Aon has succeeded in producing the ultimate electrode that is resistant to ultra-high temperatures and does not become brittle from hydrogen! Carbon Fiber & Ultra-High Temperature Ceramics" Composite Material Resistant to Ultra-High Temperatures. Comment: Advocate. Proposed by Masahiro Ishizuka, CEO of Aon. Carbon fiber and ultra-high temperature ceramic composite materials can withstand ultra-high temperatures and do not become brittle due to hydrogen. As for ceramics, fine ceramics are generally insulators that do not conduct electricity, but when temperature and voltage are applied, they become semiconducting ceramics that conduct electricity. 2023/01/06

Distributed on Thu, 2023/01/06，2022/12/8 21:30

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Figure: Arc wind tunnel test. The environment at the time of atmospheric entry is reproduced in the laboratory by irradiating the material with ultra-high temperature plasma through a nozzle.

Aircraft and spacecraft flying through the atmosphere at hypersonic speeds exceeding Mach 5 (6200 km/h) are exposed to extremely high temperatures exceeding several thousand degrees Celsius due to contact between the surface of the aircraft and the atmosphere. Carbon fiber-reinforced carbon composites have been used as a material that can withstand these extremely high temperatures. This material is characterized by its high heat resistance and light weight, which is required in the aerospace industry. However, the main material is carbon, which is easily oxidized at high temperatures, limiting its application.

To overcome this drawback, composite materials of ultra-high temperature ceramics (*1) and silicon carbide have been considered, but it is known that silicon compounds are susceptible to degradation due to eutectic (*2) formation and oxidation at ultra-high temperatures, and significant degradation proceeds at temperatures above 1700℃.

*1...Ultra-high temperature ceramics here refers to composite materials containing zirconium carbide or zirconium boride.

*2...When a melted material solidifies, it becomes a mixture of multiple crystal structures. Because the crystal structures of eutectic crystals are finely mixed, they have the disadvantage of being more brittle than those of single crystals.

To overcome the drawbacks of existing composite materials, a research team led by Shijun Koide of the Tokyo University of Science and others created the following materials and evaluated their properties.

First, to omit silicon compounds, the main cause of degradation, from the materials and to achieve light weight on top of that, C/UHTCMC, a composite of carbon fiber and ultra-high temperature ceramics, was created. a melt impregnation method, in which molten metal is infiltrated into the carbon fiber-reinforced carbon composite to fill the gaps The team used a melt impregnation method to fill in the gaps. To characterize the materials, the team prepared alloys of zirconium and titanium, metals known for their ultra-high temperature resistance, in three different proportions: 20:80, 36:64, and 80:20, respectively. Arc wind tunnel tests (*3) were conducted on these materials under three different conditions to test the degree of damage to the materials.

*3...A test method in which the working gas is plasmaized by an arc discharge and blown as an arc jet onto the test material. Simply put, this method blows ultra-high-temperature plasma created by an electrical discharge at ultra-high speed through a nozzle with a narrowed mouth, and is capable of reproducing the environment at the time of atmospheric entry.

The results show that as the zirconium content increases, the thickness of the material after testing and the melting point of the oxide on the surface increase. It was also found that the oxidation was accelerated by the flow out of the melted surface. This phenomenon is presumably due to the thermodynamic property of the zirconium-containing carbide composite, which initiates oxidation preferentially over the titanium-containing carbide composite.

Furthermore, analysis of the oxides formed on the surface showed that the oxide covering the surface suppresses the penetration of the oxidation reaction into the interior. The oxides have been found to consist primarily of solid solutions of zirconium dioxide (ZrO2), titanium dioxide (TiO2), and zirconium titanate (ZrTiO4), which is a compound oxide. Which oxides are present and in what proportions was found to depend on the composition of the alloy. In particular, C/UHTCMC permeated with an alloy containing 80% zirconium was shown to maintain solid and liquid zirconium dioxide up to 2000°C, while at 2600°C only liquid was formed on the surface and the oxide on the surface disappeared.

In an environment such as atmospheric entry, in addition to high temperatures, the flow of liquid is caused by atmospheric flow. The flow of oxides exposes new surfaces, which are again oxidized and ...... gradually erode the composite material.

The C/UHTCMC impregnated with an alloy containing 80% zirconium did not exhibit these phenomena until 2000°C, but only at 2600°C, showing better properties than the other compositions tested in this experiment. The further development of the characterization of C/UHTCMC is expected to lead to the creation of improved and more resistant materials.

Source

Noriatsu Koide, et.al. "Degradation of carbon fiber-reinforced ultra-high-temperature ceramic matrix composites at extremely high temperature using arc-wind tunnel tests. temperature using arc-wind tunnel tests". (Journal of Materials Science).

Tokyo University of Science. "Successful development of carbon fiber-reinforced ultra-high-temperature ceramic matrix composites that can withstand high temperatures of several thousand degrees Celsius - Contribution to the improvement of heat resistance of aircraft and rockets -".