Designing lutetium silicate environmental barrier coatings for silicon nitride and its recession behavior in steam jets

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.

Role of Mn and Co additives on the carbothermal nitridation of fly ash

Shunkichi Ueno,Hideki Kita,Tatsuki Ohji 한양대학교 세라믹연구소 2005 Journal of Ceramic Processing Research Vol.6 No.4

The effects of Mn and Co additives on the carbothermal nitridation of fly ash were examined at 1330, 1425 and 1475 oC in a N2 atmosphere under normal pressure. Above 1425 oC, the nitridation of fly ash occurred and oxy-nitride phases, such as β-type sialon, α-type sialon and X2N2O (X=C or Si) type oxy-nitride phases were formed. The phase ratio among these phases was changed with the amount of additives. In the case of a Mn additive, the a to b phase transformation of sialon was accelerated with the amount of the additive. On the other hand, in the case of a Co additive, no effective role on the transformation was observed. At 1475 oC, the ash completely changed to β-type sialon.

Comparison of water vapor corrosion behavior of silicon nitride with various EBC layers

Shunkichi Ueno,D. Doni Jayaseelan,Tatsuki Ohji 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.4

The water vapor corrosion resistance of silicon nitride ceramics with Lu2Si2O7, Yb2Si2O7 and ZrSiO4 environmental barrier coating (EBC) layers prepared by a reaction sintering method were examined at 1500 oC in a static state water vapor environment. The weights of these samples slightly increased during the corrosion test. The weight gain rates for Lu, Yb and zircon EBC samples were 2.218 × 10−6, 4.688 × 10−6 and 2.989 × 10−6 g/cm2·h, respectively. In the corrosion mechanism of Lu and Yb cases, the gas path through channels in the EBC layer were generated by the elimination of the boundary silica phase and then, the silicon nitride substrate was slightly oxidized. On the other hand, in the case of ZrSiO4, many cracks were introduced in the EBC layer during the corrosion test due to the difference in thermal expansion coefficient between the EBC layer and the substrate. However, the adhesion between the substrate and the EBC layer of ZrSiO4 was better than that of Lu and/or Yb EBC samples.

Comparison of water vapor corrosion mechanisms of polycrystalline and eutectic Lu2Si2O7

Shunkichi Ueno,D. Doni Jayaseelan,Tatsuki Ohji,Naoki Kondo,Shuzo Kanzaki 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.2

To clarify the water vapor corrosion mechanism of the Lu2Si2O7 system, a high temperature water vapor corrosion test was performed on two microstructurally different specimens namely, polycrystalline and eutectic. From the results, we address the problem of the application of the Lu2Si2O7 system for environmental barrier coatings (EBC) with regard to their microstructure. In the case of the polycrystalline sample, the boundaries were easily corroded and the silicon nitride substrate underwent oxidation. In the case of the eutectic sample, no weight change was observed during the corrosion test. However, a trace of corrosion and poly-crystallization was observed on the sample surface. An easy processing technique for forming an eutectic protective layer on silicon nitride ceramics is also proposed.

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.

Corrosion and oxidation behavior of ASiO4 (A=Ti, Zr and Hf) and silicon nitridewith an HfSiO4 environmental barrier coating

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.

Consideration of the Formation Mechanism of an Al2O3-HfO2 Eutectic Film on a SiC Substrate

Kyosuke Seya,Shunkichi Ueno,Toshiyuki Nishimura,Byung-Koog Jang 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.1

An Al2O3-HfO2 eutectic EBC film was prepared on a SiC substrate by using the electric furnace heating and the optical zone melting methods. All of Al2O3 phase disappeared during the heating step at a temperature below the melting point, and all of the HfO2 phase reacted with the carbon and boron, which are included in SiC bulk as sintering agents, during the heating step at a temperature below the melting point. The thermal decomposition of the SiC phase, the reduction reaction of Al2O3 phase, the vaporization of the Al2O3 component, the reduction reaction of HfO2 and the formation of the HfC phase occurred at a temperature below the melting point. However, a highly dense HfC phase was formed on the SiC substrate. A rapid heating process becomes possible by using the optical zone melting method. A solidified film that was composed of a highly dense HfC layer as the intermediate layer and the Al2O3-HfO2 eutectic structure layer as the top coat was obtained by using the optical zone melting method.

Characteristic evaluations of microwave absorbers using dielectric and magnetic composite materials

Young Joon An,Ken Nishida,Takashi Yamamoto,Shunkichi Ueda,Takeshi Deguchi 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.4

A microwave absorber for use in an electronic toll collection(ETC) device, having a central frequency of 5.8 GHz, is fabricated using a composite of magnetic (iron, Fe (coated by Fe3O4), made from Carbonyl Iron, Fe(CO)5) and dielectric (titanium oxide, TiO2) material. The reflection loss in free space, using a circularly polarized wave, was −20 dB or more around a central frequency of 5.8 GHz at incident angles of up to 60o, which satisfies the necessary conditions for ETC use in JAPAN. In this study, we explain the characteristic evaluations of microwave absorbers by changing the weight ratio of Fe/TiO2 composite materials (Fe/TiO2 = 100/0-0/100) and incidence characteristics of the transverse electric wave (TE wave), the transverse magnetic wave (TM wave) and the circularly polarized wave (CP wave) in a free-space without a characteristic deterioration. In addition, we show the experimental results by changing the arrangement of microwave absorber that also satisfied a necessary condition for ETC use. A microwave absorber for use in an electronic toll collection(ETC) device, having a central frequency of 5.8 GHz, is fabricated using a composite of magnetic (iron, Fe (coated by Fe3O4), made from Carbonyl Iron, Fe(CO)5) and dielectric (titanium oxide, TiO2) material. The reflection loss in free space, using a circularly polarized wave, was −20 dB or more around a central frequency of 5.8 GHz at incident angles of up to 60o, which satisfies the necessary conditions for ETC use in JAPAN. In this study, we explain the characteristic evaluations of microwave absorbers by changing the weight ratio of Fe/TiO2 composite materials (Fe/TiO2 = 100/0-0/100) and incidence characteristics of the transverse electric wave (TE wave), the transverse magnetic wave (TM wave) and the circularly polarized wave (CP wave) in a free-space without a characteristic deterioration. In addition, we show the experimental results by changing the arrangement of microwave absorber that also satisfied a necessary condition for ETC use.