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I usually live in Edinburgh, but since lockdown began, I’ve been at home with my family in Cheshire.

When I came to Edinburgh University in 2011 I started ballroom and Latin dancing. My dance partner is called Alistair and is from Zimbabwe. We’ve just come back from a big competition in Blackpool where over 750 couples from universities all over the UK were competing.

Mid-quickstep at the Northern Universities Dancesport Competition!

I also play the saxophone in the Edinburgh University Wind Band, which I really enjoy. Every year we go abroad on tour. The picture was taken in Ypres last year, it was about 30 degrees, so we were very pleased we could play in the shade!

EUWB playing a concert in Ypres.

A rechargeable handwarmer

Have you ever used a handwarmer like the one in the picture above? You crack a metal disc and it solidifies and heats up. The material inside that pouch is a salt called sodium acetate trihydrate (or SAT for short). When it melts it takes in lots of energy, and then when it crystallises later, it can release all that energy as heat. It relies on a change of phase/state (between solid and liquid), so it’s also known as a phase-change material (PCM).

There are three really important things I need to tell you now for my work to make sense:

1. A material’s melting and freezing points are the same (usually!). Water freezes and melts at 0 °C (we just give the solid form a different name — ice).
2. It doesn’t have to be cold for something to freeze. I know this sounds obvious, but when I started my PhD I struggled with thinking about things freezing at high temperatures. What helped me was thinking about candle wax —imagine it running down the candle, and rather than saying it’s hardening or solidifying, tell yourself that it’s freezing.
3. I’ll use the words freeze and crystallise to mean the same thing, my material going from a liquid to a solid.

My PhD is funded by a company called Sunamp who use PCMs to make heat batteries. If your house has solar panels, and you’re making more energy than you need, rather than exporting it to the national grid, you could use it to melt the PCM in your heat battery. Then later, when the sun isn’t shining, you can use it to heat your house or water. Think of a heat battery like a hot water tank, or a storage heater, but you can store much more energy in a smaller space.

The problem with each PCM is that they only work at the melting point of the material. This means that if you want a different temperature, you have to use a different PCM. Just like a rechargeable battery, you want your heat battery to work thousands of times, but a lot of PCMs won’t melt and freeze perfectly every time, so after a few melt-freeze cycles the amount of energy you can store gets a lot lower — just like the battery in an old phone.

I work in the labs at the University of Edinburgh to find new materials and try to improve them. PCMs can have lots of problems — the material might not freeze at all once it’s been melted, it might convert into different materials over time, or it might freeze so slowly it’s very difficult to get any heat out of it.

I use both experimental and analytical techniques to try to make PCMs that will cycle repeatedly, and also to try to understand why they work (or don’t in some cases!). If I’m really lucky and make one that works well, Sunamp will patent it, and it might end up in your house one day!

I’m in the final year of my PhD, and at home on lockdown, so I’m spending a lot of time writing my thesis. That’s basically a big report of all the work I’ve done over the last three years, and should explain why my work is new and important. When it’s finished, I have to do an exam called a viva where two lecturers (one from Edinburgh and one from another University) will ask me questions about what I’ve done. Hopefully I’ll pass that, and then I’ll be Dr Goddard! It’s nice to go back and put all my work together, like telling a story. It’s not as much fun as being in the lab though…

This is what I would usually be doing though:

In a typical week I’ll spend some of my time teaching in undergraduate labs (which I really enjoy), some time in the lab, and some at my desk in my office. My lab and office are at opposite ends of the building and on separate floors, so I try to be efficient, but it doesn’t always work. Running between them helps to keep me fit!

In the lab, one of the first things I’d do with a new material is called a screen, where I have lots of tiny vials of PCM and add something different to each one, then melt and freeze them. If any seem to work better, I’ll use a bigger vial (this is called scaling up) and try again.

This time I might track the temperature with a temperature probe or thermal-imaging camera, or melt and freeze the material under a microscope so I can watch what’s happening.

Crystals growing in a pouch.

If I think I’ve made something new, I’ll take my crystals to the x-ray lab. X-rays are really good for looking at the structure of a crystal, because they are small enough that they can bounce off the individual atoms. At the same time, I’ll cycle the material so it keeps melting and freezing. By doing this, I can find out if I’ve made something new, and if it will work well hundreds of times.

A crystal dish of my material freezing and giving out heat (yellow) on a cold hotplate (blue)

A crystal dish of my material taking in heat and melting (purple) on a hotplate (yellow)

I also go to Sunamp sometimes, as they’re based just outside Edinburgh. Two undergraduate students are there doing a year in industry as part of their degree, so it’s nice to say hello to them. Sometimes I’m just going for a catch-up, so Sunamp know what I’ve been doing and I know what they’ve been doing. Other times I’ll go for a meeting with their patent lawyer. I’m very lucky that I have my name on patents from two materials I’ve worked on, proving that I played a part in their invention. The best days there though, are when I’m doing an even bigger scale up of my lab work. At the University, the largest amount I would ever work with is around 500 g, but at Sunamp I might use 20 kg. This stage is vital to see whether the work I’ve done might be marketable in the future. It’s always nice to work with the Sunamp scientists, and feel like part of the team there too.

In the evenings, I might have a dance lesson or practice. On Wednesdays I have wind band rehearsals, which I always enjoy, although now our concert is only four rehearsals’ away it’s starting to feel very serious! Other nights I might go for a swim before I cook dinner, or mark lab reports.