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Hydrogen holds promise for clean energy but damages piping - scientists seek solution
Experiments seek to demonstrate theories about how hydrogen weakens metal structures, which could help to overcome the issues caused by it
The use of hydrogen as an energy source faces a major obstacle: damage to the metal piping that transports it. Although the phenomenon of hydrogen embrittlement has been described for over 150 years, the theories explaining this deterioration have yet to be demonstrated experimentally. In an article published in the journal Advanced Engineering Materials, a group of researchers, with the participation of scientists from USP, review the theories on embrittlement, expose the difficulties in demonstrating it in the laboratory, and propose two experiments to detect hydrogen and its effects on the structures of materials. “After production, the hydrogen needs to be transported to industry and domestic consumers via piping. Hydrogen causes unavoidable embrittlement of these piping, which can lead to serious accidents. If there is a mixture of natural gas and hydrogen in these piping, just 1% of hydrogen gas is enough to embrittle them,” explains physicist Matheus Tunes, a professor at Montanuniversität Leoben in Austria, to Jornal da USP. One of the authors of the article, Tunes is a graduate of USP’s Institute of Physics (IF). “There are certain strategies in materials design that reduce the deleterious effect of hydrogen through its trapping. However, these strategies do not guarantee that the materials will not eventually degrade. Hydrogen brings to metallurgy a problem of materials operating in extreme environments”.
Matheus Tunes - Photo: Personal Archive
Professor Cláudio Schön, from USP’s School of Engineering (Poli) – who researches fracture and fatigue of materials, as well as the influence of hydrogen on these two phenomena – participated in the preparation of the review article by mentoring and validating the information presented, in particular. “In addition, given the experience gained as a participant in the energy group in USP’s thematic axis program, we expanded the context of the article to the aspect of green hydrogen transport that is needed to fight the effects of global warming,” he says. “This study demonstrates that new experimental techniques for detecting hydrogen are required to advance the validation of existing theories. Detecting mobile hydrogen in the microstructure of materials is a major challenge for contemporary metallurgy.”
Cláudio Geraldo Schön - Photo: Cecília Bastos/USP Images
According to the physicist, in the 19th century, during the Second Industrial Revolution, England dominated the development and production of steel, and one of the most common applications was through wires. “These wires were stored in sheds subject to environmental conditions, which led to atmospheric corrosion of the iron, forming rust,” he says. “The industry at the time developed a cleaning method in which the wires were washed with sulfuric acid, a process now known as pickling. After this washing, it was noticed then that the steel wires lost their ductility, in other words, they became more fragile.”
Tunis points out that the British metallurgist William H. Johnson decided to scientifically investigate this phenomenon around 1874, subjecting various iron and steel wires to a bath of sulfuric acid and measuring some of their mechanical properties. “He realized that the acid inevitably reduces the elongation under tension [length variation] of these materials to the point of completely weakening them,” he says. “During bending or folding tests, Johnson noticed bubbles and foam emerging from the fracture surface of these wires when exposed to acid. To notice such bubbles, British metallurgists used their tongues to moisten the fracture surface!”.
“Johnson suggested that these bubbles were formed by hydrogen gas, which would enter the metal during pickling and then be released onto the surface during fracturing. Curiously, Johnson proposed this idea at a time when the atomic theory was not fully developed and the size of atoms was not precisely known! Niels Bohr’s atomic model was developed in mid-1913,” the researcher notes. “Johnson published his findings in two scientific papers in 1875. Since he was the first to measure and report the mechanical properties of iron and steel wires after the action of acid, which causes hydrogen to enter the metal, he is considered to be the discoverer of hydrogen embrittlement, although its permeability in metals had previously been studied by the French scientists Saint-Claire Deville and Louis Cailletet”.
Experimental validation
“Currently, the theories developed to explain this phenomenon focus on analyzing the interactions between hydrogen and metals at the atomic level and microstructural defects at the nanoscale. Since hydrogen is the smallest atom in existence, measuring it in the microstructure of metals is one of the greatest challenges for contemporary experimental science,” says the physicist. “The purpose of the review article was to show to the scientific community that, although this problem has existed for more than 150 years, we are still only at the beginning of understanding it through Physics, given the limitations existing between theory and experimental validation.”
Tunes emphasizes that atom probe tomography (APT) is the only experimental technique that allows hydrogen to be identified on an atomic scale. “Although it resolves the position of hydrogen atoms when they are trapped in traps in the microstructure of metals, it does not measure ‘hydrogen-in-action’, that is, hydrogen that moves through materials and interacts with their atoms and defects, causing their embrittlement” he points out. “In fact, trapping hydrogen is a strategy to fight embrittlement, but measurements of this nature do not answer whether the theories about the phenomenon are valid or not.”
“There are many critical aspects to using APT. For example, to ensure that the hydrogen remains in the metal before measurements, these experiments need to be carried out under cryogenic conditions [subjected to low temperatures], and only three laboratories in the world have this instrumentation, which limits its wide validation,” says the researcher. “The biggest problem is differentiating charged hydrogen from that which is present in the atmosphere and enters the material during measurements, because the APT vacuum is not perfect, which contaminates the sample. To get around this problem, the vast majority of experiments use another chemical element, deuterium, and do not measure hydrogen itself.”
Professor Tunes’ research group at Montanuniversität Leoben is currently carrying out two projects aimed at detecting hydrogen and its effects on material structures. “In the first, I propose to detect ‘hydrogen-in-action’ in metals by means of the dispersion it causes in plasmon resonance, a physical effect that I discovered experimentally in the United States in 2019,” the physicist plans. “In the second project, we are going to build a ‘hydrogen cannon’ [HydroGun] that will accelerate and implant hydrogen ions directly into the microstructure of materials and at atomic resolution.”
“One of the theories of hydrogen embrittlement hypothesizes that when the chemical element enters the structure of transition metals, the hydrogen electron interacts with the electrons of the metals, causing repulsion and leading to the formation of cracks, but this effect has never been observed in real-time and on an atomic scale,” Tunes reveals. “We are currently trying to obtain funding to carry out both projects, and USP is one of the main partner institutions in these projects.”
Cover of the publication with the article - Photo: Publicity
In addition to Tunes, the article was signed by Patrick Willenshofer, Sebastian Samberger, Thomas Kremmer, and Philip Dumitraschkewitz, from Montanuniversität Leoben, and metallurgy professors Peter J. Uggowitzer from ETH (Switzerland), Milos B. Djukic, from the University of Belgrade (Serbia), Stefan Pogatscher, from Montanuniversität Leoben (Austria), and Cláudio Schön, from USP’s School of Engineering (Poli).
Professor Schon points out that Poli researchers are carrying out basic science projects aimed at understanding the behavior of hydrogen in materials with Montanuniversität Leoben and the University of Belgrade. “There is a master’s degree thesis in progress to understand hydrogen embrittlement in high mechanical strength aluminum alloys, in partnership with Montanuniversität Leoben,” he says. “In addition, there is a doctorate in progress at Poli, under my supervision and the co-supervision of Professor Djukic, from the University of Belgrade, with cooperation between USP, Federal Institute of Espírito Santo (IFES), Federal University of Rio Grande do Sul (UFRGS) and Brazilian Center for Research in Physics (CBPF), in which we hope to identify the mechanisms of crack nucleation under the effect of hydrogen. Future experimental techniques under development could provide valuable information for this doctorate work.”
More information: e-mail matheus.tunes@gmail.com, with Matheus Tunes
English version: Nexus Traduções
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A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.