Factors Affecting the Performance of Ceramic Fibers

Ceramic fiber products possess characteristics such as high temperature resistance, low bulk density, excellent insulation properties, good chemical stability, resistance to thermal shock, erosion resistance, and ease of rapid construction. They are considered one of the most promising energy-saving and environmentally friendly insulation materials in the world today. However, ceramic fibers also have some disadvantages in application. These include poor stability, susceptibility to erosion, resistance to airflow erosion, and susceptibility to spalling, all of which lead to diminished performance. Prolonged exposure to high temperatures can lead to structural changes in the fibers, including shrinkage deformation, loss of elasticity, embrittlement, decreased fiber strength, densification, and ultimately, sintering and loss of fibrous structure. Factors such as corrosion from furnace gases and erosion from airflow contribute to the fiber’s tendency to pulverize and delaminate. The long-term operating temperature of ceramic fiber products varies under different conditions, such as industrial kiln operation systems (continuous or intermittent kilns), types of fuels used, and furnace atmosphere, all of which influence the temperature and lifespan of ceramic fibers.

Currently, there is no ideal method for determining the heat resistance index of ceramic fibers. Typically, ceramic fiber products are heated to a certain temperature, and their heat resistance is evaluated based on changes in sample heating line shrinkage and crystallinity.

1. Impact of Temperature on Ceramic Fiber Performance

From a thermodynamic perspective, vitreous ceramic fibers are in a metastable state. Heating under certain temperature conditions leads to particle rearrangement within the fibers, resulting in the transformation of the vitreous state into a crystalline state and crystallization within the fibers.

Table 2: Crystallization Changes in Ceramic Fibers at Different Temperatures (Image)

When the grain size grows to approach the diameter of the fiber, the binding force inside the fiber shifts from predominantly chemical bonding between molecules to primarily grain boundary binding between grains. Due to the relatively weak bonding at grain boundaries, the fiber becomes more brittle, making it highly susceptible to damage under external forces, ultimately leading to the loss of fiber properties.

2. Influence of Ambient Atmosphere on Ceramic Fiber Performance

In a reducing atmosphere, SiO₂ in the fibers reacts with CO and H₂ as follows:

SiO₂ + CO → SiO↑ + CO₂

SiO₂ + H₂ → SiO↑ + H₂O

As SiO₂ is reduced to volatile substances, the fiber structure gradually changes, and the surface becomes rough. When mullite crystals form inside the fiber, the fiber becomes prone to fracture, accelerating fiber degradation.

3. Impact of Impurities on Ceramic Fiber Performance

Certain impurities present in ceramic fibers, such as Fe₂O₃, Na₂O, and K₂O, react with other components in the fiber at relatively low temperatures to form eutectics. The presence of low-melting eutectics disrupts the network structure of the fibers, reduces internal viscosity, lowers the activation energy required for crystallization, decreases crystallization temperature, and accelerates grain growth, thereby promoting fiber pulverization.