New insight into the formation and oxygen barrier mechanism of carbonaceous oxide interlayer in a multicomponent carbide

Abstract

Early transition metal carbides (TMCs), possessing simple metallic structures in which small carbon atoms occupy the interstitial voids of densely packed metallic lattice, merge the advantages of covalent solids, ionic crystals, and transition metals. As a result, TMCs often demonstrate extremely high melting points, considerable hardness. and excellent electric and thermal conductivity. 1 The unique combination of these desirable properties makes them a kind of promising material for a wide range of applications including hydrogen evolution electrocatalysts, 2,3 high-temperature solar absorber, 4 energy storage devices, and extreme environment applications, 5-7. Particularly, TMCs, such HfC, ZrC, TiC, and TaC, having the requisite refractoriness to withstand ultra-high temperatures and pronounced resistance to oxidation simultaneously are well suited for oxidizing environments at temperatures exceeding 2000°C. Generally, the oxidation resistance of TMCs is largely attributed to a carbonaceous oxide interlayer (eg, Hf-O-C, Zr-O-C, and Ta-O-C), located at the interface between the external oxide layer and internal carbide (eg, HfC, ZrC, and

Oxidation Behavior of the Si-B-X (X = Mo, Cr, or Ti) Alloys in the Temperature Range of 1000–1400 °C

“…As a valuable tool for oxidation behavior studies, volatility diagrams show the thermodynamically predicted stable solid phase, the concomitant gaseous species, and their vapor pressures at different oxygen partial pressures and temperatures. 31 As shown in Figure 14 a, when the partial pressure of oxygen is 10 4 Pa (i.e., the partial pressure of oxygen at 1 atm), the Si-B-Mo alloy mainly has SiO 2 (cr) and B 2 O 3 (l) in the condensed phase and MoO 3 (g) and B 2 O 3 (g) in the vapor phase after oxidation at 1400 °C, with partial pressures of ∼9.66 and ∼32.89 Pa, respectively. Research has demonstrated that there are two scenarios for the oxidation of MoSi 2 in air: 32 , 33 Selective oxidation of Si in MoSi 2 to a pure SiO 2 oxide layer, while Mo forms the transition phase Mo 5 Si 3 at the MoSi 2 /SiO 2 interface.…”

“…It can be concluded that the oxidation rates of the Si-14.88B-7Mo and Si-14.88B-7Ti alloys are mainly controlled by the diffusion rate of oxygen in the oxide layer. As a valuable tool for oxidation behavior studies, volatility diagrams show the thermodynamically predicted stable solid phase, the concomitant gaseous species, and their vapor pressures at different oxygen partial pressures and temperatures . As shown in Figure a, when the partial pressure of oxygen is 10 4 Pa (i.e., the partial pressure of oxygen at 1 atm), the Si-B-Mo alloy mainly has SiO 2 (cr) and B 2 O 3 (l) in the condensed phase and MoO 3 (g) and B 2 O 3 (g) in the vapor phase after oxidation at 1400 °C, with partial pressures of ∼9.66 and ∼32.89 Pa, respectively.…”

Oxidation behavior of non-stoichiometric (Zr,Hf,Ti)Cx carbide solid solution powders in air

“…Zr (> 99.5 wt%, ≤ 50 µm), Hf (> 99.5 wt%, ≤ 50 µm), Ti (> 99.5 wt%, ≤ 50 µm), and carbon (graphite, 99.95 wt%, 3 µm, Macklin Biochemical Co., Ltd., China) powders were mixed by a planetary ball mill (MITR-YXQM-2L, Changsha MITR Instrument and Equipment Co., Ltd., China), using agate balls, polytetrafluoroethylene vessel, and ethanol as media. Considering the melting point of HfC is higher than those of ZrC and TiC [31][32][33], this may be related to the good ablation resistance of (Zr,Hf,Ti)C-carbon/carbon composite [29], at which the (Zr,Hf,Ti)C owned a high Hf content among metallic atom composition (i.e., Hf:Zr:Ti = 0.5:0.3:0.2). Hence, first group specimens were designed with equal molar ratio of carbon and Ti in carbides to compare the effect of Zr and Hf on the oxidation resistance of carbide, including Zr 0.5 Hf 0.25 Ti 0.25 C 0.7 and Zr 0.375 Hf 0.375 Ti 0.25 C 0.7 .…”

Nb- and Ta-doped (Hf,Zr,Ti)C multicomponent carbides with enhanced oxidation resistance at 2500 °C

“…In particular, (Hf,Zr,Ti)C medium-entropy carbides have attracted considerable attention because of their excellent ablation resistance. Li et al [19] showed that an amorphous Zr-Hf-Ti-C-O layer, reinforced by m-(Hf,Zr,Ti)O 2 nanoparticles, formed on the surface of (Hf,Zr,Ti)C after ablation at 2100 ℃, thereby enhancing its oxidation resistance. Ye et al [20] observed an intermediate Hf-Zr-Ti-O-C layer and precipitated carbon between the oxide layer and the (Hf,Zr,Ti)C matrix after ablation at 2500 ℃, which hindered rapid oxygen diffusion and contributed to good ablation resistance.…”