:50 Au-Ag alloy at lower potential than on 80:20 Au-Ag alloy surface. There are no significant differences between the reactivities of DIBDTPI and DIBMTPI with precious metals except that the dithio- compound can be oxidized to dimer on gold at high potentials, while the monothio- homologue cannot. In this regard, DIBDTPI may be a better surface active reagent for pure gold than DIBMTPI.

• Corrosion Science and Technology
• /
• v.4 no.1
• /
• pp.19-22
• /
• 2005

Two Au-Ag-Cu-Pd dental casting alloys (Au:12% and 20%) used. The test solutions used 0.9 % NaCl solution (isotonic sodium chloride solution), 0.9 % NaCl solution containing 1 % lactic acid, and 0.9 % NaCl solution containing 1 % lactic acid and 0.1 mol $dm^{-3}$ $Na_2S$. The surface of two samples in three sample solutions was not natural discoloration during one year. The alloy containing 12 % gold was easily alloyed and the composition was uniform comparing with the alloy containing 20 % gold. The rest potentials have not a little effect after three months. The kinds of metals could not definitely from the oxidation and reduction waves of metal on the cyclic voltammograms. The dissolutions of gold and palladium were 12 % Au sample in the 0.9 % NaCl solution containing 1 % lactic acid and 0.1 mol $dm^{-3}$ $Na_{2}S$. The pH of solution had an affect on dissolution of copper, and sulfur ion had an affect on dissolution of silver. The copper dissolved amount from 20 % gold sample was about 26 times comparing with that of 12 % gold sample in the 0.9 % solution containing 1 % lactic acid. Corrosion products were silver chloride and copper chloride in NaCl solution, and silver sulfide and copper sulfide in NaCl solution containing $Na_{2}S$.

• The Journal of the Korean dental association
• /
• v.20 no.12 s.163
• /
• pp.1073-1081
• /
• 1982

The purpose of this study was to measure and compare the tensile strengths, elongation and Vicker's hardness values by heat treatments of three·commercial dental casting gold-silver-palladium alloys(Type A,B and G-50 alloys) used in Korea. Instron universal testing instrument and Vicker's hardness tester were used to determine their physical properties. The following results were obtained with the alloys tested. 1. It was determined that the tensile strengths generally tended to increase as the hardened condition (55.50 - 72.98 Kg/mm₂)than in softened condition (28.75 - 41.16 Kg/mm₂). 2. The results indicated that the elongation was the highest in the softened condition(12.30 - 27.0 %), and was the smallest in the hardened condition (3.6 - 5.8 %). 3. It was found that the Vicker's hardness number was the greatest in type G-50 hardened alloys (304.0), and the smallest in the type A softened alloys (130.0).

• The Journal of Advanced Prosthodontics
• /
• v.6 no.5
• /
• pp.372-378
• /
• 2014

PURPOSE. The porcelain fused to gold has been widely used as a restoration both with the natural esthetics of the porcelain and durability and marginal fit of metal casting. However, recently, due to the continuous rise in the price of gold, an interest towards materials to replace gold alloy is getting higher. This study compared the bond strength of porcelain to millingable palladium-silver (Pd-Ag) alloy, with that of 3 conventionally used metal-ceramic alloys. MATERIALS AND METHODS. Four types of metal-ceramic alloys, castable nonprecious nickel-chrome alloy, castable precious metal alloys containing 83% and 32% of gold, and millingable Pd-Ag alloy were used to make metal specimens (n=40). And porcelain was applied on the center area of metal specimen. Three-point bending test was performed with universal testing machine. The bond strength data were analyzed with a one-way ANOVA and post hoc Scheffe's tests (${\alpha}=.05$). RESULTS. The 3-point bending test showed the strongest ($40.42{\pm}5.72$ MPa) metal-ceramic bond in the nonprecious Ni-Cr alloy, followed by millingable Pd-Ag alloy ($37.71{\pm}2.46$ MPa), precious metal alloy containing 83% of gold ($35.89{\pm}1.93$ MPa), and precious metal alloy containing 32% of gold ($34.59{\pm}2.63$ MPa). Nonprecious Ni-Cr alloy and precious metal alloy containing 32% of gold showed significant difference (P<.05). CONCLUSION. The type of metal-ceramic alloys affects the bond strength of porcelain. Every metal-ceramic alloy used in this study showed clinically applicable bond strength with porcelain (25 MPa).

• Corrosion Science and Technology
• /
• v.7 no.3
• /
• pp.152-157
• /
• 2008

New wrought magnesium alloys have increasingly been developed in recent years for the automotive industry due to their high potential as structural materials for low density and high strength/weight ratio demands. However, their poor mechanical properties and low corrosion resistance have led to a search for new kinds of magnesium alloys with better strength, ductility, and high corrosion resistance. The main objective of this research is to investigate the corrosion behaviour of new magnesium alloys: Mg-Zn-Ag (ZQ), Mg-Zn-Mn-Si (ZSM) and Mg-Zn-Mn-Si-Ca (ZSMX). These ZQ6X, ZSM6X1, and ZSM651+YCa alloys were prepared using hot extrusion. AC, DC polarization and immersion tests were carried out on the extruded rods. Microstructure was examined using optical and electron microscopy (SEM) and EDS. The addition of silver decreased the corrosion resistance. The additions of silicon and calcium also affected the corrosion behaviour. These results can be explained by the effects of alloying elements on the microstructure of Mg-Zn alloys such as grain size and precipitates caused by the change in precipitation and recrystallisation behaviour.