Refractory fibers are fibrous lightweight refractory materials whose research and development began in the early 1960s. They are characterized by their light weight, high-temperature resistance, good thermal stability, low thermal conductivity, low heat capacity, and resistance to mechanical vibrations. Compared with traditional refractory materials, the thermal conductivity and bulk density of refractory fibers are only 1/10 and 1/15 of those of traditional refractory materials, respectively. Therefore, furnace walls made of refractory fibers in high-temperature furnaces have less heat dissipation, better insulation performance, lighter wall mass, less heat storage, and lower thermal inertia.
Refractory fibers are also excellent infrared radiation materials, with good thermal radiation capabilities and infrared heating effects. The use of refractory fiber products can effectively save energy and are ideal energy-saving and efficiency-enhancing materials. Production practice has proven that the application of refractory fibers in continuous heating industrial furnaces can save more than 15% of energy, and in intermittent industrial heating furnaces, it can save more than 30% of energy. At the same time, it can improve production efficiency and product quality, achieve lightweight and large-scale furnace structures, and have good comprehensive performance.
Refractory fibers are soft and elastic, making them ideal sealing materials. They have the advantages of insulation, sound absorption, oxidation resistance, oil resistance, and water resistance, and are easy to install. Therefore, they are widely used in fields such as metallurgy, building materials, petroleum, chemical engineering, shipping, power, and aerospace.
Polycrystalline refractory fibers are a new type of high-temperature insulating material that developed in the early 1970s after amorphous refractory fibers and are mainly used in high-temperature kilns with working temperatures above 1400℃. They can save 25%–40% of energy. Polycrystalline refractory fibers can also be used as composite reinforcement materials and catalyst carriers, with good application effects. They are also used in the fields of aerospace missiles and nuclear energy.
At present, the polycrystalline refractory fibers that have been industrially produced and applied internationally mainly include polycrystalline alumina fibers (AL2O3 80%–99%, SiO2 1%–20%), polycrystalline mullite fibers (Al2O3 72%–79%, SiO2 21%–28%), and polycrystalline zirconia fibers (ZrO2 92%, Y2 8%).
Domestic: Mature Technology and Active Development
The research and development of polycrystalline refractory fibers in China did not start very early, but the current production technology has matured, the process is stable, and the comprehensive performance of fiber products is superior, having been applied in many fields.
As the main variety of polycrystalline refractory fibers, polycrystalline alumina fibers have excellent cost-performance and great commercial value. The classification temperature of 95% polycrystalline alumina refractory fibers reaches above 1750℃, with a long-term working temperature of 1450℃, AL2O3 content of 93%–95%, and fiber diameter of 2–4 micrometers. Polycrystalline alumina fiber board: AL2O3: 85%, classification temperature above 1750℃, working temperature: 1450℃. Since the 1970s, many developed countries have invested a lot of effort in the research and development of polycrystalline alumina fibers. Taking ICI of the UK as an example, the company has a history of more than 20 years in the production of polycrystalline alumina fibers, and the use temperature of the produced polycrystalline fibers can reach 1600℃. Foreign polycrystalline refractory fibers are not only used as high-temperature insulating materials but also as reinforcement materials for advanced ceramics, metals, and plastics.
The world total output of polycrystalline alumina fibers (AL2O3 72%–97%, with a maximum use temperature of 1800℃) is still relatively low, much less than that of ordinary silica-alumina fibers, of which about 50% of the total output is produced by Western European countries, and Japan accounts for about 39%. About 40% of polycrystalline refractory fibers are used in various industrial kilns and thermal processing processes, and around 25% are used in the metallurgical industry.