• Economic and Environmental Geology
• /
• v.34 no.1
• /
• pp.1-12
• /
• 2001

The crystal structure of biotite-1M from Bancroft, Ontario, was determined by Rietveld refinement method using high-resolution neutron powder diffraction data at -26.3$^{\circ}C$, 2$0^{\circ}C$, 30$0^{\circ}C$, $600^{\circ}C$, 90$0^{\circ}C$. The crystal structure has been refined to a R sub(B) of 5.06%-11.9% and S (Goodness of fitness) of 2.97-3.94. The expansion rate of a, b, c unit cell dimensions with elevated temperature linearly increase to $600^{\circ}C$. The expansivity of the c dimension is $1.61{\times}10^{40}C^{-1}$, while $2.73{\times}10^{50}C^{-1}$ and $5.71{\times}10^{-50}C^{-1}$ for the a and b dimensions, respectively. Thus, the volume increase of the unit cell is dominated by expansion of the c axis as increasing temperature. In contrast to the trend, the expansivity of the dimensions is decreased at 90$0^{\circ}C$. It may be attributed to a change in cation size caused by dehydroxylation-oxidation of $Fe^{2+}$ to $Fe^{3+}$ in vacuum condition at such high temperature. The position of H-proton was determined by the refinement of diffraction pattern at low temperature (-2.63$^{\circ}C$). The position is 0.9103${\AA}$ from the O sub(4) location and located at atomic coordinates (x/a=0.138, y/b=0.5, z/c=0.305) with the OH vector almost normal to plane (001). According to the increase of the temperature, $\alpha$* (tetrahedral rotation angle), $t_{oct}$ (octahedral sheet thickness), mean distance increase except 90$0^{\circ}C$ data. But the trend is less clearly relative to unit cell dimension expansion because the expansion is dominant to the interlayer. Also, ${\Psi}$ (octahedral flattening angle) shows no trends as increasing temperature and it may be because the octahedron (M1, M2) is substituted by Mg and Fe.

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

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.6
• /
• pp.585-592
• /
• 2011

The enhancement of the cold-start capability of polymer electrolyte fuel cells is of great importance in terms of the durability and reliability of fuel-cell vehicles. In this study, vanadium oxide films deposited onto the flat surface of metallic bipolar plates were synthesized to investigate the feasibility of their use as an efficient self-heating source to expedite the temperature rise during startup at subzero temperatures. Samples were prepared through the dip-coating technique using the hydrolytic sol-gel route, and the chemical compositions and microstructures of the films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. In addition, the electrical resistance hysteresis loop of the films was measured over a temperature range from -20 to $80^{\circ}C$ using a four-terminal technique. Experimentally, it was found that the thermal energy (Joule heating) resulting from self-heating of the films was sufficient to provide the substantial amount of energy required for thawing at subzero temperatures.

• Journal of the Korean Chemical Society
• /
• v.37 no.3
• /
• pp.302-308
• /
• 1993

Monolayers of calcium palmitate were deposited on a piezoelectric quartz crystal plate by the Langmuir-Blodgett(LB) technique, and it was found from frequency changes of the quartz crystal deposited LB films. The usual carbonyl absorbance at 1704 cm$^{-1}C$ was replaced by the split band in the 1540~1590 cm$^{-1}C$. The two absorptions at 1580 cm$^{-1}C$ and 1540 cm$^{-1}C$ were assigned to the antisymmetric stretching vibration of the calcium carboxylate group and the hydrated species due to the lowering carbonyl stretching frequency by hydrogen bonding$^1$ respectively. Besides, it was demonstrated by X-ray diffraction analysis. The swelling behaviour of LB films in water phase at 23$^{\circ}C$ was observed from the frequency change of the LB films deposited quartz crystal with time. Calcium palmitate LB films has been found to swell substantially in water without flaking, whereas hexadecanol LB films hardly swelled in water. Amount of swelling of calcium palmitate LB films was equivalent to 47 wt.${\%}$ of the dry LB films, which means that ca. 7 water molecules were incorporated per calcium palmitate amphiphile. Chemical structure of calcium palmitate LB film was estimated as [CH$_3$(CH$_2$)$_{14}$COO]$_2$Ca${\cdot}$XH$_2$O, and the hydration number was 1.

• The Journal of Engineering Research
• /
• v.1 no.1
• /
• pp.5-14
• /
• 1997

The purpose of thesis is to analyze the radiation characteristics of an offset gregorian antenna in order to design the satellite-loaded antenna. In order to compute the radiation pattern of the sub-reflector, the reflected wave is obtained by GO(Geometric Optics) at an arbitrary shaped sub-reflector. Then the total radiation EM wave is obtained by summing the diffracted fields obtained by UTD(Uniform Geometrical Theory of Diffraction) and the GO fields. In order to calculate the far field radiation pattern of the main reflector, the radiation integral equation is derived from the induced current density on reflector surface using PO(Physical Optics). The kernel is expanded in terms of Jacobi-Bessel series for increasing the computational efficiency, then the modified radiation integral is represented as the double integral equation independent of observation points. When the incident fields are assumed to be x-or y-polarized field, the characteristics of radiation patterns in the gregorian antenna is analyzed in case of the main reflector having the focal length of 62.4$\lambda$, diameter of 100$\lambda$, and offset height of 75$\lambda$, and the sub-reflector having the eccentricity of 0.501, the inter focal length og 32.8$\lambda$, the horn axis angle of $9^{\circ}$ and the half aperture angle of $15.89^{\circ}$. The cross-polarized level and side lobe level in the offset geogorian reflector are reduced by 30dB and 10dB, respectively, in comparison with those of the offset parabolic antenna.

• Polymer(Korea)
• /
• v.25 no.5
• /
• pp.691-698
• /
• 2001

Nanocomposites based on epoxy acid nanoclay were prepared employing organically modified mica type silicate (OMTS), diglycidyl ether of bisphenol A (DGEBA) type epoxy. curing agent (dicyandiamide; DICY), and catalyst (benzyl dimethyl amine; BDMA). Both melt mixing and solution mixing were und for the sample preparation and structural developments with curing reaction were analyzed using X-ray diffractometer (XRD) and small angle X-ray scattering (SAXS). Because of the different curing rate between extra-gallery and intra-gallery reactions of epoxy mixtures, only intercalated structure was observed for the sample prepared by melt mixing while fully exfoliated structure was observed for the sample prepared by solution mixing. Mechanical properties of exfoliated epoxy nanocomposite were investigated using a dynamic mechanical analyzer (DMA). The dynamic storage modulus of the nanocomposite in both glass and rubbery plateau regions were increased with increasing OMTS contents, but glass transition temperatures ($T_g$) remained unchanged. Thermal properties of epoxy nanocomposite were investigated using thermogravimetric (TGA) and limit oxygen index (LOI) methods. Thermal decomposition onset points and LOI values were increased with increasing OMTS contents due to barrier effects of OMTS sheets.

• Korean Journal of Optics and Photonics
• /
• v.8 no.1
• /
• pp.1-6
• /
• 1997

The amplitude impulse S(x) of an interferometric optical imaging system for λ=193 nm(ArF laser) and NA=0.5 is derived for the pupil with superposed three Gauss pupils $A_1$($\omega$), $A_{2-}$($\omega$) and $A_{2+}$($\omega$). It is shown that FWHM of S(x) can be far less than the Rayleigh's criterion of resolution $\frac{1}{2}{\epsilon}_R$, where ${\epsilon}_R$ is equal to λ=193 nm in the present case of NA=0.5. The three Gauss pupils are provided in an optical system which consists of a Twyman-Green interferometer and an imaging system. The system is proposed and relevent optical components are discussed. Siloxane polymer is suggested for fabrications of amplitude modulation plates. In the present work, we assumed the system is free from aberration and linear. The case that the system has residual aberrations is important, and further work is necessary.

• Journal of the Korean Chemical Society
• /
• v.31 no.1
• /
• pp.102-109
• /
• 1987

Some characteristics of $SnO_2$ film which was deposited on a slide glass substrate, using dibutyl tin diacetate and oxygen, by the chemical vapor deposition were observed. The optimum condition for the preparation of the film was found to be at 420$^{\circ}C$ of substrate temperature for 20 min of deposition. Important optical, electrical, and structural features of the film were examined. It was found that the typical $SnO_2$ film on the untreated substrate was 4000${\AA}$ in thickness, transmitted 90% of the visible liglit, and provided 5800 ohms/${\square}$ of the sheet resistance. It was also found that the surface treatments of the slide glass by acid leaching were beneficial. The film structure was found to be a mixture of polycrystalline tetragonal stannic oxide confirmed by the X-ray diffraction and to be spherical fine grains concluded by the scanning electron microscopy.

• Polymer(Korea)
• /
• v.33 no.4
• /
• pp.313-318
• /
• 2009

Copolyimides were synthesized from bis (3-aminophenyl) sulfone (APS) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) containing a fluorine substituent ($-CF_3$) with different mole ratios of 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA) containing a sulfone group (-$SO_2$-). The PI films were obtained from poly (amic acid) (PAA) by solution casting through thermal imidization on a glass plate. Wide-angle X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), universal tensile machine (UTM) measurements, and UV-Vis spectrometry were used to assess thermo-mechanical properties, morphology, and optical transparency. Thermal properties and optical transparency decreased with increasing DSDA mole fraction. In contrast, mechanical properties increased with increasing DSDA mole fraction. As compared to conventional PI films, however, the PI copolymer films in this work were found to exhibit better optical transparency.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.6
• /
• pp.1302-1307
• /
• 2006

This study describes the preparation of high-performance photocatalyst and its environmental applications. We prepared visible-light response nano-particle photocatalyst exhibiting the similar photocatalytic activity with $TiO_2$, dispersed $TiO_2$ on $SiO_2$ with an active rutile type titanium oxide prepared at low temperature. The binder and stable photocatalytic $TiO_2$ sol for photocatalytic system were also prepared. Such products were evaluated by UV/Vis spectrometer, X-ray diffraction analysis, SEM, measurement of photocatalytic activities and surface area, mechanical properties of $TiO_2$-coated surfaces. The results obtained can be applied in efficient photocatalytic systems using POF and metal plate for the purification of air.