• The Journal of Korean Academy of Prosthodontics
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• v.41 no.1
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• pp.1-19
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• 2003

The surface of metals should be as smooth as possible for optimum comfort, oral hygiene, low plaque retention, and resistance to corrosion. In this study five specimens of each precious metal(type III gold alloy, ceramic gold alloy, and Ag-Pd alloy) were divided into five groups according to finishing and polishing procedures : group 1(sandblaster), group 2(group 1+stone), group 3(group 2+brown rubber), group 4(group 3+green rubber), and group 5(group 4+rouge). Six specimens of each non-precious metal(Co-Cr alloy, Ni-Cr alloy, and Co-Cr-Ti alloy) were divided into six groups: group 1(sandblaster), group 2(group 1+hard stone), group 3(group 2+electrolytic polisher), group 4(group 3+brown hard rubber point), group 5(group 4+green hard rubber point), and group 6(group 5+rouge). Considering factors affecting the rate of abrasion, the same dentist applied each finishing and polishing procedure. In addition, the surface roughness of enamel, resin, and porcelain was evaluated. The effect of finishing and polishing procedures on surface roughness of precious and non-precious metals, enamel, resin, and porcelain was evaluated by means of Atomic Force Microscope(AutoProbe CP. Park Scientific Instruments, U.S.A.) that can image the three dimensional surface profile and measure average surface roughness values of each sample at the same time. The obtained results were as follows : 1. According to finishing and polishing procedures, the surface roughness of type III gold alloy, ceramic gold alloy, and Ag-Pd alloy was decreased in the order of group 1, 2, 3, 4, and 5 (P<0.01). 2. According to finishing and polishing procedures. the surface roughness of Co-Cr alloy, Ni-Cr alloy, and Co-Cr-Ti alloy was decreased in the order of group 1, 2, 3, 4, 5, and 6 (p<0.01). 3. There was not statistically significant difference in the surface roughness among three metals of precious metals in group 1 but was significant difference in group 2, 3, 4, and 5 (P<0.05). 4. There was not statistically significant difference in the surface roughness among three metals of non-precious metals in all groups. 5. When the surface roughness of the smoothest surface of each metal, enamel. porcelain, and resin was compared, porcelain was the smoothest and the surface roughness was decreased in the order of Ni-Cr alloy. Co-Cr alloy. Co-Cr-Ti alloy, resin. Ag-Pd alloy, ceramic gold alloy type III gold alloy, and enamel (P<0.01). The results of this study indicate that the finishing and polishing procedures should be carried out in a logical, systematic sequence of steps and the harder non-precious metals may be less resistance to abrasion than are the softer precious metals.

• The Journal of Asian Finance, Economics and Business
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• v.8 no.1
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• pp.81-91
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• 2021

This paper investigates the long run hedging ability of precious metals against the risks associated with adverse conditions of economic and financial variables for Pakistan, the USA, China, and India. Monthly data of gold, silver, platinum, stock returns, exchange rate, industrial production, and inflation was collected for the selected economies. Saikkonen and Lutkepohl (2002) unit root test was employed to access the unit root properties of the data series and identify the break dates. Furthermore, this study used the Johansen cointegration test with and without structural breaks to identify the long-run relationship between metals prices and different financial and economic variables. The findings suggest that the time series under study have unit root problem at level with and without structural breaks. Without considering structural breaks, the Johansen trace test indicates that in Pakistan and China, gold, silver, and platinum hold a cointegrating relationship with macroeconomic and financial variables. For the US, gold indicates cointegration which supports the hedging ability of gold against inflation, stock, and industrial production in the long run. The results of the cointegration test after incorporating the structural breaks provide even stronger evidence of the long-run relationship of precious metals and consumer prices, exchange rate, and stock prices.

• Journal of Technologic Dentistry
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• v.5 no.1
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• pp.27-30
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• 1983

This study was undertaken to know the difference that margin fittness in metal bond porcelain crown. When we use porcelain precious metal and non-precious metal as porcelain-fused metal, the results were as following. 1. The precious metal was showed best result in margin fittness and shade. 2. The non-precious metals were showed good results, especially Gemini II was excellent, but that was not good than precious metal. 3. 10k. gold plating on non-precious metal cap showed same result as nonprecious metal in margin fittness, and not good in shade. 4. When we use the non-precious metals at upper part of crown, and using precious metal in 2mm cervical portion, the margin fittness were very good, and the results same as full veneer precious metal.

• Resources Recycling
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• v.11 no.6
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• pp.3-11
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• 2002

Recently, waste printed circuit board (PCB) has significantly increased in its amount due to the rapid development of electronic industries. Since several kinds of noxious materials and also valuable metals are contained in it, the waste PCB is in an urgent need of recycling for the dual purposes for the prevention of environmental pollution and recovery of valuable resources. Also, the catalyst which equipped in the exhaust pipes of automobiles to reduce emission of air pollutants contains precious met-als so that their recovery from the waste auto-catalysts is required. In this study, the recovery of valuable metals from waste PCB and auto-catalyst by arc furnace melting process has been investigated, which is known to be very stable and suitable f3r less production of pollutants due to its high operating temperature. The effect of the kind of flux on the recovery of precious metals was examined by using quicklime, converter slag, and copper slag as the flux. In addition, the influence of direct and alternating current and the applying direction of direct current has been investigated. It was observed that using converter or copper slag as a flux was more desirable for a higher efficiency in the precious metal recovery compared with quicklime. For the effect of current, application of direct current taking the bottom as a negative pole generally showed a better efficiency for the extraction of valuable metals from waste PCB, which was also observed for the case of waste auto-catalyst. The average recovery of precious metals from both wastes by arc furnace melting process was very high, which was up to in the range of 95～97%.

• Resources Recycling
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• v.18 no.4
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• pp.14-23
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• 2009

In terms of resources recycling and resolving waste disposal problems, it is very important to recover precious metals like Au, Ag and Pd and valuable metals like Cu, Sn and Ni from the scraps of waste electrical and electronic equipment(WEEE) that consists of detective electrical and electronic parts discarded during manufacturing electrical and electronic equipments and waste electrical and electronic parts generated during disassembling them. In general, the scraps of WEEE are composed of various metals and alloys as well as refractory oxides and plastic components. Precious and valuable metals from the scraps of WEEE can be recovered by gas-phase-volatilization, hydrometallurgical, or pyrometallurgical processes. However, the gas-phase-volatilization and hydrometallurgical processes have been suggested but not yet commercialized. At the present time, most of the commercial plants for recovering precious and valuable metals from the scraps of WEEE adopt pyrometallurgical processes. Therefore, in this paper, the technical and environmental aspects on the important pyrometallurgical processes through literature survey are reviewed, and the scale-up result of a new pyrometallurgical process for recovering the precious and valuable metals contained in the scraps of WEEE using waste copper slag is presented.

• Applied Chemistry for Engineering
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• v.20 no.4
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• pp.430-436
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• 2009

Deactivated three-way catalysts which had been exposed to gasoline engine exhaust for a long time were remanufactured by ultra sonic cleaning with distilled water, sulfuric acid solution and impregnation with precious metals (Pt, Pd, Rh). The catalytic properties as well as conversion reactivity of CO, THC and NOx about fresh, aged and remanufactured catalysts were examined. Most of the pollutants deposited on the aged three-way catalysts were removed in the remanufacturing process of those catalysts. At the same time a little amount of precious metals like Pt and Pd were removed in the remanufacturing process. Under the experimental condition used in this study, in the case of the remanufactured catalysts with impregnation of precious metals, the catalytic activities were recovered to almost the same level, or higher level of that of the fresh catalyst.

• Applied Chemistry for Engineering
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• v.17 no.4
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• pp.343-348
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• 2006

The object of this experiment is to recover precious metals from plating rinsed wastewater generated from Lead Frame manufacturing process using electrolysis coupled hybrid process. This was achieved from Amberlite IRA 400 at 1.15 V electrolysis potential using the oxide electrode and at 1.30 V using the Al electrode and from Amberlite IRA 402 at 1.10 V using the oxide electrode and at 1.20 V using the Al electrode. During the first 10~30 min of the process, 90~95% of the silver can be recovered.

• Environmental Engineering Research
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• v.10 no.3
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• pp.131-137
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• 2005

The catalytic activity of precious metals(Rh, Pd, Pt) and nickel catalysts supported on ${\gamma}-Al_2O_3\;and\;CeO_2$ in the partial combustion of methane(PCM) to syngas was investigated based on the product distribution in a fixed bed now reactor under atmospheric condition and also on analysis results by SEM, XPS, TPD, BET, and XRD. The activity of the catalysts based on the syngas yield increased in the sequence $Rh(5)/CeO_2{\geq}Ni(5)/CeO_2>>Rh(5)/Al_2O_3>Pd(5)/Al_2O_3>Ni(5)/Al_2O_3$. Compared to the precious catalysts, the syngas yield and stability of the $Ni(5)/CeO_2$ catalyst were almost similar to $(5)/CeO_2$ catalyst, and superior to these of any other catalysts. The syngas yield of $Ni(5)/CeO_2$ catalyst was 90.66% at 1023 K. It could be suggested to be the redox cycle of the successive reaction and formation of active site, $Ni^{2-}$ and the lattice oxygen, $O^{2-}$ produced due to reduction of $Ce^{4-}$ to $Ce^{3-}$.

• Journal of Technologic Dentistry
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• v.35 no.1
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• pp.1-17
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• 2013

Purpose: This study was to assess the extents of the release of metals from the non-precious alloys used for dental casting by measuring the differences in the extents of the release of metals by types of alloys, pH level and elapsed time. Methods: Uniform-sized specimens(10 each) were prepared according to the Medical Device Standard of the Korea Food and Drug Administration(2010) and International Standard Organization(ISO22674, 2006), using four types of alloys(one type of Ni-Cr and one type of Co-Cr used for fixed prosthesis, and one type of Ni-Cr and one type of Co-Cr used for removable prosthesis). A total of 12 metal-release tests were performed at one-day, three-day, and two-week intervals, for up to 20 weeks. The metal ions were quantified using an Inductively Coupled Plasma-Atomic Emission Spectrometer. Results: The results showed that the extent of corrosion was higher in the ascending order of Jdium-$100^{(R)}$, Bellabond-$Plus^{(R)}$, Starloy-$C^{(R)}$, and Biosil-$F^{(R)}$. The lower the pH and the longer the elapsed time were, the greater the increase in metal corrosion. At pH 2.4, the release of Ni from Jdium-$100^{(R)}$, a Ni-Cr alloy, was up to 15 times greater than the release of Co from the Co-Cr alloy from two weeks over time, indicating that the Ni-Cr alloy is more susceptible to corrosion than the Co-Cr alloy. Conclusion: It is recommended that Co-Cr alloy, which is highly resistant to corrosion, be used for making dental prosthesis with a non-precious alloy for dental casting, and that non-precious alloy prosthesis be designed in such a way as to minimize the area of its oral exposure. For patients with non-precious alloy prostheses, a test of the presence or absence of periodontal tissue inflammation or allergic reaction around the prosthesis should be performed via regular examination, and education on the good management of the prosthesis is needed.

• Fashion & Textile Research Journal
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• v.23 no.4
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• pp.439-447
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• 2021

The purpose of this study is to examine the evolution of precious metal and gem stores, and to derive the characteristics of this period from the government, industry, and consumers. Correspondingly, the contents of daily newspaper articles during this period were analyzed using Naver's news library search engine. The historical development process is as follows. Before the Korean War, precious metal jewelers operated in Jongno, Namdaemun, and Chungmuro, dealing with gold, silver, and platinum. Large stores not only sold jewelry and watches, but also functioned as craftsmen and watch repairers. After the war, a shopping district for precious metals and jewelry was formed around Midopa Department Store. By 1963, the number of jewelry stores in Seoul increased to about 130 and to about 280 by 1966. The characteristics of the government, industry, and consumers are as follows. The government continued to implement a policy to regulate the precious metal and jewelry industry. Despite challenges, the industry exhibited the potential for foreign currency acquisition and growth through domestic amethyst. Consumers could access information regarding precious metal jewelry in daily newspapers. In the late 1960s, various types of jewelry were distributed in line with an increase in income levels.