• Journal of the Korean Ceramic Society
• /
• v.23 no.4
• /
• pp.41-46
• /
• 1986

When barium titanate was synthesized in solid-solid reaction the abnormal expansion occurred from 90$0^{\circ}C$ to 110$0^{\circ}C$. The equi molecular mixture of $BaCo_3$ and $TiO_2$ was sintered from 90$0^{\circ}C$ to 130$0^{\circ}C$ on the condition of air vacuum and $CO_2$ atomosphere. After that the specimens were tested closely with XDR Dilatometer and SEM The result indicated that: 1, Volume expansion to be synthesized barium titanate in solid-solid reaction was affected by atomosphere sintering. 2. The solid reaction ot fiorm barium titanate in vacuum atomosphere occurred faster than that in air atomosphere. In vacuum atomosphere the maxium volume expansion was about 30% at 90$0^{\circ}C$ for 2hrs, 3. The solid reaction to form barium titanate in 4CO_2$ atomosphere occurred slower than that in air atomosphere. In $CO_2$ atomosphere the maximum volume expansion was 13% at 100$0^{\circ}C$ for 2 hrs. 4. According to the result of x-ray the expanison was caused by the reaction to form $BaTiO_3$ and change $Ba_2TiO_4$ into 4BaTiO_3$.

• Journal of Powder Materials
• /
• v.14 no.1 s.60
• /
• pp.32-37
• /
• 2007

Using spark plasma sintering process (SPS), Ti-6Al-4V alloy powders were successfully consolidated without any contamination happened due to reaction between the alloy powders and graphite mold. Variation of microstructure and mechanical properties were investigated as a function of SPS temperature and time. Compared with hot isostatic pressing (HIP), the sintering time and temperature could be lowered to be 10 min. and $900^{\circ}C$, respectively. At the SPS condition, UTS and elongation were about 890 MPa and 24%, respectively. Considering the density of 98.5% and elongation of 24%, further improving the tensile strength would obtain by increasing the SPS pressure.

• Journal of the Korean Ceramic Society
• /
• v.49 no.4
• /
• pp.318-324
• /
• 2012

Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, $Lu_2O_3-SiO_2$ (US), $La_2O_3$-MgO (AM) and $Y_2O_3-Al_2O_3$ (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the $La_2O_3$-MgO system. Since the $Lu_2O_3-SiO_2$ system has the highest melting temperature, full densification could not be achieved after sintering at $1950^{\circ}C$. However, the system had a reasonably high bending strength of 527 MPa at $1200^{\circ}C$ in air and a high fracture toughness of 9.2 $MPa{\cdot}m^{1/2}$. The $Y_2O_3-Al_2O_3$ system had the highest room temperature bending strength of 1.2 GPa.

• Journal of Powder Materials
• /
• v.22 no.5
• /
• pp.356-361
• /
• 2015

Fe-30 wt% TiC composite powders are fabricated by in situ reaction synthesis after planetary ball milling of (Fe, $TiH_2$, Carbon) powder mixture. Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-30 wt% TiC composite powder compacts. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C/min$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts are not densified even after sintering at $1300^{\circ}C$ for 3 h, which shows a relative denstiy of 66.9%. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly full densification of 99.6% relative density under the sintering pressure of 50 MPa.

• Journal of the Korean Ceramic Society
• /
• v.32 no.2
• /
• pp.257-269
• /
• 1995

The TiC-Co/Al reaction-sintered products were prepared by the infiltration of various Co/Al metal mixture into the preform, and their microstructure, phases, and mechanical properties were investigated. With increasing the atomic ratio of Co/Al, tiC grain shape was changed from spherical to platelet particles, and the grain size increased. The crystalline phases found in the liquid matrix formed by the infiltration of Co/Al metal mixture were determined to be Al5Co2 and AlCo by EDS and XRD, and the two crystalline phases were located dominantly between TiC grains, when the Co/Al atomic ratio was lower than an unity. There was a tendency that the density, bending strength and fracture toughness increase with Co/Al atomic ratio until the infiltrated metal was 100% Co. The maximum value was achieved by the composition containing 100% Co infiltrated metal. The Vickers hardness decreased as Co/Al atomic ratio increased.

• Journal of the Korean Ceramic Society
• /
• v.39 no.1
• /
• pp.45-50
• /
• 2002

Effect of sintering additives on the densification behavior of reaction-bonded silicon nitride prepared by using coarse Si powders is discussed. Sintering additives such as 6 wt% $Y_2O_3$+1wt% $A1_2O_3$ (6YlA) did not give rise to full densification, while full densification was obtained by using the sintering additives such as 6wt% $Y_2O_3$+3 wt% $A1_2O_3$+ 2wt% $SiO_2$ (6Y3A2S) and 9wt% $Y_2O_3$+ 1.5wt% $A1_2O_3$+ 3wt% $SiO_2$ (9Yl.5A3S). In the case of 6Y3A2S addition, high fracture strength of 960 MPa and the fracture toughness of $6.5 MPa.m^{1/2}$ were obtained.

• Journal of the Korean Ceramic Society
• /
• v.34 no.5
• /
• pp.473-482
• /
• 1997

Titanium carbide(TiC) has a poor sinterability due to the strong covalent bond. Thus, it is generally fabricated by either hot pressing or pressureless-sintering at elevated temperature by the addition of sintering aids such as nickel(Ni), molybdenum(Mo) and cobalt(Co). However, these sintering methods have the following disadvantages; (1) the complicated process, (2) the high energy consumption, and (3) the possibility of leaving inevitable impurities in the product, etc. In order to reduce above disadvantages, we investigated the optimum conditions under which dense titanium carbide bodies could be synthesized and sintered simultaneously by high pressure self-combustion sintering(HPCS) method. This method makes good use of the explosive high energy from spontaneous exothermic reaction between titanium and carbon. The optimum conditions for the nearly full-densification were as follows; (1) The densification of sintered body becomes high by increasing the pressing pressure from 400kgf/$\textrm{cm}^2$ upto 1200 kgf/$\textrm{cm}^2$. (2) Instead of adding the coarse graphite or activated carbon, the fine particles of carbon black should be added as a carbon source. (3) The optimum molar ratio of carbon to titanium (C/Ti) was unity. In reality, titanium carbide body which were prepared under optimum conditions had relatively dense textures with the apparent porosity of 0.5% and the relative density of 98%.

• Korean Journal of Materials Research
• /
• v.32 no.4
• /
• pp.181-185
• /
• 2022

In this study, phase-pure titanium dioxide TiO₂ ceramics are sintered using standard high-temperature solid-state reaction technique at different temperatures (1,000, 1,100, 1,200, 1,300, 1,400 ℃). The effect of sintering temperature on the densification and impedance properties of TiO₂ ceramics is investigated. The bulk density and average grain size increase with the increase of sintering temperature. Impedance spectroscopy analysis (complex impedance Z^* and complex modulus M^*), performed in a broad frequency range from 100 Hz to 10 MHz, indicates that the TiO₂ ceramics are dielectrically heterogeneous, consisting of grains and grain boundaries. The complex impedance Z^* -plane indicates the resistance of grains of the TiO₂ ceramics increases with increasing sintering temperature, while that of grain boundaries develops in the opposing direction. The complex modulus M^*-plane shows a grain capacitance that seems to be independent of the sintering temperature, while that of the grain boundaries decreases with increasing sintering temperature. These results suggest that different sintering temperatures have effects on the microstructure, leading to changes in the impedance properties of TiO₂ ceramics.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 1999.11a
• /
• pp.114-114
• /
• 1999

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2000.11a
• /
• pp.154-154
• /
• 2000