Al or Ti? How to tell

DaveH

DaveH

Joined
Dec 2, 1999
Messages
12,249
Lets say I have a knife. The handle may either be Ti or Al. It's bead blasted so It's kinda hard to tell just by llooking.

How can I identify which type of metal the handle may be?
 
We metallurgists can tell just by looking !!... Actually color differences can tell. You could drop something like NaOH on the handle which will attack Al not Ti. Price of the knife should tell you also.
 
I was just curious if there was a quick and dirty field test that was say 80% accurate. I was wondering because of the GBU post about a company claiming Ti but sounds like Al or even stainless.
 
Isn't a magnet a fairly good test?:confused: ie the Ti shouldn't attract one whereas the Aluminum should.
 
OilMan said:
Isn't a magnet a fairly good test?:confused: ie the Ti shouldn't attract one whereas the Aluminum should.
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Magnetic attraction to aluminum would be a new one on me ...


Do you have pictures of the knife in question?
 
NaOH (lye/powdered drain uncloger/Drano) should be pretty accurate. It would defiantly be quick and dirty, and possibly eat away a portion of your knife. You could test it on some aluminum foil to see how it should act. Coatings and such might interfere with the reaction.
 
Wikipedia says that NaOH attacks Ti as well as Al so scrap that idea. If one of you had some spare Ti laying around you could test it.
 
You should really find info in places other than Wikipedia !!! "Titanium is generally very resistant to alkaline media including solutions of sodium hydroxide ..." www.timet.com
 
Here is an idea: Aluminum is a good conductor (conduction coefficent) as well as retainer (heat capacity) of heat, while titanium is a poor conductor (in relative terms) of heat. You can refrigrate it or warm in hot water for instance and then hold them in your hands and see how it feels with respect to time. Known samples would help of course, but the difference might be so large as to only require a comparison to an aluminum sample.
 
DaveH said:
How can I identify which type of metal the handle may be?
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Titanium is almost twice as dense as aluminum. You can determine the volume of an odd shaped object by just measuring how much fluid it displaces. You can also weigh it both in and out of water and use that to calculate the volume and then density.

-Cliff
 
I have often wondered this question myself.

Example 1: Spyderco Herbst in Titanium or Aluminum.
Example 2: Buck Mayo in Titanium, possibly in aluminum?



So without disolving it in corrosive material or soaking it in water, measuring displacement and precisely weighing it, I guess there is no simple way for a person to tell if a valuable crafted instrument is made of aluminum or titanium.

Edited to add: Cliff, I'm impressed with the suggestion but not well equipped to perform that test.
 
kel_aa said:
Here is an idea: Aluminum is a good conductor (conduction coefficent) as well as retainer (heat capacity) of heat, while titanium is a poor conductor (in relative terms) of heat. You can refrigrate it or warm in hot water for instance and then hold them in your hands and see how it feels with respect to time. Known samples would help of course, but the difference might be so large as to only require a comparison to an aluminum sample.
Click to expand...

Having handled both materials, I'd be surprised if you could tell by sensing relative temperature differentials by touch.

One thing you could do, since people are mentioning some pretty destructive testing scenarios:

Try finding an inconspicuous spot (like on the back where no one will be able to see, take your handy Dremel or flex-shaft tool with a stone or cut-off wheel and give it a little zap. If it sparks, it's not aluminum. Ti should emit nice white sparks.
 
jhillas said:
...not well equipped to perform that test.
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You can weigh an object as long as you have a known object of similar mass, you don't need to actually have a scale, just make one in the form of a balance. The weight of the unknown object is then the weight of the known object times the distance ratio (known/unknown) of the objects from the pivot. The reason the known object needs to be similar in mass is that otherwise the distance ratios are so large that the balance is cumbersome. For example, if the grip slab has to be hung twice as far from the pivot as your known mass then the grip slab is half as heavy. This is actually how the really precise scales used to be constructed before everything turned digital.

-Cliff
 
Having handled both materials, I'd be surprised if you could tell by sensing relative temperature differentials by touch.
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I was speaking from a thereotical point of view. I think the conduction and heat capacities properties should make it noticable if it not at room temperature to start with. But you can bring out the calorimeter...
 
I believe titanium is a fairly poor conductor of electricity, aluminum of course quite good. Perhaps a decent ohmmeter ....?
 
Her's some sample ohmeter values, taken with a digital autoranging multimeter, aligator climps and all knives with blasted finish.

Buck Mayo TNT =.4 ohm across width .6 ohm across length
Real Mayo = .5 across width, .5 acoss length
Large sebenza = .5 across width, .5 across length

I imagine the cross section of the Ti is great enough that the ohm values are low.

I don't have an Al knife to measure. If some one has an Al one give it a try.
 
DaveH said:
Her's some sample ohmeter values, taken with a digital autoranging multimeter, aligator climps and all knives with blasted finish.

Buck Mayo TNT =.4 ohm across width .6 ohm across length
Real Mayo = .5 across width, .5 acoss length
Large sebenza = .5 across width, .5 across length

I imagine the cross section of the Ti is great enough that the ohm values are low.

I don't have an Al knife to measure. If some one has an Al one give it a try.
Click to expand...
Interesting, and thanks for doing those tests, Dave. When posting that I was wondering if the cross section would be so great that the resistance would be extremely low. However I'm pretty sure even a 4-5" length of aluminum wire (16 ga. or so) is going to be <.1 ohm.

Curious ... what kind of reading do you get along the length of the lock bar?
 
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