Materials Connect

What’s the science behind fire safety?

We don’t think about it, but there’s an amazing amount of science and engineering that goes into keeping us safe. TV shows like Seconds from Disaster and industrial safety training courses show us that some big accidents rarely have a single cause but instead involve a chain of events where several things aren’t done correctly, leading to a disaster. Schoolchildren across the UK are probably familiar with the fire of London that happened in 1666 but science and engineering have moved on a lot since then and so have regulations around fabrics, buildings and personal protective equipment. What makes fire safety so complex? There is not a quick answer to that question so if we want to get to know fire, we can break things down then take a look at the materials used for different situations.

To understand fire, we need to understand the chemistry

We need to start with the very basic here. To have fire you need three ingredients: oxygen, heat and fuel. So, you can put a match out by starving it of oxygen. Fire is a chemical process: the oxygen bonds to something (i.e., oxidation). Most of the materials around us are made from hydrocarbons so lots of examples talk about oxidation of carbon-containing materials. The application of heat then kicks the system over some thermodynamic barrier and initiates oxidation. Since oxidation is an exothermic process, the heat given off continues to drive the reaction and so makes it self-sustaining.

 

Image via Wikimedia Commons (CC BY-SA 3.0)

Chemists know oxidation as a redox reaction: one part of the chemical system loses electrons (oxidation) and the other chemical gains electrons (reduction).  (This means that, for some chemical reactions, you can get a fire happening even when oxygen isn’t present: A common example is the redox reaction between hydrogen and chlorine gas which is initiated by putting some energy into the system. Adding the energy causes the chlorine molecules to break up and, now that they don’t have a complete outer electron shell they go on to react with the hydrogen. You can do this using just light but it’s quite unlikely you’d see this exact chemical system in everyday life. A barbecue or the embers from your fire provide another good example of what happens when the oxygen can’t get to the fuel. The ash (or char) that builds up on the outside of the coals prevents the oxygen from reaching them but remove the ash by carefully blowing on the fire or by giving your portable barbecue a gentle shake, then the ash is removed and the coals start to burn more brightly.

Chemistry applies to personal safety

In theaters, the stage curtain is flame resistant. I worked in theater where I was told that you could hold a blow torch to the curtain for fifteen minutes and it would not burn. This gave enough time for the audience to evacuate in the event of an emergency. Fabrics like this are often coated with a flame-resistant chemical. You can buy spray bottles of some of these fire-resistant chemicals. Some contain nitrogen with an aqueous polymeric binder. The nitrogen is released when heat is applied and so starves the material of oxygen. Others are based on compounds that contain boron. When heat is applied and endothermic reaction is initiated: the heat is absorbed, water is released from the compound and the residue melts to coat the fabric, starving it of oxygen in the process.

A lot of the regulations surrounding personal protective equipment originate from motor car racing. If you happened to watch the 2020 Bahrain Formula 1 Grand Prix you’ll be familiar with how important this is: The fireball that engulfed Roman Grojean’s car looked terrifying and it’s amazing that he walked out of it. In Formula 1 drivers can wear an inner body suit made out of a proprietary material known as Nomex (made by DuPont) and specialist outer suits that resist fire. The outer suits also use proprietary designs but one way of protecting the wearer from fire is to add air pockets that expand in the heat; this creates a layer of insulation giving you time to get out of fire. The Nomex material is self-extinguishing: it’s made from a semi-crystalline fiber with a chemical structure of rings of carbon linked by amide bonds that has a high ignition temperature. Once you remove this material from the heat source the fire will go out suggesting that the oxidation reaction isn’t self-sustaining. The suits are quite thick and transfer heat slowly which also contribute to keeping you safe. When you see these suits in action it looks like something out of sci-fi or a magic trick. The regulations in Formula 1 specify a heat transfer index for driver clothing that helps protect them from burns.

Nomex was discovered in the 1950s and, given that it’s still in use today you can imagine that little has changed in the intervening decades. Even so, advances are being made in a wide variety of applications to textiles and beyond. Fabrics that form a layer of char on the surface are common, and the char then acts as a barrier against oxidation. As an alternative to coating fabrics after they are produced, some can be made from fibers of viscose that are produced using additives that contain flame retardant organophosphorus compounds. Other fabrics made from polyester, polyamide and polypropylene tend to melt and drip when heated but adding endothermic chemicals such as aluminum trihydrate can prevent this phenomenon and so lend a degree of fire protection. There are many other ways of making fire resistant materials and future developments lie in making fibers that are easier to process and recycle.

Regulations in the construction industry

In civil engineering, fire engineering, fire safety engineering and fire protection engineering are different ways of referring to the science behind making a construction project safe. Going back to the chemistry, the buildings we inhabit will obviously contain oxygen and will have some sort of heat source for cooking and keeping people warm; this means that materials have to be designed with fire in mind. It’s not really feasible to make something fire-proof. Instead materials are chosen for their fire resistance: building materials are chosen that won’t burn for a certain amount of time when exposed to heat. In the event of an emergency this gives people time to evacuate. So having the proper material is the key to avoiding catastrophe.

In building construction, a cladding made of polyethylene sheets with an outer layer made of aluminum can be used. Polyethylene is of course flammable but it’s used to make buildings affordable and the outer layer of aluminum should ensure fire resistance. If the thickness of the sheets meets regulations then the building is deemed to be safe. Something called travelling fire is also considered which is where the fire can be transferred through the building structure. Materials should be chosen and put together in such a way to prevent travelling fire.

In the UK, all of these safety measures are detailed in building regulations, known as approved documents and supplied by government websites. While Approved Document A is about how to build a structure with safe loading, approved Document B is all about fire safety and fire resistance. This latter document specifies how long the building needs to be fire resistant for. In the USA, materials can be given a rating by the American Society for Testing and Materials based on their flame spread index which is tested in laboratory conditions. Different materials can be used depending on the local standards that are in place and the type of use of the building. A longer fire resistance time or a lower flame spread index leads to greater construction costs and the regulations state minimum fire resistance times which depend on the type of building and what it will be used for. Fire safety engineering also considers human behavior and, given that smoke is sneaker than fire and can be more dangerous, the way in which smoke travels is also taking into account when the building is designed.

Flame-retardant materials might need to change as the fumes that they produce can cause health problems, particularly for the firefighters. In addition to processing and recycling concerns, another challenge is to develop materials that are less harmful to health.

Science keeps us safe, and gives us confidence to do daring things

In the example from Formula 1, Grojean’s racing suit kept him safe from fire and probably helped give him the confidence to drive a car at several hundred miles an hour. If you understand the science, you might want to do some slightly less daring, but still quite risky things. Even tried putting a candle out by pinching it? You’ll know that you need to wet your fingers first so that you don’t get burned. And if you pass your hand through a flame fast enough, you’ll be fine: similar to the F1 outer suit, a layer of air around your hand acts as insulation. Knowledge can be powerful and knowing the science behind fire safety can help prevent disaster.

 

A version of this article appeared on medium.com and is based on an episode of a podcast. Technically Speaking (a science and engineering discussion) recreates some of those slightly odd conversations that all scientists and engineers have in the lab; conversations that incorporate scientific fact, wild speculation and often quite a few references to news stories, films, and television.

Playtime? Risky chemicals in plastic toys

Difficult to imagine a birthday party, a Christmas, or a family reunion with kids without having toys around. Toys are an important business, with the toy market being only half of that of cars, reaching more than USD$100 billion, with an annual growth of 2.5%.¹ However, contrary to cars, 90% of all toys are made of plastics, and have a life time from a few days to a few years.² Plastic toys are trashed and become the sadly famous microplastics that pollute oceans and our environment. Even a single piece of LEGO brick can take from 100 to 1300 years to completely degrade.³ But not only plastics are harmful to the environment, they also put our kids at risk as most contain harmful chemicals.

Picture of a poster found in the bus.

Earlier this year, collaborative work from the Technical University of Denmark, the University of Michigan, and the Economy Division from the UN Environment Program listed the chemicals of concern present in toys.⁴ Reviewing the published literature on chemical compounds in toys, they found 126 chemicals of concerns among which 31 are plasticizers, 18 are flame retardants, and 8 are fragrances. More importantly, they determined that at least 17 of these chemicals have high risk to induce cancer and are not prohibited in regulations, while 37 of these chemicals have unknown risks. This is alarming since they estimate a consumption of 18.3 kg of plastic toys per child per year in Western countries. Also, the authors only focused on the regulations in Europe and Northern America, which have the most stringent regulations regarding this topic. Currently, China is exporting 30% of all toys, with India taking over soon and working on implementing toy safety regulations.⁵

How do chemicals pass from toy to kids? The exposure route can be multiple: inhalation, ingestion, object to mouth and touch. However, so far it is not possible to evaluate the exposure risk from the actual toy level - the evaluated risk was established from the plastic level.

Are there toys likely to be more toxic than others? The concentration of plasticizers, among which are phtalates, can reach up to 70 % of the toys mass! These plasticizers are used in soft toys to give them flexibility.

Luckily, alternatives to plastic toys are emerging. First, recycled plastics and second-hand toys, although still containing the chemicals, reduce the environmental pollution. Secondly, bioplastics, such as derived from biomass, are biodegradable in water too. Toy manufacturer giant LEGO is now using it in its famous bricks.⁶ Thirdly, wood, rattan, hemp fibers, and other natural materials can also be used to produce toxic-free, eco-friendly toys.

Although these alternatives exist, their high cost and slow production rates are struggling to compete with injection molding of thermoplastics. LEGO can produced 2.16 million pieces per hour, or 36,000 per minute. Reaching such an output with wood is unlikely. Plastic toys also come in various shapes and colors, can be combined with electronic systems, are tough, lightweight, resistant to water and spillage, etc.

Materials science, including chemistry and processing will be key to address the toxicity of plastic toys for kids and the environment. For example, DNA extracted from biomass such as algae and bacteria can be colored and shaped in plastic-like pieces, for consumer goods including toys.⁷

Biomass DNA puzzle toy, from ref [7] (credit American Chemical Society).

References:

1. https://www.alliedmarketresearch.com/toys-market-A08309

2. https://www.theworldcounts.com/challenges/consumption/other-products/environmental-impact-of-toys/story

3. A. Turner, R. Arnold, T. Williams, Weathering and persistence of plastic in the marine environment: Lessons from LEGO, Environmental Pollution 262 (2020) 114299.

4. N. Aurisano, L. Huang, L. Mila i Canals, O. Jolliet, P. Fantke, Chemicals of concern in plastic toys, Environment International 146 (2021).

5. https://www.indiafilings.com/learn/toys-quality-control-order-2020/

6. https://www.lego.com/en-sg/sustainability/environment/sustainable-materials

7. D. Wang, J. Cui, M. Gan, Z. Xue, J. Wang, P. Liu, Y. Hu, Y. Pardo, S. Hamada, D. Yang, D. Luo, Transformation of biomass DNA into biodegradable materials from gels to plastics for reducing petrochemical consumption, J. Am. Chem. Soc. 142 (2020).

#SciComm: How to structure an article on an unwieldy topic

The US National Academies (NAS) began a series of workshops last year to determine a roadmap for US science policy for the next 75 years. One of the workshops focused on US research universities. I sat in on the Workshop online, taking notes for a news article.

The next 75 years—this task is immense. I narrowed the topic to a materials science angle for the MRS Bulletin readership.

It’s still massive.

When thinking about who to interview from the materials research community, I realized the speakers at the workshop were predominantly over 60 (maybe some as young as 50). In determining the shaping of research universities and their policies, I thought it would be good to follow up with researchers at a wider spectrum of career stages.

Along with interviewing students and early-career researchers, I contacted older materials researchers who have served on science panels or have done other work related to the topics covered in the NAS workshop. In all, I interviewed 10 researchers, from undergrads to those who have retired.

As the NAS workshop took place during the 1^st wave of the COVID-19 pandemic, this global health emergency cast light on the direction research universities should take in the future, including further development of technology that would enable laboratory research from off-site.

In my notes from both the workshop and the interviews, I had information on:

• NAS workshop discussions
• effects of COVID-19 on university researchers
• diversity & inclusion of the future workforce
• diversity & inclusion of the population affected by research conducted at the US universities

I broke down the content by high-level topics:

• wake-up call based on the pandemic
• risks for materials research
• going forward

From the interviews, one statement kept overriding all the others. It’s the statement that most got my attention. In the structure of the article, I was unhappy that it would be buried deep inside.

Then I decided to take a risk. I realized if this statement held my attention the most, I should open the article with it, and see where it leads:

“I remember first hearing this term ‘digital divide’ in the mid-1990s. It was the concept of people from lower socioeconomic status not having access to computers and the Internet,” says Tabbetha Dobbins, the Interim Vice President for Research and Dean of the Graduate School at Rowan University in New Jersey, in an interview with MRS Bulletin. “It has always been talked about in a scope of, well, there will be jobs available to people who have these computer skills; and people who don't, won't be seeing those jobs.”

Dobbins recently participated in a webinar training K–12 teachers on diversity, equity, and inclusion where she learned that some students have trouble transitioning to online learning during the pandemic because their families cannot afford a computer and access to the Internet. They are, therefore, locked out of an education. “[The Internet] is at least a $70–$80 bill per month and some families simply can't sustain that,” she says. Looking toward US research universities of the 21st century, Dobbins says, “By taking our eye off of that ball 25 years ago and not fixing the problem, how far have we disadvantaged students into pursuing computational materials studies who come from low socioeconomic grounds?”

            –from The COVID-19 pandemic informs future directions of US research universities

What do you think? Does that thought capture your attention?

-Judy Meiksin

Material, microstructure, and design, for old and new music.

 

Music emanates from a combination of material, microstructure and design, much like in any engineering application. Many stringed or wind instruments are traditionally made from wood. Now, recent progress in science and technology enables us to explore other materials and structure to create new sounds, or to re-create ancient ones.

Sounds are acoustic waves impacting our cochlea after interacting with surroundings. When a propagating wave meets a material with a different density  and stiffness than air, it can be reflected and transmitted with distortions. With different materials are associated different sounds, and various designs can further modify them. For example, tap on a piece of glass and it will sound 'sharp' and 'crystalline'; tap on a piece of polystyrene and it will sound 'mat', if any. Tap on glasses with decreasing thicknesses and diameters, and the pitch will rise. Listen to the organ-like sound of the Glass Armonica or the crystalline melodies of the Jal Tarang.

 and  are the 2 key properties that impact the acoustic performance of a material (see ref [1] for the derivation):

- the material's speed of sound (also called impedance)

- the material's radiation coefficient

- the material's damping or loss coefficient . is called the quality factor with the resonance frequency and  the frequency width of this frequency.

Since  and  can be easily measured, it is possible to draw acoustic materials maps, similarly to the Ashby plots that we use in mechanics. Making use of these maps, it is possible to understand and identify which wood species are generally used for a violin bow, or rather for a violin back (see Fig 1) [1]. Since  and  are also intimately related to the material’s microstructure, looking at the distribution of cells and vascular holes in bamboo species can explain why reed stems from P. Australis are preferred for making a hichiriki, a double-reed traditional Japanese flute (see Fig 2) [2]. Indeed, it all comes down to mechanics: the interplay of local soft and hard zones in the stems enables it to vibrate in a way deemed 'best' by professional players.

Fig 1: Acoustic material map for different types of woods, bamboos, and carbon fibre reinforced composites. Modified and adapted from ref [1]. Stradivari's back plates acoustic properties were estimated using the reported Spruce density of ˜300 kg/m³, a typical wood modulus of 10 GPa, and an increase in the typical loss coefficient of 350 %.

 

Fig 2: Optical images of the microstructure of the reed stems from P. Australis, vs that from another reed. Adapted and reproduced from [2].

The motives for musical instruments made from other materials than wood stem from artistic curiosity to historical research, along with the use of more durable, affordable, and sustainably sourced materials.

As in other engineering applications, long fibre reinforced composites can now replace the wood of violins, violas, and cellos. Made from glass, carbon, or flax fibres, with sandwich, woven, and unidirectional fibre orientations, these new instruments create new musical colours. Asking trained musicians to test the instruments, the sandwich composite ones were qualified as 'powerful', 'nasal' and 'harsh'; the unidirectional, 'warm', 'soft', and 'round'; and the woven, 'clear', 'loud' and 'rich' [3]. You can experience by yourself at this link.

From a historical perspective, another unusual approach can be used to tune the sound of violins, which is to grow fungi on the wood. Specifically, some decaying fungi can degrade the lignin, but maintain the cellulose nanofibrils in the wood, intact. This process, which takes up to 20 weeks, increases the porosity without altering the modulus. The violins made with this new lightweight material, called mycowood, have a soft sound and its high frequencies are attenuated. These characteristics make the violins sound like Stradivari's, which cannot be reproduced since the trees they were made of had grown in a cooler climate than nowadays [4]. Check out the fabrication steps and how tests were carried out at this link. 

Today's progress in 3D printing provides even more opportunities to play with materials, microstructures and designs. Using commercial plastic filaments and fused deposition modelling, any instrument can be made. But to obtain a satisfying, musical sound, design optimisation and careful study of the acoustics has to be made. Indeed, in addition to the materials properties, 3D printing comes with imperfections and roughness which requires post-processing. Using Electron Beam Melting, biocompatible baroque flutes made of Ti-6Al-4V, the same material as for hip implants, have been made. To find the right printing sequence, design, and sound, the titanium alloy was printed porous with a specific pattern, while the wall thickness tuned carefully [5]. 3D printing is also a convenient approach to design new materials, or to try to reproduce ancient instruments and sounds. For example, you can listen to a 3D printed baroque flute or a Japanese Shakuhachi.

Finally, although engineering materials for music might be a marginal niche market, similar questions and research apply to much broader applications from sound-absorbing panels for highways and houses to noiseless ceramic-based engines. Creating porous, sound-absorbing materials for structural applications in aerospace or architecture poses again the challenge of optimising material, microstructure, and design.

References:

[1]      Wegst U G K 2008 Bamboo and wood in musical instruments Annu. Rev. Mater. Res. 38 323–49

[2]      Kawasaki M, Nobuchi T and Nakafushi Y 2015 Structure and biomechanics of culms of phragmites australis used for reeds of Japanese wind instrument “hichiriki” Microsc. Res. Tech. 78 260–7

[3]      Duerinck T, Verberkmoes G, Fritz C, Leman M, Nijs L, Kersemans M and Van Paepegem W 2020 Listener evaluations of violins made from composites J. Acoust. Soc. Am. 147 2647–55

[4]      Schwarze F W M R, Spycher M and Fink S 2008 Superior wood for violins - Wood decay fungi as a substitute for cold climate New Phytol. 179 1095–104

[5]      Kolomiets A, Grobman Y J, Popov V V., Strokin E, Senchikhin G and Tarazi E 2021 The titanium 3D-printed flute: New prospects of additive manufacturing for musical wind instruments design J. New Music Res. 50 1–17

#SciComm: Interviewees make good tutors!

All around the world, federal governments are committing huge amounts of money for research and development (R&D) related to quantum projects. Quantum computers, for example, will revolutionize our ability to do calculations beyond what we could ever dream with supercomputers. They’re expected to drive incredible advances in areas such as artificial intelligence. I pursued a science policy article on R&D quantum initiatives for MRS Bulletin. The problem I faced as a writer is how to talk about quantum materials when I have no background in this subject—and, furthermore, when the concept is still elusive even to scientists who are not in this specific field.

A few years ago, when “quantum” was quickly gaining momentum, I took a free online introductory course on quantum mechanics. I particularly learned where semiconducting- and superconducting-based materials play a role in the development of quantum devices and systems. Then last year, I benefited from a Zoom call hosted by the US National Science Foundation (NSF) given for the press to help us understand more about this concept. NSF has a vested interest in helping reporters “get it right.”

While definitely beneficial, neither of these activities helped me as much as interviewing the researchers for the article!

From the online course, I understood that quantum computers are made to correct their own errors, having something to do with coherence.

From the NSF meeting, I learned that money is going into numerous “platforms” of quantum computers because we don’t know, yet, which path will prevail. Because of my familiarity with the race for a vaccine against the COVID-19 virus, I was able to put that comment into context.

However, words like “coherence,” “qubit,” “superconductor,” and “ion-trapped” still floated across my brain like “cookie,” “park,” and “good dog” fall onto the ears of our puppies.

But it was time to interview the researchers. Prior to the zoom calls, I had already looked up their websites and their recently published articles to help me determine who to interview.

The first call was to Anna Grassellino, director of Fermilab’s Superconducting Quantum Materials and Systems Center in Illinois, near Chicago. Their work is specifically on the superconductivity platform for quantum computers, as we can gather from the name of the center. I received an in-depth lesson on the transmon qubit and how long the photon can live inside the cavity before getting absorbed. “We’ll be building a quantum computer using the 3D superconducting architecture,” Dr. Grassellino told me, which is based on their ultrahigh-quality-factor (ultrahigh-q) 3D resonator.

Anna Grassellino, director of Fermilab’s Superconducting Quantum Materials and Systems Center, holding a single-cell superconducting cavity. Credit: Reidar Hahn, Fermilab

The conversation was great because I was able to let her know that I read up on their work, but have no quantum materials background, so she was very generous in showing me a superconducting radio-frequency (SRF) cavity device, explaining how it works. “The key problem that we try to overcome is quantum coherence for the lifetime of the qubit,” Grassellino says. “The lifetime fully depends on how long the photon can live inside of a cavity or the transmon qubit before the quantum state gets destroyed or the photon gets absorbed. That depends on the material we use” (MRS Bulletin, https://doi.org/10.1557/mrs.2020.288).

Next, the UK. Principal investigator David Lucas heads up the UK Quantum Computing & Simulation Hub. He is also a professor at the University of Oxford and I bet he gets good evaluations from his students! While his specialty is on trapped-ion qubits (e.g., a strontium ion-qubit), the Hub pursues the range of platforms. Dr. Lucas tutored me on ion trap and silicon processors, superconductors, diamond nitrogen-vacancy (NV) centers, cold atoms, and photonics. I’ve even saved our recorded interview for future reference, sort of like a personalized text book.

Oxford-built ion trap with a single strontium ion-qubit held at the center. Credit: David Nadlinger, winner of the UK science photo competition 2018.

Dr. Lucas and Dominic O'Brien, the director of the Hub, reinforced the NSF message that the science field does not know, yet, which platform will prevail.

And as we’ve seen with the COVID-19 vaccine, it could be more than one!

-Judy Meiksin

Say Yes

Roses are red, 

Surgical masks are blue, 

Soon I'm getting my jab, 

Will you come with me too?

Anodized templates for nanowire synthesis

Since the 1960s, when the method for the anodization of aluminum oxide was developed, we have gone far and beyond to apply and optimize this technique. We can now use anodization on alloys of aluminum, titanium, magnesium, zinc and a few other materials, to form an oxide coating over our metallic surfaces, and by doing so we can change the resistance to corrosion, the conductivity and the appearance of the material.

Figure 1. A circular section of anodized aluminum (1.3cm diameter) on a 2cm diameter aluminum slab.

 

Examples of anodized materials include the often shiny metallic tools, orthopedic implants and templates for the synthesis of nanostructures (Figure 1). Aluminum templates have been among the most cost-effective materials in recent years and are versatile enough to be used on small-scale synthesis of specific products as well as industrial scale applications. Over the last years I have been synthesizing templates for nanowire structures by taking advantage of the aluminum oxide’s hexagonal structure or honeycomb shape. 

Using an anodizing cell we were able to form a layer of porous aluminum oxide over a 99.99% aluminum slab. By dividing the anodization process in two and then removing the excess materials (the metallic aluminum and barrier layer) at the bottom of our template, we gained highly ordered pores that range from 40 nm to 80 nm (Figure 2). By sealing one of the ends of the template with a conducting metal (let us say gold) (Figure 3), then the template is perfect for the synthesis of separated nanowires.

Figure 2. Diagram showing the anodization process.

 

 

Figure 3. Back of an anodized aluminum template covered with gold (left). Top of the anodized aluminum template with gold (right).

 

After the template is sealed, then all that is left is to invoke a preferred style of synthesis (precipitation, electrochemical, physical or chemical vapor deposition, etc). And voilá - enclosed nanowires in a compact yet fragile container.

 

My experience:

We have primarily used electrochemical deposition to develop nanowires within the anodized template for the purpose of integrating nanowire circuits in gas sensing devices. To begin we found the reduction and oxidation potentials of copper(II) oxide (CuO) using cyclic voltammetry. Then, once we set the parameters in our voltage source and prepared a solution with the necessary precursors, we modified the time of electrodeposition so that the nanowires would not overflow from the porous anodized aluminum oxide template. 

Given the experimental nature, the most difficult part of the electrodeposition process was figuring out and producing the solution with the correct components and pH so that the solubility of each reagent would not affect the nanowire growth. Now, we have focused our efforts in extracting the nanowires in an efficient way so that we may integrate the nanostructures in gas sensing circuits.

Want to learn about how nanoparticles, nanowires, nanotubes, nanopores and nanocones can all be achieved using anodized aluminum? Then read the article by Zhao, H. et. al., “A mini review: Functional nanostructuring with perfectly-ordered anodic aluminum oxide template for energy conversion and storage.” Front. Chem. Sci. Eng. 12, 481–493 (2018). https://doi.org/10.1007/s11705-018-1707-x

S21MRS Blogger: Sebastián

I am Sebastián Suárez Schmidt, an undergraduate Physics student, researcher and volunteer writer for the MRS Bulleting. My scientific research is stationed at the University of Puerto Rico Rio Piedras campus in Puerto Rico, where I’ve specialized in the development of anodized aluminum layers for the growth of nanowires that can serve in the sensing of gases at trace amounts.

          This year I will be working alongside the skilled team of MRS writers to bring you an experience that allows for the immersion of the readers into the conferences, tutorials, and even the live yoga events! Because of the COVID pandemic, we have relied on the powerful advances in virtual presentation and interaction, however this will not discourage or hinder the learning and networking opportunities that the MRS Spring Meeting & Exhibit will provide. If you are interested in the marvelous artistic applications of scientific imaging I encourage you to check out the Science as Art Competition and vote for your favorite. Look forward to meeting as many of you as possible, while we work hard and push forward in the field of Material Science.

 

Stay safe.

Kind regards.

 

 

Sebastián Suárez Schmidt

On the hunt for a catalyst capable of efficient hydrogen production

It’s generally agreed that changes to our energy mix can help tackle climate change. While nuclear power is considered to be a low CO₂ emission technology for generating electricity, one suggestion is to use hydrogen to fuel our cars and heat our homes. Hydrogen can be generated from fossil fuels or by splitting water. While this latter method can be done using electrolysis, it is energy intensive. An alternative is to use ionising radiation.

You would think that the best way to generate hydrogen from water using radiation would be to simply irradiate as much of it as possible but some studies show that spreading an incredibly thin layer over a surface can actually generate more hydrogen than simply irradiating a large volume of it.

Bulk water radiolysis

When water is irradiated it can split apart into different combinations of electrons, hydroxide, peroxide and proton (e^-, OH^-, H₂O₂ and H⁺ respectively). These different species undergo a series of ultra-fast reactions that depend on the ability of these chemical fragments to diffuse through the water. When an individual gamma ray passes through bulk water it creates a track of ionised water molecules that spread out as they begin to react. Gamma rays travel very far in water which leads to a lot of water being ionised.

Some of the reactions in water radiolysis. Primary yields are commonly quoted and refers to the initial interaction of ionising radiation with matter; the period where a track, and spurs from the track, are produced.  Primary yields from the radiolysis of pure water are found by including a scavenger, a chemical that will quickly react with a targeted water fragment before it diffuses into bulk solution, effectively preventing it from reacting with the species of interest. The primary yield of H₂ can be found by including KBr; the bromide ions prevent the reaction of hydroxyl radical with molecular hydrogen. Credit: L Leay, adapted from various sources.

 

Alpha particles can also lead to the splitting of water. The alpha particles don’t travel as far as gamma rays. They still create tracks the way that gamma rays do and the ionised water molecules will still diffuse and react with other water molecules that weren’t hit by the alpha particle. Since the track is shorter, the energy is deposited into a much smaller volume of water, and so many more water fragments are created in a smaller space. A higher density of water fragments can lead to more chemical reactions and so the amount of hydrogen produced can increase. The key to generating hydrogen from water radiolysis lies in generating many fragments in a small volume and so increasing the chances that they can react in the right way. 

Now, take that water and spread it over a surface and you’ll see something quite different. 

Catalysis on a surface

Spreading water over a surface means that the water fragments don’t have as much space to diffuse; some of the reactions that may happen in the glass of water don’t happen as often. There are dozens of reactions happening between the water fragments; some lead to the generation of molecular hydrogen and some prevent it. Some of those reactions can stop hydrogen gas from forming.

The chemical make-up of the material that you use to make your surface is also important. Some materials such as tenorite (CuO) tend to generate less hydrogen gas than the glass of water does while zirconia generates more hydrogen. Some materials like silica don’t change the amount of hydrogen produced. No one knows for sure why this is but it could have something to do with the material also absorbing some of the radiation then transferring it to the water.

The nanostructure of the material is important too and studies from related fields can inform the search for a catalyst. For example, calcium-silicate-hydrates in cement pastes, which are usually studied to understand how nuclear waste might evolve over the associated long timescales, lead to nm thick layers of water sandwiched between sheets of calcium and silicate. In this material the calcium ions can trap electrons and these ions just so happen to sit in regions rich in structural water and OH groups. Since much of the hydrogen gas is formed by reactions that involve solvated electrons, it seems that this could be an excellent way of producing hydrogen.

Outlook

So what might the future technology to drive the hydrogen economy look like? Given that many nations already use nuclear power to generate electricity, it could be that this by-product is simply captured from the reactor core. This might give rise to questions about another Fukushima-like incident but it’s important to remember that the explosion at Fukushima-Daichi was caused by an unexpectedly severe event and, as its sister plant, Fukushima-Daini showed, was preventable. The nuclear industry, even with a safety record that surpasses many other industries, has learned a lot from that event.

It might also be possible to build some sort of water processing plant that spreads water over a surface and passes it through a radiation field. The radiation could be delivered by radioactive material, a particle accelerator or an x-ray generator.  This sort of conveyor-belt for water radiolysis may seem a bit far-fetched, but if climate change is to be halted, it would seem that future technologies may have to get radical (radiation chemistry pun intended).

 

 

For more information on water radiolysis see S. Le Caer’s 2011 article in Water.

For a detailed analysis of radiolytic hydrogen production from cement pastes, see S. Le Caer et al, 2017 in Cement and Concrete Research.

Materials connect playlist: plastic net shape manufacturing

Plastic is omnipresent and we are all aware of the challenges it poses. Let's review in music the conventional processing methods for plastic shaping, and recycling! Materials science and processes and intimately related, modifications at the materials level directly influences the process used, which in turn impacts the final material.

 

Start the playlist here: https://youtube.com/playlist?list=PLAtYx0idKu6sVCt0TwzHUxQlVdFqB8tgi

 

1. Synthesizing the polymer, most commonly via radical polymerization. The polymer chain structure is built at this stage that will be linked to its thermo-mechanical behavior: straight polymer chains will likely be semi-crystalline, crosslinked polymer networks will likely be more extensible (elastomers) or stiffer (thermosets). Highly branched polymer will get more viscous and high molecular weight will have a long reptation length linked to a high viscosity in molten state, etc. https://www.youtube.com/watch?v=ljvX-RMv_lw

2. Preparing the plastic formulation that contains the polymer(s) and additives like plasticizers, fillers, crosslinker, antioxidants. The formulation will greatly influence which process to use for shaping as well as the final properties of the material, including mechanical, UV-resistance, temperature resistance, porosity, etc. https://www.youtube.com/watch?v=eeu2Y3mdSkU 

and

https://www.youtube.com/watch?v=_L4qauTiCY4&t=87s

3. Dispersive and distributive mixing is necessary to produce a homogeneous plastic formulation and create the "masterbatch", which are small pellets later used in the following processes.

 https://www.youtube.com/watch?v=1wutkZ07ypA

and https://www.youtube.com/watch?v=DVP7Fjrnhlk

4. Compounding is the process to produce the masterbatch via pelletisation:

 https://www.youtube.com/watch?v=IZCWPDoN4CU

and https://www.youtube.com/watch?v=a01QQZyl-_I

5. Near net shape processing, specially for thermoplastic formulations are the most commonly used processes for producing plastic parts like PVC pipes, PET bottles, PE plastic bags, PP bottle caps, etc. Extruding using single or double screws are typically used for elongated shapes https://www.youtube.com/watch?v=Cd_msPNeItU

,whereas injection molding is preferred for complex shapes with small features https://www.youtube.com/watch?v=FH7vl-mRgWE

6. After finishing, the final plastic material is obtained. The process chosen not only provides the shape but also influence the properties. For example, during extrusion, the polymer chains of high  molecular weight polyethylene crystallize to form stiff fibers, a microstructure called in shish-kebab. https://www.youtube.com/watch?v=3bNITQR4Uso

7. After use, the plastic part is trashed. In the best closed-loop system, the trash is sorted to attain at least 99% purity to create a new masterbatch. https://www.youtube.com/watch?v=Vn2GjrsyE8U

8. After the sorting, the new masterbatch is used as any other masterbatch

9. Parts that cannot be recycled can still be valorized. This means burnt for energy reconversion: https://www.youtube.com/watch?v=CGyEd0aKWZE

 

To optimize the close-loop cycle of plastic shaping, we need you and the next generation!  https://www.youtube.com/watch?v=MLpltDCoieU