The distinction between alkali and alkali-free glass fibers is generally based on their different alkali metal oxide content.
Alkali-Free Glass Fiber (E-glass Fiber): Alkali metal oxide content is less than 0.05%. It exhibits excellent chemical stability, electrical insulation properties, high strength, and good water resistance. It is primarily used as electrical insulation material and reinforcement material in fiberglass applications.
Alkali Glass Fiber (C-glass Fiber): Alkali metal oxide content ranges from 11.5% to 12.5%, indicating a higher alkali content. It is unsuitable for electrical insulation applications, but it offers good chemical stability and strength. It is commonly used in latex cloth, grid cloth substrates, acid filter cloth, window screen substrates, and also as a reinforcement material in fiberglass applications where strict electrical performance and high strength requirements are not critical. It is cost-effective and widely applicable.
Why Does Alkali-Free Glass Fiber Have Excellent Water Resistance?
When water interacts with glass fiber, it first corrodes the alkali metal oxides on the surface of the glass fiber. As water exhibits alkaline properties, the glass fiber continues to react with the alkali solution over time, eventually leading to the destruction of the silica framework. This is where the advantages of alkali-free glass fiber become evident.
Why Does Alkali Glass Fiber Have Good Acid Resistance?
When acids interact with the metal oxides on the surface of the glass fiber, the metal oxides (Na2O, K2O) precipitate and dissolve. Acids react with the silicates in the glass fiber to form silicic acid, which rapidly polymerizes and solidifies into a thin protective film of silica on the glass surface. It has been proven that Na2O and K2O aid in the formation of this protective film.
What Factors Affect the Strength of Fiberglass?
1.Effect of Fiber Diameter and Length on Tensile Strength: Finer fiber diameters result in higher tensile strength. However, as fiber length increases, tensile strength significantly decreases.
2.Effect of Chemical Composition on Tensile Strength: Higher alkali content leads to lower strength. Alkali-free glass fibers exhibit 20% higher tensile strength compared to alkali glass fibers. Alkali-free glass fibers have higher forming temperatures, faster curing rates, and larger structural bond energies. Sodium oxide (Na2O), potassium oxide (K2O), and other alkaline oxides act as fluxing agents by breaking down the glass framework, resulting in a looser structure and enhanced solubility. Higher content of sodium oxide and potassium oxide correspondingly decreases the strength of the glass fiber.
3.Effect of Storage Time on Strength: The strength of glass fibers decreases after a certain period of storage due to fiber aging. This is caused by moisture and oxygen in the air that corrode the fibers.
4.Effect of Load Duration on Strength: The strength of glass fibers decreases with prolonged load duration, especially in environments with high humidity. This is due to the water absorbed in microcracks, which accelerates crack propagation under external forces.
In summary, alkali-free glass fibers exhibit superior strength, water resistance, and electrical insulation properties compared to alkali glass fibers. However, alkali glass fibers have better acid resistance and economic advantages compared to alkali-free glass fibers.
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