• Journal of the Korean Ceramic Society
• /
• v.23 no.1
• /
• pp.67-73
• /
• 1986

SiC and $SiC-Si_3N_4$ powder were synthesized via the carbiding and carbiding-nitriding reaction of Jecheon quartz respectively using graphite as a reducing agent. $\beta$-SiC+($\alpha$+$\beta$)-$Si_3N_4$ composite was obtained by the carbiding-nitriding reaction of Jecheon quartz-graphite mixture at 1, 35$0^{\circ}C$ in $H_2$ atmosphere. $\beta$-SiC+($\alpha$+$\beta$)-$Si_3N_4$ composite was obtained by the carbidint-nitriding reaction of Jecheon quartz-graphite mixture at 1, 35$0^{\circ}C$ in $N_2-H_2$ atmosphere. The ratio of $\beta$-SiC+($\alpha$+$\beta$)-$Si_3N_4$ content in a produced composite could be controlled by adjusting the reaction time and gaseous mixture.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2008.06a
• /
• pp.413-414
• /
• 2008

• Ceramist
• /
• v.22 no.4
• /
• pp.452-463
• /
• 2019

A quartz glass crucible is the essential material for manufacturing silicon ingots such as semiconductors and solar cells. Quartz glass crucibles for semiconductors and solar cells are made similar, but differ in surface purity, structure and durability. Recently, ultra high purity synthetic glass crucibles for semiconductors have become more important due to foreign problems. In Korea, it has succeeded in producing 28-inch quartz glass crucibles through the past 10 years. However, 32-inch synthetic quartz glass for the production of silicon ingots for semiconductors is not up to the level of advanced technology, and the technology gap is expected to be 2 to 3 years. In order to overcome these technological gaps and localize synthetic quartz glass ware, close cooperation between production companies and demand companies and localization of synthetic quartz glass powder must also be made. In addition, if government support can be added, faster results can be expected.

• Journal of Powder Materials
• /
• v.19 no.6
• /
• pp.412-415
• /
• 2012

The quartz glasses were prepared by sintering of fumed silica powders and the effect of OH concentration on their surface on sintering was studied. Through the firing process, the fumed silica was crystallized from 1180 to $1260^{\circ}C$ region. The amount of hydroxyl group decreased with increase in calcination temperature and consequently the crystallization was prevented. A transparent quartz glass was obtained from fumed silica, previously calcined at $1000^{\circ}C$, by the sintering at $1250^{\circ}C$ for 1 h.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.31 no.4
• /
• pp.295-303
• /
• 2021

Objective: Paint manufacturing industry workers are exposed to various lung cancer carcinogenic substances including hexavalent chromium and crystalline silica. Studies have been conducted on lung cancer in Paint manufacturing industry workers and the concentration of hexavalent chromium in paint industry; however, the concentration of crystalline silica and hexavalent chromium and cases of lung cancer in a single Paint factory has never been reported in Korea. Methods: To determine whether the cancer was related to his work environment, we assessed the level of exposure to carcinogens during pouring and mixing talc and pigment. In addition, a mask fit test was performed for the worker. Results: Analysis of talc and silica bulk powder materials showed that crystalline silica (quartz) was 5% in talc and 100% in silica. The green and yellow pigments contained 87% and 92% of lead chromate, respectively. Our quantitative analysis of pigment powder samples showed that the hexavalent chromium contents quantified in the green and yellow pigment samples were 87% and 92%, respectively. In order to estimate his exposure level of hexavalent chromium, we measured a personal exposure level of hexavalent chromium for a worker in accordance with the National Institute for Occupational Safety and Health #7605 method. The results showed that the worker was exposed to the high level of hexavalent chromium (0.033 mg m-3). In addition, the talc powder also contained 5% quartz, and the worker's exposure level to respirable quartz exceeded OEL. As a result of the respiratory protection fit test for workers, the overall Fit Factor was '15' when wearing a second-grade mask and '25' when wearing a first-grade mask, significantly lower than the US Occupational Safety and Health Agency (OSHA) pass value of "100". Conclusion: Workers who pouring and mixing powder materials such as talc or colored pigments in paint manufacturing company may be exposed to high concentrations of carcinogenic substances. These findings indicate that it is necessary to local ventilation system inspection, safety and health education for employers and workers, and periodically monitoring and manage the working environment.

• Journal of Animal Environmental Science
• /
• v.5 no.3
• /
• pp.157-170
• /
• 1999

This study was conducted to investigate the effects of Scoria, Quartz porphyry and Oak charcoal powder feeding by 1% level of concentrate on the fattening cross bred bulls(5/8 Korean Native Cattle, 2/8 Charolais, 1/8 Brahman germ plasma) Feeding trial was conducted with 4 treatment groups which were T1(Full feeding of concentrate and roughage for 12 months), T2(T1 and Scoria addition), T3(T1 and Quartz porphyry addition) and T4(Oak charcoal addition) for 360 days, consisting of 32 heads whose initially weights were about 299.7kg. The results obtained are summarized as follows; 1. During the over-all period, average daily gains by T3, T4, T2 and T1 were 1.024, 0.987, 0.977kg and 0.964, respectively, without a significant difference by treatments. 2. Concentrate intakes per body weight and TDN intakes required per unit of kilogram gain were lower in addition agent groups than in control, and in all the treatments feed efficiency was higher at early stage for 360 fattening day than at end stage. 3. Carcass weight, dressing percent, back-fat thickness and loin eye muscle area by treatments were 330.9 to 348.4kg(average 340.3kg), 55.2~56.2(average 55.8%), 0.41~0.55(average 0.46cm)and 76.0~80.9$\textrm{cm}^2$(average 77.6$\textrm{cm}^2$), respectively, and were improved in addition agent groups than in control. 4. Meat quality grade is higher in addition agent groups than in control, and heads of 1st grade by treatments was 3, 2, 1 and none in T4, T2, T3 and T1, respectively. 5. Incidence heads of diseases by treatment were not apparently different, but diseases of digestive system was decreased in addition agent groups than in control. 6. The nitrate nitrogen content of fattening bull dung which collected in rectum were 0.082~0.089% (average 0.084%), and the content in addition agent groups was smaller than in controll. 7. Income was higher in order of T4, T3, T2, and T1 and incomes of treatment groups were grater than that of control group by 21.4 to 33.5 percent. According to the above results it may be concluded that fattening bulls may be required to feed no more than 1% of Scoria, Quartz porphyry and Oak charcoal powder based on the concentrate feeding level during the fattening period(12 to 24 month of age) to produce high quality meat and increase income.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07b
• /
• pp.1241-1244
• /
• 2003

The materials showing high structure dispersity are developed on the natural quartz base and they are obtained by mechano-chemical technology. Depending on the processing conditions and subsequent applications the materials produced by mechano-chemical reaction (MCR) show concurrently magnetic, dielectric and electrical properties. The obtained magnetic-electrical powders classified by aggregate complex of their features as segnetomagnetics, contain a dielectric material as a carrying nucleus, particularly the quartz on that surface one or more layers of different compounds are synthesized having thickness up to $10{\sim}50nm$ and showing magnetic, electrical and other properties.

• Journal of the Korean Ceramic Society
• /
• v.46 no.3
• /
• pp.306-312
• /
• 2009

The size of various alumina ceramics used in semiconductor and display industry is also required to increase with increase in wafer and panel size. In this research, large alumina ceramics was fabricated by filter pressing of alumina slurry using commercial powder and thereafter sintering at $1600^{\circ}C$ in gas furnace. The characteristics of large alumina ceramics thereby were compared to those of small alumina ceramics prepared by pressure forming such as uniaxial pressing and CIP. Careful control of properties of alumina slurry and filter pressing made the fabrication of large alumina ceramics possible, and its characteristics were equivalent to those of small alumina ceramics. The large alumina ceramics, prepared by sintering the green body of 63% relative density at $1600^{\circ}C$, exhibited both dense microstructure corresponding to 98.5% of relative density and 99.8% of high purity as in starting powder.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.173-174
• /
• 2006

X-ray analysis on iron ores and reduced iron powders revealed that the main acid-insoluble substances were hexagonal and tetragonal quartz, another substances were sillimanite, alumina-silicate, an unnamed zeolite, all contained Si and Al. Their particle size was in the range of $3{\sim}7\;{\mu}m$. Statistics analysis showed that the AIC for high-grade magnetite powder was $(0.130{\pm}0.010)%$) during the latest five months. The predicting value for reduced iron powder should be 0.179%. However, the testing value for reduced iron powder was $(0.192{\pm}0.014)%$. The limited difference of 0.013% might imply rare pollution coming from the reduction and milling processes. The most important step for control AIC should be the separation process of iron ore powders.

• Journal of Korea Water Resources Association
• /
• v.40 no.9
• /
• pp.723-734
• /
• 2007

This study was to investigate the settling velocity which is an important factor for the prediction of cohesive deposition under the various densities of particle and dissolved ion addition$(Na^+,\;Cl^-,\;OH^-,\;H^+)$ in rivers, ports, reservoirs and lakes. Settling velocity of suspended fine particles in still water was measured with a pressure sensor (maximum 10 mbar). At the initial concentration of 20g/l of alumina and quartz the average settling velocities were high due to the aggregation behaviour of particles. At this point it was 0.185 mm/s (alumina) and 0.022 mm/s (quartz). Above this initial concentration it was on the decrease owing to the hindered settling. The higher the salinity is, the faster the settling velocity of alumina and quartz is. Furthermore, in an acid condition the average settling velocity of alumina was on the decrease. In an alkaline water, which causes strong flocculation, the average settling velocity of alumina it was observed on the increase. However, in an alkaline medium the low average settling velocity of quartz powder was measured.