• 도시과학
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• 제7권1호
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• pp.39-43
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• 2018

This study investigates microstructural characteristics of alkali-activated cements incorporating slag and fly ash. Samples were prepared with four fly ash:slag ratios, i.e., 100:0, 90:10, 70:30 and 50:50, and they were synthesized by using an alkali activator. Microstructural characteristics of the alkali-activated cements were determined by XRD, TGA, SEM, N2 gas adsorption/desorption methods, and compressive strength test. The results showed that properties of alkali-activated fly ash/slag were significantly affected by slag contents. Alkali-activated fly ash/slag with slag content of 30-50% showed higher compressive strength than ordinary Portland cement paste. An increase in slag content resulted in a denser microstructure, which composed of amorphous gel, therefore contributed to strength development of the material.

• The Korean Journal of Ceramics
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• 제3권4호
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• pp.235-238
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• 1997

Basic properties of new cement pastes based on the system $CaO-Al_2O_3-P_O_5-H_2O$were studied Phosphoric acid solutions and calcium dialuminate clinkers synthesized by the hydration-burning method were used for liquid and powder components of the paste, respectively Variation in the compositions of the paste was achieved by changing the liquid/powder ratio and the concentration of phosphoric acid solution. The hardening rate of the paste was so largely affected by the amount of phosphoric acid that hardening was inhibited with the low-concentrated solution but was explosively accelerated with the high-concentrated solution. The phosphoric acid solutions of concentration of 45~50% and the liquid/powder ratio of 0.5~1.5 were favoured for the high early-strength cement paste with the reasonable hardening rate and high strength. The binding phase of hardened paste was the dense amorphous gel of the system $CaO-Al_2O_3-P_O_5-H_2O$. in which the unreacted calcium dialuminate grains were embeded.

• 한국응용과학기술학회지
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• 제18권4호
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• pp.316-324
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• 2001

To prepare an acrylic type pressure-sensitive adhesive, quarternary polymers were synthesized from butyl acrylate (BA), 2-ethyl hexyl acrylate (2-EHA), methyl methacrylate (MMA), and 2-hydroxy ethyl methacrylate (2-HEMA). The quarternary polymers were identified by FT-IR and Molecular weight was measured by Gel Pearmeation Chromatography. Also, viscosity, solid content and peel strength were examined. The peel strength was 160 $g_{f}/25$ mm when the volume ratio of feed monomer to solvent was 1.3:1, and the ratio was relevant to commercial usage. The pot life of adhesive was 30 sec at the 50 m/min of heat treatment rate at, and it indicated that the minimum drying time was 30 sec. In weathering resistance test, peel strength of $160{\sim}180$ $g_{f}/25$ mm after 1000 h, with no residual remains on the adhesive surface.

• 한국수소및신에너지학회논문집
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• 제17권3호
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• pp.331-337
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• 2006

높은 이온전도도와 충분한 기계적 강도, 전해질 누수가 적은 새로운 형태의 고분자 전해질막(pore-gel SPE)을 연구 개발하였다. 다공성 PVDF-HFP 고분자막의 기공 내에 전해질 용액을 흡수시킨 후 막 내에서 젤화를 진행시켰다. 전해질 용액은 2:2:1의 비를 갖는 PC/EC/DMA에 1M SA(Salicylic acid)를 용해하고 여기에 고분자막을 용해시킬 수 있는 아세톤을 첨가하였다. 초음파를 이용함으로써 고분자막의 용액 흡수율을 증가시키고 또 고분자막에서 젤화를 촉진 시킬 수 있었다. 이렇게 젤화한 막의 이온전도도는 젤화 전 막보다 $1{\sim}2.2$ 배 향상되었고, 인장강도는 gel-type SPE 보다 40 배 증가하였으며, 전해질 누수실험결과 hybrid-type SPE는 13%의 누수를 보였으나 본 연구의 막(pore-gel SPE)은 6%로 감소함을 보였다.

• 한국축산식품학회지
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• 제40권2호
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• pp.254-261
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• 2020

The aim of this study was to evaluate quality characteristics of pork myofibrillar protein (MP) added with cornstarch as affected by different pH values and salt cocnentrations. MP mixtures were prepared with three different pH values (pH 6.00, 6.25, and 6.50) and three different salt concentrations (0.15, 0.30, and 0.45 M). Cooking yield (CY), gel strength, viscosity, and scanning electron microscopy were measured to evaluate characteristics of MPs. CYs of MPs with cornstarch at above pH 6.25 or salt 0.30 M were increased compared to those at pH 6.00 or salt 0.15 M. However, gel strengths of MPs at salt 0.45 M were higher than those at salt 0.30 M. In microstructure analysis, MP gels with increasing pH value and salt concentration showed compact and uniform structure. Thus, MP gels with pH 6.25 and salt concentration of 0.30 M would be better for manufacturing meat products containing cornstarch to increase their water holding ability.

• 한국세라믹학회지
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• 제50권6호
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• pp.384-389
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• 2013

Activated alumina was fabricated with aluminum hydroxide in this study. High-purity alumina gel and boehmite were prepared from aluminum hydroxide by a hydrothermal process and fired to activate alumina having a surface area of 380 ~ 480 $m^2/g$ with less loss of ignition. The aging and drying condition during the fabrication process affected the loss of ignition, the sedimentation time of the alumina suspension, as well as the surface area of the activated alumina. For pellet-type activated alumina, the pre-fired alumina gel and boehmite were press-formed and fired at $400^{\circ}C$ and $550^{\circ}C$ for 6 h, respectively. The fired pellets showed a low density of 2.0 ~ 2.2 $g/cm^3$ with 20% firing shrinkage and sufficient handling strength. In this study, a new fabrication process for high-quality activated alumina with aluminum hydroxide is introduced. The effects of the processing parameters on the activated alumina properties are also examined.

• Bulletin of the Korean Chemical Society
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• 제6권5호
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• pp.312-317
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• 1985

${\beta}$-Glucuronidase (EC 3.2.1.31) which hydrolizes D-glucuronate from ${\beta}$-D-glucuronide was purified from rat liver, using ammonium sulfate fractionation, DEAE-cellulose chromatography, Concanavalin-A Sepharose 4B chromatography and gel filtration on Sephadex G-200. This enzyme has the molecular weight of 280,000 daltons by gel filtration and 75,000 daltons by SDS-polyacrylamide gel electrophoresis. As its funtion is reverse of detoxification in the liver, the inhibition of the enzyme was tested with extracts of several food products and medicinal herbs, some are known as anti-cancer agents. Among them, Panax ginseng and Cortnellus shiiake inhibited the enzyme competitively and the $K_1$ values were $9.22 {\times}\;10^{-2}$ and 0.102 mg/ml, respectively. These inhibitors strongly bound to DEAE-cellulose. The negatively charged amino acids, L-aspartate and L-glutamate, inhibited the enzyme, and $K_1$ value of L-aspartate was 0.80 mM. The interaction between ${\beta}$-glucuronidase and p-nitrophenyl-${\beta}$-D-glucuronide was found to involve ionic forces by the effect of ionic strength on the kinetic constant, Vmax/Km. It was inferred from these findings that cationic group at the active center of the enzyme is probably involved in attacking the substrate.

• 한국물환경학회지
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• 제38권4호
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• pp.171-176
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• 2022

Recently, an autotrophic single-stage nitrogen removal (ASSNR) process based on the anaerobic ammonium oxidation (ANAMMOX) reaction has been proven as an economical ammonia treatment. It is highly evident that double-layered gel beads are a promising alternative to the natural biofilm for ASSNR because of the high mechanical strength of poly(vinyl alcohol) (PVA)/alginate structure and efficient protection of ANAMMOX bacteria from dissolved oxygen (DO) due to the thick outer layer. However, the thick outer layer results in severe mass transport limitation and consequent lowered bacterial activity. Therefore, the effects of the thickness of the outer layer on the overall reaction rate were tested in the biofilm model using AQUASIM for ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and ANAMMOX bacteria. A thickness of 0.5~1.0 mm is preferred for the maximum total nitrogen (TN) removal. In addition, a DO of 0.5 mg/L resulted in the best total nitrogen removal. A higher DO induces NOB activity and consequent lower TN removal efficiency. The optimal density of AO B and NO B density was 1~10% for a 10% ANAMMOX bacterial in the double-layered PVA/alginate gel beads. The real effects of operating parameters of the thickness of the outer layer, DO and concentrations of biomass balance should be intensively investigated in the controlled experiments in batch and continuous modes.

• 대한소아치과학회지
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• 제41권2호
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• pp.125-133
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• 2014

이 연구의 목적은 시효된 복합레진 수복물에 이산화탄소 레이저로 표면처리한 경우와 기존의 여러 가지 표면처리 방법에 따른 교정용 브라켓의 전단응력을 측정하여 비교하기 위함이다. 복합레진을 이용하여 직경 6 mm, 두께 5 mm의 시편을 96개 제작하였다. 제작된 시편을 인공타액에 침적시켜 $37^{\circ}C$의 온도로 2주 동안 시효처리 하였다. 그 후 96개의 시편을 무작위적으로 16개씩 6개의 군으로 나누었다. 1군은 표면처리를 하지 않았고, 2군은 37% 인산으로, 3군은 4% 불산으로, 4군은 입자 분사 연마로, 5군은 고속 다이아몬드 버로, 6군은 이산화탄소 레이저로 표면처리하였다. 만능 시험기를 이용하여 전단응력을 측정하였으며, 주사전자 현미경을 이용하여 표면처리 양상을 관찰하였다. 버를 사용한 5군이 가장 큰 전단응력 값을 보였으며, 이산화탄소 레이저를 사용한 6군이 그다음으로 큰 값을 보였다. 버를 사용한 5군과 이산화탄소 레이저를 사용한 6군은 나머지 표면처리 방법들보다 통계적으로 유의하게 높은 전단응력 값을 보여주었다(p < 0.05). 또한, 주사전자 현미경 사진을 통해 분석한 결과 레이저를 이용한 6군에서 표면이 가장 거칠었으며 불규칙한 요철구조가 형성되었다. 이산화탄소 레이저를 이용한 표면처리 방법은 브라켓 접착시 적절한 결합강도를 제공하므로, 시효된 레진 수복물에 교정용 브라켓을 접착하기 위한 유용한 방법이 될 수 있다.

• 한국결정성장학회지
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• 제27권6호
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• pp.295-302
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• 2017

본 연구에서는 IGCC(Integrated Gasification Combined Cycle; 석탄 가스화 복합 발전)에서 배출된 용융 슬래그(이하 용융 슬래그)를 이용한 지오폴리머의 제조 시 pre-curing 공정이 지오폴리머의 물성에 미치는 영향에 대해 연구하였다. Pre-curing이란 고온양생으로 지오폴리머를 제조하기 전에, 성형체를 상온에서 일정 시간 방치하는 공정으로서, 시편의 강도를 높이는 효과가 있다고 알려져 있다. 따라서 본 실험에서는 pre-curing 조건에 따른 지오폴리머의 압축강도 특성을 측정하였으며, SEM과 XRD로 미세구조 및 결정상 변화를 관찰하였다. W/S 비율(water/solid ratio)은 사전 실험을 통해, 성형이 가능하면서 최대 지오폴리머 강도를 확보할 수 있는 0.26으로 결정하였으며, 자극제인 알칼리 용액의 농도는 15 M로 고정하였다. 상온에서 pre-curing을 0~27일 범위 내에서 실시한 결과, pre-curing 공정을 적용한 지오폴리머의 경우, 그렇지 않은 시편에 비해 압축강도가 36~87 % 증가하는 것을 확인하였다. Pre-curing 시킨 시편에서 XRD 측정 결과, C-S-H 겔(calcium silicate hydroxide gel) 상 발현이 촉진되었고 SEM을 이용한 미세구조 관찰 결과, 부정형의 zeolite 상이 더 많이 성장된 것이 관찰되었으며 이러한 상들의 생성이 강도 증진에 영향을 미친 것으로 분석되었다.