• The Korean Journal of Rheology
• /
• v.6 no.1
• /
• pp.66-74
• /
• 1994

천연고무의 소련효과를 높이기 위하여 사용되는 소련촉진제가 천연고무 배합물의 점도나 Couette 보정치와 같은 유변학적 특성에 미치는 효과를 살펴보았다. 소련촉진제로는 BAPS, PCTP 및 ADS계의 것이 사용되었다. 실험결과 소련 촉진제의 사용에 따라 고무의 분자량이 감소하고 전단 점도도 감소하였다. Coutte 보정치는 소련촉전제의 사용량이 증가 할수록 낮은 값을 나타냈으며 압출물의 팽창도 소련촉진제를 사용하는 경우감소하였다. 그 러나 사용된 소련촉진제들 간에는 큰 차이를 보이지 않았다.

• 전기의세계
• /
• v.53 no.8
• /
• pp.31-38
• /
• 2004

최근 CDMA 방식에 기반을 둔 이동통신 시스템과 GPS, WLAN 등의 통신 시스템 시장은 전 세계적으로 급격히 팽창하고 있으며, 그 발전가능성은 무궁 무진하다. 특히, 개인 휴대 이동통신의 경우, 초기 아날로그 방식을 이용한 음성서비스에서 출발하여, 디지털 방식으로의 성능개선을 통해 가입자의 폭발적인 증가에 대응하고 다양한 콘텐츠를 제공하기 위한 대용량, 고속 신호처리를 실현하였다. 현재 무선 인터넷 및 멀티미디어 기능, GPS 기능을 탑재한 컬러 디스플레이 단말기가 전세계적으로 일반화되는 추세이며, 블루투스 시스템과의 연동을 통해 다양한 서비스를 제공할 수 있도록 연구가 진행 중이다. (중략)

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.307-307
• /
• 2008

전자부품에서 기존에 봉착, 코팅, 결합용 glass frit로 사용되어 왔던 Pb계 glass frit는 낮은 융점을 가지고 있고, 화학적으로도 매우 안정한 특성을 가지고 있다. 그러나 Pb계 glsss frit은 환경에 심각한 문제를 초래하기 때문에 이를 대체하기 위하여 저온에서 소성이 가능한 인산주석계를 기본조성계로 설정하였다. 인산주석계 glass의 취약한 내화학성, 내수성과 SnO의 환원에 의한 결정 석출 등의 문제를 해결하기 위하여 $R_2O_3$, RO 등을 첨가하여 glass frit의 특성을 향상시키고자하였다. 수분에 취약한 $P_2O_5$계 glass의 $R_2O_3$를 첨가하여 항온항습기를 이용하여 흡습성을 측정하고, 내수성에 가장 안정한 특성을 보이는 SnO-$P_2O_5-R_2O_3$ 계 glass 조성에 RO를 첨가하여 RO 첨가량에 따른 내산성과 내알칼리성의 변화를 관찰하였다. SnO-$P_2O_5-R_2O_3$계 glass의 RO첨가량에 따른 melting 특성의 변화를 flow-button test를 통해 관찰하였다. SnO-$P_2O_5-R_2O_3$계는 RO계의 변화에 따라 전이온도가 증가하고, 열팽창계수가 감소하는 결과를 보였다.

• Journal of Advanced Marine Engineering and Technology
• /
• v.41 no.3
• /
• pp.191-196
• /
• 2017

Owing to the harmful environmental effects of HCFC and CFC refrigerants discovered in the late 20th century, the need for environmentally friendly refrigerants such as $CO_2$ in cooling systems has increased. Air-source $CO_2$ heat pumps that utilize ambient heat in cold winter are less efficient because of a higher evaporation temperature, and it is difficult to manufacture the components of the heat pump owing to a super critical pressure of over 130 bar. This research aims to overcome these disadvantages and improve energy efficiency by introducing a new lower-pressure $CO_2$ auto-cascade heat pump system. $CO_2$-R32 zeotropic refrigerants were considered for two-stage expansion and effective cooling heat exchanging system configurations of the new auto-cascade heat pump. The results indicated that the efficiency of the two-stage expansion system was higher than that of the original one-stage expansion system. Furthermore, the two-stage expansion system showed significant performance improvements when the two-stage expansion stage from highest pressure of 70bar, intermediate expansion pressure of 25bar, and final low pressure of 10bar is applied. The COP of the new two-stage auto-cascade system (2.332) was 43.15% higher than that of the present simple auto-cascade system (1.629). Refrigerants having an evaporation temperature of $-10^{\circ}C$ or lower can be obtained that can be easily evaporated in an evaporator even at a low temperature.

• Journal of the Korea Concrete Institute
• /
• v.23 no.6
• /
• pp.723-730
• /
• 2011

It is very important to experimentally evaluate concrete behavior at elevated temperature because aggregates make up approximately 80 percent of volume in concrete. In this study, an experiment to evaluate mechanical properties of normal weight and light weight concrete of 60 MPa was conducted. Based on loading level of 0, 20 and 40 percent, the tests of 28 days compressive strength, elastic modulus, thermal strain, total strain, and transient creep using ${\phi}100{\times}200mm$ cylindrical specimens at elevated temperature were performed. Then, the results were compared with CEB (Committes Euro-international du Beton) model code. The results showed that thermal strain of light weight concrete was smaller than normal weight concrete. Also, the results showed that compressive strength of light concrete at $700^{\circ}C$ was higher than normal weight concrete and CEB code, similar to that obtained at ambient temperature. Transient creep developed from loading at a critical temperature of $500^{\circ}C$ caused the concrete strains to change from expansion to compression. The transient creep test result showed that internal force was high when the ratio of shrinkage between concrete and aggregate was more influential than thermal expansion.

• Journal of the Korea Institute of Building Construction
• /
• v.15 no.4
• /
• pp.359-365
• /
• 2015

Floor mortar experiences dry shrinkage by temperature and humidity difference of internal matrix with material type. Also, since floor mortar is influenced by environmental conditions during placing and curing period, cracks are likely to be occurred. In this study, it was evaluated the hardening and dry shrinkage properties of non-sintered binder based floor mortar utilizing alpha-hemihydrate gypsum which has expansibility in order to prevent crack of the floor mortar. It was applied to the construction site, and examined the effects of external environmental conditions on shrinkage deformation and cracking. Different types of slag accelerated initial and final setting in comparison with cement mortar and its compressive strength was satisfied standard compressive strength for floor mortar. Also shrinkage deformation behavior after the initial expansion exhibited a similar tendency with the cement mortar. From the field application result, no crack was found from slag mortar, and it is determined that the slag mortar has better dimensional stability than cement mortar caused by external environment conditions.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.10
• /
• pp.919-926
• /
• 2013

Experiments were conducted to determine the operating characteristics of a small-scale ORC (organic Rankine cycle) system for various low-temperature heat sources. A small-scale ORC power generation system adopting R-245fa as a working fluid was designed and manufactured. Hot water was used as the heat source, and the temperature was controlled using 110-kW electric resistance heaters that provided temperatures of up to $150^{\circ}C$. An open-drive oil-free scroll expander directly connected to a synchronous generator was installed in the ORC unit. Experiments were conducted by varying the rotational speed of the expander under the same heat source temperature conditions. The factors that influence the performance of the small-scale ORC system were analyzed and discussed.

• Applied Chemistry for Engineering
• /
• v.20 no.5
• /
• pp.465-472
• /
• 2009

The technologies for improving the capacity of hydrogen storage were investigated and the recent data of hydrogen storage by using various porous carbon materials were summarized. As the media of hydrogen storage, activated carbon, carbon nanotube, expanded graphite and activated carbon fiber were mainly investigated. The hydrogen storage in the carbon materials increased with controlled pore size about 0.6~0.7 nm. In case of catalyst, transition metal and their metal oxide were mainly applied on the surface of carbon materials by doping. Activated carbon is relatively cheap because of its production on a large scale. Carbon nanotube has a space inside and outside of tube for hydrogen storage. In case of graphite, the distance between layers can be extended by intercalation of alkali metals providing the space for hydrogen adsorption. Activated carbon fiber has the high specific surface area and micro pore volume which are useful for hydrogen storage. Above consideration of research, porous carbon materials still can be one of the promising materials for reaching the DOE target of hydrogen storage.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.28 no.5
• /
• pp.206-210
• /
• 2018

Two kinds of bioactive glass were coated on the Ti6Al4V alloy by the enameling technique. In order to reduce the thermal stress due to the difference in expansion coefficient with the alloy with the secondary coating forming hydroxyapatite, the difference in expansion coefficient between the alloy and the two glasses was adjusted at $2{\times}10^{-6}/^{\circ}C$ intervals. FE-SEM and EDS analysis showed that good adhesion was formed between the Ti6Al4V alloy and the primary coating by diffusion bonding. After immersion in SBF solution, it was confirmed from FT-IR that hydroxycarbonate apatite formed in the secondary coating was not different from bulk bioactive glass.

• Applied Chemistry for Engineering
• /
• v.26 no.1
• /
• pp.59-66
• /
• 2015

A new concept of an inorganic foaming process at low temperature was demonstrated for the production of inorganic thermal insulating materials with the properties of flexible light-weight, the advantages of organic-based thermal insulation material. The foaming process was proceeded by establishing a skeleton of the foam body by using inorganic fibrous sepiolite and aluminum silicate. A cavity was formed by the expansion of fibrous skeleton body, by the gas which was generated from foaming agent at low temperature. Then the multi-vesicular expanded perlite with low thermal conductivity was filled into the cavity in a skeleton of the foam body. Finally through these overall process, a new inorganic foamed body could be obtained at low temperature without the hot melting of inorganic materials. In order to achieve this object, various preparations such as fibrous sepiolite fibrillation process, heat treatment process of the fibrous slurry were needed, and the optimal compositional condition of slurry was required. The foam body produced showed the properties of flexible light-weight thermal insulation materials such as bulk density, yield strength, flexural strength, and high heat resistance.