Chemical Forums
Specialty Chemistry Forums => Citizen Chemist => Topic started by: xchcui on May 03, 2014, 07:30:08 AM
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Hi.
I would like to understand what happens exactly when i make electro cleaning to a copper oxide object.i browsed a lot in the web and i didn't find appropriate explanation.
I make a solution of vinegar+some salt.
I connect the copper oxide object to the negative voltage(as a cathode)and a copper wire to the positive voltage(as an anode).
I understand that in the solution there are hydrogen,oxygen,chlorine,soduim and copper ions,ch3oo- and h2o.
When i close the circuit i understand that hydrogen bubbles create around the copper object,oxygen bubbles create around the copper wire(maybe also chlorine)and the object get rid of the oxygen atom during the process.
What is actually happens?:
Does the anode-wire dissolved and get eaten in that process?does it release copper ions?
Does the copper oxide object(cathode),besides than get rid of the oxygen,also plated with a kind of material,maybe with the copper that might dissolved from the anode wire?
Does the oxygen ion release from the copper oxide object,even,before i close the circuit?
I will be very appreciate to hear an expert explanation what is happening exactly in that process.
Thanks in advance.
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I think what you're doing is called electropolishing, basically the reverse of electroplating -- you make the piece you want to polish the cathode, essentially using it to plate the anodes. This removes the underlying metal, and cleans the piece. See a fuller description here: http://en.wikipedia.org/wiki/Electropolishing
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Hi Arkon.
thanks for your link.
I read the link but it is not exactly my case.
In my case the object is connected to the negative voltage and not to the positive while i make electro-cleaning in order to get rid of the oxidation on the object.
I focused my questions on the specific things that i look for an answer which will let me understand few things about the process.
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@xchcui
Is there a link that shows the recipe' for your process?
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Hi billnotgatez.
It is very simple electrolyte.
Vinegar 5%+some salt.
Copper object as the cathode
Copper wire as the anode.
What is happening in the solution regarding to my questions?
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@xchcui
I am thinking you are electroplating and not electrocleaning or electropolishing
Maybe it is just a matter of semantics.
As the original poster, I had expected you had done some of the Internet research and had a link handy. I had expected you would post it as a courtesy.
By the way, for the ingredient salt are you referring to Sodium chloride?
Also, By the way, I am not an expert, but I am trying to get some background so we might attract an expert to the discussion.
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billnotgatez.
The pinch of salt that i had to the white vinegar 5% is regular salt NaCl.
Before i am going to plate my object by electroplating with different solution,i am going,first,to get rid of the oxide that on the copper object.so i put my object and the wire at the vinegar+salt solution in the way i described before.I know that i get rid of the oxide from the cathode(my object)but i try to found out by an expert chemist what is happening in the solution regarding my pevious questions?
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Have you checked if the cleaning doesn't work without potential source as well?
I remember reading that the combination of Cl- and mild acid dissolves CuO with CuCl (yes, Cu(I)Cl) being an important intermediate. I don't remember details and I am not sure they were in a published paper, they just came from a fellow chemist.
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Using potential source work better to clean the object surface(oxide).
Thanks for trying to help,but i hope there is some one expert that can refer to my questions and explain(describe)all the process that happens in the solution.
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Anyone?
This is very simple solution.
i am not a chemist,so i don't know what is happening in that electro cleaning process even though this is very simple reaction,so i turned to the expert of chemical forum and i am very suprise that nobody can explain the process.This is chemist forum,where are all the chemists ???
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http://chemistry.about.com/cs/demonstrations/a/aa022204a.htm
http://www.youtube.com/watch?v=H4N-iGvYrbM
http://chemistry.stackexchange.com/questions/5863/why-add-salt-to-vinegar-to-clean-pennies
http://www.exploratorium.edu/science_explorer/copper_caper.html
http://wiki.answers.com/Q/Why_do_you_clean_pennies_with_salt_and_vinegar?#slide=1
http://thehappyscientist.com/science-experiment/penny-chemistry-part-1
The above is a FYI for anyone following this thread.
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You are doing reverse electrocleaning, aka cathodic cleaning, with the setup you have. You are actually plating onto the surface of the part. Your copper wire is dissolving into the solution creating Cu2+ ions. Those ions, along with any other loose ions in the solution, will travel through the electrolyte and plate onto your part. Hydrogen is evolved at the part surface, creating a bubbly "scrubbing" action that helps to clean any dirt off. Cathodic cleaning is a good method of preparing surfaces for things like electroplating.
However, this being said, the proper way to complete this is to reverse the current and make the part anodic for a brief period. This reverses the process and actually dissolves some of the working part, essentially what you plated in the first step. Oxygen is liberated at the part surface and the copper ions dissolve back into the solution, taking impurities and metal smuts with them. Finishing this way gives you a much cleaner surface.
I don't know what else you want to know.
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At the risk of making you even more frustrated I thought I might chip in. I do a lot of copper working, and amongst other things I clean sometimes. I can not add anything to eazya description except to say that Oxidation of Cu- takes place at the anode and reduction takes place at the Cathode, there is an electron gain at he cathode and electron loss at the anode. Having said that, are you actually wanting to clean copper? If so this is not the best method - simply put a tiny amount of Copper sulphate as the electrolyte in de-ionized water and attach impure copper to Anode and the pure piece at the cathode. I wondered also at your original description: 'Copper Oxide' to me this is impossible to do, you have oxide layers on top of pure elemental copper, is this what you mean? Forgive me if I misunderstand anything, but the oxide layer is simply what you are getting rid of and revealing pure copper in the process.
Kind regards
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Hi eazye1334.
I see that the best method to clean the part is to do it in two steps.one time the part will be the cathode and after that a brief period as the anode.
It seems reasonable,but there are two thing that i try to figure out:
1)When i make the part anodic for a brief period and oxygen is liberated at the part surface.Doesn't the negative oxygen ions(O--)oxidize the part again and make the part surface to be copper oxide again(CuO)?
I know that the O-- ions give electron to the anode and become a gas,but what happens next,that cause the Cu++ ion to drop into the solution,rather than be connected with the oxygen ions in order to form CuO again?
2)When i make the part cathodic and the H+ ions take electrons from the copper oxide surface part and turns to bubbles gas,How does this action cause the oxygen from the part surface to be removed?
Also,when the oxygen is removed from the part surface in that process,the part is also being plated with Cu++ ions and with other loose ions in the solution,Isn't it disturb to the cleaning process?
Tittywahah.
In my orginal description when i said copper oxide,i mean layer of oxidation on the copper surface(CuO)
and in the electro cleaning i wanted to get rid from the oxygen on the surface before electro plate it.
But as you can see i have little problem to understand few thing at this process.
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Hi there,
???and in the electro cleaning i wanted to get rid fron the oxygen on the surface before electro plate it.???
Are you trying to clean the copper?
And then what do you want to electroplate it with?
I am failing to understand, exactly, what the end result is that you desire, are looking to achieve.
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Hi Tittywahah.
I don't want to push aside the issue that i try to understand and spend time on the electro plating or other aspects of that issue.
The electro cleaning process is the main issue that i am trying to understand.
And I would like to focus on the questions that i directed to eazye1334:
"""...1)When i make the part anodic for a brief period and oxygen is liberated at the part surface.Doesn't the negative oxygen ions(O--)oxidize the part again and make the part surface to be copper oxide again(CuO)?
I know that the O-- ions give electron to the anode and become a gas,but what happens next,that cause the Cu++ ion to drop into the solution,rather than be connected with the oxygen ions in order to form CuO again?
2)When i make the part cathodic and the H+ ions take electrons from the copper oxide surface part and turns to bubbles gas,How does this action cause the oxygen from the part surface to be removed?
Also,when the oxygen is removed from the part surface in that process,the part is also being plated with Cu++ ions and with other loose ions in the solution,Isn't it disturb to the cleaning process?..."""
The answer for those questions will help me alot to understand the issue.
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)When i make the part anodic for a brief period and oxygen is liberated at the part surface.Doesn't the negative oxygen ions(O--)oxidize the part again and make the part surface to be copper oxide again(CuO)?
===I have to assume by 'PART' you mean the dirty copper piece, if so then No, that piece of copper gets quite clean from my observations and the rubbish simply drops out of solution.====
As I understand the chemistry (and I have not looked this up so I may well be misguided, but I am learning as well), physical copper does not really drop and travel anywhere, you have electrons moving away from the anode and attaching themselves to copper cathode. Elemental copper has no charge, neither the cathode or the anode, both pieces are ZERO charge. So when an electrical current is passed electrons from the copper anode head towards the copper cathode. As the copper anode starts to lose electrons it is being Oxidized and each moment of oxidation the copper becomes negatively charged and an oxide is formed and this drops out straight away into the solution.
The rest of your questioning I find difficult to follow, call it a lack of experience, but this is as far as I can take you with my understanding. If I am mistaken then I will be glad to be corrected. Here is another link for you to watch _ I don't have time at the moment to watch it, but hope there is something here.
Kind regards http://www.youtube.com/watch?v=MTqxhUGf6s4
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"""...1)When i make the part anodic for a brief period and oxygen is liberated at the part surface.Doesn't the negative oxygen ions(O--)oxidize the part again and make the part surface to be copper oxide again(CuO)?
I know that the O-- ions give electron to the anode and become a gas,but what happens next,that cause the Cu++ ion to drop into the solution,rather than be connected with the oxygen ions in order to form CuO again?
Ok, so backing up, normally you would be using an alkaline cleaner for an electrocleaner. The normal process involves electrocleaning the part and then following up with an acid dip. Yes, through anodic cleaning, you will produce somewhat of an oxide film at the surface of the part, but a dip into acid will remove the oxide film because it has very low adhesion. The de-plating action of the anodic cleaning will help remove all other impurities on the surface, leaving you will a clean part surface and a very thin oxide layer, which as I said can be removed with an acid dip. This oxide layer can also be left on as a passivation layer that helps with corrosion resistance. However, it should not affect the appearance of the part.
2)When i make the part cathodic and the H+ ions take electrons from the copper oxide surface part and turns to bubbles gas,How does this action cause the oxygen from the part surface to be removed?
Also,when the oxygen is removed from the part surface in that process,the part is also being plated with Cu++ ions and with other loose ions in the solution,Isn't it disturb to the cleaning process?..."""
Water gets broken down at the part surface, which is where the hydrogen comes from. The hydrogen at the part surface is reducing the oxides and forming OH- ions. I would guess that if you check the pH of your cleaning solution after cathodic cleaning that the pH would be higher than when you started. I say guess because I've never used an acid for electrocleaning, it's just a thought.
The part will be plated with some ions, whether copper or anything else you have in the solution, but keep in mind that these we have very, very low adhesion. The scrubbing done by the hydrogen gas helps clean the surface and may help remove some of those plated ions. Keep in mind that the hydrogen evolution during cathodic cleaning is twice as high as the oxygen evolution during an anodic cleaning, so it is a pretty violent scrubbing action. But this is exactly why you do the anodic cleaning as the final step, because that will remove what was loosely plated. You should always end with anodic cleaning.
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Obviously I missed the boat then, misunderstood everything?
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Obviously I missed the boat then, misunderstood everything?
Honestly I couldn't tell you. I'm a chemical engineer, not a chemist, so I can't confirm or deny exactly what you said. I just know about this because I do it for a living.
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Thanks for your explanations.
[Ok, so backing up, normally you would be using an alkaline cleaner for an electrocleaner. The normal process involves electrocleaning the part and then following up with an acid dip. Yes, through anodic cleaning, you will produce somewhat of an oxide film at the surface of the part, but a dip into acid will remove the oxide film because it has very low adhesion. The de-plating action of the anodic cleaning
As i said i uses vinegar+pinch of salt(NaCl)as elctrolyte.This is cheap method for me and safer.
So after i will do the second step by connecting my object(part)to the anode and it will be covered with very thin oxide layer,Will a fresh vinegar+salt solution be enough acidic in order to remove this layer from the part by dip it in?
Can you give me the chemical reaction at the anode that shows how the oxide layer is created?
I saw in the link(that Tittywahah attached)this reaction at the anode:
4OH- ions becomes O2+2H2O+4e-.
So i get water and oxygen gas bubbles,but how does the oxygen react with the copper and become that thin oxide layer if i get only plain oxygen gas?
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Ok, I will give it my best: If wrong I hope someone will correct me:
Cu in its elemental state has no charge. In this reaction Oxygen has -2 charge, these are the oxidation states:
Now here is the reaction I believe: Cu + O2 = CuO what is really happening is this:
Cu0 + O24- = Cu2+O2-
There are TWO oxygen atoms (making ONE oxygen molecule) and only ONE oxygen atom is bonding with the copper, where does the other one go?
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Cu in its elemental state has no charge.
OK
In this reaction Oxygen has -2 charge
Not exactly, initially it is in the elemental state and has no charge as well (oxidation number of zero).
Now here is the reaction I believe: Cu + O2 = CuO what is really happening is this:
Cu0 + O24- = Cu2+O2-
There are TWO oxygen atoms (making ONE oxygen molecule) and only ONE oxygen atom is bonding with the copper, where does the other one go?
This is wrong. Correct reaction equation is
2Cu + O2 :rarrow: 2CuO
(which already explains what happens to the other oxygen).
This is a redox reaction, in which copper gets oxidized
Cu :rarrow: Cu2+ + 2e-
and oxygen gets reduced:
O2 + 4e- :rarrow: 2O2-
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ok.i see that the oxygen react with the copper and become CuO,but where is the reaction that creates the oxygen bubbles? ???
And refer to the second part of my question in my last post relating to easye1334:
... The de-plating action of the anodic cleaning will help remove all other impurities on the surface, leaving you will a clean part surface and a very thin oxide layer, which as I said can be removed with an acid dip.
Does a fresh vinegar 5%+salt(NaCl)will do this job?
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Just curious
What kind of power source are you using?
What voltage are you using?
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Does a fresh vinegar 5%+salt(NaCl)will do this job?
Yes, it should be enough and you don't need the salt. Just the vinegar will do, it's actually what we use before passivating the part through other chemical means.
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Thanks,eazye1334.
Due to the fact that your explanations were the most understandable to me(without deprive any of the nice members that help me with my questions),can you refer to and explained to me what is going on with the oxygen that created in the anode?
When you mention that the anode get thin layer of oxide on it, Tittywahah and Borek explained that the reaction is 2Cu+O2 creates 2CuO.
But what with the O2 that get out from the solution as bubbles?Not all the O2 molecule is bonded to the anode,isn't it?
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Thanks,eazye1334.
Due to the fact that your explanations were the most understandable to me(without deprive any of the nice members that help me with my questions),can you refer to and explained to me what is going on with the oxygen that created in the anode?
When you mention that the anode get thin layer of oxide on it, Tittywahah and Borek explained that the reaction is 2Cu+O2 creates 2CuO.
But what with the O2 that get out from the solution as bubbles?Not all the O2 molecule is bonded to the anode,isn't it?
That just escapes as a gas. The oxide layer you're forming in the anodic step is not a very good, as in it is very thin and poorly adhered to the part. That's why a weak acid will still remove it.
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So,we can conclude and say that the hydroxide negative ion(4HO-)give its 4 electrons to the copper-anode while half of the O2 molecules that have been creating(besides the water)stick to the copper(oxide layer)and the other half,turning to a bubbles gas that escape out.Am i right?
Just curious
What kind of power source are you using?
What voltage are you using?
This is my first time so i start with small objects,while i use standard power supply 12vdc for electro-cleaning.should i use for the electro-cleaning lower voltage?like 6v maybe?
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@xchcui
standard power supply 12vdc for electro-cleaning
Could you post make and model etc
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@xchcui
standard power supply 12vdc for electro-cleaning
Could you post make and model etc
When i said"standard power supply 12vdc FOR ELECTRO-CLEANING"i didn't meant special for electro-cleaning.
I mean to the cheap traditional power supply(not SMPS) that you connect to the wall socket while the input is 220vac or 120vac(depend where you are live)and the output is in my case 12vdc and max current of 1A.
So 12vdc is ok for electro cleaning or do i need to use less voltage like 6vdc?
And eazye1334:
Does the conclusion in my previous post is right?
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Hi billnotgatez.
So what are you saying 12v is ok. or i need to use less voltage(6v maybe?).
Hi eazye1334.
where did you disappeared :(
I would like to end this thread while i can be sure that my conclusion is right.
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billnotgatez.
What's up with you,man?
What is the purpose of your questions if you never give me even one answer? ???
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Hi billnotgatez.
So what are you saying 12v is ok. or i need to use less voltage(6v maybe?).
Hi eazye1334.
where did you disappeared :(
I would like to end this thread while i can be sure that my conclusion is right.
In general, I would probably say yes. Though as I said, I'm not a chemist so it may not be 100% correct. I know about the process and how it all works, but the exact chemistry in electroplating processes can be difficult to determine.
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Hi easye1334 and thank you for return :)
It is not critical for me to know the exactly process at high level explanation.Knowing that part of the O2 that created from the hydroxide reaction with the anode stick to the anode and part of it bubbles as gas is good enough for me.
So thanks that you confirmed my conclusion. :)
Best regards.
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@xchcui
You can ignore all I say after this next paragraph or you can read on.
Based on my failing memory, Internet searching and some reading, I have the feeling that you can get results you are looking for with less than 12 volts (maybe less than 6 volts). From what I understand if you go too high in voltage you will get side results that may adversely effect you desired outcome.
Now for my discussion --
What's up with you,man?
We are all volunteers here, so I only been on here briefly during the weekend to make sure that my moderation duties would be taken care of properly. Therefore the time to do the research necessary to answer your question was on hold.
Even then I am not sure I can give you a definitive answer. Based on the below links you will notice that there are a number of factors that effect your process. For instance the distance between wire (on one side) and the object (on other side) you have in the process could influence what you might use in voltage. From what I could glean from from my research so far is that the amperage may be a more important measurement.
http://www.ami.ac.uk/courses/topics/0223_plate/index.html
http://chem1.eng.wayne.edu/~yhuang/Papers/Book_Plating_ECHP.pdf
https://www.glastonburyus.org/staff/BREINANH/APChem/APlabs/Documents/electroplating.ap.student.doc
http://www.youtube.com/watch?v=YvYCc8F-8rQ
http://www.youtube.com/watch?v=Q8Xo43sfLgY
I was going to read more to see if I could resurrect my memory of electroplating, but decided to pause here for now.
For your part --
I had asked for more detailed information from you and I get answers from you that are too general.
I am looking for more precise answers from you for 3 reasons.
One, it is possible that someone on this forum who does or teaches electrochemistry may become more involved with participating in the discussion. I do have to admit that if there are members with this expertise, they are not always regulars.
Second, I was thinking of putting together your setup and testing for myself, so as to add to the discussion.
That is why I asked for
A link on the Internet that you might be using as a guide, since you said you looked around.
Yet you provided no link that is close to what you are doing.
The exact recipe' of ingredients you are using in the process.
Yet your answers were general.
The equipment you are using for the process.
Yet I still do not know the make and model of your power supply.
Now if the process you are working on is proprietary, you can contact me off line and I will understand.
Thirdly, IF YOU HAD READ THE FORUM RULES
We are not supposed to just dump an answer on you.
Instead we are supposed to teach you how to get the answer yourself.
So asking questions in a Socratic method is the desired approach.
In this case both you and I would have learned.
By the way, there was an entry that suggested that your process might not need the electric part, but might take longer to see the results. But, we did not take the hint.
As far as the Internet --
I can see where it is difficult to get what you want on this topic.
When I did a search using GOOGLE, using different criteria, I got results that were too general, too conflicting, erroneous or to difficult to access. It took me several tries and many pages to get the few I have above. And, I still am not sure they are entirely accurate.
As a side note --
What we are discussing here, will potentially help me. Currently I am casting sculpture in brass and aluminum. It is possible that i might want to finish some of these sculptures using electrochemistry. For my part, I will be looking for a power supply where I can both measure and control the voltage and amperage.
Finally --
I would like to end this thread
You can not end this thread.
It will live on.
And, hopefully will have additions that will make it useful to the next reader.
Additionally, it may attract another member to participate
who is more experienced
who is more current in the technology
who is more academically involved in electrochemistry.
I hope you will stick around and see where things go.
If I do any of this, I will be sure to post here.
I still have to tool up my laboratory and memory.
In the mean time I am going to probably post something about your ingredients when I have time.
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Hi billnotgatez.
First of all,thanks for your answer.
I know that you are all volunteers in the forum.This forum is very essential and be blessed all the wonderful members that help people all over the world with there questions.
Before i go and ask questions,i try to find the answer in google,but in my case(and you also realized that)i didn't find an answer,so i try in that forum.
All the other members answered my question and they were practical,but you only asked questions but never gave an answer.I found this behavior strange.
How can i know what is the hidden reasons behind that behavior.
Ok.i understand your side and what was the purpose of your questions and i just now understand,that not all the members who answer to questions are experts
in chemistry.I was absolutely sure that only experts chemist volunteers answer questions and i didn't imagine that you are going to look for an answer to my question in google.
I am very happy that you explained this issue.
Every day we learn something new.
Thanks :)