Originally Posted by
Falanx
The easiest non-destructive way is to find yourself a short, *clean* aluminium tube, take out the forks and headset, rub a little bit of scourer or scotch pad down inside the head tube and then press the short bit of aluminium to the interior wall of the headtube, making a good contact.
Break out a digital multimeter and look for a voltage, of more than 0.3v. See one, it's Ti, or a stainless steel/steel. No real big voltage difference, aluminium alloy.
Terrific idea, needs one modification: add a salt bridge between the metals. With a salt bridge you'll be able to measure the potential difference reasonably easily.
The contact potential (with no salt bridge) is pretty well impossible to measure, for reasons related to the energy distribution which causes the contact potential in the first place.
A salt bridge, preferably in gel form, will solve this because you've then got a Galvanic potential which is much more robust. Getting a salt bridge in gel form is surprisingly easy: "Personal lubricant" works OK, but adding a bit of common salt to the lube works even better.
The cell can be made using simple alfoil as the test electrode: you must hold the foil so it contacts the lube but not the Ti. Doing a quick test using this method using the salted lube I measured a potential of about 180 mV with an ordinary Fluke multimeter. This is lower than the 290 mV difference between the standard electrode potentials but you'd expect some losses with this crude setup, plus I'm not sure what the "true" potential should be given that the Ti is an alloy (with Al and V).