• Bulletin of the Korean Chemical Society
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• v.22 no.3
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• pp.263-266
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• 2001

Isopropylation of phenol with 2-propanol has been carried out over Na-exchanged ZSM-5 zeolites to determine the effect of catalyst acidity on phenol conversion and product selectivity. The acid type and strength of the catalyst such as Lewis, weak and strong Bronsted acid sites are measured by pyridine adsorbed XPS and the catalytic properties are interpreted in terms of the acid properties. The active site and mechanism for the reaction are suggested based on evidence of study from the reactant adsorbed FT-IR.

• Journal of the Korean Home Economics Association
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• v.45 no.10
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• pp.73-81
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• 2007

The purpose of this study was to increase the ultraviolet-light (UV)-cut ability of cellulose fabrics (cotton, ramie, and rayon) dyed with safflower yellow colorants. For this purpose, samples treated with UV-cut agent and tannic-acid were compared with the untreated samples after UV exposure in terms of K/S value, color changes(${\Delta}E$), SEM, and strength retention. The K/S value rapidly decreased after 28 days exposure, whereas the K/S value of the samples treated with both UV-cut agent and tannic-acid decreased to less than that of the untreated samples. In color changes, $L^*$ increased while $a^*$ and $b^*$ decreased, indicating less red and yellow character in color. This induced a change in the hue, value and chroma values. However the color change(${\Delta}E$) of the samples treated with both UV-cut agent and tannic-acid was less than that of the untreated samples. Scanning electron microscopy (SEM) pictures showed a severe degradation by exposure in all samples. Tensile strength rapidly decreased after 28 days for cotton and rayon, and after 21 days for ramie. However, the strength retention of the samples treated with UV-cut agent and tannic-acid was higher than that of the untreated samples.

• Applied Chemistry for Engineering
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• v.17 no.4
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• pp.391-396
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• 2006

When radioactive wastewater was solidified treatment by cement, the drying rate of cement and the volume reduction ratio was decreased because of boric acid component in the wastewater. In order to supplement the demerit, effects of paraffin wax investigated in this study. Paraffin wax has a hydrophobic properties and a low affinity with inorganic materials. When the radioactive wastewater was tested by a small of wax, the compressive strength of solidified waste are decreased Therefore boric acid in radioactive wastewater are first treated by alkali salt and coated by the stearic acid. During the solidification step, The amount of paraffin wax addition get the result that the compressive strength of solidification with cement was the same as that with paraffin wax. The leaching properties of radioactive waste solidified was the same CFL (cumulative fraction leached), PR (penetration rate), effective diffusivity if paraffin wax content in solidified waste was 20% or 25%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.374-379
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• 2002

Corrosion fatigue tests were carried out to clarify the influence of acid fog as environmental factor on the fatigue strength of SM55C using rotary bending fatigue tester. The fatigue strength of acid fog specimen extremely decreased about 80% compared to that of distilled water specimen. In acid fog environment, a number of cracks commenced at corrosion pit and coalesced with the adjacent cracks during they propagate, and they formed a single non-propagating circumferential crack under the endurance stress of N=5$\times$10$\^$7/ cycles. Also, the depth of the crack is smaller than that of normal fatigue crack, so the crack has a veil small aspect ratio. The reason of this peculiar crack growth characteristics is that the crack opening-closure behaviors are hindered by corrosion products on the surface crack faces, and hence it is thinkable that the strong corrosion action like anodic dissolution for crack growth in depth direction is weaker compared with surface, resulting from faint pumping action of crack during loading-shedding processes.

• The korean journal of orthodontics
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• v.43 no.1
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• pp.23-28
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• 2013

Objective: The purpose of this study was to evaluate the effect of casein phosphopeptide amorphous calcium phosphate (CPP-ACP) on the shear bond strength (SBS) of brackets bonded to non-demineralized teeth with either phosphoric acid etching or self-etching primer. Methods: Sixty human premolars were randomly assigned to 1 of 4 treatment groups (n = 15 each): phosphoric acid etching (group 1); self-etching primer (group 2); CPP-ACP for 2 weeks + phosphoric acid etching (group 3), and CPP-ACP for 2 weeks + self-etching primer (group 4). After bonding of the maxillary premolar metal brackets, specimens were subjected to shear forces in a testing machine. Scanning electron microscopy was used to observe etching patterns on the enamel surfaces of all teeth. A 2-way analysis of variance was used to test for effects of CPP-ACP and etching system on SBS. Results: Significantly higher mean SBSs were observed in groups subjected to phosphoric acid etching (i.e., groups 1 and 3; p < 0.05). On the other hand, SBSs did not appear to be influenced by CPP-ACP (i.e., groups 3 and 4; p > 0.05). We observed a uniform and clear etched pattern on the enamel surface of the phosphoric acid etching groups. Conclusions: CPP-ACP does not significantly affect the SBS of orthodontic brackets bonded to non-demineralized teeth, regardless of which adhesive method is used to bond the brackets.

• Bulletin of the Korean Chemical Society
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• v.35 no.9
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• pp.2669-2672
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• 2014

Double bond migration of butene-2 to butene-1 over ${\eta}$-alumina was investigated. The effects of calcination temperature on catalytic properties were analyzed by applying BET surface area, XRD, $NH_3$-TPD, and FT-IR of adsorbed pyridine techniques. The highest activity of the ${\eta}$-alumina catalyst calcined at $600^{\circ}C$ could be attributed not only to the highest amount of weak and medium strength acid sites, but also to the highest ratio of medium to weak strength Lewis acid sites.

• Applied Chemistry for Engineering
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• v.9 no.3
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• pp.361-363
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• 1998

The CNDO/2 calculations have been applied on cluster models for the representative hydroxyls on faujasite surface to get total energies, dipole moments, Wiberg bond orders and formal charge densities. Quantum chemical calculations indicate that the acid strength of surface hydroxyls of faujasite depends on the geometry of hydroxyls and the Si/Al ratios of framework. The $Br{\ddot{o}}nsted$ acid strength of bridging hydroxyl is higher than that of isolated hydroxyls. The stabilities of cluster models increased with increase of the Si/Al ratios.

• Journal of the Korean Ceramic Society
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• v.29 no.5
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• pp.396-402
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• 1992

Carbon solid was prepared from dormant mesophase pitch (DMPP) without using a binder and its properties were characterized. DMPP powder was stabilized with air or nitric acid in pretreatment stage so that it might not soften in later heat ttreatment stage. Optimum sintering properties were obtained from carbon powder with 2.36∼2.38 of C/H atomic ratio and 1.27∼1.40 of C/O atomic ration in air stabilization. In nitric acid stabilization, optimum sintering properties were obtained when 20∼40 vol.% of nitric acid solution was used. Compressive strength increased up to 1200$^{\circ}C$ of heat treatment temperature, and the highest compressive strength and bulk density of carbon solid from DMPP were 3000 kgf/㎤, respectively. The optical properties of carbon solid obtained was fine mosaic structure. Carbon solid after graphitization showed the properties of hard carbon due to stabilization and its shore hardness was 120.

• Journal of the Korean Society of Clothing and Textiles
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• v.22 no.8
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• pp.1060-1068
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• 1998

The effects of various catalysts and softners on the anti-crease finish of ramie with glyoxal were investigated. A number of metal salts commonly used as Lewis acid catalysts in DP finishing of cotton with formaldehyde and N-methylol agents were screened for glyoxal treatment of ramie fabric. Various organic and inorganic acids were mixed with Lewis acid catalyst as co-catalysts to improve catalytic activity. As a result, the combination of aluminum sulfate and citric acid was proven highly effective in catalyzing the crosslinking of ramie cellulose by glyoxal under lower curing temperature. With a mixed catalyst, performance properties, such as whiteness and tearing strength as well as wrinkle recovery of treated ramie fabric were improved as compared with that treated with aluminum sulfate alone. Additional improvement of tearing strength and wrinkle recovery was achieved by applying silicons softner in the treatment bath.

• Biotechnology and Bioprocess Engineering:BBE
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• v.6 no.1
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• pp.31-36
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• 2001

Optimal operation in chromatography is needed to save operation time and the solvent used in multiple chromatographic runs. To this end, many simulation studies of chromatography process have been performed. The relationship between the distribution coefficient and the ionic strength is important in gradient elution ion chromatography. Experimental runs and computer simulations were carried out under linear gradient elution condition in order to compare the experiments and the simulation. Experiments were performed with formic acid under isocratic conditions to determine the simulation equation parameters. Computer simulation was based on three equations which related distribution with ionic strength as follows; K=${\alpha}$I(sup)-${\beta}$, K=A+BI+Cl$^2$and K=y(sub)0+A$_1$$.$e(sup)(-I/m$_1$). The effects of gradient slope on the chromatograms are discussed, and good agreement between the experimental and the simulated results is shown.