|MadSci Network: Chemistry|
Though it appears to common knowledge that iron and platinum do not form alloys with mercury - which is what an amalgam is - it seems like there is evidence in the literature on the contrary. Iron-Mercury amalgam: Stability and magnetic properties of an iron-mercury alloy Journal of Physics Condensed Matter, Volume 4, Number 44, 8627 (1992). Authors: S. Linderoth, S. Morup The abstract of the article reads thus: Iron amalgams have been studied by Mossbauer spectroscopy and magnetization measurements between 7 and 425 K. The Mossbauer spectra at 12 K show that the iron is present in at least two different sites. After heat treatments the Mossbauer spectra change into the typical spectrum of alpha -Fe, and the magnetic moment per iron atom, at 275 K increases. It is suggested that the iron forms a metastable alloy with mercury, which decomposes at about 360 K. The Fe-Hg alloy is found to be ferromagnetically ordered with a corresponding Curie temperature of about 445 K. It is possible that since the alloy decomposes at 360K (87C) that it has not found use in many applications and hence is not very popular. Platinum-mercury amalgam: Found this in the book... Dental chemistry and metallurgy - Clifford Mitchell Platinum amalgam: Metallic platinum does not unite with mercury. Spongy platinum unites with mercury when triturated in a warm mortar with the latter or with acetic acid. Or Sodium amalgam if introduced into a solution of platinic chloride, will form an amalgam of silvery appearance. The amalgam containing 100 parts mercury and 15.48 parts platinum, has a specific gravity of 14.29 and has metallic lustre when rubbed. 100 mercury to 21.6 platinum is a dark gray solid; 100 mercury to 34.76 platinum is of 14.69 specific gravity dark gray but of no lustre etc. The solid amalgam containing the most mercury is PtHg2. Mercury exposed to platinic chloride for some time forms a thick pasty amalgam. The book also says the amalgam of platinum and mercury along does not harden well. So it is possible that this is a reason why it has not found use and much more is maybe now known about it. Having said this it appears that both iron and platinum dont necessarily form "strong alloys" with mercury. An alloy is a solid solution of two or more elements. At least one is usually a metal if not all components. What determines a solid solution is whether atoms of each component are able to occupy the others' position or fill in interstices of one another's lattices. It is possible - though I dont know this for sure - that iron and platinum do not have a strong interaction with mercury - and hence are not too compatible with mercury - this may result in alloys with mercury being formed only at low temperatures and these amalgams falling apart at higher temperatures. Hope this helps.
Try the links in the MadSci Library for more information on Chemistry.