Use of Platinum Clad Anodes for Hard Chrome Plating Operation(2001)
Q. We are looking for a information on use of Platinum Clad Anode for Hard Chrome Plating operation. Can it be used in Hard Chrome Plating operation in place of conventional Lead Tin / Antimony Lead Anode?R. K. Khare
- Mumbai, Maharashtra, India
A. Dear Mr. Khare,
Platinised Titanium can be definitely used for Hard chrome plating. Only disadvantage is that it very expensive and it does not convert trivalent chrome back to hexavalent chrome. The chrome chemistry should also not contain any Fluoride.GS sharma
- Mumbai, India
A. The problem of Trivalent can be solved by keeping some lead in solution. Say addition of lead carbonate in bath can create a film on platinized titanium which can keep bath in balance. The ratio of anode and cathode will also play role in maintaining balance. The life of platinized titanium anode is very long.Payal Mag
- Charlotte, North Carolina
A. Anodes for Chrome Plating in Fluoride Containing Baths Fluorides are added to Cr6+- and Cr3+- baths. Sodium fluoride up to 500 mg F-/ l is added to activate steels by polarity reversal. Fluoroborates or silicofluorides are added in self-regulating Cr6+-baths. The F--content varies with the bath producers and reaches up to 2 g F-/l.
Only the free F- attacks the metals. The severeness of the corrosion depends on the F-content, other bath parameters and the anodic current density and starts from the weakest surface areas, like scratches, fissures and pores in a coating. The user seldom knows the F--content of his bath. Therefore tests are advised for the producers or users of chrome baths.
Unplatinised Ti, Nb or desired other noble metals are submerged into the chrome bath under working conditions, contacted anodically. While increasing the voltage the tested metal shows with the jerky current increase it's breakdown-voltage.
Practical experience shows
Ti withstand F- up to 10 mg / l, a PTA with 5 microns Pt works nearly one year at 50 mg F-/ l, nevertheless we recommend for this use a PNA. Nb withstands a F--content until 600 mg / l, a PNA is used from 50 to 500 mg F-/ l up to currents of 20 Amps / sq dm. For even higher F--contents PTW can be used. But metal mesh out of tungsten cannot be produced.
Also fluoride is added to decorative black Cr3+-baths. For these baths mixed oxides activated titanium (MMOA) is applied. In the version of IrTa-oxide users have added F- up to 50-100 g F-/ l. The coating withstands up to 600 g F-/ l, but scratches and pores in the coating limits the use. The whole anode immersed inclusive the splash zone needs to be covered with the MMOA-layer.
PTA with 5 microns Pt-layer failed after 11 months in a bath of 90 mg F-/l. MMOA Ti-anodes were used for years in a trivalent chrome bath at 70 mg F-/l.
PTA can only be used at low F--content of ~ 10 mg F-/l. For F--content up to 600 mg/l PNA is be used, higher F--content requires tungsten as the base. The user is advised to test the suitability of Nb or W as anode substrates under the actual plating conditions.K.S. Selva
Sai Electro- - Chennai, India
A. Platinised Niobium anode is the best solution for Hard chrome plating bath. If you have high fluoride in the bath platinised titanium will not stand.Vanajambika Jeyakumar
- Chennai, India
Q. I have a problem that trivalent chromium amount rise.
We use platinised titanium basket anode and lead rod
What can I do about the problem?
How can I reduce amount of trivalent chromium?
June 6, 2013
A. For Fikret, you can reduce trivalents in hard chrome by using a porous pot.Zaim Frluckaj
- Los Angeles, California, USA
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