Phase transitions of silver and silver-palladium alloys immersed in mercury.
A series of Ag-Hg and Ag-Pd-Hg phases have been prepared by immersion in mercury and subsequent heat treatment of pure Ag and a series of Ag-Pd alloys. Phase transitions, along with the changes involved in morphology and chemistry, are investigated. Experimental results indicate that when mercury-immersed Ag discs are heat-treated at 90 degrees C for 12 h, large (>50 microm) crystals with Ag/Hg atomic ratios close to those of stoichiometric AgHg(2) form on the Ag surface. Heat treatment for 36 h causes these crystals to disintegrate into smaller (majority <10 microm) Ag(2)Hg(3) (gamma(1)) crystals. After 60 h, the stoichiometric gamma(1) crystals further breakdown into even smaller stoichiometric AgHg(beta(1)) crystals. The oft-referenced beta(1) phase Ag(1.1)Hg(0.9) is not supported in the present study. Addition of Pd to Ag has a dramatic effect on the morphology of the gamma(1) phase. With more addition of Pd, large-faceted and elongated gamma(1) crystals tend to grow in the midst of smaller matrix gamma(1) crystals. All three different Pd-containing crystals have (Ag + Pd)/Hg ratios very close to those of the stoichiometric gamma(1) phase, indicating that added Pd tends to replace Ag, rather than Hg, in the gamma(1) phase.
Chern Lin
J H
JH
Department of Materials Science and Engineering, National Cheng-Kung University Tainan, Taiwan, Republic of China. chernlin@mail.ncku.edu.tw
Yuan
J Y
JY
Ho
W F
WF
Ju
C P
CP
D003722:Dental Alloys / Q000737:chemistry*; D006358:Hot Temperature; D007101:Immersion; D008628:Mercury; D008855:Microscopy, Electron, Scanning; D010165:Palladium / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D018030:Silver Compounds / Q000737:chemistry*; D013499:Surface Properties; D014961:X-Ray Diffraction / Q000379:methods
D003722:Dental Alloys; D018030:Silver Compounds; D012834:Silver; D010165:Palladium; D008628:Mercury