$Al_2O_3-ZrO_2$ 복합체의 강도 및 열충격 저항의 향상에 관한 연구

황규홍,배원태,최명덕,오기동,김경운,김환,Hwang, K.H.,Bae, W.T.,Choi, M.D.,Oh, K.D.,Kim, K.U.,Kim, H. 한국세라믹학회 1988 한국세라믹학회지 Vol.25 No.3

$Y_2O_3$가 $thickapprox$1mol.% 고용된 정방정 지르코니아를 알루미나에 20vol.% 섞어 체조립에 의해 과립으로 만든 다음 여기에 알루미나에 단사정 지르코니아를 10 ~30 vol.%섞어 만든 과립을 15~30vol.%가 되도록 과립형태로 분산시켜 성형 및 소결함으로써 단사정 및 정방정 지르코니아의 분산영역이 서로 다른 불균질 조직의 $Al_2O_3-ZrO_2$복합체를 제조하여 강도 및 열충격 거동을 관찰하였다. 이러한 불균질 조직의 $Al_2O_3-ZrO_2$ 복합체는 분산 agglomerate 내의 낮은 소결밀도에 의한 기공의 존재, 단사정상에 의한 미세균열, 또 이에 따른 주위에의 압축응력 등이 복합적으로 작용하여 향상된 열충격 거동을 보여 주었다. The strength and thermal shock resistance of $Al_2O_3-ZrO_2$ composites have been studied. The tetragonal $ZrO_2$ powder containing 1 mol.% $Y_2O_3$ and monoclinic $ZrO_2$ powder were prepared by coprecipitation method and subsequently mixed with $Al_2O_3$ powder and granulated by sieving. Duplex composites were prepared by dry mixing matrix agglomerate with 15 to 30 vol.% of dispersion agglomerate, followed by pressing and sintering at 1$600^{\circ}C$ for1 hr. These $Al_2O_3-ZrO_2$ 2 composites having heterogeneous structure showed improved thermal shock behaviors because of the microcracking and pores in dispersed granules, and compressive stresses around dispersed granules resulting from $ZrO_2$ transformation.

이중조직을 갖는 Y-TZP/Y-TZP-$Al_2O_3$ 복합체의 열충격 거동

황규홍,김의훈,김환,Hwang, K.H.,Kim, E.H.,Kim, Hwan 한국세라믹학회 1992 한국세라믹학회지 Vol.29 No.4

Duplex composites such as Y-TZP/Y-TZP-20 wt.% Al2O3 and Y-TZP/Y-TZP- 40 wt.% Al2O3 were made by mixing the sieve-shaked granules followed by isostatic pressing and sintering at 150$0^{\circ}C$ for 1 hour. So Y-TZP became matrix region and Y-TZP-20 wt.% Al2O3 or Y-TZP-40 wt.% Al2O3 became dispersed regions. In these composites, propagating cracks due to thermal shock always run into the dispersed region because these regions act as compressive zone due to low thermal expansion than matrix region. So duplexes having dispersed regions of Y-TZP-40 wt.% Al2O3 showed higher retained strength after thermal shock than matrix only composites because crack propagations were stopped more or less in the dispersed region. But when crack propagations were much more easy than matrix like Y-TZP-20 wt.% Al2O3 region, retained strength was decreased than the matrix only composites despite of the low initial strength.

국산 지르콘사로부터 부분 안정화 지르코니아의 제조 및 그 응용에 관한 연구 I. 국산 지르콘사로부터 고순도 지르코니아 분말의 제조

김환,선우식,신건철,황규홍,Kim. H.,Sunwoo, S.,Shin, K.C.,Hwang, K.H. 한국세라믹학회 1987 한국세라믹학회지 Vol.24 No.2

ZrO2 powders having high purity were prepared from domestic zircon sand using the caustic fusion method and the soda ash sintering process. In the caustic fusion method, ZrO2 recovery was reached to 96% when 100/140 mesh zircon was reacted with NaOH at the NaOH/Zircon mole ratio 6 and at 650$^{\circ}C$ for 2 hours. And in the soda ash sintering process, ZrO2 was recovered to 88.5% when -325 mesh zircon was reacted with Na2CO3 at the Na2CO3/Zircon mole ratio 1.1 and 1050$^{\circ}C$ for 2 hours. In both cases, Zr component was extracted to ZrOCl2, subsequently crystallized to ZrOCl2$.$8H2O to increase the purity, and converted to ZrO2 by precipitation. And to increase the sinter ability of powder, Cl- ion was removed and strong agglomeration was avoided by methanol distribution of Zr(OH)4 precipitates.

국산 지르콘사를 이용한 부분 안정화 지르코니아의 제조 및 그 응용에 관한 연구 : II. 부분 안정화 지르코니아 소결체의 제조 및 그 특성

김환,선우식,강종봉,심규송,신건철,황규홍,Kim, H.,Sunwoo, S.,Kang, J.B.,Shim, K.S.,Shin, K.C.,Hwang, K.H. 한국세라믹학회 1988 한국세라믹학회지 Vol.25 No.2

The microstructural changes in partially stabilized MgO-ZrO2 alloys during heat treatment and mechanical properties of ZrO2(Y2O3)/Al2O3 systems have been studied. 9mol% MgO-ZrO2 powders were sintered at 1800$^{\circ}C$ for 4 hours and these specimens were aged at 1420$^{\circ}C$ and 1100$^{\circ}C$ secondly. These specimens have high thermal shock resistance and high toughness. The bend strength of Y-PSZ/Al2O3 composites conventially sintered were increased by HIP from 650MPa to 980MPa.

스피넬 결합 내화물에서의 부피 팽창 제어

황규홍,김종강,조명제,최정림,박정권 경상대학교 생산기술연구소 2001 工學硏究院論文集 Vol.1 No.-

To improve the mechanical and chemical properties of unfired A12O3-C refractories, which is widely used in metal line of steel-making ladle, MgO was added as a matrix powders and the degree of spinel formation was studied, Because the spinel was formed at the contact areas between A12O3 and MgO particles and the volume of in-situ formed spinel increased more abnormally at the side of A12O3 particles than MgO, A12O3 aggregates was more recommendable than MgO aggregates. So to compare the degree of spinel formation in the A12O3-MgO-C(AMC) refractories, two kinds of A12O3 aggregates was added in different content ratio and their effects on physical properties such as permanent volume expansion were examined. For A12O3 aggregates, low purity fused A12O3 (BFA) was more preferable than the high purity fused A12O3 (WFA) due to high density and the high degree of spinel formation. And corrosion resistance was increased with the amount of MgO added, and the finer the MgO powder, the better the residual expansion and minute structure formation was observed. But in case of a sudden increasement of spinel phase air gap would be appeared around aggregates and resulting crack showed deteriorative effect in anti-corrosion, so the appropriate quantity of MgO and it's grain size could be controlled for optimal residual expansion due to spinel formation and advancement of corrosion resistance by structural stability.

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.

Al의 산화를 이용한 반응소결 요업체의 제조

황규홍,박정환,윤태경,김의훈 국립경상대학교 공과대학 부설 첨단소재연구소 1993 尖端素材 Vol.3 No.-

The reaction-sintered alumina ceramics were fabricated using the oxidation of Al, and their properties were measured. Alumina ceramics of low dimensional changes were prepared from the Al₂O₃/Al powder mixtures using the volume expansion due to the oxidation of Al. Intensive milling process such as attrition milling was beneficial for homogeneous oxidation of Al. After isopressing at 50 to 400 MPa the specimens were oxidated at 800∼1200℃ for 8 hrs. During this process fine alumina grain was formed at the surface of Al and volume expansion was occured. Sintering was carried out at 1450 to 1600℃ for 3 hrs. The sintered density of 97% theoretical was achieved, but low contents of Al leads to relatively high shrinkage of about 8%. On the other hand Al₂O₃/AlMg powder compacts were easily densified at the relatively low sintering temperature of 1450℃. But relatively high shrinkage was obtained due to the spinel formation. So SiC was added to compensate the large shrinkage because the volume of SiC was much increased during the oxidation that near net shape product could be fabricated. But in the contrary to the Al₂O₃/Al composites, the sintered body of Al₂O₃/Al-Mg/SiC was consisted of alumina and spinel phases. And mullite was formed at the higher SiC contents.

Al_(2)O_(3)-MgO계 캐스터블 내화물의 내침식성 향상

전명곤,연상흠,양정훈,김재준,황규홍,정두화 慶尙大學校 經營行政大學院 2004 工學硏究院論文集 Vol.20 No.-

To improve the mechanical and chemical properties of unfired Al_(2)O_(3) castables which is widely used in metal line of steel-making ladle, the ρ-Al_(2)O_(3) and /or fine MgO was added as a matrix powders and the degree of spinel formation was studied. Because the spinel was formed at the contact areas between Al_(2)O_(3) and MgO particles and the volume of in-situ formed spinel increased more abnormally at the site of Al_(2)O_(3) particles than MgO side, Al_(2)O_(3) aggregates was more recommendable than MgO aggregates. And to compare the degree of spinel formation in the Al_(2)O_(3)-MgO castable refractories, ultrafine SiO_(2) and Al_(2)O_(3) powders were added and their effects on physical properties such as permanent volume expansion and cold crushing strength were examined. For ρ-Al_(2)O_(3) binder, it could be replaced the alumina cement so that the CaO content could be reduced, but low compressive strength and firing shrinkage inhibit it's application to castables. But MgO powders should be added and the finer the MgO powder, the better the residual expansion and in-situ Spinel formation was observed. And due to Spinel formation and dense microstructure, CA_(6) phase would not formed around alumina aggregates during corrosion so that the corrosion resistance was much more increased.