Xingang Luan

Corrosion of a SiC-C/PyC/SiC Composite by Sodium Sulfate Vapor at High Temperatures

The gaseous salt corrosion of a 3D woven SiCC/PyC/SiC composite in an atmosphere containing Na2S04 vapor has been investigated between 1000°C and 1400°C by an experimental approach based on mass and residual flexural strength changes. Two main temperature domains exist for the 3D woven SiCC/PyC/SiC composite. Below 1200°C, the corrosion kinetics is controlled by the competition of consumption of C fibers by S03 and gas phase diffusion through a network of microcracks in the SiC matrix and coating. Above 1200°C, the corrosion kinetics is controlled by S03 diffusion through the product film formed on the SiC coating. A more serious corrosion caused by a higher concentration of Na2S04 was discovered ih the present work. The thickness of the corrosion product film increases linearly with the temperature of the samples. Active corrosion may occur in the investigation atmosphere.

Behavior of pure and modified carbon/carbon composites in atomic oxygen environment

Atomic oxygen (AO) is considered the most erosive particle to spacecraft materials in low earth orbit (LEO). Carbon fiber, carbon/carbon (C/C), and some modified C/C composites were exposed to a simulated AO environment to investigate their behaviors in LEO. Scanning electron microscopy (SEM), AO erosion rate calculation, and mechanical property testing were used to characterize the material properties. Results show that the carbon fiber and C/C specimens undergo significant degradation under the AO bombing. According to the effects of AO on C/C-SiC and CVD-SiC-coated C/C, a condensed CVD-SiC coat is a feasible approach to protect C/C composites from AO degradation.

Modeling the Oxidation and Corrosion Behavior of 3D Carbon Fiber Reinforced SiC Matrix Composites from 400 to 1500 Degrees C

SiC coated three-dimensional textile carbon fiber reinforced SiC matrix composites (3D C/SiC) are promising materials for high temperature from 400 to 1500degreesC, oxidizing and corroding environment. In different temperature range from 400 to 1500degreesC, the oxidation and corrosion mechanisms of 3D C/SiC are quite different at different pure or mixed atmosphere including oxygen, water and sodium sulfate. The quality of SiC coating, which can be characterized with deposition times, thickness and grain size, is a key factor that effects on the weight change of the composites working in an environment. The environmental effects on the weight change of the composites have been studied through a series of oxidation and corrosion experiments. Quantitative models were developed based on the mechanism analyses and experimental data, which can predict the weight change of composites with different SiC coating in pure and mixed gaseous atmosphere from 400 to 1500degreesC. Oxygen and water are the controlling factors below and above 950degreesC, respectively. Na2SO4 causes a relatively great weight loss of C/SiC above 1300degreesC. Four layers of SiC coating with the total thickness of 80 microns can improve the oxidation and corrosion resistance of 3D C/SiC.