Greetings fellow nerds.
So i needed to make silver powder.
I can use bulk silver coins for my reactions
but powder is far easier to measure and reacts much faster due to greater surface area.
Now I could have simply ground down my coins using a file or mechanized grinder
and while that would have worked very well
i wanted to try an alternative electrochemical approach.
Granted it’s rather slow but very interesting, at least to me anyway.
In my first attempt I had a solution of 50mL water with 1g of silver nitrate.
In it I placed a silver coin and a carbon rod.
The silver was connected to the positive terminal of my power supply making it the anode
and the carbon rod was connected to the negative terminal making it the cathode.
Turning on the power, i dialed up the current
until the carbon rod just started to bubble hydrogen gas
and then dialed back about 25%.
Now the silver is being electrochemically oxidized at the anode into silver ions.
The dissolution isn’t perfectly even though so
particles of silver metal actually exfoliate off and fall to the bottom as you can see here.
This is a rather crude way of making silver powder but it works.
Meanwhile, the silver ions that did dissolve migrate over to the cathode
where they get reduced back into silver metal.
The interesting thing about this process is that
the silver doesn’t deposit as a continuous layer of bulk metal, but rather as individual crystals.
You actually saw me exploit this years ago when i filmed electrochemical crystal growth under a microscope.
你或许看过我多年前使用这样的方法 当时 我在显微镜下拍摄电化学的晶体生长过程
Now if we use a high current density like we are here
then the solution right next to the silver depletes pretty quickly,
so the growth is limited by diffusion of the ions.
Since diffusion is random,
the crystals constantly nucleate at new sites
and this in turn forms numerous weak crystals that easily crumble into a powder.
And that is exactly what we’re looking for in making electrolytic powdered silver.
Unfortunately, as you can see, we’re running into a rather annoying issue.
不幸的是 如你所见 我们遇到了一个相当烦人的问题
The silver is growing toward the anode.
This is because the electric field in the solution favors deposits of silver closer to the anode
as that has the least electrical resistance.
And as this occurs it forms dendrites that quickly travel over and contact the anode.
这种情况下 银形成枝晶 这些晶体快速转移并接触阳极
This is undesirable because when this happens the cell shorts out
and we’re unable to deposit more silver as all the current is now going through the connection rather than the solution
We’re going to need to be a little more creative in making our silver powder.
Now because the silver is very weakly connected and easily crumbles,
just some mechanical knocking will dislodge the silver connection
So I just put in a stir bar to constantly knock the anode, and it actually worked pretty well.
The silver connections that did formed were constantly knocked off the anode and settled onto the bottom.
That’s not the best solution.
The silver anode itself is dissolving, since that’s our intention when converting it into silver powder,
so as it dissolved it eventually became too small to be hit by the stir bar.
Eventually the silver connected again and shorted out the cell.
Fixing that was simple enough.
Just arrange the electrodes so that the cathode is constantly struck by the stir bar.
And now we have a viable electrolytic silver powder making cell.
The silver constantly deposits onto the cathode
but the continual striking of the stir bar knocks off the deposit
and allows this to continuously produce silver powder until the anode runs out.
At which point we submerge more of the anode to continue.
But eventually the best arrangement I found was to very carefully place the cathode just above the stir bar.
As the silver dendrites grow out they sag into the stir bar and get shredded by it.
For now i’m not removing the collected silver powder,
but if it becomes excessive that it contacts both electrodes despite the stir bar
then you should filter it out before continuing
At this point I should mention that if you have a physically large cell,
like more than ten centimeters distance between electrodes,
just the weight of the silver is usually enough to cause it to break off as it runs.
That is actually how it’s done on large scale silver refining.
So all this messing around with knocking electrodes is moot.
所以这里敲打电极 一片狼藉 其实是毫无意义的
But if you’re working on a very small scale like I am,
then you have to worry about the deposited silver bridging the electrodes
Anyway, there is the last chunk of silver.
I can’t submerge it further without also submerging the power clip.
And i don’t want that because i don’t want to dissolve the steel in it and contaminate my silver.
So i’m going to stop here.
And there is our electrolytically formed silver powder.
Now i decant off the supernatant and wash the silver a few times with water.
Then i dry it on the hotplate.
And there it is, silver powder.
Sure I could have simply filed down my silver coin
but this was a lot more fun if a lot slower and labor intensive
I’m going to use this silver to try and make batteries.
And the leftover chunk of silver metal i’ll probably keep for other experiments that need silver.
Thanks for watching.
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Greetings fellow nerds.