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Strange water behavior on aluminum oxide

Not all surfaces are created equally

March 16, 2020
March 16, 2020

Researchers adding water to the surface of alumina measured some surprising results. They were preparing the surface of an alumina crystal in ultrahigh vacuum, intending to achieve a hydroxylated surface to approximate another form of aluminum, called gibbsite (α-Al(OH)3). They're interested in gibbsite because it is part of the mix of materials that comprise highly radioactive waste stored in tanks at various former weapons production sites.

At water's interface with a defect-free face of an alumina crystal (oxygen atoms are purple, aluminum atoms are green) researchers, using temperature programmed desorption (TPD) and infrared spectra data, found evidence of molecular water only. Surprisingly, there was no dissolution of the water into its components since the expected hydroxyls (OH) are absent.

The water was supposed to adsorb to the alumina and then immediately dissociate or separate into its components creating hydroxyl or OH components. Surprisingly, the water remained intact, raising important questions regarding the fundamental reactions that govern chemical transformations of aluminum oxides and hydroxides. The new research stems from work at the Interfacial Dynamics in Radioactive Environments and Materials (IDREAM) Energy Frontier Research Center.

The work, led by Pacific Northwest National Laboratory scientists in collaboration with scientists at University of Notre Dame and Georgia Institute of Technology was published in The Journal of Physical Chemistry C in a paper titled, "Molecular Water Adsorption and Reactions on α-Al2O3(0001) and α-Alumina Particles."

Why it matters: Aluminum oxides play an important role in the processing of high-level radioactive waste because they are one of the largest, nonradioactive components of the wastes generated from defense nuclear materials production during the Cold War.

Detailed knowledge of water behavior on aluminum oxide surfaces is key to understanding corrosion and catalytic properties of alumina and other aluminum-based materials in engineering applications.

Summary:Researchers investigated the adsorption and reactions of water on well-characterized alumina under well-controlled experimental conditions: under ultrahigh vacuum (UHV), using temperature programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), electron-stimulated desorption (ESD) and other surface science techniques.

They found that water adsorbs on the pristine surface of an alumina crystal α-Al2O3(0001), with no evidence of further reaction. Conversely, when water contacts α-alumina particles under ambient conditions it dissociates and does create hydroxyls on the particles. Dissociation is energetically favorable for both surfaces, but it appears to be hindered on the defect-free surface of alumina, which is counter to some findings in the literature.

Using UHV and IR spectroscopy techniques, which is typically only done on metals, researchers observed the vibration of water when adsorbed on the face of an alumina crystal. Although surface hydroxyls from dissociation of the molecule were expected, no evidence was observed by IRAS used to measure the vibration. But when alumina nanoparticles were exposed to water, a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) instrument indicated the presence of surface hydroxyls.

What's next? More research is needed to understand why the experiments and theory indicate such different reactivities for this important surface of alumina and to discover if there’s a barrier for water to dissociate and, if so, how to get over that barrier.


This work was supported as part of IDREAM (Interfacial Dynamics in Radioactive Environments and Materials), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. The authors acknowledge the Notre Dame Radiation Laboratory, which is supported by DOE BES through Grant DE-FC02-04ER15533.

Sponsors: This work was supported as part of IDREAM (Interfacial Dynamics in Radioactive Environments and Materials), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences and led by Pacific Northwest National Laboratory (PNNL)

User Facilities: The experiments on α-Al2O3(0001) were performed in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at PNNL.

Research Team: Nikolay G. Petrik and Greg A. Kimmel (Pacific Northwest National Laboratory), Thomas M. Orlando and Patricia L. Huestis (Georgia Institute of Technology), Jay A. LaVerne and Alexandr B. Aleksandrov (University of Notre Dame).

Reference: N.G. Petrik, P.L. Huestis, J.A. LaVerne, A.B. Alekandr, T.M. Orlando, G.A. Kimmel. 2018. “Molecular Water Adsorption and Reactions on α-Al2O3(0001) and α-Alumina Particles.” The Journal of Physical Chemistry C2018, 122, 17, 9540-9551 DOI: 10.1021/acs.jpcc.8b01969

November 1, 2019

Aluminum complexes identified via vibrational fingerprints

Findings will allow complex forms of aluminum to be distinguished during aluminum processing

March 16, 2020
March 16, 2020

Dissolved aluminum formed during industrial processing has perplexed chemists by occurring in much greater concentrations than predicted. Efforts to explain the phenomenon have been hampered by an inability to accurately identify the concentrations of each aluminum species present. New research from scientists at the Interfacial Dynamics in Radioactive Environments and Materials (IDREAM) Energy Frontier Research Center sorts out which compounds are present and their concentrations, providing an important new tool with broad applicability.

Raman spectra of solutions composed of an aluminate monomer and two dimeric species. Vibrational bands predicted by ab-initio molecular dynamics (AIMD) shown in red and green. Overlapping IR and Raman bands cause different linear combinations of species to have the same overall spectra, preventing identification.

The work, led by Pacific Northwest National Laboratory scientists in collaboration with scientists at Washington State University and Washington River Protection Solutions, was featured in The Journal of Physical Chemistry B in a paper titled, "Ab Initio Molecular Dynamics Reveal Spectroscopic Siblings and Ion Pairing as New Challenges for Elucidating Prenucleation Aluminum Speciation."

Why it matters: This finding provides support for improved design of aluminum production and separations processes for energy generation and transmission to high level radioactive waste treatment.

Summary: Industrial processing of aluminum for energy production and/or high level radioactive waste clean-up requires dissolving aluminum complexes such as gibbsite (α-Al(OH)3) and boehmite (AlOOH), typically under highly alkaline conditions. Excessively high concentrations of dissolved aluminum could be explained by considering dimeric aluminum species, but spectroscopic evidence to support these species has not been conclusive. Multiple dimeric species are possible, including Al2O(OH)62- and Al2(OH)82-, which have overlapping vibrational bands that prevented unique identification, until now. 

In this work, we used a combination of Raman and infrared (IR) spectroscopies and computational methods (ab-initio molecular dynamics, AIMD) to resolve vibrational band assignments.  Solution phase monomeric Al(OH)4- and dimeric Al as either Al2O(OH)62- or Al2(OH)82- were resolved. In addition, band widths, anharmonic shifts, and average solvent effects were determined, enabling specific band assignments and providing vibrational fingerprints for each species.  Furthermore, solvent effects that are important in such concentrated solutions of electrolytes were determined.  These results provide a basis for improving equilibrium models for boehmite and gibbsite solubilities, which increases confidence in design of industrial aluminum processing schemes.

What's next? The unique identification of aluminum species using vibrational methods will now be applied to concentrated electrolyte solutions containing aluminate to resolve discrepancies in aluminum solubilities under alkaline conditions.


This work is related to the Basic Research Needs for Environmental Management, specifically the Priority Research Direction entitled "Elucidating and Exploiting Complex Speciation and Reactivity Far From Equilibrium".

Sponsors: This work was supported by IDREAM (Interfacial Dynamics in Radioactive Environments and Materials), an Energy Frontier Research Center managed for the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES).

User Facilities: A portion of the research was performed at the Environmental and Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research located at Pacific Northwest National Laboratory.

Research Team: Mateusz Dembowski, Sue B. Clark, Kevin M. Rosso, Gregory K. Schenter, Carolyn I. Pearce (Pacific Northwest National Laboratory), Maxime Pouvreau, Aurora E. Clark (Washington State University), and Jacob G. Reynolds (Washington River Protection Solutions).

Reference: M. Pouvreau, M. Dembowski, S.B. Clark, J.G. Reynolds, K.M. Rosso, G.K. Schenter, C.I. Pearce, A.E. Clark. 2018. "Ab Initio Molecular Dynamics Reveal Spectroscopic Siblings and Ion Pairing as New Challenges for Elucidating Prenucleation Aluminum Speciation." The Journal of Physical Chemistry B. DOI: 10.1021/acs.jpcb.8b04377

January 1, 2019

Improving nuclear waste storage models by studying the chemistry of material interactions

A female researcher wearing a blue lab coat and heat-resistant safety gloves pours molten glass out of a metal crucible onto a metal tray.

PNNL conducts research into glass, glass-ceramic, grout, metal, and metal-ceramic wasteforms that will withstand corrosion over geologic time.

PNNL | Andrea Starr

WastePD EFRC research on the glass-steel interface was published in Nature Materials

February 3, 2020
February 3, 2020

New research unravels the chemistry of how materials in the waste packages used for the disposal of high-level radioactive waste interact in deep geologic repository environments. Having a better understanding of the interactions between materials under various conditions provides more information to make waste storage performance models more robust.

“Many performance models use conservative approaches such as assuming that the steel canister walls don’t even exist or that they dissolve very fast. This study provides the opportunity to better incorporate the canister barrier in the models,” said Joseph Ryan, a PNNL materials scientist and coauthor on the paper, “Self-accelerated corrosion of nuclear waste forms at material interfaces,” published in Nature Materials.

The United States is converting highly radioactive nuclear waste, also known as high-level waste, into glass. The molten glass is poured into steel canisters for long-term storage and ultimate disposal in a geologic repository. The goal is to design waste storage and disposal systems that would remain safe for hundreds of thousands of years to come, even if they are exposed to water. Because of the extensive time span of waste storage, researchers turn to cutting-edge science to project what will happen during that time period. The data is used to inform extensive safety analyses—helping make sure the system is engineered to be compatible with the natural system so that waste remains separate from the environment.

“We can’t just do a test on a material and say, ‘That material corroded this much in 30 days and extrapolate that to a million years.’ It doesn’t work that way,” Ryan said. “At the most basic level, we try to understand the underlying chemistry of corrosion. Then, we feed that information into computer models to calculate the expected release over time.”

In this study, led by the WastePD Energy Frontier Research Center based at Ohio State University, researchers unpacked the chemistry that occurs when two materials are close together, focusing on glass-steel along with ceramic-steel interactions. This chemical situation could occur when water has percolated into the repository and has breached the steel canister, exposing the glass-steel interface to water.

When water finally breaches the waste package container, it will fill the microscopic space that forms between the solid glass and the steel canister. Chemical reactions that happen in localized and tiny microenvironments such as these can be quite different than those happening in a more open setting. In this case, this localized area can have a different chemistry than the surrounding solution, causing more corrosion than would be expected.

The researchers tested their theory in the laboratory. They pressed glass and steel together in salty liquid and kept it at 90° C (194° F) for a month. At the end of the experiment, they found differences in the width of thin layers that indicated higher corrosion between the glass-steel couple interface than in a control sample.

Why it matters: This research allows scientists to improve models that project how a disposal canister could perform in a deep geologic environment. Having a better understanding of the interactions between materials under various conditions provides more information to make the models more robust. Currently, some models project what happens to waste under the assumption that the steel canister walls do not exist. Operating under this pretext can result in higher projections of waste degradation than would likely occur when taking a conservative approach. But better understanding the chemistry of how the solid waste and the steel canister interact allows a scientifically based understanding of how the canisters behave and interact with the glass to be included in performance assessment models.

Summary: High-level waste is immobilized as glass in stainless steel canisters. On cooling, a confined crevice space forms at the stainless steel-glass interface. If the disposal canister is breached and if water can enter the steel-glass interface, it could result in anodic dissolution of the stainless steel, generating metal cations, which hydrolyze to form protons and strongly increase the local acidity. This acidic environment may locally enhance the corrosion of both the stainless steel and the glass, which leads to the release of cations from the glass. Further, the coupled corrosion may trigger the precipitation of additional secondary phases that may impact subsequent canister corrosion or nuclear glass durability.

What’s Next: While this study sheds light on the chemical interactions that occur at the stainless steel-glass interface, there are more interactions to explore. Ultimately, a better understanding of different chemical mechanisms will improve the overall performance model.


Sponsors: This work was supported as part of the Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under Award no. DESC0016584.

Research Team: Xiaolei Guo, Gerald S. Frankel, Gopal Viswanathan, Tianshu Li (Ohio State University); Stéphane Gin (CEA, France); Penghui Lei, Tiankai Yao, Jie Lian (Rensselaer Polytechnic Institute); Hongshen Liu, Dien Ngo, Seong H. Kim (Pennsylvania State University); Daniel K. Schreiber, John D. Vienna, Joseph V. Ryan (PNNL); Jincheng Du (University of North Texas)

January 27, 2020
JANUARY 10, 2020
Web Feature

Clark Recognized for Nuclear Chemistry Research

The world’s largest scientific society honored Sue B. Clark, a PNNL and WSU chemist, for contributions toward resolving our legacy of radioactive waste, advancing nuclear safeguards, and developing landmark nuclear research capabilities.
JUNE 7, 2019
Web Feature

A Promising Trap for Radioactive Waste

A radioactive chemical called pertechnetate is a bad actor when it’s in nuclear waste tanks. But researchers at PNNL and the University of South Florida have a new lead on how to selectively separate it from the nuclear waste for treatment.
MARCH 5, 2019
Web Feature

Radioactive Waste Within Reach

Installing new access holes (up to 6 feet in diameter) could reduce the overall time and cost to retrieve waste from Hanford's underground storage tanks, according to a structural analysis of the tank domes by PNNL and Becht Engineering.