Firstly I should note that I am not a metallurgy expert and I would
be more inclined to listen to the opinions of experts such as Mr
Binnion, rather than myself.
Secondly, on re-reading my response to Mr Korth’s original post I
was somewhat embarrassed by my sanctimonious tone and would wish to
apologise if I have inadvertently given offence.
To return to the point, titanium has some unusual characteristics as
a metal, amongst which is that the metal will ignite in a normal
oxygen atmosphere before reaching its melting point.
It also has a comparatively low rate of thermal conductivity, some
14 times less than that of gold or around 20 times less than that of
silver.
While there is not a “one for one” correspondence, because thermal
conduction is material dependant and profoundly complicated, for all
practical purposes another way of looking at it is that allowing a
torch flame to dwell on a single point, titanium will heat up at the
dwell location some 20 times faster than its silver compatriot due to
the much slower rate of thermal dissipation through the balance of
the object.
I am sure all of us are familiar with iron binding wire heating to
white heat and melting through while the object we are attempting to
solder is still 100’s of degrees below soldering temperature, a
similar effect to that described above.
All of these attributes then lead to the outcome that it is
surprisingly easy to inadvertently ignite the material and the real
issue of what happens when titanium does ignite. From first hand
personal experience I can assure you that it is a situation to be
avoided if at all possible.
The material burns very aggressively and with a significant amount
of heat, controlling the fire is decidedly counter intuitive.
In my circumstance I stabbed the burning pick,( more accurately a
spatula about 120mm long, 5 - 10mm wide and 1mm thick), into the
charcoal solder block, it did’t go out!
I dipped it into a jar of water on the bench, it did’nt go out!
By now the pick was too hot to hold and I dropped it, unfortunately
straight onto the torch hose where it promptly began to burn through
it.
It was like something out of a Marx brothers movie and would have
been hysterically funny if the possible outcomes had not been so
serious.
I managed to manoeuvre it into the pickle pot where it finally burnt
out.
On investigating the matter I found that this was probably amongst
the least desirable of the remedies I could have employed. There are
recorded instances of titanium sheet spontaneously igniting following
withdrawal from a stripping bath at temperatures as low as 330 and
there were a number of refinery fatalities from titanium fires and
the subsequent explosions following attempts to extinguish the fires
with water.
Most materials handling recommendations suggest that in the event of
ignition isolate the material and allow it to burn out, this is not
always a practical option in the limited space workbench environment.
I have subsequently switched to using tungsten.