• The Journal of Advanced Prosthodontics
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• v.12 no.3
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• pp.124-130
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• 2020

PURPOSE. The aim of this in vitro study was to evaluate the effect of sintering procedures on marginal discrepancies of fixed partial metal frameworks fabricated using different sintering-based computer-aided design and computer/aided manufacturing (CAD/CAM) techniques. MATERIALS AND METHODS. Forty resin die models of prepared premolar and molar abutment teeth were fabricated using a three-dimensional (3D) printer and divided into four groups (n = 10) according to the fabrication method of metal frameworks used: HM (via hard milling), SM (via soft metal milling), L25 (via direct metal laser melting [DMLM] with a 25 ㎛ layer thickness), and L50 (via direct DMLM with a 50 ㎛ layer thickness). After the metal frameworks were fabricated and cemented, five vertical marginal discrepancy measurements were recorded in each site (i.e., buccal, facing the pontic, lingual, and facing away from the pontic) of both abutment teeth under a stereomicroscope (×40). Data were statistically analyzed at a significance level of 0.05. RESULTS. No statistically significant differences (P>.05) were found among the four axial sites of metal frameworks fabricated by sintering-based CAD/CAM techniques. The HM and L25 groups showed significantly (P<.001) lower marginal discrepancy values than the SM and L50 groups. CONCLUSION. Marginal discrepancy in the sites facing the pontic was not influenced by the type of sintering procedure. All fabrication methods exhibited clinically acceptable results in terms of marginal discrepancies.

• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.16-23
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• 2009

The porous pellets were prepared from porphyry by slurry foaming method. The effect of sintering temperatures on pore structure of porous porphyry pellets with different extension ratio ($E_R$) was investigated by specific surface area, water absorption and porosity, which changed with sintering temperatures. When the sintering temperatures increased from $975^{\circ}C$ to $1075^{\circ}C$, specific surface area and water absorption of the all samples decreased. In case of the sample with an equal sintering temperature, $E_R=3.0$ pellets had little influence on pore structure compared to the $E_R=2.0$ pellets. As a results, it was shown by SEM that facilitated formation of micro pores at $E_R=2.0$ pellets shrunk increasingly after sintering process. At $E_R=3.0$ and sintering temperature at $1025^{\circ}C$, optimum conditions of the porous porphyry porous pellets was found. Also, Escherichia coli removal efficiency of the silver-containing porphoyry porous pellets was measured for the feasibility as a antibacterial media. The antibacterial activity of prepared silver-containing sample was maintained above 90% for 40 days.

• Korean Journal of Crystallography
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• v.3 no.1
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• pp.44-52
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• 1992

The effect of sintering atmosphere on the final properties and phase change of Ti (C, N) Cr3c2 ceramics was investigated. In the case of sintering in vacuum and N2 atmosphere, densely packed sintered body was obtained. In Ar atmosphere, however, densification was much decreased compared to sintering in vacuum and Na. XRD analysis showed that in vacuum atmosphere Cr3c2 phase was changed to Cr7c3 Phase whereas in N2 and Ar atmosphere phase change was not occurred. That is, for vacuum sintering, the formation of defects in Ti(C, N) structure occurred through de-nitridation process, and it promotes the diffusion of C in Cr3c2 and raises the densification effects. But in the case of N2 atmosphere, densification phenomenon was considered to be due to sintering mechanism that enabled formation of free carbon and removal of oxygen by free carbon and existence of carbon in the grain boundary.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.9
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• pp.561-565
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• 2014

Thermoelectric materials have been the topic of intensive research due to their unique dual capability of directly converting heat into electricity or electrical power into cooling or heating. Bismuth telluride ($Bi_2Te_3$) is the best-known commercially used thermoelectric material in the bulk form for cooling and power generation applications In this work we focus on the large scale synthesis of nanostructured undoped bulk nanostructured $Bi_2Te_3$ materials by employing a novel bottom-up solution-based chemical approach. Spark plasma sintering has been employed for compaction and sintering of $Bi_2Te_3$ nanopowders, resulting in relative density of $g{\cdot}cm^{-3}$ while preserving the nanostructure. The average grain size of the final compacts was obtained as 200 nm after sintering. An improved NS bulk undoped $Bi_2Te_3$ is achieved with sintered at $400^{\circ}C$ for 4 min holding time.

• Journal of Powder Materials
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• v.16 no.3
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• pp.223-230
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• 2009

The compaction response of $TiO_2$ nano powders with an addition of Ti powders prepared by magnetic pulsed compaction and subsequent sintering processes was investigated. All kinds of different bulk exhibited an average shrinkage of about 12% for different MPCed pressure and sintering temperature, which were approximately 50% lower than those fabricated by general process (20%) and a maximum density of around 92.7% was obtained for 0.8GPa MPCed pressure and $1400^{\circ}C$ sintering temperature. The addition of Ti powder induced an increase in the formability and hardness of the sintered $TiO_2$. But the lower densities were obtained on sintering with addition of over 10 (wt%) Ti powder due to generation of crack during sintering. Subsequently it was verified that the optimum compaction pressure in MPC and sintering temperature were 0.8GPa and $1400^{\circ}C$, respectively.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.502-508
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• 2020

This paper focuses on the electrical properties and stability against DC accelerated aging stress of ZnO-V₂O₅-MnO₂-Nb₂O₅-Bi₂O₃-Co₃O₄-Dy₂O₃ (ZVMNBCD) varistor ceramics sintered at 850 - 925 ℃. With the increase of sintering temperature, the average grain size increases from 4.4 to 11.8 mm, and the density of the sintered pellets decreases from 5.53 to 5.40 g/㎤ due to the volatility of V₂O₅, which has a low melting point. The breakdown field abruptly decreases from 8016 to 1,715 V/cm with the increase of the sintering temperature. The maximum non-ohmic coefficient (59) is obtained when the sample is sintered at 875 ℃. The samples sintered at below 900 ℃ exhibit a relatively low leakage current, less than 60 mA/㎠. The apparent dielectric constant increases due to the increase of the average grain size with the increase of the sintering temperature. The change tendency of dissipation factor at 1 kHz according to the sintering temperature coincides with the tendency of the leakage current. In terms of stability, the samples sintered at 900 ℃ exhibit both high non-ohmic coefficient (45) and excellent stability, 0.8% in 𝚫E_B/E_B and -0.7 % in 𝚫α/α after application of DC accelerated aging stress (0.85 E_B/85 ℃/24 h).

• Journal of Powder Materials
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• v.17 no.4
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• pp.289-294
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• 2010

For the aim of low-temperature co-fired ceramic microwave components, sintering behavior and microwave properties (dielectric constant ${\varepsilon}_r$, quality factor Q, and temperature coefficient of resonant frequency ${\tau}_f$) are investigated in $Bi_{18}O(Ca_{0.725}Zn_{0.275})_8Nb_{12}O_{65}$ [BCZN] ceramics with addition of $V_2O_5$. The specimens are prepared by conventional ceramic processing technique. As the main result, it is demonstrated that the additives ($V_2O_5$) show the effect of lowering of sintering temperature and improvement of microwave properties at the optimum additive content. The addition of 0.25 wt% $V_2O_5$ lowers the sintering temperature to $890^{\circ}C$ utilizing liquidphase sintering and show the microwave dielectric properties (dielectric constant ${\varepsilon}_r$ = 75, quality factor $Q{\times}f$ = 572 GHz, temperature coefficient of resonance frequency ${\tau}_f\;=\;-10\;ppm/^{\circ}C$). The estimated microwave dielectric properties with $V_2O_5$ addition (increase of ${\varepsilon}_r$, decrease of $Q{\times}f$, shift of ${\tau}_f$ to negative values) can be explained by the observed microstrucure (sintered density, abnormal grain structure) and possibly high-permittivity $Bi_{18}Zn_8Nb_{12}O_{65}$ (BZN) phase determined by X-ray diffraction.

• Journal of Powder Materials
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• v.24 no.2
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• pp.115-121
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• 2017

In this work, p-type Bi-Sb-Te alloys powders are prepared using gas atomization, a mass production powder preparation method involving rapid solidification. To study the effect of the sintering temperature on the microstructure and thermoelectric properties, gas-atomized powders are consolidated at different temperatures (623, 703, and 743 K) using spark plasma sintering. The crystal structures of the gas-atomized powders and sintered bulks are identified using an X-ray diffraction technique. Texture analysis by electron backscatter diffraction reveals that the grains are randomly oriented in the entire matrix, and no preferred orientation in any unique direction is observed. The hardness values decrease with increasing sintering temperature owing to a decrease in grain size. The conductivity increases gradually with increasing sintering temperature, whereas the Seebeck coefficient decreases owing to increases in the carrier mobility with grain size. The lowest thermal conductivity is obtained for the bulk sintered at a low temperature (603 K), mainly because of its fine-grained microstructure. A peak ZT of 1.06 is achieved for the sample sintered at 703 K owing to its moderate electrical conductivity and sustainable thermal conductivity.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.1
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• pp.17-22
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• 2004

In the present study, newly developed spark plasma sintering(SPS) technique was introduced to refine the grain size of ${\gamma}$-based TiAl intermetallic compounds. Ti-46Al-1.5Mo and Ti-46Al-1.5Mo-0.2C(at%) prealloyed powders were produced by mechanical milling(MM) in high-energy attritor. The mechanically milled powders were characterized by XRD and SEM for the microstructural evolution as a function of milling time. And then, the MMed powders were sintered by both spark plasma sintering and hot pressing in vacuum (HP). After the sintering process, MM-SPSed specimens were heat-treated in a vacuum furnace (SPS-VHT) and in the SPS equipment(MM-SPS) for microstructural control. It was found from microstrutural observation that the microstructure consisting of equiaxed ${\gamma}$-TiAl with a few hundred nanometer in average size and ${\alpha}_2-Ti_3Al$ particles were formed after both sintering processes. It was also revealed from hardness test and three-point bending test that the effect of grain refinement on the hardness and bending strength is much higher than that of carbon addition. The fully lamellar microstructures, which is less than $80{\mu}m$ in average grain size was obtained by SPS-VHT process, and the fully lamellar microstructure which is less than $100{\mu}m$ in average grain size was obtained by MM-SPS for a relatively shorter heat-treatment time.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.200-210
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• 2009

It is necessary to minimize the mismatch of sintering shrinkage between dielectric ceramic and Ni inner electrode layers for the purpose of developing the ultra high-capacity multi layered ceramic condenser(MLCC). Thus, low temperature sintering of dielectric $BaTiO_3$ ceramic should be precedently investigated. In this work, the influence of the milling condition on sintering behavior and electrical properties of $BaTiO_3$ ceramics was investigated in the $BaTiO_3$(BT)-Mg-Dy-Mn-Ba system with borosilicate glass as a sintering agent. As milling time increased, specific surface area(SSA) of the powder increased linearly, while both sinterability and dielectric property were found to be drastically decreased with an increasing SSA. It was also revealed that the sinterability of the excessively milled $BaTiO_3$ ceramics could be recovered by increasing Ba content, rather than increasing glass addition. These results suggest that the sintering behavior of $BaTiO_3$ ceramics under the high SSA was more strongly dependent on the transient liquid phase caused by Ba addition, than the liquid phase from additional glass.