• Journal of the Microelectronics and Packaging Society
• /
• v.11 no.4 s.33
• /
• pp.37-41
• /
• 2004

As mobile communication devices use wide bands for large data transmission, Low Temperature Co-fired Ceramic(LTCC) has been a candidate for module substrate, for it provides better electrical properties and enables various embedded passive devices compared to conventional PCB. The LTCC, however, has applied in limited area because of non-uniform shrinkage. Hybrid heating was developed to raise sample temperature uniformly in a short period of time This leads to unidirectional sintering which enables sample to be sintered layer by layer from the bottom, resulting in more stable shape of interconnection at the top surface of the sample than conventional electric furnace heating. When sintering properties of substrate and electrical/mechanical properties of interconnection were compared, hybrid heating showed possibility to be applicable to substrate miniaturization and interconnection densification superior to electric furnace heating.

• Proceedings of the KIEE Conference
• /
• 2008.07a
• /
• pp.1230-1231
• /
• 2008

The effect of content of $Al_2O_3+Y_2O_3$ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at 1,700[$^{\circ}C$] temperatures with an addition of $Al_2O_3+Y_2O_3$(6:4 mixture of $Al_2O_3$ and $Y_2O_3$) as a sintering aid in the range of 8${\sim}$20[wt%]. Phase analysis of $SiC-ZrB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $ZrB_2$ and In Situ YAG($Al_5Y_3O_{12}$). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.01[%], 81.58[Mpa], 31.437[GPa] and 1.34[GPa] for $SiC-ZrB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from ${\beta}$-SiC into ${\alpha}$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites. In this paper, it is convinced that ${\beta}$-SiC based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

• Nuclear Engineering and Technology
• /
• v.35 no.1
• /
• pp.14-24
• /
• 2003

This work investigates the effects of Cr$_2$O$_3$ and oxygen potential on grain growth and densification of UO$_2$ pellets. Powder mixtures of UO$_2$ and 0.03-0.4wt% Cr$_2$O$_3$ were pressed and sintered in 3 different gas atmospheres: the $H_2O$-to-H$_2$ ratios were 5$\times$10$^{-4}$ , 1$\times$10$^{-2}$ and 3$\times$10$^{-2}$ In the first gas atmosphere the Cr$_2$O$_3$ contents below 0.2 wt% have an insignificant effect on grain size, but the Cr$_2$O$_3$ contents more than 0.3 wt% promote grain growth in the inner zone of a pellet but not in the outer zone. In both the second and third atmospheres, the grain size increases with the Cr$_2$O$_3$ content. With the same level of Cr$_2$O$_3$ content the grain size is larger in the second atmosphere than in the third. Sintering behavior and developed microstructure are discussed in terms of the reduction of C$r^2$O$^3$ to Cr, the dissolution of C$r^2$O$^3$ in UO$_2$, and liquid phase sintering.

• Nuclear Engineering and Technology
• /
• v.31 no.5
• /
• pp.455-464
• /
• 1999

The effect of TiO$_2$ on the sintering behavior of mixed UO$_2$-U$_3$O$_{8}$ Powder compacts has been investigated using the U$_{3}$O$_{8}$ powder made tv oxidation of defective UO$_{2}$ pellets. Without TiO$_2$, UO$_2$ pellet density is inversely proportional to U$_3$O$_{8}$ content and is below 94 %TD in the U$_3$O$_{8}$ range above 15 wt%. Using more than 0.1 wt % TiO$_2$, however, the density decreases slightly with U$_3$O$_{8}$ content and thus is higher than about 94% TD in the whole range of U$_3$O$_{8}$ content. The grain sizes of UO$_2$ pellets with more than 0.1 wt % TiO$_2$are larger than about 30${\mu}{\textrm}{m}$. Therefore, the U$_3$O$_{8}$ Powder can be reused without any restriction on its amount in UO$_2$ pellet fabrication by sintering the mixed UO$_2$-U$_3$O$_{8}$ compact with the aid of TiO$_2$. Mechanisms for densification and grain growth are proposed and discussed, based on a dilatometry study and an examination of microstructure. microstructure.

• Korean Journal of Metals and Materials
• /
• v.50 no.11
• /
• pp.817-822
• /
• 2012

Nano powders of $Al_2O_3$ and $TiO_2$ compounds made by high energy ball milling were pulsed current activated sintered for studying their sintering behaviors and mechanical properties. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Nano-structured $Al_2TiO_5$ with small amount of $Al_2O_3$ and$TiO_2$ was formed by sintering at $1300^{\circ}C$ for 5 minute, in which average grain size was about 96 nm. Hardness and fracture toughness of the nano-structured $Al_2TiO_5$ compound with a small amount of $Al_2O_3$ and$TiO_2$ were $602kg/mm^2$ and $2.6MPa{\cdot}m^{1/2}$, respectively.

• Journal of Powder Materials
• /
• v.28 no.3
• /
• pp.246-252
• /
• 2021

The effect of sintering conditions on the austenite stability and strain-induced martensitic transformation of nanocrystalline FeCrC alloy is investigated. Nanocrystalline FeCrC alloys are successfully fabricated by spark plasma sintering with an extremely short densification time to obtain the theoretical density value and prevent grain growth. The nanocrystallite size in the sintered alloys contributes to increased austenite stability. The phase fraction of the FeCrC sintered alloy before and after deformation according to the sintering holding time is measured using X-ray diffraction and electron backscatter diffraction analysis. During compressive deformation, the volume fraction of strain-induced martensite resulting from austenite decomposition is increased. The transformation kinetics of the strain-induced martensite is evaluated using an empirical equation considering the austenite stability factor. The hardness of the S0W and S10W samples increase to 62.4-67.5 and 58.9-63.4 HRC before and after deformation. The hardness results confirmed that the mechanical properties are improved owing to the effects of grain refinement and strain-induced martensitic transformation in the nanocrystalline FeCrC alloy.

• Nuclear Engineering and Technology
• /
• v.54 no.12
• /
• pp.4491-4498
• /
• 2022

The thermal stress between W plasma-facing material (PFM) and Cu heat sink in fusion reactors can be significantly reduced by using a W-Cu functionally graded material (W-Cu FGM) interlayer. However, there is still considerable stress at the joining interface between W and W-Cu FGM in the W/W-Cu FGM/Cu portions. In this work, we fabricate W skeletons with continuous gradients in porosity by a modified sedimentation method. Sintering densification behavior and pore characteristics of the sedimented W skeletons at different sintering temperatures were investigated. After Cu infiltration, the final W-Cu FGM was obtained. The results indicate that the pore size and porosity in the W skeleton decrease gradually with the increase of sintering temperature, but the increase of skeleton sintering temperature does not reduce the gradient range of composition distribution of the final prepared W-Cu FGM. And W-Cu FGM with composition distribution from pure W to W-20.5wt.% Cu layer across the section was successfully obtained. The thickness of the pure W layer is about one-fifth of the whole sample thickness. In addition, the prepared W-Cu FGM has a relative density of 94.5 % and thermal conductivity of 185 W/(m·K). The W-Cu FGM prepared in this work may provide a good solution to alleviate the thermal stress between W PFM and Cu heat sink in the fusion reactors.

• Korean Journal of Materials Research
• /
• v.22 no.12
• /
• pp.682-688
• /
• 2012

In this study we aimed to examine the co-doping effects of 1/6 mol% $Co_3O_4$ and 1/4 mol% $Cr_2O_3$ (Co:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and the grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Co,Cr-doped ZBS, ZBS(CoCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ were formed in all systems. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi = 1.0 by Cr rather than Co. A more homogeneous microstructure was obtained in all systems affected by ${\alpha}$-spinel. In ZBS(CoCr), the varistor characteristics were improved (non-linear coefficient, ${\alpha}$ = 20~63), and seemed to form ${Zn_i}^{{\cdot}{\cdot}}$(0.20 eV) and ${V_o}^{\cdot}$(0.33 eV) as dominant defects. From impedance and modulus spectroscopy, the grain boundaries were found to be composed of an electrically single barrier (0.94~1.1 eV) that is, however, somewhat sensitive to ambient oxygen with temperature. The phase development, densification, and microstructure were controlled by Cr rather than by Co but the electrical and grain boundary properties were controlled by Co rather than by Cr.

• Journal of the Korean Ceramic Society
• /
• v.41 no.12 s.271
• /
• pp.884-888
• /
• 2004

Effects of NiO were studied in aspects of dielectric properties and microstructure of $0.96(0.91Pb(Mg_{1/3}Nb_{2/3})O_3-0.09PbTiO_3)­0.04BaTiO_3$ (PMN-PT-BT, PBT). The PBT was prepared by a conventional mixed oxide method using $(MgCO_3)_4{\cdot}Mg(OH)_2$ instead of MgO through Lewis acid-base interaction. NiO was added in the range of 0.5 to $3.0\;wt\%$ as thermally decomposable $2NiCO_3{\cdot}3Ni(OH)_2$ and it seemed to enhance densification to a large extent below $1000^{\circ}C$. But all the systems gave rise to ceramics with almost same relative sintered density of 96% by sintering at $1000^{\circ}C$ for 2 h. But it turned out that the addition of NiO was detrimental to dielectric constant but beneficial to the loss of dielectric constant.

• Journal of the Korean Ceramic Society
• /
• v.30 no.5
• /
• pp.381-388
• /
• 1993

Due to the anisotropy of thermal expansion, LAS system which has low thermal expansion property is hard to obtain a dense sintered body. Therefore, the thermal expansion coefficient and the mechanical strength were decreased. In this study, mullite, which has good mechanical properties in high temperature and comparatively low thmeral expansion coefficient, was taken as a additive in LAS system. And then, sintering, thermal, and mechanical properties were investigated. The results are follows; When mullite is added in eucryptite composition (Li2O.Al2O3.2SiO2) of LAS system, the creation of liquid phase results in the densification of sintered body and the specimen sintered at 136$0^{\circ}C$ for 2 hours shows optimum sintering condition. With the addition of mullite in eucryptite composition, mechanical strength is increased by the control of grain growth. Especially, flexual strength of EM0 specimen was about double value than the basic composition. Thermal expansion coefficients of EM0 and EM15 specimens sintered at 136$0^{\circ}C$ were -8.23$\times$10-6/$^{\circ}C$ and -4.90$\times$10-6/$^{\circ}C$ in the temperature range of RT.~80$0^{\circ}C$. As the mullite content are increased, negative thermal expansion ratios are decreased.