Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol RE 2 O 3 -alkaline earth-aluminosilicate fiber glasses: Melt properties, crystallization, and the network structures Thibault Charpentier a , Nadège Ollier b , Hong Li c, ⁎ a NIMBE, CEA, CNRS, Université Paris-Saclay, 91191 Gif-sur-Yvette, cedex, France b Ecole Polytechnique, Laboratoire des Solides Irradies, CEA - CNRS/UMR 7642, F-91128 Palaiseau cedex, France c Nippon Electric Glass, 400 Guys Run Road, Cheswick, PA 14502, USA ARTICLE INFO Keywords: Fiber glass Rare earth oxide Crystallization Glass structure Viscosity ABSTRACT Glasses and/or glass fibers of a new glass system, RE 2 O 3 (RE = Sc,Y, La)-MgO-CaO-Al 2 O 3 -SiO 2 , were studied in detail, covering rare earth (RE) effects on high temperature viscosity, liquidus temperature and crystalline phases, softening and glass transition temperature, and speciation reactions of aluminum (AlO x , x = 4, 5) and silicate network (Q n , n = 4, 3, 2) using 27 Al and 29 Si MAS NMR and Raman spectroscopic methods. Rare earth oxides (RE 2 O 3 ) were shown to have a dual functionality, i.e., decreasing melt viscosity like a network modifier depolymerizing glass network, but increasing viscosity at low temperature, i.e., glass softening temperature (T soft ) and transition temperature (T g ), strengthening the glass network functioning like Al 2 O 3 . Liquidus tem- perature (T Liq ) was found to be sensitive to the type of RE 2 O 3 modifications in terms of their ionic field strength (IFS); Sc 3+ of the highest IFS increased, but La 3+ of the lowest IFS decreased T Liq .Effect of Y 3+ (intermediate IFS) on T Liq resembles Sc 3+ only at higher concentration. The overall results suggest that RE ions of different IFS have different “true” solubility limits in the host glass matrix, above which RE 2 Si 2 O 7 crystallizes. All of the glasses with and without RE 2 O 3 contained predominately four-fold coordinated aluminum, AlO 4 ; yet replace- ment of CaO by RE 2 O 3 increased AlO 5 according to 27 Al MQMAS NMR spectroscopic measurements. Raman spectroscopic results suggested that depolymerization of the silicate network. 1. Introduction Various types of continuous glass fibers have been used to reinforce plastic composites in the fields of automotive, consumer goods, che- mical storage tanks and transportation pipes, wind turbine blades, aerospace fabrics, printed circuit board substrate, etc. In commercial composite applications demanding for high modulus or both high strength and high modulus, R-Glass and S-Glass fibers are required, respectively [1]. The former is a quaternary system of MgO-CaO-Al 2 O 3 - SiO 2 (MCAS) and the latter is a ternary system of MgO-Al 2 O 3 -SiO 2 (MAS) [1–3]. R-Glass fiber has significantly lower glass melting and fiber drawing temperature, plus lower liquidus temperature, than S- Glass fiber, and therefore, can be made using a commercial fiber glass technology for a mass production, greater than 20,000 MT/y per fur- nace [2]. However, modulus and strength of R-Glass fibers are inferior to S-Glass fiber. On the other hand, S-Glass fibers has its own drawback, i.e., much higher processing temperatures of melting and fiber drawing [3] and hence, much higher production costs. No more than 4000 MT/y production capacity has been reported by using multiple small mini melters since its commercialization several decades ago [1]. The primary production challenge of S-Glass fiber comes from its high li- quidus temperature (T Liq ) near 1430 °C, whereas its fiber drawing temperature (T F ) defined at 100 Pa∙s viscosity is lower than T Liq . In turn, to avoid glass devitrification it forces S-Glass fiber being drawn at about 1500 °C at much lower viscosity. S-Glass fiber drawing at viscosity much lower than 100 Pa∙s (against fiber glass standard drawing prac- tice) can reduce fiber forming stability, adversely lowering the process efficiency. Composition modifications of S-Glass has been discussed in literature by introducing both Li 2 O and B 2 O 3 at the expense of MgO [4] with a marginal improvement. The modified S-Glass still requires the fiber actual drawing temperature significantly greater than T F because of T Liq being greater than T F . Recently, a new glass system, RE 2 O 3 -MgO-CaO-Al 2 O 3 -SiO 2 (ReMCAS), where RE 2 O 3 represents a family of rare earth oxides, has been developed [5]. For the ReMCAS system, as will de detailed in this study, RE 2 O 3 was shown to function like a glass network modifier, depolymerizing the network, reducing melt viscosity. At lower tem- peratures where glass viscosity at or > 10 6.6 Pa.s, RE 2 O 3 functions si- milar to Al 2 O 3 , strengthening the network and increasing both glass softening temperature (T soft , at 10 6.6 Pa.s) and glass transition https://doi.org/10.1016/j.jnoncrysol.2018.04.028 Received 26 February 2018; Received in revised form 13 April 2018; Accepted 16 April 2018 ⁎ Corresponding author. E-mail address: hli@ppg.com (H. Li). Journal of Non-Crystalline Solids 492 (2018) 115–125 0022-3093/ © 2018 Published by Elsevier B.V. T