• Journal of Pharmaceutical Investigation
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• 제32권1호
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• pp.1-6
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• 2002

The mucoadhesive characteristics of [P(AA-co-PEGMM)] films by estimating the glass transition temperature $(T_g)$, analyzing surface energy and studying FT-IR was previously reported. In this study, the possibility of buccal mucoadhesive dosage form of [P(AA-co-PEGMM)] films by mucoadhesive force measurements and dissolution tests were also investigated. Mucoadhesiveness of [P(AA-co-PEGMM)] films was compared with cr-PAA and cr-PEGMM films crosslinked with 3% ethyleneglycol dimethacrylate (EGDMA). The buccal mucoadhesive force of [P(AA-co-PEGMM)] films increased with increasing content of PEGMM. [P{AA-co-PEGMM (18 mole%)}] films showed a significantly greater mucoadhesiveness than cr-PAA and cr-PEGMM films. The mucoadhesive force measured in normal saline (pH 5.0) was higher than that measured in phosphate buffer (pH 6.8) because of the pH dependence of hydrogels with carboxyl ions within the PAA. Moreover, the mucoadhesive force of [P{AA-co-PEGMM (18 mole%)}] films was at maximum after 2 hr attachment of buccal mocosa and it was maintained over $1\;N/cm^2$ for up to 10 hr. In dissolution studies, the release of butorphanol tartrate from [P(AA-co-PEGMM)] films increased with increasing PEGMM content, and films prepared with 18 mole% PEGMM gave almost zero order release kinetics.

• 열처리공학회지
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• 제6권3호
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• pp.138-143
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• 1993

Effects of aging treatment on the microstructural evolution of a rapidly solidified Al-Li-Cu alloy were investigated by differential scanning calorimetry (DSC) and transmission electron microscopy(TEM). It was found that the precipitation sequence was: supersaturated solid solution ${\alpha}^{\prime}$ ${\rightarrow}$ metastable ${\delta}^{\prime}$ + stable precipitate $T_1$ ${\rightarrow}$ stable precipitates ${\delta}+T_1$. Two exothermic and two endothermic peaks are detected by DSC analysis. The two exothermic and endothermic peaks corresponded to ${\delta}^{\prime}$ and ${\delta}+T_1$ precipitation and dissolution reactions respectively. The enthalpy of ${\delta}^{\prime}$ precipitation decreased with increasing of aging temperature and time until the finishing point of precipitation. The activation energy for precipitation of ${\delta}^{\prime}$ was measured as 80KJ/mol and the energy for dissolution was 93KJ/mol. These values arc higher than those of AI-Li binary alloy. Peak hardness value (Hv 170) was obtamed at $210^{\circ}C$ for 1hr aging treatment which coincided with finishing point of ${\delta}^{\prime}$ precipitation.

• 한국주조공학회지
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• 제37권2호
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• pp.31-37
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• 2017

A new form of austenitic heat-resistant ductile iron was developed and its microstructures and elevated temperature properties were compared to those of Ductile Ni-Resist D5S. According to JMatPro calculations, it was predicted that Mo-rich carbides would be crystallized before the eutectic reaction starts in the developed alloy. At the austenite cell boundaries of the developed alloy, both Mo-rich carbides and Cr-rich carbides were found. In addition, Ni-silicides were found adjacent to Cr-rich carbides in D5S specimen and were identified as $Ni_2Si$. The developed alloy also had greater yield strength and lower tensile strength levels with less elongation due to the dissolution of Mo atoms into the austenite matrix and the precipitation of Mo-rich carbides. From the results of elevated temperature tensile tests and stress-rupture tests, it was found that the developed alloy had elevated temperature properties superior to those of D5S. This was due to the pinning effect of the dissolved Mo atoms in the austenite matrix.

• 한국표면공학회지
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• 제17권3호
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• pp.78-86
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• 1984

Hard anodic oxide film was investigated formed on pure aluminium with various temperature (30$^{\circ}-60^{\circ}C$), current densities (1.5-3.0A/$dm^2$) and concentrations(3-15g/l) of oxalic acid in 0.5M malic acid bath. The resulting characteristic of the anodic oxide film obtained were summarized as follows in the view point of physical and mechanical properties in relation with the above process variables. 1. The film thickness increased with oxalic acid concentration and bath temperature, while the reversed phenomena were obtained at a high concentration of oxalic acid and high temperature due to the severe dissolution of the anodic oxide film. 2. The hardness and the abrasion resistance were improved by lowering the addition of oxalic acid and the bath temperature. This feature was directly dependent on the porosity formed on the anodic oxide film. 3. The maximum hardness of anodic oxide film showed Hv 579 in the temperature of 30$^{\circ}C$ with the current density, 2.5A/$dm^2$ in the 0.5M malic acid bath mixed with 5g/l oxalic acid.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2547-2552
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• 2010

CdS nano-particulate films were prepared at the air/water interface under Langmuir monolayers of arachidic acid (AA) via interfacial reaction between $Cd^{2+}$ ions in the subphase and $H_2S$ molecules in the gaseous phase. The films were made up of fine CdS nanoparticles with hexagonal Wurtzite crystal structure after reaction. It was revealed that the formation of CdS nano-particulate films depends largely on the experimental conditions. When the films were ripened at room temperature or an increased temperature ($60^{\circ}C$) for one day, numerous holes were appeared due to the dissolution of smaller nanoparticles and the growth of bigger nanoparticles with an improved crystallinity. When the films were ripened further, CdS rodlike nanoparticles with cubic zinc blende crystal structure appeared due to the re-nucleation and growth of CdS nanoparticles at the stacking faults and defect structures of the hexagonal CdS grains. These structures were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and X-ray diffraction (XRD). These results declare that CdS semiconductor nanoparticles formed at the air/water interface change their morphologies and crystal structures during the ripening process due to dissolution and recrystallization of the particles.

• 한국주조공학회지
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• 제36권1호
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• pp.1-9
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• 2016

Improvement of the mechanical properties of a commercial aluminium casting alloy, A356, was achieved through an optimised combination of alloying elements, modification, and heat treatment. 0.7 wt.% Cu and an additional 0.2 wt.% Mg were added to an Al-7Si-0.35Mg alloy for strengthening at both room and elevated temperatures, whilst a subsequent decrease in the ductility was compensated for by the modification of eutectic Si by Sr addition at a level of up to 110 ppm. It was found that the dissolution of Cu-rich or Mg-rich phases could be maximised by solid-solutionising an alloy with 40 ppm Sr at $530^{\circ}C$, increasing the tensile and yield strengths to 350 MPa and 297 MPa, respectively, with a reasonably high strain of 5% after peak-aging at $210^{\circ}C$. Further addition of Sr up to 110 ppm is, however, more likely to interfere with the dissolution of the Cu-rich or Mg-rich phases during solid solution treatment, resulting in a slight decrease in both tensile and yield strengths at room temperature. Besides the Cu addition, such undissolved phases, on the other hand, may contribute to elevated temperature strength at $200^{\circ}C$.

• Advances in concrete construction
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• 제13권1호
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• pp.71-81
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• 2022

Aluminosilicate materials as precursors are heterogenous in nature, consisting of inert and partially reactive portion, and have varying proportions depending upon source materials. It is essential to assess the reactivity of precursor prior to synthesize geopolymers. Moreover, reactivity may act as decisive factor for setting molar concentration of NaOH, curing temperature and setting proportion of different precursors. In this experimental work, the reactivities of two precursors, low calcium (fly ash (FA)) and high calcium (ground granulated blast furnace slag (GGBS)), were assessed through the dissolution of aluminosilicate at (i) three molar concentrations (8, 12, and 16 M) of NaOH solution, (ii) 6 to 24 h dissolution time, and (iii) 20-100℃. Based on paratermeters influencing the reactivity, different proportions of ternary binders (two precursors and ordinary cement) were activated by the combined NaOH and Na2SiO3 solutions with two alkaline activators to precursor ratios, to synthesize the geopolymer. Reactivity results revealed that GGBS was 20-30% more reactive than FA at 20℃, at all three molar concentrations, but its reactivity decreased by 32-46% with increasing temperature due to the high calcium content. Setting time of geopolymer paste was reduced by adding GGBS due to its fast reactivity. Both GGBS and cement promoted the formation of all types of gels (i.e., C-S-H, C-A-S-H, and N-A-S-H). As a result, it was found that a specified mixing proportion could be used to improve the compressive strength over 30 MPa at both the ambient and hot curing conditions.

• 대한기계학회논문집
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• 제6권4호
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• pp.377-383
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• 1982

Acoustic emission (AE) of a high strength steel (SCM-4) was measured under stress corrosion cracking(SCC) test at a constant displacement in 3.5% artificial NaCl solution of 18.deg.C, 45.deg.C and 60.deg.C, respectively. The results are as follows; During the SCC test, AE is detected and AE count rate is approximately proportional to the crack growth rate. Even though crack is not propagated macroscopically, AE is detected. The crack growth rate of SCC and the AE count rate are higher for the solution of higher temperature, 45.deg.C and 60.deg.C, than for the solution of lower temperature, 18.deg.C. In the early stage of SCC, AE total counts mostly depend on crack growth. In the later stage, however, AE mostly depends on the film fracture and the dissolution of anode.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 봄 학술발표회 논문집
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• pp.24-29
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• 1996

The purpose of this study is to propose new estimation method of unit cement content in hardened concrete. In general, the quantity of cement in hardened concrete is tested by hydrochlonic acid dissolving cement paste, however, hydrochloric acid dissolves sea shell contained in sea sand and lime stone in concrete. Therefore, the tested cement content is apt to estimate greater than actual cement content. The sodium gluconate solution dissolves only cement in concrete, it is hard to dissolve sea shell and lime stone as CaCo3. The effects of the quantity, concentration and temperature of sodium gluconate solution, the ignition temperature, the ignition loss of cement on the cement content and the percentage of dissolution of cement were investigated to establish a test method. From the results of these tests, the fundamental test method for cement content of hardened concrete by sodium gluconate is proposed.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제4권4호
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• pp.255-261
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• 2000

Experiments were carried out to measure the corrosion potential and current density variations in the polarization curves of polypropylene. In particular, the results were examined to identify those influences affecting the corrosion potential, such as temperature, pH, salt, and oxygen. The Tafel slope for the anodic dissolution was determined based on the polarization effect under various conditions. Furthermore, the optimum conditions for the most rapid transformation were establish based on a variety of conditions, including temperature, pH, corrosion rate, and resistance of corrosion potential. The second anodic current density peak and maximum passive current density were designated as the critical corrosion sensitivity(I(sub)r/I(sub)f). This I(sub)r/I(sub)f value was then used to measure the critical corrosion sensitivity of polypropylene. The potentiodynamic parameters of corrosion were obtained using a Tafel plot.