• 한국세라믹학회지
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• 제27권8호
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• pp.991-1003
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• 1990

A precipitation method, one of the most effective liquid phase reaction methods, was adopted in order to prepare high-tech Al2O3/ZrO2 composite ceramics. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent, various types of metal hydroxides were obtained by single precipitation(series A) and co-precipitation(series B) method at the pH condition between 7 and 11. Fine Al2O3-ZrO2 powders were prepared at optimum calcination condition and the effects of ZrO2 on microstructures and mechanical properties of Al2O3 were investigated. The composition of Al2O3/ZrO2 composites wax fixed as Al2O3-15 v/o ZrO2(＋3m/o Y2O3). ZrO2 limited the grain growth of Al2O3 and increased grain size homogeneity of Al2O3 more effectively than MgO.Flexural strength values in Al2O3 and Al2O3/ZrO2 composites were 340-430 MPa and 540-820 MPa, respectively, and the effect of strength improvement showed 20-50% by adding ZrO2 to Al2O3. Fracture toughness of Al2O3/ZrO2 composites was improved by stress-induced phase transformation of tetragonal ZrO2 and toughening effect by microcrack was not observed. Also, ZrO2 particles located at Al2O3 grain junction contributed to toughening, while spherical ZrO2 particles located within Al2O3 grain did not contribute to toughening. Weibull moduli of Al2O3 ceramics and Al2O3/ZrO2 composites of series A and series B were 4.34, 5.17 and 9.06, respectively. Above 0.5 of failure probability, strength values in Al2O3 ceramics and Al2O3/ZrO3 composites of series A and series B were above 400 MPa, 700 MPa and 650 MPa, respectively.

• 한국세라믹학회지
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• 제35권7호
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• pp.685-690
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• 1998

Al2O3에 대한 용융 Al의 자발적 침윤 기구를 밝히기 위하여 순수한 Al 및 Al-(Si)-Mg 합금의 Al2O3에 대한 wet-ting angle과 침윤 특성을 진공, 아르곤, 그리고 질소분위기에서 관찰하였다. Al2O3에 대한 용융 Al 및 Al 합금의 wetting은 진공 분위기에서만 이루어졌으나, Al2O3에 대한 용융 Al 합금의 자발적 침윤은 질소 분위기하 Al 합금에 합금 원소로써 Mg가 함유되었을 때에 일어났다. Al2O3에 대한 용융 Al 및 Al 합금의 wettability와 자발적 침윤 특성의 차이는 Al2O3 표면에 형성되는 Mg-N화합물에 직접적인 영향을 받는 것으로 나타났다. Al2O3 입자 표면에 얇게 형성되는 Mg와 질소의 화합물 즉, Mg3N2가 Al2O3에 대한 용윤 Al 합금의 wettability를 향상시켜 $700^{\circ}C$의 온도에서도 Al 합금의 자발적 침윤이 가능하여 Al/Al2O3 복합재료를 무가압 상태에서 제조할 수 있었다.

• 한국세라믹학회지
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• 제27권6호
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• pp.799-807
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• 1990

In this study, effects of oxide additives on mechanical properties and microstructure of A1N and A1N polytype ceramics were investigated. Fine A1N powder was synthesized by nitriding alumiuim hydroxide prepared from Al-isopropoxide, at 1350$^{\circ}C$ for 10h in N2 atmosphere. By adding 3w/o Y2O3, 0.56w/o CaO, and 10w/o SiO2 to AlN powder, AlN and AlN polytype ceramics were prepared by hot-pressing under the pressure of 30 MPa at 1800$^{\circ}C$ for 1h. AlN ceramics with no additives formed considerable amount of AlON phase, while AlN ceramics doped with Y2O3 or CaO decreased AlON phase and formed Y-Al or Ca-Al oxide compound. AlN＋10w/o SiO2(＋3w/o Y2O3) composition produced AlON and AlN polytype compound having 21R as a major phase. Room temperature flexural strength of AlN ceramics with no additive was 246MPa, and room temperature flexural strength and critical temperature difference by thermal shock(ΔTc) of AlN ceramics dooped with Y2O3 or CaO were 532MPa/340$^{\circ}C$ and 423MPa/300$^{\circ}C$, respectively. Y2O3 and CaO used as sintering agent played roles of densification and oxygen removal of AlN ceramics, and affected grain growth/grain morphologies of AlN ceramics.

• 한국세라믹학회지
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• 제26권3호
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• pp.423-437
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• 1989

Al2O3/ZrO2 composites were prepared by precipitation method using Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O as starting materials and NH4OH as a precipitation agent. Al2O3/ZrO2 composites(series A) were prepared by mixing Al2O3 powder obtained by single precipitation method with ZrO2(＋3m/o Y2O3) powder obtained by co-predipitation method. Al2O3/ZrO2 composites (series B) were prepared by co-precipitation method using the three starting materials. In all cases, the composition was controlled as Al2O3-15v/o ZrO2(＋3m/o Y2O3). The composites of series A showed higher final relative densities than those of series B and tetagonal ZrO2 in all cases was retained to about 95% at room temperature. ZrO2 particles were coalesced more rapidly in grain boundary of Al2O3 than within Al2O3 grain. ZrO2 particles were located at 3-and 4-grain junction of Al2O3 and limited the grain growth of Al2O3. It was observed that MgO contributed to densification of Al2O3 but limited grain growth of Al2O3 by MgO was not remarkable. In all Al2O3/ZrO2 composites, exaggerated grain growth of Al2O3 was not observed and Al2O3/ZrO2 composites were found to have homogeneous microstructures.

• 대한화학회지
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• 제37권9호
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• pp.787-792
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• 1993

$AlPO_4-5$ 분자체의 가교 OH 그룹에 대한 성질을 $AlPO_4-5$ 분자체의 구조 특성인 Al-O(P-O) 결합길이와 Al-O-P 결합각에 대한 관계를 알아보기 위하여 가교 $(OH)_3AlOP(OH)_3$ 와 $(OH)_3AlOHP(OH)_3^+$ 덩어리를 이용하여 반경험적 MNDO 계산 방법으로 연구하였다. 가교 OH 그룹의 O-H 결합해리에너지는 Al-O(P-O) 결합길이가 증가할수록, Al-O-P 결합각이 감소할수록 알 수 있었고, 가교 OH 그룹 생성은 Al-O(P-O) 결합길이가 길고, Al-O-P 결합각이 작은 가교 산소원자에서 형성된다는 것을 알았다. 또한 Al-O-P 결합각이 증가할수록 가교 산소원자의 음의 알짜전하는 증가하나 가교 수소원자의 양의 알짜전하는 감소함을 알았다.

• 한국세라믹학회지
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• 제28권5호
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• pp.422-428
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• 1991

The reaction sintering of Al2O3-ZrO2-Nb composite has been investigated using Al2O3, and ZrAl2 powders. Two kinds of specimens, 78.3Al2O3-14.0Nb2O5-7.7ZrAl2 in wt.% (AZN-5) and 72.3Al2O3-13.8Nb2O5-7.5ZrAl2-6.4ZrO2(AZN-10), were prepared. Powder compacts were sintered at various temperatures between 1$600^{\circ}C$ and 1$700^{\circ}C$ for 30 min in Ar. DTA and X-ray analysis have showen that a reaction between Nb2O5 and ZrAl2 started at 149$0^{\circ}C$ to form Al2O3, ZrO2, and Nb. The sintered density increased with the sintering temperature. AZN-10 specimen showed higher density than AZN-5 specimen for almost all the experimental conditions. Al2O3-ZrO2-Nb composite hot pressed after reaction sintering showed higher toughness and lower hardness than hot pressed Al2O3-ZrO2. The crack propagated through many metallic Nb particles which showed plastic deformation, and this is the cause of the increase in toughness of Al2O3-ZrO2-Nb composite over Al2O3-ZrO2.

• 한국세라믹학회지
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• 제35권12호
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• pp.1266-1273
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• 1998

Al2O3/(5~20vol%)LaAl11O18 composites in which the second phase was dispersed with a elongated grain shape were fabricated using Al2O3 and La2O3 composition by hot-pressing. In order investigate the in-fluence of LaAl11O18 on the toughening of LaAl11O18 on the toughening of Al2O3 matrix composites AE(acoustic emission) analysis was con-ducted together with an evaluation of fracture toughness using of SEPB technique. The degree of AE events occurred in composites were more than those in monolithic alumina. The occurrences of AE event increased with increasing the amount of LaAl11O18 phase in the Al2O3/LaAl11O18 composite is two times higher compared to monolithic alu-mina. The main toughening mechanism was attributed to the bridging of LaAl11O18 grains at tip of pro-pagating crack.

• 한국세라믹학회지
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• 제36권7호
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• pp.734-741
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• 1999

Al2O3와 t-ZrO2 분말의 압분체를 공기중 150$0^{\circ}C$ 및 1$600^{\circ}C$에서 2시간 소결하여 제조된 입자복합체의 미세구조와 기계적 성질을 조사하였다. 소수의 미세한 구상의 ZrO2입자는 Al2O3의 입내에 존재하였으나 대분분은 입계에 존재하여 Al2O3의 입계를 고정시키는 것이 가능하였고, 따라서 Al2O3의 입성장을 둔화시켰다. 소결할 동안 입계 ZrO2 입자의 조대회는 응집된 ZrO2 입자내에서의 입계의 소멸과 Al2P3 입계의 이동에 의해서 끌어 당겨진 ZrO2 입자의 합체(coalescence)에 의해서 일어날 수 있었다. ZrO2의 첨가에 의한 Al2O3의 기계적 성질의 변화는 기지상인 Al2O3의 미세구조와 분산된 ZrO2 입자의 크기와 구조에 의존하였다.

• 한국결정성장학회지
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• 제8권4호
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• pp.573-580
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• 1998

MgO와 Al 분말을 자전고온연소합성법으로 $MgAl_2O_4$ 스피넬 상을 합성하였다. MgO 와 Al을 테르밋 반응으로 생성하였으며, 가열반응생성으로 $800^{\circ}C$ 예열온도에서 반응시켰다. DTA/TG, 합성생성물, 최고온도 공정조건에 대해 연구하였고, MgO와 Al은 MgO+2Al+ 3/$2O_3$ $\rightarrow$ $MgAl_2O_4$ 로 합성되었다. 미반응된 재료로부터 MgAl2O4 스피넬의 활성화 에너지는 -264.8kcal/mol의 발생열량과 5634K의 최고 반응온도로 계산되었다. 테르밋 반응후의 시험편의 체적느 6% 증가하였다.

• 한국세라믹학회지
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• 제35권3호
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• pp.303-309
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• 1998

The fabrication of Al2O3/Al composite by pressureless infiltration was investigated by the change of Mg and Si content in Al alloy infiltration process and infiltration atmosphere. The effect of alloying elements infiltration atmosphere and interfacial reactants between Al alloy matrix and Al2O3 particles were in-vestigated in terms of bendingstrength and harness test,. The fabrication of Al2O3/Al composite by the vestigated in terms of bending strength and hardness test. The fabrication of Al2O3/Al composite by the pressureless infiltration was done in nitrogen atmosphere with Mg in Al alloy. It was successfully fabricated at $700^{\circ}C$ according to Mg contents in Al alloy and infiltration condition. Because Mg in the Al alloy and ni-trogen atmosphere of infiltratio condition produced Mg-N compound(Mg3N2) it decreased the wetting an-gle between molten Al alloy and Al2O3 particles by coating on surface of Al2O3 particles. The fracture strength of Al2O3/Al-Mg composite was 800MPa and Al2O3/Al-Si-Mg composite was 400MPa. Si in Al alloy decreased the interfacial strength between Al alloy matrix and Al2O3 particles.