• Journal of the Korean Ceramic Society
• /
• v.34 no.5
• /
• pp.505-511
• /
• 1997

The effects of sintering atmospheres(air, O2, N2) on the sintering and microwave dielectric properties of (1-x)CaTiO3-xLaAlO3 system was investigated. The sintered density of (1-x)CaTiO3-xLaAlO3 under air atmosphere increased linearly with increasing x, but it decreased in the range of x>0.5 under O2 atmosphere and x>0.6 under N2 atmosphere in spite of the increament of the smaller La(1.06$\AA$) and Al(0.5 $\AA$) ion than Ca(0.99$\AA$) and Ti(0.6$\AA$). In case of the air sintering atmosphere of (1-x)CaTiO3-xLaAlO3 the two phases of orthorhombic and rhombohedral crystal system were coexisting, and the XRD peak of rhombohedral crystalsystem was to be higher with increasing x. However, the sintering atmosphere of O2 and N2 made the monophasic crystal system of orthorhombic keep up by x=0.5 and x=0.6, respectively, and it transformed to pseudo-cubic crystal system in x>0.5 and x>0.6. The XRD peak intensity of (1-x)CaTiO3-xLaAlO3 was to be gradually higher with increasing x under the air atmosphere of sintering. Whereas, its XRD peak intensity increased till x=0.6 but decreased with increasing x in the range of x>0.6 under O2 and N2 atmosphere. The relative dielectric constant of (1-x)CaTiO3-xLaAlO3 sintered under air atmosphere decreased linearly and the Q.f0 value increased according as x increased. On the other hand, the relative dielectric constant of (1-x)CaTiO3-xLaAlO3 under O2 and N2 atmosphere decreased in the range of x$\leq$0.5 with increasing x, but increased rapidly in the range of x$\geq$0.6. And the Q.f0 value increased till x=0.6 but decreased in the range of x>0.6 with increasing x. The temperature coefficient of resonant frequency had no relation to sintering atmosphere.

• Journal of the Korean Ceramic Society
• /
• v.31 no.1
• /
• pp.1-10
• /
• 1994

Monodispersed alumina and Mg-doped alumina fine particles were prepared by controlled hydrolysis of alkoxides. Aluminium alkoxide and magnesium alkoxide were dissolved into complex solvent which was composed of hydrophobic n-octanol and hydrophilic acetonitrile. Hydroxypropyl cellulose(HPC) was used as a dispersant for the alumina particles. The size of these prepared powders was approximately 0.3 ${\mu}{\textrm}{m}$. In the case of sintering above 100$0^{\circ}C$, most of these prepared powders were transformed to $\alpha$-alumina. The relative density of the sintered body of these prepared powders at 1$600^{\circ}C$ was 98%. The sintered body of the Mg-doped alumina powder had more uniform grain size than that of the undoped alumina podwer.

• Korean Journal of Materials Research
• /
• v.30 no.2
• /
• pp.93-98
• /
• 2020

Effective control of the heat generated from electronics and semiconductor devices requires a high thermal conductivity and a low thermal expansion coefficient appropriate for devices or modules. A method of reducing the thermal expansion coefficient of Cu has been suggested wherein a ceramic filler having a low thermal expansion coefficient is applied to Cu, which has high thermal conductivity. In this study, using pressureless sintering rather than costly pressure sintering, a polymer solution synthesis method was used to make nano-sized Cu powder for application to Cu matrix with an AlN filler. Due to the low sinterability, the sintered Cu prepared from commercial Cu powder included large pores inside the sintered bodies. A sintered Cu body with Zn, as a liquid phase sintering agent, was prepared by the polymer solution synthesis method for exclusion of pores, which affect thermal conductivity and thermal expansion. The pressureless sintered Cu bodies including Zn showed higher thermal conductivity (180 W/m·K) and lower thermal expansion coefficient (15.8×10^-6/℃) than did the monolithic synthesized Cu sintered body.

• Journal of the Korean Ceramic Society
• /
• v.28 no.2
• /
• pp.130-140
• /
• 1991

The powders of the system Si3N4-Y2O3-AlN were prepared using Si(OC2H5)4 and YCl3.6H2O together with commercial AlN powder. $\alpha$-Si3N4 was prepared by the carbothermal reduction and nitridation of the hydrolyzed gel at 135$0^{\circ}C$ for 10h in N2 atmosphere. YCl3.6H2O was observed to be changed to Y2O3 during the reaction. $\alpha$-Sialon(X=0.2, 0.4, 0.6) ceramics were obtained by hot-pressing the Si3N4-Y2O3-AlN mixture at 178$0^{\circ}C$ for 1h under 30 MPa. The content of $\alpha$-Sialon increased with increasing metal solubility(x value) and $\alpha$-Sialon single phase was obtained at the metal solubility of 0.6. With increasing metal solubility, flexural strength, fracture toughness and thermal shock resistence were decreased, while the microhardness was increased. Large elongated $\beta$-Si3N4 grains were mainly observed at lower metal solubility. Mechanical prorerties of the sintered ceramics with X=0.2 were measured as follows : flexural strength ; 650 MPa, fracture toughness ; 3.63 MN/m3/2, hardness ; 14.7 GPa, thermal shock resistence temperature ; 58$0^{\circ}C$.

• Journal of the Microelectronics and Packaging Society
• /
• v.5 no.2
• /
• pp.53-58
• /
• 1998

Sintering and dielectric characteristics of substrates were estimated by mixing rate of alumina and potashborosilicate glass(PBSG) powders. PBSG powders were used 7761(corning code)and alumina powders were used in extra pure rate(99.9%) and had 0.1 ${\mu}$m mean size. After ball milling with organic additives green sheets which were casted by doctor blade machine were sintered at 800$^{\circ}C$ for 1∼3hrs. Microstructure, linear shrinkage and dielectric constant of substrates were surveyed in order to fabricate low-dielectric and low tem-perature sintering substrate.

• Journal of the Korean Ceramic Society
• /
• v.44 no.7
• /
• pp.354-357
• /
• 2007

The nitriding and post-sintering behavior of silicon powder compact containing sintering additives of 2.3 wt% and 7 wt% were investigated in this study. Regardless of the liquid phase content, elongated large grains of a typical morphology evolved in the post-sintered specimens. Phase analysis revealed a complete phase transformation into ${\beta}-Si_3N_4$ in both porous systems. Oxynitride second phases (mellilite) precipitated in the latter, while those were free in the former containing less amount of liquid phase. The post-sintering condition that yielded a favorable microstructure for a filter application was achieved when the specimens were soaked at $1800^{\circ}C$ for 2 h. It was found that the thermal conductivity of porous $Si_3N_4$ ceramics is dominated by the porosity more than this factor is influenced by the addition of $Al_2O_3$.

• Journal of the Korean Ceramic Society
• /
• v.56 no.5
• /
• pp.513-520
• /
• 2019

This study reports the improvement of mechanical properties of Al₂O₃ porous ceramics from colloidal suspension with the addition of carbon fiber by direct foaming. The initial colloidal suspension of Al₂O₃ was partially hydrophobized by surfactant to stabilize wet foam with the addition of carbon fiber from 2 to 8 wt% as stabilizer. The influence of carbon fiber on the air content, bubble size, pore size and pore distribution in terms of wet foam stability and physical properties of porous ceramics were discussed. The viscosity of the colloidal suspension was increased giving solid like properties with the increased in carbon fiber content. The mechanical properties of the sintered porous samples were investigated by Hertzian indentation test. The results show the wet foam stability of more than 90% corresponds to compressive loading of 156.48 N and elastic modulus of 57.44 MPa of sintered sample with 8 wt% of carbon fiber content.

• Journal of the Korean Ceramic Society
• /
• v.46 no.5
• /
• pp.452-455
• /
• 2009

A cost-effective route to synthesize $\beta$-SiAlONs from Si mixtures by reaction bonding followed by post-sintering was investigated. Three different z values, 0.45, 0.92 and 1.87, in $Si_{6-z}Al_zO_zN_{8-z}$ without excess liquid phase were selected to elucidate the mechanism of SiAlON formation and densification. For RBSN (reaction-bonded silicon nitride) specimens prior to post-sintering, nitridation rates of more than 90% were achieved by multistep heating to $1400^{\circ}C$ in flowing 5%$H_2$/95%$N_2$; residual Si was not detected by XRD analysis. An increase in density was acquired with increasing z values in post-sintered specimens, and this tendency was explained by the presence of higher amounts of transient liquid phase at larger z values. Measured z values from the synthesized $\beta$-SiAlONs were similar to the values calculated for the starting compositions. Slight deviations in z values between measurements and calculations were rationalized by a reasonable application of the characteristics of the nitriding and post-sintering processes.

• Korean Journal of Materials Research
• /
• v.15 no.4
• /
• pp.224-232
• /
• 2005

Dry sliding wear behavior of electro-pressure sintered Fe-Ni and Co-Fe-Ni compacts was investigated. Pin-on-disk wear tests were performed on the sintered Fe-Ni, Co-Fe-Ni disk specimens against alumina $(Al_2O_3)$ and silica $(SiO_2)$ ball counterparts at various loads ranging from 3N to 12N. A constant sliding speed of 0.1m/sec was employed. Wear rate was calculated by dividing the weight loss measured after the test by specific gravity and sliding distance. Worn surfaces and cross sections of them were examined by a scanning electron microscopy, and wear mechanism of the compacts was investigated. Wear characteristics of the compacts were discussed as a function of composition of the compacts. Relationship between the wear rate and mechancial properties of the compact was explored, and effects of the oxide layer that was formed on wearing surface of the compacts on the wear were also studied.

• Journal of Powder Materials
• /
• v.11 no.6 s.47
• /
• pp.451-461
• /
• 2004

Dry sliding wear behavior of electro-pressure sintered Co-Fe and Co-Ni compacts was investigated. Pin-on-disk wear tests were performed on the sintered Co-Fe, Co-Ni disks against alumina $(Al_2O_3)$ and silica $(SiO_2)$ balls at various loads ranging from 3N to 12N. A constant sliding speed of 0.1m/sec was employed. Wear rate was calculated by dividing the weight loss of a specimen by the measured specific gravity and sliding dis-tance. Worn surfaces and cross-sections of the specimens were examined using an SEM and EDS to investigate wear mechanism of the compacts. The wear behavior of the compacts were discussed as a function of their com-position. Effects of mechancial properties of the compact as well as oxide layers formed on wearing surface on the wear were also discussed.