International Journal of Applied Glass Science, 5/1/65-81(2014) DOI: 10. 111Iijag 12053 IN TERNATIONAL JOURNAL OF A pplied gl ass sC丨ENCE High-Performance Glass Fiber Development for Composite Applications Hong Li, *'I Cheryl Richards, * and James Watson Fiber glass Science and Technology, PPG Industries, Inc, 400 Guys Run Road, Cheswick Pennsylvania 15204 5 uQ The article provides a review of historical commercial glass fiber development and recent developments of high-perfor- mance glass fibers with improved mechanical performance for glass fiber-reinforced polymer-matrix composite applications lass composition design is outlined in conjunction with theoretical and experimental modeling approaches. Challenges in glass melting and fiber forming are briefly discussed. fiber processing. The article concludes with a summary that points to the continuous advancements in glass Glass fiber and glass fiber-reinforced plastic melting technology that meet the growing challenges of (GFRP) composite industries have been enjoying con- the commercial production of high-performance glass tinuous growth globally, especially in the most recent fibers decade. This article is intended to provide a general review, with examples, of the history of fiber glass Overview of Glass Fibers development as well as recent development. The review will cover glass fiber chemistry and composition design, mechanical property characterizations, and topics rele- Market growth vant to glass melting and fiber forming. This article by As GFRP materials have gained broader usage, no means provides a comprehensive review on the sub- global glass fiber output has steadily increased, to meet ject; rather, it provides researchers and professionals that demand, over the past decade. Applications in with an update on the state of glass fiber technology automotive, consumer goods, and industrial tanks, and with a focus on fibers with improved mechanical prop- piping markets have seen rapid expansion. Brisk growth erties. The article is divided into four major sections: has also been seen in wind turbine blades and printed (i)overview of glass fibers, (i) chemical approach to circuit board (PCB) applications. The growing glass fiber mechanical performance, (ii) glass fiber demands of existing GFRP products and identification mechanical property characterizations, and (iv) glass of new applications are further fueled by the mega ends of energy efficiency (automobile and aerospace "Members. The American Ceramic Society hlieppg.com industries requiring lighter weight), a cleaner environ- e 2013 The American Ceramic Sociery and wiley Periodicals, Inc ment(tied to energy efficiency and lower emissions)
High-Performance Glass Fiber Development for Composite Applications Hong Li,*,† Cheryl Richards,* and James Watson Fiber Glass Science and Technology, PPG Industries, Inc., 400 Guys Run Road, Cheswick, Pennsylvania 15204 The article provides a review of historical commercial glass fiber development and recent developments of high-performance glass fibers with improved mechanical performance for glass fiber-reinforced polymer–matrix composite applications. Glass composition design is outlined in conjunction with theoretical and experimental modeling approaches. Challenges in glass melting and fiber forming are briefly discussed. Introduction Glass fiber and glass fiber-reinforced plastic (GFRP) composite industries have been enjoying continuous growth globally, especially in the most recent decade. This article is intended to provide a general review, with examples, of the history of fiber glass development as well as recent development. The review will cover glass fiber chemistry and composition design, mechanical property characterizations, and topics relevant to glass melting and fiber forming. This article by no means provides a comprehensive review on the subject; rather, it provides researchers and professionals with an update on the state of glass fiber technology with a focus on fibers with improved mechanical properties. The article is divided into four major sections: (i) overview of glass fibers, (ii) chemical approach to glass fiber mechanical performance, (iii) glass fiber mechanical property characterizations, and (iv) glass fiber processing. The article concludes with a summary that points to the continuous advancements in glassmelting technology that meet the growing challenges of the commercial production of high-performance glass fibers. Overview of Glass Fibers Market Growth As GFRP materials have gained broader usage, global glass fiber output has steadily increased, to meet that demand, over the past decade. Applications in automotive, consumer goods, and industrial tanks, and piping markets have seen rapid expansion. Brisk growth has also been seen in wind turbine blades and printed circuit board (PCB) applications. The growing demands of existing GFRP products and identification of new applications are further fueled by the megatrends of energy efficiency (automobile and aerospace industries requiring lighter weight), a cleaner environment (tied to energy efficiency and lower emissions), *Members, The American Ceramic Society. † hli@ppg.com © 2013 The American Ceramic Society and Wiley Periodicals, Inc International Journal of Applied Glass Science, 5 [1] 65–81 (2014) DOI:10.1111/ijag.12053
International Journal of Applied Glass Science--Li, Richards, and Watson Vol.5,No.1,2014 and renewable energy production (wind turbines) E-Glass is the most widely used glass fber for Other key factors impacting the GFRP and is primarily composed of CaO, Al2O3, and expansion of the GFRP market have been the maturity SiOz, conditionally with B2O3 from 0 to 10 wt% of GFRP composites in commercial applications matu- E-Glass offers suitable mechanical properties(tensile rity and secure supplies of glass fiber products with strength and modulus), electrical properties [dielectric known performance features at competitive cost points. constant (Dk); dielectric loss (Df); and dielectric Figure I illustrates global glass fiber annual production, strength], and chemical stability for most GFRP appli whose growth in the recent decade has been strongly cations including those for PCB electronics and nume ous general industrial applications. General-purpose E-Glass fibers are defined according to ASTM D578 Classification and History of Commercial Glass specifications. Historically, E-Glass compositions started with relatively high concentrations of boron (B2O3)and Auorine (F or F2), which enhanced batch Glass fibers are the most common reinforcement melting, glass fining, and fiber drawing. Over the years, used for polymer-matrix composites and are classified E-Glass compositions with low or zero B2O3, and based on required key properties for specific composite essentially no fluoride, were developed to address envi- applications as highlighted in Fig. 2. The time periods ronmental and legislative regulatory requirements shown represent significant activities occurring These changes are reflected in the general purpose defi- research and development based on our literature search nition of E-Glass as shown in ASTM Standard D 578 and projections Section 4.2.2 4 A more specific designation for boron- free modified E-Glass composition is called out in Legend as improved resistance to corrosion by most acids 400 E-CR fiber development and commercialization and bushing technology that enabled high furnace fiber glass surfaced in the mid-1980s, was broadly cepted and produced in the 1990s, and is widely accepted today. Representative commercial E-CR fiber products in the market today include Advantexfrom 0042005200620072008200920102011 Owens Corning(OC, Columbus, OH), INNOFIBER CR fber glass from PPG Industries, Inc.(PPG, Pitts- burgh, PA), and E6-CR from Jushi Group Co. Ltd Fig.I. Global glass fiber production history(in metric ton). (Tongxiang, Zhejiang, China),etc. 1930194019501960197019801990200020102020 Fig. 2. History of major commercial glass fiber development
and renewable energy production (wind turbines). Other key factors impacting the growth and global expansion of the GFRP market have been the maturity of GFRP composites in commercial applications maturity and secure supplies of glass fiber products with known performance features at competitive cost points. Figure 1 illustrates global glass fiber annual production, whose growth in the recent decade has been strongly supported by Chinese production.1 Classification and History of Commercial Glass Fibers Glass fibers are the most common reinforcement used for polymer–matrix composites and are classified based on required key properties for specific composite applications as highlighted in Fig. 2. The time periods shown represent significant activities occurring in research and development based on our literature search and projections. E-Glass is the most widely used glass fiber for GFRP and is primarily composed of CaO, Al2O3, and SiO2, conditionally with B2O3 from 0 to 10 wt.%. E-Glass offers suitable mechanical properties (tensile strength and modulus), electrical properties [dielectric constant (Dk); dielectric loss (Df); and dielectric strength], and chemical stability for most GFRP applications including those for PCB electronics and numerous general industrial applications.2,3 General-purpose E-Glass fibers are defined according to ASTM D578 specifications.4 Historically, E-Glass compositions started with relatively high concentrations of boron (B2O3) and fluorine (F or F2), which enhanced batch melting, glass fining, and fiber drawing. Over the years, E-Glass compositions with low or zero B2O3, and essentially no fluoride, were developed to address environmental and legislative regulatory requirements. These changes are reflected in the general purpose defi- nition of E-Glass as shown in ASTM Standard D 578 Section 4.2.2.4 A more specific designation for boronfree modified E-Glass composition is called out in Section 4.2.4 of the standard. Known as E-CR Glass, it has improved resistance to corrosion by most acids. E-CR fiber development and commercialization have been further aided by advancements in furnace and bushing technology that enabled high furnace throughput. Large-scale commercialization of E-CR fiber glass surfaced in the mid-1980s, was broadly accepted and produced in the 1990s, and is widely accepted today. Representative commercial E-CR fiber products in the market today include Advantex from Owens Corning (OC, Columbus, OH), INNOFIBER CR fiber glass from PPG Industries, Inc. (PPG, Pittsburgh, PA), and E6-CR from Jushi Group Co. Ltd. (Tongxiang, Zhejiang, China), etc. Year 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 Glass fiber production (10 4 MT) 100 200 300 400 500 Legend Global China Fig. 1. Global glass fiber production history (in metric ton).1 Fig. 2. History of major commercial glass fiber development. 66 International Journal of Applied Glass Science—Li, Richards, and Watson Vol. 5, No. 1, 2014
amics.org/lAGS Higb-Performance Glass Fiber De Although E-CR glass fibers are evolving to beco fiber glass industry. High cost and technology barriers he GFRP industry standard for most corrosion-resis- remain as factors limiting the growth of D-Glass in tant applications, improved chemical resistance was PCB applications. One of the D-Glass derivatives, SI lly obtained from boron-free C-Glass fiber fibers (Nitto Boseki Co. Ltd, Fukushima, Japan) (Na2O, CaO, Al2O3, and Sio2), which offered good introduced small amounts of alkaline earth oxides and chemical resistance against acid attack. Boron-contain- alumina at the expense of boron to improve glass ing C-Glass fiber was invented in 1943(UE. Bowes, melting and fiber-forming characteristics. However, the US 2, 308, 857, OC, 1943), which had limited use in melting and forming processes remain significantly building material insulation applications because of challenged because of its lower resistance to acidic environments due to boron T relative to E-Glass. In late 2010, PPG introduced presence in the glass. The mechanical performance of INNOFIBER LD fiber glass, a low dielectric glass fiber boron-free C-Glass fiber is inferior to E-CR Glass and that offered glass-melting and fiber-forming characteris- E-Glass, and these properties limit its use as a rein- tics that were compatible with a E-Glass manufacturing fCO ment. Further limiting the broad commercial use pla Glass is the fact that it has lower hydrolytic resis S-Glass is primarily composed of MgO, Al2O3, tance under high humidity environments at elevated and Sio2 and was first developed in the 1960s primar temperatures. Starting in the mid-1960s, boron-free ily for high-temperature and high-strength applications C-Glass fiber and E-Glass fber products served the and later in 1970s for military ballistic protection general industrial market. Because of their lower cost, applications. S-Glass is difficult to fberize due to its boron-free C-Glass fiber products are still used in com- high liquidus temperature(1470.C). Liquidus tempera- bination with E-Glass fibers in nonstructural corrosion ture, Ti, is defined as the maximum temperature above barrier applications. However, boron-free C-Glass which all crystals are dissolved in molten glass. As a volume is <10% of fibers used in GFRP today. result, S-Glass has Ti greater than TE, indicating that Continuing on the theme of corrosion resistance, the glass exhibits a negative delta T(AT-TF-TD force concrete structures in the mid-1960s. This gla- Commercial examples include the S-2 Glass products AR-Glass fibers were developed as a solution to re from AGY(Aiken, SC). S-Glass derivatives, such as HS primarily composed of Na2O, CaO, ZrO2(17-24%), glass from Sinoma Science and Technology(Nanjing, and SiOz with a small amount of Al2O3. AR-Glass Jiangsu, China), offer melting technology improve fibers offer the highest resistance against alkaline as ments over S-2 Glass . Overall, however,commercial ell as acid-attacks. High concentrations of ZrO2 in applications using S-Glass fiber input are limited due the glass and its resultant higher melting temperature to significantly higher manufacturing costs in both (TM as defined by 10 Pa-s viscosity in glass industry) melting and fiber formi lead to very high product costs, which restricts its broad In the mid-1960s, R-Glass was first developed for use in general-purpose applications military applications. The glass is primarily composed As mentioned earlier, E-Glass offers adequate elec- of MgO, Cao, Al2O3, and SiOz. In its original chem trical properties, primarily driven by the low total alkali istry, such as S-Glass, usage was limited because of its (<2%)content of the glass, for PCB applications. high melting temperature requirement. Although these When higher signal transmission speeds in electronic early chemistries created melting challenges when man devices are required, D-Glass fibers or pure silica ufacturing R-Glass fibers, newly engineered R-Glass (SiO2) fibers offer the best achievable electrical proper- compositions have overcome the melting and fiber ties as measured using dielectric constant (Dk) and forming obstacles, becoming commercially attractive for dissipation factor(Df) among all fiber glass classes large-scale production D-Glass is also easier than pure SiO2 to melt and fiber ize. However, D-Glass fiber production is limited to small commercial scale because of its very high TN Historic Higb-Modulus and Higb-Strengtb Glass Fiber Developmen (1650° C)and high forming temperature(1400°C which is approximately 200C higher than traditional As earlier stated, both S-Glass and R-Glass have boron-containing E-Glass fiber products. Fiber-forming been restricted to limited applications because of high- temperature, TF, is defined at 100 Pa s viscosity by the temperature processing challenges preventing their
Although E-CR glass fibers are evolving to become the GFRP industry standard for most corrosion-resistant applications, improved chemical resistance was originally obtained from boron-free C-Glass fibers (Na2O, CaO, Al2O3, and SiO2), which offered good chemical resistance against acid attack. Boron-containing C-Glass fiber was invented in 1943 (U.E. Bowes, US 2,308,857, OC, 1943), which had limited use in building material insulation applications because of lower resistance to acidic environments due to boron presence in the glass. The mechanical performance of boron-free C-Glass fiber is inferior to E-CR Glass and E-Glass, and these properties limit its use as a reinforcement. Further limiting the broad commercial use of C-Glass is the fact that it has lower hydrolytic resistance under high humidity environments at elevated temperatures. Starting in the mid-1960s, boron-free C-Glass fiber and E-Glass fiber products served the general industrial market. Because of their lower cost, boron-free C-Glass fiber products are still used in combination with E-Glass fibers in nonstructural corrosion barrier applications. However, boron-free C-Glass volume is <10% of fibers used in GFRP today. Continuing on the theme of corrosion resistance, AR-Glass fibers were developed as a solution to reinforce concrete structures in the mid-1960s. This glass is primarily composed of Na2O, CaO, ZrO2 (17–24%), and SiO2 with a small amount of Al2O3. AR-Glass fibers offer the highest resistance against alkaline — as well as acid — attacks. High concentrations of ZrO2 in the glass and its resultant higher melting temperature (TM as defined by 10 Pas viscosity in glass industry) lead to very high product costs, which restricts its broad use in general-purpose applications. As mentioned earlier, E-Glass offers adequate electrical properties, primarily driven by the low total alkali (<2%) content of the glass, for PCB applications. When higher signal transmission speeds in electronic devices are required, D-Glass fibers or pure silica (SiO2) fibers offer the best achievable electrical properties as measured using dielectric constant (Dk) and dissipation factor (Df) among all fiber glass classes.5 D-Glass is also easier than pure SiO2 to melt and fiberize. However, D-Glass fiber production is limited to a small commercial scale because of its very high TM (1650°C) and high forming temperature (1400°C) which is approximately 200°C higher than traditional boron-containing E-Glass fiber products. Fiber-forming temperature, TF, is defined at 100 Pas viscosity by the fiber glass industry. High cost and technology barriers remain as factors limiting the growth of D-Glass in PCB applications. One of the D-Glass derivatives, SI fibers (Nitto Boseki Co. Ltd., Fukushima, Japan), introduced small amounts of alkaline earth oxides and alumina at the expense of boron to improve glassmelting and fiber-forming characteristics. However, the melting and forming processes remain significantly challenged because of its significantly higher TM and TF relative to E-Glass. In late 2010, PPG introduced INNOFIBER LD fiber glass, a low dielectric glass fiber that offered glass-melting and fiber-forming characteristics that were compatible with a E-Glass manufacturing platform.6,7 S-Glass is primarily composed of MgO, Al2O3, and SiO2 and was first developed in the 1960s primarily for high-temperature and high-strength applications and later in 1970s for military ballistic protection applications. S-Glass is difficult to fiberize due to its high liquidus temperature (1470°C). Liquidus temperature, TL, is defined as the maximum temperature above which all crystals are dissolved in molten glass. As a result, S-Glass has TL greater than TF, indicating that the glass exhibits a negative delta T (DT = TFTL). Commercial examples include the S-2 Glass products from AGY (Aiken, SC). S-Glass derivatives, such as HS glass from Sinoma Science and Technology (Nanjing, Jiangsu, China), offer melting technology improvements over S-2 Glass. 8,9 Overall, however, commercial applications using S-Glass fiber input are limited due to significantly higher manufacturing costs in both melting and fiber forming. In the mid-1960s, R-Glass was first developed for military applications. The glass is primarily composed of MgO, CaO, Al2O3, and SiO2. In its original chemistry, such as S-Glass, usage was limited because of its high melting temperature requirement. Although these early chemistries created melting challenges when manufacturing R-Glass fibers, newly engineered R-Glass compositions have overcome the melting and fiberforming obstacles, becoming commercially attractive for large-scale production. Historic High-Modulus and High-Strength Glass Fiber Development As earlier stated, both S-Glass and R-Glass have been restricted to limited applications because of hightemperature processing challenges — preventing their www.ceramics.org/IJAGS High-Performance Glass Fiber Development 67
International Journal of Applied Glass Science--Li, Richards, and Watson Vol.5,No.1,2014 use on large-scale commercial platforms. While no ulus have also been evaluated. For example, low silica breakthrough has been achieved in S-Glass fiber-pro- calcium aluminate glasses(by wt % 4-18 SiO2, 39-50 cessing technology, advances in R-Glass fibers, specifi CaO, and 39-48 Al2O3)were shown to offer high cally new glass composition development, have Young,s modulus between 98 and 112 GPa. All of significantly progressed since 2000. The accelerated the compositions lie across primary phase fields of ge development has been primarily driven by the market hlenite(2CaO Al2O3 SiO2), CaO A 2O3, and needs for longer wind turbine blades, which require 12Ca0. 7Al2O3 in the CaO-Al2O3-SiO2 ternary phase higher composite modulus. Commercial, large-scale diagram. These types of glasses are difficult to fiberize oduction of new R-Glass fibers, including INNOFI- because of their extremely high Ti(1335-1500C) BER XM glass fibers(PPG)o, I and OCV-HTM fibers greater than their T defined at 100 Pa's. To draw (OC), are now available for wind turbine manufac fibers without risking glass devitrification, which dis tures. The combination of new glass composition devel- ruts the continuous fber-forming process, one must opments of R-Glass fiber offerings aligned with markets draw the fibers at a higher temperature than TF or at that require higher performance has resulted in significantly lower viscosity than 100 Pas. As a result, ncreases in wind turbine blade length by 10-20% ver- fber-forming stability is adversely impacted, which will sus blades made using E-Glass fiber. In turn, the longe be discussed further lar blades improve power output by 21-41% without An extensive study of the liquidus surface of CaO, nificant increases in the overall blade weight. 3 MgO, and Cao/MgO aluminosilicate glasses has been In terms of glass chemistry, the new R-Glass fibers recently reported in a composition space(by wt %) are defined within the following space(by wt %) 56-65 0-22 CaO, 0-19 MgO, and 2-17.5 CaO and 1.5-13.5 SiO2, 13-20 Al2O3, 6-12 MgO, and 8-16 CaO. In Mgo. The reported compositions are plotted in per- addition, Li,O(<I wt %) is often used to lower glass- spective phase diagrams- where RO represents the melting and fiber-forming temperature. 10. 1f-18 The use sum of MgO and Cao (cf. Fig 3). The reported TL of other alkaline earth oxides to improve batch melting, ranges from 1280 to 1465C, with few exceptions uch as BaO and SrO, or divalent oxides, such as ZnO, >1465C. In the commercial fiber-forming process, the is also possible, but result in a penalty in glass batch cost actual fiber-forming temperature must be kept great without significant product performance improvements. than Ti by no <50C to avoid glass crystallization The new R-Glass composition development space dis- prior to exiting bushings. Should these glasses be pro- tinctively differs original duced in fber forms, their actual forming temperatures R-Glass composition space, defined as(by wt %): 50- would be between 1320 and 1515C- substantially 60 SiO2, 25-26 Al2O3, 6-15 MgO, 2-9 CaO, and no higher than any known commercially produced new alkali(H. Scheller, Glass Compositions, German Patent, R-Glass fibers P1596751.8(C38351), Saint-Gobain, France, 1965) The new R-Glass fibers developed since 2000 Besides the new glass chemistry development for (cf. Table D) exhibit TL 1230C, except for HiPer better fiber processability, it should be emphasized that tex. Comparing the literature database with the successful production of new R-Glass compositions has commercially made new R-Glass fibers, it follows that also benefited from newer manufacturing technologies the liquidus surface of the MgO-CaO-Al2O3-SiO2 is that have been implemented in fiber glass industry more highly nonlinear than the predictions based on since the 1990s. These technologies include oxyfuel the phase diagrams(cf. Fig 3)once minor oxides are combustion for better energy delivery and efficiency, introduced to the primary composition space, including higher-quality refractory materials for higher-tempera- alkalis (mostly Li2O and Na2O), iron(Fe2O3 and ture operation electrical boost melting for enhanced FeO), titanium(TiO2), etc. melting capacity of the melter, and newer bus materials that provide longer service life at higher ating temperatures.(Note: A detailed review of Chemical Approach to Fiber Glass Mechanical manufacturing technology is beyond the scope of this Performance eyond the new composition developments in the section,several known models of glass R-Glass positions that offer high mod- Youngs modulus and theory of glass fracture and
use on large-scale commercial platforms. While no breakthrough has been achieved in S-Glass fiber-processing technology, advances in R-Glass fibers, specifi- cally new glass composition development, have significantly progressed since 2000. The accelerated development has been primarily driven by the market needs for longer wind turbine blades, which require higher composite modulus. Commercial, large-scale production of new R-Glass fibers, including INNOFIBER XM glass fibers (PPG)10,11 and OCV-HTM fibers (OC),12 are now available for wind turbine manufactures. The combination of new glass composition developments of R-Glass fiber offerings aligned with markets that require higher performance has resulted in increases in wind turbine blade length by 10–20% versus blades made using E-Glass fiber. In turn, the longer blades improve power output by 21–41% without significant increases in the overall blade weight.13 In terms of glass chemistry, the new R-Glass fibers are defined within the following space (by wt.%): 56–65 SiO2, 13–20 Al2O3, 6–12 MgO, and 8–16 CaO. In addition, Li2O (<1 wt.%) is often used to lower glassmelting and fiber-forming temperature.10,14–18 The use of other alkaline earth oxides to improve batch melting, such as BaO and SrO, or divalent oxides, such as ZnO, is also possible, but result in a penalty in glass batch cost without significant product performance improvements. The new R-Glass composition development space distinctively differs from the original R-Glass composition space, defined as (by wt.%): 50– 60 SiO2, 25–26 Al2O3, 6–15 MgO, 2–9 CaO, and no alkali (H. Scheller, Glass Compositions, German Patent, P1596751.8 (C38351), Saint-Gobain, France, 1965). Besides the new glass chemistry development for better fiber processability, it should be emphasized that successful production of new R-Glass compositions has also benefited from newer manufacturing technologies that have been implemented in fiber glass industry since the 1990s. These technologies include oxyfuel combustion for better energy delivery and efficiency, higher-quality refractory materials for higher-temperature operation, electrical boost melting for enhanced melting capacity of the melter, and newer bushing materials that provide longer service life at higher operating temperatures. (Note: A detailed review of the manufacturing technology is beyond the scope of this article.) Beyond the new composition developments in the R-Glass space, other compositions that offer high modulus have also been evaluated. For example, low silica calcium aluminate glasses (by wt.%: 4–18 SiO2, 39–50 CaO, and 39–48 Al2O3) were shown to offer high Young’s modulus between 98 and 112 GPa.19 All of the compositions lie across primary phase fields of Gehlenite (2CaO·Al2O3·SiO2), CaO·Al2O3, and 12CaO·7Al2O3 in the CaO-Al2O3-SiO2 ternary phase diagram.20 These types of glasses are difficult to fiberize because of their extremely high TL (1335–1500°C), greater than their TF defined at 100 Pa·s. To draw fibers without risking glass devitrification, which disrupts the continuous fiber-forming process, one must draw the fibers at a higher temperature than TF or at significantly lower viscosity than 100 Pa·s. As a result, fiber-forming stability is adversely impacted, which will be discussed further later. An extensive study of the liquidus surface of CaO, MgO, and CaO/MgO aluminosilicate glasses has been recently reported in a composition space (by wt.%): 0–22 CaO, 0–19 MgO, and 2–17.5 CaO and 1.5–13.5 MgO.20 The reported compositions are plotted in perspective phase diagrams21,22 where RO represents the sum of MgO and CaO (cf. Fig. 3). The reported TL ranges from 1280 to 1465°C, with few exceptions >1465°C. In the commercial fiber-forming process, the actual fiber-forming temperature must be kept greater than TL by no <50°C to avoid glass crystallization prior to exiting bushings. Should these glasses be produced in fiber forms, their actual forming temperatures would be between 1320 and 1515°C — substantially higher than any known commercially produced new R-Glass fibers. The new R-Glass fibers developed since 2000 (cf. Table I) exhibit TL < 1230°C, except for HiPertexTM. Comparing the literature database20 with the commercially made new R-Glass fibers, it follows that the liquidus surface of the MgO-CaO-Al2O3-SiO2 is more highly nonlinear than the predictions based on the phase diagrams (cf. Fig. 3) once minor oxides are introduced to the primary composition space, including alkalis (mostly Li2O and Na2O), iron (Fe2O3 and FeO), titanium (TiO2), etc. Chemical Approach to Fiber Glass Mechanical Performance In this section, several known models of glass Young’s modulus and theory of glass fracture and 68 International Journal of Applied Glass Science—Li, Richards, and Watson Vol. 5, No. 1, 2014
R-Glass System Liquidus Temp TRE(Diopside, Anorthite, Quartz 1220-1410°C S-Glass System E-Glass System Sone SiO2 Liquidus Temp Cordierite) A203 1470°c Liquidus Tem CeO 9o% (Wollastonite 1070-1220°c Fig. 3. Typical cor ed as Sio Al,O, and(Cao+ MgO), of E-Glasses with and without boron(wi large blue circle), R-Glass(magenta), S-Glass (red), Low-SiO2 calcium aluminate glasses(purple), and high-Sioz alkaline earth(cao or MgO or both in gray triangle) aluminosilicate glasses on Cao-A2O3-SiOz Mgo-Al2O3-SiOz, and Cao-10%6MgO-Al2O3-SiOz phase failure probability by Weibull statistical analysis o=1/,(dUm/dr) Then, a general approach to glass chemistry design is The change of o with respect to the distance between two ions under the applied force, do/dr, leads to o=dr/ra(d Um/dr)=dE/ro(d- Um/dr) Young's Modulus of Glass and Glass Fibers The elastic modulus(E) is therefore inversely pro- Elastic modulus or Young's modulus of ionic- or portional to the fourth power of atomic spacing covalent-bonded inorganic crystalline solids is theoreti between two ions or two times of the Mandelung ally related to the electrostatic energy of attraction Uc (equal to -212241ro) of two opposite charged ions E=do/de=1/ro(d Um /dr2)=-2(a122/r4) (41, 22) with a spacing of ro. To account for many body interactions between ions within the solid. madelung energy(Um =aUo is used instead. The force applied to the two ions is dU/dr, and the related stress within Ithough the model has been cor a unit volume of the crystal r can be expressed as testing many crystalline materials, the a-value is not
failure probability by Weibull statistical analysis in conjunction with glass chemistry are first presented. Then, a general approach to glass chemistry design is outlined. Young’s Modulus of Glass and Glass Fibers Elastic modulus or Young’s modulus of ionic- or covalent-bonded inorganic crystalline solids is theoretically related to the electrostatic energy of attraction Uc (equal to z1z2e 2 /ro) of two opposite charged ions (z1, z2) with a spacing of ro. To account for many body interactions between ions within the solid, Madelung energy (Um = aUc) is used instead. The force applied to the two ions is dUm/dr, and the related stress within a unit volume of the crystal r 3 o can be expressed as r ¼ 1=r 3 o ðdUm=drÞ ð1Þ The change of r with respect to the distance between two ions under the applied force, dr/dr, leads to dr ¼ dr=r 2 o ðd2 Um=dr 2 Þ ¼ de=roðd2 Um=dr 2 Þ ð2Þ The elastic modulus (E) is therefore inversely proportional to the fourth power of atomic spacing between two ions or two times of the Mandelung energy, aU, per cubic volume of the system as E ¼ dr=de ¼ 1=roðd2 Um=dr 2 Þ¼2aðz1z2e2 =r 4 o Þ ¼ 2aUc=r 3 o ð3Þ Although the model has been confirmed from testing many crystalline materials, the a-value is not RO MgO, RO CaO, RO Al2O3 Al2O3 Al2O3 SiO2 SiO2 SiO2 E-Glass System S-Glass System R-Glass System Liquidus Temp (Wallastonite) 1070-1220oC Liquidus Temp (Diopside, Anorthite, Quartz) 1220 - 1410oC Liquidus Temp (Cordierite) ~ 1470oC Fig. 3. Typical composition projections, expressed as SiO2, Al2O3, and (CaO+MgO), of E-Glasses with and without boron (within a large blue circle), R-Glass (magenta), S-Glass (red), low-SiO2 calcium aluminate glasses (purple), and high-SiO2 alkaline earth (CaO or MgO or both in gray triangle) aluminosilicate glasses on CaO-Al2O3-SiO2, MgO-Al2O3-SiO2, and CaO-10% MgO-Al2O3-SiO2 phase diagrams.20,21 www.ceramics.org/IJAGS High-Performance Glass Fiber Development 69