Voice-over: From Diamond Light Source, this is the Diamond podcast.
Meera: Hello and welcome to the Diamond Light Source podcast with me, Meera Senthilingam. In this edition we probe into the world of engineering to see how scientists at Diamond are exploring and improving materials used in industry. We’ll be finding out about a new beamline opening at Diamond that’s revolutionising how samples can be analysed using a synchrotron.
Thomas Connolley: It’s different from other beamlines at Diamond in that X-rays can penetrate through much thicker and denser materials. It’s also designed so that we can do both imaging and diffraction experiments on the same sample.
Meera: We also learn how an understanding of cracks and defects in a materials is crucial for safety in industry.
Phil Withers: Cracks and defects happen for all sorts of reasons. It’s important to catch these cracks before they become fatal and we get catastrophic failure. So that’s materials in the aerospace industry, in the nuclear industry, where you really can’t countenance failure.
Meera: Phil Withers will explain how his team will look into these defects later in the show, where we also discover how the structure of metals can be modified to make them more resilient, and how the understanding of corrosion could be crucial for the storage of nuclear waste. All that, plus the latest news and events from Diamond coming up on the November edition of the Diamond Light Source podcast.
Voiceover: The Diamond Light Source Podcast. For more information look us up online at www.diamond.ac.uk.podcast.
Meera: Now a new beamline went into operation this month, the I12 beamline, which is changing the field of engineering research as it will allow analysis of samples up to 2 tonnes in weight with X-rays that can penetrate materials that are thicker than ever before. Here’s beamline scientist Thomas Connolley to tell us more.
Thomas: Here at Diamond we’re just about to start operations of the I12 beamline which is designed for researchers in engineering science and engineering community and also in processing to do experiments that they’ve not been able to do at a UK facility before.
Meera: What is this new beamline?
Thomas: The new beamline is called JEEP, which stands for the Joint Engineering, Environmental and Processing beamline and it’s designed to deliver a very intense beam of X-rays destined for different kinds of samples. It’s different to other beamlines at Diamond in that it uses much higher energy X-rays, that means that the X-rays can penetrate through much thicker and denser materials. It’s also designed so that we can do both imaging and diffraction experiments on the same sample. So imaging is taking an X-ray picture of something and diffraction is looking at how the X-rays are scattered as they pass through the material.
Meera: Now the beamline itself isn’t quite ready for use yet, it’s still under construction but due to be open soon, so we’re here in our fluorescent jackets, hard hats and steel toe-capped boots, but you took me on a tour earlier around all the separate areas of this beamline and it seemed very long! Just how long is this particular beamline, JEEP?
Thomas: The beamline in total is about 100 m long – that’s the distance from the X-ray source to the final sample position, but we have two sample positions, the first is at 50 m from the x-ray source and the second, as I mentioned, is 100 m from the source. The reason that we are so far away is that we want to have a big building where we can have large samples that our users want to bring, and so the 100 m point is in the external building where we are now, where we have this quite large experimental area that’s nearly 11m long, 7 m wide and 5 m high, for engineering experiments.
Meera: Yes, so we’ve got the final hutch outside here now, and from here it looks like a large warehouse, and I can’t believe that samples that large can actually be probed and looked at with these X-rays.
Thomas: Well this is the unique thing about the JEEP beamline. In engineering you want to be able to do not only small laboratory scale experiments, but you also want to be looking at what’s happening in real components, what’s happening in real industrial processing, and sometimes you can’t take small samples from a component, you need to be able to bring the whole component here to be able to study it. An example of that might be say the engine casing from a jet engine or from a passenger airliner. An engineer may be interested in measuring the internal stresses in a small part of that engine casing, but you can’t cut out that small part and take it to a beamline, because that would change the conditions of the component itself. You need to bring the whole component so that you can study and probe it as it would be in service.
Meera: So how does the beamline actually work, to create these high intensity X-rays in order to then probe these large samples?
Thomas: The beamline starts with an X-ray source that’s in the synchrotron storage ring of Diamond. So there we have a device called a wiggler which oscillates an electron beam and generates a very intense beam of X-rays. We then take that X-ray beam and we do a couple of things to it; the first thing we do with it is filter it, and we do that by passing it through different thicknesses of material, different types of material, to condition the beam to the energy, to the wavelengths we want to use. The second thing we can do is monochromate the beam and that means that we chose a particular wavelength for the experiments and we can switch between the two modes so we can just use the filtered beam or we can put the monochromator in and pick out a particular wavelength for the experiment.
Meera: So what kind of samples are you expecting to come in here and what kind of research are you expecting to take place at JEEP?
Thomas: There’s all kinds of research we’re expecting, probably the more traditional engineering materials, so steel samples, maybe aircraft components. We’ve already got users who are interested in looking at aluminium alloys and how they solidify, so they’re going to come with a little furnace and watch how the aluminium behaves as it freezes, and also we’re expecting users who might want to look at chemical processing, they might be interested in deformation of materials at high temperatures so they might want to come with a test rig so they can not only heat the sample but also stretch it or apply a load to it and that’s important for understanding how materials behave in service. It’s difficult to say what’s going to come in, but things I might expect to see would be quite large steel components, say a steam pipe from a power station or maybe say a wheel from a railway carriage. Because engineers are also interested in studying the entire sample, maybe looking at the internal stresses that can be a problem – it’s very important to measure those stresses because they can affect the way that cracks grow, and if you’ve got a power station and you want to be sure it’s going to be good under serious conditions for the thirty or forty years that the power station is operating.
Meera: That was Diamond’s in-house beamline scientist Thomas Connolley explaining the importance of the new Joint Engineering, Environment and Processing beamline, or JEEP, at Diamond. Now, we’ve had an insight into the role of the new JEEP beamline, so now we meet the scientist who’ll be using it. Now a wide range of scientists will be using JEEP to look into their research, and the first user to try it out will be Professor Alexander Korsunsky from the University of Oxford. He looks into the granular structure of materials such as metals to try and understand their strengths and weaknesses in order to improve their role in industries such as the aeronautical industry. I spoke to Alexander, to find out what he sees at the granular level and how this can be studied to improve a material.
Alexander Korsunsky: The main interest for me and the team of scientists that I work with is the origin of material strength and weakness. This has very interesting implications for the design of engineering structures, from mobile phones to biomedical devices, to aircraft engines, to bridges and power stations.
Meera: And what kind of materials do you look into?
Alexander: We study the full complement of materials that are used for structural applications. Materials like structural alloys based on nickel or aluminium or titanium that are used in the construction of jet engines, but we also have an interest in polymer materials such as those that are used in tissue scaffolding, biomedical applications, or the ceramics that are used for dental applications.
Meera: How do you actually go about looking into these materials? Because you basically visualise the grains, the granular structure of the material, so how can you see that, and what exactly is that structure?
Alexander: OK, in order to try and imagine what the materials are like, it might be helpful to think of a cube of sugar. Now a cube of sugar is really a result of gluing together individual grains which we can see with our naked eye. Now most of the metals that we use and metallic alloys are similar in their structure, except those grains are much smaller and for us, we need microscopy in order to be able to see them usually, and also they are held together in a much stronger way, which is why metals perform slightly better than a lump of sugar! But in order to see those grains inside we usually use a development of what we’re all familiar with as X-ray radiography. Now in medical radiography we use a stream of X-rays directed at a body in order to obtain a shadow picture. That shadow picture shows high absorption or high density where we have a lot of material in the path, and lower absorption where there isn’t a lot of material. The only difficulty with that is that you only gain information about one projection, one view, so to say. And we all know that in order to understand the three dimensional nature of an object we need to look at it in different directions. So by performing this kind of radiography experiment from different angles, that allows us to see the way the grains fit together, and then the next question that arises is how can we measure the strains and stresses inside those grains. Now that requires a further development of this approach, known as tomography, and so what we are working on now is strain tomography. In other words we are trying to reconstruct the full three dimensional distribution of stresses inside the material and obviously because the grains behave in a slightly different way the strains and stresses between grains are different and we can recognise that from our analysis.
Meera: What are these stresses that you look into, and also what have you found so far happens to the granular structure of the materials when these stresses fall upon them?
Alexander: If we consider a lump of metal being subjected to external loading, and this loading can be mechanical or thermal, which often happens in practice as well, then we find that external forces are transmitted through the body by ways of the load being shared by different loads present there. We also know from our analysis that some grains would be very stiff, in other words they would resist plastic deformation better than others, and those will carry the load, a large fraction of the load applied. There are other grains that are more compliant and then will deform more readily. But anyway, if we apply a large enough force the grains start to deform plastically, that is to deform permanently and again there are differences between neighbouring grains. So we end up with a situation where the material externally may look homogeneous, so a uniform lump of metal in fact is full of little peaks of stress, and we believe that those local peaks of stress are the ones that are ultimately responsible for failure and the initiation of cracks.
Meera: What can you do then with these peaks of deformation within the material in order to try and prevent it from failing in the end and improve it?
Alexander: Since the stress concentrations, as we call them, depend on both the shape, orientation and the structure of a particular grain but on the shape and orientation of the grains around it then by controlling this grain structure we can control the maximum stress concentration that occurs in the piece. In other words, by careful control and optimisation of the treatment procedure that we apply to a lump of metal we can force it to have the internal arrangement of grains which is the least susceptible to the problems associated with stress concentration and the possibility of crack initiation.
Meera: Having then having understood this and being able to control it in this way, what materials could it improve, and what benefits would this improvement provide?
Alexander: So for example we would like to be able to proscribe the processing conditions that would allow dental bridges to be stronger so they don’t need to be replaced even in 20 or 30 years rather than after 5. By controlling the processing operations we can help design better polymer composites that are used in the building of aircraft bodies or fast ships. The understanding and the tools that we’ve developed are sufficiently generic to apply them to a vast variety of situations.
Meera: Alexander Korsunsky from the University of Oxford.
Voice-over: Did you know that the Diamond experimental hall is so large that a jumbo jet could drive around the inside?
Meera: You’re listening to the Diamond Light Source podcast with me, Meera Senthilingam and coming up we’ll be hearing about how an understanding of crack formation can improve the ability of materials at high temperatures and how an insight into pitting corrosion will benefit the disposal of nuclear waste. But before that, let’s join Sarah Bucknall from Diamond’s Communications team for a round-up of the news and events that took place at Diamond over the past couple of months.
Sarah Bucknall: We recently announced that we’ve reached a significant milestone and solved our 100th protein structure at Diamond, and it was solved by Professor Nick Keep’s group at Birkbeck University of London, as part of research carried out by Dr Jing-Jiang Zhou from Rothamsted Research, and that’s the largest agricultural research centre in the UK.
Meera: And what was the protein structure that they found?
Sarah: They solved a protein structure from the silkworm moth which is a model organism from within the field of insect molecular biology in terms of how insects locate mates and their hosts. This particular protein is related to how insects smell and plants use chemical signals to repel and attract insects so if we can learn more about these signals then for example farmers can plant companion species to either repel or attract insects depending on what they require. So this research can feed into areas such as pest control in agriculture and also the development and refinement of biosensors.
Meera: Now that was your 100th milestone, but that was a month or so ago, so what protein figure are you at now?
Sarah: Well we’re currently experiencing an exponential growth in structures solved at Diamond, so we’re already at about 140 just one month on and we hope to reach around 200 next year.
Meera: I’m assuming this is across a wide range of scientific disciplines?
Sarah: That’s right, for example we recently had a first paper published from one of our Phase II beamlines which is also a crystallography beamline, that’s I19, it’s small molecule single crystal diffraction. So they are actually looking at smaller parts of the protein and they’ve recently solved a structure on that beamline and the results were published in the journal Angewandte Chemie. And also we’ve had another paper published on one of our Phase II beamlines and it was the first one for I11 which is the high resolution powder diffraction beamline. In October they’ve had some research published in Nature Materials and this was on Porous Organic Cages and these are important in areas such as catalysis.
Meera: You’ve also had a recent discovery to do with the flu virus?
Sarah: That’s right, we’ve had an interesting paper published in the Proceedings of the National Academy of Sciences, PNAS. Scientists from the Medical Research Council have been using Diamond to look at a protein, hemagglutinin, which is part of the flu virus that binds to human cells when a person is infected. In the last century there were three flu pandemics, one in 1918, one in 1957 and one in 1968 and these scientists are looking at the virus strain that caused the 1957 pandemic and compare it to the other two outbreaks. What they’re trying to discover is why some avian flu viruses are more able to jump the species gap than others. So this may help identify which avian flu viruses are more likely to bind to human cells and therefore could help in planning for future pandemics.
Meera: Stepping aside from the science that’s going on at Diamond, what other extra-curricular activities have Diamond been involved in?
Sarah: Well we’re continuing our outreach programme and we recently had a successful A-level Inside Diamond day pilot in early October as well as another one for the public. The next Inside Diamond is on January 8th next year and as usual people can register via our website. Also in January next year we’re going to be exhibiting our growing artwork collection.
Meera: And what features of the collection will you be exhibiting?
Sarah: Well thanks to past projects such as Designs for Life, and our Artists in Residence we have a number of art pieces now so we have 30 textile panels which were worked on by the Oxfordshire Federation of the WI, and each of our Artists in Residence each produced a fantastic piece of artwork which was inspired by Diamond, so we have a sculpture and we have a number of paintings as well and they are all going to be on public display from 11th – 29th January in the North Wall gallery in Summertown in North Oxford.
Meera: Thanks Sarah. Sarah Bucknall, from Diamond’s Communications team, who’ll be back in the next edition of the podcast with more news from Diamond. Now this month we’re looking into the field of engineering to find out how engineers at Diamond have been looking into how to improve materials such as metals and ceramics that we use in industries varying in areas as diverse as aeronautics to dentistry. So now we meet Professor Phil Withers from the University of Manchester who is looking into the failure of materials used in engineering by analysing the formation of cracks and defects in these materials to basically stop them from failing!
Phil Withers: We tend to look at materials where failure has to be avoided at all costs, so that’s materials in the aerospace industry, the nuclear industry, where you really can’t countenance failure.
Meera: Now when you say failure, what does it mean for a material to fail exactly?
Phil: There are all sorts of reasons why materials might fail. Often it’s because the applied stresses or internal stresses exceed a certain threshold and cause immediate catastrophic failure. Sometimes it’s because of a defect in the materials, so that it fails at a stress lower than you would otherwise expect it to fail.
Meera: So how do you actually go about looking into these materials to find faults and find cracks?
Phil: To create a picture we shine very intense X-rays at our object and we collect pictures just like an X-ray picture you might collect at a hospital. These pictures show the defects and by collecting lots of these pictures we can build up a three dimensional picture of what’s going on inside the material. We do two kinds of imaging, one is simply to create a picture like a shadow pattern where we can see straight through the material and we can see straight through the material and identify cracks and pores to create an image. The other thing we do is we scatter X-rays off the object and use the atoms as a strain gauge to measure the stresses deep inside the material.
Meera: Now you mentioned that you visualised breakages and cracks within the materials, but how did these actually get there in the first place? What causes these cracks to happen?
Phil: Cracks and defects happen for all sorts of reasons. Sometimes the way the material has been made has introduced a defect, sometimes because a small crack or a small notch has started at the surface and this has grown deep inside the material. It’s important to catch those cracks before they become fatal and we get catastrophic failure.
Meera: And so as well as looking at the actual presence of these cracks you also look at the effect of external stresses on these cracks, so what kind of stresses do you look into, and what kind of effect do these stresses have on the various defects?
Phil: We look at both kinds, we look at applied stresses - the kind of stresses you put on when the material is under load in service – and we also look at residual stresses, which lie locked in to the material. A good example of residual stress is the stress that resides in thermally toughened glass. I’m sure you’re aware that when you see broken glass at the side of a bus shelter, those small pieces of glass have occurred because of the stresses that were locked in the glass before the crack started to propagate.
Meera: So if you understand how the stresses affect the cracks and then finally result in the end breakage, what have you understood about the formation of these cracks, or what have you understood in your research so far in order to get in there and prevent this from happening?
Phil: Well it’s very important to be able to predict how long a crack will take to grow until it becomes a fatal crack. So we are developing the understanding that will enable us to measure cracks and to plot their growth before they become fatal, and also to find ways of stopping cracks. There are lots of ways in which you can interrupt the growth of a crack and stop it. We’ve been working with companies such as Rolls Royce to find ways of putting stress into materials such that the crack will actually stop before it becomes a fatal crack.
Meera: What kind of things can you put into it to stop it from cracking then?
Phil: What you do is you make sure that the cracks are held shut. Cracks only grow when you try and pull the material apart. So if you can put the cracks into compression, that’s to hold them shut, then the cracks, even of they do exist, will simply not grow.
Meera: Having now understood this then, what are the treatments that you’ve come up with that are available then for the industries that are using these materials to prevent these cracks from happening or growing?
Phil: Well one of the processes we’re working on with a small company is to use lasers to shock the surface of the material. You shine a very bright laser at the surface and it creates a plasma on the surface, and that plasma creates a shock wave that penetrates deep into the material and puts the surface into compression.
Meera: And therefore if it’s under compression any cracks that are in there won’t grow?
Phil: You’ve got the idea, spot on!
Meera: When you mention materials, then to what industrial materials can this be done on?
Phil: Commonly we apply the technique to metals to protect fan blades or to ensure that materials that are operating in power plants are operating safely, such as stainless steels, but we can also apply the method to ceramics, for use in bio-material applications.
Meera: You’ve managed to do this so far with X-rays from synchrotron light, but now the new JEEP beamline will be opening at Diamond soon which allows larger samples to be monitored and penetrated, so how will it change your research?
Phil: It will enable us to look at materials operating in all sorts of conditions. For example we’ll be able to look at components operating at temperature, and we’ll be able to look at the growth of cracks in corrosive environments. There’s a whole range of exciting experiments that we’ll be able to watch operating under realistic conditions for the very first time.
Meera: Phil Withers from the University of Manchester with his insight into the failure and improvement of industrial materials. Now as well as cracks and strains, another problem affecting the integrity of engineering materials is corrosion, which can wear away even the toughest metals, causing irreversible damage. Dr Alison Davenport looks into the causes and defects of corrosion, or more specifically pitting corrosion in her case, and she looks into this at the University of Birmingham. So I spoke to her about how this corrosion can be stopped, and with regard to pitting corrosion, just what it is.
Alison Davenport: Most metals are covered with a thin skin of oxide called a passive film, which protects them from the environment and usually that’s pretty effective, but when there is damage to this film or perhaps if there are some imperfections or impurities in the metal you can get a little local site where corrosion can start to develop. And once corrosion happens you produce corrosion products which in themselves are quite aggressive: it’s a concentrated metal chloride which is very acidic, and this is confined in a little pit in the metal surface and this can grow, because it’s so aggressive it can grow and penetrate down into the interior of the metal.
Meera: Now what is this, the actual coating made up of then? And when you say corrosion can happen, what is this corrosion that can happen to it?
Alison: The coating is a thin skin of metal oxide, and it’s remarkably thin, usually just a couple of nanometres, that’s tens of atomic layers, and yet it’s very effective in isolating the metal from the environment in which we live, and we’re worried about wet environments here, and when the corrosion takes place the metal will actually dissolve in the wet environment and react with the water to generate some acidity. And that’s the corrosive element which will then allow the pit to continue growing.
Meera: So what’s the initial reaction that happens, to cause the beginnings of the pits?
Alison: That can be quite controversial in the field, there’s quite a bit of discussion about flaws in oxide films, but it’s usually well known that in engineering materials, these are impurity particles in the metal.
Meera: And so then how are you going about looking into when a pit forms and this corrosion that happens within the pit?
Alison: Well we’ve got two types of experiment that we’re interested in doing. The first is looking at the shape of the corrosion site in three dimensions and it’s quite difficult to study this in three dimensions as the pit grows because most of the really good techniques for studying the shapes of small objects are actually vacuum based, but because we’re interested in corrosion in a wet environment those won’t work, so what we do instead is we use micro-tomography. So we do is we take a little pin of metal, we put some salt on the tip so that it will corrode, and then we measure, radiograph, as we rotate the pin and these can then be reconstructed to give the three-dimensional shape of the pit. So if we want to know how pits grow in three dimensions, so the way in which they can start penetrating down into the interior of the metal we can look at this in real time.
Meera: So as well as visualising this pit growing in action, are you looking into the actual chemistry within this pit?
Alison: Right, well that’s the other aspect of the work, it is known fairly well that these solutions are highly concentrated in metal ions and are quite acidic, but the details of the chemistry aren’t very well known at all, but again X-rays are great for those, because what we can do is take a little foil of the metal and start corroding it from the edge and pass an X-ray beam through the cavity next to the dissolving interface and measure things like the oxidation state of the metal there, the coordination environment of the ions and also if there’s any corrosion products, we can identify those with the X-ray diffraction. We found this quite useful actually because most of the models that predict how corrosion sites grow assume that there’s lots of water in there but we’ve actually found some quite dehydrated phases there next to the dissolving metal, which rather changes the way you might think about modelling the growth of the pit.
Meera: So on what scale do these pits actually occur?
Alison: Well some pits do actually grow to quite a big size, there are reports of millimetre and even bigger than that sized pits, but normally the ones that we’re dealing with are tens or hundreds of microns, and what’s more difficult as, in the case of stainless steel, they penetrate beneath the surface, so they are actually very difficult to see with the naked eye, apart from the fact that you can see a little patch of rust where the corrosion products have come out to the surface.
Meera: And so what effect do these pits have on the material as a whole?
Alison: Well it very much depends on the application, so for example if you were concerned about having a pipe, if the pit grows the whole way through the pipe it will start to leak, but there can also be other problems whereby if the pit has a rather narrow shape, if it’s in a metal under stress it can act as a site where a crack can start to propagate, and this can lead to quite catastrophic failures of metals. There are quite a few different areas where people are developing pit growth models in order to predict how long a piece of metal will last in a particular application, and we’re trying to provide the ability to validate those models.
Meera: And what kind of applications will this have? So what kind of structures and materials in industry are you looking into?
Alison: A particular example of what we are working on at the moment are canisters for nuclear waste storage. The long-term aim obviously, with nuclear waste storage, is to put the canisters underground, but it’s going to take quite a long while before this can actually be done, so in the intervening time they are going to be stored above ground and it’s very important that the environment in which they are stored is one in which they won’t undergo pitting corrosion, and therefore perforate and potentially allow release of radioactive contents. And so the people who want to store them want to be able to predict the rate at which the pitting might take place under controlled conditions of humidity or deposition of dust which might contain salts and be sure that it will be safe to keep them above ground for long periods of time. And so we’re providing the underpinning knowledge of how the corrosion takes place and the rate at which the corrosion takes place that can be used to validate the models over short periods of time and give us confidence that the longer term predictions will actually be safe.
Meera: Alison Davenport from the University of Birmingham explaining the causes and modelling of pitting corrosion, and how an understanding of this can predict the lifetime of materials that are crucial in industries such as the nuclear industry. Now that’s it for this edition of the Diamond Podcast, but make sure you join us again in January, when we’ll be looking back at the past year to bring you the research highlights from Diamond in 2009. In the meantime though, if you have any questions about Diamond or the research taking place there, the email address is firstname.lastname@example.org. Thankyou to Sarah Bucknall, Thomas Connolley, Alexander Korsunsky, Phil Withers and Alison Davenport, thank you for listening and I’ll see you next year!