We have to fly less. And make flying climate-neutral.
Climate change is our reality. And while aviation contributes a lot to the well-being and prosperity of people around the world, it contributes to this climate change. Flying as often and as far as we do now is simply no longer sustainable. We all need to make much more conscious choices. Is it really necessary to make this trip? What is the most environmentally friendly mode of transport for the journey?
At the same time, the real expectation is that not fewer, but many more people worldwide will fly. This is because more and more people worldwide are affluent enough to travel. For that reason, we should be fully committed to making aviation as climate-neutral as possible.
At TU Delft, we are convinced that with knowledge, technology, innovation and a new generation of aviation engineers, we can make a major contribution to climate-neutral aviation in 2050 or earlier. To develop the right innovations and also get them introduced quickly, we cooperate with other knowledge institutes and with companies from the aviation sector and the manufacturing industry, among others. In this way, we contribute to ensuring that aviation can continue to connect the world for future generations.
Dean Faculty of Aerospace Engineering TU Delft
How do we work on making aviation sustainable?
Reduce energy consumption
We make aircraft and aircraft engines as efficient as possible. Our Flying-V aircraft design for example aims at saving 20% on fuel consumption just as a result of improved aerodynamics and reduced weight. The SmartX is an energy efficient aircraft wing. It mimics the steering and wing movements of birds making it possible to reduce the weight of aircraft. Another example is the Delft Laminar Hump. This innovation changes the wing’s surface in such a way that the airflow over it remains laminar (not turbulent) for longer, thereby reducing the aerodynamic drag of the aircraft. But lightweight aircraft materials and new systems for Air Traffic Management, such as a Single European Sky, so that aircraft can always fly the shortest distance possible, will also save energy.
We want aviation to run completely on a mix of sustainable energy and propulsion technologies. We for example work on electric and electric/hybrid aircraft. But also on the sustainable production of green aviation fuels, such as synthetic kerosene, LNG and hydrogen. By re-using CO2 for the production of green fuels, we make aviation CO2 neutral. All options need to be on the table. Sustainable fuels are better suited for long-haul flights and electric aircraft for shorter routes.
Sustainable aviation operations
This covers topics ranging from sustainable airports in healthy environments – including clean ground operations, such as electric taxiing - to sustainability-focused Air Traffic Management systems and fleet management (we can fly more on electric aircraft if they make more stops on the way to recharge). In addition, we also study the effect of new aircraft and fuels on the earth’s atmosphere. By doing so we can optimise route and cruise altitude to minimise climate effects, and to greatly reduce air and noise pollution.
Minimising the environmental impact of materials and structures
We work on minimising the impact of aircraft and spacecraft materials and structures on our planet. To this end, we follow different approaches including design for life cycle, development of bio-based and bio-degradable aerospace-grade materials, development of energy- and resource-efficient manufacturing technologies, and of reuse and recycling methods, thereby making the circular aerospace industry of the future a reality. This topic also includes sustainable aircraft maintenance. Condition-based maintenance, for example, where the aircraft’s health is constantly monitored through sensors and Artificial Intelligence, allows airlines to replace components when they’re truly at the end of their lifetime, rather than during preventive inspections, which reduces waste.
Veni grant for ’Simulate the interaction between flows and surfaces in computer models’Five promising researchers from TU Delft's Faculty of Aerospace Engineering have been granted Veni funding by the Dutch Research Council (NWO). This funding, totaling EUR 280,000 for each recipient, will empower the awardees to advance their individual research concepts over the course of the upcoming three years. Today we introduce Frits de Prenter.
Veni grant for ‘Unveil with Laser Diagnostics the local NOx and Flashback physics of H2 flamesFive promising researchers from TU Delft's Faculty of Aerospace Engineering have been granted Veni funding by the Dutch Research Council (NOW). This funding, totaling EUR 280,000 for each recipient, will empower the awardees to advance their individual research concepts over the course of the upcoming three years. Today we introduce Francesca De Domenico.
Veni grant for ‘Listen to the future: Enabling sustainable aircraft technologies by minimizing their noise annoyance’Five promising researchers from TU Delft's Faculty of Aerospace Engineering have been granted Veni funding by the Dutch Research Council (NOW). This funding, totaling EUR 280,000 for each recipient, will empower the awardees to advance their individual research concepts over the course of the upcoming three years. Today we introduce Roberto Merino Martinez.
Veni grant for morphing wind turbine blades - a way to enhance the energy production in turbulent environmentsFive promising researchers from TU Delft's Faculty of Aerospace Engineering have been granted Veni funding by the Dutch Research Council (NWO). This funding, totaling EUR 280,000 for each recipient, will empower the awardees to advance their individual research concepts over the course of the upcoming three years. Today we introduce Delphine de Tavernier.
Dean Henri Werij is one of five winners of the Clean Aviation High Five AwardsHenri Werij, Dean of the faculty of Aerospace Engineering, is one of the five winners of the Clean Aviation High Five Awards. This was announced by the Clean Aviation Joint Undertaking research and innovation programme at a ceremony during the Paris Air Show on 20 June 2023.
AeroDelft and KLM Partner to Explore Hydrogen in AviationAeroDelft, a student team from Delft University of Technology, and KLM Royal Dutch Airlines have announced a partnership to explore hydrogen in aviation. The partnership will support AeroDelft’s Project Phoenix, focused on researching and developing new technologies that can reduce the aviation industry's environmental impact.
Making the energy transition happen for aviationIn his inaugural speech as a Full Professor of Sustainable Aircraft Propulsion Arvind Gangoli Rao will defend the right for people to move up the transportation ladder and explain how he intends to reduce the climate impact this causes: by making the energy transition happen in aviation. Gangoli Rao’s inaugural speech will take place in Delft at 15.00 on 31 March. It will also be available online live and on-demand.
TU Delft crowns best climate and energy publicationEen algoritme dat voor een hogere energieopbrengst van windparken zorgt én een onderzoek waaruit blijkt dat niet alleen brandstofverbruik maar ook seizoenseffecten een belangrijke rol spelen bij het optimaliseren van vliegroutes en vlieghoogtes. Dit zijn – in één zin samengevat – de twee grote winnende publicaties van de Beste Climate & Energy Paper Award. De awardceremonie, die woensdag 15 maart plaatsvond op de TU Delft, stond volledig in het teken van grote en kleine innovaties die een bijdrage leveren aan het versnellen van de energietransitie en het beteugelen van klimaatverandering.
D-STANDART project makes lightweight composites more durableAdvanced composites are gaining ground in many areas, also in aerospace and in the wind energy sector, as they are lightweight and help to save energy. What is still missing are accurate and fast pre-production methods to optimise the durability of such large-scale composite structures. TU Delft researchers contribute to the recently launched EU-funded project D-STANDART led by the Netherlands Aerospace Centre Royal NLR.
Free Online Course: Sustainable Aviation by TU expertsCan we fly climate-neutral in the future? What will the aircraft of the future look like, what energy carriers or fuels will they fly on and what choices can you make yourself? From 16 February, TU Delft experts share their knowledge on sustainable aviation in the free online course 'Sustainable Aviation: The Route to Climate-Neutral Aviation'.
Nature Materials: functional materials from 3D printed fungiLiving materials such as bone, wood or fungi have the ability to adapt to their environment. They can renew, strengthen and even heal themselves when conditions demand it. Associate Professor of Aerospace Structures and Materials Dr Kunal Masania investigates how to apply this exceptional adaptability from Nature into functional materials, for example for use in aerospace.
COMP-ECO: TU Delft teams up with Polish composites ecosystemTU Delft is partnering with Technology Partners Warsaw, TU Dresden, the Polish Air Force Institute of Technology and Warsaw University of Technology to strengthen the Polish Mazovia region’s position as a competence hub for multifunctional composites and smart structures.
ERC Consolidator Grant for Kunal Masania's living compositesThe European Research Council has awarded Associate Professor of Aerospace Structures and Materials, Dr Kunal Masania an ERC Consolidator Grant of €2 million for his research proposal AM-IMATE. This research on living composites can lead to ground breaking technology for making aviation more sustainable.
Flight altitude determines climate impact of hypersonic aircraftResearchers at the German Aerospace Centre DLR, TU Delft and the Université Paris-Saclay have found that the climate impact of hypersonic aircraft flying on liquid hydrogen at 25 and 35 km altitude is at least 10 to 20 times worse than that of a regular subsonic aircraft at around 10 km altitude serving the same routes and number of passengers. This is due to the accumulation of water vapour in the stratosphere.
This is how we fly in the futureRoelof Vos and his team are developing the Flying-V that looks completely different than a traditional aircraft and therefore flies a lot more energy efficient. Watch the video where Universiteit van Nederland interviews Roelof and find out more about our revolutionary aircraft design.
Most nitrogen deposition from aviation comes from high altitudeAircraft emit nitrogen oxides and other emissions during both the LTO-phase (taxiing, take-off and landing) and when flying at high altitudes. These emissions return to the ground, resulting in nitrogen deposited over land and water bodies. Using an atmospheric model, researchers at TU Delft have quantified - for the first time - that in 2019 aviation was responsible for just under 1.2% of total global nitrogen deposition from all sources.
ERC Starting Grant for Francesco Avallone and Ivan LangellaThe European Research Council (ERC) has announced the ERC Starting Grants for young researchers. Two of them are scientists from the faculty of Aerospace Engineering at TU Delft. This European grant of €1.5 million for a five-year programme is designed to allow individual scientists to build their own teams and carry out pioneering research.
OVERLEAF: safe and economical hydrogen storage in aircraftEarlier this year the Horizon Europe innovation consortium OVERLEAF was launched. The 10-strong consortium from 6 European countries develops a novel low-pressure cryogenic liquid hydrogen storage tank for aircraft. TU Delft researchers Dr. Roger Groves (Aerospace Engineering) and Dr. Lars Bannenberg (Applied Sciences) and technician Herman Schroeders (Applied Sciences) are part of the consortium.
How the aviation industry can leave behind fewer climatic trailsIt is widely known that aircraft with their CO₂ emissions contribute to climate change, however less attention is paid to the effects of the condensation trails they leave behind. Those trails have a significant impact on the greenhouse effect. Assistant professor Feijia Yin is investigating how the formation of persistent condensation trails can be better predicted, so that aircraft can avoid areas in which they occur.
Climate neuroscience for aviationThere is a knowledge gap when it comes to how non-CO2 emissions of aviation affect global warming. Jin Maruhashi modeled the global transport patterns of nitrogen oxide (NOx) emissions and then used a neuroscience machine learning algorithm to find patterns in these data. It landed him the award for Best Climate Action Paper of the TU Delft.
Smart certification for sustainable aviationRapid innovation is needed to reach the 2050 sustainability goals for the aviation sector. But rather than a lack of ideas, or the effort needed to bring these to fruition, the main bottleneck in reaching these goals are the existing, very lengthy certification procedures. Three TU Delft professors therefore propose a radically different approach towards certification in aviation.
Looking over the shoulder of the pilot of a Flying-VThe first scale model test proved last year that the Flying-V is an airworthy, stable and controllable aircraft. In early November, it was time for the next step: the first simulator flight. Test pilot Thibaut Cappuyns had the honour of taking control of the stick of the SIMONA simulator. The pilot's experience of this revolutionary type of aircraft is crucial.
Is hydrogen-powered air travel the future?Hydrogen is a sustainable alternative to kerosene-powered air travel because there are no CO₂ emissions. But hydrogen is also associated with challenges and risks, such as the danger of explosion. TU Delft scientist Dr. Ivan Langella aims to use mathematical models, high-fidelity computational simulations and experiments to develop a zero-emission hydrogen-powered engine that will enable aircraft to fly safely and efficiently.
Airplanes cross borders, so do their environmental effectsWhen it comes to the health effects of aviation, reducing total fuel burn may not necessarily be the optimal strategy. And, perhaps even more surprisingly, your flight from Amsterdam to Rome contributes to premature deaths in Asia. Dr. Irene Dedoussi models the global human health impact of air pollution from aviation emissions, helping both airplane designers and policy makers in weighing the various mitigation strategies to make aviation sustainable.
Aerospace students revive Leonardo da Vinci’s aerial screw (and turn it into an electric personal aerial vehicle for today)In the midst of the corona pandemic, five aerospace engineering students from Delft University of Technology designed a vertical take-off and landing vehicle based on Leonardo da Vinci’s Aerial Screw and demonstrated its feasibility and physics.
Sustainable aviation starts on the groundFlying needs to become more sustainable, quieter and more efficient. For this you need to think far beyond the aircraft itself: airports for example, can contribute as well. In the newly launched Airport Technology Lab, TU Delft researchers are testing their ideas, from better weather forecasting models to faster baggage handling. All of these ideas contribute to improved efficiency in aviation, and a more sustainable industry. Already before the current coronavirus crisis, the aviation industry was facing huge challenges in areas such as sustainability, capacity and noise nuisance. The goal of the Airport Technology Lab (ATL) is to contribute to solving these problems. Since recently, it offers a special environment at Rotterdam The Hague Airport, where new services and products can be developed and tested under realistic and “live” conditions. Knowledge institutions as TU Delft, government bodies such as the City of Rotterdam, and the business community such as the airport and its innovation foundation RHIA, are collaborating closely. Fieldlab for aviation innovation “In other words, ATL is a fieldlab for innovations in aviation, where smart technologies are conceived, developed, tested and put into production", says project manager Elise Bavelaar from TU Delft. “We actually embarked on this course back in 2016 with the Innovation Airport initiative launched by Deltas, Infrastructures & Mobility Initiative (DIMI) and the faculty of Aerospace Engineering. This originated from the need to align all airport-related expertise at TU Delft and to link it together smartly. Of course the ultimate goal is to share this knowledge with parties beyond the university. An important part of Innovation Airport is our ambition to create a Fieldlab and the collaboration with the innovation foundation Rotterdam The Hague Innovation Airport.” The sector remains strongly convinced of the need for innovation, to be honest, I think even more than before the corona crisis. Read more Huge puzzle Airport Technology Lab is meeting this ambition and is thus an important follow-up from the Innovation Airport initiative. “All in all it has been a long journey to get the ATL to take off. It has taken us more than 18 months”, says Bavelaar, who has been involved with Innovation Airport from the start. “An important part of the process was our successful application for ERDF (European Regional Development Fund) funding. It was a huge and complex puzzle to coordinate everything and everyone, with on the one hand the many parties and areas of expertise (within TU Delft alone three faculties are involved, AE, EEMCS and IDE, plus the Innovation & Impact Centre), and on the other hand the different aspects that need to be addressed, ranging from financial affairs to legal issues. A key question was for example whether there was any unlawful state aid for the project.” Personal passion This made the ATL a very special environment for Bavelaar, who has a background in technology. She graduated five years ago from the Faculty of Aerospace Engineering at TU Delft. “Yes, it's a completely different job I have now, but I see that it is a considerable advantage to be well up-to-date on advancements in technology and engineering.” “It is precisely the combination of technology with other aspects that appeals to me. I experienced this in Germany during an internship for my Master's degree. I was working for Air Berlin and focused on improving airport processes. During that internship I discovered I like being involved with more than just the technology.” “My personal passion is to translate academic knowledge into practice. It is important that scientific insights can have a quicker impact on the real world.” Improved forecasting Back to ATL, which was officially opened at the end of May 2020. What makes this specific project unique? “For the most part this is because of the access to relevant airport data that we can use to test and develop new innovations. Of course appropriate measures related to privacy issues have been taken.” Meanwhile, the first tangible research projects have kicked off. “We have started working on three topics”, explains Bavelaar. “They all involve technology to make ground and air activities at airports more efficient and more sustainable in the near future. The first project is on expanding and refining the radar system at the airport. An extremely accurate model for current weather forecasting is being developed which will give Air Traffic Control increased insight into the current weather situation. This model can be used to predict possible turbulence between aircraft under changing weather conditions and this will ultimately lead to more efficient take-off and landing procedures. This part of the ATL project primarily involves the faculty of EEMCS.” Pleasant working environment In the second project, researchers are developing a new tool that can predict airside disruptions using machine learning techniques. This information can be used by planners at the airport to help them make tactical and operational decisions which will also lead to more efficient procedures. As part of the first project, the ‘flight-to-gate planning’ module is being tested. And finally, a tool is being developed which can simulate the efficiency, safety and resilience of processes in the airport terminal. Among other things, this tool enables development of applications for a call-to-gate strategy and passenger flow optimisation. In addition, this tool could be used to assess how the baggage drop-off points impact the flow of passengers in the terminal. According to Bavelaar: “The researchers’ initial experiences are positive. The airport has proven to be a pleasant working environment, with good accessibility and opportunities to test innovations. Moreover, the airport staff and the other stakeholders are more than happy to work with us.” The coronavirus situation demanded a great deal from the students’ capacity for improvisation. Nonetheless, in virtually no time at all they made the necessary practical adjustments, as did the other researchers in the project. This is really something to be proud of. Student involvement “So we're making good progress”, concludes Bavelaar. “An important factor is that we continue to reinforce the vision of DIMI within the project and in particular the emphasis on a multidisciplinary and holistic research approach. Of course there is the link with teaching at TU Delft. For example several student groups of the Interactive Technology Design course, at the faculty of Industrial Design Engineering, have already worked on airport assignments.” “The coronavirus demanded a great deal from the students’ capacity for improvisation. However, in no time at all they made the necessary practical adjustments, as did the other researchers in the project. This is really something to be proud of.” Bavelaar is aware that the current times have huge consequences for the aviation sector as a whole. “Yet the impact on the ATL project seems less bad than we feared, and if anything the coronavirus crisis has reinforced the need for innovation.” Read more stories of Aerospace Engineering Project Manager ir. M.E. (Elise) Bavelaar M.E.Bavelaar@tudelft.nl More stories More stories
The first Flying-V test flightSince 2017, a team of researchers from TU Delft has been working on a new, more sustainable type of passenger aircraft, the Flying-V. After the research phase, July saw an exciting and significant next step in the programme: the scale model’s first test flight. Would the aircraft remain stable when airborne, even at low speeds?
Lockdown presents unique opportunity to study sustainable taxiing at SchipholStarting a PhD on the first day of the Covid-19 lockdown was a bit challenging for Bieke von den Hoff. But the lockdown also gave her an unexpected and unique opportunity. As part of a trial programme at Schiphol Airport, she was asked to measure noise levels of a sustainable aircraft towing vehicle called the TaxiBot.
Flying in a VThe lorry pulls up very slowly, en route from the Faculty of Aerospace Engineering to Schiphol. The cargo on board is precious: the 3-meter-wide flying scale model of the revolutionary Flying-V aircraft. Chief engineer Malcom Brown: “The Flying V will use far less energy thanks to its aerodynamic V-shape.”
Bringing silent aviation closerHundreds of millions of people living near airports are still at increased risk of developing hearing problems cardiovascular diseases. Roberto Merino-Martinez, who himself lives near Rotterdam Airport, is researching a relatively new topic in the field of aerospace engineering: Aeroacoustics. An annoying whistle Although aircraft engine noise has decreased substantially over the past decades, air flow around the airplane structure itself is still a considerable source of noise. In wind turbines, this mechanism causes the typical swooshing sound. During the first part of his PhD, in which Merino-Martinez focused on flyover measurements at Schiphol airport, he was surprised to find that many types of planes produced a huge tonal peak at a frequency of 1720 Hz. That is a sound about as annoying as a heart monitor flatlining. “It was especially loud for the Airbus A320, one of the most popular passenger aircraft of all time,” Merino-Martinez says. “It turned out to be caused by a cavity in the nose landing gear, acting like a whistle. It is my most cited research paper to date, and I believe Airbus may fix this in their newer models.” An array of van microphones “The noise models used when designing new planes are simply not good enough. They lack sufficient detail and often predict noise levels to be lower than they actually are”, explains Merino-Martinez. “Improvements in acoustic imaging and its algorithms are essential. A single microphone suffices to measure a general noise level. Add a second and some directionality can be obtained. But to really understand aircraft noise, to make a high-resolution image of all its sound sources, you need to use a microphone array.” Noise created by aircraft wings As it turned out, Merino-Martinez worked most of his PhD on integrating a versatile microphone array into the existing TU Delft laminar flow anechoic wind tunnel, in order to be able to perform the desired measurements. “The solution we came up with allows for the microphones to be rearranged depending on the details of the experiment,” he says. “Sometimes you want to move them further apart for a higher resolution image, or closer together to improve the array’s frequency response.” He also spent a lot of time improving the algorithm for reconstructing the sound sources. “I wanted to accurately measure the sound levels created by airfoils, such as the wings of an airplane or the blades of a wind turbine. A lot of noise can be created by instabilities in the airflow at the trailing edge.” Most acoustic imaging algorithms are based on point sources because they are mathematically simpler. Merino-Martinez rewrote the algorithm so that it was also possible to accurately reproduce line sources of sound. "Our approach gives better results than existing solutions, even those developed by NASA." The silent flight of owls Using the new array and algorithm, Merino-Martinez and his colleagues performed measurements on variations of two noise-reduction techniques. “They are both inspired by the silent flight of owls,” he says. “Their feathers create a saw-tooth profile, called serrations, which interferes with the scattering of the airflow at the trailing edge.” The researchers also investigated the insertion of porous materials or metal foams at the trailing edge, causing a similar interference. “It’s a great solution from a scientific point of view,” he says, “but real-world application is difficult, as these materials can get dirty or attract lightning.” Whereas serrations are already being commercially used by some wind turbine manufacturers, it may take another ten years for the conservative airplane industry to follow suit. “Safety first.” Roberto Merino-Martinez +31 (0)15 27 81736 firstname.lastname@example.org This is a story from Aerospace Engineering An annoying whistle Although aircraft engine noise has decreased substantially over the past decades, air flow around the airplane structure itself is still a considerable source of noise. In wind turbines, this mechanism causes the typical swooshing sound. During the first part of his PhD, in which Merino-Martinez focused on flyover measurements at Schiphol airport, he was surprised to find that many types of planes produced a huge tonal peak at a frequency of 1720 Hz. That is a sound about as annoying as a heart monitor flatlining. “It was especially loud for the Airbus A320, one of the most popular passenger aircraft of all time,” Merino-Martinez says. “It turned out to be caused by a cavity in the nose landing gear, acting like a whistle. It is my most cited research paper to date, and I believe Airbus may fix this in their newer models.” An array of van microphones “The noise models used when designing new planes are simply not good enough. They lack sufficient detail and often predict noise levels to be lower than they actually are”, explains Merino-Martinez. “Improvements in acoustic imaging and its algorithms are essential. A single microphone suffices to measure a general noise level. Add a second and some directionality can be obtained. But to really understand aircraft noise, to make a high-resolution image of all its sound sources, you need to use a microphone array.” Noise created by aircraft wings As it turned out, Merino-Martinez worked most of his PhD on integrating a versatile microphone array into the existing TU Delft laminar flow anechoic wind tunnel, in order to be able to perform the desired measurements. “The solution we came up with allows for the microphones to be rearranged depending on the details of the experiment,” he says. “Sometimes you want to move them further apart for a higher resolution image, or closer together to improve the array’s frequency response.” He also spent a lot of time improving the algorithm for reconstructing the sound sources. “I wanted to accurately measure the sound levels created by airfoils, such as the wings of an airplane or the blades of a wind turbine. A lot of noise can be created by instabilities in the airflow at the trailing edge.” Most acoustic imaging algorithms are based on point sources because they are mathematically simpler. Merino-Martinez rewrote the algorithm so that it was also possible to accurately reproduce line sources of sound. "Our approach gives better results than existing solutions, even those developed by NASA." The silent flight of owls Using the new array and algorithm, Merino-Martinez and his colleagues performed measurements on variations of two noise-reduction techniques. “They are both inspired by the silent flight of owls,” he says. “Their feathers create a saw-tooth profile, called serrations, which interferes with the scattering of the airflow at the trailing edge.” The researchers also investigated the insertion of porous materials or metal foams at the trailing edge, causing a similar interference. “It’s a great solution from a scientific point of view,” he says, “but real-world application is difficult, as these materials can get dirty or attract lightning.” Whereas serrations are already being commercially used by some wind turbine manufacturers, it may take another ten years for the conservative airplane industry to follow suit. “Safety first.” Roberto Merino-Martinez +31 (0)15 27 81736 email@example.com This is a story from Aerospace Engineering Read more stories of Aerospace Engineering Related stories The responsibility gap of self-driving cars Roboats in Amsterdam The flying V
Can ancient algae help replace chromium-6 in coatings?Timelapse: corrosion protection of the letters ‘TUDelft’ What seemed like a wild idea in 2014, using the external skeletons of algae to prevent corrosion, has now been shown to provide long term protection of aluminium used in airplanes. In a few years’ time, it may provide a safe and environmentally-friendly replacement for the use of chromium-6. “Because of its toxicity, the European Commission has forbidden the use of chromium-6,” says Paul Denissen, PhD researcher in the Novel Aerospace Materials group at the faculty of Aerospace Engineering. “Use of chromium-6 is only still tolerated in situations where good alternatives are lacking, for example to protect airplanes against corrosion.” He explains that the aluminium alloy most used in aviation is especially susceptible to corrosion because of the copper that has been added to increase material strength. Typically, multiple boundary layers are applied to protect this aluminium against weathering. One of these layers is a primer coating loaded with chromium-6. “Our research focusses on using the external skeletons of a sort of algae to develop an environmentally friendly alternative for the use of chromium-6 in this layer.” Challenging chromium-6 Chromium-6 is a so-called active corrosion-inhibitor. When a treated surface is damaged, for example by scratching, the chromium-6 atoms will be released from the primer layer. They will create a thin layer of chromium oxide on the exposed metal surface, preventing further corrosion. After their release, chromium-6 atoms can continually redistribute themselves, providing continuous protection of the damaged area. “There are a number of alternative corrosion-inhibitors that are also very good at creating a protective barrier,” Denissen explains. “Unlike chromium-6, however, they can oxidize only once, and the protective layer they create is not permanent. Long-term protection therefore requires the continuous release of these inhibitors. More importantly, these alternative inhibitors may already chemically react with the primer coating at the time of its fabrication or application, thereby weakening their anti-corrosive power.” Quite some challenges to overcome, with a possible solution coming from the world of algae. Various shapes of the external skeleton of diatom algae Source : https://paleonerdish.files.wordpress.com/2013/06/diatoms.jpg Pill-box protection Diatoms are a group of microalgae that have been roaming the earth for more than 100 million years. These single cell organisms come in various sizes, ranging from one to a few tens of micrometres. They have a hard, inorganic shell to protect them from the environment. This cell wall is made out of silica, the same material as glass, and contains many nanometre-sized pores. Inspired by the pill-box shape of these shells ( see figure ), it was Santiago Garcia, associate professor in the same group and the supervisor of Denissen, who came up with the idea to use them for active corrosion protection in coatings. Garcia explains that “my idea was to fill these shells with alternative corrosion-inhibitors, and then add these loaded shells to the primer coating. I envisioned the pill-box structure to prevent the unwanted chemical reaction between inhibitors and coating.” He also imagined the pores to allow the immediate and sustained release of these inhibitors when the protective layers are damaged, and the metal surface is exposed. “And these algae shells are easily available at low-cost,” Denissen adds. Rapid development Denissen explains that his 2015 master’s thesis was merely a feasibility study, to see if this approach could be successful. “Now, we are three years into my PhD and despite limited resources we have just shown corrosion protection potentially equalling that of chromium-6. We still use our first pick of algae shells, but we have substantially increased their filling with inhibitors as well as their release efficiency, leading to a much-improved protection.” 30-day protection by algae coating with corrosion-inhibitors Testing in Paris After intensive work in Delft to proof the concept, the researchers travelled to Paris for a challenging experiment. “We were curious as to the long-term protective power of our coating for large damages, as required by several companies,” Denissen says. Together with their collaborators from the group of Polina Volovich at Chimie ParisTech, they applied a 1 mm wide scratch to samples of aluminium used for airplanes, covered in a variety of their test ‘algae-coatings’. These samples were subsequently immersed in large volumes of a highly corrosive environment. The researchers got what they bargained for ( see figure ). “We were astounded,” continues Denissen, “what we saw was full protection against corrosion, even after thirty days of immersion. Only a couple of alternative solutions come this close to the results obtained with chromium-6. It’s an amazing result after only such a short period of development.” Visualising corrosion protection Denissen and Garcia have also developed a novel method to study the onset and development of corrosion. It allowed them to gain a detailed understanding of the results they obtain with their algae shells, guiding further optimisation. “It is relatively simple technology, using a basic optical camera,” Garcia explains. “Optical techniques have traditionally been used to obtain qualitative information or to make beautiful pictures. What we have shown is that optics can be used to monitor and quantify local corrosion processes at a very high resolution, in real time. It is mature technology, allowing us to analyse any coating, commercially available or still in development.” Optimal protection “We use our experimental findings to build a computer model for further optimization of our coatings,” Denissen says. This can prove very beneficial as these algae shells come in more than 100.000 sizes and shapes. And there are more variables to tune, such as the type of corrosion-inhibitor used, whether or not to add an outside layer to the algae shell to even better regulate inhibitor release, or the optimal concentration of shells in the coating. “We may for example want to use disc-shaped shells to reduce our protective layer to the thickness currently used by the industry,” Denissen explains. “We are also looking into using combinations of inhibitors and shells in our coatings, further improving corrosion protection.” A small revolution It is not an easy task to replace chromium-6. “There are many barriers, resulting in a lack of good alternatives,” Denissen says. “For example, the Dutch Ministry of Defence wants proof that alternatives will provide twenty-year protection of their military equipment. But there are no good methods to accelerate this evaluation, to validate it in only a limited time-span.” More importantly, he explains, many of the tests used to validate the efficiency of new coating materials are designed specifically for chromium-6. “It is not a level playing field. It means that you have to prove your alternative coating to behave similar to chromium-6, rather than prove that it provides adequate protection.” Nevertheless, a small revolution has recently taken place. Rather than waiting for coating manufacturers to replace chromium-6, airplane manufacturers are now actively developing their own solutions as well. “At the moment, we are already talking to both.” Future perspective Despite very promising results, Denissen stresses that “we need a few more years to develop and demonstrate our algae-based coating before it can be used on planes, bridges or any metal surface that needs protection against corrosion. Does our coating protect sufficiently against scraping and scratching? Can it withstand frequent variations in outside temperature? Will it bond well with the other protective layers?” Garcia adds that “our main commitment is to find solutions to societal problems. We are currently talking to several industry partners about collaboration. Together we can speed up the development and launch of our technology and we expect to be ready for operational experiments by 2022, on an airplane.” Until completion of those experiments and passing the required certifications, the airplane industry may require the European Commission to again extend its leniency, tolerating the use of chromium-6 for the time being. You can find scientific publications, related to this research, here in Corrosion Science and in Electrochimica Acta .
In a breakthrough experiment Marios Kotsonis used plasma to actively interfere with the airflow on the wings of jet airliners.