• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.13-17
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• 1997

The densification of $Al_2$O$_3$/15v/o ZrO$_2$ (Zirconia Toughened Alumina: ZTA) to the 99% of theoretical density was attempted by controlling the processing parameters affecting the each processing step i.e., milling, spray-drying, forming and pressureless sintering. The ZTA processed under the identical conditions showed a large variation in the green and sintered densities, and the mechanical properties. The deviation of 4-point bending strength was more than 100MPa for the ZTA with ~99% of theoretical density. Moreover, the relative green and sintered densities were deviated greatly from the average value. This low reproducibility could be caused by the variation of spray-dried granule properties. Thus, the effect of yield strength and morphology of spray-dried ZTA granule on the green and sintered densities and the mechanical properties needs to be studied in detail. The objective of this work is to fine out the optimum condition of compaction pressure and compaction method depending on the properties of spray-dried granules.

• 한국재료학회지
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• 제22권6호
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• pp.285-291
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• 2012

Hydroxyapatite (HA) is well known as a biocompatible and bioactive material. HA has been practically applied as bone graft materials in a range of medical and dental fields. In this study, two types of dense hydroxyapatite ceramics were prepared from natural bones and synthetic materials. The biocompatibility of HA ceramics for supporting osteoblast cell growth and cytotoxicity using an in vitro MG-63 cell line model were respectively evaluated. Artificial hydroxyapatite shows relative density of 93% with 1-2 ${\mu}m$ after sintering, but a hydroxyapatite compact derived from bovine bone has low sintered density of 85% with a small content of MgO. Irrespective of the starting raw materials, both types of sintered hydroxyapatite displayed similar biocompatibility in the tests. FE-SEM observations showed that most MG-63 cells had a stellar shape and formed an intercellular matrix containing fibers on sintered HA. The cells were well attached and grown over the HA surface, indicating that there was no toxicity.

• 한국세라믹학회지
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• 제25권4호
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• pp.364-372
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• 1988

The mechanical properties and microstructure of ceramics of the system Al2O3-ZrO2-Y2O3 sintered at 1$650^{\circ}C$ for 2h after powder preparation by the precipitation method from Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were investigated. The Al2O3-ZrO2-Y2O3 ceramics sintered at 1$650^{\circ}C$ for 2h after mixing alpha-Al2O3 and ZrO2-Y2O3 powders, both were separately precipitated and calcined, were found to have the relative density higher than 97.5% so that the strengthening and toughening mechanisms could be explained mainly as the stress-induced phase transformation. On the other hand, the sintered bodies prepared by co-precipitating the three starting materials were measured to have the relative density lower than 85% so that the degradation of strength were observed above 15 vol% ZrO2 contents due to the high porosity by which the effect of stress-induced phase transformation was assumed to be depressed.

• 한국결정성장학회지
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• 제7권4호
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• pp.632-639
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• 1997

단일상으로서는 치밀한 소결이 힘든 TiC 와 $TiB_2$ 혼합조성을 상압소결하여 얻어진 TiC-$TiB_2$ 고온복합체의 소결밀도와 미세구조를 연구하였다. 소성조제의 임계첨가량은 1 wt% Fe 및 3 wt% Ni으로 최대 소결밀도는 약 95%이었다. TiC-$TiB_2$ 복합체의 미세구조에서 TiC상은 matrix로서 $TiB_2$입자성장을 저지하였고, wave 흑은 계단식 상계면의 존재는 석출된 Ni-rich phases가 소결중 액상으로 존재하다가 냉각시 고화한 것으로 TEM분석결과 확인할 수 있었다. 또한, 이들 Ni-rich phases는 matrix grain안에서 dislocation형성 요인으로 작용하고 있음이 확인되었다.

• 한국분말재료학회지
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• 제21권2호
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• pp.97-101
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• 2014

The 304 stainless steel powders were prepared by high energy ball milling and subsequently sintered by spark plasma sintering, and the microstructural characteristics and micro-hardness were investigated. The initial size of the irregular shaped 304 stainless steel powders was approximately 42 ${\mu}m$. After high energy ball milling at 800 rpm for 5h, the powders became spherical with a size of approximately 2 ${\mu}m$, and without formation of reaction compounds. From TEM analysis, it was confirmed that the as-milled powders consisted of the aggregates of the nano-sized particles. As the sintering temperature increased from 1073K to 1573K, the relative density and micro-hardness of sintered sample increased. The sample sintered at 1573K showed the highest relative density of approximately 95% and a micro-hardness of 550 Hv.

• 한국세라믹학회지
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• 제31권7호
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• pp.703-714
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• 1994

Sintering and microstructure of Ce-TZP/Al2O3 composite with $\alpha$-Al2O3 matrix containing dispersed 5~50 vol% ZrO2 were discussed. Sintered density was increased with elevating forming pressure in range of 6~300 MPa and about >99.2% of theoretical density was obtained at 1$600^{\circ}C$ for 2h in case of 300 MPa of 6~300 MPa uniaxially cold-pressed compacts containing 20 vol% ZrO2. All kinds of different batch composition exhibited nearly the same shrinkage behaviour with end-point shrinkage between 20 and 24%, and had the maximum shrinkage rate (0.41~0.54%/min) around 140$0^{\circ}C$. Grain growth was occurred faster in $\alpha$-Al2O3 than in {{{{ gamma }}-Al2O3 starting matrix during sintering at 1$600^{\circ}C$. Bimodal pore size distribution of interaglomerate pores with size of 0.03~0.2 ${\mu}{\textrm}{m}$ and of interaglomerate pores with size of around 60 ${\mu}{\textrm}{m}$ was obtained in Ce-TZP/$\alpha$-Al2O3 composite sintered at 130$0^{\circ}C$. But unimodal pore size distribution with around 0.1 ${\mu}{\textrm}{m}$ was observed in Ce-TZP/{{{{ gamma }}-Al2O3 composite sintered at the same temperature. Microcracks were occurred due to the tlongrightarrowm transformation of ZrO2 on cooling process.

• E2M - 전기 전자와 첨단 소재
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• 제8권3호
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• pp.267-271
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• 1995

The electrical properties of (S $r_{0.50}$P $b_{0.25}$B $a_{0.25}$)Ti $O_{3}$ ceramics were studied. Specimens were prepared by the conventional mixed oxide method, and fired between 1300[.deg. C] - 1375[.deg. C], for 2[hr.]. The electrical and structural preperties of specimens were investigated with sintering temperature. Increasing the sintering temperature from 1300[.deg. C] to 1375[.deg. C], average grain size was increased from 2.61[.mu.m] to 4.53[.mu.m]. (S $r_{0.50}$P $b_{0.25}$B $a_{0.25}$)Ti $O_{3}$ specimen sintered at 1350[.deg. C] for two hours showed good dielectric constant(2147) and dielectric loss(1.7[%]) properties at 1[khz]. Sintered density and breakdown field strength were the highest value of 5.75[g/c $m^{3}$], 20[kV/cm], respectively. Dielectric properties with applied voltage were independent of the sintering temperature.temperature.

• 한국세라믹학회지
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• 제33권11호
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• pp.1267-1275
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• 1996

Green sheet was prepared by tape casting in the composition of (1-x)Pb(Mg1/3Nb2/3)O3-PbTiO3 system using Pb(Mg1/3Nb2/3)O3 and PbTiO3 synthesized with PbO, Nb2O5 MgO and TiO2 The densest green sheet was obtained in the weight ratio 70:30 of powder to binder. Green sheet wasmultilayered in metal mould and formed into lamination at 7$0^{\circ}C$, 300kg/cm2 The lamination was sintered at 110$0^{\circ}C$ 2hr, Dielectric constant and Curie temperature of disc type sintered body was highered with increasing the amount of PbTiO3 and was in the range of 19000-21000, -7~45$^{\circ}C$ respectively. Green and sintered relative density of lamination was 61% and 95% respectively.

• 한국세라믹학회지
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• 제41권2호
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• pp.111-117
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• 2004

고순도 3Y-TZP에 알루미나를 0.3∼l.2wt%까지 첨가하여 attrition milling을 하고 slip-casting하여 시료를 제조하였다. 1390∼151$0^{\circ}C$까지 열처리하여 소결체의 소결특성을 기제적 물성과 미세구조 분석을 통하여 확인하였다. XRD를 이용하여 monoclinic-ZrO$_2$의 생성량을 정량적으로 확인하였으며, 147$0^{\circ}C$ 이장에서 열처리한 시료의 경우 m-ZrO$_2$의 생성으로 밀도의 저하를 보였으며, 비정상 입자성장을 유발하여 경도가 저하되었다. 알루미나의 첨가량이 0.9wt% 미만, 열처리 온도143$0^{\circ}C$에서 microhardness가 1360Hv 이상의 소결체를 제조할 수 있었다.

• Journal of Mechanical Science and Technology
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• 제18권3호
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• pp.388-394
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• 2004

Composites of Si$_3$N$_4$-SiC containing up to 30 wt% of dispersed SiC particles were fabricated via hot-pressing with an oxynitride glass. To determine the effect of sintering time and SiC content on the mechanical properties and the cutting performance, the composites with fixed 8hr-sintering time and 20 wt% SiC content were fabricated and tested. Fracture toughness of the composites increased with increasing sintering time, while the hardness increased as the SiC content increased up to 20 wt%. The hardness of the composites was relatively independent of the grain size and the sintered density. For machining heat-treated AISI4140, the insert with 20 wt% SiC sintered for 8hr showed the longest tool life while the insert with 20 wt% SiC sintered for 12hr showed the longest tool life for machining gray cast iron. An effort was made to relate the mechanical properties, such as hardness, fracture toughness and wear resistance coefficient with the tool life. However, no apparent relationship was found between them. It may be stated that tool life is affected by not only the mechanical properties but also other properties such as surface roughness, density, grian size and the number of the inherent defects in the inserts.