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Comparison of hot-corrosion behavior of Al2O3, Lu2O3 and their silicates
Shunkichi Ueno,Tatsuki Ohji,Hua-Tay Lin 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.3
The hot-corrosion behavior of Al2O3, Lu2O3, mullite and Lu2Si2O7 phases were examined at 1500 oC. In the case of Lu2O3, no phase change was observed and no anisotropical corrosion occurred. In the case of the Lu2Si2O7 phase, anisotropic corrosion was observed. The Lu2Si2O7 crystal grains were well sustained to the hot-corrosion, however, the sodium element diffused though the boundary phase and anomalous grain growth occurred. On the other hand, in the case of Al2O3, the grains at the bulk surface corroded anisotropically. The corroded grain had a characteristic morphology as terrace field. In the case of mullite, the surface of the bulk was decomposed to the Al2O3 phase and the silica component was completely removed from the bulk surface. The sodium ions diffused though the sample during the corrosion test. The hot-corrosion behavior of Al2O3, Lu2O3, mullite and Lu2Si2O7 phases were examined at 1500 oC. In the case of Lu2O3, no phase change was observed and no anisotropical corrosion occurred. In the case of the Lu2Si2O7 phase, anisotropic corrosion was observed. The Lu2Si2O7 crystal grains were well sustained to the hot-corrosion, however, the sodium element diffused though the boundary phase and anomalous grain growth occurred. On the other hand, in the case of Al2O3, the grains at the bulk surface corroded anisotropically. The corroded grain had a characteristic morphology as terrace field. In the case of mullite, the surface of the bulk was decomposed to the Al2O3 phase and the silica component was completely removed from the bulk surface. The sodium ions diffused though the sample during the corrosion test.
Shunkichi Ueno,Tatsuki Ohji,Hua-Tay Lin 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.1
To protect silicon nitride ceramics from water vapor corrosion and oxidation, a new multi-layered environmental barrier coating (EBC) system was developed. The EBC system consisted of a highly dense Lu2SiO5/Lu2Si2O7 binary phase layer and slightly porous Lu2SiO5/Lu2Si2O7 layer, which were coated by a sputtering and dipping technique, respectively. A steam jet exposure test was conducted at 1300 oC for 500 hours with 35 m/s water vapor velocity. Each grain of the dip-coated layer was peeled off from the surface during the test. Also, the highly dense sputter coated layer converted into a porous layer after the test.
이세훈,고재웅,박영조,김해두,Hua-Tay Lin,Paul Becher 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.4
Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, Lu2O3-SiO2 (US), La2O3-MgO (AM) and Y2O3-Al2O3 (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the La2O3-MgO system. Since the Lu2O3-SiO2 system has the highest melting temperature, full densification could not be achieved after sintering at 1950oC. However, the system had a reasonably high bending strength of 527 MPa at 1200oC in air and a high fracture toughness of 9.2 MPa·m1/2. The Y2O3-Al2O3 system had the highest room temperature bending strength of 1.2 GPa.
이새훈,조춘래,박영조,고재웅,김해두,Hua-Tay Lin,Paul Becher 한국세라믹학회 2013 한국세라믹학회지 Vol.50 No.3
The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain Lu2O3-SiO2 additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at 1850oC through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at 1950oC. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine Si3N4 particles after nitridation and sintering at and above 1600oC. The amount of residual SiO2 within the specimens was not strongly affected by adding fine Si powder because most of the SiO2layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and 8.0 MPa·m1/2, respectively.
Shunkichi Ueno,D. Doni Jayaseelan,Tatsuki Ohji,Hua-Tay Lin 한양대학교 세라믹연구소 2005 Journal of Ceramic Processing Research Vol.6 No.1
The oxidation and water vapor corrosion behavior of sintered HfSiO4, ZrSiO4, TiSiO4 compacts and high density HfSiO4 coated silicon nitride ceramics were examined at 1500 oC in a static state water vapor environment. The bulk weights of HfSiO4 and ZrSiO4 decreased after the water vapor corrosion test with a weight loss rate of 7.080 × 10−6 and 1.333 × 10−6 g/cm2·h, respectively. The weight of TiSiO4 remained unchanged within the experimental error after the corrosion test. A trace of corrosion was observed on the surface of grains of corrosion-tested compacts. On the other hand, the weight of high density HfSiO4 layer (Environmental Barrier Coating, EBC layer) coated silicon nitride specimens increased with a weight gain rate 1.495 × 10−6 g/cm2·h, which is attributed by the oxidation of the silicon nitride substrate.
Lee, Sea-Hoon,Cho, Chun-Rae,Park, Young-Jo,Ko, Jae-Woong,Kim, Hai-Doo,Lin, Hua-Tay,Becher, Paul The Korean Ceramic Society 2013 한국세라믹학회지 Vol.50 No.3
The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain $Lu_2O_3-SiO_2$ additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at $1850^{\circ}C$ through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at $1950^{\circ}C$. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine $Si_3N_4$ particles after nitridation and sintering at and above $1600^{\circ}C$. The amount of residual $SiO_2$ within the specimens was not strongly affected by adding fine Si powder because most of the $SiO_2$ layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and $8.0MPa{\cdot}m^{1/2}$, respectively.
Lee, Sea-Hoon,Ko, Jae-Woong,Park, Young-Jo,Kim, Hai-Doo,Lin, Hua-Tay,Becher, Paul The Korean Ceramic Society 2012 한국세라믹학회지 Vol.49 No.4
Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, $Lu_2O_3-SiO_2$ (US), $La_2O_3$-MgO (AM) and $Y_2O_3-Al_2O_3$ (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the $La_2O_3$-MgO system. Since the $Lu_2O_3-SiO_2$ system has the highest melting temperature, full densification could not be achieved after sintering at $1950^{\circ}C$. However, the system had a reasonably high bending strength of 527 MPa at $1200^{\circ}C$ in air and a high fracture toughness of 9.2 $MPa{\cdot}m^{1/2}$. The $Y_2O_3-Al_2O_3$ system had the highest room temperature bending strength of 1.2 GPa.