• 한국세라믹학회지
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• 제33권9호
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• pp.995-1002
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• 1996

The TiC-(Ni/Ti) composites were prepared by reaction bonding between TiC preforms and the melted mixture of Ni/Ti metal the atomic ratio of which were the ranges of 0.3 to 3. And their microstructures phase composi-tions and mechanical properties were investigated. During reaction bonding Ni/Ti metal mixture had a good wettability an permeability with TiC preforms and pore-free and fully dense sintered bodies were fabricated. TiC particle shape changed from spherical to angular platelet-like and grain size was grown with Ni/Ti atomic ratio increasing from 0.3 to 1. whereas grain growth of TiC particle was restrained and its shape changed gain from angular platelet-like to spherical when Ni/Ti atomic ratio was more than 2. Maximum bending strength and fracture toughness were obtained at the Ni/Ti atomic ratio being 1 their values were 582 MPa and 11.1 MPa.m1/2 respectively.

• Bulletin of the Korean Chemical Society
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• 제20권1호
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• pp.89-94
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• 1999

Carbon dioxide reforming of methane on Ni/γ-Al2O3 catalyst was studied. A new 10 wt% Ni/γ-Al2O3 catalyst prepared by the liquid phase oxidation method (L10O) exhibited much higher activity as well as resistances to both sintering and coke formation during the reaction than the catalyst prepared by the conventional impregnation method (D10). The electrically strong attractive interaction between nickel and support during the liquid phase oxidation process and the resultant high nickel dispersion made the L10 have superior activity and stability to the D10. To elucidate the results, the experiments with nickel catalysts on the other supports as well as 7-AI203 were performed. The effect of sodium as a promoter was also studied.

• 한국해양공학회지
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• 제22권4호
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• pp.59-64
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• 2008

The mechanical properties of liquid phase sintered (LPS) SiC materials, with the addition of oxide powder, were investigated, in conjunction with a detailed analysis of their microstructures. LPS-SiC materials were fabricated at a temperature of 1820 $^{\circ}C$ under an argon atmosphere, using three different starting sizes of SiC particles. The sintering additive for the fabrication of the LPS-SiC materials was an $Al_2O_3-Y_2O_3$ mixture with a constant composition ratio ($Al_2O_3/Y_2O_3$: 1.5). The particle sizes of the commercial SiC powderswere 30 nm, 0.3 $\mu$m, and 3.0 $\mu$m. The flexural strength of the LPS-SiC materials was also examined at elevated temperatures. A decrease in the starting size of the SiC particles led to an increase in the flexural strength of the LPS-SiC materials, accompanying a highly dense morphology with the creation of a secondary phase. Such a secondary phase was identified as $Y_3Al_2(AlO_4)2$. The flexural strength of the LPS-SiC materials greatly decreased with an increase in the test temperature, due to the creation of a large amount of pores.

• 한국분말재료학회지
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• 제6권4호
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• pp.307-313
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• 1999

The effect of carbon content on the shape of WC grains dispersed in the Co-rich matrix during liquid phase sintering of WC-35%Co hard metals has been determined. The shape of WC grains was observed using SEM stereography after removing cobalt matrix with boiling hydrochloric acid solution. The WC grains changed from hexagonal to trigonal prism as the carbon content increased in the two-phase region of(WC + $\beta$ - Co), while the morphology of WC grains changed from trigonal to hexagonal shape as the carbon content decreased. The morphology of WC grains changes reversibly along with carbon loss or carbon pick-up. Morphology change of WC grains is attributed to crystal structure of WC, which has an asymmetric array of carbon atoms. There are two types of prismatic planes having different numbers of broken W-C bonds in WC grains. It is scrutinized that as the carbon content increases, the high energy prism planes grow fast and the crystals change from hexagonal to trigonal shape. On the other hand, when the carbon content decreases, the high energy prism planes are dissolved accompanying split of (100) plane into (101) and (101) planes.

• 한국세라믹학회지
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• 제33권1호
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• pp.83-91
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• 1996

Monolithic AlN and AlN-W composites were fabricated by pressure-less sintering at 190$0^{\circ}C$ under nitrogen atmosphere and the influences of tungsten phase on the microstructure and mechanical properties were investi-gated. In the fabrication of sintered specimen no additive was used. And monolithic AlN showed substantial grain growth and low relative density. AlN-W composites were fully densified and grain growths of matrix were inhibited. The densification behavior of composites were inferred to be achieved through the liquid phase sintering process such as particle-rearrangement and solutino-reprecipitation. Also the oxid phases which is expected to form liquid phases duringsintering process were detected by XRD analysis. As the tungsten volume content increases fracture strength was decreased and fracture toughness was increased. It was suppo-sed that the strength decrease of composites with tungsten content was due to existence of interface phases. The subcritical crack growth behavior was observed from the stress-strain curve of composites. The effect of the secondary phase and interface phases on toughness in crease were studied through observation of crack propagation path and the influence of residual stress on crack propagation was investigated by X-ray residual stress measurement. In the result of residual stress measurement the compressive stress of matrix in composi-test was increased with tungsten volume content and the compressive stress distribution of matrix must have contributed to the inhibition of crack propagation.

• 한국재료학회지
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• 제13권8호
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• pp.503-508
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• 2003

The purpose of this study is to investigate the effect of $V_2$$O_{5}$ addition on the Ag and Cu precipitation in the NiCuZn ferrite layers of 7.7${\times}$4.5${\times}$1.0 mm sized multi-layer chip inductors prepared by the screen printing method using 0∼0.5 wt% $V_2$$O_{5}$ -doped ferrite pastes. With increasing the $V_2$$O_{5}$ content and sintering temperature, Ag and Cu oxide coprecipitated more and more at the polished surface of ferrite layers during re-annealing at $840^{\circ}C$. It was thought that during the sintering process, V dissolved in the NiCuZn ferrite lattice and the Ag-Cu liquid phase of low melting point was formed in the ferrite layers due to the Cu segregation from the ferrite lattice and Ag diffusion from the internal electrode. During re-annealing at $840^{\circ}C$, the Ag-Cu liquid phase came out the polished surface of ferrite layers, and was decomposed into the isolated Ag particles and the Cu oxide phase during the cooling process.

• 한국세라믹학회지
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• 제28권7호
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• pp.525-530
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• 1991

The effects of 0.15mol% Y2O3 doped semiconducting (Ba1-xPbx)TiO3 ceramics with 0.5 mol% Pb5Ge3O11 as sintering additives have been investigated as function of Pb contents (from 0.05 mol to 0.3 mol) and sintering temperatures (from 1050$^{\circ}C$ to 1200$^{\circ}C$). As the Pb content increases in the (Ba1-xPbx)TiO3 system, the size and resistance of the grain increase but the capacitance of the grain boundary decreases due to the formation of liquid phase during the sintering. And with increasing the sintering temperatures, the resistance of the grain decreases but the capacitance of the grain boundary increases. The PTCR effects decrease with increasing the Pb content and the sintering temperature.

• 한국분말재료학회지
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• 제7권2호
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• pp.93-101
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• 2000

In order to clarify the enhanced sintering behavior of nanostructured(NS) W-Cu powder prepared by mechaincal alloying, the sintering behavior during heating stage was analysed by a dilatometry with various heating rates. The sintering of NS W-Cu powders was characterized by the densification of two stages, having two peaks in shrinkage rate curves. The temperature at which the first peak appear was much lower than Cu melting point, and dependent on heating rate. On the basis of the shrinkage rate curves and the microstructural observation, the coupling effect of nanocrystalline W-grain growth and the liquid-like behavior of Cu phase was suggested as a possible mechanism for the enhanced sintering of NS W-Cu powder in the state.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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• pp.61-62
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• 2006

In this study, in order to develop the low temperature sintering ceramics for multilayer piezoelectric actuator, PMN-PNN-PZT ceramics using ${Fe_2}{O_3}$ and $WO_3$ as sintering aids were manufactured with the amount of $WO_3$ addition, and the specimens were sintered at 900, 930, $960^{\circ}C$, respectively. Thereafter, their dielectric and piezoelectric properties were investigated. The sintering aids were proved to lower the sintering temperature of piezoelectric ceramics due to the effects of ${Fe_2}{O_3}$ and $WO_3$ liquid phase. At 0.3wt% $WO_3$ added specimen sintered at $930^{\circ}C$, kp, Qm, dielectric constant and $d_{33}$ showed the optimum values of 0.60, 1402, 1440 and 360[pC/N], respectively, for multilayer piezoelectric actuator application.

• 한국세라믹학회지
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• 제49권6호
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• pp.485-492
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• 2012

Dense and single phase $BiFeO_3$ (BFO) ceramics were prepared using attrition milled calcined (coarse) powders of an average particle size of ${\approx}3{\mu}m$ by conventional sintering process. A relative density of ${\approx}96%$ with average grain size $7.3{\mu}m$ was obtained when the powder compacts were sintered at $850^{\circ}C$ even for a shorter duration of 10 min. In contrast, densification barely occurred at $800^{\circ}C$ for up to 12 h rather the microstruce showed the growth of abnormal grains. The grain growth behavior at different temperatures is discussed in terms of nonlinear growth rates with respect to the driving force. The sample sintered at $850^{\circ}C$ for 12 h showed enhanced electrical properties with leakage current density of $4{\times}10^{-7}A/cm^2$ at 1 kV/cm, remnant polarization $2P_r$ of $8{\mu}C/cm^2$ at 20 kV/cm, and minimal dissipation factor (tan ${\delta}$) of ~0.025 at $10^6$ Hz. These values are comparable to the previously reported values obtained using unconventional sintering techniques such as spark plasma sintering and rapid liquid phase sintering.