Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Zensation on February 04, 2014, 12:30:02 AM
-
I've noticed a lot of electroplating is done with chlorides. Platinum Plating -> Platinum Chloride, Palladium Plating -> Palladium Chloride, Gold plating -> Gold Chloride.
I understand that chlorides are much more soluble in water... but is it not possible to plate with oxides instead? Platinum Oxide, Palladium Oxide, Gold Oxide, etc. I understand these are less soluble in water, but the ions should still dissolve to some extent correct? Plating should still happen, just at a slower rate, right?
Is it simply irrelevant what form the ion is in as long as some of it dissolves in the solution? I'm curious since I have been looking into electroplating, and it seems plating with mere oxides(from water electrolysis) would be much easier to handle than plating with hydrochloric acid to form chlorides...
-
The problem is that Oxides made from water. Plating solutions are either acidic or alkaline. At least the non solubility you figured out by yourself already.
-
The problem is that Oxides made from water.
Sorry, this makes no sense at all.
Platinum Oxide, Palladium Oxide, Gold Oxide, etc. I understand these are less soluble in water, but the ions should still dissolve to some extent correct? Plating should still happen, just at a slower rate, right?
Is it simply irrelevant what form the ion is in as long as some of it dissolves in the solution? I'm curious since I have been looking into electroplating, and it seems plating with mere oxides(from water electrolysis) would be much easier to handle than plating with hydrochloric acid to form chlorides...
Oxides of the noble metals are unstable and they decompose on its own. Solubility is low to non-existent. I don't see any reason why oxides should be more convenient.
-
My post: Oxide are made from water I mean like a sulfate is made from sulfuric acid like H2SO4 ==> Mex(SO4)y a oxide is obtained from H2O => MexOy. I am not saying that all oxides are produced from water.
-
My post: Oxide are made from water I mean like a sulfate is made from sulfuric acid like H2SO4 ==> Mex(SO4)y a oxide is obtained from H2O => MexOy. I am not saying that all oxides are produced from water.
In a few, particular cases, it will work this way. You make it sound as if it was a general rule, which it is not.
-
Water is the mother of oxides. Sulfuric acid of sulfates, nitric acid of nitrates, hydrochloric acid of chlorides, etc.
Plating solutions at least seldom neutral, they are acidic or alkaline, or containing complexions like cyanide. There are no soluble oxides at all, Oxides of alkali metals form hydroxide and this is again alkaline. I dont know any oxide what is dissolved in water and form a O2- ion and the corresponded Mex+ ion.
-
Hmmm
I'm just trying to figure out how I would plate onto a copper work piece, since copper is very reactive to Hydrochloric Acid, Sulfuric acid on the other hand not so much. Is sulfuric acid able to be used for plating solutions? I have just never heard of Gold Sulfate, Palladium Sulfate, Platinum Sulfate, though I have heard of Vanadyl(Vanadium) Sulfate for plating. Do the nobel and other precious metals form sulfates that can be used for plating?
Alternatively the only way to plate something of copper with chlorides would be to neutralize the remaining HCL after the solution has been created, and then extract the chlorides, which, being soluble in water, while simultaneously needing to get the salt out(from the neutralization reaction), might prove challenging. If it's even needed at all. Not sure how salt would effect the plating solution, though, it could act as an electrolyte.
-
Noble metal's are used in form of complexes - if memory serves me well gold is used as a cyanide complex, also for best results silver is electroplated from cyanide bath.
Copper can be electroplated from the sulfuric acid solution - dissolve 200 g of copper sulfate pentahydrate in 1L of water, add 25 mL of concentrated sulfuric acid.
-
I meant to plate these various metals onto copper.
Would I just have to anodically dissolve the metal into the form that it is most soluble in, and if for instance that were the metal has to be a chloride and HCL Acid is used, would I just neutralize the acid before introducing a copper work-piece for plating? I don't imagine I would need to reacidify the mixture. With the salt being in it from the neutralization reaction to act as the electrolyte, I assume the dissolved metal chlorides would plate directly onto the work peice/cathode?
If not, is there some specific reason that the solution needs to be acidic for plating to take place?
-
Would I just have to anodically dissolve the metal into the form that it is most soluble in
There is no single answer "we do this and this and all cases". Many of the recipes have a strong experimental component to them - ie, "we don't exactly know why it works this way, but we have checked its gives best results". Sometimes you will use anode that is going to dissolve, sometimes you will dissolve huge amount of some salt in the bath. Sometimes anodic dissolution would be best, but anodes of pure meta are hard to get.
If not, is there some specific reason that the solution needs to be acidic for plating to take place?
Again, it will depend on the solution composition. In the case of many metals solution has to be acidified to prevent precipitation of hydroxides, but acidifying baths containing cyanides is asking for troubles.
-
Oh yeah I wouldn't be messing with any cyanides.... Pure metals are no problem to get. I'm not worried about that... Kinda sad there are many simple chemistry phenomena that is yet to be understood. Really makes me want to study the field.
I guess regarding the metals I intend to plate I will just have to research each one individual and the past examples. I was hoping there would be some general mechanism that is to be understood.
-
As I tell a lot of the people who ask about what I do, plating is honestly a lot of voodoo and black magic. Most information is passed along as trade secrets, so it's not always easy to follow how to do something. If you want to get into specifics of what you're doing, I'm certified in electroplating so I may be able to set you on the right path at least.
-
I appreciate your offer truly.
I do not intend to take up electroplating as a profession, though, I do need to electroplate a few metal work pieces for use in electrochemistry school project, experimenting with the effects of different electrode materials on reactions. A few of the metals I wish to electroplate I have found patents for online, and scholarly articles as well. It seems with enough digging most things turn up. If I'm truly at a wall I will definitely shoot you a message.
-
Ok cool. Also check out finishing.com (http://www.finishing.com/letters/index.html) as they have a wealth of information from people in the industry. It's usually the first place I turn when I'm stuck on something.
-
@eazye1334
Could you give your experience as related to the original question posted here.
but is it not possible to plate with oxides instead?
-
@eazye1334
Could you give your experience as related to the original question posted here.
but is it not possible to plate with oxides instead?
No, it's not possible that I know of, outside of cadmium. It's unlikely you'd have enough conductivity due to the solubility issues. Also, the hydrogen evolved at the cathode surface would form hydroxides with the oxide in the tank, wreaking havoc on the pH. Hydroxide formation is an unwanted occurrence already, so upping that concern would not be a good plan.
Chlorides also play a role in the properties of the final plating. For example, copper can be plated in a whole bunch of ways: acid copper, cyanide, pyrophosphate (the only neutral bath I can think of), fluoroborate, alkaline non-cyanide, etc. The only one of those to use chlorides is the acid copper, in which case they help to brighten the deposit and dissolve the anodes. Each bath has different throwing power, speeds, ductility, adhesion, etc. Some nickel baths will use chlorides, though again it's dependent on what you want in the end. Nickel sulfamate, for example, does not require chlorides if sulfur-bearing nickel is used. Basically, the short answer is that chlorides affect more than just how you get your ions.
-
Oxides cannot be directly dissolved because O2- is a too heavily charged ion and converts to OH- in water.
Most soluble hydroxides - the alkali metal and alkaline earth metal ones - are of very active metals (potentials below -2,7 volts) that cannot be reduced (because hydrogen is reduced).
There is, however, one conspicuous exception. Thallium I hydroxide is a very soluble strong base, yet thallium metal is less active than iron - potential just -0,34.
By contrast, thallium chloride is insoluble.
Is metallic thallium easy to electroplate out of thallium hydroxide solution?
-
Thallium salts were once used as a gold plating bath additive to improve brightness, but outside of that, not a clue.
And like I said, cadmium oxide can be used as the metal source for a cadmium bath, with an alternative being cadmium cyanide.
-
Just as an aside
WIKI states
Cadmium cyanide is an inorganic compound with the formula Cd(CN)2. This white crystalline compound is used in electroplating. It is very toxic, along with other cadmium and cyanide compounds.
Soluble thallium salts (many of which are nearly tasteless) are highly toxic in quantity, and were historically used in rat poisons and insecticides.