Journal of the American Ceramic Society Awards Symposium: Journal of the American Ceramic Society Awards Symposium Session II
Sponsored by: ACerS Other
Program Organizers: William Fahrenholtz, Missouri University of Science and Technology

Wednesday 2:00 PM
November 4, 2020
Room: Virtual Meeting Room 14
Location: MS&T Virtual

Session Chair: Bill Fahrenholtz, Missouri University of Science and Technology

2:00 PM
Thermochemical Investigation of Lithium Borate Glasses and Crystals: Alexandra Navrotsky¹; Lili Wu²; Anastasia Koryttseva²; Christoph Grob³; ¹Arisona State University; ²University of California, Davis; ³Schott AG
    Lithium borate glasses and crystals with x = Li/(Li + B) of 0.2–0.5 have been synthesized by the quenching method. Their thermodynamics was analyzed by high–temperature oxide melt solutioncalorimetry. The formation enthalpies from oxides of glasses range from −33.6 to −67.3 kJ/mol and those of crystals range from −42.1 to −77.4 kJ/mol. The formation enthalpies of both glasses and crystals become more negative with increasing Li2O mole fraction up to 0.5. The enthalpies of formation of glasses can be fit over the entire composition range (0 < x < 1) by a quadratic polynomial. The vitrification enthalpies were derived for x = 0.2 to 0.5 and ranged from 8.5 to 17.6 kJ/mol. The main factors controlling energetics are the strongly exothermic acid–base reaction between the network former (B2O3) and the network modifier (Li2O) and the formation of tetrahedrally coordinated boron.

2:30 PM
Effect of CaF₂, B₂O₃ and the CaO/SiO₂ Mass Ratio on the Viscosity and Structure of B₂O₃–Containing Calcium–silicate–based Melts: Gihyun Kim¹; Il Sohn²; ¹The University of Tokyo; ²Yonsei University
    The relationship between the viscosity and structure of B₂O₃–containing calcium–silicate–based oxides and the effects of CaF₂, CaO, and B₂O₃ on the viscosity and their correlation with the structural aspects were studied using a rheometer with Fourier transformation infrared and Raman spectroscopy at below 1673K. The viscosity decreased with increasing CaF₂ addition up to 28wt% at a fixed CaO/SiO₂ ratio of 0.3 by depolymerization. At higher C/S ratios, the viscosity decreased in the presence of greater Ca²⁺ and O^2- supplied from CaO. With regard to the B₂O₃–melt, the structural polymerization was observed by comparing the B₂O₃–free to 4.4wt% B₂O₃ content. However, the viscosity was relatively constant with increasing B₂O₃ addition. However, the viscosity decreased due to greater simplification of the network structure above 4.4wt% B₂O₃.

3:00 PM
Glass-ceramics as Potential Waste Forms for Actinide Immobilization: Yingjie Zhang¹; Tao Wei¹; Zhaoming Zhang¹; Linggen Kong¹; Pranesh Dayal¹; Daniel Gregg¹; ¹ANSTO
    Actinide-bearing waste streams present a unique set of challenges for their immobilization and long-term disposal. They can range from pure to very impure forms, have long half-lives and can contain fissile material (e.g., Pu-239), thus requiring criticality control and safeguards measures. In this regard, glass-ceramics have been developed as potential waste forms for the immobilization of such actinide-rich radioactive wastes arising from the nuclear fuel cycle. They combine the advantages of conventional borosilicate glasses and their chemical and processing flexibilities such that they can accommodate processing chemicals which may not be incorporated in the ceramic phases, with the superb chemical durability of ceramic phases to host actinides. Recent advances have been made including new glass-ceramic systems, simplified processing techniques and actinide validations using plutonium. This invited talk is intended to provide an overview on some fundamental research activities at ANSTO focusing on the latest development of various glass-ceramic systems.

3:30 PM
Substitutional Effect of Na₂O with K₂O on the Viscosity and Structure of CaO-SiO₂-CaF₂-based Mold Flux Systems: MINSEOK SEO¹; Il Shon¹; ¹Yonsei University
    This study investigated the substitutional effect of Na₂O with K₂O on the viscosity and structure of molten CaO-SiO₂-CaF₂-based mold fluxes containing alkali-oxides at high temperature. The CaO/SiO₂ mass ratio (C/S) was fixed at 0.8 and CaF₂ was fixed at 10 mass pct. The total alkali-oxide was fixed at 20 mass pct. The K₂O/(Na₂O+K₂O) mass ratio was modified between 0.0 and 1.0 to determine the effect on substitution. Viscosity of the systems were measured by rotating spindle method at high temperatures, the viscosity was found to increase with higher K₂O/(Na₂O+K₂O). An apparent activation energy increased with higher K₂O/(Na₂O+K₂O), from 96 to 154 kJ/mol. Structure of the as-quenched fluxes was studied using Raman spectroscopy, it is found that the mole fraction of Q³ increase, while the mole fractions of Q² and Q⁰ decreased with higher K₂O/(Na₂O+K₂O). The NBO/Si (nonbridged oxygen per silicon cation) decreased from 1.97 to 1.58 with increasing K₂O/(Na₂O+K₂O).

4:00 PM
Advances in Polymer-assisted Sol-gel Synthesis of Aluminosilicate Precursors for Modern Cementitious Materials: Juan Pablo Gevaudan¹; Jaqueline Wallat²; Bimala Lama²; Wil V. Srubar²; ¹Pennsylvania State University; ²University of Colorado at Boulder
    This presentation explores recent advances and future trajectories in the utilization of polymer-assisted sol-gel (PSG) synthesis to produce modern cementitious materials. By leveraging nuclear magnetic resonance, X-ray diffraction and infrared spectroscopy experiments, we demonstrate how critical PSG factors (e.g., pH aging conditions, ion concentration, polymer type and architecture) affect the atomic structure of a sodium-stabilized aluminosilicate hydrate (N-A-S-H) geopolymer cement. More specifically, results demonstrate that polymer architecture is a key factor in producing undesirable phase segregation and incomplete dehydroxylation (vicinal silanol) in cement precursors. PEG-derived aluminosilicate precursors yield partial dissolution and produce geopolymer cements with variable silicate incorporation. Contrastingly, PVA-derived aluminosilicate powders produce geopolymer cements with identical mineralogy to that of metakaolin-based geopolymer cements and exhibit both Brønsted-acid sites near the aluminum nuclei and geminal silanol groups. We hypothesize three plausible metal-complexation processes of PSG, which can be leveraged to postulate future trajectories in the manufacturing of sustainable cementitious materials.