Different Glass Fibers in Composites

here are different kinds of glass used in composites.  Such as E-glass, S-glass, C-glass. Electrical or E-glass fiber, so named because its chemical composition makes it an excellent electrical insulator, is particularly well suited to applications in which radio-signal transparency is desired, such as aircraft radomes, antennae and printed circuit boards. However, it is also the most economical glass fiber for composites, offering sufficient strength to meet the performance requirements in many applications at a relatively low cost. It has become the standard form of fiberglass, accounting for more than 90% of all glass-fiber reinforcements. At least 50% of E-glass fibers are made up of silica oxide; the balance comprises oxides of aluminum, boron, calcium and/or other compounds, including limestone, fluorspar, boric acid and clay.

When greater strength is desired, high-strength glass, first developed for military applications in the 1960s, is an option. Known by several names — S-glass in the US, R-glass in Europe and T-glass in Japan, its strand tensile strength is approximately 700 ksi, with a tensile modulus of up to 14 Msi. S-glass has appreciably greater silica oxide, aluminum oxide and magnesium oxide content than E-glass and is 40-70% stronger than E-glass.

E-glass and S-glass lose up to half of their tensile strength as temperatures increase from ambient to 540°C, although both fiber types still exhibit generally good strength in this elevated temperature range. Manufacturers are continually tweaking S-glass formulations. A new S-3 UHM (for ultra-high modulus) Glass, for example, was introduced by AGY (Aiken, SC, US) in 2012. The new S-3 glass has a tensile modulus of 14,359 — higher than S-glass and 40% higher than E-glass — due to improved fiber manufacturing as well as proprietary additives and melt chemistry. 

Although glass fibers have relatively high chemical resistance, they can be eroded by leaching action when exposed to water. For example, an E-glass filament 10μ in diameter typically loses 0.7% of its weight when placed in hot water for 24 hours. The erosion rate, however, slows significantly becuase the leached glass forms a protective barrier on the outside of the filament; only 0.9% total weight loss occurs after seven days of exposure. To slow erosion, moisture-resistant sizings, such as silane compounds, are applied during fiber manufacturing.

Corrosion-resistant glass, known as C-glass or E-CR glass, stands up better to an acid solution than does E-glass. However, E-glass and S-glass are much more resistant to sodium carbonate solution (a base) than is C-glass. A boron-free glass fiber, with performance and price comparable to E-glass, demonstrates greater corrosion resistance in acidic environments (similar to that of E-CR glass), higher elastic modulus and better performance in high temperatures than does E-glass. In addition, taking boron out of the manufacturing process produces fewer environmental impacts, a decided advantage.

 

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