December 02, 2020, 10:20:16 PM
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Topic: Chrome plating  (Read 376 times)

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Offline tms9918

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Chrome plating
« on: October 18, 2020, 05:28:53 AM »
Many screws appear yellow, like this

They are known as chrome plated, but, if I am not wrong,  chrome plating is for having a shiny, silver like color.
What do they add that makes them yellow?
I had some oxidized screws (the oxide was white). I stripped the oxide with acetic acid. This removed the plating as well, so I plated them with nickel. This clearly changed the color to gray. I would like to restore them to the original color, how can I do that? 
And, is there something other than acetic acid that only dissolves the oxide and not the plating itself?
« Last Edit: October 18, 2020, 05:47:44 AM by tms9918 »

Offline Enthalpy

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Re: Chrome plating
« Reply #1 on: October 18, 2020, 09:03:55 AM »
Chromated. This screw is anodized.

Offline tms9918

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Re: Chrome plating
« Reply #2 on: October 19, 2020, 02:03:47 AM »
Sorry, I just posted a pic of a screw I found online to describe the color. I attach a pic of the actual screw. I would doubt they went so far at anodizing. It's a screw from a sega console, manufactured in 1982, and my guess would be they tried to choose the cheapest possible screws.

Offline Borek

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Re: Chrome plating
« Reply #3 on: October 19, 2020, 04:04:49 AM »
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline tms9918

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Re: Chrome plating
« Reply #4 on: October 19, 2020, 04:13:54 AM »
Thank you, I believe it's exactly this!
It seems a pretty nasty chemical
https://labchem-wako.fujifilm.com/sds/W01W0116-0365JGHEEN.pdf
Is it this bad even at low concentrations?
« Last Edit: October 19, 2020, 04:24:35 AM by tms9918 »

Offline Borek

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Re: Chrome plating
« Reply #5 on: October 19, 2020, 06:37:06 AM »
For the record: that's the same process Enthalpy referred to, not sure why he called it anodization though.

As long as you treat it seriously (gloves, glasses, not doing anything stupid like tasting or breathing in a cloud of dust) and you don't deal with it on a daily basis (so that effects can't accumulate) it is not much worse than most chemicals used in the lab (and as a matter of habit they all should to be treated seriously, just in case). It can be PITA to dispose off properly though, as Cr compounds are heavily regulated.
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Offline tms9918

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Re: Chrome plating
« Reply #6 on: October 19, 2020, 08:32:45 PM »
Thank you! that sounds much better.

Wikipedia reports

Quote
The widely used Cronak process for zinc and cadmium consists of 5–10 seconds of immersion in a room-temperature solution consisting of 182 g/L sodium dichromate (Na2Cr2O7 · 2H2O) and 6 mL/L concentrated sulfuric acid.[5]

If I am not wrong, 1 mol of sodium dichromate  is 298g. That gives 0.6 mol/L.
Searching for places they sell solutions (for instance this ), I found concentrations of 1/60(=0.0166) to 1/6(=0.166), way lower than than.
Should I go for the powder instead? Or is the wikipedia's value off?




Offline Borek

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Re: Chrome plating
« Reply #7 on: October 20, 2020, 03:09:06 AM »
Ready solutions are most likely for applications in analytical chemistry and their concentrations reflect that.
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Offline tms9918

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Re: Chrome plating
« Reply #8 on: October 24, 2020, 01:52:21 AM »
Thank you. I found someone selling the mix (probably a variation of it).
https://janekits.com.au/products/150-ml-gold-bright/

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