• Korean Journal of Materials Research
• /
• v.8 no.9
• /
• pp.860-864
• /
• 1998

We investigated the photoluminescence and the crystalline properties with Ga doping concentrations (0-12 mol%) in $\textrm{Zn}_{1.98}\textrm{Mn}_{0.02}\textrm{SiO}_{4}$ green phosphors prepared by the solid state reaction. The photoluminescence was improved by a doping of Ga element in $\textrm{Zn}_{1.98}\textrm{Mn}_{0.02}(\textrm{Si_{1-x}\textrm{Ga}_{x})\textrm{O}_{4}$ phosphors which showed the highest emission intensity and good color purity in the doping concentration of x=0.08. The emission intensity of $\textrm{Zn}_{1.98}\textrm{Mn}_{0.02}(\textrm{Si_{1-x}\textrm{Ga}_{x})\textrm{O}_{4}$(x= 0.08) phosphors was increased to 7 times with increasing the sintering temperatures from $1100^{\circ}C$ to $1400^{\circ}C$, showing the improved crystalline quality. The decay time was not affected by Ga doping concentrations with constant values around 24ms. It was found from SEM and PSA analyses that the phosphors were composed of a large number of small grains around 1-3$10\mu\textrm{m}$ with a small amounts of agglomerated particles above $10\mu\textrm{m}$.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.16 no.1
• /
• pp.32-37
• /
• 2006

Rare-earth niobates, ag (Ln = Y, La, Gd) are well-known self-activated phosphors due to charge transfer in $NbO^{3-}_4$ showing a broad and strong emission band in the spectral region around 410 nm. In order to find new blue and red phosphors for FED, $LaNbO_4$ : X (X = Bi, Eu) phosphors are prepared through solid-state reactions at high temperature. The optimum reaction condition for these phosphors to give maximum emission intensity is obtained when it is first fired at $1250^{\circ}C$ for 2 h followed by second firing at $1400^{\circ}C$ for 1 h. Under irradiation at 254 nm, $1mol\%\;Bi^{3+}$ doped $LaNbO_4$ phosphor shows strong blue emission band with a range of $420\~450nm$. Also $10mol\%\;Eu^{3+}$ doped $LaNbO_4$ phosphor shows the maximum emission intensity at about 610 nm. Emission peaks at $415\~460nm$, $530\~560nm$and $570\~620nm$are observed in phosphors below $10mol\%\;Eu^{3+}$ doped $LaNbO_4$. Similar results are obtained in cathodoluminescent property of these phosphors.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.22 no.6
• /
• pp.305-311
• /
• 2012

In order to recycle the coal bottom ashes (denoted as BA) produced from a thermal power plant, the artificial aggregates (denoted as AAs) containing BA and red clay were manufactured, and the physical properties of AAs were studied as a function of particle size of BA and batch compositions. As-received BA had 38 wt% coarse particles of above 2 mm and many unburned carbon mass and porous slag particles were co-existed. So the two particle sizes of BA, the fine (< 100 ${\mu}m$) and coarse (< 2 mm), were prepared by milling and screening process. The AAs containing fine BA sintered at $1100{\sim}1200^{\circ}C$ had the higher bulk density and lower water absorption compared to the specimen made of coarse BA. The inside core of AAs manufactured by using coarse BA showed nonuniform and porous microstructure, while the AAs made of fine BA had a uniform and dense microstructure. In this research, the AAs containing BA and red clay with various bulk density (1.2~1.7) and water absorption (13~21 %) could be manufactured by controlling the particle size of BA and batch compositions, so the AAs of various physical properties could be applied to the wide fields such as construction/building materials in near future.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.31 no.5
• /
• pp.218-227
• /
• 2021

A thick film NTC thermistor for low temperature co-firing was manufactured by printing and sintering a paste prepared using NTC powder of Mn_1.5Ni_0.4Co_0.9Cu_0.4O₄ composition, lead free frit, and RuO₂ on a 96 % alumina substrate. The effect of frit and RuO₂ on the electrical properties of thick film NTC thermistor was studied. The resistance of the thick film NTC thermistor was higher than that of the bulk phase sintered at the same temperature, but it was found that the negative resistance temperature characteristic appeared more clearly and linearly in the resistance - temperature characteristic. On the other hand, the area resistance decreased as the sintering temperature increased, and the area resistance increased as the amount of frit added increased. The B constant of the thick film NTC thermistor was 3000 K or higher. Among them, it was found that the B constant of the thick film NTC thermistor made of paste with 5 wt% of frit added and sintered at 900℃ showed the highest B constant. Also, it can be seen that the area resistance decreased with the addition of RuO₂, and the change in the area resistance decrease of the thick film NTC thermistor obtained by sintering the paste containing 5 wt% of RuO₂ at 900℃ is the most obvious.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.10 no.1
• /
• pp.35-46
• /
• 2007

In the study digital imagery was used to examine asphalt concrete pavements. With digitally mastered-image information that was filmed with a video camera fixed on a car travelling on road at a consistent speed, a road surface management system that can gain road surface information (Crack, Rutting, IRI) was developed using an object-oriented language "Delphi". This system was designed to improve visualized effects by animations and graphs. After analyzing the accuracy of 3-D coordinates of road surfaces that were decided using multiple image orientation and bundle adjustment method, the average of standard errors turned out to be 0.0427m in the X direction, 0.0527m in the Y direction and 0.1539m in the Z direction. As a result, it was found to be good enough to be put to practical use for maps drawn on scales below 1/1000, which are currently producted and used in our country, and GIS data. According to the analysis of the accuracy in crack width on 12 spots using a digital video camera, the standard error was found to be ${\pm}0.256mm$, which is considered as high precision. In order to get information on rutting, the physically measured cross sections of 4 spots were compared with cross sections generated from digital images. Even though a maximum error turned out to be 10.88mm, its practicality is found in work efficiency.

• Korean Journal of Materials Research
• /
• v.6 no.2
• /
• pp.166-174
• /
• 1996

경제적이고 단순성의 공정특성을 갖는 닥터 블레이드법을 이용하여 평판형 고체산화물 연료전지의 고체전해질용 이트리아 안정화 지르코니아 박막을 제조하였다. 슬러리의 최적 제조조건과 그린 필름의 최적 소성조건을 얻었으며, 이 제조 조건에서 제조된 전해질의 결정구조, 미세구조 그리고 전기적 성질을 각각 X-선 회절, 주사전자현미경 그리고 교류 임피던스 분석기를 이용하여 조사하였다. 동량의 8mol% 이트리아를 첨가한 경우, 닥터 블레이드법에 의해 제조된 이트리아 안정화 지르크니아 박막은 금형가압성형법에 의해 제조된 이트리아 안정화 지르코니아 펠렛과 거의 비슷한 전기전도도를 나타내었다. 닥터 블레이드법에 의해 제조된 이트리아 안정화 지르크니아 박막의 경우, 8mol%이트리아를 첨가한 경우의 전도도가 3mol%이트리아를 첨가한 경우 보다 993K 이상과 523K 8mol% 이트리아를 첨가한 경우의 전도도가 3mol%이트리아를 첨가한 경우의 전도도가 3mol%이트리아를 첨가한 경우 보다 993K이상과 523K이하의 온도에서는 더 높고, 523-933K사이의 온도구간에서는 낮게 나타났다. 게다가, 모든 시편에 있어서 전체 전도도에 대한 벌크 전도도의 기여도에 대한 기여도보다 더 크게 나타났다.

• Journal of the Korean Institute of Gas
• /
• v.5 no.4 s.16
• /
• pp.27-32
• /
• 2001

It is desired that carbon dioxide causing a greenhouse effect be removed at a high temperature and high pressure in a steam reforming reaction. In this research, a pellet form of adsorbent CaO is employed to capture $CO_2$. The adsorbent was manufactured using a high pressure molding on powdered $CaCO_3$ followed by calcination. Then its properties were analyzed and the adsorption experiments were carried out in a batch adsorption chamber. The pore area was found to be dependent on a molding pressure and the pore distribution showed two peaks. It is examined that $CO_2$ binds to CaO by means of chemisorption and its maximum conversion is nearly $80\%$ at $700^{\circ}C$.

• Korean Journal of Materials Research
• /
• v.25 no.2
• /
• pp.81-89
• /
• 2015

A strain-gradient crystal plasticity constitutive model was developed in order to predict the Hall-Petch behavior of a Ni-base polycrystalline superalloy. The constitutive model involves statistically stored dislocation and geometrically necessary dislocation densities, which were incorporated into the Bailey-Hirsch type flow stress equation with six strength interaction coefficients. A strain-gradient term (called slip-system lattice incompatibility) developed by Acharya was used to calculate the geometrically necessary dislocation density. The description of Kocks-Argon-Ashby type thermally activated strain rate was also used to represent the shear rate of an individual slip system. The constitutive model was implemented in a user material subroutine for crystal plasticity finite element method simulations. The grain size dependence of the flow stress (viz., the Hall-Petch behavior) was predicted for a Ni-base polycrystalline superalloy NIMONIC PE16. Simulation results showed that the present constitutive model fairly reasonably predicts 0.2%-offset yield stresses in a limited range of the grain size.

• Korean Journal of Materials Research
• /
• v.7 no.7
• /
• pp.592-596
• /
• 1997

LI$_{2}$형 결정구조를 갖는 Ni-20at.%AI-10at%Fe 금속간화합물에 boron, zirconium 과 hafnium을 최고 0.5at.% 까지 첨가하여 항복강도, 연성, 파괴 등 기계적 성질의 변화를 인장시험과 X선분석 및 XPS분석 등을 통하여 관찰하였다. Ni-20at.% AI-10at.% Fe금속간화합물에 boron을 첨가하였을 때는 연신율의 현저한 증가가 나타났으나 zirconium이나 hafnium첨가의 경우에는 별다른 효과가 나타나지 않았다. Ni-20at.%AI-10at%Fe 금속간화합물의 경우, boron의 양이 증가할수록 인장연신율이 증가하였으며 0.1at.%의 boron을 첨가한 경우 최고 48.5%의 상온인장연신율을 나타내었다. 첨가물을 넣지 않은 경우와 zirconium과 hafnium을 첨가한 경우, 파괴모드는 입계파괴의 형태를 나타내었으나 boron을 첨가한 경우에는 파괴모드가 입계파괴에서 입내파괴로 변화되었다. XPS분석을 통하여 boron이 입계에 편석된 것을 관찰할 수 있었으며 이는 이미 제시된 여러가지 해석들과 일치하는 결과이다. 이로부터 boron의 첨가에 따른 인장연신율의 증가는 boron의 입계편석거동과 관련이 있음을 알 수 있다.

• Journal of the Korean Ceramic Society
• /
• v.35 no.8
• /
• pp.807-812
• /
• 1998

Mechanical properties of two types of polycrystlline {{{{ { { Ti}_{3 }SiC }_{2 } }} with different grain size were investigated. A fine grain {{{{ { { Ti}_{3 }SiC }_{2 } }} has a higher fracture strength and hardness. Plot of strength versus Vickers indentation load indicated that {{{{ { { Ti}_{3 }SiC }_{2 } }} has a high flaw tolerance. Hertzian indentation test using a spherical indenter was used to study elastic and plastic behavior in {{{{ { { Ti}_{3 }SiC }_{2 } }}. Indentation stress-strain curves of each material are made to evaluate the plasticity of {{{{ { { Ti}_{3 }SiC }_{2 } }} Both find and coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} showed high plasticity. In-dentation stress-strain curve of coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} deviated even more from an ideal elastic limit in-dicating exceptional plasticity in this material. Deformation zones were formed below the contact as well as around the contact area in both materials but the size of deformation zone in coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} was much larger than that in fine grain {{{{ { { Ti}_{3 }SiC }_{2 } }} Intragrain slip and kink would account for high plasticity. Plastic behavior of {{{{ { { Ti}_{3 }SiC }_{2 } }} was strongly influenced by grain size.