• Journal of the Korean Ceramic Society
• /
• v.30 no.11
• /
• pp.933-940
• /
• 1993

SO42-/Al2O3 powder was prepared by the coprecipitation method from the Al(NO3)3.9H2O and NH4OH and followed by being treated with various concentrations of sulfuric acid. The characterization of these powders was performed with XRD, BET and FT-IR. The surface charge density at alumina/KCl(aq) interface was measured by potentiometric titration method. From the experimental data it was shown that acid strength, specfic surface area, and structure of surface treated alumina were independent on the amount of exchanged SO42-. However, the acid amounts of alumina were increased with the amounts of SO42- formed on alumina surface. The relation between the acid amount of SO42- ion exchanged alumina surface and the surface charge density for SO42-/Al2O3/KCl(aq) interface was investigated.

• Bulletin of the Korean Chemical Society
• /
• v.16 no.6
• /
• pp.507-511
• /
• 1995

Catalytic chlorination of chlorobenzene was studied in vapor phase using various solid-acid catalysts such as silica-alumina, alumina, zeolite and a modified clay prepared by impregnating bentonite with ferric chloride. The conversions of both chlorine gas and chlorobenzene showed high over silica-alumina, alumina and modified clay catalysts. However relatively large amounts of polychlorinated benzene derivatives were also observed. The active species of catalytic activity in chlorination of chlorobenzene in vapor phase were proved to be as Lewis acid sites by in-situ IR experiments. The strength of Lewis acid sites which were effective for the vapor-phase chlorination seemed to be having Hammett acidity Ho >-3.0. The selectivity to dichlorobenzenes was proved to be high over the zeolite catalyst due to their shape-selective properties. p-Dichlorobenzene or dichlorobenzene selectivities were improved more or less by changing the reaction conditions.

• Journal of the Korean Society of Industry Convergence
• /
• v.24 no.2_1
• /
• pp.79-89
• /
• 2021

Poly(lactic acid) (PLA) is considered as one of the most promising bio-based polymers due to its high strength, high modulus, good processability, transparency after processing, and commercial availability. This study aimed to investigate the mechanical, thermal, and migration properties of poly(lactic acid)/zeolite (10 phr) composites prepared with various biocompatible plasticizers, such as triethyl citrate(TEC), tributyl citrate(TBC), and poly(ethylene glycol)(PEG400), through differential scanning calorimetry(DSC), thermo-gravimetric analysis(TGA) and standard tensile testing. The incorporation of PEG400 significantly increased the elongation at break, and DSC results showed that the addition of plasticizers drastically decreased the T_g of PLA/zeolite composites and improved the melt flow and processability. Besides, it was found from TGA results that PLA/zeolites composites plasticized by TEC and TBC were more easily to be thermally degraded than the composites plasticized by PEG400.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.29 no.1
• /
• pp.37-44
• /
• 2013

Sodium hypochlorite and ethylene diamine tetra acetic acid are substances usually used during endodontic treatment. Several studies found that the bonding was negated with certain irrigants and some of the used irrigants have demineralizing and chealating effects, so it was advocated to omit the etching step in etch and rinse adhesive systems. The purpose of this in vitro study was to evaluate the influence of NaOCl & EDTA on the bonding strength of ethanol wet bonding. Thirty human molars were selected and mesiodistally sectioned into halves, thus providing sixty specimens. The specimens were randomly assigned to 4 groups(n=15) according to the irrigant regimen used : (1) irrigated with distilled water for 10min (control); (2) irrigated with 5.25% NaOCl(10min), flushed with 5.25% NaOCl(1min) (3) irrigated with 5.25% NaOCl, flushed with 17% EDTA (4) irrigated with 5.25% NaOCl, flushed with 17% EDTA. Each group was acid-etched with 37% phosphoric acid(except group 4) and had their dentin surfaces dehydrated with ethanol solutions : 50%, 70%, 80%, 95%, 3x100%, 30s for each application. After dehydration, a primer( 50% all bond 3 resin + 50% ethanol) was used, followed by the adhesive(ALL-BOND 3 RESIN) application. Resin composite build-ups were then prepared using an incremental technique. Specimens were sectioned into beams and submitted to a tensile load using a Micro Tensile Tester(Bisco Inc.). The data were statistically analyzed using one-way ANOVA and Tukey HSD at p<0.5 level. There was no significant difference on G1(control) and G2(irrigated with NaOCl only ). (p>0.05). G3(flushed with EDTA) showed significantly high tensile bonding strength compared to the G2 (p<0.05). G4( treated with EDTA but no acid-etching) was significantly lower value than G3. (p<0.05) Although there was no significant difference, 5.25% NaOCl seemed to have an adverse effect on the bonding strength of ethanol wet bonding. The flushing with EDTA after NaOCl irrigation prevents the decrease of bonding strength. The use of 17% EDTA as a final flush can enhance the bonding strength but EDTA flushing can't substitute for a acid-etching.

• Restorative Dentistry and Endodontics
• /
• v.21 no.2
• /
• pp.470-488
• /
• 1996

The end products of the metabolism of the oral microorganism, organic acids, are an element that produces dental caries. Four organic acids in plaque fluid, lactic acid, acetic acid, succinic acid, propionic acid which take the important role in producing dental caries, were chosen to evaluate the effect of acid type and concentration. The subject, $100{\mu}m$ in thickness, were immersed in acid-buffer solution which has the different acid concentration of 10mM, 25mM, 50mM, 100mM and pH 4.3 and degree of saturation was $0.153{\pm}0.003$ kept in constant and were operated to produce artificial caries under different demineralization time (1, 2, 3 day) at x25. The results were obtained by observing under polarizing microscope at x25. 1. The subsurface lesion, specific finding of incipient enamel caries, showed positive birefringence. but surface zone and sound enamel showed negative birefringence. 2. The demineralization rate of enamel was increased as the acid concentration increased. 3. The subsurface lesion showed increasing depth in the order of lactic, acetic, propionic acid, succinic acid. 4. The concentration of organic acid in artificial caries system had an independent effect on demineralization rate in enamel under the constant pH and degree of saturation. The result of this study showed that not only pH and the acid strength but the concentration of organic acid had an independent effect on demineralization rate in early enamel caries. And through the further research on the factors influencing enamel demineralization, it will be necessary to develop an effective caries preventive therapy.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.7 no.1
• /
• pp.51-59
• /
• 2012

The cold weather concrete poured in the winter season can cause the problem of the Due to recent high-rise building is made. In this research, the nominal mix of the early strength in concrete tried to be set through the mixing proportion experiment for each empirical variable and each component strength properties for the early strength improvement tries to be examined. In the cold weather concrete experiment, the cement and high early strength (type3) cement improving in OPC than OPC was excellent. The polycarboxylic acid based compound was exposed to be excellent in the intensity revelation properties. Because the using of the fly ash was disadvantageous it was excluded from this experiment. It showed the optimum temperature for the intensity revelation up over $12^{\circ}C$.

• Journal of Biomedical Engineering Research
• /
• v.16 no.4
• /
• pp.533-542
• /
• 1995

The present study investigated the effectiveness of pretreatment on dentin bonding. The adhesive resin was 5% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in methyl methacrylate (MMA) combined with poly-MMA powder. Polymerization of this resin was initiated by tri-n-butyl borage (TBB). Ground bovine dentin samples were etched with either an aqueous solution of 10% citric (10-0 solution) (Group I) or aqueous solution of 10% citric acid and 3% ferric chloride(10-3 solution) (Group ll ). After etching, the primer (an aqueous solution of 35% hydroxyethyl methacrylate (HEM- A) and 5% glutaraldehyde was applied on the differently etched surfaces (Group III , Group IV). The 10-0 treatment showed the lowest tensile bond strength, followed by the 10-3 treatment, primer application after the 10-0 treatment and primer application after the 10-3 treatment. The relationship among the surface morphology after pretreatment, fractured surface morphology and tensile bond strength was examined. It revealed that the surface morphology change by different pretreatment influenced the bond strength and the resulting fractured surface morphology. The correlation of tensile bond strength with the fracture morphology was explained.

• Tribology and Lubricants
• /
• v.35 no.2
• /
• pp.132-138
• /
• 2019

In this study, we demonstrate the effects of the acidic properties of montmorillonite (MMT), which is commonly used as a catalyst, on the conversion and selectivity of the dimer acid methyl ester (DAME) synthesis. We synthesize DAME by the dimerization of conjugated linoleic acid methyl ester (CLAME) and oleic acid methyl ester using MMT KSF. Incidentally, trimer acid methyl ester was formed as a by-product during the DAME synthesis. There is a necessity to adequately adjust the strength and quantity of the acid site to control the selectivity of DAME. Therefore, we vary the pH of the MMT acid by using various metal hydroxides. The purpose of this study is to increase the yield of monocyclic dimer acid methyl ester, which is a substance with adequate physical properties for industrial applications (e.g., lubricant and adhesive, etc.), using a heterogeneous catalyst. We report the dimerization of fatty acid methyl ester by using base treated-KSF, and apply it to conjugated soybean oil methyl ester. Then, we transmute the acid site properties of KSF, such as pH of 5 wt.% slurry KSF and various alkali metals (Li, Na, K, Ca). Characterization of base treated-KSF using a pH meter, x-ray diffraction, inductively coupled plasma-atomic emission spectrometer, Brunauer-Emmett-Teller surface analysis, and temperature-programmed desorption. We conduct an analysis of CLAME and DAME using nuclear magnetic resonance spectroscopy, gas chromatography, and gel permeation chromatography. Through these experiments, we demonstrate the effects of the acidic properties of KSF on the conversion and selectivity of the DAME synthesis, and evaluate its industrial potential by application to waste vegetable oil.

• The korean journal of orthodontics
• /
• v.40 no.2
• /
• pp.87-94
• /
• 2010

Objective: Many studies have carried out research on comparisons between laser etching and conventional etching systems to investigate methods of reinforcing shear bond strength. The purposes of this study were to assess the efficiency of bonding with erbium, chromium doped: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser etching combined with the conventional etching technique. Methods: Sixty-four sound premolars, extracted for orthodontic purposes, were randomly divided into 4 groups and treated in the following manner. First group, conventional etching of 37% phosphoric acid for 15 seconds (control); second group, 1.5 W laser etching for 10 seconds followed by conventional etching; third group, conventional etching followed by 1.5 W laser etching; fourth group, 1.5 W laser etching for 15 seconds only. We assessed the shear bond strength, the surface characteristics, and the adhesive remnant index scores between all groups. Results: Experimental groups showed higher shear bond strength than the control group. But no statistically significant differences were found between the second and third groups. Adhesive remnant scores were compared with the Kruskal-Wallis test, and no statistically significant differences were found between all groups. Conclusions: To obtain maximum shear bonding strength, a combined technique of Er,Cr:YSGG and 37% phosphoric acid is useful even though it may be inconvenient.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.28 no.3
• /
• pp.522-529
• /
• 2001

This study seeks to know the effect of fluoride topical application on the shear bond strength between enamel and fissure sealant. On group 1,2,3,4, Teethmate A(unfilled sealant) and on group 5,6,7,8 Ultraseal XT(filled sealant) were used. Group 1 and 5 were not pre-treated with fluoride and group 2 and 6 were pre-treated with 1.23% APF for 4minutes. Group 3 and 7 were pretreated with 2.0% NaF for 4 minutes. and group 4 and 8 were pumiced with abrasive containing fluoride for 10 seconds. Prepared specimens were acid etched for 30 seconds using 35% phosphoric acid, and then sealant was cured to the specimen using a 3mm diameter by 2mm height mold. They went through thermocycling. Its shear bond strength was measured, and then acid etched both groups that were pretreated with fluoride and that were not pretreated with fluoride. Then we examined the surface of the specimen with EM and came up with these results. In groups using unfilled sealant(group 1,2,3.4) there were no significant differences between oops pretreated with fluoride and groups not pretreated with fluoride. In groups using filled sealant(group 5,6,7,8), groups 6 and 7(treated with 1.23% APF 2.0% NaF respectively) showed significantly lower shear bond strength, compared to group 5 (not pretreated with fluoride) and group 8 (pumiced with abrasive containing fluoride) (p<0.05).