• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.552-560
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• 1994

A composite of TiB2-Al2O3 system was successfully prepared from a mixture of TiO2, B2O3, and Al by self-propagating high temperature synthesis (SHS) with a novel characteristic, utilizing the internal oxidation heat of aluminium metal of the mixture, instead of by a conventional technique, externally heating a mixture of Ti, B and Al2O3. From a mixture with B/Ti molar ratio of =2.0, pure two phases of TiB2 and $\alpha$-Al2O3 with good crystallinity and small, uniform sizes were formed. However, when the B/Ti molar ratio of the mixture goes to a value less than 2.0, in addition to the above main minerals, a small smounts of metastable phases such as TiB and Ti3B4 were formed. It was found that about 60%, the optimum green density of compacts gave their highest reaction rate and temperature during SHS process. TiB2-Al2O3 system composite with B/Ti molar ratio of =2.0 could be pressurelessly sintered even at 190$0^{\circ}C$ under Ar gas flows without any addition of sintering aids, showing their good properties such as 91.2% in relative density, 2750 kgf/$\textrm{mm}^2$ in Vickers hardness and 2620 kgf/$\textrm{cm}^2$ in flexural strength.

• Journal of the Korean institute of surface engineering
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• v.38 no.4
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• pp.150-155
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• 2005

Highly conductive and transparent in the visible region tin-doped indium oxide(ITO) thin films were deposited on Corning glass by r.f sputtering. To achieve high transmittance and low resistivity, we examined various parameters such as r.f power and deposition time. The films crystallinity shifted from (222) to (400) and (440) orientation as deposition time and r.f power increased. Surface roughness RMS value increased proportionally with deposition time. The lowest resistivity was $5.36{\times}10^{-4}{\Omega}{\cdot}cm$ at 750 nm thickness, $200^{\circ}C$ substrate temperature and 125 w r.f power. All of the films showed over $85\%$ transmittance in the visible wavelength range.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.43 no.3
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• pp.73-79
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• 2011

The annals of Joseon Dynasty is one of the UNESCO's Memory of the World Register. For the safety preservation of wax applied volumes of the annals of Joseon Dynasty, the aging behavior of beeswax and beeswaxed Hanji with $CO_2$, $O_3$, $SO_2$ and $NO_2$ gas has been evaluated. The weight loss of beeswaxed Hanji after aging under ozone gas were increased because of strong acidity of ozone. The acid value and relative intensity of carbonyl groups in beeswax were stabilized with aging time. The physical strength of dewaxed Hanji after ozone aging were rapidly decreased by aging time. The crystallinity of dewaxed Hanji were stabilized at all aging times.

• Korean Journal of Materials Research
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• v.19 no.3
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• pp.125-131
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• 2009

In this report, the structural and optical properties of sol-gel derived $Mg_xZn_{1-x}O$ thin films upon changes in the composition and annealing temperature were investigated. The $Mg^{2+}$ content and the annealing temperature were varied in the range of $0{\leq}x{\leq}0.35$ and $400^{\circ}C{\leq}T{\leq}600^{\circ}C$, respectively. The films exhibited a hexagonal wurtzite structure of a polycrystalline nature. The optical transmittance exceeded 85% and the optical band gap of the film was tuned as high as 3.84 eV at a value of x = 0.35 (annealed at $400^{\circ}C$), which was evidently the maximum $Mg^{2+}$ content for the single-phase polycrystalline $Mg_xZn_{1-x}O$ thin films prepared in this experiment. The optical band gap and photoluminescence emission were tailored to the higher energy side while maintaining crystallinity without a significant change of the lattice constant.

• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.631-638
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• 1988

Effect of Ca/P mole ratio on the precipitates and powder properties of hydroxyapatite was investigated. Powder and precipitates of hydroxyapatite were synthesized by the reaction of Ca(NO3)2.4H2O and (NH4)2 HPO4 solutions at room temperature. The pH value and compositions (Ca/P mole ratio) in starting solutions were 11 and 1.64-1.79(or 1.85), respectively. Rodlike hydroxyapatite precipitates were agglomerated together. The average agglomerated particle size was ranged from 2-8${\mu}{\textrm}{m}$. Among compositions, the minimum agglomerated particle size was shown at the Ca/P mole ratio 1.75. CO2 was contained in hydroxyapatite powders and these ultrafine powders had poor crystallinity. The specific surface area and specific total pore volume of hydroxyapatite powders were 104-137$m^2$/g and 0.396-0.467cc/g, respectively. When the Ca/P mole ratio was 1.75, these values were the maximum. And water content increased with the Ca/P mole ratio(Ca/P mole ratio>1.67). In most cases, hydroxyapaite was stable to 130$0^{\circ}C$. However, in the case of Ca/P mole ratio 1.64, hydroxyapatite was changed to $\alpha$-whitlockite at 120$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.44 no.6 s.301
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• pp.313-318
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• 2007

ITO (Indium-tin oxide) thin films have been prepared by a sol-gel spinning coating method and fired and annealed in the temperature range of $450-600^{\circ}C$. The XRD patterns of the films indicated the main peak of (222) plane and showed higher crystallinity with increasing an annealing temperature. The surface of the ITO thin films were treated with 0.1 N HCl 20% solution at room temperature. The effects of surface treatment on electrical properties and surface morphologies of the ITO films were investigated with the results of sheet resistance and FE-SEM, AFM images. The samples, subsequently treated with acidic solution for 40 sec showed the sheet resistance of $0.982\;k{\Omega}/square$. The surface treatment using acidic solution diminished the RMS (root mean square) value and the residual carbon content of the ITO films. It seemed that the acid-cleaning of the ITO thin films lead to the decrease of surface roughness and sheet resistance.

• Proceedings of the Materials Research Society of Korea Conference
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• 1993.05a
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• pp.99-100
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• 1993

Calorimetric (D.S.C) studies were carried out on the nylon 4,6 single crystals grown from 1,4-butanediol solution at various crystallisation temperatures, based on the assessment of the lamellar thickness by small angle x-ray scattering. Samples were annealed mainly ot get rid of residual solvents inside the crystals. The effect of annealing on the crystal perfection is inferred from the measured thermal properties of the crystals. Accordig to the scanning rates less than 80 K/min., D. S C. melting peaks indicate that changes in the internal morphology of nylon 4,6 crystals preapred at different crystallisation temeratures yield a thermodynamic melting temperature. Tm, of 319 $^{\circ}C$, for the infinitely extended crystal thickness (1/ι). The obtained heat of fusion value for the inginite crystal thickness, Ho, was 270 J/g from the plot of measured feat of fusion ($\Delta$Hm) vs. reciprocal crystal thickness (1/ι). based on these values, the fold surface energy, $\delta$e. of 65.4 erg/$\textrm{cm}^2$ was obtained from Hoffman-Waeeks equation. The thermodynamic melting temperature and heat of fusion of the infinite crystal thickness for the solution grow nylon 4,6 single crystals are found to be higher than of the reported corresponding solution grown nylon 6,6 single crystals. pbtained crystallinity from D. S. C measurements ranges from 40 to 50 %, which is close to the reported yalue for the nylon 6,6 single ctystals but lower than we expected.

• Journal of the Korean Ceramic Society
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• v.45 no.1
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• pp.36-42
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• 2008

Carbon/$TiO_2$ composite photocatalysts were thermally synthesized with different mixing ratios of anatase to phenol resin through an ethanol solvent dissolving method. The XRD patterns revealed that only anatase phase can be identified for Carbon/$TiO_2$ composites. The diffraction peaks of carbon were not observed, however, due to the low carbon content on the $TiO_2$ surfaces and the low crystallinity of amorphous carbon. The results of chemical elemental analyses of the Carbon/$TiO_2$ composites showed that most of the spectra for these samples gave stronger peaks for carbon and Ti metal than that of any other elements. The BET surface area increases to the maximum value of $488\;m^2/g$ with the area depending on the amount of phenol resin. From the SEM images, small $TiO_2$ particles were homogeneously distributed to a composite cluster with the porosity of phenol resin-based carbon. From the photocatalytic results, the MB degradation should be attributed to the three kinds of synergetic effects, such as photocatalysis, adsorptivity, and electron transfer by light absorption between supporter $TiO_2$ and carbon.

• Journal of the Korean institute of surface engineering
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• v.23 no.2
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• pp.18-23
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• 1990

Thin films of tin oxide were prepared by chemical vapor deposition (C.V>D) using the hydrolysis reaction of SnCl4, Deposition rate increased with the increase of temperature up to $500^{\circ}C$and then decreased at $700^{\circ}C$, Deposition rate with SnCl4 partial pressure showed RidealEley behavir. It was found that SnO2 thin film deposited at the temperature above $400^{\circ}C$ had(110) and (301) plane preferred orientation with crystallinity of rutite structure. Electrical resisvity of SnO2 thin film decreased with increase increase of deposition temperature and showed minimum value of 10-3 ohm at $500^{\circ}C$and than largely increased increased with further increase of deposition temperture.

• Korean Journal of Materials Research
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• v.15 no.9
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• pp.604-607
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• 2005

Dependence of the crystallinity, surface roughness, carrier concentration, carrier mobility, electrical resistivity and transmittance of Al-doped ZnO films deposited on glass substrates by RF-magnetron sputtering on effects of the ratio of the RF power for AlZnO to that for ZnO (R) have been investigated. X-ray diffraction spectra show strong preferred orientation along the c-axis. The full width at half maximum (FWHM) of the ZnO (002) peak decreases slightly as R increases in the range of R<1.0, whereas it increases substantially in the range of R>1.0. Scanning electron micrographs (SEM) show that the ZnO film surface becomes coarse as R increases. The carrier concentration and the carrier mobility in the ZnO thin film are maximal for R=1.5 and 1.0, respectively. The electrical resistivity is minimal for R=1.0 The transmittance of the ZnO:Al film tends to increase, but to decrease slightly in the range of R>0.5. It may be concluded that the optimum R value is 1.0, considering all these analysis results. The cause of the changes in the structure and physical properties of ZnO thin films with R are also discussed.