• Applied Chemistry for Engineering
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• v.34 no.6
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• pp.670-673
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• 2023

The biocompatibility of hydroxyapatite (HAP) has led to its application in various fields. To accomplish practical biological applications, such as drug/gene delivery, the colloidal stability of HAP in phosphate-buffered saline (PBS) is particularly important. In this study, we prepared a glycerol incorporated-HAP (Gly-HAP) by heating HAP in a glycerol environment at 200 ℃. To compare morphology and colloidal stability, HAP prepared at room temperature (RT-HAP) was thermally treated in water at 200 ℃ (H₂O-HAP). The heat treatment of HAP in both water and glycerol solutions results in an increase in the crystallinity of HAPs. Due to the low solubility of HAP in glycerol and the adsorption of glycerol on the HAP surface, crystal growth is limited. However, the heat-treated HAP under water increased in size by approximately four times compared to the initial crystallites. Compared to RT-HAP and H₂O-HAP, Gly-HAP shows improved colloidal stability in PBS, which originates from the adsorption of glycerol on the HAP surface that inhibits the agglomeration of individual HAP precipitates.

• Applied Chemistry for Engineering
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• v.34 no.2
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• pp.111-120
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• 2023

The nucleation mechanism was studied using a calcium ion selective electrode (Ca ISE) to observe the formation of CaCO₃, a representative mineral in the CO2 cycle, and to analyze the effect of the Mg/Ca-ratio and temperature on the formation of pre-nucleation cluster (PNC) and CaCO₃. As a result of the experiment, a small amount of crystal was formed. Energy dispersive X-ray spectroscopy (EDS) was used for surface element analysis, and a field emission scanning-electron microscope (FE-SEM) was used for the morphology analysis of synthesized carbonates. These results showed that various shapes of crystalline CaCO₃ (calcite, aragonite, etc.) were observed for each Mg/Ca ratio and temperature. In addition, the calibration plot obtained from Ca ISE showed information on the formation process of CaCO₃. Our results showed that as magnesium ions interfered with the binding of calcium and carbonate ions and delayed the aggregation between PNCs, the nucleation and formation of CaCO₃ were delayed. On the other hand, the temperature showed an opposite trend as compared to the effect of magnesium under our experimental conditions, indicating that temperature accelerated the formation of CaCO₃. Furthermore, the morphology of CaCO₃ clearly changed according to the Mg/Ca ratio and temperature, and it was confirmed that the two factors are very important for CaCO₃ formation in that they could affect the overall process.

• Composites Research
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• v.31 no.2
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• pp.43-50
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• 2018

The effects of deposition temperature on chemical vapor deposited silicon carbide (CVD-SiC) were studied to obtain high deposition rates and excellent bending strength characteristics. Silicon carbide prepared at $1250{\sim}1400^{\circ}C$ using methyltrichlorosilane(MTS : $CH_3SiCl_3$) by hot-wall CVD showed deposition rates of $95.7{\sim}117.2{\mu}m/hr$. The rate-limiting reaction showed the surface reaction at less than $1300^{\circ}C$, and the mass transfer dominant region at higher temperature. The activation energies calculated by Arrhenius plot were 11.26 kcal/mole and 4.47 kcal/mole, respectively. The surface morphology by the deposition temperature changed from $1250^{\circ}C$ pebble to $1300^{\circ}C$ facet structure and multi-facet structure at above $1350^{\circ}C$. The cross sectional microstructures were columnar at below $1300^{\circ}C$ and isometric at above $1350^{\circ}C$. The crystal phases were all identified as ${\beta}$-SiC, but (220) peak was observed from $1300^{\circ}C$ or higher at $1250^{\circ}C$ (111) and completely changed to (220) at $1400^{\circ}C$. The bending strength showed the maximum value at $1350^{\circ}C$ as densification increased at high temperatures and the microstructure changed from columnar to isometric. On the other hand, at $1400^{\circ}C$, the increasing of grain size and the direction of crystal growth were completely changed from (111) to (220), which is the closest packing face, so the bending strength value seems to have decreased.

• Journal of the Mineralogical Society of Korea
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• v.17 no.3
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• pp.245-265
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• 2004

This study was to compare the geological occurrences and geneses of the Myogi, Tsukinuno, Dobuyama and Kawasaki bentonite deposits distributed in the Tertiary sedimentary basins of NE Japan, and to compare the mineralogical and physicochemical properties of their bentonites. The Japanese bentonite deposits are mainly distributed in the Green-tuff region which was formed in Neogene. The shape of ore body of the Myogi, Tsukinuno and Kawasaki deposits formed by the diagenesis are layered and stratiform. In contrast to this, the Dobuyama deposit formed by hydrothermal alteration shows the cone shape. The mineralization age of four deposits are 1.8 ～ 21 Ha from Early Miocene to Pliocene. The Dobuyama bentonite with the highest montmorillonite content shows the highest surface area, CEC, MB adsorption, and strengths. The Tsukinuno bentonite with a little high montmorillonite content is characterized by strong alkalinity, high viscosity and swelling. The Kawasaki bentonite, the Na-Ca mixed type, shows higher viscosity and swelling than the Ca-type Dobuyama bentonite. The Myogi bentonite with the lowest montmorillonite content shows the properties of low viscosity, In adsorption, strengths and a little high CEC and surface area. The high CEC and surface area of this deposit is due to the sufficient occurrence of zeolite. A strong dispersion in the Na-type bentonite and a strong flocculation in the Ca-type bentonite took place, and both the types show a slow flocculation with time. The physicochemical properties of the bentonite are mainly controlled by the montmorillonite content, interlayer cations, and impurity minerals such as zeolite. But bentonites inconsistent to this factors are sometimes occurred. This is maybe due to the crystal chemistry such as layer charge of montmorillonite and crystal morphology of montmorillonite such as aspect ratio.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.1
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• pp.14-22
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• 2020

Purpose: The aim of this study is to evaluate the effectiveness of MnO₂-diatom microbubbler (DM) on the surface of prosthetic materials as a mouthwash by comparing the biofilm removal effect with those previously used as a mouthwash in dental clinic. Materials and methods: DM was fabricated by doping manganese dioxide nanosheets to the diatom cylinder surface. Scanning electron microscopy (SEM) was used to observe the morphology of DM and to analyze the composition of doped MnO₂. Stereomicroscope was used to observe the reaction of DM in 3% hydrogen peroxide. Non-precious metal alloys, zirconia and resin specimens were prepared to evaluate the effect of biofilm removal on the surface of prosthetic materials. And then Streptococcus mutans and Porphyromonas gingivalis biofilms were formed on the specimens. When 3% hydrogen peroxide solution and DM were treated on the biofilms, the decontamination effect was compared with chlorhexidine gluconate and 3% hydrogen peroxide solution by crystal violet staining. Results: Manganese dioxide was found on the surface of the diatom cylinder, and it was found to produce bubble of oxygen gas when added to 3% hydrogen peroxide. For all materials used in the experiments, biofilms of the DM-treated groups got effectively removed compared to the groups used with chlorhexidine gluconate or 3% hydrogen peroxide alone. Conclusion: MnO₂-diatom microbubbler can remove bacterial membranes on the surface of prosthetic materials more effectively than conventional mouthwashes.

• Journal of the Mineralogical Society of Korea
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• v.22 no.3
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• pp.241-248
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• 2009

Kaolinite was synthesized from amorphous $SiO_2$ and $Al(OH)_3{\cdot}xH_{2}O$ as starting materials by hydrothermal reaction conducted at $250^{\circ}C$ and $30\;kg/cm^2$. The acidity of the solution was adjusted at pH 2. The synthesized kaolinite was characterized by XRD, IR, NMR, FE-SEM, TEM and EDS to clarify the formational process according to the reaction time from 2 to 36 hours. X-ray diffraction patterns showed after 2 h of reaction time, the starting material amorphous $Al(OH)_3{\cdot}xH_{2}O$ transformed to boehmite (AlOOH) and after the reaction time 5 h, the peaks of boehmite were observed to be absent thereby indicating the crystal structure is partially destructed. Kaolinite formation was identified in the product obtained after 10 h of reaction and the peak intensity of kaolinite increased further with reaction time. The results of TGA and DTA revealed that the principal feature of kaolinite trace are well resolved. TGA results showed 13 wt% amount of weight loss and DTA analysis showed that exothermic peak of boehmite observed at $258^{\circ}C$ was decreased gradually and after 10 h of reaction time, it was disappeared. After 5 h of the reaction time, the exothermicpeak of transformation to spinel phase was observed and the peak intensiy increased with reaction time. The results of FT-IR suggested a highly ordered kaolinite was obtained after 36 hours of reaction. It was identified by the characteristic hydroxide group bands positioned at 3,696, 3670, 3653 and $3620\;cm^{-1}$. The development of the hydroxyl stretching between 3696 and $3620\;cm^{-1}$, depends on the degree of order and crystalline perfection. TEM results showed that after 15 h reaction time, curved platy kaolinite was observed as growing of (001) plane and after 36 h, the morphology of synthetic kaolinite exhibited platy crystal with partial polygonal outlines.

• Korean Journal of Optics and Photonics
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• v.13 no.3
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• pp.197-203
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• 2002

The TiO$_2$ coating solutions were synthesized with different concentrations (T1-0.7N, T2-2.0N) of hydrochloric acid used as catalyst. and TiO$_2$ thin films were prepared by sol-gel dip coating. Their structural and optical properties were examined as a function of calcination temperature. XRD results showed that T1 thin films calcined at 400~80$0^{\circ}C$ had the anatase phase, while those calcined at 100$0^{\circ}C$ had the rutile phase. T2 thin films calcined at 40$0^{\circ}C$ and $600^{\circ}C$ had the anatase phase, with the rutile phase for calcination at 80$0^{\circ}C$. Crystallinity of T2 thin films was superior to that of T1 thin films. The crystallite size of TiO$_2$ thin films increased with increasing calcination temperature, and the crystallite size of anatase phase in T2 thin films was larger than that in T1 thin films, but the crystallite size of rutile phase in T2 thin films was smaller. The surface morphology of the films showed that the films were formed more densely in the rutile phase than in the anatase phase, this phenomenon appeared conspicuously in T2 thin films. The transmittance of the samples with thin films on quartz glass calcined at 100$0^{\circ}C$ was significantly reduced at wavelength range about 300-700 nm due to the increased absorption originating from the change of crystallite phase and composition of the films and the scattering effect originating from increasing crystallite size. The refractive index of TiO$_2$ thin films increased, and hence the film thickness as well as the porosity of TiO$_2$ thin films decreased with increasing calcination temperature. Furthermore, the refractive index of T2 thin films was higher than T1 thin films, and porosity of T2 films was lower.

• 보존과학연구
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• s.33
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• pp.33-43
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• 2012

The corrosion phenomena of the iron artifacts was studied by morphology observation and instrumental analysis(EDS, XRD, Raman) with various corrosion factors in oder to verify to confirm the danger of corrosion factors. Corrosion compounds were collected by depositing pure Fe powder(99%) into a HCl, $HNO_3$, $H_2SO_4$, and $H_2O$ solution which contained the corrosion factors. Stereoscopic-microscope observations were then conducted determine the colors and shapes of the collected corrosion compounds, and SEM-EDS analysis was conducted to confirm the corrosion factors and the growth of these compounds. X-ray diffraction (XRD), Raman analyses were conducted to examine the crystal structure and compositions of the created corrosion compounds. The results of the experiment revealed that corrosion speed was faster in an acidic environment and corrosion of HCl and $H_2SO_4$ was greater than that of $HNO_3$. The corrosion compounds of HCl grew into a needle or chestnut-like shape after being affected by Cl- ion, and XRD and Raman analyses detected goethite and lepidocrocite. The corrosion compounds of $H_2SO_4$ was affected by S ion and grew into a slender-needle-like or cylindrical shape, and the XRD and Raman analyses detected goethite and lepidocrocite. The corrosion compounds of $HNO_3$ grew into a spherical or plate-like shape after being affected by O ion and the XRD and Raman analyses detected magnetite and lepidocrocite. Although the corrosion compounds of $H_2O$ grew into a spherical or plate-like shape after being affected by O ion, most of them were observed to have had spherical shapes, and the XRD and Raman analyses failed to detect corrosion compounds in them. It was found in the study that corrosion characteristics and compounds are diversely displayed according to the corrosion factor.

• Korean Journal of Dental Materials
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• v.45 no.4
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• pp.257-274
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• 2018

The purpose of this study was to evaluate the effect of acid-treatment conditions on the surface properties of the RBM (Resorbable Blast Media) treated titanium. Disk typed cp-titanium specimens were prepared and RBM treatments was performed with calcium phosphate ceramic powder. Acid solution was mixed using HCl, $H_2SO_4$ and deionized water with 4 different volume fraction. The RBM treated titanium was acid treated with different acid solutions at 3 different temperatures and for 3 different periods. After acid-treatments, samples were cleaned with 1 % Solujet solution for 30 min and deionized water for 30 min using ultrasonic cleanser, then dried in the electrical oven ($37^{\circ}C$). Weight of samples before and after acid-treatment were measured using electric balance. Surface roughness was estimated using a confocal laser scanning microscopy, crystal phase in the surface of sample was analyzed using X-ray diffractometer. Surface morphology and components were evaluated using Scanning Electron Microscope (SEM) with Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoemission Spectroscopy (XPS). Values of the weight changes and surface roughness were statistically analyzed using Tukey-multiple comparison test (p=0.05). Weight change after acid treatments were significantly increased with increasing the concentration of $H_2SO_4$ and temperature of acid-solution. Acid-treatment conditions (concentration of $H_2SO_4$, temperature and time) did not produce consistent effects on the surface roughness, it showed the scattered results. From XRD analysis, formation of titanium hydrides in the titanium surface were observed in all specimens treated with acid-solutions. From XPS analysis, thin titanium oxide layer in the acid-treated specimens could be evaluated. Acid solution with $90^{\circ}C$ showed the strong effect on the titanium surface, it should be treated with caution to avoid the over-etching process.

• Journal of the korean academy of Pediatric Dentistry
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• v.48 no.4
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• pp.467-475
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• 2021

The purpose of this study was to compare the effect of sodium fluoride(NaF) varnish and potassium iodide(KI) on remineralization efficacy of silver diamine fluoride(SDF) by measuring microhardness and evaluating surface morphology by scanning electron microscope(SEM). Artificial caries lesions were induced on extracted primary molars and vickers microhardness was measured. Specimens were randomly separated into 4 groups for treatment. The specimens in group I were treated with SDF, group II with NaF varnish after SDF, group III with KI after SDF and group IV with distilled water. After 8 days of pH cycling, vickers microhardness was measured and difference before and after treatment was calculated. For SEM, 2 samples were evaluated respectively after enamel polishing, lesion formation and after pH cycling. Group III showed highest increase in microhardness. Group I showed higher increase in microhardness than Group II but without statistical difference. Group IV showed lowest increase in microhardness value among 4 groups. On SEM image, group I, II and III showed smoother and less irregular surface compared to group IV. Amorphous crystal pellicles were observed in group III. In conclusion, SDF, SDF and NaF, SDF and KI groups showed smoother surface and increase in microhardness suggesting the possibility that remineralization effect might take place in oral conditions. In addition, in limited conditions of this study, applying NaF varnish after SDF did not increase the remineralization efficacy of SDF while KI significantly increased the remineralization efficacy of SDF. However, additional study considering various conditions that might affect demineralization and remineralization in clinical situations need to be conducted.