• Korean Journal of Materials Research
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• v.33 no.4
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• pp.135-141
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• 2023

The volatilization of alkali ions in (K,Na)NbO₃ (KNN) ceramics was inhibited by doping them with alkaline earth metal ions. In addition, the grain growth behavior changed significantly as the sintering duration (t_s) increased. At 1,100 ℃, the volatilization of alkali ions in KNN ceramics was more suppressed when doped with alkaline earth metal ions with smaller ionic size. A Ca²⁺-doped KNN specimen with the least alkali ion volatilization exhibited a microstructure in which grain growth was completely suppressed, even under long-term sintering for t_s = 30 h. The grain growth in Sr²⁺-doped and Ba²⁺-doped KNN specimens was suppressed until t_s = 10 h. However, at t_s = 30 h, a heterogeneous microstructure with abnormal grains and small-sized matrix grains was observed. The size and number of abnormal grains and size distribution of matrix grains were considerably different between the Sr²⁺-doped and Ba²⁺-doped specimens. This microstructural diversity in KNN ceramics could be explained in terms of the crystal growth driving force required for two-dimensional nucleation, which was directly related to the number of vacancies in the material.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.870-877
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• 1998

With impedance spectrum measurements, impedance was studied in the interface between sample solutions for $K^+-ion$ selective PVC membrane electrode containing neutral carriers [dibenzo-18-crown-6 (D18Cr6) and valinomycine (Val)]. Response characteristics of electrode were examined by measuring AC impedance spectra that were resulted from the chemical structure and the content of carrier, variation of plasticizer, membrane thickness, doping of base electrolytes, and concentration variation of sample solution. Transport characteristics of PVC membrane electrode were also studied. It was found that the equivalent circuit for the membrane in $K^+$ solution could be expressed by a series combination of solution resistance and a parallel circuit consisting of the bulk resistance and geometric capacitance of the membrane system. But the charge transfer resistance and Warburg resistance were overlapped a little in the low concentration and low frequency ranges. The carrier, D18Cr6 was best for electrode and impedance characteristics, and ideal electrode characteristics were appeared especially in case of doping of the base electrolyte[potassium tetraphenylborate(TPB)]. The optimum carrier content was about 3.23 wt% in case of D18Cr6 and Val. DBP was best as a plasticizer. As membrane thickness decreased the impedance characteristics was improved, but electrode characteristics were lowered for membrane thickness below the optimum. In the case of D18Cr6, the selectivity coefficients by the mixed solution method for the $K^+$ ion were the order of $NH_4{^+}>Ca^{2+}>Mg^{2+}>Na^+$.

• Journal of the Korean Electrochemical Society
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• v.1 no.1
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• pp.1-7
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• 1998

For the purpose of finding new cathode materials for medium-temperature $(700\~800^{\circ}C)$ solid oxide fuel cells, $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3,\;(x=0.0\~0.5)$ are prepared, and their thermal stability and conductivity characteristics are investigated. Also, the cathodic activities are measured after the cathode layer being attached on CGO (cerium-gadolinium oxide) electrolyte disk. The X-ray analyses indicate that the materials prepared by calcining the citrate-gels at $800^{\circ}C$ have the orthorhombic perovskite structure without discernible impurities. The thermal stability of the undoped Co perovskite is so poor that it is decomposed to the individual binary oxide even at $1300^{\circ}C$. But the partially Fe-doped cobaltates exhibit a better thermal stability to retain their structural integrity up to $1400^{\circ}C$. The observation whereby both the undoped and Fe-doped cobaltates melt at ca. $1300^{\circ}C$ leads us to perform the electrode adhesion at <$1300^{\circ}C$. The cathodic activity of $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3,\;(x=0.0\~0.5)$, electrodes is superior to $La_{0.9}Sr_{0.1}MnO_3$, among the samples of $x=0.0\~0.5$, the x=0.2 cathode shows the best activity for the oxygen reduction reaction. It is likely that the Fe-doping provides a better thermal stability to the materials but in turn imparts an inferior cathodic activity, such that the optimum trade-off is made at x=0.2 between the two factors. The total electrical conductivity and ion conductivity of $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3$, are measured to be 51 S/cm and $6.0\times10^{-4}S/cm\;at\;800^{\circ}C$, respectively. The conductivity values illustrate that the materials are a mixed conductor and the reaction sites can be expanded to the overall electrode surface, thereby providing a better cathodic activity than $La_{0.9}Sr_{0.1}MnO_3$.

• The Korean Journal of Food And Nutrition
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• v.21 no.1
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• pp.35-42
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• 2008

To develop physiological functionality of Omija extracted with water was evaluated on antioxidative activity. Omija, high acid material with pH 3.6, contain $57.5{\pm}1.03%$ of moisture, and $18.8{\pm}0.12%$ of crude fat. This material have $12.6{\pm}0.04%$ of carbohydrate and $11.1{\pm}0.07%$ of crude protein as well, but ash and crude protein contents were found less than 10%. 10 mineral contents were also found, too; K and Ca showed the highest level, then Al, Mg, Na and Mn were followed. In composition amino acid contents, glutamic acid took the largest portion, $131.7{\pm}1.3$ mg/100 g, aspartic acid $51.5{\pm}0.6%$, and other composition amino acid under 50%. In case of free sugar contents, 7 types were found. Most of them were glucose and fructose. Total phenolic compounds showed the highest level, $2,862.6{\pm}31.7$ mg/100 g. $197.8{\pm}14.6$ mg/100 g of flavonoid and $225.6{\pm}18.2$ mg/100 g were included. In terms of electron donating ability, radical scavenging ability activated as the amount of Omija extract increased. In particular, Omija extract in 1,000 ${\mu}g/m{\ell}$ demonstrated almost similar electron donating ability, $72.4{\pm}0.21%$, to BHT. It was also found that antioxidant activities of electron donating ability, SOD-like ability, hydroxyl radical scavenging ability and nitrite scavenging ability were highly promoted as Omija extract concentration increased. The nitrite scavenging ability was significant when the extract belonged to strong acid region and doping concentrations increased.

• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.695-702
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• 1994

Current study was undertaken to explain the structural evolution and corresponding changes in the properties of calcium aluminate glasses with the variation of SiO2 doping concentration. Calcium aluminate glasses in the compositional ranges of (100-x)(0.6CaO+0.4Al2O3)+xSiO2(where x=0~60) were fabricated. DTA analysis confirmed an anomalous behavior in glass transition temperature (Tg) with the maximum of 887$^{\circ}C$ and minimum of 859$^{\circ}C$ when x=5 and 50, respectively. densities and refractive indices monotonically decreased with increasing SiO2 content and IR transmitting cutoff shifted to shorter wavelength side when the amount of added SiO2 exceeded 5 mole%. IR fundamental vibration absorption peaks showed the change that NBOs were inclined to SiO4 tetrahedron in the low-silica region and NBO per SiO4 tetrahedra changed from 2 to 0 with increasing silica content. Based on the analysis of IR fundamental vibration absorption peaks, the model of the structural change can be proposed in three step: 1) SiO4 scavenged the NBOs located at AlO4-tetrahedra, which resulted in the increased of Tg values, 2) NBOs located in the main network again with a decrease in Tg, and 3) dominated by the decrease in the relative amount of NBOs in the glass system, where Tg re-increased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.3
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• pp.216-221
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• 2010

Employing statistical design of experiments, the difference in doping behaviors of rare-earth ions and their effects on the dielectric property and microstructure of $BaTiO_3$-MgO-$MnO_2$-($Ba_{0.4}Ca_{0.6}$) $SiO_3-Re_2O_3$ (Re = $Y_2O_3$, $Er_2O_3$) system were investigated. Through the statistical analysis we have found that the amount of $Re_2O_3$ are significantly affecting on the dielectric properties. The $Re_2O_3$ improved the dielectric constant, dielectric loss and R*C constant, so the appropriate contents of $Y_2O_3$ and $Er_2O_3$ were 0.8 ~ 1.2 mol% and 0.8 ~ 1.3 mol%, respectively. The MLCC(mutilayer chip capacitor) with $2.0{\times}1.2{\times}1.2mm$ size and 475 nF was also suited for X7R with the above composition. It showed that the dielectric constant and RC constant were 2,839 and 3,675 ${\Omega}F$, respectively in the sintering condition at $1250^{\circ}C$ in $Po_2$ $10^{-7}$ Mpa.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.596-601
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• 2020

Silicon carbide is considered a potentially useful material for high-temperature electronic devices because of its large band gap energy and p-type or n-type conduction that can be controlled by impurity doping. Accordingly, the thermoelectric properties of -SiC powder prepared by refined diatomite were investigated for high value-added applications of natural diatomite. -SiC powder was synthesized by a carbothermal reduction of the SiO₂ in refined diatomite using carbon black. An acid-treatment process was then performed to eliminate the remaining impurities (Fe, Ca, etc.). n-Type semiconductors were fabricated by sintering the pressed powder at 2000℃ for 1~5h in an N2 atmosphere. The electrical conductivity increased with increasing sintering time, which might be due to an increase in carrier concentration and improvement in grain-to-grain connectivity. The carrier compensation effect caused by the remaining acceptor impurities (Al, etc.) in the obtained -SiC had a deleterious influence on the electrical conductivity. The absolute value of the Seebeck coefficient increased with increasing sintering time, which might be due to a decrease in the stacking fault density accompanied by grain or crystallite growth. On the other hand, the power factor, which reflects the thermoelectric conversion efficiency of the present work, was slightly lower than that of the porous SiC semiconductors fabricated by conventional high-purity -SiC powder, it can be stated that the thermoelectric properties could be improved further by precise control of an acid-treatment process.

• Journal of the Korean Electrochemical Society
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• v.3 no.4
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• pp.200-203
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• 2000

Boron doped conducting diamond thin films were grown on Si substrate by microwave plasma chemical vapor deposition from a gaseous feed of hydrogen, acetone/methanol and solid boron. The doping level of boron was ca. $10^2ppm\;(B/C)$. The Si substrate was tilted ca. $10^{\circ}$ to make Si substrate, which have different height and temperature. Experimental results showed that different crystalline of diamond thin films were made by different temperature of Si substrate. There appeared $3\~4$ steps of different crystalline morphology of diamond. To characterize the boron-doped diamond thin film, Raman spectroscopy was used for identification of crystallinity. To survey surface morphology, microscope was used. Grain size was changed gradually by different temperature due to different height. The Raman spectrum of film exhibited a sharp peak at $1334cm^{-1}$, which is characteristic of crystalline diamond. The lower position of diamond film position, the more non-diamond component peak appeared near $1550 cm^{-1}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.2
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• pp.77-82
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• 2022

Recently, research on the development of low-cost/high-efficiency water electrolysis catalysts to replace noble metal catalysts is being actively conducted. Since overvoltage reduces the overall efficiency of the water splitting device, lowering the overvoltage of the oxygen evolution reaction (OER) is the most important task in order to generate hydrogen more efficiently. Currently, noble metal catalysts show excellent characteristics in OER performance, but they are experiencing great difficulties in commercialization due to their high price and efficiency limitations due to low reactivity. In this study, a water electrolysis catalyst Ni-MWCNT was prepared by successfully doping Ni into the MWCNTs structure through the pulsed laser ablation in liquid (PLAL) process. High resolution-transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS) were performed for the structure and chemical composition of the synthesized Ni-MWCNT. Catalytic oxygen evolution reaction evaluation was performed by linear sweep voltammetry (LSV) overvoltage characteristics, Tafel slope, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and Chronoamperometry (CA) was used for measurement.

• Applied Chemistry for Engineering
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• v.8 no.2
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• pp.172-178
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• 1997

Polyaniline(PANI)-stearic acid(SA) composite monolayer was formed at the air-water interface. The stearic acid as a surfactant was used to promote PANI monolayer formation. Uniform PANI-SA monolayer assemblies with Y type and transfer ratio of ca. 1 were fabricated using the Langmuir-Blodgett(LB) technique. The PANI-SA composite LB films with high electrical conductivity of $10^{-1}{\sim}10^{-2}S/cm$ were obtained by doping of HCl or $I_2$, and their conductivity revealed essentially close value as that of conventional PAHI-HCl complex. Especially, iodine is found to be the most promising dopant, since it gives a remarkable stability for the application as a polymer electrode in the MIM molecular device consisted of acceptor, sensitizer, and donor. The structure and physical properties of PANI-SA LB films were investigated through the near-ir UV, FT-IR, and Cyclic voltammetry.