• Journal of the Korean Ceramic Society
• /
• v.31 no.9
• /
• pp.1069-1075
• /
• 1994

When ceramics are used as the parts of an engine and a machine, the tribological properties are very important. For the preparation of the resistance material for wear applications by the method of Reaction-Bonded Sintering, metal silicon and carbon black are mixed up into SiC powder, and Al2O3 and Fe2O3 are put as an additive. As the general properties, the bending strength and water absortion are measured in the normal temperature and the phase changies are investigated with XRD. The property of the resistance for wear applications is measured with the amount of friction and wear, friction coefficient and maximum asperties. And, the surface of wear is observed with SEM. With the results of this study, the optimal mol ratio of Si : C and the suitable quantity of the mixture of SiC are 7 : 3 and 40 wt%, respectively. In the case of the addition of Al2O3 (2 wt%), the resistance for friction and wear applications is prominent. The bending strength showed the highest peak when Al2O3 (4 wt%) and Fe2O3 (4 wt%) were added. The properties of friction and wear were related with the propagation velocity of crack rather than the bending strength.

• Journal of the Korean Ceramic Society
• /
• v.25 no.3
• /
• pp.261-267
• /
• 1988

$\beta$-Sialon powder was prepared by the reduction-nitridation reaction from the mixture of Wando Pyrophyllite and carbon black at 135$0^{\circ}C$ in $N_2$ atmosphere. $\beta$-SiC powder was added to the prepared $\beta$-Sialon powder to make $\beta$-Sialon-SiC composite. The $\beta$-Sialon-SiC composites were sintered pressurelessly at 175$0^{\circ}C$ for 2h, using $Y_2O_3$ and $ZrO_2$(monoclinic) as sintering aids. Comparatively higher values of the fracture toughness (3.8 MN/㎥/2), M.O.R. (470 MN/$m^2$) and vickers microhardness (13.7 MN/$m^2$) were obtained when 10 wt% $Y_2O_3$ was added as a sintering aid. The improved fracture toughness and M.O.R. are assumed to be the results of crack deflection and crack branching by the second phase SiC particles.

• Journal of Korea Foundry Society
• /
• v.19 no.6
• /
• pp.493-500
• /
• 1999

Squeeze casting was used for fabricating a light metal base composite having high strength and wearresistance. Reactive sintering was used to prepare the preform of Squeeze casting. To utilize Fe-Al intermetallic compounds and SiC particle as a reinforcement, there needs to prepare Fe-Al mixed powder at 50, 60, 70at.%Al, and add SiC powder to the above mixture at 4, 7, 16, 24wt.%. The prepared mixture with SiC was reactive sintered in a tube furnace at $660^{\circ}C$ to get a porous hybrid preform of intermetallic compound and SiC. The preform prepared above was placed in a metal mold, preheated at $660^{\circ}C$ AC4C matrix was injected into the mold with the temperature of the melt at $610^{\circ}C$ After these processes, 66MPa was applied to the mold for 5 minute to finish the whole procedure. The maximum reaction temperature was increased with the increased Al amount, but decreased with the increased SiC amount. The density of the preform was decreased with SiC amount increase in the compacts due to swelling of the preform. An optical microscope was applied to observe the micro structure and the dispersion of the reinforcements. To analyze phases, We utilized XRD, EDS. Hardness test were chosen to get the information of mechanical properties. There were no significant changes in micro structure between the composite and preform. However, it was shown that uniform dispersion of the reinforcers and complete infiltration of the melt into the preform were achieved through the procedure of the squeeze casting. It was observed that the hardness of the composite is decreased with increased SiC amount, resulting from the volumetric expansion of the preform.

• Korean Journal of Materials Research
• /
• v.9 no.8
• /
• pp.817-824
• /
• 1999

The $Al_2$$O_3$-SiC composite powder was prepared by Self-propagating High-Temperature Synthesis(SHS) process using $SiO_2$Al and C powders as raw material. The effects of the molar ratio in raw material, compaction pressure, initial temperature of reactants on the products and combustion process were studied. Self-propagating high temperature synthesis of $SiO_2$/Al/C system should be preheated above $400^{\circ}C$ owing to the low combustion temperature. As the result of the combustion reaction, the purity of final product became better than that of reactants. In this system, the optimum molar ratio of $SiO_2$:Al:C was 3.0:4.0:6.0. The free carbon was removed by roasting at $650^{\circ}C$ for 30min. In this study, pressureless sintering was very dffective both for controlling the disintegration of specimen with powder bed and for obtaining dense sintered-body at $1700^{\circ}C$. The sintered-body produced with hot-pressing was about 98% of the theoretical relative density.

• Journal of the Korean Society of Industry Convergence
• /
• v.27 no.2_2
• /
• pp.397-402
• /
• 2024

Silicon carbide materials undergo an oxidation reaction in a high-temperature oxidizing environment and show different characteristics depending on the test temperature and time. In particular, the added oxides form a secondary phase within the sintering process and exhibit different oxidation characteristics depending on the added sintering materials. Therefore, to evaluate the oxidation characteristics, the weight of the test piece and the thickness of the oxidation layer were observed, and the structure and oxidation characteristics of the material were analyzed using SEM. SEM observation showed that an oxide layer was formed on the surface of the liquid sintered silicon carbide material after it was oxidized at 1200 ℃, 1300 ℃, and 1400 ℃ for 10 hours, respectively. Then, a bending test was performed at each temperature on the test piece with the oxidation layer formed to evaluate the change in flexural strength. The strength was 466.6 MPa at 1200 ℃, 363.1 MPa at 1300 ℃, and 350.8 MPa at 1400 ℃. Al₂O₃-SiO₂ oxidized at 1200 ℃ for 10 hours showed an increase in strength of about 21.0 MPa compared to the data before the oxidation test.

• Journal of the Korean Ceramic Society
• /
• v.23 no.5
• /
• pp.67-74
• /
• 1986

To investigate the effects of unreacted silicon on the $\alpha$/$\beta$transfornation variation of morphology and mechanical strength of Sintered Reaction Bonded Silicon Nitride the mixtures of $\alpha$-$Si_3N_4$ and Si powder and Reaction Bonded Silicon Nitride were heat treated. The heat-treatments were performed in Ar atmosphere in order to inhibit the nitridation of silicon. In the mixtures heat-trated at 1$700^{\circ}C$ the amount of $\beta$-TEX>$Si_3N_4$transformed from $\alpha$-TEX>$Si_3N_4$was sigmoidally increased and the equiaxed $\alpha$-TEX>$Si_3N_4$grains elongated with the amount of silicon and heat treating time. And large $\beta$-TEX>$Si_3N_4$grains grown into silicon were observed. On the other hand there was no change in the heat-treatment of pure $\alpha$-TEX>$Si_3N_4$In case of the heat-treatment of RBSN the same phenomena due to the silicon appearing from the decomposition of $\alpha$-Smatte and needle were observed. From the three point bending test the strength of the sintered specimens with the and without 5wt% silicon addition had 53Kg/$mm^2$ and 73Kg/$mm^2$ respectively.

• Journal of the Korean Ceramic Society
• /
• v.26 no.4
• /
• pp.583-587
• /
• 1989

Various $\alpha$-silicon carbied and colloidal graphite particles were sintered at 155$0^{\circ}C$ in vacuum atmosphere by reaction bonding sintering method, and the physical properties and microstructural analysis of specimen were investigated. With decreasing particle size, sintered density and 3-point bending strength of materials were increased and 3.2${\mu}{\textrm}{m}$ specimen showed high density and strength, 3.05g/㎤, 40kg/$\textrm{mm}^2$, respectively. The results of X-ray diffractometer and optical micrographs analysis showed that graphite and silicon melt reacted to convert to fine $\beta$-SiC particle and the body was changed to dense material.

• Korean Journal of Materials Research
• /
• v.9 no.12
• /
• pp.1170-1175
• /
• 1999

The microstructures and mechanical properties of $Si_3N_4$ ceramics produced by nitridation and post-sintering using semiconductor-waste-Si sludge were investigated. Lots of microcracks were observed in the waste-Si powders which contained some amounts of amorphous $SiO_2$. The nitridation rate of waste-Si compacts showed lower value than that of commercial Si powder compacts. The nitridation rate was increased with increasing nitridation temperature and then the percent of nitridation at 1470$^{\circ}C$ showed 98%. The phases of $Si_3N_4$ in the reaction-bonded bodies were mixed with ${\alpha}$ and ${\beta}$-type, and small amounts of $Si_2N_2O$ phase while those after post-sintering were ${\beta}$-$Si_3N_4$ and ${\alpha}$-Sialon. The sample post-sintered at 1950$^{\circ}C$ showed the fracture toughness of 5.6 $^MPa{\cdot}m^{1/2}$ and the fracture strength of 497 MPa which were lower than those of sintered body using commercial Si powder possibly due to the formation of ${\alpha}$-Sialon phase.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.05a
• /
• pp.15-15
• /
• 2011

As you know, boron compounds, borax ($Na_2B_4O_5(OH)_4{\cdot}8H_2O$) etc. were known thousands of years ago. As for natural boron, it has two naturally occurring and stable isotopes, boron 11 ($^{11}B$) and boron 10 ($^{10}B$). The neutron absorption $^{10}B$ is included about 19~20% with 80~81% $^{11}B$. Boron is similar to carbon in its capability to form stable covalently bonded molecular networks. The mass difference results in a wide range of ${\beta}$ values between the $^{11}B$ and $^{10}B$. The $^{10}B$ isotope, stable with 5 neutrons is excellent at capturing thermal neutrons. For example, it is possible to decrease a thermal neutron required for the nuclear reaction of uranium 235 ($^{235}U$). If $^{10}B$ absorbs a neutron ($^1n$), it will change to $^7Li+^1{\alpha}$ (${\alpha}$ ray, like $^4He$) with prompt ${\gamma}$ ray from $^{11}B$ $^{11}B$ (equation 1). $$^{10}B+^1n\;{\rightarrow}\;^{11}B\;{\rightarrow}\; prompt \;{\gamma}\;ray (478 keV), \;^7Li+4{\alpha}\;(4He)\;\;\;\;{\cdots}\; (1)$$ If about 1% boron is added to stainless steel, it is known that a neutron shielding effect will be 3 times the boron free steel. Enriched boron or $^{10}B$ is used in both radiation shielding and in boron neutron capture therapy. Then, $^{10}B$ is used for reactivity control and in emergency shutdown systems in nuclear reactors. Furthermore, boron carbide, $B_4C$, is used as the charge of a nuclear fission reaction control rod material and neutron cover material for nuclear reactors. The $B_4C$ powder of natural B composition is used as a charge of a control material of a boiling water reactor (BWR) which occupies commercial power reactors in nuclear power generation. The $B_4C$ sintered body which adjusted $^{10}B$ concentration is used as a charge of a control material of the fast breeder reactor (FBR) currently developed aiming at establishment of a nuclear fuel cycle. In this study for new boron compound, silicon boride ceramics for capturing thermal neutrons, preparation and characterization of both silicon tetraboride ($SiB_4$) and silicon hexaboride ($SiB_6$) and ceramics produced by sintering were investigated in order to determine the suitability of this material for nuclear power generation. The relative density increased with increasing sintering temperature. With a sintering temperature of 1,923 K, a sintered body having a relative density of more than 99% was obtained. The Vickers hardness increased with increasing sintering temperature. The best result was a Vickers hardness of 28 GPa for the $SiB_6$ sintered at 1,923K for 1 h. The high temperature Vickers hardness of the $SiB_6$ sintered body changed from 28 to 12 GPa in the temperature range of room temperature to 1,273 K. The thermal conductivity of the SiB6 sintered body changed from 9.1 to 2.4 W/mK in the range of room temperature to 1,273 K.

• Journal of the Korean Ceramic Society
• /
• v.35 no.7
• /
• pp.706-714
• /
• 1998

The MgO-{{{{ { {Al }_{2 }O }_{3 } }}-{{{{ { {SiO }_{2 } }_{ } }}system containing alumina powder was fabricated sintered at various temperature and analyzed in order to study the sintering mechanism and crystallization characteristics. The specimen composed of glass powder with average particle size of 8.27 $\mu\textrm{m}$ and 0-40 vol% alumina powder were sint-ered for 3 hrs at the temperature between 850$^{\circ}C$ and 1350$^{\circ}C$ The sintering mechanism consists of the redis-tribution of particles occuring at 750$^{\circ}C$ and the viscous flow at 850∼950$^{\circ}C$. The degree of crystallization and sintering temperatue were dependent upon the ratio of glass/alumina. The second phase from the reaction between glass and alumina was not observed which was confirmed by XRD and properties analysis. The density dielectric constant and specific resistivity of specimen were 2.30∼3.26g/cm2 5.8∼7.38 at 1 GHz density dielectric constant and specific resistivity of specimen were 2.30∼3.26g/cm3 5.8∼7.38 at 1GHz and 1.23∼4.70${\times}$107 $\Omega$$.$m respectively.