• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.556-560
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• 2007

In this study, both structural and microwave dielectric properties of the $Mg_5B_4O_{15}$ (B=Ta, Nb) cation-deficient perovskite ceramics with sintering temperature were investigated. All sample of the $Mg_5B_4O_{15}$ (B=Ta, Nb) ceramics were prepared by the conventional mixed oxide method and sintered at $1400^{\circ}C{\sim}1500^{\circ}C$. The bulk density and quality factor of the $Mg_5B_4O_{15}$ (B=Ta, Nb) ceramics were increased with increasing sinterning temperature in the range of $1400^{\circ}C{\sim}1450^{\circ}C$, but these were decreased the sintering temperature of above $1450^{\circ}C$. The dielectric constant of the $Mg_5Ta_4O_{15}$ ceramics was increased continuously with increasing sintering temperature. And the dielectric constant of the $Mg_5Nb_4O_{15}$ ceramics was increased in as the sintering temperature increasesfrom $1400^{\circ}C{\sim}1450^{\circ}C$ but was decreased at the temperatures above $1475^{\circ}C$. In the case of the $Mg_5Ta_4O_{15}\;and\;Mg_5Nb_4O_{15}$ ceramics sintered at $1450^{\circ}C$ for 5h, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 8.2, 259,473 GHz, $-10.91ppm/^{\circ}C$ and 14, 37,350 GHz, $-52.3ppm/^{\circ}C$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.7
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• pp.543-546
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• 2011

We studied sintering temperature to enhance the piezoelectric properties of $0.98(Na_{0.5}K_{0.5})NbO_3-0.02Li(Sb_{0.17}Ta_{0.83})O_3$+0.01wt%ZnO (hereafter NKN-LST+ZnO) lead free piezoelectric ceramics. The synthesis and sintering method were the conventional solid state reaction method and sintering was executed at $1,080\sim1,120^{\circ}C$. We found that NKN-LST+ZnO ceramics at optimal sintering temperature showed the improved piezoelectric properties at the optimal sintering temperature. The NKN-LST+ZnO ceramics show good performance with piezoelectric constant $d_{33}$= 153 pC/N sintered at $1,090^{\circ}C$. The results reveal that NKN-LST+ZnO ceramics are promising candidate materials for lead-free piezoelectric application.

• Resources Recycling
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• v.21 no.4
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• pp.35-43
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• 2012

This study was carried out for the purpose of obtaining basic data to utilize the AMD sludge as sorbent for heavy metal ions. The sludge from the treatment process of Acid Mine Drainage mainly consists of fine iron hydroxide or iron oxide hydrate and calcite, and the fine iron hydroxide or iron oxide hydrate has a property of adsorbing heavy metal ions. In this study, we investigated the physical property of the AMD sludge like as mineral composition, particle size and shape and chemical composition and also investigated the influence of dosage of sludge, adsorbing time, pH, initial concentration and sintering temperature on the adsorption of heavy metal ions.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.98-100
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• 2003

The microwave dielectric properties and microstructure of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were investigated. All sample of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were prepared by conventional mixed oxide method. The sintering temperature was $1375^{\circ}C{\sim}1450^{\circ}C$. The structural properties of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were investigated by X-ray diffractormeter. According to the X-ray diffraction patterns of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics, the major phase of the hexagonal $Mg_4Ta_2O_9$ were presented. In the case of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics sintered at $1425^{\circ}C$, density, dielectric constant, quality factor were $5.799g/cm^2$, 23.26, 40,054 GHz, respectively.

• Journal of Powder Materials
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• v.22 no.2
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• pp.100-104
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• 2015

The porous metals are known as relatively excellent characteristic such as large surface area, light, lower heat capacity, high toughness and permeability. The Fe-Cr-Al alloys have high corrosion resistance, heat resistance and chemical stability for high temperature applications. And then many researches are developed the Fe-Cr-Al porous metals for exhaust gas filter, hydrogen reformer catalyst support and chemical filter. In this study, the Fe-Cr-Al porous metals are developed with Fe-22Cr-6Al(wt) powder using powder compaction method. The mean size of Fe-22Cr-6Al(wt) powders is about $42.69{\mu}m$. In order to control pore size and porosity, Fe-Cr-Al powders are sintered at $1200{\sim}1450^{\circ}C$ and different sintering maintenance as 1~4 hours. The powders are pressed on disk shapes of 3 mm thickness using uniaxial press machine and sintered in high vacuum condition. The pore properties are evaluated using capillary flow porometer. As sintering temperature increased, relative density is increased from 73% to 96% and porosity, pore size are decreased from 27 to 3.3%, from 3.1 to $1.8{\mu}m$ respectively. When the sintering time is increased, the relative density is also increased from 76.5% to 84.7% and porosity, pore size are decreased from 23.5% to 15.3%, from 2.7 to $2.08{\mu}m$ respectively.

• Journal of Powder Materials
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• v.19 no.6
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• pp.435-441
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• 2012

A new manufacturing process of Fe-Cr-Al powder porous metal was attempted. First, ultra-fine fecralloy powders were produced by using the submerged electric wire explosion process. Evenly distributed colloid (0.05~0.5% powders) was dispersed on PU (Polyurethane) foam through the electrospray process. And then degreasing and sintering processes were conduced. In order to examine the effect of sintering temperature in process, pre-samples were sintered for two hours at temperatures of $1350^{\circ}C$, $1400^{\circ}C$, $1450^{\circ}C$, and $1500^{\circ}C$, respectively, in $H_2$ atmospheres. A 24-hour TGA (thermo gravimetric analysis) test was conducted at $1000^{\circ}C$ in a 79% $N_2$+21% $O_2$ to investigate the high temperature oxidation behavior of powder porous metal. The results of the high temperature oxidation tests showed that oxidation resistance increased with increasing sintering temperature (2.57% oxidation weight gain at $1500^{\circ}C$ sintered specimen). The high temperature oxidation mechanism of newly manufactured Fe-Cr-Al powder porous metal was also discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.3
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• pp.244-252
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• 2002

The electrical and dielectric behavior fort DC accelerated aging stress of P $r_{6}$ $O_{11}$-based Zno varistors cnsisting of ZnO-P $r_{6}$ $O_{11}$-CoO-C $r_2$ $O_3$-E $r_2$ $O_3$ were investigated with sintering temperature in the range of 1325~1345$^{\circ}C$. The varistor ceramics with increasing sintering temperature were more densified. A more densified varistors leaded to high stability for DC accelerated aging stress. Furthermore, the stability for DC accelerated aging stress was increased with the leakage current and dtan $\delta$/dV decreasing in order of 1325longrightarrow1335longrightarrow1345longrightarrow134$0^{\circ}C$ in sintering temperature. It was found that the stability for DC stress is affected more greatly by the leakage current and dtan $\delta$/dV than the densification. It is considered that the stability of varistors for DC stress can be estimated by considering the factors, such as the densification, leakage current, and dtan $\delta$/dV. As a result, the varistor sintered at 134$0^{\circ}C$ exhibited the highest stability, with %$\Delta$ $V_{lmA}$=-1.54%, %$\Delta$$\alpha$=-2.49%, %$\Delta$ $I_{\ell}$=+240.68%, 5%$\Delta$tan$\delta$=+29.96%.96%.96%.%.

• Journal of Technologic Dentistry
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• v.36 no.1
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• pp.9-15
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• 2014

Purpose: Generally dental technicians clinically decide the sintering temperature of zirconia artificial teeth to match the color of the teeth. However, the sintering temperature influence the microstructure and mechanical strength of ceramic body. In this study, to evaluate the free choice of sintering temperature which leads to color the problems in zirconia false teeth, the variation of microstructure, mechanical strength, and colortone of zirconia ceramics according to the change of sintering temperature was investigated. Methods: Bar type specimens were prepared from commercial zirconia blocks by cutting and polishing into $0.8cm(L){\times}1.0cm(W){\times}4.8cm(H)$. Specimens were fired from 1,400 to $1,700^{\circ}C$ at $50^{\circ}C$ intervals and held for 1hour at highest temperature. Apparent porosity, water absorption, firing shrinkage, bulk density, bend strength, whiteness were tested. Microstructures were observed by SEM. Results: When fired above $1450^{\circ}C$, all specimens showed 0% apparent porosity and water absorption, 20% firing shrinkage, and $6.1g/cm^3$ bulk density regardless of firing temperatures. SEM photomicrographs showed grain growth of zirconia occurred above $1,600^{\circ}C$. Whiteness was also largely changed above this temperature. Maximum bend strength of 1,05MPa was obtained at $1,550^{\circ}C$. Bend strength lowered slightly above this temperature and showed $950{\ss}\acute{A}$ at $1,700^{\circ}C$. Conclusion: In order to fit the colortone of zirconia artificial teeth, arbitrary choice of firing temperature higher than $1,500^{\circ}C$, up to $1,700^{\circ}C$ did not influence the mechanical strength.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.3
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• pp.463-470
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• 1996

Ceramic membrane consisting of an ${\alpha}-Al_{2}O_{3}$ support and Fe doped $TiO_{2}$ top layer was prepared by the sol-gel method. The supported Fe doped $TiO_{2}$ top layer was made by dip coating the support in a mixed sol. The microstructure of the composite membranes was studied by SEM after calcination at $550~850^{\circ}C$. After sintering at $650^{\circ}C$ for 1 hr., the average particle diameter of the Fe doped $TiO_{2}$ top layer was ~40 nm. The supported Fe doped $TiO_{2}$ composite membranes exhibited much higher heat resistance than the $TiO_{2}$ membrane. The Fe doped $TiO_{2}$ composite membrane retained a crack-free microstructure and narrow particle size distribution even after calcination up to $650^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.7
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• pp.572-577
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• 2001

The electrical properties of Pr$_{6}$ O$_{11}$ -based ZnO varistors consisting of ZnO-Pr$_{6}$ O$_{11}$ -CoO-Cr$_2$O$_3$-Er$_2$O$_3$ ceramics were investigated with sintering temperature in the range of 1325~f1345$^{\circ}C$. As sintering temperature is raised., the nonlinear exponent was increased up to 1335$^{\circ}C$, reaching a maximum 70.53, whereas raising sintering temperature further caused it to decrease, reaching a minimum 50.18 and the leakage current was in the range of 1.92~4.12 $\mu$A. The best electrical properties was obtained from the varistors sintered at 1335$^{\circ}C$, exhibiting a maximum (70.53) in the nonlinear exponent and a minimum (1.92 $\mu$A) in the leakage current, and a minimum (0.035) in the dissipation factor. On the other hand, the donor concentration was in the range of (0.90~1.14)x10$^{18}$ cm$^{-3}$ , the density of interface states was in the range of (2.69~3.60)x10$^{12}$ cm$^{-2}$ , and the barrier height was in the range of 0.77~1.21 eV with sintering temperature. With raising sintering temperature, the variation of C-V characteristic parameters exhibited a mountain type, reaching maximum at 134$0^{\circ}C$. Conclusively, it was found that the V-I, C-V, and dielectric characteristics of Pr$_{6}$ O$_{11}$ -based ZnO varistors are affected greatly by sintering temperature.