• Laser Solutions
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• v.16 no.3
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• pp.1-10
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• 2013

In this study, Al-Si coated boron steel(1.2 mm) were laser welded by $CO_2$ laser and hot-stamping was applied to the laser joints. Tensile properties and microstructures of the joints were investigated before and after hot-stamping. Tensile and yield strengths of the as welded specimen similar with base metal and fracture occurred base metal of boron steel. Although, in case of heat treated specimen, fracture occurred fusion zone that Al segregated zone near the bond line. These could be explained by the existence of ferrite, in the Al segregated zone near the bond line and base metal of boron steel. Before hot-stamping, hardness of base metal is lower than fusion zone and heat affected zone in spite of exist Al segregation zone($Fe_3$(Al,Si)). So fracture occurred base metal. Although, after hot-stamping, microstructure of base metal and welds zone transformed to martensite and bainite except in Al segregation zone near the bond line that $Fe_3$(Al,Si) transformed to a-ferrite. So fracture occurred Al segregation zone near the bond line.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.68-75
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• 2018

The introduction of advanced water treatment facilities has increased as the conventional purification method cannot remove the substance clearly. However, the internal waterproofing and Anticorrosion materials of the advanced water treatment facility using ozone deteriorate due to the oxidation power of ozone and affects the concrete, which causes a decrease in durability. This study is to evaluate the ozone resistance according to the type of spray metal and the surface treatment method of the coating, and the bond strength after ozone treatment in order to develope a finishing method to prevent deterioration of concrete structure of water treatment facility using metal spraying method as a way to construct metal panel with excellent ozone resistance and chemical resistance by an easier way than the previous. The Experimental results show that spray metal Ti has superior ozone resistance even after spraying. It is considered to be the most suitable method for ozone resistance and bond performance by finishing using Teflon sealing as surface treatment method.

• Journal of the Korean Ceramic Society
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• v.31 no.4
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• pp.381-388
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• 1994

A new process which co-fires the low-firing-substrate and copper conductor was studied to achieve good bond strength and low sheet resistance of conductor. Cupric oxide is used as the precursor of conductive material in the new method and the firing atmosphere of the new process is changed sequently in air H2N2. The addition of cupric oxide and variations of firing atmosphere permited complete binder-burnout in comparison with the conventional method and contributed to the improvement of resistance and bonding behaviors. The potimum conditions of this experiment to obtain the satisfactory resistance and bond strength are as follows (binder-burnout temperature in air; 55$0^{\circ}C$, reducing temperature in H2; 40$0^{\circ}C$ for 30 min, ratio of copper and cupric oxide; 60:40~30:70 wt%). The bonding mechanism between the substrate and metal was explained by metal diffusion layer in the interface and the bond strength mainly depended on the stress caused by the difference of shrinkage and thermal expansion coefficient between the substrate and metal.

• Journal of the Korean Ceramic Society
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• v.32 no.5
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• pp.601-607
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• 1995

The bond strength between the low-firing-substrate and Cu conductor depended on the softening point and the amount of frit added to the metal paste. The addition of 3 wt% frit (softening point: 68$0^{\circ}C$) to the metal paste resulted in the improvement of bond strength, which was approximately 3 times higher (3kg/$\textrm{mm}^2$) than that of non frit condition. It was also found that fracture surface shifted to the ceramic substrate in the interface region. These phenomena were attributed to the frit migration into the metal-ceramic interface. It was thought that the migration of glass frit occurred extensively when the softening point of glass firt was 68$0^{\circ}C$. The sheet resistance of Cu conductor remained constant by the addition of 4 wt% frit regardless of softening point of frit. For all samples with more than 4 wt% frit, the sheet resistance increased abruptly.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.4
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• pp.662-684
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• 1995

The purpose of this study was to evaluate the shear bond strength between various resin-bonded retainers and enamel according to the adhesive resins and retention types and observe the bond filure modes with scanning electron microscope(SEM). For this purpose, the followin eight sub-groups were tested in shear bond strength : 1) electrochemically etched group(Verabond) using Panavia EX and Superbond C&B 2) tin-plated group(PG-S) using Panavia EX and Superbond C&B 3) salt-treated group(Verabond) using Panavia EX and Superbond C&B 4) meshtreated group(Verabond) using Panavia EX and Superbond C&B. Thermocycling test was conducted on the condition of 15 second dwell time each in $5^{\circ}C$ and $55^{\circ}C$bath. Shear bond strength was measured by Instron Universal Testing Machine(medel 1125). The obtained results were as follows : 1. After thermocycling, the shear bond strengths of tin-plated group and electrochemically etched group were significantly greater than those of salt-treated group and mesh-treated group. And the shear bond strength of Panavia EX was greater than that of Superbond C&B with salt-treated group and tin-plated group(p<0.05). 2. Before thermocycling, electrochemically etched group using Superbond C&B produced the greatest shear bond strength(p<0.01). 3. The shear bond strength of electrochemically etched group using Superbond C&B was significantly decreased after thermocycling(p<0.01). 4. In observation of bond failure modes before thermocycling, Panavia EX highly exhibited enamel fracture. Tin-plated group using Superbond C&B adhesive failure between metal and resin and electrochemically etched group using Superbond C&B exhibited adhesive failure between enamel and rdsin. 5. In observation of failure modes after thermocycling, Panavia EX exhibited cohesive failure and Superbond C&B exhibited adhesive failure between resin and metal.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.4
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• pp.500-509
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• 2000

In general, the three major oral functions of edentulous patients-mastication, phonation, esthetics-can be rehabilitated by the complete dentures, and both the resin based complete denture and the metal based complete denture are commonly used by many clinicians today. For the sake of many advantages such as the excellent thermal conductivity, low volumetric change, high strength, low risk of fracture and the better patient's adaptation, the metal based complete dentures are indicated to the several cases. But, there are common failures of these type of dentures mainly by the fracture or the debonding between the resin structures and the metal frameworks which is caused by the discrepancies of the flexural strength and the coefficient of thermal expansion. This is aggravated by the water contamination of the interface when exposed to the oral environment and results in the failure of complete denture treatment. So, the purpose of this study is to compare the bond strength and the fracture patterns of the gold alloy based and the Co-Cr alloy based complete dentures using the PMMA resins and the 4-META adhesive resins. The results of this study were as follows. 1. Both to the PMMA resin and the 4-META resin, the flexural bond strength of gold alloy is lower than that of Co-Cr alloy(P<0.05) 2. To the Co-Cr alloy, the bond strength of the 4-META resin is significantly higher than that of PMMA resin(P<0.05). 3. The flexural strength of the group with the mechanical retention form is significantly higher than that of the group without retention form(P<0.05). 4. Comparing with the other groups, the fracture patterns of the group 3 are quite different from the group 1,2,5.

• Journal of Technologic Dentistry
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• v.32 no.3
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• pp.195-207
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• 2010

Purpose: The purpose of this study was to observe the microstructural changes of surface in the specimens, performing the shear bond strength testing. The currently most used non-precious alloys are nickel-chromium based alloys with or without beryllium. However, their biocompatibility has been questioned concerning possible damages to the health of the patient and professionals involved in the fabrication of prosthesis caused by long exposure to Ni and Be. An option to nickel-chromium alloys is the cobalt-chromium alloy, an alternative that does not sacrifice the physical properties of the metal porcelain systems. Studies in the animals substantially show that the cobalt-chromium alloys are relatively well tolerated, being therefore more biocompatible than the nickel-chromium alloys. Methods: Non-addition Be to nickel-chromium based alloy(Bellabond plus) and cobalt-chromium alloy which has been widely used(Wirobond C) fused with ZEO light porcelain classified control group and cobalt-chromium alloy which is developing alloy of Alphadent company in Korea(Alphadent alloy) fused with ZEO light porcelain classified experimental group. The specimens of $4mm{\times}4mm{\times}0.5mm$ were prepared as-cast and as-opaque to cast body to analyze the mechanical characteristic change, the microstructure of alloy surface. The phase change was used to observe through XRD analysis and OM/SEM was used to observe the surface of specimens as-cast and as-opaque to cast body. Chemical formation of their elements was measured with EDS. Then hardness was measured with Micro Vicker's hardness tester. Shear bond strength test thirty specimens of $10mm{\times}10mm{\times}2mm$ was prepared, veneered, 3mm high and 3mm in diameter, over the alloy specimens. The shear bond strength test was performed in a universal testing machine(UTM) with a cross head speed of 0.5mm/min. Ultimate shear bond strength data were analyzed with one-way ANOVA and the Scheffe's test (P<0.05). Within the limits of this study, the following conclusions were drawn: The X-ray diffraction analysis results for the as-cast and as-opaque specimens showed that the major relative intensity of Bellabond plus alloy were changed smaller than Wirobond C and Alphadent Co-Cr based alloys. Results: Microstructural analysis results for the opaque specimens showed all the alloys increased carbides and precipitation(PPT). Alphadent Co-Cr based alloy showed the carbides of lamellar type. The Vickers hardness results for the opaque specimens showed Wirobond C and Alphadent Co-Cr based alloys were increaser than before ascast, but Bellabond plus alloy relatively decreased. The mean shear bond strengths (MPa) were: 33.11 for Wirobond C/ZEO light; 25.00 for Alphadent Co-Cr alloy/ZEO light; 18.02 for Bellabond plus/ZEO light. Conclusion: The mean shear bond strengths for Co-Cr and Ni-Cr based alloy were significantly different. But the all groups showed metal-metal oxide modes in shear bond strengths test at the interface.

• The korean journal of orthodontics
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• v.34 no.5 s.106
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• pp.429-438
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• 2004

The purpose of this study was to compare the effects of different light direction exposure times and setting times when using plasma arc light on shear bond strength of metal brackets. 240 extracted human premolars were randomly assigned to one of 16 groups Standardized brackets were bonded to enamel using different light curing units (Plasma arc light and Halogen light), exposure times (Plasma arc light 2. 4, 6 seconds and Halogen light 20 seconds). and light directions [Vertical direction [V] and Oblique direction [O]). 8 groups were tested after 5 minutes and the remaining 8 groups after 24 hours. The metal brackets were bonded with Transbond XT. Shear bond strength was measured by a universal testing machine. The results were as fellows: There were as differences between the shear bond strengths of the Vertical groups (V) and Oblique groups (O). regardless of exposure times and types of light curing units (p>0.05). The shear bond strength of the group with 2 seconds of plasma light were significantly lower than other exposure time groups (P<0.05). The shear bond strength tested after 5 minutes was lower than after 24 hours (p<0.05) The Adhesive Remment Index (ARI) score showed no statistically significant difference among the different groups. The results of this study suggested that the light direction of plasma arc light had no influence on the shear bond strength of metal brackets to enamel. and exposure times more than 4 seconds produced shear bond strengths similar to those Produced with a conventional halogen curing light.

• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1920-1926
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• 2008

We investigated the C-H bond activation mechanism of aldimine by the [RhCl$(PPH_3)_3$] model catalyst using DFT B3LYP//SBKJC/6-31G*/6-31G on GAMESS. Due to their potential utility in organic synthesis, C-H bond activation is one of the most active research fields in organic and organometallic chemistry. C-H bond activation by a transition metal catalyst can be classified into two types of mechanisms: direct C-H bond cleavage by the metal catalyst or a multi-step mechanism via a tetrahedral transition state. There are three structural isomers of [RhCl$(PH_3)_2$] coordinated aldimine that differ in the position of chloride with respect to the molecular plane. By comparing activation energies of the overall reaction pathways that the three isomeric structures follow in each mechanism, we found that the C-H bond activation of aldimine by the [RhCl$(PH_3)_3$] catalyst occurs through the tetrahedral intermediate.

• The Journal of Korean Academy of Prosthodontics
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• v.27 no.1
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• pp.31-47
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• 1989

The purpose of this study was to evaluate the chemical bond strength of successively recast Pd-Ag ceramic alloys with porcelain and to investigate changes of quantity of trace elements at the metal-porcelain interface. Porcelain was fired as usual manner on the each successively recast specimen. Rectangular planar shear test was performed and bond strength was measured by Instron universal testing machine. Diffusion of trace elements at the each interface was observed by ESCA (Electron Spectroscopy for Chemical Analysis). The obtained results were as follows : 1. Chemical bond strength was significantly decreased after second recasting. But in case of first recasting, there was no significant decrease of bond strength statistically (p<0.05). 2. Bond strength was not significantly decreased in each generation, when fifty percents new alloy was added (p<0.05). 3. Ag, Sn and In were observed at the porcelain interface. But Pd was not observed. 4. The quantity of Ag, In ions were progressively increased at the metal-porcelain interface as the casting was repeated. Silver ion was most significantly increased.