DEALLOYING OF PdNi5 ALLOY IN 0.5M SULFURIC ACID

Abstract

Palladium alloys with low nickel content are commonly used as catalyst-trap for platinum or platinum-rhodium catalysts in the process of production of nitric acid. Pure palladium and, consequently, alloys with a high concentration of Pd are highly resistant in many corrosion environments across the full pH range, from 0 to 14 and beyond, in the presence of different anions. Mineral acids do not affect palladium, especially at lower concentrations; they can be dissolved just in the mix of them. However, nickel in the alloy can be selectively dissolved in single mineral acid with the use of an oxidation agent or anodic polarization, which is the more controllable process. The aim of the work is the research of dealloying of PdNi5 in 0.5M sulfuric acid under anodic polarization conditions. This study used open circuit potential, linear polarization resistance, and chronoamperometry as electrochemical methods. Scanning electronic microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and inductively coupled plasma mass spectrometry (ICP-MS) were used as structural and analytical techniques for the study of PdNi5 alloy dealloying in 0.5M sulfuric acid at three different anodic potentials.

Legure paladijuma sa niskim sadržajem nikla se obično koriste kao havatači katalizatora za platinu ili platina-rodijum katalizatore u procesu proizvodnje azotne kiseline. Čisti paladijum i posledično legure sa visokom koncentracijom Pd su visoko otporni u mnogim korozionim sredinama u punom pH opsegu, od 0 do 14 i više, u prisustvu različitih anjona. Mineralne kiseline ne utiču na paladijum, posebno na nižim koncentracijama; može se rastvoriti samo u njihovoj mešavini. Međutim, nikl u leguri može se selektivno rastvoriti u jednoj mineralnoj kiselini uz upotrebu oksidacionog agensa ili anodne polarizacije, što je proces koji se može više kontrolisati. Cilj rada je istraživanje dealloying-a PdNi5 u 0,5M sumpornoj kiselini u uslovima anodne polarizacije. Ova studija je koristila potencijal otvorenog kola, otpor linearne polarizacije i hronoamperometriju kao elektrohemijske metode. Skenirajuća elektronska mikroskopija sa energetski disperzivnom rendgenskom spektroskopijom (SEM-EDS) i masena spektrometrija induktivno spregnute plazme (ICP-MS) korišćene su kao strukturne i analitičke tehnike za proučavanje dealloying-a legure PdNi5 u 0,5M sumpornoj kiselini na tri različita anodna potencijala.