platinum &iridium loops

[wajdi]

HI
I have loops made of 85% platinum and 15% iridium. It brokes down after 3 or 4 steralization cycles (by getting red on Bunsen Burner) please advice reason and solution
thanks

[Gokul43201]

To diagnose a reason, if lucky, we would need more information. Can you specify the dimensions of the loops, the details of the heat treatment and the mode of failure? Also, the quality of the alloy is important - can you tell us the complete composition, including trace impurity levels?

As for providing a solution, we need to know what you are using the hoops for and why you are sterilizing them?

I've heard of Pt-Ir screens being used in rocket engine chambers where temperatures get to be close to 1000C. There's also one or two reports of embrittlement at high temperatures due to Group III impurities. I may have something bookmarked on my work computer.

[Astronuc]

The fracture could be due to embrittlement due to high temperature oxidation of the grain boundaries.

In rocket motors, the environment is likely oxidation deficient. In LOX/LH2 motors, the working fluid is usually slightly enriched in H2 to enhance specific impulse, Isp.

[Gokul43201]

The fracture could be due to embrittlement due to high temperature oxidation of the grain boundaries."It has to be grain boundary embrittlement" (for brittle failure) - that was my first thought too.

In rocket motors, the environment is likely oxidation deficient. In LOX/LH2 motors, the working fluid is usually slightly enriched in H2 to enhance specific impulse, Isp.I think the stuff I'd read was with hydrazine fuel engines - again a highly reducing atmosphere, that serves as an oxidation inhibitor. So again, I think you're right that it's probably oxidation related embrittlement. The reason I was a little wary to suggest oxidation is because of the nature of the alloy. Pt-15%Ir is probably the most corrosion resistant alloy there is. That's the reason the SI uses it as a Pt-Ir block as the standard measure of the kilogram (and until some years ago, used it as the standard measure of the meter as well).

(long time, no see, Astro - you been traveling?)

[Astronuc]

"It has to be grain boundary embrittlement" (for brittle failure) - that was my first thought too. Oxygen attack on the grain boundaries is a notorious problem for refractory metals and alloys.

I think the stuff I'd read was with hydrazine fuel engines - again a highly reducing atmosphere, that serves as an oxidation inhibitor. So again, I think you're right that it's probably oxidation related embrittlement. The reason I was a little wary to suggest oxidation is because of the nature of the alloy. Pt-15%Ir is probably the most corrosion resistant alloy there is. That's the reason the SI uses it as a Pt-Ir block as the standard measure of the kilogram (and until some years ago, used it as the standard measure of the meter as well). At room or low temperature, that is very true. At high temperature, oxidation of grain boundaries is a problem. Good point about the impurities. I hope you post whatever you have bookmarked on your computer.

(long time, no see, Astro - you been traveling?) Yep.

[Gokul43201]

I hope you post whatever you have bookmarked on your computer.Can't find it Astro. Guess I didn't bookmark it after all. :frown: