Figure 1 - available from: Oxidation of Metals
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Microstructure of the as-hot-pressed ZrB2–SiC composites, showing the ZrB2 phase (light) and SiC (black) phase: a for ZS10 and b for ZS30
Source publication
The oxidation behavior of ZrB2–SiC composites in air was studied at 1650 °C. Diffusion-controlled oxidation kinetics were found for the composites studied. A parabolic rate constant of 1.2 × 10−8 g2 cm−4 s−1 was measured for ZrB2–10 % SiC composite. A transition in the oxidation kinetics was observed for ZrB2–30 % SiC composite with the initial par...
Citations
... S. Gangireddy et al found that ZrB 2 -SiC composites formed bubbles after a certain period of oxidation at 1450°C [12]. Patel et al found that significant bubbles were observed when ZrB 2 -SiC ceramics were oxidized at 1650°C for 30 min [13]. The presence of bubbles causes the oxide layer of the sample to thicken [14]. ...
... The gas evolves from the sample during oxidation, disrupting the scale. Bubbles were observed and reported by multiple authors as a result of gas generation [13]. Figure 5 presents the XRD results for the oxidized surfaces of these samples. ...
ZrB2-SiC ceramics are potential candidates for thermal protection materials
for re-entry and hypersonic vehicles. Phases are typically added to ZrB2-SiC to enhance
the oxidation resistance of the material. MoAlB is an attractive nanolaminated ternary
boride compound. Due to its damage tolerance, crack healing ability, and good
oxidation resistance, MoAlB is a promising material for high-temperature applications.
Therefore, the effect of MoAlB substitution on the oxidation of ZrB2-SiC at 1600℃ for
10 hours was evaluated. Five samples with different MoAlB contents (0vol%, 4vol%,
8vol%, 12vol%, 16vol%) were prepared. The results indicate that ZrB2-SiC-
8vol%MoAlB exhibits improved oxidation resistance compared to ZrB2-SiC. After
This study investigates the influence of separate and combined addition of 5 vol.% TiC and/or WC on the isothermal oxidation behaviour of ZrB2–20 vol.% SiC composites consolidated by a spark plasma sintering route. The oxidation performance of the composites was evaluated in the temperature range of 1500–1600 °C in air for up to 4 h. Following oxidation, the samples were subjected to a detailed characterization of the microstructure, micro-composition, phase aggregate, and oxide scale growth kinetics. The thermodynamic feasibility of probable reactions and the phase stability of Zr–B–O, Zr–Si–O, Ti–B–O, Ti–C–O, Ti–W–O, and W–C–O systems were examined by dedicated software. While addition of TiC or WC was found to result in protective oxide scale formation, the highest oxidation resistance in terms of reduced mass gain and oxide layer thickness was offered by ZrB2–20SiC–2.5TiC–2.5WC (vol.%) composite at 1500–1600 °C in air.
This study aims to develop a novel TiC-doped ZrB2-SiC-TiC composite with enhanced sinterability, densification, phase and microstructural stability and oxidation resistance for high-temperature structural application. Due to 5 vol pct TiC addition, higher sintered density (99.6 pct) was obtained by spark plasma sintering (SPS) at 1700 ∘C, which is about 200 ∘C less than the SPS processing temperature needed for ZrB2-20 vol pct SiC. The improved sinterability was ascribed to in-situ formation of (Zr,Ti)B2 solid solution in this new ZrB2-20 vol pct SiC-5 vol pct TiC composite. The effect of TiC addition on oxidation kinetics of ZrB2-SiC composites was critically evaluated. Consequent upon oxidation at 1600 ∘C for 0–240 minutes in static air, relatively low mass gain and thin oxide layer was observed in the TiC-containing composite. Phase and microstructural analyses of the oxidized samples revealed the formation of a protective oxide scale in both composites. Interestingly, the thickness of SiC-depleted region was found to be much lower in ZrB2-SiC-TiC composite, compared to that of ZrB2-SiC binary system.
In this work, a 1 MW Plasma wind tunnel was employed to study the dynamic oxidation mechanisms of ZrB2-SiC at heat flux ranging 0.5∼5.0 MW/m² in reduced pressure. The results show a transition in the uppermost oxide layer from SiO2-rich glass to SiO2 when increasing heat flux from ≈0.55 and ≈1.70 MW/m² (≈1100 °C and ≈1340 °C) to ≈2.50 MW/m² (≈1550 °C). A temperature fluctuation was highlighted at ≈2.50 MW/m². At higher heat flux (≥3.5 MW/m²), a ‘thermal instability’ always occurred at ≈1650 °C. In addition, the ZrO2 grain structure was temperature dependent, particularly at ≈1.70 MW/m² where the ZrO2 grain evolved from tiny grain, to equiaxed grain and to columnar grain. At higher heat flux (≥2.50 MW/m²), columnar grains were observed prior to the ‘thermal instability’. Finally, as oxidation of ZrB2-SiC was a diffusion-control process, the oxidation rate was dependent not only on temperature, but on grain structure of ZrO2.
The formation of HfB2–SiC (10–65 vol % SiC) ultra-high-temperature ceramics by hot pressing of HfB2–(SiO2–C) composite powder synthesized by the sol–gel method was studied. By the example of HfB2–30 vol % SiC ceramic, it was shown that the synthesis of nanocrystalline silicon carbide is completed at temperatures of as low as ≥1700°C (crystallite size 35–39 nm). The production of the composite materials with various contents of fine silicon carbide at 1800°C demonstrated that the samples of the composition HfB2–SiC (20–30 vol % SiC) are characterized by the formation of SiC crystallites of the minimum sizes (36–38 nm), by the highest density (89%), and by higher oxidation resistance during heating in an air flow to 1400°C.
ZrB2 powders were successfully prepared via carbothermal reduction of ZrO2 with H3BO3 and carbon black under flowing argon. By introducing SiC species into reaction mixtures, the effects of SiC addition on phase composition and morphology of ZrB2 powders thermally treated at different temperatures were investigated. The resultant samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The highly pure ZrB2 with the mean size of 5 μm could be obtained at 1600 °C for 90 min and the grains presented columnar shapes. After addition of SiC, ZrB2 revealed relatively better crystallinity and finer particle size. Regular columnar ZrB2 grains ranging from 1 to 2 μm were seen existing after reaction at 1500 °C for 90 min.
