Hi everyone,

I am trying to make an underwater vehicle that can go about 4Km deep that is fully autonomous. Apparently, it is possible to cast a syntactic foam out of tiny glass microspheres made by 3m in an epoxy-resin matrix to obtain bouyancy. This bouyancy will not change due to pressure (as a regular compressible foam would) and can survive great pressures.

I ended up getting some samples of some 10000PSI glass bubbles, unfortunately they have a pretty high density of 0.6g/cm^3. The ones that I wanted were unavailable and had a density of ~0.4g/cm^3 and can withstand about 6000PSI. I calculated about a 0.85g/cm^3 density, which is pretty horrible consider I may need to support a few kilograms. I have over 30lbs of 'samples' on my living room floor.

My question is, do I need to even use an epoxy to bind the glass bubbles? What would happen if I had a cavity, then just poured in the glass bubbles? Then, I could fill it with water and enclose it. The reasons for this is, I won't have to worry about air-bubbles in the epoxy mixture. Epoxy is expensive. Epoxy is actually heavier than water, so it is weighing me down.

Does anyone have experience with syntactic foam? Or, can anyone thing of a reason (other than glass bubbles can escape) why not to use water as a filler?

Thanks for your input guys!

Steve

 

I should also add that the glass bubbles are ~50uM in diameter. So, having openings to let water in is out of the question, since these would surely escape.

Steve

 

I just came across the product that I wanted, which is much lighter. It's going to cost me about 150$ for 10lbs, but it's worth it. I need to get rid of the 30lbs that I have I guess I can sell the stuff I don't need to buy the stuff I need!

Steve

 

What would happen if I had a cavity, then just poured in the glass bubbles? Then, I could fill it with water and enclose it.

I've never even heard of syntactic foam before, let alone played with tiny glass bubbles. But ol' Howard Hughes ran a similar trick with ping-pong balls.

Would an alcohol or oil fill be lighter than water?

 

thingmaker,

Syntactic foam is wonderful stuff, it's strong and light. It's also bloody expensive to buy, but not too much money to make. It's just getting the stuff in small quantities that is the problem.

These glass bubbles are soo tiny, they look like a fine white powder. It makes me very nervous to cross the border with, I am sure they would think it is cocaine.

I never thought of that, alcohol can actually be lighter than water. It depends on what type obviously, but they're actually pretty good. Keeping it sealed would be a challenge though, especially under tremendous pressures.

I am shocked that I found the exact glass bubbles I need, although they're a bit more expensive than I thought. I'm selling off the stuff I got now, which is sad. A specific gravity of 0.38g/cm^3 is a lot nicer to work with than 0.6g/cm^3. Especially, when I have a heavy epoxy binder with about 1.12g/cm^3 with a volumetric packing density of about 0.6 (glass bubbles).

Steve

 

Some liquids are much more compressible than others--so much so that they can be used in pulse dampeners. I couldn't find a list right off. Isopropyl alcohol and silicone oil are mentioned in one of the patents as being compressible. Some of the straight-chain hydrocarbons are perhaps better and have SG's around 0.7 to 0.8. John

 

What about hydraulic fluid? Does it float on water? It is specifically formulated to handle pressure.

 

Wax is as oil and alcohol, lighter than water. And will retain your microbubbles.

 

My question is, do I need to even use an epoxy to bind the glass bubbles? What would happen if I had a cavity, then just poured in the glass bubbles? Then, I could fill it with water and enclose it.

How would you fill the cavity with water? To do this, you would have to allow air to escape while retaining the bubbles. How will you do that?

 

Thanks for all of the replies! I didn't consider using a lighter than water fluid, very interesting way to do it. The wax idea is great, I guess you would heat it up until it melts and mix in as many bubbles as possible, pour it and hope for the best. The only thing would be that the bubbles will float to the top of the mixture. This is true of anything with a specific gravity greater than 0.38.

Ron,

You're right, these things are incredibly small. They're a lot smaller than you'd think judging by the photographs(which are actually taken from a microscope perspective). I am either going to go with the wax method or using epoxy. The epoxy has the benefit of allowing it to be a structural component with high stiffness and strength at virtually no cost.

Steve

 

The first bathyscape, Trieste, used gasoline as an incompressible fluid in a big float above the pressure ball. Wax sounds safer, but not as buoyant.

 

Cool! That's really interesting stuff. The density is pretty low and it is an incompressible fluid. Part of my project is solar-powered, which is emphasizing green and oil-free energy, so maybe using gasoline as a bouyancy medium is a bit hypocritical.

Neat idea though!

Steve

 

Steve wrote:
The only thing would be that the bubbles will float to the top of the mixture. This is true of anything with a specific gravity greater than 0.38.

The glass microspheres would not float in wax if the proportion is kept to little wax and lots of microspheres to form a nearly 'dry' paste instead of a solution.

The most interesting propulsion scheme I have ever known about is by changing the density of an engineered substance in the submarine. At depth, make it less dense by exposition to cold temperature, at the warmer surface make it more dense. (it would be a 'ping-pong up-and-down' action) which translates into average horizontal propulsion with the use of 'wings'. Zero use of energy from batteries and can run 'forever' around the globe at the expense of thermoclines.

 

Yes, I have actually considered such a scheme, but it is very difficult to implement. In my application, I need to maintain specific depths, etc. So, it isn't a very effective scheme in my case. Although, for the 'long distance' traveling mode, it would be a great strategy.

Very interesting stuff! The ocean needs more attention by explorers, so much neat stuff down there!

Steve

 

The glass microspheres would not float in wax if the proportion is kept to little wax and lots of microspheres to form a nearly 'dry' paste instead of a solution.

This would be akin to mulling sand with binder. If the wax could be maintained at high sub-liquidous temperature, this could work.

What about simply foaming the epoxy? Well, maybee not "simply," but foaming?

 

thingmaker,

The issue with foaming the epoxy is the effect of compression. The first to be compressed would be the air bubbles, which would shrink. This would cause a reduction in bouyancy at high depths, which would cause it to potentially sink.

Steve