Analysis of factors affecting the performance of ceramic fiber

Ceramic fiber products are characterized by high temperature resistance, small bulk density, good thermal insulation performance, good chemical stability, good thermal shock resistance, good wind erosion resistance, convenient and fast construction, and are the most promising energy-saving and environment-friendly thermal insulation materials in the world today. However, ceramic fiber also has some disadvantages in application: poor stability, poor resistance to erosion, airflow erosion, peeling and other properties. When exposed to high temperature for a long time, due to the crystallization and grain growth of glass fiber, high temperature creep and other factors, the fiber structure changes - shrinkage deformation, fiber elasticity loss, brittle fracture, fiber strength reduction, densification, until sintering loss of fibrous structure occurs, In addition, it is easy to pulverize and fall off due to the erosion of corrosive furnace gas and the scouring of gas flow. The long-term use temperature of ceramic fiber products varies under different conditions. For example, the operating system of industrial kiln (continuous or intermittent kiln), fuel type, furnace atmosphere and other process conditions are all factors that affect the service temperature and service life of ceramic fiber.

At present, there is no ideal method to determine the heat resistance index of ceramic fiber. Generally, the ceramic fiber product is heated to a certain temperature, and the heat resistance of the ceramic fiber product is evaluated according to the linear shrinkage change and crystallization degree of the sample.

1. Effect of temperature on properties of ceramic fiber

From the perspective of thermodynamics, the glassy ceramic fiber is in a metastable state. So as long as the fiber is heated at a certain temperature, the particle rearrangement will occur inside the fiber, the glass state will be converted into crystalline state, and the fiber will be crystallized.

*Table 2 Crystallization change of ceramic fiber at different temperatures*

When the grain size grows to be close to the fiber diameter, the binding force inside the fiber will change from the chemical bond between molecules to the grain boundary between grains. Due to the fragile binding force of grain boundary, it will lead to the strengthening of fiber brittleness. Under the action of external force, the fiber is very vulnerable to damage and eventually lose its fiber properties.

2. Effect of ambient atmosphere on properties of ceramic fiber

In the reducing atmosphere, SiO ₂ in the fiber is easy to react with CO and H2 as follows:

SiO₂+COSiO+CO₂

SiO₂+H₂SiO +H₂O

As SiO2 is reduced to volatile substances, the fiber structure changes slowly and the surface becomes rough gradually. When mullite grains are formed inside the fiber, the fiber is easy to break, which accelerates the degradation of the fiber.

3. Influence of impurities on the properties of ceramic fibers

Some impurities in ceramic fiber, such as Fe  O , Na  O, K  O, etc., will react with other components in ceramic fiber to form eutectic at a lower temperature. The existence of eutectic destroys the network structure of the fiber, reduces the viscosity inside the fiber, reduces the crystallization activation energy to be overcome by ion group rearrangement during crystallization, and reduces the crystallization temperature. At the same time, the existence of eutectic accelerates the growth of grains, It promotes the pulverization of fiber.