Jordan Taylor Profile picture
Dec 15, 2023 13 tweets 6 min read Read on X
How do you create the sharpest thing in the world? And why would you do it?

In this thread we take a voyage into true sharpness... Image
We've all at some point wielded something that is truly sharp. You give it respect, because it's dangerous, but it's also magical, a parer of reality. There's a subtle, definite power to a scalpel.

But we can do better than that... Image
An obsidian blade can be encouraged to chip along the lines of it's own molecular lattice, creating a molecular sharpness down to 3 nanometres thickness that no steel can match. It's delicate, prone to chipping and blunting, but obsidian scalpels exist. Image
That said, obsidian scalpels are seldom licensed for use on humans because of their delicacy. Nonetheless, their sharpness on a microstructure level shames a steel scalpel.

But we can do better than that... Image
Introducing the Tungsten Nano-needle: The sharpest thing on the planet. Produced by electrolytic etching, it can get down to tip thickness below a few nanometres (nm): You can fit 1 million nm into a mm, and 25 million nanometres into an inch.

But we can get sharper... Image
A tungsten wire is placed into a tungsten wire loop in a concentrated potassium hydroxide solution. Electrolytic etching acts most aggressively just beneath the eldctrolyte surface, so a "necking" region develops, eventually splitting the wire in two. The lower half is discarded.
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Additional pulse etching is applied to the remaining half: The necked geometry influences electric field concentration and etch rate and a characteristic conical taper is formed. The shape, radius of tip curvature & taper angle is defined by pulse duration, count & voltage. Image
In 2006, the National Institute for Nanotechnology ' the University of Alberta set an unbeatable record: A tungsten Nano-needle tapering to a tip thickness of just one atom.

The sharpest object in the world. Image
Why would you do this? Well for one you can use the concentrating effect of nanoneedle geometry as a point electron source for electron microscopes: Literally using something very small to see things that are very small.
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But you don't just have to etch nanoneedles: You can also use chemical vapour deposition. This is a far more industrially scalable method for producing lots of them.

Here's CVD grown tungsten oxide nanoneedle in an experimental gas sensor, for example. Image
You can also use this technique to produce carbon nanotubes: A 1nm wide graphene cylinder. These have remarkable properties: Thermal conductivity exceeding diamond, high surface area for uses as a catalyst and the highest tensile strength of any material.
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This barely scrapes the surface, but there you go: The story of the world's sharpest thing, some of the world's smallest structures and a nascent industry of developing materials technology.

I hope you enjoyed this! Image
Some free downloadable papers used are shown here, showing some different methods of creating carbon & tungsten Nano-needle structures.


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More from @Jordan_W_Taylor

Aug 30
It's the greatest story never told: It's the story of how a frugal county in the North of England invented the modern world.

Put on a flat cap and call up the whippet, because this is a thread about my home county, and the inventions that came out of Yorkshire! Image
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Steel!

Benjamin Huntsman invented high homogeneity crucible steel in Sheffield in the 1740s, firing with coke to fully melt the steel and homogenise the carbon content.

This became used… everywhere, and supercharged the ongoing industrial revolution. Image
Steam trains.

Steam locomotion had been in development for some decades by 1812, but arguably the world's first commercially successful steam locomotive was Matthew Murray's Salamanca. To him, we owe speed. Image
Read 14 tweets
Aug 26
A liquid rocket boost stage needs to pump fuel and cryogenic oxidiser to the combustion chamber at a rate that beggars belief: The 33 engines on the boost stage of SpaceX's monstrous ‘Superheavy’ booster each chew through about 700 kg of propellant every second. Put all those engines together and the flow rate of liquid fuel & oxygen would be sufficient to empty an Olympic swimming pool in under 2 minutes, if you could find an Olympic swimming pool for cryogenic propellant.

Can you think of any conventional lightweight pump that can do this? Me neither. You need something special…

The turbopump comprises a typically-axial turbine powered by hot, pressurised gas flow that powers centrifugal compressor pumps that pump the colossal quantities of propellant required and pressurize it to, potentially, hundreds of standard atmospheres.

It's a handy, lightweight way to provide pumping power, but it does require that you have a source of hot, high-pressure gas to work with.

Now, where would you find that in a rocket engine?

Indeed. In order to burn fuel, we must pump it. In order to pump it, we may have to burn some of it.

Um…Image
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The Gas Generator Cycle.

A small quantity of the pressurised fuel & oxidiser flows are tapped, brought to a small combustor, vaporised, ignited then expanded through a turbine that powers the fuel and oxygen compressor cycles.

Inevitably the gas generator can't run with a completely nominal fuel:oxy mix, as it would get so hot that it would melt the turbine blades, so typically a gas generator will trade off some efficiency and run fuel rich to power the turbopumps.

-Why not oxy rich? Because fuel has a higher specific heat at constant pressure (Cp) and so you need less mass flow through the gas generator if it's fuel rich than oxy rich, meaning more useful propellant goes to the main combustor & nozzle that moves the rocket.

So the upside of a gas generator cycle is relative simplicity and robustness, which is why it's used on the most reliable rocket motors around, the SpaceX Merlin. The downside is that you trade away efficiency by throwing away some of your propellant, meaning that the tyranny of the Tsiolkowsky rocket equation will kick you where the sun don't shine.Image
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Staged combustion attempts to address this, by taking either a fuel rich or oxy rich preburner, operating at a much higher flow volume than a standard gas generator, and routing the hot gases that leave the turbine straight to the combustion chamber so that they're not lost. This not only increases the average propellant exhaust velocity (since none of it is lost) and therefore efficiency, but also allows a lower average temperature in the preburner and turbine, since there's a higher volume throughput instead.

On the flipside you must deal with hugely increased engineering complexity, an increased potential for feedback control problems between the different parts of the engine, and also a much higher pressure preburner, since it will still need to deliver high working pressures to the combustion chamber after the losses of the turbine and injectors.

The Soviets got there first, and some of their genius manifested in the Russian RD180 oxy-rich staged combustion engine, which was bought by the Americans and used in Atlas rockets for many years. Its unique oxy-rich staged combustion cycle was efficient but not without drawbacks, as high temperature gaseous oxygen is brutal to exposed metal surfaces, demanding an enamel coating on many parts of the engine.

And it gets even more complex than that…Image
Read 5 tweets
Jul 18
Last month Rolls-Royce won the UK's small modular reactor competition to develop and build SMRs in the UK. It could be a new dawn for nuclear power.

But who else was in the competition, what was special about each design, and which is your favourite?

An SMR thread… Image
What's an SMR?

A small modular reactor is a way of beating the brutally high capital costs of building nuclear power: By simplifying assembly (modularity) and minimising subsystem size so almost all of it is factory built you harvest industrial learner effects and low costs. Image
Boiling water vs pressurised water reactors.

All designs in this list are either PWRs or BWRs, the most common reactor styles today. I've a thread on the basics if you need it, but otherwise on with the show!
Read 21 tweets
Jul 4
In April on a mountain in Chile the Vera Rubin observatory gathered first light, and this telescope will be world-changing! -Not because it can see the furthest… but because it can see the fastest!

The Vera Rubin telescope thread! The value of speed, and unique technology… Image
Who was Vera Rubin?

She first hypothesized the existence of dark matter, by observing that the rotation speed of the edge of the galaxy did not drop off with radius from the centre as much as it should. The search for dark matter, and other things, will drive this telescope… Image
Does it see a long way?

Yes, but it’s not optimized for that: The battle of the big mirrors is won by the Extremely Large Telescope which, yes, is meant to see a long way. Vera Rubin is not that big, but that doesn’t matter because it has a different and maybe better mission. Image
Read 22 tweets
Jun 20
Rotating detonation engines: Riding the shockwave!

A technology that could revolutionise aviation, powering engines with endlessly rotating supersonic shockwaves. It could bring us hypersonic flight, super high efficiency and more.

The detonation engine thread… Image
Almost all jet engines use deflagration based combustion, not detonation, but while fuel efficiency has been improving for decades, we're well into the phase of decreasing returns and need some game-changing technologies.

One is the rotating detonation engine (RDE). Image
To understand the appeal of RDEs, you need to know that there are two forms of combustion cycle: Constant pressure, where volume expands with temperature, and constant volume, where pressure goes up instead.

Most jet engines use constant pressure. RDEs use constant volume. Image
Read 21 tweets
Jun 6
As a new graduate I once had to sit down and draft an engine test program for a subsystem of a new model of Rolls-Royce aero engine. It was illuminating.

So here's a thread on some of the weirder things that this can involve: The jet engine testing thread! Image
Fan Blade Off!

Easily the most impressive test: A jet engine needs to be able to contain a loose fan blade. In the FBO test, either a full engine or a fan & casing rig in low vacuum is run to full speed, then a blade is pyrotechnically released.
Frozen.

The Manitoba GLACIER site in Northern Canada is home to Rolls-Royce's extreme temperature engine test beds. Not only must these machines be able to start in temperatures where oil turns to syrup, but in-flight ice management is crucial to safe flying. Image
Read 15 tweets

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