Many people ask what can be actually seen from the black and white lines of a Scanning Electron Microscope (SEM) image. For carbon fiber insulation materials, an SEM acts like a CT scan, revealing the "micro-skeleton" that closely dictates the material's final thermal conductivity, mechanical strength, service life, and even cleanliness. By comparing the SEM images of PAN-based and Rayon-based carbon fiber rigid felts, we can understand why they are suited for different thermal fields.
While the images are black and white, the focus should be on whether the fibers are continuous and how they are connected. These factors determine over 80% of a rigid insulation felt's performance.
PAN-Based Rigid Felt: A "Steel Rebar" Skeleton
SEM of PAN-based Rigid Felt
The SEM image reveals slender, continuous, and relatively stretched-out fibers that resemble steel rebars in construction. The defining characteristic of this structure is its continuity, meaning loads can be continuously transferred along the fibers. As a result, it offers:
- Higher compressive strength.
- Better bending resistance.
- Greater dimensional stability over prolonged use.
- High resistance to overall collapse caused by thermal cycling.
PAN Felt Cylinder
When asked why PAN-based carbon fibers are more durable, the answer lies in this structure. The fibers have a smooth surface and a small specific surface area, making them less susceptible to oxidation and corrosion.
Rayon-Based Rigid Felt: "Fluffy Insulation Cotton"
SEM of Rayon Rigid Felt
This structure is distinctly different and features:
- Gray slender lines: Individual carbon fibers.
- Bright white areas: resin
- Black areas: Abundant pores.
Rayon Felt Cylinder
Compared to PAN-based felt, Rayon fibers are noticeably shorter, with more intersections, greater porosity, and many visible white resin "bridges" connecting the fibers. If PAN-based felt is like steel rebar, Rayon-based felt is like the down in a jacket, relying on its completely porous structure to block heat conduction rather than just the carbon fibers themselves.
Rayon provides better insulation because it contains more "thermal barriers". The SEM shows randomly arranged fibers in completely different directions with a high quantity of pores. Heat does not travel in a straight line; it constantly changes direction, encounters pores, and scatters. Like walking through a maze, the actual distance traveled increases significantly, creating a complex path that lowers the material's thermal conductivity.
Thermal Field Design: Never "Best," Only "Most Suitable"
Customers often ask which material is better, but there are no universal materials in thermal field design:
Choose Rayon-Based Felt: If your goals are to reduce furnace heat loss, improve insulation efficiency, and lower energy consumption.
Choose PAN-Based Felt: If your targets are a long service life, high cleanliness, high dimensional stability, and high mechanical reliability.