What is Ceramic Fiber? | Types of Ceramic Fibers | Uses/Applications of Ceramic Fiber

What is Ceramic Fiber? | Types of Ceramic Fibers 

Ceramic fibers have a very large aspect ratio and a very small contrasting surface. Commercially available ceramic fiber, for example, has a fiber diameter of about 10 mm. Because of their geometry, the structures of the fibers are very different from those of the same type of material. In particular, fibers have very high strength, high pressure failure but also high chemical exposure. Fibers can be made as a fiber fabric, flowing, with short or long strands. Fine fibers are usually folded into what is called ‘rowing’, consisting of one 500–10,000 threads. Blending bonds keep the fibers flexible, making it much easier to process and handle, and it makes it possible for it to be synthesized into a wide variety of fibers.

Ceramic fibers were originally called Refractory Ceramic fibers when they were produced in the 1940s, and this material is now called high temperature heat wool. In the last half century, there have been significant advances in the processing and application of fine-grained ceramic fibers. Generally, it is made of equal parts of alumina and silica, and ranges from white to cream in color. The need for reinforcement of ceramic matrix composites (CMCs) to be used in the air at temperatures above 1000 ° C, as well as for solidification of metals (MMCs), has encouraged major changes in low-density ceramic fibers since their early development. as refractory insulation. Ideally, the ceramic fiber should show sufficient flexibility so that the preforms are woven and subsequently absorbed by the matrix material. The applications in question are located on gas turbines, both aeronautical and ground-based, temperature switches, pre-blocking fusion reactor walls, and the non-matrix use required for them as high-pressure candle filter filters.

Ceramic fiber is available in two forms, continuous (long length) and stop (short length). Alumina- and continuous silicate-based fibers of oxide are subjected to a sol-gel process but shorter oxide fibers with a melting point. On the other hand, silicon- and boron-based nonoxide ceramic fibers are currently being developed and produced by thermal modification of the polymer precursor process.

Types of Ceramic Fibers

Mainly ceramic fibers are of two types,

1. Ceramic oxide fibers

2. Ceramic nonoxide fibers

1. Ceramic oxide fibers

Ceramic oxide fibers in the form of long and short strands have been on sale since the 1970s. These fibers are usually composed of alumina (Al2O3) and alumina-silica alloy (Al2O3-SiO2) due to their high melting points are commonly used in very hot applications.

Ceramic oxide fibers are used both as insulation and reinforcement material. The best known examples of oxide ceramic fibers are composed of oxides such as silica (SiO2), mullite (3Al2O3.2SiO2), alumina (Al2O3), and zirconia (ZrO2) with distinct properties.

Recently, various methods such as slurry spinning, sol-gel spinning, and single crystal growth have been developed for the production of oxide-based ceramic fibers.

Alumina-based fibers (Al2O3) are the most common oxide fibers. These fibers exhibit excellent thermal, mechanical, and electrical properties such as high temperatures, high heat shock and crawling resistance, high dimensional stability, low coefficient of thermal expansion, and excellent dielectric properties. Alumina fibers are often used as building blocks in a variety of metal, ceramic, and polymer composites, which make them stronger and more durable. Suitable for load applications; the resulting compounds are resistant to higher temperatures than metals.

Nextel ceramic fibers are twisted, dried, and sintered at high temperatures. Nexel fibers are manufactured from composite-grade oxide fibers designed for use in a load-bearing structure in metallic, ceramic, and polymer metrics.

The Nexel 610 and 720 fibers have crystalline structures based on α-alumina and α-alumina / mullite, respectively. The Nexcel 610 fibers have higher power at room temperature than the Nexcel 720 fibers. The Nextel 650 commercial based alumina fiber was developed as an integrated reinforcement for high-performance applications. Nexel 650 oxide fibers contain phases of α-alumina and cubic zirconia.

2. Nonoxide ceramic fibers

The production of nonoxide fibers is difficult due to their high melting points and resistance to stiffness. Oxidation resistance is often their main deficiency. In these threads, extensive research has been done and reported on processing, microstructure, mechanical, and thermal stability. These ceramic wires can be of good or large diameter.

Silicon carbide fibers

Silicon carbide (SiC) fibers have an excellent combination of high strength, modulus, and thermal stability, which combines excellent oxidation resistance and mechanical properties (pressing forces) at high temperatures. Silicon carbide-based fibers are commonly used as a continuous fiber in a ceramic matrix. This type of CMC is used in the hot engine phase for power generation, etc.

Boron fibers

Boron fibers are produced commercially for CVD techniques; boron is usually covered with a thin layer of ground tungsten (~ 12 μm diameter) below. But the carbon substrate can also be used. Boron fiber with a diameter of 100 μm has a diameter of 2.6 g / cm3. It has a high melting point of 2040 ° C. The strongest strength of boron fiber is 3–4 GPa, while Young’s modulus is between 380 and 400 GPa. Thanks to their high-quality materials and density, they are used in aerospace, aerospace, and sports facilities such as golf shelves, tennis racks, and bicycle frames.

Other threads

There are many different types of nonoxide fiber, in addition to those mentioned above. Another type of synthetic ceramic fiber is silicon oxynitride (SiNO). SiCN based ceramic fibers and Si-Al-O-N ceramic fibers are also important types of nonoxide fiber.Basic Compositions of Ceramic Fiber:

1.      SiO₂ ——————->50-60 %

2.     Al₂O₃ ——————>30-50 %

3.      Na₂O-H₂O ————->0.1 %

4.     Fe₂O₃ ——————>0.04 %

5.      Leachable Chlorides —>10 ppm

Properties of Ceramic Fiber Textile Products

1.  Resistance to oils, solvents and chemicals

2. Proper resistance to oil

3. Good chemical resistance

4. Proper resistance of solvents

5. Flame retardant

6. Low thermal conductivity

7. Heat-resistant — can withstand temperatures of up to 1,260 ° C

8. Resistance to abrasions.

9. Severity of high temperatures

10. Excellent thermal shock resistance

11. Good dimensional stability

12. Low density

13. Non-combustible

14. Good flexibility

15. Continuous use limit 1260 ° C

16. Melting point 1790 ° CCVD technique

CVD is the most common method of producing ceramic fibers. Many nonoxide fibers used in CMC, MMC, and intermetallic compounds (IMCs) are made from CVD. This process is based on the placement of a layer of physical vapor on the backbone substrate as a monofilament.

1.      Melt Spinning Technique

In the normal melting process of a soluble substance, precursors (eg, oxides such as Al2O3) are dissolved and subjected to the spinning process. During spinning, the oxides in the molten state are all forced into the nozzle with great pressure and solidified by cooling. Fibres produced due to high cooling levels usually exhibit amorphous formation leading to instability. Rapid viscosity changes due to large temperature fluctuations lead to a lack of control over the width. In addition, a number of parameters such as spinning speed, pull rate, temperature and environmental conditions greatly affect the properties of synthetic fibers.

2.     Slurry spinning

This method is designed to avoid the deformation of the melt-spinning method. Both oxide and nonoxide fibers can be made by extrusion (spinning) of ceramic slurry. In this process, the solution is composed of three basic components: alumina particles (either solid or submerged in water), a suspension of the alumina precursor (eg, aluminum chlorohydroxide), and organic polymers. The precursor used in this process promotes overcrowding during sintering.Chemical conversion:
The chemical conversion/processing approach is based on the conversion of ceramic/inorganic precursor fibers into a different composition via chemical reactions by using an external compound. In this technique, the precursor fiber is subjected to the (atomic) deposition of the external compound that diffuses through the fiber surface.

After successful reaction of the components, the final fiber exhibits the desired chemical material composition. The most common example of this process is the conversion of a carbon precursor into SiC fibers using Si or SiO agents (the materials that make up the carbide) in the vapor phase.

Sol-Gel Process

In traditional processing techniques, it is relatively difficult to manufacture high-purity fibers and various compositions of composite ceramic oxide filaments. In particular, liquid immiscibility at melting temperatures and phase separation/crystallization during cooling are the main problems in those techniques. The sol-gel method is commonly used to produce oxide based ceramic fibers. Theoretically, the "sol" is composed of either colloidal particles, which may be crystalline or amorphous, or may be polymers in a solvent. The "gel" comprises a three-dimensional (3-D) continuous network that envelops a liquid phase, and in a colloidal gel, agglomerations of particles form this network. In a typical sol–gel route, low-molecular-weight metal alkoxides, which are dissolved in a liquid, are used as starting materials.

The resulting properties (eg, physical, mechanical, electrical and optical) of the fiber can be modified with the addition of various oxide and metal components. The final diameter of continuous filaments produced by the sol-gel method is generally in the range of 10–20 µm where the elastic modulus of the products changes from 150 to 373 GPa.

Uses/Applications of Ceramic Fiber

The use of ceramic fibers in composite applications has been attracting attention for the past decades. In particular, continuous ceramic fibers/filaments are commonly employed in high temperature applications rather than metals because of their high thermal tolerance and corrosion resistance.

From an industrial implementation point of view, ceramic fiber reinforced composites are used in many different commercial products such as aircraft engine components (turbine combusters, compressors and exhaust nozzles), automotive and gas turbine elements, aerospace missiles, heat exchangers, hot gas is done. Filter, rocket nozzle, gasket and wrapping insulation. Ceramic fiber is used in ballistic vests, bulletproof vests or bullet-resistant vests. Metal or ceramic plates can be used with a soft vest. High-tech ceramics are used in watch making to make watch cases.

Mainly for high temperature door seals and linings for furnaces. It is also used for security curtains, cable and pole protection, expansion joint seals and high temperature filtration systems in theatres. In the automotive industry, it is used to insulate catalytic converters, brake pads, airbags, clutch facings and seat belt controls. In the aerospace industry, ceramic fibers are used for tiles on the Space Shuttle and for heat shields on other spacecraft and airplanes. Ceramic thread is coated with Teflon so that sewing thread can be used on ceramic fabrics. In the home, ceramic fibers insulate toasters, deep* fryers, self-cleaning ovens, and boilers. Ceramic fiber products can be used for high temperature electrical insulation such as fire doors, fire curtains, fire blankets, spark pads and insulation covers.

Oxide and nonoxide ceramic fibers are increasingly being used as reinforcement materials for composites due to their unique properties of high elastic modulus and high temperature durability. Their properties make them valuable for use in automotive, aerospace and heat-resistant structural applications.