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Thermal vacuum furnace processing of Glass-Metal sealed sensors or switches

I am an Electrochemist in glass-metal fusion assemblies for hermetically sealed switches as well as Ceramic Insulator- metal fusion for Aircraft high temperature sensors. My question today is why is it that Invar or kovar (Ni- Fe) alloy films are often used for to coating the Fe - Ni base metal terminals in the metal- glass fusion switch assemblies instead of Fe-Mn alloy films whose coefficient of thermal expansion is nearer that of Glass (alumina silicate or borosilica)?

Bassey J. Udofot
Musgegon, Michigan
2006

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Probably because Nickel Iron is commercially available and easier to plate.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2006

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The Answer given by Khozem Vahaanwala from Bangalore, India that Fe-Mn alloy films is difficult to plate in comparison to Fe-N alloy plating, is not correct. Additionally, Bright alloy films is plateable and the microstructures demonstrated in a thesis published from the University of Birmingham, Edbaston UK. The alloy films of intermediate composition has been demonstrated to be depositable from bath of simple salt with or without the use of complexing agent or additives for commercial aircraft application already in the USA. Electroless or electro deposition processing techniques is simple and possible commercially and is the basis of my question. Fe-Mn, Fe-MnP, or Fe-Ni, Fe-NiP, Fe-Zn, Fe-ZnP, Zn-Pcr possesses low frictional coefficient properties, available commercially as lubricants, anti- galling, corrosion and heat resistant coating on surfaces. I hope this article is a good information to the reading public.

Bassey J. Udofot
Musgegon, Michigan
2007

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KV's answer and his inclusion of the word "probably" admits of the possibility that there may be additional reasons that Ni-Fe is usually used. But since you've didn't like his answer, please tell us why you think Ni-Fe should be chosen for this application. Thanks.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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2007

In the first instant, Fe, Ni and Mn are commercially available and are easily depositable from aqueous solution of simple or complex baths. The microstructures of Fe-Mn and Fe-Ni alloy films are quite different from each other and therefore their properties are distinctively different. Similar to Fe-Ni, Fe-Mn alloy film possesses good sacrificial corrosion protection to structures by galvanic action and both have soft magnetic properties. In recent days, Fe-Mn films has been successfully deposited from aqueous solution, characterised and found to have interesting properties superior to Fe-Ni alloy films. I belief therefore, that the reason Khozem in his remark that "Probably because Nickel Iron is commercially available and easier to plate" is also perhaps he has not yet been aware of the fact that coherent bright thick, thin, ultra thin and nano films of Fe-Mn alloy films of various at weight compositions, surface morphologies, and nano structures have been easily deposited just as the Fe-Ni alloy films have been produced. It is not clearly understood all the reasons Fe-Ni alloy films is preferably used except perhaps that the latest advances in the electrochemical deposition of Fe-Mn alloy films has not yet been widely publicised or demonstrated for commercially applications.

Thanks

Bassey J. Udofot
Musgegon, Michigan