Abrasion-resistant platinum-rhodium layers for sparkling jewelry
With the strongly acidic alloy electrolyte PLATUNA®-Alloy RH, smooth, bright and crack-free platinum-rhodium coatings can be deposited up to a layer thickness of 0.5 μm. The deposited coatings are characterized by a brilliant luster and, in contrast to conventional platinum coatings, do not exhibit a yellow tint.
An important advantage of the coating is the high hardness due to the rhodium content. Furthermore, the electrolyte has a low sulfuric acid content and is therefore less aggressive to the coating substrate. The deposition rate is independent of the current density, which leads to an optimum layer thickness distribution. No precipitation occurs and the platinum concentrate does not have to be stored in the refrigerator.
Electrolyte characteristics
Electrolyte type Strongly acidic
Metal content 1.2 (0.8 - 1.6) g/l Pt, 0.3 (0.2 - 0.4) g/l Rh
pH value < 1
Operating temperature 60 (55 - 65) °C
Current density range 5 (0.5 - 10) A/dm²
Plating speed approx. 0.12 μm/min at 5 A/dm²
Deposition rate approx. 4.7 mg/Amin at 5 A/dm²
Coating characteristics
Coating Platinum rhodium
Alloy composition approx. 80 % Pt, approx. 20 % Rh
Colour of deposit White
Brightness Bright, brilliant
Hardness not measurable, approx. 600 HV
Max. coating thickness approx. 0.5 μm
Density of the coating approx. 18.7 g/cm³
Advantages
Excellent brightness without yellow tint
Longer durability
High abrasion resistance
Current density independent
Easy handling - no cold storage and no precipitation
Applications
Jewelry
Watches
Writing implements
Spectacles frames
Bathroom fittings
