Metallic glasses (MGs) are an emerging class of materials possessing multiple desirable properties including high strength, hardness, and corrosion resistance when compared to their crystalline counterparts. However, most previously studied MGs are not useful in high temperature environments because they undergo the glass transition phenomenon and crystallize below the melting point. In addition, bulk MGs are typically found in multi-component systems, meaning that searching compositional space with a reasonable resolution using computational or experimental methods can be costly. In this study, an in-house developed genetic algorithm-based tool was used to locate alloy compositions with high glass forming ability (GFA) and high-temperature stability in the Ta-Ni-Co-(B) and Ta-Ni-Co-Nb alloy systems. GFA was predicted using an empirical predictive parameter known as P HSS. High-temperature stability was predicted using the CALPHAD method to calculate liquidus temperature. Justification for the use of P HSS to predict GFA of high-temperature MGs, as well as the use of liquidus temperature as a predictor of general high-temperature stability, is given in the form of a meta-analysis of previously reported MG compositions. The predictions made using this algorithm were analyzed and are presented herein. While high-temperature stability was the property of interest for this research, this framework could be used in the future to locate alloys with other application-specific material properties. This genetic algorithm-based tool enables the coupling of empirical parameters and CALPHAD to efficiently search multi-component space to locate glass-forming alloys with desirable properties.

The production of hydrogen through water electrolysis is a major limiting step in the implementation of hydrogen-based energy storage. Currently used materials for catalyzing the hydrogen evolution reaction require large overpotentials, reducing the efficiency of hydrogen production. Metallic glasses are of interest for use in electrocatalysis due to their high activity and diversity of catalytic sites. However, only a small selection of metallic glass compositions can be manufactured into bulk parts, necessitating the use of metallic glass coatings. In this research, a Zr-based metallic glass was produced as a thin film using sputtering deposition. Combinatorial co-sputtering was used to produce a library of quaternary Zr-based metallic glasses to enable high-throughput characterization of the anode material and electrochemical testing. Metallic glass surfaces were characterized prior to and after electrochemical testing using a range of techniques to explore the physiochemical properties of the catalytic surface. Nano-structured metallic glass coatings are a promising material for catalysis of the hydrogen evolution reaction. This work is funded by ARPA-e under DE-AR0001697. JRH is funded as a fellow under the NSF GRFP.

Instability of the solid-electrolyte interphase (SEI) formed on the surface of the anode is a major cause of capacity degradation in Li-ion and Li metal batteries. High-capacity anode materials which form a stable SEI are desirable for improving the lifetime performance of batteries made using these technologies. One such class of materials that has been suggested are Si-based metallic glasses. Si alloys have a high theoretical capacity, and the amorphous structure has been shown to improve capacity. The SEI layer that forms on these anodes is thin and highly stable. In this research, a genetic algorithm method was used to locate optimal compositions of Si-based metallic glasses for use in Li metal batteries. Sputtering was then employed as a high-throughput, combinatorial method to produce a library of compositions for initial characterization and electrochemical testing. Nanostructured metallic glass anodes with improved capacity and high electrochemically active surface area were then synthesized. The capacity and stability of these anode materials were tested in Li metal batteries. After battery testing, the SEI formed on the anode was characterized to understand its chemistry and structure. This work is funded by NASA under grant 80NSSC19M0152. JRH is funded as a fellow under the NSF GRFP.

Hydroxyapatite (HA) is commonly used as a bone substitute material, but it lacks mechanical strength when compared to native bone tissues. To improve the efficacy of HA as a bone substitute by improving the mechanical strength and cell growth attributes, porous composite scaffolds of HA and titania (HA-TiO2 ) were fabricated through a freeze-casting process. Three different compositions by weight percent, 25-75 HA-TiO2 , 50-50 HA-TiO2 , and 75-25 HA-TiO2 , were custom-made for testing. After sintering at 1250°C, these composite scaffolds exhibited improved mechanical properties compared to porous HA scaffolds. Substrate mixing was observed, which helped reduce crystal size and introduced new phases such as β-TCP and CaTiO3 , which also led to improved mechanical properties. The composition of 50-50 HA-TiO2 had the highest ultimate compressive strength of 3.12 ± 0.36 MPa and elastic modulus 63.29 ± 28.75 MPa. Human osteoblast cell proliferation assay also increased on all three different compositions when compared to porous HA at 14 days. These results highlight the potential of freeze casting composites for the fabrication of bone substitutes, which provide enhanced mechanical strength and biocompatibility while maintaining porosity.

Titanium dioxide nanotubes (NTs) anodically grown on a titanium metal substrate are of great interest to many fields due to their unique physiochemical properties and electrochemical behavior. For many applications, a heat treatment is required to impart the NTs with a useful crystalline structure. The exact processes which occur in NTs during this high-temperature transformation, including the anatase-to-rutile transition (ART), were not well understood. Previous studies conducted to understand this phenomenon largely made use of conventional materials characterization techniques on annealed NTs attached to the titanium substrate. Therefore, it was challenging to determine if and/or how the substrate influenced the ART. In this study, in situ transmission electron microscopy was used to observe the morphological and phase changes occurring at the oxide/metal interface of anodically formed NTs during annealing. Samples were prepared both with and without the substrate to understand the effects of the substrate on phase changes within the NTs. These investigations revealed that when the substrate is present, the oxide/metal interface is a bilayer structure in which the ART is initiated from the upper layer of the interface while hydride and nitride precipitation occurs in the bottom layer. At elevated temperatures (> 500°C), the substrate undergoes spalling and loses its ordered morphology and crystallinity. When the NTs are not attached to the substrate, there is no evidence of ART or precipitation. These findings highlight the crucial role that the titanium substrate plays in the morphological and phase transformation of NTs during annealing. In situ transmission electron microscopy (enabled observation of the changes occurring at the oxide/metal interface during annealing. In situ TEM identified the oxide/metal interface as the epicenter of the morphological and crystal phase transformation. The in situ TEM investigation revealed the influence of substrate on anatase to rutile phase transformation.

Pyroprocessing is a potential route to close the nuclear fuel cycle. Used nuclear fuel (UNF) is electrolytically reduced from UO2 to U0 at a stainless-steel cathode while oxygen evolution occurs at a platinum anode in a molten LiCl-Li2O environment. Platinum is consumed during this process as a result of the formation and spallation of lithium platinate. To increase the economic viability of pyroprocessing, alternative low-cost, electrochemically efficient materials are needed to replace platinum. In this study, metal-oxide coated 316L stainless streel rods were explored as potential replacements. The characteristics of these coatings in molten LiCl-Li2O was evaluated through electrochemical techniques. The surface chemistry of the coatings was explored through X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy and scanning electron microscopy before and after exposure to molten salts to understand the degradation of the coatings. Results detailing the performance of the coatings will be presented.

Introduction: Pulpitis results from the infiltration of mixed populations of bacteria which trigger inflammation in the dental pulp, causing significant disruption to these tissues. Clinically, pulpitis frequently leads to devitali-zation or extraction, as disinfection of the dental pulp while maintaining its vitality is extremely difficult. Here we describe the use of an electrocatalytic titanium dioxide (TiO2)-based apparatus adapted from water purifi-cation technology, which can efficiently deliver anti-microbial oxidants (e.g., hydroxyl radicals) when low voltages are applied. As these oxidants are also potentially harmful to pulp cells, oxidant exposure protocols that disrupt oral bacteria, yet are innocuous to dental pulp cells must be established. Methods: Stem cells from Human Exfoliated Deciduous teeth (SHEDs) and mixed salivary bacteria were exposed to apparatus generated oxidants for time points of 15, 100 or 300 s. SHED apoptosis, necrosis, and vitality post exposure were analyzed by florescent marker staining and flow cytometry. Destruction of mixed salivary bacteria was analyzed by post exposure counts of adherent bacterial cells. Results: When applied to SHEDs the apparatus generated oxidants do not significantly induce apoptosis or ne-crosis at any exposure time. SHED cell vitality is not decreased with apparatus exposure. Exposure to apparatus generated oxidants destroys mixed salivary bacteria, with significant destruction seen at 15 s and maximal destruction achieved at 100 s. Conclusions: This technology has the potential to be useful in the disinfection of deep lesions and pulp tissues, efficiently producing oxidants which eliminate bacteria but do not harm native pulp cells after relatively brief exposures. Clinical Significance: Incomplete disinfection of inflamed dental pulp is a significant cause of pulp destruction, leading to devitalization or extraction. Novel technology which enhances the disinfection of the pulp may provide clinicians with treatments options that preserve pulp vitality and tooth structure.

Molten eutectic LiCl-KCl salt is a widely used electrolyte for electrorefining uranium from spent nuclear fuel. Due to the hygroscopic nature of this salt, such operations must be performed under controlled atmospheric conditions, and waste salts require careful storage to avoid deliquescence and corrosion of container materials. This study investigated a potential processing path for reducing the degree of deliquescence through dilution to varying extents with NaCl. The hydration behavior of LiCl-KCl salts diluted with NaCl was evaluated in terms of mass gain due to water absorption, degree of deliquescence (including first appearances of standing water), and evidence of corrosion to stainless steel containers in a humid air environment (40 degrees C, 20% relative humidity). In this humid air environment, pure eutectic LiCl-KCl exhibited a 50 mass % increase due to water absorption and showed evidence of standing water after 24 h. Waste salt diluted with NaCl required loadings of 89 mass % NaCl in order to prevent deliquescence and exhibited a 3 mass % increase due to water absorption. After periodic observation for 48 h, standing water was observed near all ingots with the exception of the 89 mass % NaCl samples. Dilution with 89% NaCl was also found to reduce evidence of corrosion when stored in stainless steel crucibles. While dilution with NaCl greatly decreases steady-state hydration, the storage volume is increased similar to 10x through this procedure.

A sol–gel biotemplating technique for the creation of a cellulose–silica composite from Apium graveolens (Pascal celery) has been investigated. The sol–gel biotemplating technique was inspired by pH catalyzed methods used for the creation of hydrogels. This technique did not require the use of highly toxic chemicals or an elevated temperature, and therefore is more environmentally friendly than existing biotemplating techniques. The resulting cellulose–silica composites were geometrically similar to the templated live celery, demonstrating permeability under gas flow at elevated pressure, and the elastic modulus and ultimate compressive strength (UCS) increased by 15.05 × 10 4 % and 3880%, respectively, when compared to live celery. The lack of toxic chemicals or elevated temperature, and the dramatic increase in modulus and UCS provide a low-toxicity alternative to harness the complex and multiscale structure and porosity of organic tissues in bioinspired materials.

Metallic glasses that combine the mechanical properties of metals with the chemical durability of glasses are highly desirable, especially for applications in extreme environments such as those in nuclear and aerospace industries. However, commonly studied metallic glasses often crystallize at lower temperatures and are not suitable for such applications. In this research update, the authors highlight recent advances in metallic glasses with crystallization temperatures above 700\ifmmode \mathring{}\else \r{}\fi{}C. These high temperature metallic glasses are discussed in terms of the formation methods, the glass forming ability, as well as the thermodynamic properties and mechanical properties. An outlook section provides the reader with an overview of the areas of research that have thus far been neglected with a specific focus on corrosion and mechanical properties. Successful development of high temperature metallic glasses can lead to a new class of materials for extreme environments.

Evaluation of the physicochemical behavior and setting reactions of a novel inorganic pulp capping cement which makes use of the unique corrosion properties of sodium metasilicate (NaSi) glass. NaSi and calcium phosphate (CaP) glass powders were synthesized through a melt-quench method. Cements were created by mixing various amounts of the glasses with deionized water at a powder-to-liquid ratio of 2.5 g mL−1. Working and setting times were measured using the indentation standard ISO 9917-1. Sealing ability was tested by placing set samples of each composition in methylene blue dye solution for 24 h. Set samples were also submerged in phosphate buffered saline and incubated at 37 °C for one week. X-ray diffraction was used to identify mature crystalline phases after incubation. Infrared spectroscopy and scanning electron microscopy were used to characterize cements before and after setting and after incubation. Working and setting times measured in the ranges of 2–5 and 10–25 min, respectively. Working and setting time generally decrease with increased NaSi concentration. Cements with compositions of 25 and 33 wt% NaSi were found to resist the infiltration of dye and maintain their shape. Compositions outside this range absorbed dye and collapsed. Infrared spectroscopy provided insight into the setting mechanism of these cements. After one week in vitro, cements were found to contain crystalline phases matching chemically stable, bioactive phases. The combination of NaSi and CaP glasses has favorable setting behavior, sealing ability, and mature phases for pulp capping while relying on a relatively simple, inorganic composition.