• Journal of the Mineralogical Society of Korea
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• v.31 no.1
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• pp.47-55
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• 2018

Talc, hydrous magnesium phyllosilicate, is one of the most popular industrial minerals due to their chemical stability and adsorptivity. While micro-sized talc has long been used as a filler and coating, nano-sized talc recently is attracting attention as additives for improving the stability of nanocomposites. In this study, we produced the nano-sized talc powder by mechanical method using high energy ball mill and investigated the changes in particle size and crystallinity with increasing milling time up to 720 minutes. X-ray diffraction results show that the peak width of talc gradually as the milling proceeded, and after 720 minutes of pulverization, the talc showed an amorphous-like X-ray diffraction pattern. Lase diffraction particle size analysis presents that particle size of talc which was ${\sim}12{\mu}m$ decreased to ${\sim}0.45{\mu}m$ as the milling progressed, but no significant reduction of particle size was observed even after grinding for 120 minutes or more. BET specific surface area, however, steadily increases up to the milling time of 720 minutes, indicating that the particle size and morphology change steadily as the milling progressed. Scanning electron microscope and transmission electron microscope images shows that layered particles of about 100 to 300 nm was aggregated as micro-sized particles after pulverization for 720 minutes. As the grinding time increases, the particle size and morphology of talc continuously change, but the nano-sized talc particles form micro sized agglomerates. These results suggest that there is a critical size along the a, b axes in which the size of plates is reduced even though the grinding proceeds, and the reduction of plate thickness along the c axis leads the increase in specific surface area with further grinding. This study could enhance the understanding of the mechanism of the formation of nano-sized talc by mechanical grinding.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2013.04a
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• pp.116-116
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• 2013

마그네슘은 스마트폰, 전자기기 케이스, 내화벽돌과 아크용접봉 제조시의 첨가물 등으로 사용되고 있는데, 최근에는 재활용을 위한 마그네슘 용해로를 취급하거나 가공하는 사업장이 증가하고 있어 사고위험성이 높아지고 있다. 금속분을 취급하는 사업장에서의 금속분진은 저장이나 축적 등과 같이 주로 퇴적물로서 존재한다. 퇴적분진의 발화온도는 퇴적물 형상과 두께, 입경, 분위기 가스의 유속, 산소농도, 부유분진의 농도, 퇴적밀도, 수분 등의 많은 영향인자가 관여하기 때문에 이론적 예측이 힘들고 실험적인 측정에 의존할 수 밖에 없는 것이 현실이다. 본 연구에서는 연소성이 높고 화재폭발사고사례가 많은 마그네슘(Mg) 분진을 사용하여 승온속도 변화에 따른 열분해특성을 조사하였다. 퇴적분진의 열적특성을 조사하기 위하여 METTLER TOLEDO의 TGA/DSC1를 사용하였으며, Mg 시료의 평균입경은 38, $142{\mu}m$이다. 입경 $38{\mu}m$의 Mg 시료의 열중량분석 결과, 중량증가는 $400{\sim}500^{\circ}C$의 범위에서 시작되며 $550^{\circ}C$에서 급격하게 중량이 증가하고 있으며, 증량증가개시온도(Temperature of weight gain)는 $460^{\circ}C$에서 시작하여 $900{\sim}950^{\circ}C$ 범위에서 중량 증가 포화값에 도달하였다. 입경 $142{\mu}m$의 Mg에 대하여 공기중 승온속도를 5, 10, $20^{\circ}C/min$으로 변화시키면서 실온에서 $900^{\circ}C$까지 가열 시키는 경우의 시료의 중량 변화에 따른 열분해 특성은 승온속도가 증가할수록 2단계의 S자 곡선은 완만하게 상승을 나타내며 중량증가개시온도가 높아지는 경향을 보이고 있다. 중량증가개시온도가 승온속도에 따라 변화하는 결과를 나타내고는 있지만, 시료량의 증가에 따른 영향을 열중량분석 실험방법의 제약으로 인하여 확인할 수 가 없었다. 그러나 만일 시료량이 크게 증가하는 경우에는 동일한 승온조건에서 중량증가 개시온도는 낮아질 가능성이 있다. 중량증가는 시료의 산화반응에 의한 것이므로 시료량의 증가는 시료 내부에의 열의 축적을 용이하게 하여 보다 낮은 온도에서도 산화반응이 충분히 일어나는 조건이 형성되기 때문이다. 승온속도가 증가할수록 산화 반응한 괴상형태의 연소입자가 크게 증가하고 있는 것을 알 수 있다. 승온속도에 따른 중량개시온도 곡선을 보면 [그림 24]와 같으며 승온속도 5, 10, $20^{\circ}C/min$의 증가에 따라 중량개시온도는 각각 490, 510, $530^{\circ}C$가 얻어졌으며 승온속도의 증가에 따라 중량개시온도가 증가하는 경향을 보이고 있다.

• Journal of the Korean Institute of Gas
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• v.21 no.4
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• pp.84-91
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• 2017

Recent years have witnessed the increased usage of flammable metals, such as aluminum or magnesium, in wide range of high-tech industries. These metals are indispensable for the improvement of physical properties of materials as well as the design capability of the final product. During the process, unwanted metal dusts could be released to the environment. This can lead to an occupational health and safety issues. Due to their flammable nature, more serious problem of an explosion can happen in extreme cases. The explosion is the combustion of tiny solid particles and vapor mixture, caused by pyrolysis. This complex composition makes engineering analysis more difficult, compared to simple gas explosions or vapor cloud combustions. The study was conducted to assess this light metal dust explosion in an effort to provide the bases for a risk assessment. Dust explosion characteristics of each material was carefully evaluated and an appropriate analysis tool was developed. A comprehensive database was also constructed and utilized for the calibration of the developed response model and the verification for its accuracy. Subsequently, guidelines were provided to prevent dust explosions that could occur in top-notch industrial processes.

• Proceedings of the KOR-BRONCHOESO Conference
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• 1981.05a
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• pp.11.2-11
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• 1981

Compared with other medical parts, there are relatively rare cases of the calculi in the Otolaryngologic field. The authors have recently experienced cases of the tonsillolith and huge rhinolith. They were removed successfully under the local anesthesia. Small quantities of calcareous or gritty particles are often found in the center of the caseous plugs filling the crypts of the tonsil in chronic follicular tonsillitis. The patients usually give a history of repeated tonsillitis in the earlier years. The patient may be aware of a constant sensation as of a foreign body in the throat. The breath is often fetid. The tonsillar calculi was found to be the accumulated keratohyalin masses in the crypts. The rhinoliths are rare in nasal cavity. They usualy have a foreign body nucleus of bacteria, blood, pus cells, mucus, crusts, or some foreign material from outside the body. They are largely composed of calcium and magnesium salts, principally carbonate with traces of sodium chloride. The condition is commonly found in adults and in female. They are usualy unilateral and are located, in the majority of instances, in the lower portion of the nasal cavity. The first well documented cases of rhinolithiasis, however, were reported by Bartholin in 1654. Since then over 400 cases have been reported.

• Journal of the Mineralogical Society of Korea
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• v.30 no.4
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• pp.161-172
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• 2017

Clay minerals play a major role in the geochemical cycles of metals in the Critical Zone, the Earth surface-layer ranging from the groundwater bottom to the tree tops. Atomistic scale research of the very fine particles can help understand the fundamental mechanisms of the important geochemical processes and possibly apply to development of hybrid nanomaterials. Molecular dynamics (MD) simulations can provide atomistic level insights into the crystal structures of clay minerals and the chemical reactivity. Classical MD simulations use a force field which is a parameter set of interatomic pair potentials. The ClayFF force field has been widely used in the MD simulations of dioctahedral clay minerals as the force field was developed mainly based on dioctahedral phyllosilicates. The ClayFF is often used also for trioctahedral mineral simulations, but disagreement exits in selection of the interatomic potential parameters, particularly for Mg atom-types of the octahedral sheet. In this study, MD simulations were performed for trioctahedral clay minerals such as brucite, lizardite, and talc, to test how the two different Mg atom types (i.e., 'mgo' or 'mgh') affect the simulation results. The structural parameters such as lattice parameters and interatomic distances were relatively insensitive to the choice of the parameter, but the vibrational power spectra of hydroxyls were more sensitive to the choice of the parameter particularly for lizardite.