Quartz Fiber: High Temperature Resistant, Flame Retardant, and Thermal Insulation

1. Abstract

Quartz fiber is a type of high-performance special glass fiber known for its high purity, high heat resistance, low dielectric constant and loss. It is commonly used in high-tech fields such as aerospace. Generated by intelligent technology.

2. Quartz Fiber Performance Characteristics

Quartz fiber has a high silica content, retaining some characteristics and performance of solid quartz. It exhibits high heat resistance, electrical insulation at high temperatures and frequencies, excellent chemical stability, can be used long-term below 1050℃, and withstand instantaneous high temperatures up to 1700℃. 

Its tensile strength is three times that of ordinary fibers. Additionally, it possesses superior dielectric properties, being the mineral fiber with the lowest dielectric constant and dielectric loss coefficient, with a 1MHz dielectric constant of 3.70 and a dielectric loss coefficient lower than 0.001. 

In high-frequency and below 700℃ regions, quartz fiber maintains the lowest and most stable dielectric constant and loss, while retaining over 70% of its strength. It is commonly used as structural reinforcement, thermal insulation and wave-transparent materials for critical parts of aircraft and spacecraft.

3. Preparation Process

l The manufacturing methods of quartz fiber mainly include direct melt drawing, rod drawing, and sol-gel methods, among which rod drawing is the primary industrial preparation method.

l The rod drawing process involves placing raw crystal or pure silica powder into a vacuum pressurized resistance furnace, melting it, then drawing it into fine rods (about 2mm in diameter). During drawing, a wetting agent is first applied to the quartz fiber, followed by drawing in an electric heating or oxyhydrogen flame environment to obtain monofilaments about 8μm in diameter. Finally, the fiber strands are twisted together to form fiber yarn or fabric.

l The specific drawing process can be briefly described as follows: High-temperature liquid quartz drips from the bottom end of the quartz rod, and the drawing machine maintains a constant rotation speed to stretch and solidify the fiber, forming continuous fibers. A new crescent-shaped fine filament called "fiber root" forms at the bottom of the quartz rod. It should be noted that the temperature of the single fiber drops significantly after it is drawn out, which can affect product performance.

4. Quartz Fiber Products and Application Areas

l Quartz fiber can be processed into various products such as quartz fiber yarn, cotton, felt, cloth, sleeves, short cut fibers, etc. Quartz fiber yarn is a common product widely used in the manufacture of aircraft radome antennas.

l Short cut fibers are made from pre-cut fixed length quartz glass fibers.

l Quartz fiber yarn is made from high-purity silica and natural quartz crystals into continuous long fibers with a SiO2 content of over 99.95%, capable of long-term use at high temperatures up to 1050℃, and features extremely low and stable dielectric constant and loss, making it an excellent flexible inorganic fiber material with high temperature resistance.

l Quartz fiber cloth is woven from quartz fiber yarn through various weaving methods like plain, satin twill and leno into cloth of different thicknesses and weaves, featuring high temperature resistance, high strength, low dielectric, low thermal conductivity, burn resistance, etc.

l Quartz fiber cotton consists of pure quartz fibers without binders, irregular in shape and arrangement giving it a curly appearance preventing compression of filler improving insulation; it is a good substitute for high silica fiber cotton, ceramic fiber cotton, basalt fiber cotton.

5. Factors Affecting Quartz Fiber Strength

l Fiber diameter and length generally, the finer the diameter of quartz fiber, the higher its tensile strength. Tensile strength is related to fiber length, decreasing significantly as length increases. The effect of diameter and length on quartz fiber can be explained by the microcrack hypothesis: as fiber diameter and length decrease, microcracks within the fiber decrease accordingly, increasing fiber strength.

l Glass liquid quality affects the strength of quartz fiber. Impurities in the glass composition or fluctuations in leak plate temperature may lead to crystallization in the fibers. Practice has shown that fibers with crystallization are weaker than amorphous fibers. Moreover, bubbles in the glass liquid can also reduce fiber strength.

l Surface treatment impacts strength. During continuous drawing, a wetting agent must be applied to individual fibers or bundles forming a protective film on the fiber surface to prevent mutual friction during textile processing which could damage the fiber and reduce strength. After heat treatment to remove wetting agent, quartz fiber cloth's strength decreases significantly but generally recovers after treatment with an intermediate binder because the coating protects the fiber and compensates for surface defects.