PtNb
Platinised niobium anodes

PtNb consists of a Nb-base activated with a layer of platinum. PtNb is a superior anode-material for acidic conditions instead of PtTi. It offers a longevity where PtTi as well as PtNb can be used.

Nb is a valve metal, protected against corrosion by a very dense oxide layer. The corrosion rate of this oxide is very low and a measure for the electrochemic stability of Nb. A 10-times higher breakdown voltage than that of Ti protects the platinum layer upon the Nb-base to be under-corroded. Under anodic polarisation the pH around an anode drops and the temperature increases proportional to the current density. As the stabillity of a valve metal depends on the electrolyte, pH and temperature, these conditions are stressed under anodic polarisation with high current densities.

The Nb-base is used, where the stability of Ti is exceeded: high temperature, low pH, high current density and the need for high electric conductivity. Where PtTi- as well as PtNb-anodes are to be used, PtNb is preferred to minimize losses of Pt by under-etching and to have an electric conductivity 3-times that of Ti.

METAKEM produces PtNb with excellent Pt-adherence upon the the Nb and with every desired thickness of the Pt-layer. The 4-times higher volume price of Nb is compensated, as METAKEM re-platinises these anodes and current distributing frames can be formed out of unplatinised Ti. The mentioned pH-drop happens only at the active parts of the anode! The investment for a Nb-substrate is only once and concentrated on the active parts.

METAKEM supplies Nb in 8 standard mesh types A – H, sheets, plates, rods, wires and tubes. Semifinished Nb is on stock and can be platinised in a short time.

PtNb-anodes are used in electrolytes which do not attack the Nb. They are suitable for the following applications:

• gold strike and rhodium and other acidic baths
• high current density applications in continuous plating lines for electronic parts, for brush and jet plating
• fluoride free chromium baths operated at current densities aboves 75 A / dm²
• chromium fluoroborate and boric acid buffered baths as well as chromium baths with a minor fluoride content (approx. 0,5 g fluoride / litre)
• in cases where a mounted anode/cathode set passes a fluridic pre-treatment, rinsing is neccessary
• oxidation of Cr³ to Cr⁶ in etching solutions
• production of Cr⁶
• applications where the low electric conductivity limits the use of Ti (internal plating processes)
• cathodic corrosion protection
• redox processes of inorganic and organic substances
• contact parts for electrochemical machining

Let us know your requirements and we give recommendations and supply samples for your own evaluation.