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We call the Mach number less than 1 for the subsonic speed, the Mach number greater than 1.2 for the supersonic aircraft, and the Mach number greater than 5 for the supersonic aircraft. Flying at a speed of Mach 5 will produce an ultra-high temperature of up to 2000~3000 °C on the surface of the aircraft. The coating material of the aircraft is easily broken down at this high temperature. The development of supersonic aircraft must solve the problem of heat accumulation on the surface of the aircraft. Recently, the team of Chinese and British scientists discovered a new carbide ceramic coating that will help speed up the supersonic aircraft.
Carbide is currently the most resistant material, expressed by the general formula MxCy. Depending on the nature of the M, the carbides are roughly classified into metal carbides and metalloid carbides. Carbide ceramics are the most commonly used high temperature resistant structural ceramics. Common high temperature resistant ceramics are: silicon carbide, zirconium carbide, boron carbide, tungsten carbide, and the like. These ceramic materials generally have properties such as high melting point, high hardness and chemical stability. It is used in many areas of the national economy.
Any material leaking at a sufficiently high temperature will loosen the molecular chain, and if it is washed by high-speed particles, it will ablate; it will react with oxygen and be easily oxidized. For example, the conventional ceramic coating material zirconium carbide is effective in heat resistance, but is very susceptible to deterioration. Zirconium diboride is a new hope for high temperature coating materials for aircraft. Zirconium diboride is resistant to oxidation at high temperatures, and has low density and low cost. But a fatal disadvantage is that boron in the zirconium diboride further promotes ablation when the boron atom is oxidized.
The newly developed carbide coating material gives the coating a strong and oxidation-resistant structure that resists the problems of ablation and oxidation in high temperature environments.
The new coating is a ternary alloy mixture made of zirconium, titanium, carbon and boron, which is deposited into the carbon composite by a process called reactive melt infiltration, although it has properties with other carbide ceramics. Similarly, the relatively low boron concentration makes it less likely to be ablated, while the carbon structure helps prevent the tearing of previous materials under thermal shock. The experimental results show that the carbide coating exhibits better ablation resistance at 2000-3000 °C than the existing candidate UHTC (such as high temperature composites such as zirconium carbide and diboride).
At present, civil aviation aircraft generally fly at subsonic speeds. Once the civilian supersonic aircraft is realized, it will greatly reduce global travel time. Supersonic aircraft can cross the globe within a few hours. The coating material is optimistic about Boeing, and the company plans to achieve a smooth operation of the supersonic passenger aircraft within a decade. Although the supersonic airliner is far away from our lives, the discovery of this coating material will undoubtedly help the supersonic aircraft to become commercially available at an early date.
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