• Korean Journal of Materials Research
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• v.10 no.12
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• pp.825-830
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• 2000

The copolymers with various composition of vinylbenzyl chloride (VBC), methyl methacrylate (MMA), and 2-hydroxyethyl methacrylate(HEMA) were synthesized as a humidity sensitive material and quaternized with N, N, N', N'-tetraethylene diamine.. Resistance versus relative humidity decreased with increase in the content of MMA in the copolymer. The introduction of HPMA increased the resistance of the humidity sensor as well as enhanced the adherence to the alumina substrate. In the case of VBC/MMA/HEMA=80/10/10, the hysteresis and temperature dependency coefficient were $\pm$2%RH and -0.46~0.42%RH/$^{\circ}C$. The average resistance at 30%RH, 60%RH and 90%RH were 3.0M$\Omega$ ,200k$\Omega$ and 9k$\Omega$, respectively.

• Korean Journal of Materials Research
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• v.18 no.5
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• pp.283-288
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• 2008

The effect of sintering aids and glass-frit on the densification and resistivity of silver paste was investigated in an effort to enhance the sintered density and electrical conductivity of the silver electrode. To prepare Pb-free silver paste for use at low sintering temperatures, two commercial silver powders ($0.8\;{\mu}m$ and $1.6\;{\mu}m$ in size) and 5wt.% lab-synthesized nanoparticles (30-50 nm in size) as a sintering aids were mixed with 3 wt.% or 6 wt.% of glass frit ($Bi_2O_3$-based) using a solvent and three roll mills. Thick films from the silver paste were prepared by means of screen printing on an alumina substrate followed by sintering at $450^{\circ}C$ to $550^{\circ}C$ for 15 min. Silver thick films from the paste with bimodal particles showed a high packing density, high densification during sintering and low resistivity compared to films created using monomodal particles. Silver nanoparticles as a sintering aid enhanced the densification of commercial silver powder at a low sintering temperature and induced low resistivity in the silver thick film. The glass frit also enhanced the densification of the films through liquid phase sintering; however, the optimum content of glass frit is necessary to ensure that a dense microstructure and low resistivity are obtained, as excessive glass-frit can provoke low conductivity due to the interconnection of the glass phase with the high resistivity between the silver particles.

• Journal of the Korea Institute of Building Construction
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• v.17 no.3
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• pp.261-268
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• 2017

Red mud is an inorganic by-product obtained from the mineral processing of alumina from Bauxite ores. A highly alkali inorganic waste product with a pH level over 11, red mud in its original state negatively impacts the ecosystem, so appropriate treatment is necessary. The development of alkali activated slag-red mud cement can be a representative study aimed at recycling the strong alkali of the red mud as a construction material. However, Alkali-activated binders that use sodium activators have been reported to be more vulnerable to efflorescence. Therefore, in this study, the compressive strength, pore characteristics, water absorption, elution characteristics, and efflorescence properties of alkali-activated slag cement mortar were assessed according to their red mud substitution ratio.

• Journal of Sensor Science and Technology
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• v.5 no.6
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• pp.7-14
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• 1996

In order to develop gas sensor operating at low temperature, thick film $Co_{3}O_{4}$ sensor was fabricated. $Co_{3}O_{4}$ powder was prepared by precipitation from cobalt nitrate solution and the powders containing ethylene glycol as a binder was screen-printed on alumina substrate. Characteristics of sensitivity, response time, and recovery were investigated in terms of binder content and heat treating conditions. The $Co_{3}O_{4}$ sensor contained 15% ethylene glycol and heat-treated at $300^{\circ}C$ for 24hr showed the highest sensitivity at the operating temperature of $250^{\circ}C$. Its sensitivity of 1.1 to 5000ppm butane gas was very high, as compared with $0.8{\sim}0.85$ at the operating temperature of $350{\sim}400^{\circ}C$ for a commercial $SnO_{2}$ gas sensor. It is found that response time was fast, but recovery was poor for the sensor.

• Korean Journal of Materials Research
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• v.29 no.4
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• pp.233-240
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• 2019

This study analyzes the mechanical properties, including the attrition rate, of $50{\mu}m$ size yttria-stabilized zirconia (YSZ) beads with different microstructures and high-energy milling conditions. The yttria distribution in the grain and grain-boundary of the fully sintered beads relates closely to Vickers hardness and the attrition rate of the YSZ beads. Grain size, fractured surfaces, and yttrium distribution are analyzed by electronic microscopes. For standardization and a reliable comparison of the attrition rate of zirconia beads with different conditions, Zr content in milled ceramic powder is analyzed and calculated by X-ray Fluorescence Spectrometer(XRF) instead of directly measuring the weight change of milled YSZ beads. The beads with small grain sizes sintered at lower temperature exhibit a higher Vickers hardness and lower attrition rate. The attrition rate of $50{\mu}m$ YSZ beads is measured and compared with the various materials properties of ceramic powders used for high-energy milling. The attrition rate of beads appears to be closely related to the Vickers hardness of ceramic materials used for milling, and demonstrates more than a 10 times higher attrition rate with Alumina(Hv ~1650) powder than $BaTiO_3$ powder (Hv ~315).

• Journal of Sensor Science and Technology
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• v.10 no.4
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• pp.222-231
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• 2001

The material properties of $SnO_2$ were investigated as a function of the amount of $Fe_2O_3$, the partial pressure of oxygen, the concentration of CO gas, and temperature. $Fe_2O_3$-doped $SnO_2$ thick films were prepared by the screen printing technique on alumina substrate. The specimens sintered at $700^{\circ}C$ for 6 hours showed little difference of the grain size and narrow distribution with the content of $Fe_2O_3$. The electrical conductance of undoped $SnO_2$ is high at low firing temperature and at low partial pressure of oxygen. The electrical conductance of $Fe_2O_3-$-doped $SnO_2$ is increased with measurement temperature, but decreased with the content of $Fe_2O_3$. The dependence of oxygen partial pressure is decreased with dopant addition. The highest sensitivity and the good properties of response speed and repeatability for CO gas were observed on the specimen with 0.1 mol% $Fe_2O_3$ at $350^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.912-918
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• 2002

Ni-Mn-Co-Fe oxide thick films were coated on an alumina substrate by screening printing technique. The microstructure and electrical properties of the thick films, as a function of composition and sintering temperature, were investigated. The components of the NTC thick films sintered at 1150${\circ}C$ were distributed homogeneously. On the other hand, in the case of the NTC thick films sintered at 1200 and 1250${\circ}C$, Co element was distributed homogeneously, but Ni, Mn and Fe elements were distributed heterogeneously, resulting in the formation of Ni rich and Mn-Fe rich regions. All the thick film NTC thermistors prepared showed a linear relationship between log resistance (log R) and the reciprocal of absolute temperature (1/T), indicative of NTC characteristics. At a given NiO and $Mn_3O_4$ content, the resistance, B constant and activation energy of $(Ni_{1.0}Mn_{1.0}Co_{1-x}Fe_x)O_4$ (0.25${\le}$x${\le}$0.75) and $(Ni_{0.75}Mn_{1.25}Co_{1-x}Fe_x)O_4$ (0.25${\le}$x${\le}$0.75) thermistors increased with increasing $Fe_2O_3$ content.

• Journal of the Mineralogical Society of Korea
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• v.24 no.3
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• pp.151-164
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• 2011

Mineralogical and petrological characteristics were investigated on matrix of dense gray, vesiculate gray, brown and black pumice in Ulleung Island by using XRD, FT-IR, XRF, SEM and thermal analysis. According to the analysis, most of pumice matrix are amorphous and include very small amount of sanidine and anorthoclase. Since the adsorption moistures, which commonly observed as O-H peak in FT-IR spectrum, are not identified in thermal analysis, it seems reasonable to conclude that content of the adsorption moisture has very low level. Although pumice has a large specific surface area, with long time elapsed after eruption, pumice matrix shows very low degree of hydration alteration due to the low level of water content. In SEM images, most surfaces of pumice show morphological characteristics such as various shapes of vesicle with wrinkled and thin walls resulted from ductile coalescence. Dense gray pumice formed in the initial stage includes small vesicles less than $15{\mu}m$ in size with subangular to angular shapes, free of ovoid vesicle. These characteristics are interpreted to have related to the hydrous environment derived from phreato-plinian eruption. Submicron particles observed as amorphous alumina silicate assemblages in vesicle surface are considered as particles sticked to the matrix surface through rapidly cooling process during ascent of alkali phonolitic magma. It indicates that these particles coexisted partly with crystallized alkali feldspar.

• The Journal of Engineering Research
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• v.4 no.1
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• pp.69-85
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• 2002

The chemical composition of bottle glass is consisted of Na2O-CaO-SiO2. However the cullet is mornally used in order to decrease the melting tsmperature. This induce the productivity of bottle and decreases the cost. The addition of plate glass decreases the Al2O3 content and in fluence the stone phenomenon and devitification in botle glass. Tus the Feldspar is added in order to increase the Al2O3 content when plate cullet was added in melting. The Tridymite crystal was observed over 7.5% Al2O3 contents, which shown as white crystal in appearance. It is Supposed that the Wollastonite Would be occurred in more over 7.5% Al2O3. This fad id well consised With the Litertctures.

• Conservation Science in Museum
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• v.25
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• pp.63-84
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• 2021

In order to investigate the diverse physicochemical changes that occurred in traditional Korean pottery during its production, including before and after firing, this study produced six replicas of a celadon maebyeong inlaid with cloud-and-crane designs, respectively corresponding to the process of shaping, carving, inlaying designs, first firing, glazing and second firing, respectively. It then conducted a scientific study of these six replicas and analyzed their images through high-resolution three-dimensional transmission imaging. The materials used for the replicas show different mineral phases and even colors depending on the components of each material. For example, black inlay with a high content of iron oxide (Fe₂O₃) shows dark colors and white inlay with a high alumina (Al₂O₃) content appears white. Physicochemical properties such as chromaticity and magnetic susceptibility and major components of the replicas were confirmed by the differences in the density in the computed tomography (CT) images. The characteristics of fired products such as fine structure, absorption ratio, apparent porosity, and other characteristics of the major mineral components were identified by the presence of pores and the formation of cracks inside the replicas in the image analysis.