• Journal of the Korean Ceramic Society
• /
• v.40 no.5
• /
• pp.481-487
• /
• 2003

A technique for determination of proportions of char, coal ana coke is needed in order to monitor pulverized coal injection performance in operating blast furnace. Quantitative X-ray powder diffraction analysis can be applied to the problem providing that structural information on carbonaceous materials, coal, char, coke and their mixture are known. Chars were prepared from a coal at different temperatures (1000∼1400$^{\circ}C$) and were characterised by X-Ray powder Diffraction (XRD). The XRD result gave crystallite size (height Lc and diameter, La), aromaticity, number of (002) plane in carbon, and d-spacing. As a result, with increasing heat treat temperature of char, Lc$_{(002)}$, La$_{(10)}$ and number of (002) plane in carbon were increased, and d-spacing and FWHM(Full With Half Maximum) were decreased. Result of prediction of amount of char from the mixtures (char, coke and ore) based on the Lc$_{(002)}$ information of two mixtures (coke and char) showed very close values expected.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.11
• /
• pp.975-982
• /
• 2010

In this study, the laser sintering of inkjet-printed silver lines was evaluated. Silver-nanoparticle ink and a drop-ondemand (DOD) inkjet printer were used for printing on glass and polyethylene terephthalate (PET) substrates with various thicknesses. To sinter the printed silver nanoparticles, the silver layer printed on the transparent substrates was irradiated by focused CW laser beams that were incident normal to the substrates; the irradiation was carried out for various beam intensities and for various irradiation times. The electrical conductivity of the laser-sintered silver patterns was measured and compared with the conductivity of silver patterns sintered by using an oven. The increase in the temperature caused by laser irradiation was also calculated on the basis of the laser beam intensity, irradiation time, surface reflectivity, and thermophysical property of the substrate in order to estimate the increase in the electrical conductivity caused by laser sintering.

• Journal of the Korean Ceramic Society
• /
• v.45 no.2
• /
• pp.94-98
• /
• 2008

Silicon nitride($Si_3N_4)$ is one of the most widely used structural ceramic materials. However silicon nitride is difficult to sinter because of its strong covalent bonding characteristics. In this study, $Si_3N_4$ ceramics were fabricated by spark plasma sintering process with $Y_2O_3$ and $Al_2O_3$ addition to improve the sinterability and the mechanical properties and their phase transformation behavior, microstructure and mechanical properties were evaluated. Fully densified $Si_3N_4$ ceramics could be obtained by spark plasma sintering process at a lower temperature than conventional sintering method. The formation of network microstructure was affected by the addition of $Al_2O_3$ because it could accelerate a to ${\alpha}$ to ${\beta}$ phase transformation of $Si_3N_4$. As a result, the mechanical properties depended on amounts of $Al_2O_3$ addition. The hardness value increased with increasing ${\alpha}$-phase fraction, but fracture toughness value increase with increasing ${\beta}$-phase fraction.

• Journal of the Korean Ceramic Society
• /
• v.23 no.6
• /
• pp.37-44
• /
• 1986

Yttria-antimonia-stabilized zirconia was investigated with respect to the amount of $Sb_2O_3$ addition in the range of 0.5~5mole% to the base composition of $(ZrO)_{0.92}(Y_2O_3)_{0.08}$ The sinterbility modulus of rupture Vickers hardness evaporation of components phase form-tion and mcicrostructure were evaluated with antimonia content. Also two probe A. C conductivity measurement was subjected to all specimens and the best results are achieved with 1mol% $Sb_2O_3$ as a sinter agent and relative density of~98% obtained at 140$0^{\circ}C$ and this composition has a maximum electrical conductivity due to the possible substition of $Sb^{3+}$ for $Zr^{4+}$ site. The effect of $Sb_2O_3$ on the electrical conductivity of th bulk and the grain boundaries has on investigated using frequency dispersion analysis (5~106 Hz) Antimonia addition has a negative in-fluence on both the bulk and the grain boundary conductivity except for a 1 mon% addition. The additive antimonia has improve a modulus of rupture to 60~MPa due to metastable-tetragonal phase apparence and decrease the hardness with increasing the $Sb_2O_3$ content.

• Journal of the Korean Ceramic Society
• /
• v.19 no.3
• /
• pp.179-186
• /
• 1982

This research is to aim at the study of sintering mechanism through the observation of microstructure by scanning electron microscopy, after the mixture of 30wt% $Al_2O_3$ (White Alundum) powder is fired in air at the temperature range of 1350~150$0^{\circ}C$ in order to sinter $Al_2O_3$-Al through the oxidation of Al powder. The results obtained in this experiment are as follows: 1. While the compressive strength of $Al_2O_3$(WA) body fired at $1450^{\circ}C$ for 5hrs in air is 150kg/$\textrm{cm}^2$, that of Al-$Al_2O_3$ body fired at 135$0^{\circ}C$, $1400^{\circ}C$ for 5hrs in air is 1100kg/$\textrm{cm}^2$, 1600kg/$\textrm{cm}^2$ respectively, and the higher the firing temperature, the more the compressive strength increases. These results from the sintering effect between $Al_2O_3$(WA) grains and surrounding Al-oxidation layer. 2. While the compressive strength of Al2O3(WA) body fired at 150$0^{\circ}C$ for 5hrs in air is 250kg/$\textrm{cm}^2$, the compressive strength of Al-$Al_2O_3$body fired under the same condition is 2050kg/$\textrm{cm}^2$ and water absorption 9.0%, porosity 23.3%, bulk density 2.60gr/$cm^3$. It is assumed that these results come from not only the grain growth of oxidized Al grains but also the increase of bonding strength between $Al_2O_3$(WA) grains.

• Journal of the Korean Ceramic Society
• /
• v.43 no.6 s.289
• /
• pp.338-343
• /
• 2006

The effects of lead-borosilicate glass frits on the sintering behavior and microwave dielectric properties of ceramic-glass composites were investigated as functions of glass composition of glass addition ($10{\sim}50vol%$), softening point (Ts) of the glass, and sintering temperature of the composites ($500{\sim}900^{\circ}C$ for 2 h). The addition of 50 vol% glass ensured successful sintering below $900^{\circ}C$. Sintering characteristics of the composites were well described in terms of Ts. PbO addition in to the glass enhanced the reaction with $Al_{2}O_3$ to form liquid phase and $PbAl_{2}Si_{2}O_8$, which was responsible to lower Ts. Dielectric constant(${\epsilon}_r$), $Q{\times}f_0$ and temperature coefficient of resonant frequency (${\tau}_f$) of the composite with 50 vol% glass contents ($B_{2}O_{3}:PbO:SiO_{2}:CaO:Al_{2}O_3$ = 5:40:45:5:5) demonstrated 8.5, 6,000 GHz, $-70\;ppm/^{\circ}C$, respectively, which is applicable to substrate requiring a low dielectric constant. When the same glass composition was applied sinter $MgTiO_3\;and\;TiO_2,\;at\;900^{\circ}C$ (50 vol% glass in total), the properties were 23.8, 4,000 GHz, $-65ppm/^{\circ}C$ and 31.1, 2,500 GHz, $+80ppm/^{\circ}C$ respectively, which is applicable to filter requiring an intermidiate dielectric constant.

• Journal of the Korean Ceramic Society
• /
• v.46 no.6
• /
• pp.602-608
• /
• 2009

The yield is increasing as the manufacturing technology of ceramics progresses, however, there are many ceramics of poor quality due to variables upon producing ceramics. Some of those waste ceramics are recycled by sanitary ware or tile manufacturers, but most of them are filled in making environmental problem. Therefore, a research begins to recycle waste ceramic ware as alternative to some imported ceramic ware materials and to reduce environmental pollution. This study, succeeding last study which applied waste white ware as ceramic body material, aimed to solve problems of environment and materials by recycling waste ceradon generated in specially formed areas for ceramic in Gyeonggi-do such as Icheon, Yeoju and Gwangju as the ceramic body material. Consequently, the addition of waste ceramic ware into the ceramic body was judged to have limit up to 30% according to plasticity measurement. As we added shredded waste ceramic ware as much as 30% into basic ceramic body and checked its features, the pore rate and absorption rate were good to be average 4% and 3% respectively. In addition, it showed strength more than 720 kgf/$cm^2$ which is higher than existing ceradon body on the market with good sinter state; so it is judged to be available or developed as new ceramic body.

• The Journal of Advanced Prosthodontics
• /
• v.9 no.4
• /
• pp.308-314
• /
• 2017

PURPOSE. The purpose of this study was to analyze the retention force changes and wear behaviours of double-crown systems over long-term use. MATERIALS AND METHODS. Ten groups, each consisting of six samples, were evaluated. Specifically, casting gold alloy primary crown - casting gold alloy secondary crown (AA), laser sintering primary crown - laser sintering secondary crown (LL), casting Cr alloy primary crown - casting Cr alloy secondary crown, (CC) zirconia primary crown - electroformed secondary crown (ZA), and CAD/CAM titanium alloy primary crown - CAD/CAM titanium alloy secondary crown (TT) groups were evaluated at cone angles of $4^{\circ}$ and $6^{\circ}$. The samples were subjected to 5,000 insertion-separation cycles in artificial saliva, and the retention forces were measured every 500 cycles. The wear levels were analyzed via SEM at the beginning and end of the 5,000 cycles. RESULTS. In all samples, the retention forces increased when the conus angle decreased. The highest initial and final retention force values were found in the $LL-4^{\circ}$ group (32.89 N-32.65 N), and the lowest retention force values were found in the $ZA6^{\circ}$ group (5.41 N-6.27 N). The ZA groups' samples showed the least change in the retention force, and no wear was observed. In the other groups, wear was observed mostly in the primary crowns. CONCLUSION. More predictable, clinically relevant, and less excursive retention forces can be observed in the ZA groups. The retention force values of the LL groups were statically similar to those of the other groups, except the ZA groups.

• Korean Journal of Materials Research
• /
• v.9 no.5
• /
• pp.520-527
• /
• 1999

As a new approache(extrusion-sintering process) to fabricate the thermoelectric materials, it has been at tempted to extrude and sinter the powders simultaneously. It was possible to produce the highly dense <$(Bi,Sb)_2(Te,Se)_3$-based thermoelectrics with sound surface appearances and microstructures by adjusting the process variables. For the p-type materials, the Seeback coefficient was increased with the amount of Te dopants, and the thermoelectric figure of merit appeared to be $2.5\times10^{-3}/K$ at room temperature when doped with 3 at % Te. The n-type specimen doped with 0.16 mol% $SbI_3$ showed the thermoelectric figure of merit of $1.8\times10^{-3}/K$. In both p-type an 우-type materials, the carrier mobility an the thermoelectric figure of merit parallel to the extrusion direction were higher than those perpendicular to it.

• Journal of Sensor Science and Technology
• /
• v.6 no.6
• /
• pp.491-499
• /
• 1997

We fabricated the ceramic PLT tablet which was composed of 5, 10 and 15 mol% lanthanum concentration and thin film PLT to develope pyroelectric materials, and investigated their characteristics. Using TG/DTA, we determined calcination and sintering temperature to sinter the PLT completely and to prevent volatilization of the Pb components. The calcination and sintering temperature were $850^{\circ}C$, $1150^{\circ}C$ respectively, and there was a lot of mass loss at higher sintering temperature. By measuring temperature-dielectric constant characteristics of ceramic tablet we investigated dielectric constant characteristics depends on La concentration. The Curie point of PLT with 5, 10 and 15 mol% lanthanum concentration were $330^{\circ}C$, $269^{\circ}C$ and $210^{\circ}C$ respectively. Using PLT ceramic tablet we observed IR detection characteristics, and then deposited PLT thin film by rf magnetron sputtering. We verified that PLT thin film fabricated with completely sintered PLT target had the same structure to target by investigating lattice constant and optical transparency.