Anodic polarization experiments in H2SO4 and normalHCl electrolytes show that amorphous Ni‐20P alloy passivates at potentials between −0.3 and about 0.2V (SCE) and dissolves transpassively above 0.2V (SCE). In 0.2N normalHCl , in which crystalline Ni pits readily, Ni‐20P resists pitting and passivates as effectively as in 0.2N H2SO4 . Analysis by x‐ray photoelectron spectroscopy of Ni‐20P surfaces after polarization indicates an enrichment of elemental P on the alloy surface, the presence of hypophosphite anions and the absence of oxidized nickel species. Thus, the Ni‐20P alloy does not passivate by development of a three‐dimensional oxide film, such as the normalNiO film that forms on nickel. A chemical passivation process is proposed that is controlled by the formation and surface retention of hypophosphite anion, which acts as a barrier between the alloy and the electrolyte.

With the eventual phase-out of chlorofluorocarbons, and restrictive regulations concerning the use of cleaning solvents such as hydrochlorofluorocarbons, and other volatile organic compounds, it is essential to seek new, environmentally acceptable cleaning processes. In the DOE Complex and in industry, an environmentally sound process for precision cleaning of machined metal parts is one of the issues that needs to be addressed. At Sandia, we are investigating the use of supercritical carbon dioxide (CO2) as an alternative cleaning solvent for this application. Carbon dioxide is nontoxic, recyclable, and relatively inexpensive. Supercritical CO2 has been demonstrated as a solvent for many nonpolar organic Compounds, including hydrocarbon-based machining and lubricating oils. The focus of this work is to investigate any corrosive effects of supercritical CO2 cleaning on metals. Sample coupons of several common metals were statically exposed to pure supercritical CO2, water saturated supercritical CO2, and 10 wt% methanol/CO2 cosolvent at 24,138 kPa (3500 psi) and 323°K (50°C) for 24 hours. Gravimetric analysis and magnified visual inspection of the coupons were performed before and after the exposure tests. Electron microprobe, x-ray photoelectron spectroscopy (XPS), and Auger electron surface analyses were done as needed where visual and gravimetric changes in the samples were evident. The results of these experiments will be reported. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

The effect of alloyed P on the dissolution of Ni was investigated with glassy Ni‐P alloys. The anodic behavior of Ni‐P in 0.2N H2SO4 and 0.2N normalHCl differed substantially from that of Ni. In 0.2N H2SO4 , glassy Ni‐P passivated at potentials up to several hundred mV anodic to Enormaloc , whereas Ni dissolved in the active state at comparable anodic overpotentials. At higher overpotentials, Ni‐P underwent transpassive dissolution, but Ni passivated. The behavior of Ni‐P in 0.2N normalHCl was virtually identical to that in 0.2N H2SO4 , but Ni pitted severely in 0.2N normalHCl at small anodic overpotentials. The kinetics of passivation of Ni‐P did not vary over a range of chloride concentration from 0.2 to 3.0N, and the alloy completely resisted chloride‐induced pitting at potentials below about 800 mV(SCE). Coulometric and gravimetric measurements indicated that, during dissolution of Ni‐P at passive potentials, the P was not oxidized as completely as it was during polarization at transpassive potentials.