• Journal of Korean Ophthalmic Optics Society
• /
• v.13 no.3
• /
• pp.73-77
• /
• 2008

Purpose: This research is that prepare amorphous or crystalline ZnO thin films with pure strong UV emission on soda-lime-silica glass (SLSG) substrates by low-temperature annealing. Methods: Growth characteristic and optical properties of the amorphous or nano-crystalline ZnO thin films prepared on soda - lime - silica glass substrates by chemical solution deposition at 100, 150, 200, 250 and $300^{\circ}C$ were investigated using X-ray diffraction analysis, ultraviolet - visible - near infrared spectrophotometer, and photoluminescence. Results: The films exhibited an amorphous pattern even when finally annealed at $100^{\circ}C{\sim}200^{\circ}C$ for 60 min, while crystalline ZnO was obtained by prefiring at 250 and $300^{\circ}C$. The photoluminescence spectrum of amorphous ZnO films shows a strong NBE emission, while the visible emission is nearly quenched. Conclusions: These results indicate it should be possible to cheaply and easily fabricate ZnO-based optoelectronic devices at low temperature, below $200^{\circ}C$, in the future.

• Safety and Health at Work
• /
• v.15 no.1
• /
• pp.96-101
• /
• 2024

Background: Silicosis among workers who fabricate engineered stone products in micro or small-sized enterprises (MSEs) was reported from several countries. Workplace exposure data of these workers at high risk of exposure to respirable crystalline silica (RCS) dust are limited. Methods: We surveyed workers performing cutting, shaping and polishing tasks at 6 engineered stone fabricating MSEs in Sydney, Australia prior to regulatory intervention. Personal exposure to airborne RCS dust in 34 workers was measured, work practices were observed using a checklist and worker demography recorded. Results: Personal respirable dust measurements showed exposures above the Australian workplace exposure standard (WES) of 0.1 mg/m³ TWA-8 hours for RCS in 85% of workers who performed dry tasks and amongst 71% using water-fed tools. Dust exposure controls were inadequate with ineffective ventilation and inappropriate respiratory protection. All 34 workers sampled were identified as overseas-born migrants, mostly from three linguistic groups. Conclusions: Workplace exposure data from this survey showed that workers in engineered stone fabricating MSEs were exposed to RCS dust levels which may be associated with a high risk of developing silicosis. The survey findings were useful to inform a comprehensive regulatory intervention program involving diverse hazard communication tools and enforcing improved exposure controls. We conclude that modest occupational hygiene surveys in MSEs, with attention to workers' demographic factors can influence the effectiveness of intervention programs. Occupational health practitioners should address these potential determinants of hazardous exposures in their workplace surveys to prevent illness such as silicosis in vulnerable workers.

• Safety and Health at Work
• /
• v.7 no.3
• /
• pp.251-255
• /
• 2016

Background: Building demolition can lead to emission of dust into the environment. Exposure to silica dust may be considered as an important hazard in these sites. The objectives of this research were to determine the amount of workers' exposure to crystalline silica dust and assess the relative risk of silicosis and the excess lifetime risk of mortality from lung cancer in demolition workers. Methods: Four sites in the Tehran megacity region were selected. Silica dust was collected using the National Institute for Occupational Safety and Health method 7601 and determined spectrophotometrically. The Mannetje et al and Rice et al models were chosen to examine the rate of silicosis-related mortality and the excess lifetime risk of mortality from lung cancer, respectively. Results: The amount of demolition workers' exposure was in the range of $0.085-0.185mg/m^3$. The range of relative risk of silicosis related mortality was increased from 1 in the workers with the lowest exposure level to 22.64/1,000 in the employees with high exposure level. The range of the excess lifetime risk of mortality from lung cancer was in the range of 32-60/1,000 exposed workers. Conclusion: Geometric and arithmetic mean of exposure was higher than threshold limit value for silica dust in all demolition sites. The risk of silicosis mortality for many demolition workers was higher than 1/1,000 (unacceptable level of risk). Estimating the lifetime lung cancer mortality showed a higher risk of mortality from lung cancer in building demolition workers.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.26 no.5
• /
• pp.188-192
• /
• 2016

In this work, the SiC powders were synthesized through the carbonized matter from the mixture of silica powder and rice husks. The SiC powders, obtained from the carbothermal reduction reaction of silica and carbonized rice husks, were investigated by XRD patterns, XPS, FE-SEM and FE-TEM. In the XRD patterns, the specimens showed clearly very high strong peak of (111) plane near $35^{\circ}$ as well as weak (220) and (311) peak respectively at approximately $60^{\circ}$ and $72^{\circ}$. Under Ar atmosphere, the power synthesized from the mixture (in case of mixing ratio, 6 : 4) of carbonized rice husks and silica showed mainly cubic SiC crystalline phase showing relatively lower ratio of hexagonal phase without residual carbon in XRD pattern. In the TEM analysis, the specimen, synthesized from carbonized rice husks and silica with mixing ratio of 6 : 4 under Ar atmosphere, showed relatively fine particles under $5{\mu}m$ and a crystalline SiC phase of (100) diffraction pattern.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.27 no.4
• /
• pp.302-312
• /
• 2017

Objectives: In this study, an evaluation of the working environment of furnace workers was performed and the work-relatedness of the occupational diseases were examined Methods: In this study, two electric furnaces at a single casting business site producing manganese-based iron alloy were selected, and occupational exposures to hazardous substances were evaluated for furnace workers and furnace worker assistants. Results: As a result, total dust concentration were $0.407{\sim}3.001mg/m^3$ and respirable dust concentration were $0.196{\sim}0.584mg/m^3$. The highest concentration of crystalline silica was $0.079mg/m^3$ In the case of Masato and Sosuckwhoi crystalline silica, they contained 90.85% and 4.17% respectively. Manganese concentration was the highest at a $0.205mg/m^3$ maximum. The average of black carbon is $11.56{\mu}g/m^3$ and the maximum concentration is $604.23{\mu}g/m^3$. PAHs concentration was the highest at a $78.301{\mu}g/m^3$ of naphthalene. The concentration of carbon monoxide was 18.82 ppm(total average 3.89 ppm) during pouring, and the maximum is 131 ppm. The formaldehyde concentration was 0.003 to 0.007 ppm. Conclusions: It seems that conditions in the past were worse, since casting has recently been performed only twice per day for about 20 minutes, reducing the amount of pouring, and local exhaust systems have been installed one-by-one. In addition, it was judged that the past exposure levels were higher considering the points measured on the back-side due to the risk of damage to the individual samples. It was found that operators could be exposed to high concentrations of crystalline silica, and that they were also exposed to high concentrations of metal(fume) and carbon monoxide during pouring. Therefore, there is a risk that occupational diseases such as lung cancer and COPD may occur with long-term work in such a process.

• Journal of the Korean Ceramic Society
• /
• v.14 no.4
• /
• pp.230-235
• /
• 1977

In this paper the conditions of surface crystallization of glass were studied. The basic glass which is apt to crystallize, with $SiO_2$ 72.50, $Al_2O_3$ 5, 00, $Na_2O$ 8.00 $K_2O$ 3.50, CaO 5.00, MgO 3.00, $B_2O_3$ 3.00 Wt% is chosen. The strain point and softening point of this glass is 4$25^{\circ}C$ and 778$^{\circ}C$ each, and between the two temperatures we could get grystal on its surface by immersion in salt baths during some controlled hours. The kind of crystal on the surface of glass was confirmed by X-ray diffraction analysis and the change of the thickness of crystalline layers depending on temperature and time, was surveyed by using optical microscope. The results are as follows; 1. The chloride group is more suitable than sulfate group for the treating salt. 2. In the condition with 50 LiCl.50NaCl at 62$0^{\circ}C$ for 2 hrs and with 50 LiCL.20-30 NaCl.30-20 $CaCl_2$ at 72$0^{\circ}C$ for 15-20 min. we could get the best crystalline layers. 3. The crystal was silica-O and petalite with a little tridymite and nepheline. 4. The thickness of crystalline layers increased with increasement of temperature and time.

• Journal of the Korean Ceramic Society
• /
• v.31 no.10
• /
• pp.1231-1239
• /
• 1994

In this study, gel powder which had relatively high hydration reactivity in CaO and P2O5 rich composition of CaO-P2O5-SiO2-H2O system was prepared by sol-gel process and its hydrated specimen was manufactured. The it was investigated to appropriate calcination temperature in sol-gel process which hydrated specimen of gel powder have proven to strength and the effect of factors influenced strength in hydration process. The major product of before and after hydration reaction was hydroxyapatite, and crystalline phase of C-S-H was already formed during gelation process. After hydration reaction of pressed specimen, crystalline phase of C-S-P-H was formed. It was hydrated product of silicocarnotite (5CaO.P2O5.SiO2). Gel phases of C-S-H and C-S-P-H occured as a result of partial substitution of amorphous silica by P2O5 was formed. The strength of hydrated hardened body is developed by strong bonding and bridging between the gel phases of C-S-H or C-S-P-H and the crystalline products such as hydroxyapatite, Ca(OH)2 C-S-H and C-S-P-H. In addition, the ultrafine gel powder have an great effect on increase of hydration reaction.

• Journal of the Korean Ceramic Society
• /
• v.55 no.3
• /
• pp.285-289
• /
• 2018

We synthesized silicon carbide (${\beta}-SiC$) nanowires with nano-scale diameter (30 - 400 nm) and micro-scale length ($50-200{\mu}m$) on a porous body using low-grade silica and carbon black powder by carbothermal reduction at $1300-1600^{\circ}C$. The SiC nanowires were formed by vapor-liquid-solid deposition with self-evaporated Fe catalysts in low-grade silica. We investigated the characteristics of the SiC nanowires, which were grown on a porous body with Ar flowing in a vacuum furnace. Their structural, optical, and electrical properties were analyzed with X-ray diffraction (XRD), transmission electron microscopy (TEM), and selective area electron diffraction (SAED). We obtained high-quality SiC single crystalline nanowire without stacking faults that may have uses in industrial applications.

• Journal of the Korean Ceramic Society
• /
• v.53 no.5
• /
• pp.535-540
• /
• 2016

Effects of compositions and sintering conditions on glaze properties are shown in the diagram constructed by using the unity molecular formula (UMF) method in this study. Glossy characteristics of glaze were clearly differentiated by compositional area in the diagram and sintering process. As alumina and silica contents were increased, texture of the glaze became rough and opaque, akin to having been devitrified or underfired. The correlation between glossiness and surface roughness was found to be non-linear and inversely proportionate. Crystalline phases formed in the glaze were also influenced by the compositional area. Due to the high concentration of CaO, anorthite and wollastonite were formed depending on the compositions. Hardness was increased with an increase of alumina and silica concentrations in the glaze.

• Applied Microscopy
• /
• v.34 no.1
• /
• pp.23-29
• /
• 2004

In this study, we introduce the structural analysis of amorphous silica nanoparticles by EF-TEM electron diffraction and in-situ heating experiments. Three diffused rings were observed on the electron diffraction patterns of initial silica nanoparticles, while crystalline spot patterns were gradually appeared during the insitu heating process at $900^{\circ}C$. These patterns indicate the basic unit of $SiO_4$ tetrahedra consisting amorphous silica and gradual crystallization into the ideal layer structure of tridymite by heating. Under high vacuum condition in TEM, SiO nanoparticles were redeposited on the carbon grid after evaporation of SiO gas from $SiO_2$ above $850^{\circ}C$ and the remaining $SiO_2$ were crystallized into orthorhombic tridymite, consistent with ex-situ heating results in furnace at $900^{\circ}C$.