Tag Archives: research

Predicting release rates of hydrogen from stainless steel

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Decorative photograph showing electrolysis cellThe influence of hydrogen on the structural integrity of nuclear power plant, where water molecules in the coolant circuit can be split by electrolysis or radiolysis to produce hydrogen, has been a concern to engineers for decades.  However, plans for a hydrogen economy and commercial fusion reactors, in which plasma-facing structural components will likely be exposed to hydrogen, has accelerated interest in understanding the complex interactions of hydrogen with metals, especially in the presence of irradiation.  A key step in advancing our understanding of these interactions is the measurement and prediction of the uptake and release of hydrogen by key structural materials.  We have recently published a study in Scientific Reports in which we developed a method for predicting the amount hydrogen in a steel under test conditions.  We used a sample of stainless steel as an electrode (cathode) in an electrolysis cell that split water molecules producing hydrogen atoms that were attracted to the steel. After loading the steel with hydrogen in the cell, we measured the rate of release of the hydrogen from the steel over two minutes by monitoring the drop in current in the cell, using a technique called potentiostatic discharge.  We used our measurements to calibrate a model of hydrogen release rate, based on Fick’s second law of diffusion, which relates the rate of hydrogen motion (diffusion) to the surface area perpendicular to the motion and the concentration gradient in the direction of motion.  Finally, we used our calibrated model to predict the release rate of hydrogen over 24 hours and checked our predictions using a second measurement based on the hydrogen released when the steel was melted.  So, now we have a method of predicting the amount of hydrogen in a steel remaining in a sample many hours after exposure during electrolysis without destroying the test sample.  This will allow us to perform better defined tests on the influence of hydrogen on the performance of stainless steel in the extreme environments of fission and fusion reactors.

Source:

Weihrauch M, Patel M, Patterson EA. Measurements and predictions of diffusible hydrogen escape and absorption in cathodically charged 316LN austenitic stainless steel. Scientific Reports. 13(1):10545, 2023.

Image:

Figure 2a from Weihrauch et al , 2023 showing electrolysis cell setup for potentiostatic discharge experiments.

Conflicted about cost-benefit analysis of international conferences

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Decorative image of an aircraftLast week I wrote about my stimulating experience of attending a conference in Orlando, Florida and presenting our recent research to the experimental mechanics community for the first time in four years.  Whilst there, I was conscious of the ecological footprint of my trip – the venue was making extensive use of single use plastics on a scale that surprised me.  However, my trans-Atlantic flight had an order of magnitude larger impact.  It is difficult to find a reliable estimate of the carbon emissions for a return flight between the UK and Florida but 1,267 kg CO2 from the Guardian newspaper website lies between a lower bound estimate of 856 kg CO2 from iata.org and and an upper bound of 2,200 kg CO2 from myclimate.org.  This is equivalent to about one-sixth of my annual domestic carbon footprint of 9,000 kg CO2 using the calculator on the World Wildlife Fund website.  The UK average footprint is 9,300 kg CO2/capita and the global average is 6,300 kg CO2/capita.  The question is whether it is justifiable to generate additional emissions to attend a research conference?  The prime motivation of the research that I presented is to support the development of aircraft which are lighter with less embedded carbon and use less energy while also having a longer useful life.  Ultimately, supporting the aviation industry to achieve its target of zero-net emissions by 2050.  The carbon emissions of the global aviation industry in 2021 were 720 Mt CO2 [see IEA report]; hence, if my research contributes towards one hundredth of a percent reduction in these emissions then this would be 72,000 kg CO2/year.  It seems reasonable to cause a tenth of this annual saving each year (7,200 kg CO2/year) for the next ten years in order to deliver the required technology, i.e., committing one year’s savings to achieve an annual saving in perpetuity.  The problem is that I do not have a reliable estimate of the carbon footprint of my research activities.  I supervised an MSc student a couple of years ago who conducted a carbon audit of the School of Engineering and estimated the carbon emissions due to research alone to be 61,531 kg CO2 excluding heating, lighting and travel.  My group might be responsible for 10% of these emissions, i.e., about 6000 kg CO2; hence, adding about 1,200 kg CO2 to interact with other researchers at a conference seems reasonable and within a budget of 7,200 kg CO2. However, it is difficult to find reliable data to use in estimating carbon emissions for these activities and so perhaps the key conclusion is that we need more and better carbon audits to allow more informed decision-making.  In the meantime, perhaps attendence at an international conference once every four years is sufficient.

Image: Tayeb Mezahdia

Addressing societal challenges by engaging 100% of society’s intellectual capital

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Decorative photograph of author's research groupToday is International Women in Engineering Day (INWED).  I have written previously about the lack of progress in achieving gender equality in the engineering profession in most Western countries (see ‘Reflecting on the lack of women in engineering’ on March 16th 2022) and the seismic shift in attitudes required to increase the number of women in engineering at all levels (see ‘A big question for engineers’ on June 8th, 2016).  I can see signs of change locally.  My research group has hovered around an equal number of men and women for some years.  In the School of Engineering in Liverpool four women have been promoted to be professors in the last four years – though at a reception following an inaugural lecture given by one of the pair of women who were the first female professors in the School, I was gently admonished by a senior female colleague in another school about why it had taken so long.  Of course, she is right.  Progress is very slow and we need to do better.

Simone de Beauvoir wrote in her book, The Second Sex first published in 1949: ‘Representation of the world, like the world itself, is the work of men; they describe it from their own point of view, which they confuse with absolute truth.’  More than seventy years later, this still appears to be true, at least in the engineering profession who are responsible for the technology everyone uses everyday.  About twenty years ago, the then President of the US National Academy of Engineering, Bill Wulf said, ‘As a consequence of a lack of diversity [in engineering] we pay an opportunity cost, a cost in designs not thought of, in solutions not produced’.  However, diversity on its own is not enough, we have to be inclusive and treat everyone equally – as we would like to be treated ourselves.  If we do not engage women in the engineering enterprise then we ignore 50% of society’s intellectual capital and we cannot hope to solve the challenges facing society, in part because we will be confused about the truth.

Thank you to my two guest editors who reviewed this post for me.

Photo: Author’s research group in 2022.

 

How many engineers do you need when the lights go out?

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An exemplar adverse outcome pathway for microplastics in aquatic species

From Galloway & Lewis, 2016

One to change the lightbulb and five to perform a Fault Tree Analysis (FTA).  A fault tree is a diagram that illustrates the relationship between failures at component and system levels.  Engineers use them to understand the mechanisms or logic that lead from component malfunctions to system breakdowns and to identify components that are critical to system reliability.  They are useful in optimizing designs, demonstrating compliance with safety requirements and as diagnostic tools when things go wrong.  There are some simple examples of fault trees for ‘no light in room’ and ‘missing the bus’ amongst others available from Visual Paradigm Online.  All of these examples illustrate qualitative relationships but we can also establish quantitative relationships using the rate of occurrence of each initiating event to arrive at a probability of failure (PoF) for the system.  There is an example for an indicator light in an automobile in a 2016 paper by Nabarun Das and William Taylor (see figure 2 in the paper).  An equivalent in biology are Adverse Outcome Pathways (AOPs) that identify the relationship between a molecular initiating event and a toxic effect through a series of key events.  For instance, microplastics causing altered gene expression and oxidative damage leading to altered fatty acid metabolism, stress response and altered cellular division resulting ultimately in population decline in aquatic species as shown in the graphic from a paper by Tamara Galloway and Ceri Lewis also published in 2016. Most AOPs are qualitative; however, quantitative Adverse Outcome Pathways (qAOPs) are starting to be developed as tools for quantitative risk assessment of chemicals.  Biologists and engineers are not using the same words, actually they are using entirely different vocabularies; nevertheless they are talking about the same methodologies.  An AOP network and an FTA are essentially the same concept and a probabilistic fault tree analysis is a quantitative adverse outcome pathway.  However, it seems unlikely that either biologists or engineers will adopt the language used by the other so they will be reliant on a few foolhardy interlocutors prepared to cross the discipline boundaries and highlight the opportunities for cross-fertilization of ideas and solutions.

Sources

Das N, Taylor W. Quantified fault tree techniques for calculating hardware fault metrics according to ISO 26262. In2016 IEEE Symposium on Product Compliance Engineering (ISPCE), pp. 1-8. IEEE, 2016. Also available at https://incompliancemag.com/article/quantified-fault-tree-techniques-for-calculating-hardware-fault-metrics-according-to-iso-26262/

Galloway TS, Lewis CN. Marine microplastics spell big problems for future generations. Proceedings of the national academy of sciences. 113(9):2331-3, 2016.