• 한국전기전자재료학회논문지
• /
• 제16권12호
• /
• pp.1131-1135
• /
• 2003

In the sintering of YIG, abnormal grain growth phenomena were observed. This abnormal grain growth is related to the sintering temperature in this experiment. In the sintering below 1450$^{\circ}C$, the sintered body showed narrow size distribution. However, in the sintering at 1450$^{\circ}C$, a few grains grew rapidly with respect to other grains, and bimodal size distribution was appeared. From the observation of the microstructure, liquid phase was not observed far from the abnormally grown large grains, but only near the large grains. This means that the abnormal grain growth was caused by the nonuniform distribution of liquid phase which promote the grains growth. Because the growth rate of grains near the liquid phase is much higher than that of the other grains, a few grains grow rapidly. This nonuniform distribution of liquid phase was thought to be due to the nonuniform mixing of the calcined powders. This abnormal grain growth was suppressed by enhancement of the compositional uniformity by multiple calcination.

• 한국세라믹학회지
• /
• 제29권3호
• /
• pp.232-240
• /
• 1992

Densification behavior, microstructural evolution, and mechanical properties of hot-pressed specimens using $\beta$-SiC and $\alpha$-SiC powder with Al2O3 additive were studied. Beta-SiC powder was fully densified as 205$0^{\circ}C$, but $\alpha$-SiC powder was at 210$0^{\circ}C$. The maximum flexural strength and the fracture toughness of the specimen hot-pressed using $\beta$-SiC powder were 681 MPa and 6.7 MPa{{{{ SQRT {m } }}, and thosevalues of specimen hot-pressed using $\alpha$-SiC powder were 452 MPa and 4.7 MPa{{{{ SQRT {m } }}, respectively. The strength superiority of specimen hot-pressed using $\beta$-SiC powder was due to the finer grain size, and higher density. The higher toughness of specimen hot-pressed using $\beta$-SiC powder than $\alpha$-SiC powder than $\alpha$-SiC powder was due to the crack deflection mechanism arised from the difference of thermal expansion coefficient between $\alpha$ and $\beta$-SiC phases which were co-existed in the sintered body.

• 한국세라믹학회지
• /
• 제28권11호
• /
• pp.865-872
• /
• 1991

LAS (lithium aluminosilicate) sol was synthesized using the hydrolysis-condensation reaction of TEOS, chelated Al(OBus)3 and LiNO3 with H2O in alcohol (ethanol+2-propanol) medium. Lowering Li content by a factor of 1/2 significantly enhanced densification and retarded the crystallization of LAS gel by ~30$0^{\circ}C$. Dense LAS specimen with essentially pore-free microstructure was obtained by sintering the sol-gel derived gel at 80$0^{\circ}C$ for 4 h and annealing at 120$0^{\circ}C$ for 2 h. Similary, a mixed colloidal processing was attempted as a convenient, alternative route for the fabrication of dense LAS sintered body. The $\beta$-spodumene seeding (~0.8 ${\mu}{\textrm}{m}$) in the sol-gel derived LAS modified the sequence of phase transformations and lowered the temperature of crystallization by ~12$0^{\circ}C$. Combining the epitaxial seeding with the sol-gel process, we could lower the crystallization temperature to the sintering temperature range (~80$0^{\circ}C$) and, demonstrate a possibility of making the viscous sintering/crystallization as a continuous as a continuous unit process.

• 한국세라믹학회지
• /
• 제48권2호
• /
• pp.152-159
• /
• 2011

The green and hard machining characteristics of dental ceramics are of great interest to dental industry. The green bodies of TZP/$Al_2O_3$ composites were prepared by the cold isostatic pressing, and machined on the CNC lathe using PCD (polycrystalline diamond) insert under various machining conditions. With increasing nose radius of PCD insert, surface roughness initially increased due to increased cutting resistance, but decreased by the onset of sliding fracture. The lowest surface roughness was obtained at spindle speed of 1,300 rpm and lowest feed rate. Hard bodies were prepared by pressureless sintering the machined green bodies at several temperatures. The grinding test for sintered hard body was conducted using electroplated diamond bur with different grit sizes. During grinding, grain pull out in the composite was occurred due to thermal expansion mismatch between the alumina and zirconia. The strength of the composite decreased with alumina contents, due to increased surface roughness and high monoclinic phase transformed during grinding process. The final polished samples represented high strength by the elimination of a phase transformation layer.

• 한국세라믹학회지
• /
• 제48권6호
• /
• pp.604-609
• /
• 2011

Additives for low temperature sintering of mullite ceramics were investigated for matching Mo-Cu conducting paste with that ceramics at 1,400$^{\circ}C$. $SiO_2$, MgO and $Y_2O_3$ were chosen as the additives for low temperature sintering, and the amounts of those additives were varied with sintering temperature of 1,400$^{\circ}C$ to 1,500$^{\circ}C$. With additives of 1.0 wt% of $SiO_2$, 1.0 wt% of MgO, and 1.5 wt% of $Y_2O_3$, the densest sintered body of 3.12 g/$cm^3$ was obtained at 1,400$^{\circ}C$ in reducing atmosphere. The flexural strength of that was 325 MPa and the CTE (Coefficient of thermal expansion) was 4.33 ppm/$^{\circ}C$.

• 한국재료학회지
• /
• 제9권2호
• /
• pp.199-204
• /
• 1999

As the engine design change to get high efficiency and performance of commercial diesel engine, surface wear of the cam follower becomes an important issues as applied load increasing at the contact face between cam follower and cam. Purpose of this study is the developing of the ceramic cam follower made of silicon nitride ceramic which is more wear resistant than the cast iron and sintered cam follower. Ceramic cam follower was made by direct brazing of thin ceramic disk to steel can follower body using active bracing alloy. Effect of joining condition on the interfacial phases and joining strength wer examined at bvarious joining temperatures, times, and cooling rates. Crowning resulted from the difference of thermal expansion coefficient after direct brazing without using any stress-relieving inter layer was measured. Interfacial phases are mainly titanium silicide and titanium nitride which are the products between active metal(Ti) in brazing alloy and silicon nitiride. Maximum joining strength of the ceramic metal joint, measured by DBS method, was 334MPa. Crowning(R) of the prototype ceramic cam follower was 1595mm. As machining for crowning is not necessary, production cost can be reduced.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1996년도 추계학술대회 논문집
• /
• pp.59-62
• /
• 1996

The effect of NiO addition on the microstructure and microwave dielectric properties of (Zr$_{0.8}$Sn$_{0.2}$)TiO$_4$(ZST) was investigated. With the NiO addition, a dense ZST body of density higher than 95% has been achieved in the sintering temperature range of 1400 to 150$0^{\circ}C$. Energy dispersive X-ray spectrometry (EDS) analysis of sintered specimen shows the presence of second phase at grain boundaries, which is considered to be NiTiO$_3$. Dielectric constant of the specimen is found to increase linearly with density. Q-values and TC$_{f}$decrease with increasing NiO content. The variation of dielectric properties with NiO content is discussed in term of the second phase. The ZST ceramics with small amount of additive gave $\varepsilon$$_{r}$=38, Q=7000 at 7 GHz and TC$_{f}$=-0.5 ppm/$^{\circ}C$, comparable with the values obtained by previous investigation.stigation.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
• /
• pp.822-823
• /
• 2006

The compaction and sintering behavior of zirconium titanate $(ZrTiO_4)$ was investigated by means of the measurement of sintering density and shrinkage, and the observation of microstructure. With increasing the content of $Al_2O_3$ additive, $Al_2O_3$-modified zirconium titanate samples fired at $1300^{\circ}C$ showed the anisotropic shrinkage behavior that the upper region of sintered body has higher sintering shrinkage than the low region. This difference of sintering shrinkage decreased with increasing firing temperature from 1300 to $1400^{\circ}C$. The SEM micrographs of powder compation show that the anisotropic shrinkage behavior is related with non-uniform density in a uniaxial compaction.

• 한국결정성장학회지
• /
• 제25권1호
• /
• pp.6-12
• /
• 2015

율속제어소결은 소결 공정 중 실시간으로 측정되는 시편의 팽창/수축거동을 이용해 일정한 수축거동을 하도록 로의 파워를 조정하는 소결방법으로, 온도를 조절하기 위해 로의 파워를 제어하는 일반적인 소결에 비해 시편의 소결 과정을 세밀히 제어할 수 있으며, 특히 소결공정의 최적화를 이룰 수 있는 장점이 있다. 본 연구에서는 탄화붕소의 소결에 율속 제어소결을 적용해 각 공정변수의 조절에 따른 소결온도 및 입자성장의 변화를 조사하여 그 상관관계를 규명하고 이를 기존의 이론에 맞추어 해석함으로써 율속제어소결을 어떻게 소결공정 최적화에 이용할 수 있는지 그 가능성을 알아보았으며 이를 통해 향후 미지 소재의 소결공정에 율속제어공정을 어떻게 적용할 수 있는지 고찰해 보았다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
• /
• pp.47-47
• /
• 2008

P-type transparent semiconductor $SrCu_2O_2$ thin films have been prepared by RF sputtering using low-alkali glass for LCD and quartz as substrates. Single phase of $SrCu_2O_2$ powder was obtained by heating a stoichiometric mixture of CuO and $SrCO_3$ at 1223K for 96h under N2 gas flow, and target was fabricated at 1243K for 24h. Room temperature conductivity of the sintered body was about 0.02S/cm, and the activation energy in the temperature range of $-50^{\circ}C$~RT and RT~$150^{\circ}C$ were 0.18eV, 0.07eV, respectively. Effects of deposition pressure and post-annealing temperature on the electrical and optical properties of the obtained thin film have been investigated.