• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.25-31
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• 2023

In this study, the basic properties of CO₂ immobilized desulfurized gypsum (CFBG) and the possibility of being used as a stimulus for slag cement were reviewed, and performance evaluation was conducted through a concrete mixing test. The main components of CFBG were CaO and SO₃, and CaO and SO₃ increased as the drying temperature increased. The moisture content of undried CFBG was 15.7 %, the drying temperature was 1.7 % and the drying temperature was 0.03 % at 105 ℃. Mortar using CFBG tended to have a lower flow value as the drying temperature increased, and the compressive strength was equivalent to that of the FGB use mixture. As a result of the concrete experiment using CFBG SC, both slump and air volume satisfied the target range after 60 minutes, and the compressive strength tended to increase overall compared to the ternary binder mixture.

• Composites Research
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• v.22 no.3
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• pp.66-73
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• 2009

Total thickness, areal density and mass moment of inertia of materials are important material factors for structural characteristics. In this work, a material-structural optimization was performed up to the maximum ballistic limit of multi-layered composite structures under high impact velocity followed by the investigation of the influence of these factors on an impact absorption performance. A unified model combined with Florence's and Awerbuch-Bonder's models was used in optimizing the multi-layered composite structure consisting of CMC, rubber, aluminum and Al-foam. Total thickness, areal density and mass moment of inertia were used for the optimization constraint. As shown in the results, the ballistic limit determined from a newly developed unified model was closely similar to the finite clement analysis. Additionally, the ballistic limit and impact absorption energy obtained by the optimized structure were improved approximately 16.8% and 26.7%, respectively comparing with a not optimized multi-layered structure.

• Resources Recycling
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• v.14 no.2
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• pp.19-27
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• 2005

The recycling possibility of aluminum waste dross(AWD) as a ceramic raw material of porous light-weight material was examined. A aluminum waste dross was washed 4-7 consecutive times and roasted at 900$^{\circ}% for 1hour as pre-treatments. The properties of the pre-treatment of aluminum waste dross was investigated. It was conformed by XRD result that the spinel crystalline was grown in AWD, after roasting. After the roasted AWD was ground in aqueous state, the sodium hexaphosphate(SHP) as a dispersant which is used for stabilizing the concentrated slurry was added to the AWD slurry. The porous material was prepared by slurry foaming method with surfactant at room temperature. The foamed slurry volumes were 2 and 3 times of the original slurry volume. The properties of porous material with extended volume of 3 times was following: the porosity was about 84%, bulk density was 0.59 g/cm$^3$, the range of pore was from 50 ${\mu}m$ to 500 ${\mu}m$ and mean pore size was about 200 ${\mu}m$. AWD porous material was sintered at 1150$^{\circ}C-1250$^{\circ}C. It was colcluded that AWD was sintered well at 1200$^{\circ}C from material surface observation by SEM.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.3
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• pp.97-103
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• 2012

The combustion chamber and nozzle of a liquid rocket engine should be protected from the high temperature combustion gas generated by the chamber. An upper-stage nozzle extension has a large expansion ratio, therefore, The light-weight refractory materials have been used since the weight impact on the launcher performance is crucial. Gas film cooling method was used before, but was not applicable nowadays. Ablative cooling method and radiative cooling method with niobium alloy, Ni-based superalloy and ceramic based composite have been used to this day.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.6
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• pp.384-389
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• 2015

In this paper, we fabricated ceramic body and sapphire wafer in order to develop a hydraulic pressure sensor with high sensitivity and high temperature stability. The sapphire wafer was adopted with a membrane of capacitance ceramic pressure sensor. The capacitance value of the sensor for the finite element analysis(FEM) showed a linear pressure characteristics. Membrane was processed with a diameter of 32.4 mm and a thickness of 1 mm by using alumina powders. Ceramic body was processed with a diameter 32.4 mm and a thickness 5 mm. The capacitance pressure sensor was made with high heat treatment of the ceramic body and the sapphire wafer. Initially capacitance of the pressure sensor was 50 pF and a capacitance of 110 pF was measured from 5 bar pressure. Output voltage of 5 V was appeared at 5 bar pressure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.10
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• pp.4392-4397
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• 2012

In this study, we used the commercial package (Unigraphics) to construct a junction box cable car when laser plastic parts have been processed using urethane resin(TSR-755) as a starting mold material. After construction, we carried out the filing, packing, cooling, and deforming analyzation using Injection Molding Analysis (Simpoe-Mold) to determine the gate positioning and automatic cooling cycle through the examination. The results show that inserting into the injection mold after processing ceramic has reduced the time of thermal conductivity of molding and cooling; and quick selection of gates and cooling lines could possibly cause an improvement of productivity.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.134-134
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• 2016

CMC(Ceramic Matrix Composites)는 $1500^{\circ}C$ 이상의 고온에서 내열성, 내산화성, 내식성이 우수하여, 초음속 비행체, 가스터빈 엔진 및 원자로용 초고온 부품 등에 수요가 증가하고 있다. 하지만 이러한 특성은 비산소 환경에 국한되는 것으로 약 $400^{\circ}C$ 이상의 산화 분위기에는 탄소섬유가 산화되는 문제로 인하여 적용의 한계를 가지고 있다. 따라서 CMC의 적용범위 확대를 위하여 내산화 코팅으로 CMC의 초고온 산화특성을 개선하는 것이 필수적이며, 장시간 초고온 산화환경 분위기에서 사용되기 위하여 안정적인 코팅기술이 최근 기술개발의 핵심현안으로 부각되고 있다. 본 연구에서는 pack cementation 공정을 이용하여 내산화성이 우수한 SiC 코팅층을 제조하였다. Pack cementation 공정에 사용된 코팅 분말은 57wt.% SiC, 30wt.% Si, 3wt.% B, 10wt.% Al2O3의 비율로 혼합된 것이다. 실험은 3D 직조된 CMC 모재를 혼합분말 내에 침적한 후, Ar 분위기에서 $1600^{\circ}C$, 4~12시간 반응시켜 수 마이크론 두께의 SiC 코팅층을 형성하였다. 더 우수한 산화 특성을 부여하기 위하여 pack 처리된 CMC 표면에 초고온 세라믹인 TaC 소재를 진공플라즈마 코팅 공정으로 적층시켰다. 제조된 코팅층을 SEM, XRD를 이용하여 미세구조 및 결정구조를 분석하였으며, pack cementation에 따른 내산화 특성을 비교 분석하고자 $2000^{\circ}C$에서 산화 실험을 진행하였다. 산화 실험 이후 미세구조 및 결정구조 분석으로 산화거동을 규명하고자 하였다.

• Electrical & Electronic Materials
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• v.9 no.2
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• pp.146-151
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• 1996

PZT powders were prepared by the molten salt synthesis method. The porous PZT ceramics were made from a mixture of PZT and polyvinylalcohol(PVA) by BURPS(Bumout Plastic Sphere) technique. The 3-3 type composites were fabricated by impregnating an sintered porous PZT ceramics with various polymer matrices. The relative permittivity of 3-3 type composite specimens was shown 860-1,100 smaller than that of solid PZT ceramics(2,100), and the dissipation factors of composite specimens were about 0.02 to 0.03. The piezoelectric coefficient d$_{33}$ of composite specimens(285-328*10$^{12}$ C/N) was comparable with that of single phase PZT specimens(364*10$^{-12}$ C/N). The thickness mode coupling factor k$_{t}$(O.5-0.6) of composite specimens was comparable with that of single phase PZT specimens(k$_{t}$-0.7), and the mechanical quality factor of composite specimens was smaller than 10, and thus these 3-3 type composite specimens would be believed as a good candidates for broad band transducer applications.ons.

• Electrical & Electronic Materials
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• v.7 no.6
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• pp.534-542
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• 1994

Microstructures and dielectric properties of (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$+0.006Nb$_{2}$O$_{5}$ (0.05.leq.x.leq.0.2) ceramic were investigated. The specimens fired in a reducing atmosphere(N$_{2}$) were painted on the surface with CuO paste, and then annealed at 1100.deg. C for 2 hr. SEM and EDAX revealed that CuO penetrated rapidly into the bulk along the grain boundaries during the annealing. Grain size increased with increasing Ca content up to 15[mol%], but decreased with further addition. In the specimens with 10-15[mol%l of Ca, excellent dielectric properties were obtained as follows; dielectric constant <25000, dielectric loss(tan .delta[%]) <0.3[%] and capacitance change rate with temperature <.+-.[%], respectively. All the specimens in this study exhibited dielectric relaxation with frequency as a function of the temperature. The dispersive frequency was over 10$^{6}$ [Hz].z].

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.1
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• pp.32-38
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• 2003

Engineering ceramics have many unique characteristics both in mechanical and physical properties such as high temperature hardness, high thermal, chemical and electrical resistance. However, its machinability is very poor in conventional machining due to its high hardness and severe tool wear. In the current experimental study alumina($Al_2O_3$) was ultrasonically machined using SiC abrasives under various machining conditions to investigate the material removal rate and surface quality of the machined samples. Under the applied amplitude of 0.02mm, 27kHz frequency, three slurry ratios (abrasives water by weight) of 11, 13 and 15 with different tool shapes and applied pressure levels, the machining was conducted. Using the mesh number of 240 abrasive, slurry ratio of 11 and static pressure of $25kg/cm^2$, maximum material removal rate of $18.97mm^3/mm$ was achieved with mesh number of 600 SiC abrasives and static pressure of $30kg/cm^2$, best surface roughness of $0.76{\mu}m$ Ra was obtained.