Connection between copper and titanium

[Marcopolo]

Hello,

I am currently investigating how to connect copper busbars or cables to a titatium busbar on a DC voltage system.

What are the requirements/standards?

 

[James]

This sounds like a specialist device, have you asked the manufacturer how they recommend connecting it?

 

[pc1966]

I must say I have never seen titanium being used for electrical work, only as a high strength to weight material for specialist bolts, etc, in aerospace applications (with very high price to match it). For example:

RS PRO Titanium Alloy Hex Socket Cap Screw, DIN 912, M5 x 20mm | RS

uk.rs-online.com

And yes, that is about £13 for a single screw!

Chemically it is a bit like aluminium in that it has good corrosion resistance due to a thin film of oxide that forms, but electrically it is far poorer than aluminium (about 15 times higher resistivity) so worse than iron (about 5 times Al) closer to stainless steel (about 24 times Al).

Can you share with us the application?

 

[Marcopolo]

Hello, this will be the connection between a converter's DC bus to a hydrogen electrolysis stack. The converter has copper busbar, whereas the stack titanium.
Does anyone have any experience or know the contact resistance between titanium and copper or tinned copper or nickel plated copper?

 

[pc1966]

Hello, this will be the connection between a converter's DC bus to a hydrogen electrolysis stack. The converter has copper busbar, whereas the stack titanium.
Does anyone have any experience or know the contact resistance between titanium and copper or tinned copper or nickel plated copper?

Off hand, no.

You can get specialised low resistance meters using Kelvin clip probes (separate current force and voltage monitor) to allow the measurement of very low resistances, typically done in substations and similar when very high currents flow and a poor connection will fail in a short time. For example, the "Megger DLRO10X Ductor" but they are expensive (around £3k) so often hired for occasional tests.

Megger DLRO10X Ductor Micro-Ohmmeter

Megger DLRO10X Low Resistance Ohmmeter - Ductor The Megger DLRO10X is a fully automatic ductor that will select the most suitable output current (up to 10A DC) in order to measure resistance values between 0.1 micro-Ohms to 2000 Ohms, across seven separate ranges. For users who desire more...

www.test-meter.co.uk

In your application I would worry about galvanic corrosion, and in this case the chart Figure 4 has the various conductors:

Titanium - Types of Corrosion

Titanium is susceptible to corrosion in some environments despite its relative stability. Some of these types include general, galvanic and crevice corrosion, as well as stress corrosion cracking, anodic breakdown pitting and hydrogen embrittlement.

www.azom.com

It shows Titanium as similar in electronegativity to nickel, so nickel plated copper is potentially a good choice. However, copper itself is not very far off it. I don't know what the risk would be for contamination or the operating temperature, but in humid or outdoor applications you would often see special grease used to inhibit corrosion.

The cheapest and nicest to work with it Vaseline (petroleum jelly) as it is safe for use on human skin, hence it frequently was used on car battery terminals to reduce corrosion with the humidity and risk of sulphuric acid contamination.

You can also get variations on the theme for connections involving aluminium where it is a petroleum base with fine zinc particles included (such as 'Noalox' and 'Penetrox') as well as much nastier versions with zinc chromate in them (quite toxic). However, I have no idea if zine-based compounds are a good idea with titanium/copper, I strongly suspect not!

Also sometimes used are silicone based grease, that is typically low toxicity and flammability but I'm not sure it is as low a pressure lubricant as the other.

Extreme pressure greases that are typically used for lubrication of bearings or fasteners for reliable torque-based tightening are not good for electrical work as they are designed to minimise metal-metal contact!

I suspect you are going to have to find someone else with such knowledge, or to work with a local university or similar to develop something special for this application.

 

[Marcopolo]

Thank you. The second site gives some info. I will dig deeper.