[nigelpeckfield]

Hello, I wonder if anyone can help me. My colleague is trying to make an alloy with c70% Si, 3% B and the balance Iron. He has tried melting scrap, Silicon and Ferro Silicon along with Ferro Boron (18% B, 72% Fe) but when analyzing the finished alloy, most of the boron is lost. I think the Boron may be reacting with the Silicon to create a boron silicide which will float into the slag. Can anybody confirm this from a chemical perspective as my A level chemistry was many years ago. If this is the case I assume it will be very difficult to create this alloy as the B will always react with the Si.

Many thanks in advance for any advice.

[Enthalpy]

Hi nigelpeckfield, welcome!

I'm not easy with that, but here's what I've found, perhaps you can make more sense of it.

Silicon makes compounds with boron, for instance SiB₆
https://en.wikipedia.org/wiki/Binary_compounds_of_silicon#Group_13

SiB₆ has a very high melting point
http://www.himikatus.ru/art/phase-diagr1/B-Si.php
which exceeds the melting points of Si-Fe and of pure Si
http://www.himikatus.ru/art/phase-diagr1/Fe-Si.php
however, at 11at% B in Si (without Fe) little seems to happen. I suppose that any Si-B compound dissolves in liquid Si with this limited proportion of B.

Did you take precautions to prevent the oxidation of B by the air? B₂O₃ is seriously volatile
https://en.wikipedia.org/wiki/Boron_trioxide

Hey, if you achieve a silicon alloy that is stiff and light but not brittle, everyone is interested! Some uses need a good strength too but others (acoustics) don't.

Wish you to get better answers.

[nigelpeckfield]

Hi Enthalpy and thank you for your comprehensive reply. We did use an argon shroud to try and protect from atmospheric oxygen. The next plan is to try again but use much more Ferro Boron to see if this increases the B in the finished alloy.

Thanks once again for the time you have taken to respond.