Encyclopedia of Glass Science, Technology, History, and Culture. Группа авторов
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Note: CTE values correspond to temperature range from room temperature to 300 oC; Tsoft corresponds to glass viscosity of 107.6 Pa∙s as typically used in fiber glass production; TF is defined by melt viscosity of 102 Pa∙s as a reference temperature for drawing fibers; TM is defined by melt viscosity of 10 Pa∙s as a reference fining temperature to be reached in the industrial melting process.
2.1.6 S‐Glass
Known as S‐glass, fibers primarily composed of MgO, Al2O3, and SiO2 were first developed in the late 1960s for high‐temperature and high‐strength applications and further expanded into military ballistic protection applications in the 1970s [6]. Because of high liquidus temperature (1470 oC), fibers must be drawn at temperatures significantly greater than 1500 oC to avoid fiber breakage caused by crystallization as the fibers are formed. This property attribute means that S‐glass fibers must be drawn in a much lower viscosity range than that of typical commercial fibers (Section 3.2). The challenges of this severe process limit the number of product forms and result in very high costs that have limited the commercial utility of S‐glass fibers to high‐performance markets such as aerospace and military applications where strength and weight combined can justify a premium over other materials. There are no large‐scale commercial production platforms in the S‐glass family. Derivatives of S‐glass have been investigated through introduction of small amounts of B2O3 and other oxides (Li2O, CeO2) to improve glass melting and fiber‐forming performance. To date no large commercial‐scale production has materialized.
2.1.7 R‐Glass
For military applications, R‐glass was first developed in the mid‐1960s within the quaternary SiO2–Al2O3–CaO–MgO system. In its original chemistry, its production, like that of S‐glass, was limited because of the requirements imposed by its high melting temperature. The addition of CaO to the S‐glass ternary system improved the processing conditions required to make glass fibers while still providing a high level of strength, but conditions were still more challenging than E‐glass. Developments centered around the R‐glass compositional range increased in the mid‐00s, driven by the needs of wind‐turbine blade producers who required longer blades with higher‐modulus glass fibers to reduce the unit cost of electricity generation. Most of the improved technology made is based on reducing glass melting temperature while increasing fiber modulus, which has been realized by optimization of mixed alkaline earth oxides (MgO/CaO). As a result, large‐scale furnaces and large direct‐draw bushing operations are possible. [4]. These developments have provided a balance of mechanical performance, cost, and large‐volume production capability that is in good alignment with the scale of production and cost of energy drivers in the wind‐energy composites market. The speed at which these new high modulus fibers have been put on the market is unprecedented in glass‐fiber history.
2.1.8 Glass Type Summary
With its derivatives such as ECR glass, E‐glass continues to dominate global commercial sales of glass fibers for reinforcement applications. The unique combination of mechanical properties, weight savings, and durability combined with a wide array of available form factors in the form of fiber diameter, strand size, resin compatibility as delivered by sizing chemistry, continuous or chopped forms, and cost‐effectiveness make E‐glass fibers by far the best value for designing and manufacturing high‐performance composites on a large scale. In parallel with ongoing improvements in E‐glass performance, technology developments associated with high‐performance fibers, i.e. re‐engineered or derivatives of S‐glass, R‐glass, and D‐glass will continue to be key focus areas in the future. These technologies serve to expand the growth of glass‐fiber reinforcements in transportation, aerospace, both traditional and renewable energy, and safety and security markets. These added technology options in glass fiber address light weight, high strength and high modulus [4, 6], improved durability, and improved electrical performance such as low signal loss and high‐speed communication in the PWB industry [5].
In developing new glass fibers, a fundamental understanding of glass network structures and glass properties for both performance and processing are critical. In boron‐containing glasses such as E‐ and D‐glass, speciation of boron in the network, i.e. BO4 ↔ BO3 + NBO (non‐bridging oxygen), is affected by both melting temperature and glass composition [8]; in turn, melt viscosity and glass dielectric property are affected. Besides the speciation of silicate network affected by modifying oxides [9], all commercial silicate glass fibers contain alkaline earth oxides and alumina; an in‐depth understanding of composition effect (particularly high field strength metal oxides, MOx) on speciation of aluminum, i.e. MOx + AlOy ↔ MOx −