Carbon Felt --- A Comprehensive Guide to the Multi-Domain Applications of Flexible Carbon Materials

    In laboratory and industrial production scenarios, the safe storage and transportation of high-temperature test tubes remain one of the core requirements. The container used to hold high-temperature test tubes, as a dedicated accessory, directly affects the experimental accuracy, production safety, and operational efficiency. This article will comprehensively explain this specialized equipment from aspects such as product introduction, core performance, key parameters, application industries, usage precautions, and maintenance and care, to help relevant practitioners make precise selections and use it in a standardized manner. 

1. Basic Understanding of Carbon毡： Raw Materials and Preparation Process 

    Carbon felt is a porous and flexible carbon material, with a carbon content typically ranging from 90% to 98%. Unlike graphite felt that undergoes high-temperature graphitization treatment, it is one of the most widely used flexible carbon materials. Depending on the source of the raw materials, the mainstream carbon felt used in industry can be divided into three types, each with its own applicable scenarios. 

    Polyacrylonitrile-based (PAN-based) carbon felt is currently the category with the best overall performance and the widest application range. It has high purity of raw materials and excellent fiber strength. After carbonization, the felt structure becomes dense with low impurity content, making it suitable for high-end manufacturing fields. Viscose-based (artificial silk-based) carbon felt has excellent flexibility and outstanding heat radiation resistance, being friendly to both the human body and the environment. It is mostly used in precision equipment and environmental protection scenarios. Asphalt-based carbon felt has the core advantage of low cost. Its raw materials have a wide source. Although its performance is slightly inferior to the former two, it has outstanding cost-effectiveness in ordinary industrial insulation, filtration and other scenarios. The preparation process involves key steps such as fiberization of raw materials, non-woven needle-punching molding, pre-oxidation (removal of impurities and volatile components at 200-300℃), carbonization (conversion of organic components to carbon structure at 800-1500℃), and surface treatment. Eventually, a uniform thickness and moderate porosity finished product is formed. 

    2. Core Performance: The Superiority of Flexible Materials in Terms of Hardness 

    The core competitiveness of carbon felt lies in its combined advantage of "flexible form + extreme environmental adaptability". Compared with traditional rigid carbon materials and insulation materials, its performance is more diverse: 

    High temperature resistance and thermal stability are the core highlights. In a vacuum or inert atmosphere, carbon felt can withstand temperatures ranging from 1000 to 1800°C for a long period. Some PAN-based products can reach a short-term usage temperature of 2000°C. Moreover, they have an extremely low thermal expansion coefficient, making them less prone to deformation or cracking at high temperatures and capable of maintaining structural integrity stably. At the same time, their heat insulation and heat preservation performance is excellent. At room temperature, the thermal conductivity is only 0.05 - 0.1 W/(m·K), and the thermal conductivity increases slowly at high temperatures, effectively reducing heat loss and meeting the insulation requirements of high-temperature equipment. 

    It has outstanding chemical stability and can resist the erosion of most acid and alkali solutions, organic solvents, and does not undergo chemical reactions with metal melts or high-temperature gases. It also does not produce harmful volatiles at high temperatures and can ensure the cleanliness of the application environment. In addition, the carbon felt has good conductivity and adsorption properties. PAN-based carbon felt has a volume resistivity as low as 10-20 Ω·cm, which is suitable for applications such as electrodes and conductive shielding. At the same time, it is lightweight (with a volume density of 0.05-0.15 g/cm³), has good flexibility, and can be cut into any shape as needed to meet the installation requirements of complex working conditions. 

3. Key Parameters: The Core Basis for Selection 

    The parameters and indicators of carbon felt directly determine its applicable scenarios. The core parameters of different types of products vary significantly. The following are the mainstream industry standard parameters for reference during selection: 

    In terms of purity and composition, the PAN-based carbon felt has a carbon content of ≥ 95%, with a residue content of ≤ 0.1%, and the impurities are mainly iron, silicon, and aluminum, with the content being lower than 50 ppm; the viscose-based carbon felt has a carbon content of 90% - 93%, with a residue content of ≤ 0.3%; the asphalt-based carbon felt has a carbon content of 88% - 92%, with a residue content of ≤ 0.5%. For high-end scenarios, PAN-based products should be preferred to control the impact of impurities. In terms of density parameters, the volume density range is 0.05 - 0.15 g/cm³, and the surface density can be flexibly customized. The conventional range is 300 - 1200 g/m². Low-density products have better heat insulation performance, while high-density products have higher strength. 

    In terms of mechanical properties, the parallel direction tensile strength of PAN-based carbon felt is ≥ 150N/5cm, and the vertical direction is ≥ 50N/5cm; the parallel direction tensile strength of adhesive-based products is ≥ 80N/5cm, and the vertical direction is ≥ 20N/5cm; the strength of asphalt-based products is relatively lower, with the parallel direction being ≥ 50N/5cm. In terms of specifications and dimensions, the regular width ranges from 400 to 2000mm, the length can be customized according to requirements, the thickness is 3 to 20mm, and special scenarios can be processed into cylindrical, block-like, or other irregular structures. In addition, parameters such as thermal conductivity and resistivity need to be confirmed based on specific application scenarios. For example, in the electrode application scenario, resistivity should be given priority consideration, and in the heat insulation application scenario, thermal conductivity should be the key factor to consider. 

4. Application Industry: Practical Materials with Broad Applications 

    Thanks to its comprehensive performance and cost advantages, carbon felt has been widely applied in various fields such as industrial manufacturing, new energy, aerospace, and environmental protection, and has become a key material in the industrial chain: 

    The high-temperature equipment sector is the core application area, accounting for over 55% of the total demand for carbon felt. In equipment such as single-crystal silicon ingot pulling furnaces, polycrystalline silicon ingot casting furnaces, carbonization furnaces, and sintering furnaces, carbon felt is used as an insulation layer to wrap the heaters, which can precisely maintain the temperature gradient inside the furnace, reduce heat loss, and improve the energy efficiency of the equipment and the product qualification rate. With the rapid development of the photovoltaic industry, the domestic usage of carbon felt in the photovoltaic field has exceeded 30,000 tons by 2025, with PAN-based products accounting for over 70%. 

    The application potential in the field of new energy is enormous. In vanadium redox flow batteries and zinc-bromine flow batteries, carbon felt is used as the electrode material. With its high specific surface area and excellent conductivity and stability, it enhances the efficiency and cycle life of the battery stack. In the production of lithium battery negative electrode materials, carbon felt is used for insulation in the carbonization furnace, helping to improve the electrochemical performance of the negative electrode material. Moreover, carbon felt can also be used for high-temperature insulation and conductive shielding in aerospace equipment, for high-temperature gas filtration and catalyst carriers in the chemical industry, as well as for wastewater treatment and exhaust gas adsorption in the environmental protection field. The application scenarios are continuously expanding. 

5. Usage Notes and Maintenance Procedures 

    The service life of carbon felt is closely related to the usage specifications and maintenance methods. Correct operation and maintenance can extend its service life by more than 30%. Please strictly follow the following key points: 

    Regarding the usage precautions, it is necessary to avoid using at high temperatures in an oxidizing atmosphere. Carbon felt will oxidize and flake off when exposed to air at temperatures above 400℃, accelerating aging. For high-temperature conditions, it should be used under vacuum or in the presence of inert gases (such as nitrogen or argon). During operation, it is prohibited to scrape or strike the felt with hard objects to prevent damage to the fiber structure. When transporting, handle with care and gently place it. When stacking, use soft padding to prevent pressure concentration from causing deformation. During installation, ensure a tight fit with the inner wall of the equipment to reduce heat leakage through gaps. At the same time, avoid direct contact with high-temperature heating elements. A隔热 coating can be used in combination. 

    Maintenance and upkeep should be carried out in several steps: When cleaning, start by using compressed air to blow away surface dust. If there is oil or stains, you can soak and clean them in organic solvents such as ethanol or acetone in a well-ventilated environment. Do not use strong acids or strong bases. After cleaning, thoroughly dry at 80-100℃ to avoid residual moisture affecting usage. Regularly inspect the appearance. If there are obvious burn marks, fiber detachment, cracks, etc., replace it immediately. Regularly test key parameters such as resistivity and thermal conductivity. If the performance degrades by more than 20%, perform surface activation treatment or replace with a new product. 

The storage environment should meet the requirements of being dry, dust-free and cool. The temperature should be controlled at 20-25℃, and the relative humidity should be less than 40%. Avoid direct sunlight and humid environments. For long-term storage, it needs to be vacuum-sealed. To prevent oxidation and moisture absorption. After using at high temperatures, it should be naturally cooled to room temperature before cleaning and storage. Avoid sudden cooling or heating to prevent the felt from cracking. 

    6. Industry Trends: Performance Enhancement and Scenario Expansion 

    Currently, driven by the upgrading of the downstream industry and the "dual carbon" strategy, the carbon felt industry is developing towards high performance, low cost and greenness. Enterprises are improving the purity, strength and stability of carbon felt by optimizing the carbonization process and introducing nano-modification technology. The self-sufficiency rate of high-end PAN-based carbon felt has exceeded 65%, gradually replacing imported products. At the same time, the technology for recycled carbon felt is gradually mature. Through the secondary carbonization treatment of recycled carbon felt, production costs are reduced while resource waste is minimized. The market penetration rate will continue to increase in the future. 

As a carbon material with both flexibility and extreme environment adaptability, the application scenarios of carbon felt are still expanding continuously. Especially with the increasing demand in the fields of new energy and high-end manufacturing, it will drive the technological iteration and capacity expansion of this material. Mastering the correct selection, usage and maintenance methods can not only fully utilize the performance advantages of carbon felt but also reduce the usage cost, providing a guarantee for the improvement of production efficiency.