Regarding bubbles on the metal surface, if you have a ultrasonic bath you could put the beaker in it, and the ultrasonic agitation will help disperse both bubbles and dissolved gas.
...(but too strong and it will tear layers off the the aluminium. In fact a common way to test the piezos on ultrasonic baths is to see if it can disintegrate aluminium foil).
It's been a while since I did this, but the sonication does help. I also remember electropolishing in one solution, then switching to another solution briefly and repeating the cycle. It might have been electropolish in sulfuric then etch off the oxide in phosporic. As long as you didn't get too much current, you could get beautiful surfaces.
This is awesome stuff, I've been doing electropolishing as my job for 3 years now and i still learnt something! (polishing stainless in case you were wondering)
Hi Ben, I have done electroremoving before. I looked at different phases of superalloys. ASTM E407-07 covers the solutions and procedures for etching all sorts of alloys. It states that 10% H3PO4 immersed for 1 to 3 minutes at 50 deg C is good for 2000, 3000, 5000, and 6000 series Aluminum alloys for general structure, phase identifications, and grain structure under polarized light. So you were right to use H3PO4 as a etchant and polish solution. I got a little creative with my project and tried electroremoving a pattern using press-n-peel blue transfer film. I know for a fact it sticks to Nickel, Nickel superalloys, and Copper; I haven't tried it with Aluminum, but I think it sticks to practically any metal.
I used heat transfer PCB resist via printer-bubble or toner type I can't recall, maybe it was on a copier machine- probably, it worked well. I made a two piece die with this metode and casted lead into it. though the relief was very slight, the image was well prepared. I had less good results etching stainless steel. with electrochemical etching current control is critical.
Just some stuff. Rather then a pure solution of phosphoric acid, you would have less etching if you used an aluminum salt. If you want simple math, you should try using aluminum phosphate, but that stuff is hard to find (something about it being used to make explosives.). A good aluminum salt will help prevent etching, and over etching on a short term basis, because it reduces the amount of aluminum that will immediately need to go into solution to satisfy Le Chatelier's principle. It ensures that the only etching going on is the stuff that's being driven by electrical current. This needs to be fine tuned though. Functionally speaking, the difference between an electo-platting solution and an electro-polishing solution should be the amount of dissolved aluminum in solution; if you're not watching your concentrations, you can reach a point where the reaction is less then optimal, though it can't run in reverse. I would speculate that people are advising you to use sulfuric acid because aluminum sulfate is easier to get a hold of then aluminum phosphate, but mixing the phosphoric acid and sulfuric acid makes the math more complex. Sometimes aluminum phosphate is sold in nurseries as a special fertilizer for hydrangea. Hydrangea change colors when the pH of the soil they're grown in changes, and aluminum ions are a good way to shift the pH towards acidic for extended periods of time (assuming you want a pink color hydrangea). Aluminum sulfate is also known as Alum.
@ I've found that it's rather a fire retardant www.chemicalland21.com/industrialchem/inorganic/ALUMINIUM%20PHOSPHATE.htm but I dont know everything. It may release the oxygens at high temperatures, in rocket propellants, thermites,... it's possible, but it's readily available and no one is writing about it as such. I think he meant another substance
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@@trollmcclure1884 You're right. I remember wanting some for pyrotechnics but reading about it I must have been wrong back then. Its berlinite and its apparently toxic. Thanks for setting the record straight.
I’ve heard the term, ‘electropolishing’ and it application but nothing about the procedure. Thanks for the primer. A thought is that a battery charger although providing DC is not filtered (e.g. capacitors, inductors, etc.) and the 60 Hz ripple may cause a bit of a ‘electrochemical hammering’ effect on the surface of the aluminum promoting the pits. Maybe, I don't know. Cheers, Mark
Thank you for the video, I've done some experimenting myself trying to etch images into aluminium plate using laser printer ink as a resist. Electropolishing sounds super interesting and I'll have to try it out!
I'm not sure the air stone is actually a good idea if the polishing requires some sort of layer on the part surface. and may explain your results. Do you know if it is possible to use a graphite electrode? I have had good results with stainless using a carbon fibre brush as my electrode, it gives me lots of control. Also great for weld and silver soldering clean up.
I guess everyone has a personal/social responsibility in using any chemicals other than day-to-day table salt or butter etc, in a sensible manner. This vid, without frills and creases shows how to get the job done in a short and sweet manner. Further research, customization and improvising is left to the DIYer. Great work !!
BTW the industry doesn't show and tell. they have all the solutions for electroplating and polishing very hidden. NI has a handbook but if you don't work for then you don't get the real deal
I read once about finish polishing aluminum to 99.999% reflectivity swishing/vibrating with successively thinner solutions of India ink (which apparently has some natural quantity of bucky balls). These apparently bump into any nanoscopic hills and peaks and smooth them out.
good presentation, very helpful. Permit me to just add this; that is, the reason why the current density plot is not looking like the one you found on the internet. The plot observed from the "internet" is due to a layer formed between the sample and the electrolyte (it is called the anolyte layer). however, for the electrolyte that you used (phosphoric acid), the anolyte layer is not visible. hence, the plot you will be getting will be not be exactly what you got from the internet. therefore the plots that you got are not too out of place.
Agitation can be used, for small parts its normally not necessary. Ultrasonic baths do work, with water, then a glass beaker, to break the liquid/gaseous plastron that forms on the surface of the part, and keeps fresh electrolyte close to the surface interface. Using full strength acid can lead to uneven brightness and micro pitting.
I was wondering if my bottle of descaler would do as a source of phosphoric acid but I was worried that it would be too weak... it's also "contaminated" with surfactants and "fragrance"... but then you suggested adding surfactant any way... so that's one problem disappeared. ;)
Can you make a video explaining how to anodize aluminum, and the differences between electropolishing, anodizing, and electroplating? (differences in terms of the science, but also the practical methods for doing it all.)
Just thought to let you know that the drawing shown has the x and y axis are the wrong way around. The voltage is usually on the x axis with current density on the y axis. Maybe this is why you had issues recreating the plot. Happy polishing.
Cool. I assume this is different than the shiny (I won't say polished) aluminum bars you find in Home Depot in the bath and shower section. The surface of those is non electrically conductive.
I think those are anodized. Btw, anodizing is a something you can try in your home lab. You can use dilute sulfuric acid as the electrolyte, and the aluminum is connected to an anode. Constant current is passed through it, and as the honeycomb AlO2 layer builds up, resistance increases. That's how you know when the process is done. You can get it as battery acid from an auto supply store. I've tried with different electrolytes, too. It's pretty neat to try. Varying acid temp will give different layer cell sizes. Varying voltage while anodizing titanium will yield different colors.
Applied Science For the vessel could you use one of those mechanical milk frother machines? I think they only heat to about 80c but you could always modify it..
Can you please share some of the literature you used to make this video. I am doing an internship where I need to electropolish aluminium and thinking about using phosphoric acid as the electropolishing liquid. I am most interested in what is discussed from 3:50 onward. Thanks in advance.
Thank you for another interesting video. The pitting below a certain depth is an interesting phenomena. That it does not happen within a certain distance of the surface is curious and doesn't seem to be well accounted for by the current per area theory. It would be interesting to attempt the electropolishing on a hotplate with a stirring magnet, to see if eliminating the bubbles from the air stone would reduce the pitting. Bubbles may be sticking to the metal preferentially at greater depths, but adhering less when moving faster near the surface.....
I would love to get into electropolishing myself (for stainless steel, and copper, and bronze). Can I contact you for info on this? I can’t find it anywhere on the internet :(
Nice work! I have found it better to NOT agitate the solution. Leave the viscous (often brown) layer to form quietly. Agitation will mess with your middle diagram I think.
Have you tried using a similar technique to electrosharpen edges and points? I've wanted to do this for a while to make AFM stylus. Most recipes seem to use sulfamic or phosphoric acid, some in a rather viscous solution, including one that had organic resins in it.
I have done this with a regular wood nail. This was ~8years ago. My steps were: * solution: water+ table salt (NaCl), quite probably not saturated * a graphite electrode ( from a regular "A" battery) * iron nail the other electrode, nail head connected to the cable, out of solution. Be sure the nail is grease or oil free. I do not recall which electrode was negative. Start with a "hi" current (5~10A), you will see the nail starts to get thinner, and the solution will look rusty and lots of bubling (O2 and H2 being released), as time goes on, reduce the current, so you have better control of the "thinning" process. The thinned part will also be extremely polished, with a really nice shinny look. The part of the nail in the solution will get an extremely fine point. Graphite is not affected, and solution be full of iron oxides black and orange ones. Not sure what happens to NaCl. The nail I used was about 1/8 in diameter, and took a few days.
Yes. However, the method that I used requires that the wire be slowly withdrawn from the bath so that the tip has more time in contact with the chemical reaction than the rest of the item. This gives another dimension of control, allowing the taper to be adjusted, or even made non-linear. I'm not so sure the method would produce atomically sharp objects, though.
Ivan Kocher From what I remember of the inorganic chemistry classes that covered this sort of electro-chemical process, I'm pretty sure the Cl from the salt formed a chlorine gas when you applied current, making some of the bubbles you noticed(because it has a decent reduction potential, meaning that it tends to receive the electrons from your power supply and use then for going from the oxidized to a reducted state)... not sure about the Na, but it's most likely it stayed in the solution since Alkaline metals have a high tendency to remain oxidized. The salt is added to the solution so there are enough eletroclites in the water to make it a decent electrical conductor (pure water is a poor electrical conductor) practically any other salt would work too (except different chemical reactions could happen).
+Ivan Kocher The NaCl is added to facilitate conductivity to the distilled water(or increase conductivity of tap water) in any electrolysis process that doesn't have an acid or base as an electrolyte!
That's really interesting. I wonder if it could be used as a surface prep method for DCEN aluminum welding (which needs to be much cleaner than AC welding), or if there are residues left on the metal.
I would be EXTREMELY surprised if you could do a DCEN on ali regardless of the prep (removing oxyide layer) you do. Let us know how it goes if you try it
@@Bakanelli Yeah have done it before, with mechanical scraping and chemical etch. We used it to make high quality butt welds turning 18" sheet into tubes for pressure vessels.
amaraojiji I'm pretty sure that vibration would work instead of bubbles. My first thoughts were using a geared motor or stepper with an embedded neodymium magnet on a disk attached to the motor shaft, below a plexi-glass shelf, then a plastic/silicone coated magnet inside the flask/vessel - to recreate a magnetic lab 'stirrer'. Fascinating stuff! @ +Applied Science I've often wanted to try anodising so I'm headed to your uploads .... >subbed< :)
Now that I think of it water will separate above 1.9 volts and produce gas. Could this process be done under 1.9 volts? That could reduce the effect the gas has with the pitting.
now i'm gonna have to look up the process of chrome plating, this looks very similar to what i thought the process of applying a chrome surface to a metal was, i'd like to see what actually happened to the pieces of steel as well since i thought phosphoric acid would act more aggressively on steel than aluminium
The concentrated layers of oxidation on the aluminium from being exposed to the elements, over time these levels have built up, the pitting has occurred from the solution and cavitation removing fine loose scale, but the pitting is like rust pockets or decaying in the aluminium material, the surface areas coming in contact with the solution it not strong enough to dissolve the oxide layers, the aluminium has to be polished flat
Aluminum (and zinc) is very very acid sensitive - next time buffer with a little sodium carbonate or substitute acid for sodium citrate. Also, use a lower voltage make sure your work is totally oil/petroleum free (never use torches to dry parts after de-greasing).
What if you immersed the beaker in a sonic cleaner filled with water to the same level as the acid without the airbrick? That would increase agitation (enabling hydrogen gas to release easier) and eliminate oxygen.
I've been trying to replicate the same chart, do the same sort of thing, but with steel. Without buying a lot of extra supplies, spending money on a whim. So far I haven't been able to get that graph to happen either. I've read, not a lot, but some about electropolishing steel, from stuff as far back as the early 1900's, and they all describe the same graph. Well, I'll fool around with it a while longer. Also trying an etching with photoresist film, sort of different project. For that I need to stay in the 'etch' region, so far that seems to work fine vis a vis the steel, but the photoresist keeps lifting. Not sure why. I'm starting to suspect the etched piece gets a zone of more acidic solution around it, and that makes the photoresist hard and flake off. Anyway, I remembered you did this video, and watched it again to check what you were using specifically. Thanks
Interesting results, but it doesn't really seem to being polishing but electroplating SS onto AL. However, I have been told to never use SS for an electrode in soltion due to it releasing Hexavalent Chromium. (The same stuff that caused severe birth defects, health issues and water contamination in the true story movie "Erin Brokovich.") Can't you use aluminum plates?
Better nate than lever: Just tried it out with a 5x4x3cm piece of aluminum (75% H3PO4, 70-75°C, magnetic stirrer, 20-30V). I started out with a much too low mA/cm^2 so in the beginning I was only etching. If the part would be a cube it had a surface area of 114cm^2 but it as inner surfaces so its probably 3 times that. This would result in 30A but my powersupply only goes to 5A. Luckily enough that was enough to produce a very nice polished surface. I am wondering if the acid concentration might be too high though. When submerging the part it immediately starts bubbling which results probably in etching. Therefore after finishing I quickly rinsed the part. But in the seconds from turning off the voltage and rinsing it, a little etching might occur, maybe I try it again with more diluted acid.
If my memory of water chem is not too messed up, the formation of the bubbles cause a very high local concentration of, in this case acid, causing the pitting. I would think that the agitation would cause a similar effect or at the very least cause problems with maintaining a stable current across the piece, now that I think about it that might be preventing you from reproducing the graph, I would be curious about that. I would think a laminar flow would be better, help maintain that viscous boundary, with maybe a desonic to keep any bubbles as small as possible, I know absolutely nothing about electroplating tho.
I know I'm 4 years late but.... Would this increase the thermal conductivity of aluminum if it were used as a heatsink with thermal paste? I'm guessing yes but I was wondering if anyone knows for sure
Would this process affect the ability of the part to be anodized afterwards? You mentioned a combination of sulfuric acid which is used for anodizing, so maybe this could polish and anodize at the same time?
It seems to me that having a bubbler adds to the formation of bubbles on the surface of the part you want to electropolish. I would try getting rid of that.
So you are moving the heavy metals from the stainless steel to the aluminum? I know if you use stainless in electrolysis rust removal, you get toxic heavy metals as a byproduct.
Wow (shine and genius) I think the hydrogen in the phosphoric acid did the pitting, but not sure . Why, because I believe sodium carbonate (laundry detergent) is a possible solution for “electro polish “ worked in rust removal. Great polish.
Pretty sure a detergent and parts per million and total divsolved salts to perfefect the mix . At work we have a parts washer for washing diesel transmission parts it works on a ph based system to check otherwise it etches the parts darker or blk
@AppliedScience Were you able to characterise the change in surface Morphology before vs after? I'd be curious to know how the new morphology/lowered surface roughness correlates to the improved reflectivity of the surface.
Very interesting, I remember using a old computer PSU to plate nails with copper. Of course I used salt, and did not consider the chlorine gas it produced, and wondered why it smelled like bleach. If I had known this I would have used baking soda. I must try this sometime.
Might it be that that viscous layer formation is some form of inverse corona effect due to high current? Did you try a high frequency pulsed dc power source?
I noticed two things happening in this video. One definite, one theoretical. Getting the acid up to a set temperature is pretty pointless if you are then going to introduce a lot of cold objects which are going to make the temperature drop rapidly and dramatically. If the working temperature is vital then add everything and then heat the acid up. I wondered if the pitting on the surface was more to do with the bubbles coming from the air stone having a cavitation effect?
I That electrons went from negative to positive right theory is positive to negative but actually they flow negative to positive am I right? It’s been a minute
Ben - Why doesn't the aluminium re-oxidize back to it's usual grey appearance immediately it's exposed to the air? Al is incredibly reactive normally (when not coated with oxide)...
Aluminium always is coated with oxide layer when exposed to source od oxygen for example air. Usually it forms very quickly few to several dozen nanometers thick layer of oxide, which you can't see even on polished metal. This layer is hermetic, it prevent any futher oxidation. Grey appereance is from corrosion, or rough surface, or often aluminium is anodized - artificial created few microns thick layer of oxide, which is hard and prevents corrosion.
IIRC aluminum is so reactive, it will steal oxygen from water to oxide itself, releasing H2 in the process. But as Woloszow said, the layer is nanometers thick, hermetic and is pretty fast. You will not see it "happening".
Ivan Kocher Thanks All. I had assumed that oxidized Al had that grey appearance, but actually the layer can be so thin that polished Al still looks shiney even though it's oxidized.
Excellent as always. Just curious if you used a stir rod/heat plate like most chemist use rather than the air stone if you'd be able to eliminate some of that pitting? Removing the gas bubbles and just using physical agitation might be an improvement.
Regarding bubbles on the metal surface, if you have a ultrasonic bath you could put the beaker in it, and the ultrasonic agitation will help disperse both bubbles and dissolved gas.
...(but too strong and it will tear layers off the the aluminium. In fact a common way to test the piezos on ultrasonic baths is to see if it can disintegrate aluminium foil).
nucleochemist Tearing layers off a solid and destroying a thin layer would seem rather different.
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It's exactly the same effect, caused by cavitation.
nucleochemist If you put a lump of ali in an ultrasonic bath nothing happens, that's been my experience.
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I love this channel: SO MANY NERDS!!! :-)
It's been a while since I did this, but the sonication does help. I also remember electropolishing in one solution, then switching to another solution briefly and repeating the cycle. It might have been electropolish in sulfuric then etch off the oxide in phosporic. As long as you didn't get too much current, you could get beautiful surfaces.
I remember covering this in a college course way back when. In 7 minutes you summarized quite a bit of material - nice work.
What do you teach?
this is awesome since i've recently started getting into removing rust with electrolysis.
This is awesome stuff, I've been doing electropolishing as my job for 3 years now and i still learnt something! (polishing stainless in case you were wondering)
Hi Ben, I have done electroremoving before. I looked at different phases of superalloys. ASTM E407-07 covers the solutions and procedures for etching all sorts of alloys. It states that 10% H3PO4 immersed for 1 to 3 minutes at 50 deg C is good for 2000, 3000, 5000, and 6000 series Aluminum alloys for general structure, phase identifications, and grain structure under polarized light. So you were right to use H3PO4 as a etchant and polish solution. I got a little creative with my project and tried electroremoving a pattern using press-n-peel blue transfer film. I know for a fact it sticks to Nickel, Nickel superalloys, and Copper; I haven't tried it with Aluminum, but I think it sticks to practically any metal.
I used heat transfer PCB resist via printer-bubble or toner type I can't recall, maybe it was on a copier machine- probably, it worked well.
I made a two piece die with this metode and casted lead into it.
though the relief was very slight, the image was well prepared. I had less good results etching stainless steel.
with electrochemical etching current control is critical.
Just some stuff.
Rather then a pure solution of phosphoric acid, you would have less etching if you used an aluminum salt. If you want simple math, you should try using aluminum phosphate, but that stuff is hard to find (something about it being used to make explosives.).
A good aluminum salt will help prevent etching, and over etching on a short term basis, because it reduces the amount of aluminum that will immediately need to go into solution to satisfy Le Chatelier's principle. It ensures that the only etching going on is the stuff that's being driven by electrical current.
This needs to be fine tuned though. Functionally speaking, the difference between an electo-platting solution and an electro-polishing solution should be the amount of dissolved aluminum in solution; if you're not watching your concentrations, you can reach a point where the reaction is less then optimal, though it can't run in reverse.
I would speculate that people are advising you to use sulfuric acid because aluminum sulfate is easier to get a hold of then aluminum phosphate, but mixing the phosphoric acid and sulfuric acid makes the math more complex. Sometimes aluminum phosphate is sold in nurseries as a special fertilizer for hydrangea. Hydrangea change colors when the pH of the soil they're grown in changes, and aluminum ions are a good way to shift the pH towards acidic for extended periods of time (assuming you want a pink color hydrangea). Aluminum sulfate is also known as Alum.
@ It has to be a typo. Its widely available and I've found no refference to pyrotechnics.
@ I've found that it's rather a fire retardant www.chemicalland21.com/industrialchem/inorganic/ALUMINIUM%20PHOSPHATE.htm
but I dont know everything. It may release the oxygens at high temperatures, in rocket propellants, thermites,... it's possible, but it's readily available and no one is writing about it as such. I think he meant another substance
@@trollmcclure1884 You're right. I remember wanting some for pyrotechnics but reading about it I must have been wrong back then. Its berlinite and its apparently toxic.
Thanks for setting the record straight.
I’ve heard the term, ‘electropolishing’ and it application but nothing about the procedure. Thanks for the primer. A thought is that a battery charger although providing DC is not filtered (e.g. capacitors, inductors, etc.) and the 60 Hz ripple may cause a bit of a ‘electrochemical hammering’ effect on the surface of the aluminum promoting the pits. Maybe, I don't know. Cheers, Mark
Do you have some sources? Where you found the graph, and such. I'd like to read a bit about how this process works.
Thank you for the video, I've done some experimenting myself trying to etch images into aluminium plate using laser printer ink as a resist. Electropolishing sounds super interesting and I'll have to try it out!
I'm not sure the air stone is actually a good idea if the polishing requires some sort of layer on the part surface. and may explain your results. Do you know if it is possible to use a graphite electrode? I have had good results with stainless using a carbon fibre brush as my electrode, it gives me lots of control. Also great for weld and silver soldering clean up.
Where do you get a carbon fibre heat resistant brush from?
Take some loose fibres (you can buy them on a roll) insert into a piece of metal tube and crimp.
I guess everyone has a personal/social responsibility in using any chemicals other than day-to-day table salt or butter etc, in a sensible manner. This vid, without frills and creases shows how to get the job done in a short and sweet manner. Further research, customization and improvising is left to the DIYer. Great work !!
Well I will be damned!, I get SS electropolished all the time at work (pool cover and heating industry) but I had no idea it could be applied to AL
yes also Nickel /Monel / Inconel
BTW the industry doesn't show and tell. they have all the solutions for electroplating and polishing very hidden. NI has a handbook but if you don't work for then you don't get the real deal
I read once about finish polishing aluminum to 99.999% reflectivity swishing/vibrating with successively thinner solutions of India ink (which apparently has some natural quantity of bucky balls). These apparently bump into any nanoscopic hills and peaks and smooth them out.
Does electropolished aluminum count as a finish/sealer? Or does it still oxidize, etc.
Nice to see you found the time to make a few more videos!
good presentation, very helpful.
Permit me to just add this;
that is, the reason why the current density plot is not looking like the one you found on the internet.
The plot observed from the "internet" is due to a layer formed between the sample and the electrolyte (it is called the anolyte layer).
however, for the electrolyte that you used (phosphoric acid), the anolyte layer is not visible.
hence, the plot you will be getting will be not be exactly what you got from the internet. therefore the plots that you got are not too out of place.
the pitting is a result Al2O3. Add the Al to the acid till it starts to bubble, then add the current and reduce the voltage too.
and you are not polishing, you are plating with Stainless.
Good explanation, nice.
Agitation can be used, for small parts its normally not necessary. Ultrasonic baths do work, with water, then a glass beaker, to break the liquid/gaseous plastron that forms on the surface of the part, and keeps fresh electrolyte close to the surface interface. Using full strength acid can lead to uneven brightness and micro pitting.
Have you thought about trying ultrasonic agitation?
I believe that this process is used on things like bicycle brakes and kitchen tools like traditional garlic presses; lots of Italian stuff.
I was wondering if my bottle of descaler would do as a source of phosphoric acid but I was worried that it would be too weak... it's also "contaminated" with surfactants and "fragrance"... but then you suggested adding surfactant any way... so that's one problem disappeared. ;)
Can you make a video explaining how to anodize aluminum, and the differences between electropolishing, anodizing, and electroplating? (differences in terms of the science, but also the practical methods for doing it all.)
Would this give the part a nicer finish if it were to be anodized afterword or would it not matter, or perhaps make anodizing more difficult?
Just thought to let you know that the drawing shown has the x and y axis are the wrong way around. The voltage is usually on the x axis with current density on the y axis. Maybe this is why you had issues recreating the plot. Happy polishing.
If you would use ultrasound vibration on the polishing part, would be there less bumping ?
Cool. I assume this is different than the shiny (I won't say polished) aluminum bars you find in Home Depot in the bath and shower section. The surface of those is non electrically conductive.
I think those are anodized. Btw, anodizing is a something you can try in your home lab. You can use dilute sulfuric acid as the electrolyte, and the aluminum is connected to an anode. Constant current is passed through it, and as the honeycomb AlO2 layer builds up, resistance increases. That's how you know when the process is done. You can get it as battery acid from an auto supply store. I've tried with different electrolytes, too. It's pretty neat to try. Varying acid temp will give different layer cell sizes. Varying voltage while anodizing titanium will yield different colors.
Anodized...actually a very thin surface 'conversion' to Aluminum oxide, slightly porous and often colored with dye....
Is there oposite to this method, i.e. make surface of metal rough on atomic scale? To increase surface area.
Do it in the etching area of the graph. Low current.
Applied Science For the vessel could you use one of those mechanical milk frother machines?
I think they only heat to about 80c but you could always modify it..
Can you please share some of the literature you used to make this video. I am doing an internship where I need to electropolish aluminium and thinking about using phosphoric acid as the electropolishing liquid. I am most interested in what is discussed from 3:50 onward. Thanks in advance.
Ben, could ultrasonic wave agitates the hydrogen bubble produced?
Thank you for another interesting video.
The pitting below a certain depth is an interesting phenomena. That it does not happen within a certain distance of the surface is curious and doesn't seem to be well accounted for by the current per area theory.
It would be interesting to attempt the electropolishing on a hotplate with a stirring magnet, to see if eliminating the bubbles from the air stone would reduce the pitting. Bubbles may be sticking to the metal preferentially at greater depths, but adhering less when moving faster near the surface.....
I wonder how it would behave if you tig welded it after the elctropolish?
Oh ideal tool creation for you drum roll ... a lead stripping hand held tool for removing rust and lead from bridges?
would the pitted surface be reduced if you diluted the acid with demineralised water?
Why don't you use a halogen light bulb to heat the solution
I would love to get into electropolishing myself (for stainless steel, and copper, and bronze). Can I contact you for info on this? I can’t find it anywhere on the internet :(
Nice work! I have found it better to NOT agitate the solution. Leave the viscous (often brown) layer to form quietly. Agitation will mess with your middle diagram I think.
Good stuff as always Ben, Keep up the science!
Why not use an ultrasonic cleaner instead of a bubbler for more even polishing?
Have you tried reducing the flow from the air pump. Reduce the air a bit .
Have you tried using a similar technique to electrosharpen edges and points? I've wanted to do this for a while to make AFM stylus. Most recipes seem to use sulfamic or phosphoric acid, some in a rather viscous solution, including one that had organic resins in it.
I have done this with a regular wood nail. This was ~8years ago.
My steps were:
* solution: water+ table salt (NaCl), quite probably not saturated
* a graphite electrode ( from a regular "A" battery)
* iron nail the other electrode, nail head connected to the cable, out of solution. Be sure the nail is grease or oil free.
I do not recall which electrode was negative.
Start with a "hi" current (5~10A), you will see the nail starts to get thinner, and the solution will look rusty and lots of bubling (O2 and H2 being released), as time goes on, reduce the current, so you have better control of the "thinning" process. The thinned part will also be extremely polished, with a really nice shinny look.
The part of the nail in the solution will get an extremely fine point. Graphite is not affected, and solution be full of iron oxides black and orange ones. Not sure what happens to NaCl.
The nail I used was about 1/8 in diameter, and took a few days.
Yes. However, the method that I used requires that the wire be slowly withdrawn from the bath so that the tip has more time in contact with the chemical reaction than the rest of the item. This gives another dimension of control, allowing the taper to be adjusted, or even made non-linear. I'm not so sure the method would produce atomically sharp objects, though.
Ivan Kocher From what I remember of the inorganic chemistry classes that covered this sort of electro-chemical process, I'm pretty sure the Cl from the salt formed a chlorine gas when you applied current, making some of the bubbles you noticed(because it has a decent reduction potential, meaning that it tends to receive the electrons from your power supply and use then for going from the oxidized to a reducted state)... not sure about the Na, but it's most likely it stayed in the solution since Alkaline metals have a high tendency to remain oxidized. The salt is added to the solution so there are enough eletroclites in the water to make it a decent electrical conductor (pure water is a poor electrical conductor) practically any other salt would work too (except different chemical reactions could happen).
..AFM stylus... I see references to that in Scientific American, but don't they use tungsten...?
+Ivan Kocher The NaCl is added to facilitate conductivity to the distilled water(or increase conductivity of tap water) in any electrolysis process that doesn't have an acid or base as an electrolyte!
That's really interesting. I wonder if it could be used as a surface prep method for DCEN aluminum welding (which needs to be much cleaner than AC welding), or if there are residues left on the metal.
I would be EXTREMELY surprised if you could do a DCEN on ali regardless of the prep (removing oxyide layer) you do. Let us know how it goes if you try it
@@Bakanelli Yeah have done it before, with mechanical scraping and chemical etch. We used it to make high quality butt welds turning 18" sheet into tubes for pressure vessels.
Why air bubbles? May be redo it without bubbles, but with vibrator attached to aluminum detail?
amaraojiji I'm pretty sure that vibration would work instead of bubbles. My first thoughts were using a geared motor or stepper with an embedded neodymium magnet on a disk attached to the motor shaft, below a plexi-glass shelf, then a plastic/silicone coated magnet inside the flask/vessel - to recreate a magnetic lab 'stirrer'. Fascinating stuff! @ +Applied Science I've often wanted to try anodising so I'm headed to your uploads .... >subbed< :)
What metal is your heater made from? I suppose it's actually important.
Now that I think of it water will separate above 1.9 volts and produce gas. Could this process be done under 1.9 volts? That could reduce the effect the gas has with the pitting.
Perhaps by increasing the conductivity of the electrolyte, adding those chemicals he mentioned...
now i'm gonna have to look up the process of chrome plating, this looks very similar to what i thought the process of applying a chrome surface to a metal was, i'd like to see what actually happened to the pieces of steel as well since i thought phosphoric acid would act more aggressively on steel than aluminium
The concentrated layers of oxidation on the aluminium from being exposed to the elements, over time these levels have built up, the pitting has occurred from the solution and cavitation removing fine loose scale, but the pitting is like rust pockets or decaying in the aluminium material, the surface areas coming in contact with the solution it not strong enough to dissolve the oxide layers, the aluminium has to be polished flat
So does the voltage just assist in the acid eroding away the metal?
Can you please share the article?
Aluminum (and zinc) is very very acid sensitive - next time buffer with a little sodium carbonate or substitute acid for sodium citrate. Also, use a lower voltage make sure your work is totally oil/petroleum free (never use torches to dry parts after de-greasing).
I would like to see how aluminum in a bath of the same solution in a sonicator would turn out.
What if you immersed the beaker in a sonic cleaner filled with water to the same level as the acid without the airbrick? That would increase agitation (enabling hydrogen gas to release easier) and eliminate oxygen.
I've been trying to replicate the same chart, do the same sort of thing, but with steel. Without buying a lot of extra supplies, spending money on a whim. So far I haven't been able to get that graph to happen either. I've read, not a lot, but some about electropolishing steel, from stuff as far back as the early 1900's, and they all describe the same graph. Well, I'll fool around with it a while longer.
Also trying an etching with photoresist film, sort of different project. For that I need to stay in the 'etch' region, so far that seems to work fine vis a vis the steel, but the photoresist keeps lifting. Not sure why. I'm starting to suspect the etched piece gets a zone of more acidic solution around it, and that makes the photoresist hard and flake off.
Anyway, I remembered you did this video, and watched it again to check what you were using specifically. Thanks
Would you please let me know Where is your aluminum source where does the aluminum come from all I see is acid and stainless steel
What effect would an added surfactant have on forming that viscous acid layer on the surface of the work piece?
I wonder if it's more dangerous than vinegar
Interesting results, but it doesn't really seem to being polishing but electroplating SS onto AL. However, I have been told to never use SS for an electrode in soltion due to it releasing Hexavalent Chromium. (The same stuff that caused severe birth defects, health issues and water contamination in the true story movie "Erin Brokovich.") Can't you use aluminum plates?
you can clean up welds on Stainless steel using a similar principle
Better nate than lever: Just tried it out with a 5x4x3cm piece of aluminum (75% H3PO4, 70-75°C, magnetic stirrer, 20-30V). I started out with a much too low mA/cm^2 so in the beginning I was only etching. If the part would be a cube it had a surface area of 114cm^2 but it as inner surfaces so its probably 3 times that. This would result in 30A but my powersupply only goes to 5A. Luckily enough that was enough to produce a very nice polished surface.
I am wondering if the acid concentration might be too high though. When submerging the part it immediately starts bubbling which results probably in etching. Therefore after finishing I quickly rinsed the part. But in the seconds from turning off the voltage and rinsing it, a little etching might occur, maybe I try it again with more diluted acid.
Can one use coke instead of acid?
Just a thought, could you conduct this process under pressure? Eliminating the gas bubble trouble.
what happens to the aluminum you are etching off the surface to polish it? is it forming alumina *aluminum oxide* ?
If my memory of water chem is not too messed up, the formation of the bubbles cause a very high local concentration of, in this case acid, causing the pitting. I would think that the agitation would cause a similar effect or at the very least cause problems with maintaining a stable current across the piece, now that I think about it that might be preventing you from reproducing the graph, I would be curious about that.
I would think a laminar flow would be better, help maintain that viscous boundary, with maybe a desonic to keep any bubbles as small as possible, I know absolutely nothing about electroplating tho.
Very useful video. I used to order all of my aluminum straight from electropoland, but it's easier to just do it at home.
I know I'm 4 years late but.... Would this increase the thermal conductivity of aluminum if it were used as a heatsink with thermal paste? I'm guessing yes but I was wondering if anyone knows for sure
i would love to see the electropolished aluminum under the scanning electron microscope (or a regular microscope)... bet it looks awesome
Dude - best video out there. thanks for covering the mistake so clearly!! Cant wait to experiment with carbs.. them being zinc will this method work?
Is it possible to electro polish Aluminum by spraying that hot charged solution directly on the huge parts 🤔?
can this technique apply to an 99,98 pure aluminium with a thickness of about 0.3 mm?
To do this is it imperative to use phosphoric acid or would an acid such as hydrochloric acid still work?
What if you buff it with a compound , is the result going to be better
once you've polished the surface, how long will the shiny finish last before it oxidizes again
is this similar to how wheel brightening/wheel cleaner acid works for car wheels?
Hi would this work on an old piece of alloy that has corroded such as a motorcycle engine case ?
pure phosphoric acid? ie 85% aqueous or crystalline "pure" phosphoric acid?
Would this process affect the ability of the part to be anodized afterwards? You mentioned a combination of sulfuric acid which is used for anodizing, so maybe this could polish and anodize at the same time?
It seems to me that having a bubbler adds to the formation of bubbles on the surface of the part you want to electropolish. I would try getting rid of that.
So you are moving the heavy metals from the stainless steel to the aluminum?
I know if you use stainless in electrolysis rust removal, you get toxic heavy metals as a byproduct.
Or you could use a coulombic explosion generated by negative surface tension to
Can this work for mild steel?
Any substitutions for the phosphoric acid i.e. can I use vinegar?
Wow (shine and genius) I think the hydrogen in the phosphoric acid did the pitting, but not sure . Why, because I believe sodium carbonate (laundry detergent) is a possible solution for “electro polish “ worked in rust removal. Great polish.
With EDM machining the frequency highly affects the the surface finish. Any chance this has an affect here?
Can you use 85%? I can't find 75% in less than a gallon.
Pretty sure a detergent and parts per million and total divsolved salts to perfefect the mix . At work we have a parts washer for washing diesel transmission parts it works on a ph based system to check otherwise it etches the parts darker or blk
@AppliedScience Were you able to characterise the change in surface Morphology before vs after? I'd be curious to know how the new morphology/lowered surface roughness correlates to the improved reflectivity of the surface.
Very interesting, I remember using a old computer PSU to plate nails with copper. Of course I used salt, and did not consider the chlorine gas it produced, and wondered why it smelled like bleach. If I had known this I would have used baking soda. I must try this sometime.
Might it be that that viscous layer formation is some form of inverse corona effect due to high current? Did you try a high frequency pulsed dc power source?
I noticed two things happening in this video. One definite, one theoretical. Getting the acid up to a set temperature is pretty pointless if you are then going to introduce a lot of cold objects which are going to make the temperature drop rapidly and dramatically. If the working temperature is vital then add everything and then heat the acid up.
I wondered if the pitting on the surface was more to do with the bubbles coming from the air stone having a cavitation effect?
Bubbles moving past shouldn't be a problem. Bubbles sticking to the surface are.
You're right about the temperature dropping from the added colder metal.
Ben, do you think edta in the soap would have effected your results for pitting?
Would this same process work for electropolishing copper?
Can you electro polish other metals? can you do it to gold or silver?
I That electrons went from negative to positive right theory is positive to negative but actually they flow negative to positive am I right? It’s been a minute
Would this process for for stainless steel?
Ben - Why doesn't the aluminium re-oxidize back to it's usual grey appearance immediately it's exposed to the air? Al is incredibly reactive normally (when not coated with oxide)...
u answered yourself
Aluminium always is coated with oxide layer when exposed to source od oxygen for example air. Usually it forms very quickly few to several dozen nanometers thick layer of oxide, which you can't see even on polished metal. This layer is hermetic, it prevent any futher oxidation. Grey appereance is from corrosion, or rough surface, or often aluminium is anodized - artificial created few microns thick layer of oxide, which is hard and prevents corrosion.
IIRC aluminum is so reactive, it will steal oxygen from water to oxide itself, releasing H2 in the process. But as Woloszow said, the layer is nanometers thick, hermetic and is pretty fast. You will not see it "happening".
Ivan Kocher Thanks All. I had assumed that oxidized Al had that grey appearance, but actually the layer can be so thin that polished Al still looks shiney even though it's oxidized.
Excellent as always. Just curious if you used a stir rod/heat plate like most chemist use rather than the air stone if you'd be able to eliminate some of that pitting? Removing the gas bubbles and just using physical agitation might be an improvement.
is it possible to perform the same process on AL alloys?? AlSi10Mg or 7Mg??