• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07b
• /
• pp.1113-1115
• /
• 2002

Mesoporous silica, MCM-41, was synthesized by sol-gel method. The organic structure-directing agent must be removed to make the desired proes. To achieve this, alternative calcination method using microwave oven was adapted to this removal stage. Microwave calcination was shown to provide a novel, rapid and inexpensive method of praparing nanoporous material. It was studied how the porous structure, surface area and pore size distribution were changes under microwave calcination.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.252-255
• /
• 1999

The effect of calcination temperature(1st and 2nd calcining at 110$0^{\circ}C$ , 120$0^{\circ}C$ and 130$0^{\circ}C$ respectively) on physical properties of BMNT Ceramics ware investigated. The optimum 1st and 2nd calcination temperature were 120$0^{\circ}C$ , and sintering temperature was 155$0^{\circ}C$. In this condition, the sintering density was 7.53 [g/㎤] and the dielectric constant, Q.f$_{0}$ and $\tau$$_{r}$ were 26, 80, 300[GHz] and +1.5[ppm/$^{\circ}C$] respectively in the microwave range.e.e.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.06a
• /
• pp.281-282
• /
• 2007

$Mg_4Nb_2O_9$ (MN) ceramics have been prepared by a sol-gel method. The powder characteristics, phase evolution, and microwave dielectric properties of the MN were investigated in various processing conditions such as sol-gel compositions, calcination, and sintering temperatures. A Qxfo value of 111,717 GHz with a ${\varepsilon}_r$ of 10.59 and a ${\tau}_f$ of $+1.736\;ppm/^{\circ}C$ was obtained after sintering at $1300^{\circ}C$ for 5 h.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.05c
• /
• pp.282-286
• /
• 2003

We investigated the effects of calcination temperature and sintering additives on the sintering behaviors and microwave dielectric properties of $(Zn_{0.8}Mg_{0.2})TiO_3$. Highly densified samples were obtained at the sintering temperatures below $1000^{\circ}C$ with additions of 0.45 wt.% $Bi_2O_3$ and 0.55 wt.% $V_2O_5$. From the examination of the existing phases and microstructures before and after sintering of $(Zn_{0.8}Mg_{0.2})TiO_3$ system calcined at the various temperatures ranging from $800^{\circ}C$ to $1000^{\circ}C$, it was found that high $Q{\times}f_o$ values were obtained when unreacted or second phases in calcined body were reduced. When calcined at $1000^{\circ}C$ and sintered at $900^{\circ}C$, it consists of hexagonal as a main phase with uniform microstructure and exhibits $Q{\times}f_o$ value of 42,000 GHz and dielectric constant of 22.

• Journal of the Korean Ceramic Society
• /
• v.38 no.8
• /
• pp.749-754
• /
• 2001

마이크로파 추출 및 하소 공정을 통하여 카올린으로부터 베타 알루미나 전구체 및 베타 알루미나 분말을 합성하였다. 황산 알루미늄 및 가성소다의 혼합 용액을 교반되는 에탄올 용액 중에 적하시켜서 $Al_2$(SO$_4$)$_3$.17$H_2O$ 및 $Na_2$SO$_4$.10$H_2O$의 균일한 침전물을 얻었다. $\beta$- 및 $\beta$\"-Al$_2$O$_3$상으로 구성된 베타 알루미나를 얻기 위하여 재래식 및 마이크로파 하소법으로 주어진 온도에서 약 2h 동안 침전물 시료를 하소하였다. 재래식 하소된 시료에 비하여 마이크로파 하소된 시료는 $\beta$\"-Al$_2$O$_3$상이 상대적으로 많이 존재하였다. 또한, 재래식 하소된 시료와 마이크로파 하소된 시료의 미세구조는 매우 상이하였다. 매우 상이하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.12S
• /
• pp.1205-1209
• /
• 2003

We investigated the effects of calcination temperatures on the sintering behaviors and microwave dielectric Properties of (Z $n_{0.8}$M $g_{0.2}$)Ti $O_3$ system. Highly densified samples were obtained at the sintering temperatures below 100$0^{\circ}C$ with additions of 0.45 wt.%B $i_2$ $O_3$ and 0.55 wt.% $V_2$ $O_{5}$. From the examination of the existing phases and microstructures before and after sintering of (Z $n_{0.8}$M $g_{0.2}$)Ti $O_3$ system which is calcined at the various temperatures ranging from 80$0^{\circ}C$ to 100$0^{\circ}C$, it was found that higher Q${\times}$ $f_{o}$ values were obtained when unreacted phases in calcined body were reduced. When calcined at 100$0^{\circ}C$ and sintered at 90$0^{\circ}C$, it consists of hexagonal as. a main phase with uniform microstructure and exhibits Q${\times}$ $f_{o}$ value of 42,000 GHz and dielectric constant of 22. 22. 22.

• Journal of Powder Materials
• /
• v.16 no.3
• /
• pp.203-208
• /
• 2009

$Y_2O_3$:Eu red phosphor was prepared by microwave synthesis. The crystal phase, particle morphology, and luminescent properties were characterized by XRD, SEM, and spectrofluorometer, respectively. The prepared $Y_2O_3$:Eu particles had good crystallinity and strong red emission under ultravioletet excitation. The crystallite size increased with calcination temperature and satuarated at $1200^{\circ}C$. The primary particle size initially formed was varied from 30 to 450 nm with microwave-irradiation (MI) time. It was found that the emission intensity of $Y_2O_3$:Eu phosphor strongly depends on the MI time. In terms of the emission intensity, it was recommended that the MI time should be less than 15 min. The emission intensity of $Y_2O_3$:Eu phosphor prepared by microwave syntehsis strongly depended on the crystallite size of which an optimal size range was 50-60 nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07b
• /
• pp.642-645
• /
• 2002

Microwave dielectric properties of $ZnWO_4$ ceramic were investigated with calcination and sintering temperatures. The dielectric properties required for such application are high dielectric constant$(\varepsilon_r)$, high $Q{\times}f_o$ value and low temperature coefficient of resonant frequency$(\tau_f)$. These requirement correspond to necessities for size reduction, excellent frequency selectivity, good temperature stability of devices. $ZnWO_4$ ceramics could be sintered at low $1075^{\circ}C$, which was comparatively low temperature for microwave dielectrics. As a result, $ZnWO_4$ showed the dielectric constant of 13, quality factor($Q{\times}f_o$ value) of 22000 and 'temperature coefficient of resonant frequency$(\tau_f)$ of $-65{\pm}5ppm/^{\circ}C$.

• Applied Chemistry for Engineering
• /
• v.9 no.4
• /
• pp.481-485
• /
• 1998

Hydrated aluminum sulfate, an inorganic polymer, was synthesized from kaolin in $H_2SO_4$ solution using microwave energy. The maximum rates of alumina extracted from calcined kaolin were 72.8% in a conventional process ($80^{\circ}C$, 1M, and 180min) and 99.9% in a microwave process ($90^{\circ}C$, 1M, and 60 min). Compared with the conventional one, the hydrated aluminum sulfate synthesized under the microwave process had layer structure consisting of plate-shaped large grains. After synthesis and then calcination at $1100^{\circ}C$, both products on conventional and microwave processes were ${\gamma}-Al_2O_3$ with agglomerated powders of spherical shape. The specific area of the products in conventional and microwave processes were 113.5 and $106.6m^2/g$, and their average grain sizes were 46.5 an $26.3{\mu}m$, respectively.

• Journal of the Korean Ceramic Society
• /
• v.43 no.4 s.287
• /
• pp.235-241
• /
• 2006

Mullite short fibers have been fabricated by adapting the Kneading-Drying-Calcination (KDC) process and characterized. The effect of the addition of foaming agent and calcination temperature on the formation of mullite fibers from coal fly ash, was examined. In the present work, ammonium alum $NH_4Al(SO_4)_2\;12H_2O$ synthesized trom coal fly ash and sodium phosphate $Na_2HPO_4\;2H_2O$ were used as foaming agents. After calcination at $1300^{\circ}C$ for 10 h and then etching with 20% HF solution at $50^{\circ}C$ for 5 h using a microwave heating source, the alumina-deficient $(AI_2O_3/SiO_2$ = 1.13, molar ratio) orthorhombic mullite fibers with a width of ${\sim}0.8mm$ (aspect ratio >30), were prepared from the coal fly ash with $AI_2O_3/SiO_2$ = 0.32, molar ratio by the addition of $NH_4AI(SO_4)_2\;12H_2O$, and with further addition of 2 wt% sodium phosphate. The excessive addition of sodium phosphate rather decreased the formation of mullite fibers, possibly due to the large amount of liquid phase prior to mullitization reaction.