Corrosion of Au-Pd-In alloy in simulated physiological solutions

The corrosion of Au-Pd-In alloy, which is of great importance in dentistry, has been studied using an electrochemical quartz crystal microbalance (EQC M) in simulated physiological solutions. The alloy was deposited on quartz substrates by means of magnetron sputtering (MS). Analysis performed using X-ray photoelectron spectroscopy showed that the chemical composition of th e sputtered deposit was similar to that of the MS target made of convention al casting alloy. Investigations by X-ray diffraction indicated a crystalli ne structure of the MS alloy. The electrochemical and corrosion behaviour o f the Au-Pd-In alloy was studied in three simulated physiological solutions : 0.9 M NaCl, 0.1 M NaCl + 0.1 M lactic acid and artificial saliva. Determi nation of break down potential was complicated by the anodic gold dissoluti on due to formation of a chloride complex. The onset of anodic currents, th erefore, indicated not the potential at which the passive layer starts to b e destroyed, but the exceeding of the Au/AuCl4- equilibrium potential, whic h does not directly reflect corrosion resistance. The EQCM measurements und er open circuit conditions indicated corrosion as an increase in mass, caus ed by the accumulation of corrosion products on the alloy surface. The incr ease in mass in acidic solution (pH 2.2) was similar to that in neutral sol ution (pH 6.5), which implies dissolution of corrosion products to be insig nificant.