Tanja Matković

Passivity of Co-Cr-Mo alloys in lactic acid solutions

The method of potentiodynamic polarization was used to obtain the electrochemical measurements of ten experimental Co-Cr-Mo alloys with different chemical composition in two solutions of 0.1 % lactic acid (LA): medium A containing Cl--ions (0.1 % LA in artificial saliva, pH 6.52) and medium B without Cl--ions (0.1 % LA in distilled water, pH 2.99). These solutions as representative of oral cavity conditions were chosen in order to see if the alloys could be used in dental practice. Wironit® was used as reference material. In vitro experiments have shown that susceptibility to local corrosion was more pronounced in solution A. In contrast, the tendency to general corrosion was greater in solution B. Referring to pitting potential of Wironit®, samples 3 (Co55Cr40Mo5), 6 (Co60Cr30Mo10) and 9 (Co55Cr20Mo25) have shown the best performances with the highest Epitt value in both media. The same is valid for these three alloys if general corrosion was considered.

A new intermetallic phase in the Pd-Pb-As system

Abstract A new ternary compound was identified in the Pd-Pb-As system. The Pd 3 Pb 2 As phase crystallizes with an orthorhombic structure in the space group Cmc 2 1 , a = 1.1857(2) nm, b = 0.6861 (1) nm and c = 0.5808(1) nm, Z = 4, although the crystals show quasi-hexagonal symmetry. This structure shows a complex similarity to the NiAs type of structure. The palladium atoms are octahedrally coordinated by four lead and two arsenic atoms; the lead and arsenic atoms are (six) coordinated by palladium atoms in the form of a distorted trigonal prism. The trigonal prisms are connected by sharing edges to form a framework. The Pd 3 Pd 2 As structure was determined from single-crystal X-ray diffraction data and refined by full-matrix least-squares methods to R = 0.073 for 309 reflections.