Tunnels are never boring…

I know I promised to write a blog post about my trip down the Crossrail tunnels at Tottenham Court Road, but you’ll have to forgive me and accept this photo gallery as a consolation prize! Like everyone, I have lots to wrap up before Christmas, and transcribing the audio recording hasn’t happened quite yet! I promise I’ll get to it eventually though :)

HUGE thanks to Andy Adler for looking after me, and for answering hundreds of questions without complaint. I learned  a huge amount about spray concrete lining and I can’t wait to share it with you!

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A step forward for smart windows?

This was published on 8th December 2014 on Materials Today – you can read it in-situ here: http://www.materialstoday.com/energy/news/a-step-forward-for-smart-windows/

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Multilayer windows that are self-cleaning, energy-saving and anti-fogging may be one step closer, thanks to a team of Chinese researchers.

Windows are an important factor in a building’s energy efficiency, and with tall, glass-clad structures becoming the norm in our cities, teams of researchers are looking at ways to improve their efficiency, while maintaining their appearance. In the UK alone, 40% of the nation’s total energy bill comes from the way buildings are lit, heated and used, so even small changes in window technology could have a significant effect in reducing total energy consumption.

Much of the research on “smart windows” has focused on titanium dioxide (or titania, TiO2) which can be used to produce a self-cleaning surface, thanks to its photocatalytic properties. But Chinese researchers have taken this to a new level, by adding another “smart” ingredient, vanadium oxide (VO2), which can control infrared transmittance while maintaining transparency to visible light. The resulting material offers improved thermal insulating properties, is photocatalytically-active and doesn’t fog up. [DOI:10.1016/j.nanoen.2014.09.023]

This performance is the result of the composite’s unique crystal structure – it is effectively a sandwich of two forms of TiO2 (rutile and anatase) and VO2 in its monoclinic phase. In addition, the sandwich structure can be produced using standard thin-film production techniques. The bottom slice of the sandwich consists of TiO2 (rutile), which serves as an antireflection layer. This is followed by the ‘filling’ – a layer of VO2, which controls the amount of solar heat transmitting through the glass in response to temperature changes. The top layer of TiO2 (anatase) provides the photocatalytic properties that make this glass self-cleaning.

The team, led by Ping Jin from the Chinese Academy of Sciences, carried out a series of tests to characterise the final composite thin-film. Optical measurements showed that the 400 x 400 mm3 sample displayed excellent regulation of infrared light, while remaining transparent at visible wavelengths. UV radiation of the material also resulted in a photo-induced hydrophilicity, which produced in an antifogging surface. By measuring the degradation of stearic acid under UV light, the film was found to be highly photocatalytically-active.

The team are confident that their thin film has real applications in the development of a true “smart window”. Their multilayer film offers three functions at once – it is antifogging, self-cleaning and energy-saving – but until the robustness of this film has been measured, it may remain in the research lab.

Nano Energy, Volume 11, January 2015, Pages 136–145 “TiO2(R)/VO2(M)/TiO2(A) multilayer film as smart window: Combination of energy-saving, antifogging and self-cleaning functions.” DOI:10.1016/j.nanoen.2014.09.023

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I’m a Crossrail fangirl

** WARNING – this post may make you a little bit jealous **

The thing I’m most enjoying about writing my book is the fact that I now have a completely valid excuse to be an engineering fangirl :) ….not that I need an excuse, but I definitely experience fewer raised eyebrows when I talk transport these days. Anyway. in the past few months, I’ve been lucky enough to speak to the Bill Baker (Chief Engineer of the Burj Khalifa) and Ron Slade (Lead Engineer on the Shard). But last week, I had my biggest fangirl moment yet – when I was invited to the head office of Crossrail at Canary Wharf to meet the Chief Engineer of the entire project, Chris Dulake.

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Situated in the heart of London’s second financial heart, the Crossrail offices occupy the upper floors of 25 Canada Square – a location that feels about as far away from a building site as its possible to get. But as I glanced out the windows, the eye-catching roof of Canary Wharf’s future Crossrail station reminded me that we were, in fact, very close to the coolest new engineering project London’s seen in a hundred years.

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If you don’t know what Crossrail is, here is a tiny summary. It is Europe’s largest construction project, which started back in May 2009. It aims to deliver high frequency, high capacity train service linking Reading in the west, to Abbey Wood in the east. In order to do this, they’ve had to construct 21 km of new twin-bore tunnels under central London. These huge tunnels thread their way through a packed subterranean city – just think about all of the tunnels for the tube network, cables and pipes for utilities and various sites of archaeological importance. And these are large trains that completely dwarf a tube train. And they’ve managed to do it without closing any existing station. Engineering at its finest. Oh and currently, there are over 10,000 people working on it, across over 40 construction sites. Yep.

crossrail FT

Anyway, some months ago, Peter MacLennan, Head of Media Relations at Crossrail (and all-round top bloke) had responded to a very cheeky email from me, asking if I could speak to some of the engineers working on the project. I think my ridiculous questions about escalators won Peter over, and before I knew it, I had a meeting with Chris Dulake in my diary.

Cut to Thursday. A shiny lift and (equally shiny) lift attendant escorted me skyward to Crossrail HQ. Chris’s office has a killer view of the Docklands which I can’t imagine ever getting tired of – he told me that when a giant rubber duck visited the area earlier this year, he could see it from his desk :) Within minutes of meeting, I think Chris has me all sussed out, so we’ve dove straight into equations and whiteboard sketches. The major aim of Crossrail, Chris says, is to do all the work while minimising inconvenience to Londoners. And I see his point – for the most part, all we see at each of the sites is the blue hoarding, and some heavy-lift machinery. But beneath our feet, two tunnels with a total length of a marathon route are being constructed from scratch.

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Key to the tunnelling are eight tunnel boring machines (TBMs) which weigh in at 1000 tonnes each. They cut through London clay at the rather impressive rate of 100m a week. It may not sound all that fast when compared to your car, but looking back into history provides some context. It took Brunel 16 years to dig the original Thames Tunnel. Crossrail’s new Thames Tunnel took just 8 months.

Another engineering titbit that I learned about was compensation grouting - this is how the tunnellers minimise the structural damage to buildings while displacing tonnes of excavated material. Every single building that sits along the route of Crossrail was identified and characterised in order to understand how tunnelling beneath it would affect its structural integrity. Where predicted damage exceeded acceptable limits, a cement-like substance called grout is injected into the ground at defined positions in order to firm up the area where settlement is expected to occur.

The Fifteen Billion Pound Railway

Anyone who is familiar with Soho Square will be familiar with the central ‘grout shafts’ used to carry out this task (there are four around the square because it is surrounded by historically important buildings). They are dug in identified areas at risk of settlement and manned by small teams. Small-diameter underground pipes which spread out from the grout shaft in a radial pattern allow workers to very precisely target areas which may lose more material than acceptable.

88% of the tunnels are now complete, with the remaining two TBMs planned to complete their journey towards the summer of 2015. Once that is complete, all effort will switch to making the tunnels train and passenger-friendly, with trackbed prep, platforms and access tunnels already in the early stages of development. The trains that will eventually speed through these tunnels in 2018 will be incredibly safe, fire-hardened to cope with even the worst catastrophe (no doubt, with a safety nod to the deadly Kings Cross fire back in 1987) and will be super-efficient, employing similar regenerative braking technology to that used in F1 cars.

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I left Chris’s office with lots of things – an invite to come back, a book of papers on Crossrail’s construction and some other awesome gifts. Even more importantly, I left feeling totally inspired by this major engineering undertaking, and more than a little jealous of Chris’s scale models! I don’t want to give away all of the secrets I learned from chatting with Chris and Peter – for that, you’ll have to wait for the book – but there is one last thing….

I’ve been invited to visit some of the tunnels myself!

Cannot. Express. The. Excitement.

Promise to blog about that when it happens ;)

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Reinforced 3D printing for biomedical applications

This story originally appeared here

German researchers have demonstrated that the mechanical properties of 3D-printed structures can be improved with the addition of fibre reinforcement.

Since entering the mainstream a few short years ago, 3D printing has grown from strength to strength, with systems now capable of printing everything from 3D chocolate shapes to titanium implants. But the technique’s origins in industrial rapid prototyping have not been forgotten, with companies across the globe using 3D printing to create complex components quickly and reliably.

Research from a team at University Hospital Würzburg in Germany has focused on improving one type of 3D printing – three-dimensional powder printing. Their results, published in Materials Letters 139 (2014) 165–168 (DOI: 10.1016/j.matlet.2014.10.065) show that a range of different short fibres can greatly improve the mechanical robustness of a final printed piece when compared to non-reinforced printed samples.

Three-dimensional powder printing (3DP) is used to create complex 3D structures by selective application of a liquid binder into a bed of powder, using an inkjet print head. As each successive thin layer of powder is similarly treated, a shape can be built up, with the excess powder removed in a process called “de-powdering”. While 3DP benefits from accurate control and the ability to 3D print at room temperature, its application is often limited by the low mechanical strength of the printed samples.

The team, led by Uwe Gbureck, developed a fibre reinforcement approach similar to mineral bone cements used in orthopaedics and dentistry. A series of short (length 1–2 mm), commercially-available fibres were added to a matrix of cellulose-modified gypsum powder. Identical structures were produced with each of the reinforced powers, and the mechanical properties determined using a four-point bending test regime.

Even at low concentrations of 1 %w/w, it was found that structures produced using the reinforced powers outperformed those produced without fibres, in terms of both their green strength (resistance to deformation) and their fracture toughness. When short glass fibres were used, despite no increase in apparent density, the material’s flexural strength was significantly higher (up to 180%) than that of non-reinforced structures.

This work has demonstrated that reinforced powders may have a role to play in biomedical applications where strength is key. The next stage for Gbureck and his team is to extend their technique to biocompatible fibers. If they manage this, your next filling may be 3D-printed specifically for you.

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Mechanical properties of contact lenses

This appeared here on 5th November 2014 – thanks MT :)

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A team from Georgia Tech have measured the mechanical properties of soft contact lenses under practical conditions using an atomic force microscope (AFM).

With more than 30 million contact lens wearers living in the US, making lenses more comfortable is a growing research issue, and defining their properties is key to understanding their performance. Researchers from Georgia Institute of Technology have measured the complex mechanical properties of commercial soft contact lenses, and found that conventional measurement techniques are no longer fit for purpose.

Contact lenses have to fulfil a number of contradictory functions while remaining optically clear – they need to be flexible enough to make them comfortable, but must also maintain their shape in saline conditions. Current mechanical characterisation of lens materials is based solely on tensile tests, which measure only the averaged elastic modulus of the entire lens. With coatings and wetting agents widely used in the latest multiphase lenses, it is becoming increasingly important to measure the local mechanical properties of these materials.

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Surface topography of submerged soft contact lenses used in this study. a) Lotrafilcon B, b) Balafilcon A, c) Senofilcon A, d) Comfilcon A.

Led by Vladimir V. Tsukruk, Georgia Tech engineers turned to AFM-based surface force spectroscopy (SFS) to characterise the micromechanical properties of commercial contact lenses at the nanoscale. This technique has been used to study surface topography, friction, and protein absorption in contact lens materials and in eye tissue, but the paper from Tsukruk (Polymer 55 (2014) 6091–6101 [DOI: 10.1016/j.polymer.2014.09.053]) is the first to probe the surface mechanical properties in wet conditions. The team’s technique combined two AFM modes – high frequency (tapping mode) measurements, which provide high resolution maps of topography and mechanical properties, and static (force volume) nanoindentation, which utilises tip sample interactions to accurately calculate mechanical properties.

Small pieces of four commercial lenses were submerged in their original saline solution and probed with sharp (10-30nm) aluminium-coated AFM tips, which had been previously characterised. The surface topography of the outer (convex) surface of the contact lens was measured, alongside indentation mapping experiments that characterised both the coating, a soft thin film, and the supporting stiffer lens substrate at nanoscale resolution. The researchers also looked at the lenses in cross-section and in all cases, found a complex, non-uniform sub-surface structure.

The multiphase nature of today’s soft silicone hydrogel contact lenses means that old measurement techniques are not sufficient. In this paper, Tsukruk’s team have proposed a new experimental protocol, based on AFM characterisation, for these materials.

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Bioinspired graphene aerogel for oil spills

Originally appeared on Materials Today

Marine mussels may not be an obvious first step on the route to developing a material to soak up oil spills or act as a chemical sensor, but a team from China’s Xiamen University did just that. Combining the adhesive properties of mussel with the mechanical properties of graphene, they produced a bio-inspired aerogel with high absorption capacity.

Graphene’s unique combination of electrical, thermal and mechanical properties positions it firmly at the top of the nanomaterials agenda. One route to transferring its properties into larger scale structures is to prepare graphene sheets in the form of an aerogel. To do this, the researchers, led by Xi Chen, looked to the properties of dopamine, a molecule that mimics the adhesive proteins found in marine mussels.

Published in Carbon (DOI:10.1016/j.carbon.2014.08.054), Chen’s paper reports on the low-cost development of a nitrogen-doped graphene structure. Because dopamine spontaneously polymerizes, and can modify virtually all material surfaces, it can be a good adhesive. It also a source of nitrogen atoms, which dopes graphene, enhancing its electrocatalytic properties.

A graphene-dopamine gel was first prepared and annealed at 800 °C, to form an ultra-low density aerogel. Structural characterisation showed that the aerogel consisted of a network of twisted and cross-linked graphene sheets that formed nano- and micro-pores. The nitrogen atoms from the dopamine were shown to be incorporated into the carbon–carbon bonds of the graphene, and the aerogel exhibited excellent electrochemical activity. The mechanical properties of the aerogel were also remarkable. A 10 mg piece could sit on a delicate flower without causing any damage, but could also support 5000 times its own weight.

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(a) Photograph of two NGAs (cylinder size: diameter 1.9 cm, length 1.2 cm) standing on a Calliandra haematocephala flower. (b) SEM image of the sample in (a). (c) Typical TEM image of the NGA. (d) HRTEM image of the NGA.

The surface of the aerogel was found to be hydrophobic, so when combined with its remarkable mechanical stability, demonstrated that the aerogel would be an ideal candidate for highly efficient extraction of organic pollutants and oils. In tests, the aerogel was shown to absorb liquids (including pump oil, chloroform and diesel) of up to 156 times its own weight. The absorbed liquids could also be removed by direct combustion in air.

The team are confident that their graphene-aerogels have a wide range of potential applications, from use as a suction skimmer in marine oil spillage, to an electrode material for electrochemical sensors.

This paper was originally published in Carbon 80 (2014) 174–182

To read more about this article, click here.

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Engineering a room-temperature multiferroic, in theory…

Appeared on Materials Today on 14 October 2014 (Be warned, it’s a bit more technical than most of my posts)

A group of theoreticians have demonstrated that the key to producing a room temperature multiferroic may lie with a new family of perovskite materials.

Often described as the “holy grail” of data storage, room temperature multiferroic materials have been at the forefront of functional materials research for two decades. And the reason is that they are ‘adaptable’. Multiferroic materials simultaneously exhibit two often contradictory properties – they can be both electrically charged (ferroelectric) and maintain a permanent magnetic field (ferromagnetic). In principle at least, it is possible to control the magnetic phase of multiferroic materials with an applied electric field, and to control their electric polarization with an applied magnetic field.

A collaboration of Chinese and US scientists now report that by inducing structural distortions in a specific family of perovskite superlattices, it is possible to create a new room-temperature multiferroic. Published in Computational Materials Science [DOI: 10.1016/j.commatsci.2014.09.011], the paper describes the first-principles approach used by Xifan Wu and his colleagues to explore the functionalities of this material group, ATcO3 (A = Ca, Sr, Ba). In 2011, ATcO3 was experimentally shown to be antiferromagnetic. In this work, density functional theory investigations of the structural instabilities in perovskites found that a mismatch between BaTcO3 and CaTcO3 could induce ferroelectricity at the interface. The researchers also found that the Néel temperature of their superlattice – that is, the temperature above which ferromagnetic order is lost – is 816K, making this theoretical material a multiferroic at room temperature.

A mismatch between two different materials can be induced either because of epitaxial strain – a result of different lattice spacing between crystals – or by “engineering” the interface. Earlier work has shown that epitaxial strain in perovskite superlattices can result in ferroelectricity. But Wu and his team used a thorough theoretical approach to demonstrate that enhanced ferroelectricity can be induced by interface engineering. The Néel temperature of both BaTcO3 and CaTcO3 is well above room temperature, meaning that the superlattice maintains its unique magnetic ordering and ferroelectric properties at vastly-elevated temperatures relative to most multiferroics.

This paper presents a theoretical approach, so the team now await experimental confirmation of their results. If successful, this discovery may lead to a material whose magnetic properties can be easily controlled at room temperate, and, eventually, to a new generation of extremely low-power magnetic storage devices.

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