• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.16 no.3
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• pp.254-263
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• 2006

Manganese has a role as both toxic and essential in humans. Manganese is also an essential component in the welding because it increases the hardness and strength, prevents steel from cracking of welding part and acts as a deoxidizing agent to form a stable weld. In this study, manganese generation rate and its content was determined in flux cored arc welding on stainless steel. Domestic two products and foreign four products of flux cored wires were tested in the well designed fume generation chamber as a function of input power. Welding fume was measured by gravimetric method and metal manganese was determined by inductively coupled plasma-atomic emission spectrophotometer. The outer shell of the flux cored wire tube and inner flux were analyzed by scanning electron microscopy to determine their metal compositions. Manganese generation rate($FGR_{mn}$) was increased as the input power increased. It was 16.3 mg/min at the low input power, 38.1 mg/min at the optimal input power, and up to 55.4 mg/min at the high input power. This means that $FGR_{mn}$ is increased at the work place if welder raise the current and/or voltage for the high productivity. The slope coefficient of $FGR_{mn}$ was smaller than that of the generation rate of total fume(FGR). Also, the correlation coefficient of $FGR_{mn}$ was 0.65 whereas that of FGR is 0.91. $FGR_{mn}$ was equal or higher in the domestic products than that of the foreign products although FGR was similar. From the electron microscopic analytical data, we concluded that outer shell of the wire was composed mainly of iron, chromium, nickel and less than 1.2 % of manganese. There are many metal ingredients such as iron, silica, manganese, zirconium, titanium, nickel, potassium, and aluminum in the inner flux but they were not homogeneous. It was found that both $FGR_{mn}$ and content of manganese was higher and more varied in domestic flux cored wires than those of foreign products. To reduce worker exposure to fumes and hazardous component at the source, further research is needed to develop new welding filler materials that improve the quality of flux cored wire in respect to these points. Welder should keep in mind that the FGR, $FGR_{mn}$ and probably the generation rate of other hazardous metals were increased as the input power increase for the high productivity.

• Journal of Environmental Impact Assessment
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• v.8 no.2
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• pp.1-8
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• 1999

The research centers on the concentration profile and risk assessment of toxic metals for ambient air in Taejon industrial complex. Airborne concentrations of each toxic metal for risk assessment were obtained from 2-year sampling by high volume air sampler and analysis by ICP-MS and ICP-AES in the complex. The long-term arithmetic mean of human carcinogen, arsenic, hexavalent chromium and nickel subsulfide was 5.53, 2.16 and $3.46ng/m^3$ while the mean of probable human carcinogen, beryllium, cadmium and lead was 0.08, 2.35, $293.29ng/m^3$, respectively. And the long-term arithmetic mean concentration of non-carcinogenic metal, manganese was $55.91ng/m^3$. The point risk estimate for the inhalation of carcinogenic metals was $3.6{\times}10^{-5}$, which was higher than a risk standard of $10^{-5}$. About 75% of the cancer risk was to the inhalation of human carcinogen, arsenic. Thus, it is necessary to properly manage arsenic risk in Taejon industrial complex. The point hazard index by the inhalation of manganese was 1.1. Therefore, an investigation into Taejon industrial complex is needed to obtain more fine long-term concentration data for airborne non-carcinogenic metals including manganese.

• Journal of the Korean Society of Industry Convergence
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• v.7 no.3
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• pp.259-263
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• 2004

In the manufacture progress of LCD or semiconductor, there are used many kinds of gas like erosion gas, dilution gas, toxic gas as a progress which used these gas there are required high puritize to increase accumulation rate of semiconductor or LCD materials work progress of semiconductor or LCD it demand many things like the material which could minimize metallic dust that could be occured by reaction between gas and transfer pipe laying material, illumination of the surface, emition of the gas, metal liquation, welding etc also demand quality geting stricted. Material-Low-sulfur-contend (0.007-0010), vacuum-arc-remelt(VAR), seamless, high-purity tubing material is recommend for enhance welding lower surface defect density All wetted stainless steel surface must be 316LSS elecrto polishinged with ${\leq}0.254{\mu}m$($10.0{\mu}in$) Ra average surface finish, $Cr/Fe{\geq}1.1$ and $Cr_2O_3$ thickness ${\geq}25{\AA}$ From the AES analytical the oxide layer thickness (23.5~36 angstroms silicon dioxide equivalent) and chromum to iron ratios is similar to those generally found on electropolished stainless steel., molybdenum and silicon contaminants ; elements characteristic of stainless steel (iron, nickel and chromium); and oxygen were found on the surface Phosphorus and nitrogen are common contaminants from the electropolish and passivation steps.

• The Journal of Advanced Prosthodontics
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• v.9 no.3
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• pp.170-175
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• 2017

PURPOSE. The aim of the present study was to evaluate the fracture resistances of zirconia, cast nickel-chromium alloy (Ni-Cr), and fiber-composite post systems under all-ceramic crowns in endodontically treated mandibular first premolars. MATERIALS AND METHODS. A total of 36 extracted human mandibular premolars were selected, subjected to standard endodontic treatment, and divided into three groups (n=12) as follows: cast Ni-Cr post-and-core, one-piece custom-milled zirconia post-and-core, and prefabricated fiber-glass post with composite resin core. Each specimen had an all-ceramic crown with zirconia coping and was then loaded to failure using a universal testing machine at a cross-head speed of 0.5 mm/min, at an angle of 45 degrees to the long axis of the roots. Fracture resistance and modes of failure were analyzed. The significance of the results was assessed using analysis of variance (ANOVA) and Tukey honest significance difference (HSD) tests (${\alpha}=.05$). RESULTS. Fiber-glass posts with composite cores showed the highest fracture resistance values ($915.70{\pm}323N$), and the zirconia post system showed the lowest resistance ($435.34{\pm}220N$). The corresponding mean value for the Ni-Cr casting post and cores was reported as $780.59{\pm}270N$. The differences among the groups were statistically significant (P<.05) for the zirconia group, as tested by ANOVA and Tukey HSD tests. CONCLUSION. The fracture resistance of zirconia post-and-core systems was found to be significantly lower than those of fiber-glass and cast Ni-Cr post systems. Moreover, catastrophic and non-restorable fractures were more prevalent in teeth restored by zirconia posts.

• Environmental Analysis Health and Toxicology
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• v.31
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• pp.6.1-6.10
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• 2016

Objectives This study examined the spatial distribution and the extent of soil contamination by heavy metals resulting from primitive, unconventional informal electronic waste recycling in the Agbogbloshie e-waste processing site (AEPS) in Ghana. Methods A total of 132 samples were collected at 100 m intervals, with a handheld global position system used in taking the location data of the soil sample points. Observing all procedural and quality assurance measures, the samples were analyzed for barium (Ba), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn), using X-ray fluorescence. Using environmental risk indices of contamination factor and degree of contamination ($C_{deg}$), we analyzed the individual contribution of each heavy metal contamination and the overall $C_{deg}$. We further used geostatistical techniques of spatial autocorrelation and variability to examine spatial distribution and extent of heavy metal contamination. Results Results from soil analysis showed that heavy metal concentrations were significantly higher than the Canadian Environmental Protection Agency and Dutch environmental standards. In an increasing order, Pb>Cd>Hg>Cu>Zn>Cr>Co>Ba>Ni contributed significantly to the overall $C_{deg}$. Contamination was highest in the main working areas of burning and dismantling sites, indicating the influence of recycling activities. Geostatistical analysis also revealed that heavy metal contamination spreads beyond the main working areas to residential, recreational, farming, and commercial areas. Conclusions Our results show that the studied heavy metals are ubiquitous within AEPS and the significantly high concentration of these metals reflect the contamination factor and $C_{deg}$, indicating soil contamination in AEPS with the nine heavy metals studied.

• The Journal of Advanced Prosthodontics
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• v.9 no.2
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• pp.110-117
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• 2017

PURPOSE. This laboratory study assessed the effect of different dentin cleaning procedures on shear bond strength of resin cements for recementing prosthesis. MATERIALS AND METHODS. A $4{\times}4$ flat surface was prepared on the labial surface of 52 maxillary central incisors. Metal frames ($4{\times}4{\times}1.5mm$) were cast with nickel-chromium alloy. All specimens were randomly divided into 2 groups to be cemented with either Panavia F2.0 (P) or RelyX Ultimate (U) cement. The initial shear bond strength was recorded by Universal Testing Machine at a crosshead speed of 0.5 mm/min. Debonded specimens were randomly allocated into 2 subgroups (n = 13) according to the dentin cleaning procedures for recementation. The residual cement on bonded dentin surfaces was eliminated with either pumice slurry (p) or tungsten carbide bur (c). The restorations were rebonded with the same cement and were subjected to shear test. Data failed the normality test (P < .05), thus were analyzed with Mann Whitney U-test, Wilcoxon signed rank test, and two-way ANOVA after logarithmic transformation (${\alpha}=.05$). RESULTS. The initial shear bond strength of group P was significantly higher than group U (P = .001). Pc and Uc groups presented higher bond strength after recementation compared to the initial bond strength. However, it was significant only in Pc group (P = .034). CONCLUSION. The specimens recemented with Panavia F2.0 provided higher bond strength than RelyX Ultimate cement. Moreover, a tungsten carbide bur was a more efficient method in removing the residual resin cement and increased the bond strength of Panavia F2.0 cement after recementation.

• The Journal of Advanced Prosthodontics
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• v.8 no.3
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• pp.224-228
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• 2016

PURPOSE. This study aimed to investigate whether dentin surface preparation with diamond rotary instruments of different grit sizes affects the shear bond strength of resin-bonded restorations. MATERIALS AND METHODS. The buccal enamel of 60 maxillary central incisors was removed with a low speed diamond saw and wet ground with silicon carbide papers. The polished surfaces of the teeth were prepared with four groups of rotary diamond burs with super-coarse (SC), coarse (C), medium (M), and fine (F) grit sizes. Following surface preparation, 60 restorations were casted with nickel-chromium alloy and bonded with Panavia cement. To assess the shear bond strength, the samples were mounted on a universal testing machine and an axial load was applied along the cement-restoration interface at the crosshead speed of 0.5 mm/min. The acquired data was analyzed with one way ANOVA and Tukey post hoc test (${\alpha}=.05$). RESULTS. The $mean{\pm}SD$ shear bond strengths (in MPa) of the study groups were $17.75{\pm}1.41$ for SC, $13.82{\pm}1.13$ for C, $10.40{\pm}1.45$ for M, and $7.13{\pm}1.18$ for F. Statistical analysis revealed the significant difference among the study groups such that the value for group SC was significantly higher than that for group F (P<.001). CONCLUSION. Dentin surface roughness created by diamond burs of different grit sizes considerably influences the shear bond strength of resin bonded restorations.

• The Journal of Advanced Prosthodontics
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• v.4 no.2
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• pp.89-92
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• 2012

PURPOSE. Adequate passive-fitting of one-piece cast 3-element implant-supported frameworks is hard to achieve. This short communication aims to present an alternative method for section of one-piece cast frameworks and for casting implant-supported frameworks. MATERIALS AND METHODS. Three-unit implant-supported nickel-chromium (Ni-Cr) frameworks were tested for vertical misfit (n = 6). The frameworks were cast as one-piece (Group A) and later transversally sectioned through a diagonal axis (Group B) and compared to frameworks that were cast diagonally separated (Group C). All separated frameworks were laser welded. Only one side of the frameworks was screwed. RESULTS. The results on the tightened side were significantly lower in Group C ($6.43{\pm}3.24{\mu}m$) when compared to Groups A ($16.50{\pm}7.55{\mu}m$) and B ($16.27{\pm}1.71{\mu}m$) ($P$ <.05). On the opposite side, the diagonal section of the one-piece castings for laser welding showed significant improvement in the levels of misfit of the frameworks (Group A, $58.66{\pm}14.30{\mu}m$; Group B, $39.48{\pm}12.03{\mu}m$; Group C, $23.13{\pm}8.24{\mu}m$) ($P$ <.05). CONCLUSION. Casting diagonally sectioned frameworks lowers the misfit levels. Lower misfit levels for the frameworks can be achieved by diagonally sectioning one-piece frameworks.

• Korean Journal of Soil Science and Fertilizer
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• v.28 no.4
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• pp.295-300
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• 1995

In order to find out the natural content of heavy metals(Cd, Cu, Pb, Zn, Cr, Ni)in paddy soil of Korea, a total of 1,196 soil samples of 15cm top layers all over the country 1995 were collected and analyzed. The average heavy metal contents in soils were 0.133mg/kg of Cd, 4.52mg/kg of Cu, 4.62mg/kg of Pb, 3.90mg/kg of Zn, 0.362mg/kg of Cr and 1.38mg/kg of Ni. These results are similar to the results of survey conducted in 1981.

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.6
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• pp.639-646
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• 2003

In this study, we evaluated genotoxicity of heavy metals among particulates with Tradescantia-micronucleus (Trad-MCN) assay in the various working environment. In a synthetic fiber factory and a rubber factory, chromium concentration was higher than any other heavy metals. On the other hand, nickel concentration was the highest in a semi-conductor factory. The difference in genotoxicity among the working environment was statistically significant as Trad-MCN frequencies were 4.07 $\pm$0.35 MCN/100 tetrads (p< 0.01) for the synthetic fiber factory,5.73 $\pm$0.81 MCN/100 tetrads (p< 0.01) for the rubber factory, and 15.60$\pm$2.58 (p< 0.01) (p< 0.001) for the semi -conductor factory. As a result, heavy metals among particulates in the working environment can be considered to have hazardous potential to human health, although they cannot directly induce DNA damage to the workers in the working environments.