Fibers, Specialty Inorganic

This product review presents information on inorganic fibers other than glass and carbon fibers. The fibers covered include

• High-performance reinforcing fibers (boron fibers, ceramic fibers and whiskers)
• High-temperature insulation wools
• Silica fibers
• Alumina-boria-silica fibers
• Zirconia fibers
• Metal and metal-conducting fibers
• High-temperature superconducting fibers

There is some crossover from one category to another, such as high-temperature insulation wools used as reinforcements. Increasingly, fibers are valued for some combination of their mechanical, thermal and electrical properties. Carbon, glass and aramid fibers are considered only as they relate competitively to the subject materials. However, metal-coated glass, graphite and aramid fibers are discussed here.

It is necessary to report a diversity of information to adequately cover the wide ranges of manufacturing processes, applications and states of development of these fibers and wools. Consumption volumes vary from negligible amounts for certain developmental reinforcing or metal fibers to millions of kilograms for alumina-silica wools. However, certain issues are common to all these materials: the challenge of creating fibers from nonductile materials, the importance of fiber surface modification and the properties of composites relative to homogeneous materials. Data for the major producing world regions are included in each of the fiber and wool sections.

High-performance reinforcing fibers (boron fibers, ceramic fibers and whiskers) can be used as reinforcements in polymer, metal and ceramic matrices. The high strength-to-weight and modulus-to-weight (i.e., stiffness-to-weight) ratios of the fibers allow the fabrication of composite materials that are superior in physical properties to much heavier homogeneous metal materials.

High-temperature insulation wools are man-made mineral wools suitable for use as heat-insulating materials above 600°C. They are used principally for insulating and refractory qualities in the absence of heavy mechanical loading. They are used primarily in the form of blankets, boards or modules as insulation and refractory materials for furnace linings and related applications (alumina-silica, alumina and zirconia).

Silica fibers are high-purity silicon dioxide (greater than 94% SiO2) materials that are used in a variety of insulation, heat-protection and reinforcement applications for both industrial and aerospace industries. They have high mechanical strength against pulling and even bending, provided that the fiber is not too thick and that the surfaces are well prepared. The mechanical strength of a fiber can be further improved with a suitable polymer jacket. Cleaving silica fiber ends can also provide nicely flat surfaces with sufficient optical quality to meet requirements for aerospace applications.

Zirconia fibers, based on zirconium dioxide, are high-performance/high-cost ceramic refractory fibers that exhibit maximum use temperatures significantly exceeding those of most other commercially available refractory fibers. The maximum use temperature for the highest-performance zirconia product exceeds that of alumina board by as much as 450°C. Additionally, zirconia fiber products show excellent resistance to chemical attack and good thermal insulation properties.

This product review discusses metal fibers made of low-carbon steel, stainless steel, nickel and various alloys and metal-coated fibers, which include glass, carbon or aramid fibers that are coated with nickel, aluminum, copper or other metals. In addition, specialty aluminum flake is discussed, since it is manufactured by a process similar to that used to make glass or textile fibers.

Since their discovery in 1986, high-temperature superconducting (HTS) ceramics have captured the imagination of the scientific and business communities with their potential in transportation, electrical power generation and many other commercial and technical applications. Ultimate commercialization must cost-effectively overcome inherent problems of brittle-ceramic material fabrication without compromising the intrinsic HTS properties. If fabrication and application development problems were overcome, the market for HTS fibers could grow rapidly.

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