The electrochemical behaviour of various non-precious Ni and Co based alloys in artificial saliva.

Five non-precious Ni-Co based alloys were analyzed with respect to their corrosion behaviour. The correlation between the amount of the elements Cr, Mo, V and the corrosion behaviour, expressed by the PREN (pitting resistance equivalent number) index in the case of the allied steels, was extended for Ni-Cr and Co-Cr dental alloys characterization. Open circuit potential, corrosion current densities, as a measure of the corrosion rate, and main parameters of the corrosion process were evaluated from linear and cyclic polarization curves, for five Ni-Cr or Co-Cr alloys in an Afnor type artificial saliva. The maintenance times of the alloy in the corrosive medium influence the corrosion rate; the corrosion current values decrease with the maintenance time due to their passivation in solution. The microscopic analysis of the alloy surfaces shows that this passivation in solution does not modify the corrosion type. The alloys with PREN

Bioactive polymers. LX. Kinetics of delayed release neomycin-xanthan complex.

The kinetics of delayed release neomycin-xanthan complex, and its antimicrobial activity, were studied. Delayed release neomycin (53.13% free neomycin) had zero-order release kinetics, when artificial tear solution was used as eluent. Microbiological tests revealed an activity of 380 units/mg, 10% higher than neomycin in its free form.

Bioactive polymers. 70. The kinetics of controlled release of neomycin in an alkaline medium.

Neomycin is coupled on xanthan--a polysaccharide of microbial biosynthesis produced by Xanthomona campestris--through ionic complexation. The kinetics of neomycin release, in vitro, at pH = 8.2 is studied. A release of neomycin, following a zero order kinetics, is observed, regardless of the eluent flow-rate. The neomycin-xanthan complex, protected by a cellulosic membrane, behaves like a monolithic-type device. Diffusion coefficients--increasing with increasing the eluent flow-rate--are also calculated.

[Some aspects concerning the electrochemical corrosion of the Gaudent-S dental alloy]. / Unele aspecte privind coroziunea electrochimica a aliajului dentar Gaudent-S.

The potentiodynamic polarization methods have been employed to evaluate the corrosion resistance of the Gaudent-S dental alloy in a slightly acid artificial saliva (Fusayama's saliva; pH = 6.18), a slightly alkaline artificial saliva (Rondelli's saliva; pH = 7.75) and in an acid saline solution (NaCl/lactic acid; pH = 2.64). The results were compared with those obtained for copper and aluminium--the principal components of the studied alloy. In Fusayama's artificial saliva both the copper and Gaudent alloy exhibit close indentic cyclic voltammograms, typical for pitting corrosion; the pitting potentials being 1550 mV (SCE) for Gaudent-S and 1350 mV (SCE) for copper, while the repassivation potential is 700 mV (SCE), the same for the two analysed metals. In the Rondelli's artificial saliva and in acidic saline solution the passivation domain is considerable reduced; the corrosion potential and the repassivation potential coincides. In the saline acid solution the current densities are two times higher than those obtained in the other two solutions. In the aluminium case it can be noticed that the passivation domain is very reduced, no cathodic peak is observed and much more current densities are registered in the positive potential domain.