For nickel felt, porosity is a core parameter that determines its performance. TOPTITECH's nickel felt features a standard porosity of 60%-80%, meeting the requirements of transport layer applications in many industries, particularly the electrolytic industry.
While this seemingly broad porosity range is the result of a delicate balance between filtration efficiency, electrode reactivity, sound absorption, and mechanical strength, this article will delve into the underlying logic and practical processes of nickel felt porosity control, revealing key technical secrets within the industry.
Porosity: The "Baton" of Nickel Felt Performance
In the microscopic world of nickel felt, the pore structure is like a city's transportation network:
►High porosity (75%-80%) creates a well-developed three-dimensional through-pore structure, providing low-resistance pathways for fluids (gases, liquids, and ions), enabling efficient filtration, high-current battery electrodes, and excellent sound absorption.
►Medium-to-high porosity (60%-75%): This range maintains good permeability while balancing mechanical support and electrical/thermal network stability. It represents the optimal range for applications such as catalytic supports, sealing materials, and electromagnetic shielding.
Precisely controlling porosity is the core competitiveness of nickel felt products in their target applications.
Key Processes for Porosity Control
1. Fiber Construction Unit
Fine fibers (e.g., 8-15μm in diameter) allow for denser networks, resulting in more pores and a high surface area. Coarse fibers (20-50μm in diameter) tend to create structures with larger pores and high permeability. Diameter control through precision drawing or melt spinning sets the tone for porosity.
2. Mat Laying and Forming
Airflow/Wet Laying: Airflow velocity, fiber concentration, and uniformity of deposition directly determine the initial porosity of the fiber stack.
Low concentration and slow deposition are key to achieving high initial porosity (up to 85%+), but agglomeration must be carefully prevented.
Mechanical felting (key process): The carding gauge, number of layup layers, and crossover angle finely control the density of the felt.
Industry experience: Reducing the number of layup layers + increasing the carding gauge = a fluffier felt ≈ a higher final porosity.
Pre-pressing and shaping: The "fine-tuning knob" for porosity
Applying controlled pressure (range: 0.05-1.0 MPa) to the fluffy felt before sintering is the most direct and effective means of controlling porosity.
3. Sintering
Under H₂ or vacuum protection, high temperatures (800-1100°C) allow the fibers to form metallurgical bonds at their contact points through surface diffusion and grain boundary diffusion. Sintering is essentially a trade-off between strength and porosity.
4. Post-processing
After sintering, micro-rolling is performed to minimize porosity loss while ensuring flatness. This is standard practice for products with a porosity of 60-70%.
Controlling the porosity of nickel felt is a culmination of materials science, process engineering, and practical experience. From the microscopic design of the fibers to the atomic diffusion during sintering, every step profoundly impacts the fate of the pore network. Mastering the synergistic art of fiber morphology, mat density, pre-pressing pressure, sintering window, and post-processing allows for the precise manufacture of nickel felt products that meet diverse application requirements.
