용융 Al의 치환반응에 의한 $Al_2O_3/Al$ 복합체의 제조

정두화,김용진,배원태 한국세라믹학회 1997 한국세라믹학회지 Vol.34 No.6

Al2O3/Al composites were produced by displacement reaction method, which was carried out by immersing the sintered silica preform, which was prepared from fused silica powder, in molten aluminum. Because the molten aluminum did not penetrate into the silica preform with higher than 20% of porosity when the displacement reaction was accomplished at 100$0^{\circ}C$ for 10 hours in air atmosphere, the optimum range of sintering temperature of silica preform was from 135$0^{\circ}C$ to 140$0^{\circ}C$. The microstructure of this Al2O3/Al composites showed three-dimentionally co-continuous alumina, which provides wear resistance and high stiffness, and aluminium which acts as a toughnening phase. The grain size of the alumina in composites did not change with the particle size of the silica preform. The exact shape of the preform was retained and a net-shaped composite was produced. The representative Al2O3/Al composite prepared in this study showed 3.30mg/㎤ of bulk density, 350-430 MPa of flexural strength, 7.0 MPa.m1/2 of fracture toughness, and good machinability.

턴디쉬용 마그네시아질 댐블록의 제조와 그특성

정두화,김상모,이석근 한국세라믹학회 1999 한국세라믹학회지 Vol.36 No.8

In order to develop high performance basic dam block for tundish vessel in steel-making binders and additives on hydration and thermal characteristics of magnesiz castable refractories were studied. Crack initiation and propagation in cement bonded magnesia castables due to slaking of magnesia clinker at drying process were suppressed by using spinel clinker instead of magnesia powder. In case of Na2O$.$2CaO$.$P2O5(NC2P) bonded castable crack initiation due to slaking of magnesia clinker did not occur but bending strength at high temperature was low. Mechanical properties of NC2P bonded castable refractories at high temperature were improved by using magnesia clinker that contains low SiO2 contents.

Al$_2$O$_3$/Al 복합체 제조시 용융 알루미늄의 치환반응에 미치는 금속 마그네슘의 영향

정두화,배원태 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.1

전융실리카 분말로 소결하여 만든 sihca preform을 마그네슘이 함유된 용융 알루미늄에 침적시킨후 공기중에서 반응시켜 Al2O3/Al 복합체를 제조하였다. 복합체 제조시 반응온도의 변화에 대해 용융 알루미늄의 침투거동을 조사한 결과 3가지 영역, 즉 저온영역(75$0^{\circ}C$-85$0^{\circ}C$), 중온영역(90$0^{\circ}C$-95$0^{\circ}C$), 고온영역(100$0^{\circ}C$$\leq$)으로 구분되었다. 저온영역에서는 반응온도에 비례해서 침투속도가 증가하였으나, 중간온도 영역은 치환반응에 의해 생성된 알루미나의 상전이에 따른 영향으로 저온영역인 85$0^{\circ}C$에서보다 오히려 침투속도가 감소하였다. 고온영역중 100$0^{\circ}C$이상에서 침투가 일어나지 않는 것은 용융 알루미늄중의 마그네슘이 먼저 실리카와 반응하여 silica preform의 표면에 치밀한 스피넬층을 형성하기 때문으로 판명되었다. Al2O3/Al composites were produced by immersing the sintered silica preform in molten aluminum which contained magnesium as impurity. Three distinct regions existed in the penetration behavior of molten me-tal with changing the reaction temperature. These regions are denoted as low temperature regime(75$0^{\circ}C$-85$0^{\circ}C$) intermediate regime(90$0^{\circ}C$-95$0^{\circ}C$) and high temperature regime(100$0^{\circ}C$$\leq$) In the low temperature regime the penetration speed of molten aluminum increased with increasing reaction temperature whereas it decreased in the intermediate regime due to the phase transition of alumina formed by displacement reac-tion. In the high temperature regime the penetration speed of molten aluminum was the highest at 100$0^{\circ}C$ which was 3.6 mm/hr But above 105$0^{\circ}C$ molten aluminum did not penetrate into the silica preform because of the formation of a dense spinel layer at the preform surface by magnesium in molten Al.

$\alpha$-SiC 소결체의 특성에 미치는 소성조건의 영향

정두화,김인술,김효준 한국세라믹학회 1991 한국세라믹학회지 Vol.28 No.10

$\alpha$-SiC(B; 0.4 wt, C; 3 wt%) was sintered in Ar atmosphere from 205$0^{\circ}C$ to 220$0^{\circ}C$ by means of pressureless sintering and gas pressure sintering in order to find optimum sintering condition of $\alpha$-SiC. Mechanical properties and microstructures of sintered bodies were investigated according to sintering method. The effect of sintering condition on sinterability of $\alpha$-SiC was also examined by using the dilatometer. 97.5% and 98.8% of theoretical density were obtained from pressureless sintering and gas pressure sintering of $\alpha$-SiC powder, respectively. And modulus of rupture was measured as 270~350 MPa and 420 MPa respectively.

실리카 소결체와 용융 알루미늄과의 반응에 의한 $Al_2$O$_3$/Al 복합체의 제조

정두화,배원태 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.9

Al2O3/Al composites were produced by displacement reaction method which was carried out by imm-ersing the sintered silica preform which was prepared form fused silica powder in molten aluminu. an ac-tivation energy of 94kJ/mole was calculated from Al-SiO2 reaction data in 1000-130$0^{\circ}C$ temperature range With increase of reaction temperature the alumina particle in the Al2O3/Al composites produced with pur metal Al showed grain growth and the growth of alumina particle in Al2O3/Al composite produced by using of Mg contained Al alloy was inhibited. The flexural strength of Al2O3/Al composites produced at 100$0^{\circ}C$ showed the highest value as 393 MPa. Flexural strength of the composite fabricated at 85$0^{\circ}C$ showed higher deviation than that of the composite produced at above 100$0^{\circ}C$ Low flexural strength of the composite fa-bricated at 120$0^{\circ}C$ due to the growth of pore and alumina particle size. The hardness of composites de-pended on alumina content in Al2O3/Al composite decreased with increasing of aluminium content in case the same alumina content and increased with increasing of silicon content in composite.

전기 자동차 배터리를 이용한 ESS 구축

정두화(Doo-Hwa Jung),이용환(Yong-Hwan Lee) 한국정보기술학회 2015 Proceedings of KIIT Conference Vol.2015 No.6

Al$_2$O$_3$-SiC-C 내화물의 특성에 미치는 MgO의 첨가효과

조문규,정두화,이석근 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.2

The effects of MgO on the resistance to corrosion and oxidation of Al2O3-SiC-C refractory have been in-vestigated. The resistance to oxidation was improved as the amount of MgO increased. The resistance to corrosion was enhanced until 2 wt% MgO content but degraded over that content. From the dependence of temperatuer on the oxidation resistance oxidation was suppressed by the microstructural densification caused by spinel formation over 1200~130$0^{\circ}C$and the formation MgO-Al2O3-SiO2 liguid-phase over 130$0^{\circ}C$ The weight loss of specimens containing MgO with various purity at range of 95 to 99% and par-ticle size of -0.045 mm to -0.074 mm was examined. The oxidation resistance was not changed signficantly with the particle size and purity of MgO powders.

필터댐에 의한 강중 개재물 저감효과

조문규,이석근,정두화,남수희,이재우 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.2

A tube-type filter dam(or baffle with holes) for ferrous melt refining is applied to the tundish operation for molten steel having low carbon and ultra-low carbon. The changes in the total oxygen content insoluble aluminum content and the distribution of inclusion size in molten steel during tundish operation were in-vestigated at the pouring part strand and mold of tundish. Removal mechanism of inclusions is considered to be caused by buoyancy action of the filter dam better than filtration action and the size range of in-clusions filtrated by the filter dam was for 30-50$\mu\textrm{m}$. Decrease in deviation of inclusion content in molten steel was confirmed for appling the filter dam in comparison with using conventional dam and weir. Also the filter dam had the advantage of baffle with holes at lower part in the efficiency of inclusions removal.

Pitch Carbon의 내산화성 증진

황규홍,배원태,조명제,연상흠,정두화 경상대학교 생산기술연구소 2003 工學硏究院論文集 Vol.19 No.-

For improving the oxidation resistance of pitch carbon, anti-oxidant and graphite were incorporated with fused pitch and followed by palletizing by cooling and pulverizing. Oxidation resistances were evaluated by DTA-TG, weight loss in crucibles and in MgO castables. By increasing the softening point of pitch, the oxidation resistance could be increased. But due to relatively small increase it was not preferable to refractories. And by adding anti-oxidant powders such as Al and/or B_(4)C the oxidation resistances of pitch carbons could be increased than the increasement of softening point. But the oxidation resistance of pitch carbons could not exceed that of natural graphite. So in order to utilizing graphite which have high oxidation resistance but poor water resistance, graphite was impregnated in pitch and pulverized to pellet. Graphite containing pitch, especially containing Al and/or B_(4)C also in pitch, was excellent in oxidation resistance among all type of pitch. Finally pitch and graphite containing pitchs were incorporated in MgO castables by using surfactant and defloculant very well and shows very high oxidation and moisture resistances to utilizing MgO-C castables.

Processing of Vermiculite-Silica Composites with Prefer-Oriented Rod-Like Pores

엄정혜,김영욱,이승석,정두화 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.4

Vermiculite-silica composites with a layered structure were fabricated by adding cellulose fibers as a pore former and by a simple uniaxial pressing and subsequent sintering process. Three different combinations of additives were used and their effects on the compressive strength and thermal conductivity of the composites were investigated. Both compressive strengths (42-128 MPa) and thermal conductivities (0.75-1.48 W/m· K) in the direction perpendicular to the pressing direction (T) were higher than those (19-81 MPa and 0.32-1.04 W/m·K) in the direction parallel to the pressing direction (S) in all samples. The anisotropy in both properties was attributed to the microstructural anisotropy, which was caused by the layered structure developed in the composites.