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

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

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.107.1-107.1
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• 2012

Because of beautiful glossy and color, the value of gold leverage is very high in Europe. For improve the quality of white gold, we performed heat treatment on 14K white gold alloys at various age-hardening conditions. Age-hardening behavior and the related phase transformation changes were studied to elucidate the hardening mechanism of 14K white gold alloys. For solid solution treatment [ST], casted 14K white gold alloy specimens were treated at high temperature ($750^{\circ}C$) during 30 minute, and the specimens dropped to water for quenching immediately. For Age-hardening treatment [AT], the specimens were treated at various temperatures ($250^{\circ}C{\sim}300^{\circ}C$). After the heat treatment, we observed increased hardness from 144 Hv to 214 Hv by Vicker's hardness tester. Variation of the grain size measured by optical microscopy (OM) and scanning electron microscopy (SEM) images. By electron probe micro-analysis (EPMA) mapping analysis, we investigated that irregular particles were changed uniformly. After heat treatment, 14K white gold alloys showed improved hardness and became uniformity of grain size by age-hardening treatment.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.283-283
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• 2013

Because of beautiful glossy and color, the value of gold leverage is very high in Europe. To improve the quality of gold alloys, we performed heat treatment on 14 K white gold alloys by variously changing age-hardening conditions. Age-hardening behavior and the related phase transformation changes were studied to elucidate the hardening mechanism of 14 K white gold alloy. For solid solution treatment [ST], casted gold alloy specimens were treated at high temperature ($750^{\circ}C$) for 30 minutes, and the specimens dropped to water to quench them. For Age-hardening treatment [AT], the specimens were treated at various temperatures ($250{\sim}300^{\circ}C$). After the heat treatment, we observed the phenomenon to increase hardness from 126 Hv to 166 Hv by Vicker's hardness tester. Through electron probe micro-analysis (EPMA) mapping analysis, we investigated that irregular particles were changed uniformly. In the SEM and OM images, two phases of matrix and particle-likestructures were observed, and the precipitation of these elements from the matrix progressed during age-hardening. By transmission electron microscope and X-ray diffraction observation, it was revealed that the formation of the Au3Cu superstructure contributed to the age-hardening at $270^{\circ}C$ in the gold alloy. After the heat treatment, this analysis shows that casted gold alloys were to improve hardness and to moderate surface defects at specific temperatures and duration.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.4
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• pp.645-661
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• 1995

As the mechanical property of composite resin improved, composite resin has been widely used esthetic dentistry. In the field of esthetic dentistry, the color of prosthetic material is very important. The purpose of this study was to evaluate the color difference of specimens, by the types of alloys and gold electrodeposit. Experimental groups were as follows : Group Prec : Au-Pt alloy with no gold coating and no resin veneer. Group Semi : Pd-Ag alloy with no gold coating and no resin veneer. Group BAse : Ni-Cr alloy with no gold coating and no resin veneer. Group Gsem : Pd-Ag alloy with no gold coating and no resin veneer. Group Gbas : Ni-Cr alloy with no gold coating and no resin veneer. Group PreR : Resin veneer on the Pd-Ag alloy without gold coating. Group SemR : Resin veneer on the Pd-Ag alloy without gold coating. Group GbsR : Resin veneer on the Ni-Cr alloy with gold coating Group BasR : Resin veneer on the Ni-Cr alloy without gold coating. In this study, colors of metal surfaces and veneered resins were evaluated by the CIE $L^{*}a^{*}b$ system. The results obtained were as follows : 1. different alloy types and gold coating make the $L^{*}a^{*}b$ system. 2. The ${\Delta}E^*$ab value between groups semi and Base was less than 1.5 and there was no $a^*$ and $b^*$ value difference between groups Gsem and Gbas 3. The values of $L^*$ and $a^*$ ain groups GsemR and GbasR were so similar that the ${\Delta}E^*$ab value was as small as 0.58. 4. In resin specimens with gold coated semiprecious or base alloys showed yellower and redder deviation than the resin specimens with precious alloy. 5. The ${\Delta}E^*$ab values between goups PreR-GsemR and groups PreR-GbasR were as small as 2.68 and 2.22 respectively.

• The Journal of the Korean dental association
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• v.9 no.6
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• pp.293-296
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• 1971

Histochemical observations on the effect of gold alloys crown margin in the periodontal membrane were caried out by use of rabbits. The animal were setted with gold alloys crown on the incisor teeth. The cervical margins were given extence into gingival sockets. The animals were sacrificed at the 30 days experimented period. Specimens of tissue were obtained from the mandibular incisor teeth with jaw. All tissues were fixed immediately in 10% neutral formalin solution. Different histochemical staining methods for the determination of fibrous components were the Mallory-Heidenhain Bielschowsky-Gomori, Gomori's aldehyde fuchsin. Periodic acid-Schiff reaction and Hematoxylin eosin stanin method. The results were as follows. The periodontal membrane is composed primarily of collagenous fibers and fibrous component run functional arrangement but in lower gold content groups, horizontal fiber groups were irregularly run. Elastic fibers were obligue run in experimental groups. There were no significant differences in reticularfibers in distribution.

• Journal of Technologic Dentistry
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• v.28 no.1
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• pp.27-41
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• 2006

The physical property and phase transformation in a commercial dental casting high gold alloy was investigated as a function of ageing temperature and time using microvickers hardness tester, X-ray diffraction, optical and electron microscopy and EPMA analyser. 1. With increasing ageing time, the hardness of solution-treated gold alloys increased slowly at the initial stage of ageing treatment at an ageing temperature of $300{\sim}400^{\circ}C$, and it reached a maximum value of hardness at the medium stage. Finally, it decreased gradually during further ageing. The maximum value of hardness at was similar with that of the conventional materials and suitable for using as the crown & bridge. 2. During isothermal ageing at a temperature range of $300{\sim}400^{\circ}C$, three phases consisting of the Au-rich ${\alpha}_1$phase with a face-centered cubic structure, the Pt3Zn ${\alpha}_2$phase with an ordered AuCu3(L12) type(f.c.c.) and the Pt-rich ${\alpha}_3$phase with face-centered cubic structure in solution-treated gold alloys were transformed into different three phases consisting of the ${\alpha}_1$phase, the ${\alpha}_3$phase and the PtZn $\beta$phase with an ordered AuCu I(L10) type. 3. The hardening of gold alloys was attributed to the lattice strains of the matrix resulting from the transformation of the ${\alpha}_2$phase to the $\beta$phase. 4. The softening of gold alloys during over-ageing was attributed to the coarsening of the nodules consisting of the $\beta$phase and ${\alpha}_1$matrix.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.3
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• pp.475-488
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• 1996

The opaque porcelain layer of porcelain-fused-to-metal(PFM) restoration is critical for the success of PFM restoration because it is the first layer placed over the treated alloy. But, the methods of opaquing technique have not been confirmed. Usually, the one layer method and two layer method have been used for the application of opaque porcelain. In the past, alloys with porcelain veneers which have been used successfully have contained various precious metals. Recent increase in the cost of precious metals stimulates considerable interest in nonprecious alloys. Although nickel-chromium alloys and nickel-chromium-beryllium alloys have been widely used, the use of cobalt-chromium alloys would be gradually increased with elimination of any potential risk of nickel-related allergic responses and/or beryllium-related toxic responses. This investigation examined one- and two-layer opaque porcelain applications to determine the effect on the bond strength of titanium added cobalt-chromium metal ceramic alloy. Bond strength of Ceramco II porcelain to titanium added cobalt-chromium alloy(2Dentitan) and gold-platinum-palladium alloy(Degudent H) were evaluated by direct shear bond strength test with Instron universal testing machine. The results were as follows; 1. When the mean shear bond strength of each experimental group were compared in $0.25cm^2$ unit area, the titanium added cobalt-chromium alloy/two layer method exhibited the greatest strength(79.7kg), followed by titanium added cobalt-chromium alloy/one layer method(76.2kg), gold-platinum-palladium alloy/two layer method(71.4kg), gold-platinum-palladium alloy/one layer method(64.2kg). 2. No significant differences in bond strength were recorded between the two opaquing techniques for gold-platinum-palladium alloy and titanium added cobalt-chromium alloy. 3. No significant differences in bond strength were recorded between the gold-platinum-palladium alloy and the titanium added cobalt-chromium alloy.

• Korean Journal of Materials Research
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• v.28 no.2
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• pp.89-94
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• 2018

The properties of 18 K red gold solder alloys were investigated by changing the content of In up to 10.0 wt% in order to replace the hazardous Cd element. Cupellation and energy dispersive X-ray spectroscopy (EDS) were used to check the composition of each alloy, and FE-SEM and UV-VIS-NIR-Colormeter were employed for microstructure and color characterization. The melting temperature, hardness, and wetting angle of the samples were determined by TGA-DTA, the Vickers hardness tester, and the Wetting angle tester. The cupellation result confirmed that all the samples had 18K above 75.0wt%-Au. EDS results showed that Cu and In elements were alloyed with the intended composition without segregation. The microstructure results showed that the amount of In increased, and the grain size became smaller. The color analysis revealed that the proposed solders up to 10.0 wt% In showed a color similar to the reference 18 K substrate like the 10.0 wt% Cd solder with a color difference of less than 7.50. TGA-DTA results confirmed that when more than 5.0 wt% of In was added, the melting temperature decreased enough for the soldering process. The Vickers hardness result revealed that more than 5.0 wt% In solder alloys had greater hardness than 10.0 wt% Cd solder, which suggested that it was more favorable in making a wire type solder. Moreover, all the In solders showed a lower wetting angle than the 10.0 wt% Cd solder. Our results suggested that the In alloyed 18 K red gold solders might replace the conventional 10.0 wt% Cd solder with appropriate properties for red gold jewelry soldering.

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