Titanium myths

[metalbass.com]

Just curious about a few things. They made the SR-71 out of Titanium and the space shuttle. I'm sure they use O2 all over both these machines. How can they do it but the Scuba industry can not? Also, How many flashfires, etc. etc. have been documented in standard brass or any other metal regs. or valves?

Titanium gets smaller when it gets hot. The characteristic that
makes titanium desireable for high temperature use is its crystal
structure shrinking at temperature.

The airframe of the SR-71 is very unique. To withstand the friction-generated heat at Mach 3+, over 90 percent of the airframe is made of a hybrid titanium composite. Also to withstand heat, portions have been impregnated with aluminum and are filled with nitrogen.

 

[Halthron]

Four year old thread alert. There have been more recent threads with better comments.

 

[WarmWaterDiver]

Adiabatic refers to a process at a constant temperature, or amount of heat.

What does it have to do with this? Can titanium dust combust at room temperature?

What's different about titanium than the other metals listed that makes it dangerous for oxygen service?

(I just bumped into this discussion, I'm just playing devil's advocate to feed my curiosity )

Even at 4 years old, I'm compelled to comment.

Isothermal is the term for processes at constant temperature.

Adiabatic is the term for processes with no heat exchange with their surroundings. So, heat of compression does increase temperature - as the surroundings provide no heat sink.

In the real world, nothing is ever 100% adiabatic given time - but very quick events can provide a very close approach to true adiabatic conditions.

 

[hdtran]

Titanium gets smaller when it gets hot. The characteristic that
makes titanium desireable for high temperature use is its crystal
structure shrinking at temperature.

The airframe of the SR-71 is very unique. To withstand the friction-generated heat at Mach 3+, over 90 percent of the airframe is made of a hybrid titanium composite. Also to withstand heat, portions have been impregnated with aluminum and are filled with nitrogen.

I know this is a *WAY* old thread, but I've just got to refute this.

Near standard conditions (20C to 600C or thereabouts), Titanium has a positive coefficient of thermal expansion, i.e. it grows as it gets hot. The SR-71 was designed such that the fuel tanks didn't seal until the aircraft was at supersonic speeds (and the metal around the joints expanded to seal). That said, Titanium (& alloys) coefficient of thermal expansion is lower than steel or aluminum.

With very rare exceptions, you absolutely do not want design structures using a material that changes phase (crystal structure from hexagonal close-packed to face-centered cubic, for example) and reverse the phase change in normal operation. The one exception that comes to mind is Nitinol (nickel-titanium shape memory alloy).

 

[WarmWaterDiver]

I think it's the 'reactive metal' designation / property that's the real key here. Titanium resists corrosion due to being very reactive and thus rapidly forming a tenacious oxide layer, which reduces sites for further reaction.

Shock loads and proximity to other materials which can react exothermally (like elastomers with oil) makes for a scenario where the titanium components themselves can ignite. Once started, a reactive metal fire can be quite difficult to extinguish (fire extinguisher rated for "D" materials required).

 

[Capt Tom McCarthy]

Just throwing this out there. I have a friend in the aerospace industry who makes titanium parts. He tells me that large solid pieces of titanium (such as pieces the size of a reg) wouldn't be exposed to the heat level needed to combust in any normal circumstance. However he also said that titanium dust is very combustable and burns very similar to magnesium. He's not a scientist or anything but It sounds reasonable. It's much easier to light saw dust on fire than a log.