Physical changes of carbon fiber at high temperatures

Introduction

As a high-performance material, carbon fiber has been widely used in many fields such as aerospace, automobile manufacturing, and sporting goods due to its excellent physical and chemical properties. However, the physical changes of carbon fibers at high temperatures have a significant impact on their properties. This article will explore the physical changes of carbon fiber at high temperatures, including its structural changes, performance changes, and possible application impacts.

structural changes

Structural transformations at high temperatures

The structural changes of carbon fiber at high temperatures are mainly reflected in changes in its internal chemical bonds and crystal structure. During the pre-oxidation process, highly oriented polyacrylonitrile (PAN) protofilaments will physically shrink at high temperatures and increase in conformation, making them in a thermodynamically stable state. This process causes the fiber's linear molecular chains to transform into pre-oxidized filaments with a heat-resistant ladder structure. Subsequently, in a high-temperature carbonization environment under the protection of inert gas, the pre-oxidized wire does not melt or burn, maintains the fiber shape, and is then transformed into carbon fiber with a turbostratic graphite structure.

Thermal decomposition of carbon fiber

Research shows that the thermal decomposition temperature of carbon fiber is generally higher than 1000°C, and it usually begins to melt above 1500°C. At high temperatures of around 500°C, the material properties of carbon fiber will attenuate, and its strength and stiffness may drop by more than 50% due to defects such as micro-cracks and holes. When the temperature exceeds the thermal stability limit of carbon fiber, thermal decomposition reactions may cause the carbon fiber to begin to melt.

Performance changes

Decrease in mechanical properties

As the temperature increases, the mechanical properties of carbon fiber will decrease significantly. At high temperatures of around 500°C, the strength and stiffness of carbon fiber may drop by more than 50% due to the presence of defects such as micro-cracks and holes. This is because high temperatures can cause defects within the carbon fiber to expand, thereby reducing its load-bearing capacity.

Changes in electrical conductivity

Carbon fiber is an electrical insulator, but it will have obvious electrochemical reactions at high temperatures and is easily oxidized, reduced and corroded. Therefore, in practical applications, carbon fiber needs to be careful to avoid contact with harmful media such as high-temperature gases and liquid metals to avoid corrosion and damage.

Application impact

Application limitations in high temperature environments

Although carbon fiber has the characteristics of light weight, high strength, and high stiffness, its application in high temperature environments is still subject to certain limitations. For example, in aviation, although carbon fiber is widely used in engines, aerodynamic devices, brakes and other components, the impact of high temperature on the performance of carbon fiber must be considered to ensure the performance and reliability of the system.

Protective measures in high temperature environments

To overcome the effects of high temperatures on carbon fiber properties, researchers are exploring various protective measures. For example, by improving the manufacturing process and quality control of carbon fiber, its stability in high-temperature environments can be improved. In addition, the high-temperature resistance of carbon fiber can be enhanced through coating or other surface treatment technologies.

in conclusion

To sum up, the physical changes of carbon fiber at high temperatures mainly include changes in its structural transformation, mechanical properties and electrical conductivity properties. These changes have a significant impact on its application in high temperature environments. Therefore, when designing and using carbon fiber materials, their performance changes under high temperature conditions must be fully considered, and corresponding protective measures must be taken to ensure their long-term stability and reliability.