Ultra-high Temperature Oxidation Research Articles

Ultrahigh-Temperature Oxidation of 4H-SiC(0001) and an Impact of Cooling Process on SiO<sub>2</sub>/SiC Interface Properties

This paper reviews our recent work on ultrahigh-temperature oxidation of 4H-SiC(0001) surfaces. Our rapid thermal oxidation experiments demonstrated the reaction-limited linear growth at temperatures ranging from 1200 to 1600°C. The Arrhenius plot of linear growth rate of thermal oxidation can be fitted by a linear line, and the activation energy of oxide growth in dry O2 oxidation was estimated to be 2.9 eV. We also found that unintentional oxidation during the cooling down process severely degrades SiO2/SiC interface properties, resulting in positive flatband voltage shift (VFB) and hysteresis in capacitance-voltage (C-V) characteristics regardless of oxidation temperature. By effectively suppressing oxide growth during the cooling process, we have clarified that SiO2/SiC interface properties depend on oxidation temperature and the lowest interface state density was obtained for the oxide formed at 1450°C.

Evaluation of the high temperature performance of HfB2 UHTC particulate filled Cf/C composites

AbstractRoom and high temperature flexural strength and coefficient of thermal expansion (CTE) of HfB2 ultra‐high temperature ceramic (UHTC) particulate filled Cf/C composites are determined along with UHT oxidation behavior. Both room and high temperature strength of the composites were found to be broadly comparable to those of other thermal protection system materials currently being investigated. The CTE of the composites was measured both along and perpendicular to the fiber direction up to 1700°C and the values were found to depend on fiber orientation by approximately a factor of 3. Arc‐jet testing of the UHTC composites highlighted the excellent ultra‐high temperature oxidation performance of these materials.

Impact of rapid cooling process in ultrahigh-temperature oxidation of 4H-SiC(0001)

We conducted a rapid water-quenching procedure with ultrahigh-temperature oxidation to avoid degradation of the high-quality SiO2/SiC interface formed by ultrahigh-temperature oxidation during the cooling process. A reduction in the interface state density was observed for the SiO2/4H-SiC(0001) interface formed by ultrahigh-temperature oxidation in dry O2 ambient using the water-quenching process, compared with other natural cooling processes. The oxidation temperature dependence of interface state density for the thermally grown SiO2/SiC structures formed using the water-quenching process revealed that degradation of the interface properties occurred not only during the cooling process but also during the continuous oxidation process at exceedingly high temperatures, above 1500 °C, in 100% dry O2 ambient at 1 atm.

Polyzirconosilane Preceramic Resin as Single Source Precursor of SiC–ZrC Ceramics

Novel polyzirconosilane resin, prepared by Wurtz–Fittig copolymerization, was applied as a single source precursor for SiC–ZrC ceramics preparation. It could be rheologically much easily tailored catering to the precursor-infiltration–pyrolysis process in the production of ceramic composites. Polyzirconosilane resin could be thermally cured at 110–200 °C to form a solidified monolith and finally transformed at 1000–1400 °C to SiC–ZrC monoliths at a yield of around 65 wt%. The polyzirconosilane derived SiC–ZrC exhibited ultra-high thermo-oxidation resistance up to 1200 °C. The polyzirconosilane preceramic resin was an ideal candidate for SiC–ZrC multi-component ceramic under ultra-high temperature oxidation conditions.

Ultra-high temperature oxidation of a hafnium carbide-based solid solution ceramic composite

Hafnium carbide-based solid solution ceramics with yttria additions were consolidated via hot pressing utilizing chromium carbide as a transient liquid sintering agent. Selected samples were oxidized at temperatures exceeding 2200°C under high velocity airflow to determine their potential for service in ultra-high temperature environments. Cross-sectional examination revealed a complex multi-layer scale comprising a highly porous exterior region, a dense multi-phase interior region, and an oxygen- and carbon-containing interlayer consisting of nanocrystalline graphite in an amorphous or nanocrystalline oxide matrix. Outward diffusion of mobile cations is speculated to play an important role in establishing the observed scale morphology.

Synthesis and structure–property relationships of a new family of layered carbides in Zr-Al(Si)-C and Hf-Al(Si)-C systems

Abstract The layered ternary and quaternary carbides in Zr-Al(Si)-C and Hf-Al(Si)-C systems with general formulae of ( T C) n Al 3 C 2 , ( T C) n Al 4 C 3 and (TC) n [Al(Si)] 4 C 3 (where T = Zr or Hf, n = 1, 2, 3…) have attracted increasing attentions due to their fascinating properties such as high specific stiffness, high strength and fracture toughness, refractory, machinability by electrical discharge method, thermal shock resistance, as well as high-temperature and ultrahigh-temperature oxidation resistance. The combination of these properties makes them promising as structural components or coatings for high- and ultrahigh-temperature applications. In this review, the progresses on processing, and structure–property relationships of the novel layered carbides are comprehensively outlined. The crystal structure characteristics are introduced first. Then, methods for processing powders and bulk samples are summarized. The third section focuses on the multi-scale structure–property relationships. Finally, the potential applications and further trends in tailoring the properties and developing low cost processing methods are highlighted.

A novel ultra-high temperature oxidation technique in flowing gas with controlled oxygen partial pressure

For the purpose of investigating ultra-high temperature oxidation, a novel induction heating facility has been established. The oxidation kinetics of several typical ultra-high temperature materials (UHTMs), including two graphite-based composites (C/C and ZrB2/C) and two ternary Zr-Al-C ceramics (Zr2Al3C4 and Zr2[Al(Si)]4C5), were tested by utilizing this facility. It has been identified that the tested cylindrical samples with dimensions of Φ 20 mm × 20 mm can be oxidized uniformly. The maximum temperature of 2450°C can be achieved on graphite-based composites, and the oxygen partial pressure can be controlled in the range of 102–105 Pa. This novel technique exhibits many advantages, such as an extremely high heating rate of about 20°C/s, easy controlling of temperature and gas pressure, low energy consumption, low cost, and high efficiency. Therefore, it provides a potential way for profoundly investigating the ultra-high temperature oxidation behaviors of UHTMs.

Formation mechanism of micro-arc oxidation coatings formed on ZrB 2–SiC ceramics

The uniform coatings were fabricated successfully on the surface of the ZrB 2–SiC ceramic through the micro-arc oxidation (MAO) technique in sodium aluminate solution. The results of XRD analysis of the MAO coatings were obvious to indicate that the predominant phases for the surface of the MAO coatings were α-Al 2O 3, t-ZrO 2 and m-ZrO 2. The contents of α-Al 2O 3 and t-ZrO 2 in the MAO coatings gradually decreased as the coating thickness decreased. The effect of the MAO coatings on the ultrahigh temperature oxidation resistance of the ZrB 2–SiC ceramic was investigated, indicating that the oxidation resistance of the ZrB 2–SiC ceramic with the MAO coatings was significantly improved from 1700 °C to at least 2000 °C compared with bare ZrB 2–SiC ceramic.

Ultrahigh-temperature oxidation of Zr 2Al 3C 4 via rapid induction heating

The oxidation behavior of Zr 2 Al 3 C 4 at 1600 and 1750 °C was studied by means of induction heating. The oxidation kinetics follows a linear law and the interfacial reaction between Zr 2 Al 3 C 4 and O 2 is the rate-limiting step for scale growth. The microstructure of oxide scales gradually changes from intragranular (small ZrO 2 particles embedded in large Al 2 O 3 grains) to an interpenetrating dual-phase form as the exposure time increases, which is ascribed to the temperature decay of the top scale surface with scale growth.

A technique for ultrahigh temperature oxidation studies of ZrB 2-SiC

A new oxidation method, high frequency induction heating, was introduced to investigate the rapid oxidation characteristics of ZrB 2-SiC at 1800 °C up to 50 min. A high temperature was achieved within 30 s by adjusting the current or voltage. According to the isothermal test at 1800 °C, the oxidation kinetics for the composite followed a para-linear law. The specific weight gains increased from 4.86 to 12.89 mg/cm 2 when the exposure time increased from 10 to 50 min. When exposure for 30 min, a thin outmost layer of SiO 2, a ZrO 2 layer and a thick SiC-depleted layer formed on the surface of specimens. The structural characteristic of oxidation layer obtained by high frequency induction heating was similar to those formed by standard oxidation furnace.

High temperature oxidation resistance coating on niobium

An ultrahigh temperature oxidation resistance MoSi2 coating on niobium substrate was prepared by a slurry sintering technique. The static antioxidation property was tested at 1600°C. The microstructure and phase composition of the coating were investigated by SEM, EDS, and XRD analysis. Results were correlated to the coating oxidation resistance. The results indicated that, when exposed to a high temperature oxidation atmosphere, the MoSi2 coatings oxidised selectively to form an oxide glass with a self healing function on the coating surface. Any impurities existing in the slurry deteriorated the integrity of the surface, and hence the antioxidation properties of the coating. A transitional layer formed by diffusion was found at the interface between the coating and the substrate.

Phase Constitution and Oxidation Resistance of B2 (Ir, Co)Al

ABSTRACTB2 iridium aluminide (IrAl) is hopeful for use as an ultrahigh temperature oxidation resistant coating above 1600K. In this study, the effect of Co substitution for Ir on phase constitution, hardness and oxidation behavior was studied for IrAl alloys. Alloys of (Ir, Co)-50mol%Al with various Co contents were fabricated by Ar-arc melting followed by hot-forging at 1773K. Oxidation behavior was evaluated using thermogravimetry (TG) in Ar-67%O2 up to 1823K. XRD and SEM were also carried out for alloy characterization. It was found that a continuous B2 solid solution (Ir,Co)Al is formed between IrAl and CoAl. Depending on the Co concentration, the oxidation products identified after heating to 1873K in Ar-67%O2 were Ir, IrO2 and A2O3 and/or Co2AlO4. Thin and continuous Al2O3 layers were observed after isothermal oxidation at 1673K when Co content is more than 20mol%Co. In this case, the weight change by isothermal oxidation at 1673K becomes higher with decreasing Co content. The (Ir,Co)Al alloys containing 20–40mol%Co exhibit higher oxidation resistance than CoAl and IrAl, and thus oxidation resistance of CoAl is improved by Ir addition.

超高温耐酸化性高強度Ｃ／Ｃ複合材の開発

超高温耐酸化性高強度Ｃ／Ｃ複合材の開発