• Journal of the Korean Ceramic Society
• /
• v.30 no.8
• /
• pp.629-634
• /
• 1993

Dielectric and electrostrictive properties of 0.99Pb(Mg1/3Nb2/3)O3-0.01Pb(Mn2/3W1/3)O3 system using KCl-NaCl salts have been investigated as a function of the amount of excess MgO. For the specimens calcined at $700^{\circ}C$ for 1h and then sintered at 115$0^{\circ}C$ for 4h, the perovskite phase and the relative density were about 98% and 95%, respectively. With the addition of excess MgO up to 10mol%, the dielectric constant and the electrostrictive strain increased due to the increase of density and grain size, and these properties were degraded by the further addition of excess MgO. For the 10mol% excess MgO added specimen, the maximum electrostrictive strain, Xmax, and the electrostrictive coefficient, Q11, were 4.5$\times$10-4, 3.5$\times$10-2m4/C2, respectively. These results were correlated with the property of PMW and microstructure.

• Journal of Powder Materials
• /
• v.9 no.5
• /
• pp.352-358
• /
• 2002

The effects of boron or manganese added as $B_4C$, Mn, $TiB_2$, B on TiC-30vo1.%$Ni_3Al$ cermet sintered at 1380 and $1400^{\circ}C$ for 1 hour, were examined in relation with shrinkage, relative density, microstructure, lattice parameter, hardness and fracture toughness ($K_{IC}$). The results are summarized as follows: 1) The highest shrink-age showed about 30.5% in the specimen added B$_4$C and the maximum relative density was about 99% in the specimen added $TiB_2$; 2) The grains of TiC were grown during sintering and made the surrounding structure by adding boron and manganese. The largest grain size showed about $2.8\mutextrm{m}$ in the specimen with boron sintered at $1400^{\circ}C$;3) The lattice parameter of TiC was about $4.325\AA$ and $Ni_3Al$ about $3.592\AA$ by adding other elements; 4) The highest hardness was about $1100kgf/\textrm{mm}^2$ in the specimen with B4C; 5) The fracture toughness ($K_{IC}$) showed about $15MNm^{-3/2}$ in the specimen added $TiB_2$.

• Bulletin of the Korean Chemical Society
• /
• v.26 no.6
• /
• pp.935-938
• /
• 2005

Nucleophilic addition reactions of benzylamines (BA; $XC_6H_4CH_2NH_2$) to $\alpha-cyano-\beta$-phenylacrylamides (CPA; $YC_6H_4CH=C(CN)CONH_2$) have been investigated in acetonitrile at 25.0 ${^{\circ}C}$. The rate is first order with respect to BA and CPA and no base catalysis is observed. The addition of BA to CPA occurs in a single step in which the addition of BA to $C_{\beta}$ of CPA and proton transfer from BA to $C_{\alpha}$ of CPA take place concurrently with a four-membered cyclic transition state structure. The magnitude of the Hammett ($\rho_X$) and Bronsted ($\beta_X$) coefficients are rather small suggesting an early tansition state (TS). The sign and magnitude of the crossinteraction constant, $\rho_XY$ (= −D0.26), is comparable to those found in the normal bond formation processes in the $S_N2$ and addition reactions. The normal kinetic isotope effect ($k_H/k_D\;{\gt}$ 1.0) and relatively low ${\Delta}H^{\neq}$ and large negative ${\Delta}S^{\neq}$ values are also consistent with the mechanism proposed.

• Journal of the Korean Ceramic Society
• /
• v.29 no.8
• /
• pp.646-650
• /
• 1992

Effect of Li2O.4B2O3 frit addition on microstructural and thermal expansion behaviour of the $\beta$-spodumene ceramics made from kaolinite was investigated. With 2.0~4.0 wt% frit addition, the densification by liquid phase sintering caused low water absorption below 3% and enhancement of beding strength. As the amount of frit addition was increased, thermal expansion coefficient was increased to large scale, but in 2 wt% frit addition, its thermal expansion coefficient was constrained to 1.92$\times$10-6$^{\circ}C$-1.

• Journal of Microbiology and Biotechnology
• /
• v.26 no.7
• /
• pp.1290-1302
• /
• 2016

Microalgae are being researched for their potential as attractive biofuel feedstock, particularly for their lipid production. For maximizing biofuel production, it is necessary to explore the effects of environmental factors on algal lipid-producing potential. In this study, the effects of nitrogen (N) sources (NO₂-N, NO₃-N, urea-N, NH₄-N, and N-deficiency) and carbon-to-nitrogen ratios (C/N= 0, 1.0, 3.0, and 5.0) on algal lipid-producing potential of Chlorella sp. HQ were investigated. The results showed that for Chlorella growth and lipid accumulation potential, NO₂-N was the best amongst the nitrogen sources, and NO₃-N and urea-N also contributed to algal growth and lipid accumulation potential, but NH₄-N and N-deficiency instead caused inhibitory effects. Moreover, the results indicated that algal lipid-producing potential was related to C/N ratios. With NO₂-N treatment and carbon addition (C/N = 1.0, 3.0, and 5.0), total lipid yield was enhanced by 12.96-20.37%, but triacylglycerol (TAG) yields decreased by 25.52-94.31%. As for NO₃-N treatment, carbon addition led to a 17.82-57.43%/25.86-82.67% reduction of total lipid/TAG yields. When NH₄-N was used as the nitrogen source, total lipid/TAG yields were increased by 46.67-113.33%/28.99-74.76% with carbon addition. The total lipid/TAG yields of urea-N treatment varied with C/N ratios. Overall, the highest TAG yield (TAG yield: 38.75 ± 5.21 mg/l; TAG content: 44.16 ± 4.35%) was achieved under NO₂-N treatment without carbon addition (C/N = 0), the condition that had merit for biofuel production.

• Journal of the Korean Ceramic Society
• /
• v.39 no.6
• /
• pp.550-557
• /
• 2002

TiO$_2$ particles coated on fly ash composites for use in photocatalyst were synthesized by the precipitation dropping method and heated at $700^{\circ}C$ for 2 h. The pH of reaction solution, the addition rate of NH$_4$HCO$_3$, the stirring speed, the reaction temperature and the concentration of TiC1$_4$ had a pronounced effect on the nature of precipitated TiO$_2$ particles on the surface off fly ash and the crystal structure of precipitated TiO$_2$ particles. At an addition rate of NH$_4$HCO$_3$; 1.0 ml/min, the pH of the reaction solution; 6, the stirring speed; 1,000 rpm and the reaction temperature; 8$0^{\circ}C$, about 10 nm of TiO$_2$ particle size and homogeneous precipitated layer on the surface of a fly ash was achieved. On the contrary, at an addition rate of NH$_4$HCO$_3$; 0.3,0.5 ml/min, the pH of the reaction solution; 2 and 11, the stirring speed; 300~500 rpm and the reaction temperature; lower than 5$0^{\circ}C$:, Inhomogeneous precipitated layer was developed on a fly ash. TiO$_2$ particles with anatase phase was formed as-dried precipitation at the low concentration of Tic14, the high addition rate of NH$_4$HCO$_3$ and the high reaction temperature, the crystalline fraction of anatase increased with raising heat-treatment temperature and rutile phase began to formation at 80$0^{\circ}C$. The crystal size of TiO$_2$ particles increased with raising the heat-treatment temperature, the crystal size was showed about 21 m at $700^{\circ}C$. Anatase type of TiO$_2$ coated on the fly ash heated at $700^{\circ}C$ for 2 h showed 1.25 g/cm$^3$of particle density, 82.8% of strength and 69.5 Lab of whiteness and can be used as a photocatalyst.

• Journal of the Korean Ceramic Society
• /
• v.25 no.6
• /
• pp.609-614
• /
• 1988

This study was carried out to investigate the effects of B4C or Y2O3 additives on the tendency of sintering, $\beta$-SiC synthesis and mineral phase changes by reaction bonding of SiC at 145$0^{\circ}C$. At the sintering temperature of 145$0^{\circ}C$, the additives such as B4C or Y2O3 did not improved porosity and bending strength. Added more than 1.5% of Y2O3, 0.5-0.3% of B4C, the formation of $\beta$-SiC was increased. At higher temperature above 145$0^{\circ}C$, it seems that the bodies added B4C, contained 3C form of SiC were denser than that of Y2O3 added. Because the transition of 3Clongrightarrow4Hlongrightarrow6H promoted sintering.

• 전기의세계
• /
• v.21 no.6
• /
• pp.17-20
• /
• 1972

The magnetic properties of Ba-Ferrite ( $M^{+2}$O.nF $e_{2}$ $O_{3}$ is highly improved under the condition of composition ratio n=4.4 when B $i_{2}$ $O_{3}$ is added to Ferrite, the adding amount and sintering temperature which affect the magnetic properties were investigated and the following results; were obtained; 1. Magnetic properties are varied with B $i_{2}$ $O_{3}$ content and singering temperature, and coercive force and residual induction can be improved with B $i_{2}$ $O_{3}$. 2. The optimal content of B $i_{2}$ $O_{3}$ amount is about 4 mol %, 3. Without the addition of B $i_{2}$ $O_{3}$, the optimal sintering temperature is about 1300.deg. C, but when 4 mol % of B $i_{2}$ $O_{3}$ is added, the optimal sintering temperature falls to the range of 900.deg. C to 1100.deg. C and it also improves magnetic properties. 4. Residual induction increases as the singering temperature is raised to 1100.deg. C. Coercive force also increased as the sintering temperature is raised to 1000.deg. C, but it rapidly decreases when sintering temperature goes beyond 1000.deg. C. 5. Only a negligible change may be noticed in the decrease of Curie temperature by the addition of about 4 mol % of B $i_{2}$ $O_{3}$.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.55 no.9
• /
• pp.434-441
• /
• 2006

The effect of pressureless-sintered temperature on the densification behavior, mechanical and electrical properties of the $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at temperatures in the range of $1,750{\sim}1,900[^{\circ}C]$, with an addition of 12[wt%] of $Al_2O_3+Y_2O_3$(6:4 mixture of $Al_2O_3\;and\;Y_2O_3$) as a sintering aid. The relative density and mechanical properties are increased markedly at temperatures in the range of $1,850{\sim}1,900[{^\circ}C]$. The relative density, flexural strength, vicker's hardness and fracture toughness showed the highest value of 81.1[%], 230[MPa], 9.88[GPa] and $6.05[MPa\;m^{1/2}]$ for $SiC-ZrB_2$ composites of $1,900[{^\circ}C]$ sintering temperature at room temperature respectively. The electrical resistivity was measured by the Pauw method in the temperature ranges from $25[{^\circ}C]\;to\;700[{^\circ}C]$, The electrical resistivity showed the value of $1.36{\times}10^{-4},\;3.83{\times}10^{-4},\;3.51{\times}10^{-4}\;and\; 3.2{\times}10^{-4}[{\Omega}{\cdot}cm]$ for SZ1750, SZ1800, SZ1850 and SZ1900 respectively at room temperature. The electrical resistivity of the composites was all PTCR(Positive Temperature Coefficient Resistivity). The resistance temperature coefficient showed the value of $4.194{\times}10^{-3},\;3,740{\times}10^{-3},\;2,993{\times}10^{-3},\;3,472{\times}10^{-3}/[^{\circ}C}$ for SZ1750, SZ1800, SZ1850 and SZ1900 respectively in the temperature ranges from $25[{\circ}C]\;to\;700[{\circ}C]$, It is assumed that because polycrystallines such as recrystallized $SiC-ZrB_2$ electroconductive ceramic composites, contain of porosity and In Situ $YAG(Al_5Y_3O_{12})$ crystal grain boundaries, their electrical conduction mechanism are complicated. In addition, because the condition of such grain boundaries due to $Al_2O_3+Y_2O_3$ additives widely varies with sintering temperature, electrical resistivity of the $SiC-ZrB_2$ electroconductive ceramic composites with sintering temperature also varies with sintering condition. It is convinced that ${\beta}-SiC$ based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

• Journal of the Korean Ceramic Society
• /
• v.40 no.11
• /
• pp.1120-1126
• /
• 2003

Yttrium Aluminum Garnet (YAG) powders were prepared by precipitation of Y hydroxides during milling of alumina powders. The powder calcined at 1200$^{\circ}C$ for 4 h contained a small amount of Yttrium Aluminum Monoclinic (YAM) in addition to YAG. However, phase-pure YAG was obtained in the compact of the milled powder with an average particle size of 0.57 ${\mu}$m at 1300$^{\circ}C$, which is much lower than those (l500∼1600$^{\circ}C$) for a mixed oxide method. The powder was found to exhibit an excellent sinterability regardless of the addition of a sintering aid, SiO$_2$(350 ppm Si). The undoped sample were sintered to a relative density of 98% at l600$^{\circ}C$. In contrast, the addition of SiO$_2$ caused a considerable densification to occur at 1500$^{\circ}C$ and the relative density reached 97.7%. But the sintering aid had little effect on the densification at 1600$^{\circ}C$, showing a similar relative density to the undoped sample.