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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Recycling of Lead Pastes from Spent Lead–Acid Batteries: Thermodynamic Constraints for Desulphurization

Lead–acid batteries are important to modern society because of their wide usage and low cost. The primary source for production of new lead–acid batteries is from recycling spent lead–acid batteries. In spent lead–acid batteries, lead is primarily present as lead pastes. In lead pastes, the dominant component is lead sulfate (PbSO 4 , mineral name anglesite) and lead oxide sulfate (PbO•PbSO 4 , mineral name lanarkite), which accounts for more than 60% of lead pastes. In the recycling process for lead–acid batteries, the desulphurization of lead sulfate is the key part to the overall process. In this work, the thermodynamic constraints for desulphurization via the hydrometallurgical route for recycling lead pastes are presented. The thermodynamic constraints are established according to the thermodynamic model that is applicable and important to recycling of lead pastes via hydrometallurgical routes in high ionic strength solutions that are expected to be in industrial processes. The thermodynamic database is based on the Pitzer equations for calculations of activity coefficients of aqueous species. The desulphurization of lead sulfates represented by PbSO 4 can be achieved through the following routes. (1) conversion to lead oxalate in oxalate-bearing solutions; (2) conversion to lead monoxide in alkaline solutions; and (3) conversion to lead carbonate in carbonate solutions. Among the above three routes, the conversion to lead oxalate is environmentally friendly and has a strong thermodynamic driving force. Oxalate-bearing solutions such as oxalic acid and potassium oxalate solutions will provide high activities of oxalate that are many orders of magnitude higher than those required for conversion of anglesite or lanarkite to lead oxalate, in accordance with the thermodynamic model established for the oxalate system. An additional advantage of the oxalate conversion route is that no additional reductant is needed to reduce lead dioxide to lead oxide or lead sulfate, as there is a strong thermodynamic force to convert lead dioxide directly to lead oxalate. As lanarkite is an important sulfate-bearing phase in lead pastes, this study evaluates the solubility constant for lanarkite regarding the following reaction, based on the solubility data, PbO•PbSO 4 + 2H + ⇌ 2Pb 2+ + SO 4 2– + H 2 O(l).

25 ENERGY STORAGE↗
DOE OSTI2023

Pu(VI) Oxalate Crystal Structure and Evidence of Photoreduction to Pu(IV) Oxalate

We report the first crystal structure of a Pu(VI)-oxalate compound. This compound, [PuO 2 (C 2 O 4 )(H 2 O)]·2(H 2 O) (1), crystallizes in space group P21/c with a = 5.5993(3) Å, b = 16.8797(12) Å, c = 9.3886(6) Å, and β = 98.713(6)°. It is isostructural with the previously reported U(VI) compound, [UO 2 (C 2 O 4 )(H 2 O)]·2(H 2 O). Each plutonyl ion (PuO 2 2+ ) is coordinated in the equatorial plane by two side-on bidentate oxalates, creating an infinite chain along [001]. A coordinated water molecule and twisting of the oxalates lead to a distorted pentagonal bipyramidal geometry of the Pu. A photochemical degradation was observed for 1, which resulted in the formation of a secondary crystalline phase. The absorption spectrum of this secondary phase confirmed the presence of Pu(IV), but it did not match the spectrum of Pu(C 2 O 4 ) 2 ·6H 2 O, which is considered to be the primary product of Pu-oxalate precipitation. While compound 1 has previously been proposed to exist in solution, this is the first time it has been isolated via crystallization. Although redox interactions between Pu and oxalate have been documented in the literature, the present study is the first observation of a photochemical reduction of Pu(VI)-oxalate. Finally, this study has expanded on the limited understanding of the Pu(VI)-oxalate system, which is important for nuclear fuel cycle applications.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Guiding Principles for Geochemical/Thermodynamic Model Development and Validation in Nuclear Waste Disposal: A Close Examination of Recent Thermodynamic Models for H + —Nd 3+ —NO 3 - (—Oxalate) Systems

Development of a defensible source-term model (STM), usually a thermodynamical model for radionuclide solubility calculations, is critical to a performance assessment (PA) of a geologic repository for nuclear waste disposal. Such a model is generally subjected to rigorous regulatory scrutiny. In this article, we highlight key guiding principles for STM model development and validation in nuclear waste management. We illustrate these principles by closely examining three recently developed thermodynamic models with the Pitzer formulism for aqueous H + —Nd 3+ —NO 3 - (—oxalate) systems in a reverse alphabetical order of the authors: the XW model developed by Xiong and Wang, the OWC model developed by Oakes et al., and the GLC model developed by Guignot et al., among which the XW model deals with trace activity coefficients for Nd(III), while the OWC and GLC models are for concentrated Nd(NO 3 ) 3 electrolyte solutions. The principles highlighted include the following: (1) Principle 1. Validation against independent experimental data: A model should be validated against experimental data or field observations that have not been used in the original model parameterization. We tested the XW model against multiple independent experimental data sets including electromotive force (EMF), solubility, water vapor, and water activity measurements. The results show that the XW model is accurate and valid for its intended use for predicting trace activity coefficients and therefore Nd solubility in repository environments. (2) Principle 2. Testing for relevant and sensitive variables: Solution pH is such a variable for an STM and easily acquirable. All three models are checked for their ability to predict pH conditions in Nd(NO 3 ) 3 electrolyte solutions. The OWC model fails to provide a reasonable estimate for solution pH conditions, thus casting serious doubt on its validity for a source-term calculation. In contrast, both the XW and GLC models predict close-to-neutral pH values, in agreement with experimental measurements. (3) Principle 3. Honoring physical constraints: Upon close examination, it is found that the Nd(III)-NO 3 association schema in the OWC model suffers from two shortcomings. Firstly, its second stepwise stability constant for Nd(NO 3 ) 2+ (log K 2 ) is much higher than the first stepwise stability constant for NdNO 3 2+ (log K 1 ), thus violating the general rule of (log K 2 –log K 1 ) < 0, or $\frac{K1}{K2}$>1. Secondly, the OWC model predicts abnormally high activity coefficients for Nd(NO 3 ) 2 + (up to ~900) as the concentration increases. (4) Principle 4. Minimizing degrees of freedom for model fitting: The OWC model with nine fitted parameters is compared with the GLC model with five fitted parameters, as both models apply to the concentrated region for Nd(NO 3 ) 3 electrolyte solutions. The latter appears superior to the former because the latter can fit osmotic coefficient data equally well with fewer model parameters. The work presented here thus illustrates the salient points of geochemical model development, selection, and validation in nuclear waste management.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Probing the thermal decomposition of plutonium (III) oxalate with IR and Raman spectroscopy, X-ray diffraction, and electron microscopy

The thermal decomposition of Pu(III) oxalate was analyzed by Raman microspectroscopy, infrared spectroscopy, scanning electron microscopy, and powder X-ray diffraction. These data show that crystalline Pu 2 (C 2 O 4 ) 3 •9H 2 O progressively loses water and oxalate ligands as it is heated, which leads to a decrease in long-range lattice ordering, though minimal changes are observed in gross crystalline morphology. The onset of PuO 2 formation was observed between 200 - 250 °C. Thermal decomposition of oxalate ligands leads to the formation of CO 2 and plutonium oxalate-carbonate moieties, which had not been observed in previously published thermogravimetric measurements of Pu(III) oxalate. Formation of plutonium oxalate-carbonate moieties is believed to be associated with a change in the plutonium oxidation state from 3+ to 4+, which occurs prior to PuO 2 formation. The data provided herein demonstrate the rich spectroscopic nature of a rather underexplored, and technologically relevant, plutonium system. Ideally these results will further future investigations into the Pu(III) oxalate system both experimentally and computationally.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Selective Electrochemical Reduction of CO 2 to Metal Oxalates in Nonaqueous Solutions Using Trace Metal Pb on Carbon Supports Enhanced by a Tailored Microenvironment

In this work, the electroreduction of carbon dioxide (CO 2 ) to oxalate is enabled by incorporating trace metallic lead (Pb) on carbon‐based supports (CBS) with polymer overlayers. These composite materials serve as an efficient electrocatalytic system for the facile conversion and storage of CO 2 , a pernicious atmospheric pollutant. Results from controlled potential electrolysis experiments indicate that 1) trace metallic Pb on the ppb scale is active toward the reductive coupling of CO 2 to oxalate at comparable Faradaic efficiencies to bulk metallic Pb and 2) polymer encapsulation of this trace metallic Pb leads to promotion of CO 2 reduction (CO 2 R) selectively to metal oxalates over other products such as CO. Importantly, metal oxalates are important alternative cementitious materials and precursors for other materials’ synthesis applications. The solid products undergo rigorous spectroscopic characterization, including 13 CO 2 labeling experiments, to ensure the metal oxalates are in fact produced from CO 2 R. These findings serve as a model for leveraging microenvironment effects to enhance activity and selectivity for CO 2 R using trace‐metal catalysts for carbon utilization and storage technologies.

alternative cementitious materials↗
DOE OSTI2022

Experimental demonstration of necessary conditions for X-ray induced synthesis of cesium superoxide

Absorption of sufficiently energetic X-ray photons by a molecular system results in a cascade of ultrafast electronic relaxation processes which leads to a distortion and dissociation of its molecular structure. Here, in this work, we demonstrate that only decomposition of powdered cesium oxalate monohydrate induced by monochromatic X-ray irradiation under high pressure leads to the formation of cesium superoxide. Whereas, for an unhydrated form of cesium oxalate subjected to the same extreme conditions, only degradation of the electron density distribution is observed. Moreover, the corresponding model of X-ray induced electronic relaxation cascades with an emphasis on water molecules’ critical role is proposed. Our experimental results suggest that the presence of water molecules in initially solid-state systems (i.e. additional electronic relaxation channels) together with applied high pressure (reduced interatomic/intermolecular distance) could potentially be a universal criteria for chemical and structural synthesis of novel compounds via X-ray induced photochemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Priming mechanisms providing plants and microbes access to mineral-associated organic matter

Mineral-associated organic matter (MAOM) is considered a stable reservoir for soil nutrients that influences long-term soil carbon (C) and nitrogen (N) dynamics. However, recent experimental and theoretical evidence shows that root exudates may mobilize MAOM, thereby providing plants and microbes access to a large and N-rich pool. Given the mechanisms underlying MAOM C and N mobilization remain largely untested, we examined direct and indirect pathways by which root exudates destabilize this nutrient pool in laboratory mesocosms. We simulated root exudation with 13 C-labeled oxalic acid to test whether root exudates are directly capable of mobilizing MAOM from mineral surfaces; and with 13 C-labeled glucose to test whether indirect stimulation of microbial and extracellular enzyme activity leads to MAOM decomposition. We also tested the potential for oxalic acid and glucose to mobilize MAOM in an additional subset of sterilized soils to clarify the potential for non-microbial pathways of MAOM destabilization. Over the course of the 12-day MAOM incubation with and without simulated exudates, we measured C cycling (CO 2 respiration rates, 13 C–CO 2 efflux), N cycling (inorganic N pools, gross N mineralization) and related microbial processes (enzyme activities and microbial community composition via phospholipid fatty acid analysis). Both of the simulated root exudates enhanced MAOM-C mineralization, with cumulative respiration increasing 35–89% relative to the water-only control. Likewise, glucose additions enhanced the production of an exo-cellulase and a chitinase by up to 130% and 39%, respectively, while oxalic acid enhanced oxidative enzyme activities up to 91% greater than control rates. We observed a positive association between glucose-induced shifts in enzyme activities, MAOM-C mineralization, and gross ammonification. Oxalic acid additions were associated with initial increases in fungal relative abundance and in sterile soils appeared to stimulate the release of metals and dissolved organic nitrogen into exchangeable pools. Our results indicate that common root exudates, like glucose and oxalic acid, can significantly increase the turnover and potential release of C and N from MAOM through indirect (e.g., enzyme induction) and direct (e.g., mobilization of metal oxides) mechanisms.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Mechanistic Pathways for the Molecular Step Growth of Calcium Oxalate Monohydrate Crystal Revealed by In Situ Liquid-Phase Atomic Force Microscopy

Calcium oxalate monohydrate (COM) crystal is the most common crystalline component of human kidney stones. The molecular-scale inhibitory mechanisms of COM crystal growth by urinary biomolecules such as citrate and osteopontin adsorbed onto the crystal surface are now well understood. However, the pathways by which dissolved calcium and oxalate ions are incorporated into the molecular step of the COM crystal surface, leading to COM crystal growth—a prerequisite to be elucidated for developing effective therapeutics to inhibit COM stones—remain unknown. Here, using in situ liquid-phase atomic microscopy along with a step kinetic model, we reveal the pathways of the calcium and oxalate ions into the COM molecular step via the growth speed analysis of the molecular steps with respect to their step width at the nanoscale. Our results show that, primarily, the ions are adsorbed onto the terrace of the crystal surface from the solution—the rate-controlling stage for the molecular step growth, i.e., COM crystal growth—and then diffuse over it and are eventually incorporated into the steps. This primary pathway of the ions is unaffected by the model peptide D-Asp6 adsorbed on the COM crystal surface, suggesting that urinary biomolecules will not alter the pathway. These new findings rendering an essential understanding of the fundamental growth mechanism of COM crystal at the nanoscale provide crucial insights beneficial to the development of effective therapeutics for COM kidney stones.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

X-ray induced synthesis of beta tin (β-Sn)

The destabilization of molecular structures via hard X-rays has been previously utilized to synthesize novel compounds. Here, in this study, we report that the monochromatic X-ray induced decomposition of tin(II) oxalate (SnC 2 O 4 ) at ambient and 0.6 GPa pressures lead to the formation of beta tin (β-Sn). At 1 GPa, only the degradation of SnC 2 O 4 crystal structure is observed without any indication of β-Sn at the end of irradiation. The maximum transformation yield is achieved at 0.6 GPa suggesting the critical role of intermolecular distance in X-ray induced synthesis of β-Sn. Moreover, a modified Avrami equation is utilized to describe the kinetics and geometry of structural synthesis at ambient and 0.6 GPa. The obtained results demonstrate that X-ray irradiation can induce photochemical synthetic pathways different from conventional methods (e.g., high pressure, temperature, stoichiometric mixing) and that high pressure (HP) can be considered a tool to control X-ray induced photochemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Non-thermal atmospheric pressure plasma–liquid synthesis of organic acids in aqueous solution from carbon monoxide

This work aims at understanding the conversion of CO to organic acids, namely oxalic acid and formic acid, using non-thermal atmospheric pressure plasma over aqueous solutions. CO exhibited significantly higher conversion to organic acids (more than 15×) compared to CO 2 under the same reaction conditions. The result bolsters a proposed two-step process for CO 2 fixation, whereby CO 2 is first converted to CO, and then CO is converted to organic acids. The organic acids produced from CO are intermediates in the water–gas shift (WGS) reaction of CO in the presence of an aqueous solution to dissolved CO 2 and hydrogen gas. Based on a simple thermodynamic analysis, the organic acid yield was increased by lowering the plasma–liquid reaction temperature using an ice bath to cool the reaction flask. The composition of the organic acids could be varied by changing the pH of the solution. Oxalate was formed in higher concentrations with increasing solution pH above the pK a of the radical species (CO 2 )˙ − . Below the pK a value, formate was the exclusive organic acid formed. The production of formate has a rather weak pH dependence but is enhanced slightly at a basic pH above 10. Furthermore, at basic pH, the effect of electrolyte concentration comes into play. Higher electrolyte concentrations, leading to shorter electrolyte Debye lengths, resulted in lowered organic acid yields. The highest yields of organic acids obtained in our system were 122 mg L −1 for oxalate and 77 mg L −1 for formate at an optimum 1 mM NaOH concentration in the starting solution. This work is a successful pioneering example of CO to organic acids conversion using non-thermal plasmas, which opens the pathway for a promising two-step conversion process of CO 2 to organic acids.

Sudagar, Alcina Johnson [Washington University in ↗
DOE OSTI2023

Methylmercury Degradation by Trivalent Manganese

Methylmercury (MeHg) is a potent neurotoxin and has great adverse health impacts on humans. Organisms and sunlight-mediated demethylation are well-known detoxification pathways of MeHg, yet whether abiotic environmental components contribute to MeHg degradation remains poorly known. Here, in this paper, we report that MeHg can be degraded by trivalent manganese (Mn(III)), a naturally occurring and widespread oxidant. We found that 28 ± 4% MeHg could be degraded by Mn(III) located on synthesized Mn dioxide (MnO 2–x ) surfaces during the reaction of 0.91 μg·L –1 MeHg and 5 g·L –1 mineral at an initial pH of 6.0 for 12 h in 10 mM NaNO 3 at 25 °C. The presence of low-molecular-weight organic acids (e.g., oxalate and citrate) substantially enhances MeHg degradation by MnO 2–x via the formation of soluble Mn(III)-ligand complexes, leading to the cleavage of the carbon–Hg bond. MeHg can also be degraded by reactions with Mn(III)-pyrophosphate complexes, with apparent degradation rate constants comparable to those by biotic and photolytic degradation. Thiol ligands (cysteine and glutathione) show negligible effects on MeHg demethylation by Mn(III). This research demonstrates potential roles of Mn(III) in degrading MeHg in natural environments, which may be further explored for remediating heavily polluted soils and engineered systems containing MeHg.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Sequential Selection for Minimizing the Variance with Application to Crystallization Experiments

For many crystal-based products (e.g., pharmaceuticals, energy storage), the size uniformity is not only a key quality attribute, but sometimes also an indicator of other attributes such as solid purity. This article proposes a sequential selection approach to find a proper experimental setting that leads to high uniformity, or equivalently, small variance for crystal sizes, from the advanced slug flow reaction crystallization process of a model crystal, called manganese oxalate hydrate. The proposed sequential selection approach contains a Bayesian adaptive method to incorporate new uniformity measurements in each step and two design acquisition functions to improve the selection of the most promising experimental setting in terms of minimizing the variance. We study the performance of the proposed approach through multiple synthetic numerical studies, as well as a case study based on data from slug flow crystallization experiments. Throughout these studies, the proposed approach shows competitive performance in identifying the best experimental setting.

Expected improvement↗
DOE OSTI2022

Electrolytes Containing Triethyl Phosphate Solubilized Lithium Nitrate for Improved Silicon Anode Performance

An electrolyte consisting of lithium nitrate (LiNO3) and lithium difluoro(oxalato)borate (LiDFOB) in ethylene carbonate (EC), ethylmethyl carbonate (EMC), and triethyl phosphate (TEP) is used to improve the long-term cycling stability of silicon anodes. TEP was selected for its ability to dissolve LiNO 3 in carbonates to a concentration of ~0.2 M. The large amount of LiNO 3 combined with the LiDFOB salt leads to a capacity retention of 87.1% after one hundred cycles due to the formation of a relatively stable solid electrolyte interphase (SEI). Ex-situ surface analysis reveals that the SEI consists of oxalates, lithium alkyl carbonates, borates, and nitrate reduction products. By selecting two components which are preferentially reduced (LiNO 3 and LiDFOB), the SEI is able to inhibit continuous solvent decomposition and allows for improved electrochemical cycling for pure silicon anodes.

25 ENERGY STORAGE↗
DOE OSTI2023

Bioleaching to produce clean loblolly pine for thermochemical conversion

Lignocellulosic biomass contains inorganic elements that could induce slagging, ash fouling, and emission of both corrosive and harmful gases during thermochemical conversion. Water leaching pretreatment can remove most of the water-soluble elements, while it has limited industrial applicability due to its ineffectiveness in removing water-insoluble elements. Bioleaching is an alternative pretreatment method which has not been fully studied. In this work, bioleaching by Aspergillus niger strains NRRL 2001, NRRL 3122, and NRRL 567 was conducted to pretreat loblolly pine biomass with added water. Further, the removal of inorganic elements (K, Ca, Mg, and S) by bioleaching with A. niger NRRL 2001 was compared with chemical leaching with citric acid, HCl, and NaOH. It was shown that the pH reduction during bioleaching greatly improved K and Mg leaching to the point comparable to acid leaching, whereas Ca was precipitated by oxalic acid produced by the fungus. Bioleaching was also conducted in manually separated needles and chips components of loblolly pine. Glucose was added at different levels to assist bioleaching. At higher glucose levels, gluconic acid and citric acid were produced during bioleaching, leading to the increase of K, Ca, and Mg removal rates by more than 35%, 180%, and 390%, respectively, from the feedstock as compared with water leaching. Overall, bioleaching greatly improved removal of K, Ca, Mg, but not S from loblolly pine feedstocks as compared with water leaching.

09 BIOMASS FUELS↗
DOE OSTI2024

SELF-HEALING PNEUMATIC ACTUATOR DIAPHRAGMS

In the oil and gas industry, damaged diaphragms in pneumatic actuators can lead to unintended methane leaks, increasing emissions. In this work, replacement self-healing diaphragms are manufactured for a commercial pneumatic actuator. To enable self-healing, hollow microvascular networks are created within the diaphragms using sacrificial 3D printed PLA w/ tin(II) oxalate. These microvascular networks are filled with healing chemistries and, upon damage, rupture. After rupturing, the healing chemistries mix and cure to “heal” the damage and reduce leaks. Separate actuator test stands using nitrogen gas and using natural gas were developed to assess the healing performance of diaphragms. A fatigue stand was also developed to evaluate the effects of the different microvascular network geometries on the fatigue life of diaphragms. Our results demonstrate self-healing in diaphragms subjected to damage and tested for leaks. In fatigue testing, our results indicate that the introduction of microvascular networks does not influence the fatigue life.

Self-healing, pneumatic actuator↗
DOE OSTI2022

Hematite Crystallization from a Two-Line Ferrihydrite Suspension

Rational design and synthesis of materials, determination of environmental conditions at the time of mineral formation, and definition of mechanisms in biomineralizing systems all require an understanding of the effect of multiple factors on modulating crystallization pathways. In this study, we investigate the influence of temperature, oxalate additive, aging time, and addition of seed crystals on hematite (α-Fe 2 O 3 , Hm) crystallization from a two-line ferrihydrite (Fe 2 O 3 ·xH 2 O, Fh) suspension. We also investigate the effect of temperature on the aging of spindle-shaped Hm mesocrystals, which we synthesize through the addition of sodium oxalate. The results show that Hm mesocrystals form in a temperature window of 45 °C-130 °C. Temperatures ≥ 140 °C favor formation of rhombohedral Hm, suggesting classical monomer-by-monomer growth dominates, whereas crystallization by particle attachment (CPA) is dominant between 45 and 90 °C, while the two processes compete in the intermediate temperature range. Aging of mesocrystals in the original solution at 90 °C or 180 °C leads to a slow morphological evolution towards rhombohedral crystals due to Ostwald ripening. Then, by utilizing rhombohedral Hm and rod-shaped goethite as substrates on which to assemble the mesocrystals, we demonstrate formation of complex heterogeneous structures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Chloride Molten Salt Electrolysis Enables Integrated and Energy-Efficient Process for NdFeB Magnet Fabrication

Rare-earth elements (REEs) have been identified by NATO, the USDOE, and USGS as critical materials, i.e., materials which have significant demand yet pose supply-chain risks. Many of the existing processes for separations, metallization, and final parts production used across the REE supply chain involve energy intensive steps. For example, neodymium (Nd or NdPr) is produced using oxyfluoride electrolysis of Nd 2 O 3 , which requires hydrofluoric acid to produce a key electrolyte component (NdF 3 ) and generates undesired perfluorocarbon (PFC) gases. Such challenges make securing a resilient supply chain for NdFeB permanent magnets in countries like the United States prohibitively difficult. Here, we propose a chloride-based MSE process that circumvents these challenges, delivering high-purity NdPr from a (NdPr)Cl 3 feed from upstream REE separations. This eliminates environmentally-damaging steps of oxalate or carbonate precipitation and calcination, and enables superior production rates due to greater solubility of (NdPr)Cl 3 in chloride melts compared to Nd 2 O 3 . We show that CMSE generates high-purity NdPr (99.4 wt.%) while being energy-efficient (~ 6 kWh/kg-Nd). NdPr from CMSE was used to fabricate a NdFeB magnet with an excellent maximum energy product (> 40 MGOe), comparable to commercially available NdFeB magnets. This establishes CMSE as a leading approach for integrated, energy-efficient NdFeB magnet production.

Materials science↗
DOE OSTI2022

ELASTOMERIC MICROVASCULAR SELF-HEALING MATERIALS

Damaged elastomeric diaphragms within pneumatic controllers used in the oil and gas industry lead to an unintended release of methane. Self-healing microvascular materials capable of healing various types of damage have been fabricated. These microvascular materials are designed to replace currently available commercial diaphragms found in pneumatic controllers and provide a solution to reduce unintended methane leaks. Poly(dimethylsiloxane) (PDMS) was used as the main matrix material, with additional testing conducted on polyurethane and flexibilised epoxy materials. Microvascular networks were implemented into the elastomeric membranes to act as ves- sels to deliver healing agents to the damaged areas. The complex, interdigitated channel networks were created using a 3D printed custom compounded filament composed of polylactic acid (PLA) and tin(II) oxalate. Two-part liquid casting polymers were poured around the channels into a mould to create samples with the scaffolding of the microvascular channels intact. Hollow microvascular networks were created by placing the samples within a vacuum oven at 250◦C which causes the thermal depolymerisation of PLA into its gaseous monomers. The manufactured materials were placed in test stands and pressurized using nitrogen gas to determine their healing and mechanical behaviour. Self-healing behaviour was demonstrated using PDMS matrix materials and healing chemistries within a pressure test cell. This test cell was designed to detect any damage to a sample by record- ing an outlet pressure. Damages including puncture holes, diagonal cuts and star-shaped central iv cuts were applied to the samples and a reduction in the outlet pressure was recorded for all sam- ples. A variation in channel spacing and diameter was studied to determine the optimal design of the microvascular network for self-healing performance. The mechanical performance of elastomeric membrane materials within a diaphragmatic pressurised stand was observed. Deformations and strains around the channels and channel inter- sections at the midplane of the materials were recorded using digital image correlation. Normal stresses were calculated using Hooke’s law and the material properties of the PDMS matrix. A reduction in leak rate, implying the success of self-healing, was recorded within manu- factured diaphragm samples tested within a commercial valve. PDMS is the favourable material when compared to polyurethane and flexibilised epoxy for creating

03 NATURAL GAS↗