You post is lacking in information as foils are not normally porous and sheets can be.
Just do a Google search on porous Ni or porous metal and you will find a lot information.
I am interested in porous foil. Realizing that this is likely a non-standard product, I expanded my question to include sheet. A google search for porous nickel comes up with plenty of scientific references, but lean on links to actual sources.
There is porous Ni used as filter material in air bag inflaters. They are made by both rolling a stack of woven wire mesh that has been sintered together. There is also one that used a Ni felt material that is sintered and rolled to get the desired pore size.
Thickness 0.002-0.004 inch. A suitable material would be microporous, to give high specific surface area. Absolute porosity is less important - around 30-50% would be reasonable. My application does not require convective flow through the pores, so it is rather different from most porous-metal applications (e.g., filtration).
Hm. Start with 1-mil or thinner etched foil to form a substrate, then plasma-spray (or sputter?) both sides with more nickel to create a porous surface layer?
Would it be possible to get a Ni foam and press it to the desired thickness. As you state absolute porosity isn't a concern, this would give you a very large surface area but at the sacrifice of porosity.
UncleSyd, I thought about that too, but it would seem that you'd have to hot roll the foam to get enough reduction (down to 2-4 mils!) and that much reduction would likely close up the pores...
Also thought about dusting foil with metal powders then giving it a light press/sinter, but again it would tend to reduce porosity, and I have my doubts about how well the powder would stay attached.
I also tried to think of a way to pre-reduce a polymer foam (i.e. roll it down thin) before it gets plated with metal, but can't see a way to ensure you'd get enough porosity that way either. In my rocket days, we would make catalysts by soaking metal salt solutions into various substrates (typically alumina grit), then reduce them to active metal with hot hydrogen. We also made foams via electroplate processes. There is always some loss in porosity with these processes, as the deposited metals tend to fill in available voids.
An interesting approach might be to try and form metal whiskers on a surface, but I don't know enough about whiskers, even tin ones, to know if it would work. But it would certainly increase active sites on a surface by orders of magnitude. Here's a possible starting point..
I agree that you may not be able to start with the 1 mm thickness. I would have to try one time and check the results.
By reducing the thickness say from the 1 mm thickness this maybe possible. I would reduce the thickness first by EDM or diamond wire. Then one would have to try different starting porosities to check the end results.
btrueblood
In a similar in a similar idea as you elude to there are several other approaches that I'm looking into.
There are Ni plating processes that give a microporous product. They are normally used as substrate for different Cr plating processes. Looking for a suitable substrate.
Also
Isostatic pressing with a suitable material say SiO2 and removing the SiO2 with hot dry Hf.
Isostatic pressing with a plastic that can be easily removed by chemical or thermal means, like Nylon or PET. This might have a problem with pore size.
Yeah, good ideas there, Syd. The "porous plating" is a fairly relative term though, I thought, compared to some of the other stuff we've kicked around, but I could be wrong.
Another whacko idea - start with very thin foils (less than 1 mil?), maybe with intentional porosity (etched holes), and laminate them (diffusion bonding?), then subject them to hot hydrogen at high pressure, followed by explosive decompression. The goal would be to try to get the edges of the pores to "blow open", and get micro-tears to increase surface area.
Whee, what fun. I think the OP needs to hire us as consultants. Dibs on the corner office.
btrueblood
You can get various degrees of porosities and thickness with Ni plating. It's hard to get information as the process is used mostly as a base for Cr plating.
We used this approach where we iron plated to recover size then 2 layers of Ni plating with the second being porous. The final plate was a mirocracked hard chrome. We also tested it as an anode for an electrolytic process. We abandoned nickel for iron.
As for you whiskers idea I ran across a paper where they shoot holes, laser, in a plastic mask and then used EN to plate through the mask to the substrate. This was to make straight appendages, something like whiskers on the substrate. They were also able to make domes on the whiskers to increase the surface area.
Will go for the consultant role. I'll just a take window as I worked for 41 years in a window less environment. My last year of actually having to report to work I got my window.
