Author Archives: joshuagallaway

Extracting data from a plot

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All the time I end up trying to extract data from a published plot, for example with the XRD traces above. My brute force method is to load the plot into some image program, then draw straight lines to all the important features. Up above I’ve drawn lines to peaks L, C, G, and F using 30 degrees as the origin. The line lengths tell you exactly where the peak maxima are, after you normalize them to a line drawn along the axis to get the scale.

Hey it’s a decent method and it works, but I was thinking how useful it would be to have a tool that reads an image file and can spit out the original data as a CSV. Turns out there are a few programs that do exactly that. I haven’t tried WebPlotDigitizer yet, but I will soon. If it’s the answer to all my hopes and dreams I’ll let you know.

A simple fuel cell

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fuel cell drawing edit

When I was a grad student I had to run a lab for undergrads to make their own fuel cells. This was a drawing I made to explain the basic components and how they went together. The metal plates on the outside are the current collectors. At the center is the membrane-electrode assembly or the MEA. It’s a piece of solid electrolyte membrane that feels a bit like a piece of rubber. On each side is a small square of catalyst, usually platinum particles.

I have to tell you, I sort of miss painting platinum onto MEAs. However, I do not miss helping people put these together. Getting all that lined up and sandwiched together is harder than it looks.

A battery scientist’s trivial dilemma

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You may find yourself hunting through all the batteries at the drugstore, trying to find an LR44 to buy instead of a 303/357. All because you want to be ‘faithful’ to MnO2. (By the way, this particular day you won’t find one.)

Functionally, these button cells are essentially interchangeable, but they have different active materials inside them. The LR44 is an “alkaline” battery which has the overall reaction:

3 MnO2 + 2 Zn = Mn3O4 + 2 ZnO

The 303/357 is a silver oxide battery having the overall reaction:

Zn + Ag2O = 2 Ag + ZnO

They both give you a potential of about 1.5 V. Actually, the silver oxide battery voltage is a little higher, and its capacity is a bit bigger. But if you’ve been concentrating on MnO2 for a couple years in your work … you know … your loyalty might kick in.

Battery researchers

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Pictured above are Daniel and Jerome, in the battery lab at CUNY. Both of these guys are going to grad school in the fall after working here for a while. It’s been great having them, and we’ll miss them a lot.

Jerome was a student in my transport phenomena class at NYU three years ago. When class was over he was about to enter his last year, and he asked if he could do his senior project working with me. One day a week he took the train up to Harlem, where CUNY is, and built batteries for a year. He must have liked it, because after graduating he started working here as an engineer, and now has a hand in just about everything we do.

Each year since then I’ve had a new student from NYU working on batteries at CUNY. They get their senior thesis out of it, but also they get a chance to see how research really works, and I think that’s important for someone who wants to work in science and engineering. Interpersonal skills, how to get time on lab equipment, how to organize your data, how to find important variables, how to tell what experimental noise looks like, etc. Back in the 90s I was a co-op student at Owens Corning, and I learned a lot of things there … skills I still use today.