Viscose-based Felt in Induction Heating Furnace

The suitability of viscose-based carbon fiber for insulation systems in high-temperature induction heating environments is primarily due to its key properties, including low thermal conductivity, high thermal stability, excellent thermal shock resistance, high purity and low impurity content, and lightweight processability. These properties work together to make it a highly efficient, clean, and reliable insulation material for extreme high-temperature environments, possessing irreplaceable strategic value, especially in high-end fields such as aerospace and semiconductor manufacturing.

I. Low Thermal Conductivity

The thermal conductivity of viscose-based carbon fiber at room temperature is approximately 1.26 W/m·K, far lower than that of metallic materials (such as stainless steel, approximately 15 W/(m·K)) and many ceramic materials. This characteristic stems from its "disordered graphite structure" and "developed porous structure." In high-temperature induction heating systems, low thermal conductivity means that heat is less easily lost from the heating area to the external environment, thus achieving efficient insulation.

The thermal conductivity of viscose-based carbon fiber remains low even at high temperatures. Its microstructure contains numerous nanoscale and microscale pores, which form "low heat transfer channels" at temperatures above 2000℃, effectively hindering heat conduction. Simultaneously, carbon materials transfer heat through lattice waves, while the lattice arrangement of viscose-based carbon fibers is more disordered (non-graphitized structure), lengthening the heat conduction path and further reducing thermal conductivity. In high-temperature equipment such as single-crystal silicon furnaces, insulation felts or heat insulation boards made of viscose-based carbon fibers can significantly reduce heat loss and improve energy efficiency.

II. High Temperature Resistance and Thermal Stability

Viscose-based carbon fibers can operate stably up to "above 2800℃" in inert or vacuum environments, making them an ideal insulation material for high-temperature areas in induction heating systems. At extreme temperatures above 2000℃, most materials undergo significant physicochemical changes, while viscose-based carbon fibers maintain their basic structure and properties.

The high thermal stability of viscose-based carbon fibers stems from their "difficult-to-graphitize" properties. Compared to PAN-based or pitch-based carbon fibers, viscose-based carbon fibers are less likely to form a highly ordered graphite structure at high temperatures. However, this also means they are less prone to drastic structural phase transitions at high temperatures. Experiments show that viscose-based carbon fibers treated at 2200℃ still maintain a non-graphitized structure with a density of only 1.39 g/cm³ and a carbon content of over 98.5%. This stable carbon structure prevents them from melting or decomposing at high temperatures, allowing them to maintain their thermal insulation properties over a long period.

It is worth noting that viscose-based carbon fibers are prone to oxidation in oxidizing environments (significantly accelerated above 400℃). However, in induction heating systems, the use of a protective atmosphere (such as argon or nitrogen) or a vacuum chamber effectively avoids this oxidation problem, fully leveraging their high-temperature resistance.

III. Excellent Thermal Shock Resistance

Induction heating systems typically require frequent start-ups and shutdowns, leading to drastic temperature changes. The high elongation at break (>2%) and low density (1.39-1.7 g/cm³) of viscose-based carbon fibers endow them with excellent thermal shock resistance, enabling them to withstand rapid temperature fluctuations without easily cracking.

Thermal shock resistance refers to a material's ability to resist cracking under drastic temperature changes. The positive linear expansion coefficient of viscose-based carbon fibers (2.184 × 10⁻⁶/K at 800℃) ensures a high degree of matching between their expansion behavior and that of the resin matrix during heating, significantly reducing thermal stress concentration. Furthermore, their flexible structure and high elongation at break allow for the absorption of thermal shock energy through flexible deformation, preventing cracking caused by thermal stress.

In studies of 2D-C/C composites, it was found that the free thermal strain of viscose-based carbon fibers at 800℃ is 1/8 that of PAN-based reinforced materials, and the simulated thermal stress during carbonization is 1/60 that of PAN-based reinforced materials. This extremely low level of thermal stress gives it excellent stability under frequent temperature changes in induction heating systems, significantly extending the service life of the insulation system.

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