• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.1
• /
• pp.47-53
• /
• 2011

The artificial aggregates (AAs) were manufactured from the parent batch powders consisting of bottom ash containing excess unburned carbon and dredged soil, 7 : 3 weight ratio by direct sintering method and those physical properties were evaluated. Especially, the effects of waste glass or frit (NWG) which was made by addition of 5 wt% $Na_2O$ to the waste glass upon the bloating phenomenon of AAs were analyzed. The AAs manufactured from the parent batch powders showed a lower specific gravity than that of specimens containing waste glass or NWG due to excess u$Na_2O$nburned carbon which usually obstructs a sintering process. But, the waste glass added on parent batch powders promoted the sintering and densification thus increased the specific gravity of AAs. Also the specific gravity of AAs added with 5 wt% NWG, was lowered compared to that of AAs added with as-received waste glass. This is because of bloating of shell which captures gases owing to the lowered viscosity of liquid formed at the specimen surface caused by $Na_2O$ addition. In conclusion, the AAs sintered at above $1100^{\circ}C$ in this study showed characters of lightweight aggregate of specific gravity 1.15~1.34 and water absorption 11~19 %, and the bloating phenomenon of AAs was occurred at the shell rather black core part.

• Proceedings of the KIEE Conference
• /
• 2008.07a
• /
• pp.1244-1245
• /
• 2008

Recently, piezoelectric transformer is applied to wide fields. Multi layer piezoelectric transformer has the advantage of high step up ratio, electromechanical coupling coefficient(Kp) and mechanical quality factor(Qm), but is indicated of peeling-phenomenon of electrode, rising sintering temperature made price of costly electrode. So in this study, it discuss on method for fabrication of rosen type piezoelectric transformers. For the fabrication as rosen type piezoelectric transformers, synthesized the powder using 0.01Pb$(ni_{1/3}Nb_{2/3})O_3$ - 0.08Pb$(Mn_{1/3}Nb_{2/3})O_3$ - 0.91Pb$(Zr_{0506}Ti_{0496})O_3$ (abbreviated as PNN-PMN-PZT) ceramics. The density, microstructure, dielectric and piezoelectric properties as a function of sintering temperature were investigated. The results indicated that the optimized properties of ceramics were obtained at sintering temperature of 1200$^{\circ}C$, showed the value of $d_{33}$=273pC/N, $K_p$=0.60 $Q_m$=1585, ${\varepsilon}_r$=1454, density=7.917$g/cm^3$ and $tan{\delta}$=0.0064.

• Korean Journal of Materials Research
• /
• v.16 no.4
• /
• pp.235-240
• /
• 2006

We investigated the effect of ZnO filler on the microstructure of $BaO-B_2O_3-ZnO-P_2O_5$ glass system to find an etching mechanism of barrier ribs. The sintering behavior of composites heated in the temperature range $560-600^{\circ}C$ was studied by volumetric shrinkage rate and microstructure. The etching test was carried out in $HNO_3$ solution at $50^{\circ}C$ for 10 min. The volumetric shrinkage of sintered sample decreased with the increased firing temperature because of the formation of two crystals. Glass and ZnO filler react forming the $BaZn_2(PO_4)_2$ crystal phases during the sintering process. Etching phenomenon of sintered samples by $HNO_3$ showed that the $BaZn_2(PO_4)_2$ crystal phase was strongly leached compared to glass matrix, crystal phases and fillers. Therefore, the control of interface by condition of sintering is so important to achieve etching effect in barrier ribs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.06a
• /
• pp.279-279
• /
• 2007

Synthesis and dielectric properties of glass-ceramic composites with zinc borosilicate glass(here after ZBS glass) were investigated as functions of $ZnAl_2O_4$ phase synthesis method, glass addition (50~60 vol%) and sintering temperature ($600{\sim}950^{\circ}C$ for 2 hrs). The 50 vol% ZBS glass-$Al_2O_3$ and 60 vol% ZBS glass-$ZnAl_2O_4$ ensured successful sintering below $900^{\circ}C$. But the composition of 100-x-y vol% ZBS glass-x vol% $Al_2O_3-y$ vol% ZnO exhibited poor sinterability below $900^{\circ}C$ and the swelling phenomenon occurred in this composite with the large amount of ZBS glass. The sintering behavior of Glass-ceramic composites was affected by the crystallization of $ZnAl_2O_4$ which was formed by the reaction between ZBS glass and $Al_2O_3$. Dielectric constant (${\varepsilon}_r$), $Q{\times}f$ value and temperature coefficient of resonant frequency (${\tau}_f$) of the composite with 50 and 60 vol% ZBS glass contents demonstrated $ZBS-Al_2O_3({\varepsilon}_r=5.7)$, $ZBS-ZnAl_2O_4({\varepsilon}_r=5.8)$ which is applicable to substrate requiring an low dielectric properties.

• Economic and Environmental Geology
• /
• v.51 no.6
• /
• pp.485-492
• /
• 2018

About 300 thousand tones of oyster shells are produced annually and, thus, their massive recycling methods are required. Recently, a method, utilizing them as wet desulfurization materials after removal of organic matters and changing $CaCO_3$ phase into CaO through calcination, is under consideration. This study investigates the mineralogical changes (specific surface area, phase changes, surface state, etc.) of oyster shells by calcination and their characteristics were compared with those of limestone. Uncalcined oyster shells showed the higher specific surface area than limestone because the former are composed of platy and columnar structures. In contrast, investigated limestone showed a dense structure. The phase change of oyster shells occurred at lower temperature than that of limestone. The specific surface area of oyster shell decreased significantly after calcination while limestone depicted a drastic increase. Small amount of Na contained in oyster shell was suggested as the cause of this phenomenon; in that, it acted as a flux causing melting and sintering of oyster materials at lower temperature. Because of this, an additional phenomenon was observed that a part of shell materials remained untransformed even at higher calcination temperature and after longer treatment period due to the sintered surface, which covers the rest parts. Further studies investigating the effect of this phenomena from the perspective of desulfurization is required.

• Electrical & Electronic Materials
• /
• v.8 no.6
• /
• pp.744-751
• /
• 1995

This paper describes a study on absorption properties of electromagnetic wave by the composition ratio of Ni-Zn ferrite. Ni-Zn ferrite was composed of 48-52mol% Fe$\_$2/O$\_$3/, 18-22mol% NiO and 26-34mol% ZnO. The sintering of the composition was carried out at 1200.deg. C for 2 hours. Through the experiments, it was found that the resonance phenomenon occured at low frequency range for high permeability and vice versa. In the case of the composition of 49mol% Fe$\_$2/O$\_$3/, 20mol% NiO and 31mol% ZnO, the bandwidth ranged from 0.35GHz to 0.95GHz with the absorption thickness of 10mm. Also, in the case of the composition 51mol% Fe$\_$2/O$\_$3/, 22mol% NiO and 27mol% ZnO, the bandwidth ranged from 0.48GHz to 1.2GHz with the absorption thickness of 6mm.

• Resources Recycling
• /
• v.20 no.1
• /
• pp.54-60
• /
• 2011

The spherical artificial aggregates (AAs) with a diameter of 8 mm, which contains fly ashes discharged from the fluidized bed combustion in a thermal power plant and clay were manufactured by direct sintering method at $1050{\sim}1250^{\circ}C$ for 10 minutes. The effect of fly ash contents on the bloating phenomenon in the AAs was analyzed. The AAs containing fly ash of the amount under 50 wt% showed the black-coring and bloating phenomena. The AAs containing fly ash of the amount over 5Owt%, however, the specific gravity was increased and the color of specimens fully changed to black. These color change phenomena were caused from the formation of FeO by the reduction reaction of almost $Fe_2O_3$ component by the excessive reducing atmosphere formed simultaneously with the rapid emission of the gases generated from the high contents of unburned carbon of with increasing the added fly ash amount. Specific gravity was decreased as fly ash contents increased in the case of sintering at the same temperature condition. Water absorption of all specimens except of the specimens containing 10 wt% fly ashes decreased with increasing sintering temperature. These were because a liquid phase was formed as the increasing the sintering temperature. In the case of the specimens manufactured in this study containing fly ashes discharged from the fluidized bed combustor in a the thermal power plant and 10~90 wt% of clay, the specific gravity was 0.9~1.8 and the water absorptivity was 8~60%, therefore it is considered that those results can be applied to the light or heavy aggregates.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.19 no.1
• /
• pp.54-59
• /
• 2009

It was difficult for the existing rotary kiln to fabricate the fine aggregates under 3 mm due to the sticking phenomenon between specimens. In this study, the vertical type fluidizing furnace was designed and manufactured by which the lightweight fine aggregates of specific gravity $1.1{\sim}1.7$, water absorption $11{\sim}19%$ could be fabricated from the green body of clay: stone sludge: spent bleaching clay = 60 : 30 : 10 (wt%) without sticking-together happening. The minimum sintering temperature for bloating of aggregates was $1130^{\circ}C$. The specimens sintered over $1140^{\circ}C$ showed the typical bloating characteristics of lightweight aggregates and an inner layer was discovered due to widened cracks on a surface. But the crack on a surface did not propagate into a black core area so had no effect on a water absorption of aggregates. The sintering temperature made the thickness of shell and the black core area thin and expanded respectively but the sintering time did not affect the microsturcture of aggregates. The water absorption of aggregates decreased with increasing temperature owing to increased amount of liquid formed on a surface. Also sintering time affected a lot on a water absorption because it takes a time to form a liquid, which change the open pores to closed pores by blocking.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.17 no.1
• /
• pp.11-17
• /
• 2007

The spherical NiZn ferrite particles were prepared by ultrasonic spray pyrolysis with mixed solution of aqueous metal nitrates. The NiZn ferrite particle was observed with nano-sized primary particles of about 10 nm or less before annealing which represented as paramagnetic behavior measured at 77 K and room temperature. The typical abnormal growth of primary particles like polyhedral primary particles was observed by annealing at 1273 K with Zn-concentration dependency. The XRD patterns showed good crystallinity of NiZn ferrite powder after annealing. In annealing process, the intra-particle sintering phenomenon was observed and the spherical particle morphology was collapsed at 1673 K. The saturation magnetization of NiZn ferrite powder for each annealing temperature was decreased with measuring temperature of $77{\sim}$300K.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1305_1306
• /
• 2009

Recently, piezoelectric transformer is applied to wide fields. Multi layer piezoelectric transformer has the advantage of high step up ratio, high electromechanical coupling coefficient(Kp) and high mechanical quality factor(Qm), however it shows the peeling-phenomenon of electrode, and high price due to high sintering temperature. Therefore this study focus on the method for fabrication of high power rosen type piezoelectric transformers.