Yet Another Cycling Forum

General Category => The Knowledge => OT Knowledge => Topic started by: hubner on August 30, 2019, 12:27:12 am

Title: Titanium and magnet
Post by: hubner on August 30, 2019, 12:27:12 am
If a magnet sticks to a piece of metal , would that prove the metal is not titanium?
Title: Re: Titanium and magnet
Post by: rafletcher on August 30, 2019, 01:29:17 am
Yes. It's also the reason my wife can get through airport scanners with two metal hips.
Title: Re: Titanium and magnet
Post by: Wobbly John on August 30, 2019, 06:50:58 am
I have a '90s MTB with the handlebars marked as titanium, but a magnet sticks to them...  >:(
Title: Re: Titanium and magnet
Post by: pcolbeck on August 30, 2019, 07:15:39 am
Titanium bikes arent pure titanium though are they. They are an alloy of titanium and vanadium (and maybe aluminium sometimes). Isn't vanadium very magnetic? Its used in superconducting magnets.
Title: Re: Titanium and magnet
Post by: LittleWheelsandBig on August 30, 2019, 07:20:11 am
A few Ti bike frames and components were made of commercially pure Ti in the old days but most modern frames are made from 3/2.5 or 6/4 Ti which have pretty low percentages of alloying materials.
Title: Re: Titanium and magnet
Post by: gibbo on August 30, 2019, 08:04:04 am
A quick search into the properties of my Ti bike shows a vanadium content of 2.5%. I have no idea if vanadium is magnetic (I thought it was only ferrous materials that are??).

I'll put a magnet to the frame and see what happens. I know it's Ti because it has a sticker on it saying so  ;D.
Title: Re: Titanium and magnet
Post by: vorsprung on August 30, 2019, 08:38:26 am
A quick search into the properties of my Ti bike shows a vanadium content of 2.5%. I have no idea if vanadium is magnetic (I thought it was only ferrous materials that are??).

I'll put a magnet to the frame and see what happens. I know it's Ti because it has a sticker on it saying so  ;D.

Iron, Cobalt and Nickel are strongly magnetic
According to wikipedia Vanadium alloy is used in "super conducting magnets"
Title: Re: Titanium and magnet
Post by: Vernon on August 30, 2019, 09:01:16 am
Vanadium is paramagnetic at room temperature, so will not stick to a magnet. A lot of vanadium used in alloys is ferro-vanadium, so can contain an amount of iron, but is more likely used when alloying steel. A Ti/Vn alloy used for bike frames is unlikely to show any magnetic attraction, since any Fe will only be present in trace amounts. Disclaimer - I don't know this for certain and haven't studied magnetism since about 25 years.
Title: Re: Titanium and magnet
Post by: Brucey on August 30, 2019, 10:04:39 am
simple answer;

Magnets don't 'stick to' titanium alloys (as found in bike parts). This is very easy to demonstrate to yourself by wafting a magnet at some new, genuine Ti parts.

There are lots of plated steel bike parts which are 'titanium coloured'. Often the owners live in blissful ignorance until their 'titanium parts'  go rusty....

The more nuanced answer is that there can be a weak attraction between some materials and magnets; for example most nominally austenitic stainless steels contain a small percentage of ferrite and a weak attraction can be felt; this attraction is about 1/10th or 1/20th as strong as the attraction of the same magnet to a piece of ordinary  steel; the magnet won't 'stick' per se and at most, commercial Ti alloys won't even exhibit this amount of magnetism.  Thus if the magnet 'sticks to' a piece of 'titanium' then it ain't titanium, simple as that. 

cheers
Title: Re: Titanium and magnet
Post by: mrcharly-YHT on August 30, 2019, 11:19:34 am
A lot of stainless steel isn't very magnetic.

I have a lump of it (6mm thick, ~140mm long) in my wrist. Not even disk magnets stick to my arm or show any sign of being attracted to it.
Title: Re: Titanium and magnet
Post by: Brucey on August 30, 2019, 11:56:20 am
A lot of stainless steel isn't very magnetic...

It varies, hence my mention of 'nominally austenitic'.  There are ferritic, martensitic, austenitic , precipitation hardening and duplex grades, amongst others; they all have different magnetic properties.

FWIW very few nominally austenitic  grades contain absolutely no ferrite whatsoever, but it would take a very strong magnet or a sensitive instrument to pick  up a small percentage  if it is buried in your arm.

cheers
Title: Re: Titanium and magnet
Post by: The French Tandem on August 30, 2019, 12:00:44 pm
I'll put a magnet to the frame and see what happens. I know it's Ti because it has a sticker on it saying so  ;D.

If it's unpainted, ridden in the rain, and not rusty, chances are that it's not a ferrous material! Okay, it does not prove that it is titanium.

A
Title: Re: Titanium and magnet
Post by: Kim on August 30, 2019, 02:04:07 pm
The more nuanced answer is that there can be a weak attraction between some materials and magnets; for example most nominally austenitic stainless steels contain a small percentage of ferrite and a weak attraction can be felt; this attraction is about 1/10th or 1/20th as strong as the attraction of the same magnet to a piece of ordinary  steel

Where's that picture...

(http://www.ductilebiscuit.net/gallery_albums/random/IMG_1253.sized.jpg)
Title: Re: Titanium and magnet
Post by: caerau on August 30, 2019, 04:06:10 pm
Titanium bikes arent pure titanium though are they. They are an alloy of titanium and vanadium (and maybe aluminium sometimes). Isn't vanadium very magnetic? Its used in superconducting magnets.


Couple of things about superconducting magnets.  With (very) rare exceptions, you're going to be needing liquid helium to be getting to the temperature at which it is a superconductor.  Even the superconducting materials with the highest temps still need cooling with liquid nitrogen.  I suspect you're not using cryogenic liquids in your experimentation ;)
Without looking it up - most high-temp superconductors are compounds - not metal alloys.  I.e. it might contain 'vanadium' in the same way that rust contains iron.  I.e. it's not in its metallic form and isn't magnetic (in a superconducting material - without being cooled to like ~4 K)


As has been said - if it's ferro-magnetic - it's not titanium.
Title: Re: Titanium and magnet
Post by: mrcharly-YHT on August 30, 2019, 04:31:49 pm
the superconducting materials I've seen looked like a lump of black beeswax and required liquid nitrogen
Title: Re: Titanium and magnet
Post by: hellymedic on August 30, 2019, 04:43:50 pm
A lot of stainless steel isn't very magnetic.

I have a lump of it (6mm thick, ~140mm long) in my wrist. Not even disk magnets stick to my arm or show any sign of being attracted to it.

[OT]
Some certainly is!
I tend to play with cutlery whilst awaiting restaurant meals and some knife handles are sufficiently magnetic to lift other cutlery...
Title: Re: Titanium and magnet
Post by: sizbut on August 30, 2019, 05:35:36 pm
The more nuanced answer is that there can be a weak attraction between some materials and magnets; for example most nominally austenitic stainless steels contain a small percentage of ferrite and a weak attraction can be felt; this attraction is about 1/10th or 1/20th as strong as the attraction of the same magnet to a piece of ordinary  steel

Where's that picture...

(http://www.ductilebiscuit.net/gallery_albums/random/IMG_1253.sized.jpg)

Nope. The position of the other hand and the curving of the palm are all "magicians sleight of hand" alarms.
Title: Re: Titanium and magnet
Post by: caerau on August 30, 2019, 05:52:24 pm
the superconducting materials I've seen looked like a lump of black beeswax and required liquid nitrogen


Liquid helium mostly, only the very top-end ones have a superconducting temperature within the reach of liquid N2.


The superconducting magnets we use in our NMR spectrometers (that's the same as MRI in hospitals) have a liquid helium core jacket and then a larger outer liquid nitrogen jacket to keep the liquid helium cold!



Title: Re: Titanium and magnet
Post by: Kim on August 30, 2019, 07:09:28 pm
The more nuanced answer is that there can be a weak attraction between some materials and magnets; for example most nominally austenitic stainless steels contain a small percentage of ferrite and a weak attraction can be felt; this attraction is about 1/10th or 1/20th as strong as the attraction of the same magnet to a piece of ordinary  steel

Where's that picture...

(http://www.ductilebiscuit.net/gallery_albums/random/IMG_1253.sized.jpg)

Nope. The position of the other hand and the curving of the palm are all "magicians sleight of hand" alarms.

The palm's curved due to general lack of bones, and because barakta's wrist is fused in that position by the pins the magnet is sticking to.  Her other hand's in that position to prevent wobble because her shoulder's out of joint to hold her left hand up like that.  The magnet doesn't stick strongly enough to the ostensibly stainless steel pins to allow you to do the really cool magnet hanging upside down photo, and that's a bastard strong magnet.
Title: Re: Titanium and magnet
Post by: chrisbainbridge on August 30, 2019, 08:40:11 pm
I do not know how long barajas wrist has been fused but titanium wrist fusion plates are relatively new.  If it is more than 5 years ago it is a steel alloy with steel screws. The only wrist fusion plate for donkeys years was made by AO foundation and being swiss-German steel was the thing.
Title: Re: Titanium and magnet
Post by: Kim on August 31, 2019, 04:17:18 pm
It's a pair of late-1980s pins, not a plate, and as far as we know it's a stainless steel (that's presumably paramagnetic).  We didn't expect the magnet to do anything, and were really impressed when it just barely stuck.