Hot nitric acid diffusion in fluoroelastomer composite and its degradation.

Area of Science:

• Materials Science
• Chemical Engineering
• Polymer Chemistry

Background:

• Fluoroelastomers (FKM) are critical for sealing in acidic environments.
• FKM failure poses significant safety risks.
• Investigating FKM degradation is essential for material reliability.

Purpose of the Study:

• To investigate the diffusion model of acidic solutions into FKM composites.
• To understand the degradation behavior and mechanism of FKM in hot nitric acid.
• To analyze the impact of nitric acid concentration on FKM.

Main Methods:

• Fick diffusion model analysis for nitric acid solutions.
• Scanning Electron Microscopy (SEM) for surface topography.
• Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR), SEM-Energy Dispersive X-ray Spectroscopy (EDS), and Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) for structural and chemical analysis.

Main Results:

• Nitric acid diffusion into FKM follows Fick's model at low concentrations.
• Acid concentration influences solvent diffusion and filler dissolution.
• SEM revealed significant surface topography changes.
• ATR-FTIR, SEM-EDS, and MAS NMR confirmed decrosslinking via hydrolysis and backbone cleavage by dehydrofluorination.

Conclusions:

• FKM degradation in hot nitric acid involves hydrolysis of crosslinks and dehydrofluorination.
• Degradation leads to reduced crosslinking degree and impaired mechanical properties.
• This research provides insights into FKM chemical changes in acidic conditions.