• Journal of the Korean Ceramic Society
• /
• v.36 no.8
• /
• pp.853-858
• /
• 1999

To investigate the effect of H2 flow rate and TMS[Si(CH3)4] concentration on synthesizing ultrafine ${\beta}$-SiC powder by vapor phase reaction the experiment was performed at 1100$^{\circ}C$ of the reaction temperature under the condition of 200-2000 cc/min of H2 gas flow rate and 1-10% of TMS concentration respectively. The shape of ${\beta}$-SiC particles synthesized was spherical and the size of particles decreased and the distribution of particles was more uniform with increasing H2 gas flow rate. In this case Si powders were coexisted with ${\beta}$-SiC Pure and ultrafine ${\beta}$-SiC powders without Si were obtained under the condition of above 2% of TMS concentration and below 1500 cc/min of H2 gas flow rate.

• Journal of Korean Society for Atmospheric Environment
• /
• v.29 no.5
• /
• pp.656-667
• /
• 2013

The non-exhaust coarse, fine, and ultrafine particles were characterized by on-road driving measurements using a mobile sampling system. The on-road driving measurements under constant speed driving revealed that mass concentrations of roadway particles (RWPs) were distributed mainly in a size range of 2~3 ${\mu}m$ and slightly increased with increasing vehicle speed. Under braking conditions, the mode diameters of the particles were generally similar with those obtained under constant speed conditions. However, the PM concentrations emitted during braking condition were significantly higher than those produced under normal driving conditions. Higher number concentrations of ultrafine particles smaller than 70 nm were observed during braking conditions, and the number concentration of particles sampled 90 mm above the pavement was 6 times higher than that obtained 40 mm above the pavement. Under cornering conditions, the number concentrations of RWPs sampled 40 mm above the pavement surface were higher than those sampled 90 mm above the pavement. This might be explained that a nucleation burst of a lot of vapor evaporated from the interaction between the tire and the road pavement under braking conditions continuously occurred by cooling during the transport to the sampling height 90 mm, while, for the case of cornering situations, the ultrafine particle formation was completed before the transport to the sampling height of 40 mm.

• Journal of Korean Society for Atmospheric Environment
• /
• v.24 no.4
• /
• pp.404-414
• /
• 2008

A Transient Differential Mobility Particle Spectrometer (TR-DMPS) with a short response time was recently developed to monitor high concentration of ultrafine particles emitted from vehicles. To investigate the availability of the TR-DMPS for monitoring transient roadside aerosols, the number size distribution of ultrafine particles was monitored at the Cheongnyangni roadside in Seoul on March 23, 2007 together with a Scanning Mobility Particle Sizer (SMPS). The roadside aerosols were monitored every 5 min and 0.1 sec by using the SMPS and the TR-DMPS, respectively. The concentration of ultrafine particles at the roadside was highly fluctuated for a short duration. From the comparison of particle number concentrations and size distributions between two instruments, it was confirmed that the SMPS provided fairly good time-averaged number size distribution although it did not follow rapid change of particle number concentration at the roadside. The TR-DMPS quickly responded to a rapid change of particle number concentration due to abrupt traffic flow. However, the TR-DMPS frequently showed electrical noise events, resulting in underestimated particle contamination. A more stable operation of the TR-DMPS is needed in application of roadside aerosol monitoring.

• Atmosphere
• /
• v.28 no.3
• /
• pp.337-355
• /
• 2018

Ultrafine particles (< 100 nm in diameter, UFP) are known to be more toxic per unit mass than larger particles and contribute to more than 90% in particle number concentrations in urbanized cities but much less in mass. The major sources of UFP are vehicle emissions in urban areas. Due to their tiny size (the sizes of UFP from vehicle emissions range from 10 to 60 nm depending on engine and fuel types), inhaled UFP can reach the deepest area of respiratory track (e.g., pulmonary alveoli) as well as all of the body via lymph and blood circulation causing various adverse health effects. This article reviews the sources and emission factors of UFP, temporal and spatial distributions in urban areas and their health effects reported by toxicological and epidemiological studies. We also compared the levels of UFP concentrations measured in other countries with those in Korean cities to evaluate the public exposure to UFP in Korea. Ultimately, we expect this study can contribute to developing the risk assessment techniques for public exposure to UFP in the urbanized cities in Korea.

• Asian Journal of Atmospheric Environment
• /
• v.1 no.1
• /
• pp.1-8
• /
• 2007

Vehicle exhaust is a dominant source of air pollutants in urban areas. Since people are easily exposed to vehicle exhaust particles while driving a car and/or traveling via public transportation, air pollution near traffic has been extensively studied in developed countries. In this paper, investigations on vehicle-related fine particulate air pollution at roadsides and on roads in Seoul, Korea were reviewed to understand air pollution near traffic. Comparison of $PM_{10}$ concentrations in Seoul showed that roadside air is more contaminated than urban air, implying that exposure levels near vehicular emissions are more critical to sensitive persons. Concentrations of ultrafine particles and BC (black carbon) at roadsides of Seoul fluctuate highly for short durations, responding to traffic situations. Diurnal variations of ultrafine particles and BC concentrations at roadsides seem to be affected by traffic volume, mixing layer height, and wind speed. Concentrations of ultrafine particles and BC decrease as distance from the road increases due to dilution during transport. On-road air pollution seems to be more severe than roadside air pollution in Seoul. Since nearby traffic air pollution has not been well understood in Seoul, further studies including various vehicular air pollutants and representative locations are needed.

• Journal of the Korean Ceramic Society
• /
• v.32 no.1
• /
• pp.37-44
• /
• 1995

TiO2 fine powders were synthesized using oxygenolysis and hydrolysis reaction of TiCl4 vapor in gas phase. The TiO2 powder synthesized showed morphological differences depending on reaction system as follows: TiCl4-O2 reaction system produced the monosized particles having polyhedral shape with well-defined crystal planes and the particles did not agglomerate into secondary particles. TiCl4-H2O reaction system, whereas, produced the spherical secondary particles which consisted of fine primary particles. Other powder characteristics such as particle size, impurity content and rutile content are also reported in this study.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.4
• /
• pp.48-53
• /
• 2010

Roadside measurement of ultrafine particles, black carbon, and NOx was carried out to investigate air pollution at a junction area contaminated with vehicle emissions in Seoul from March 19 to 23, 2007. Diurnal variation of ultrafine particles, black carbon, and $NO_x$ concentrations at a roadside showed minimum at around 2-4 a.m. and two peak modes during the morning and evening rush hours. Since these pollutants might be mainly emitted from vehicles, the roadside was highly contaminated with vehicles.

• Corrosion Science and Technology
• /
• v.5 no.1
• /
• pp.23-26
• /
• 2006

Recent development of ultrafine grained (UFG) low carbon steels by using equal channel angular pressing (ECAP) and their room temperature tensile properties are reviewed, focusing on the strategies overcoming their inherent mechanical drawbacks. In addition to ferrite grain refinement, when proper post heat treatments are imposed, carbon atom dissolution from pearlitic cementite during ECAP can be utilized for microstructural modification such as uniform distribution of nano-sized cementite particles or microalloying element carbides inside UFG ferrite grains and fabrication of UFG ferrite/martensite dual phase steel. The utilization of nano-sized particles is effective on improving thermal stability of UFG low carbon ferrite/pearlite steel but less effective on improving its tensile properties. By contrast, UFG ferrite/martensite dual phase steel exhibits an excellent combination of ultrahigh strength, large uniform elongation and extensive strain hardenability.

• The Korean Journal of Ceramics
• /
• v.5 no.3
• /
• pp.303-305
• /
• 1999

Ultrafine cobalt ferrite particles have been synthesized using a microemulsion method. All peaks of X-ray diffranction patterns are fairly broad but correspond to a cubic spinel structure with the lattice constant 8.39$\AA$. The coercivity measureed at 5K is 15.1 kOe. The maximal magnetization measured at 5 and 300 K are 13.2 and 10.7 emu/g, respectively. The particles behave ferrimagnetically at 5 K but superparamagnetically at 300K. Superparamagnetic behavior of the particles at room temperature was confirmed by the conincidence of the M vs. H/T at different temperatures and the Mossbauer spectrum.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.5
• /
• pp.710-715
• /
• 2002

The spherical nonagglomerated and uniform nanometer-size SiO$_2$particles are synthesized by the injection of TEOS vapor, irons and reaction gas in a furnace. Ions are generated by corona discharge and these ions charge SiO$_2$particles. As a result, spherical, nonagglomerated and ultrafine particles are generated in various conditions. Their morphology, charging portion and size distribution are examined by using TEM, ESP and SMPS. As the applied voltage of electrode changes from 0 to 5.0 kV, it is observed that the melon diameter of SiO$_2$particle decreases from 94 nm to 42 nm.