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ABSTRACT Neuroprostheses significantly enhance the independence of people with disabilities by restoring movement and function. A Networked Neuroprosthetic System (NNPS) that electrically stimulates nerve and muscle to provide functional enhancements is being developed. Due to good mechanical properties, corrosion resistance and high electrical conductivity, MP35N alloy wire with a silver core is used for implantable cables, lead wires and interconnects of the networked system. This study investigates the corrosion behavior of silver-cored conducting wires and cables in saline solution utilizing electrochemical methods, scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). An overall objective for subsequent work is to determine the likelihood and extent of silver release in the body should the silver core be exposed. INTRODUCTION Neuroprostheses significantly enhance the independence of people with disabilities by restoring movement and function. For example, neuroprosthetic devices that electrically stimulate nerves and muscle provide functional enhancements for individuals with spinal cord injuries or stroke. Current implanted neuroprosthetic systems utilize considerable external powering and signal processing, and each system is tailored to the specific application for which it was intended. The Networked Neuroprosthetic System (NNPS) system design is based on a network of small implanted modules, distributed throughout the body. The modules are interconnected using small diameter network cables. These cables route both power and communication signals to the modules. The implantable cables and leadwires of the NNPS use wires with a corrosion resistant and mechanically strong outer tube that is filled with a highly conductive metal core. Drawn filled tube wires of MP35N-Ag have an MP35N alloy outer tube and a silver core. Alloy MP35N, a Co-based superalloy with a nominal composition of 35Co-20Cr-35Ni-10Mo, provides strength and corrosion resistance while the silver core provides high conductivity for transmission of signals and power in the NNPS. In the NNPS, multiple 50µm diameter wires comprise the conductor cable, and the cables are polymer coated with materials such as perfluoroalkoxy (PFA) or silicone rubber. In the nominal condition, the cables of the implantable system are intact and the silver core is isolated from in vivo exposure by the polymeric coating on the cables and enclosure in the corrosion resistant alloy outer tube of the individual wires. In the event of mechanical failure of a cable, the silver core of some wires may be exposed to an in vivo environment. The toxicology of silver and silver compounds for humans and animals has been studied, and adverse effects such as argyria have been reported. An overall objective of our work is to determine the likelihood and extent of silver release in the body should the silver core be exposed. This initial study investigates the corrosion behavior of silvercored conducting wires and cables in saline solution utilizing electrochemical methods, scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). The intent is to examine the wires boldly exposed to saline and over a range of oxidizing conditions to determine the baseline corrosion behavior of the silver core of the wire. Subsequent tests will be directed to more closely examine behavior for in vivo conditions.
- Health & Medicine > Therapeutic Area > Neurology (0.54)
- Materials > Metals & Mining > Silver (0.35)
- Energy > Oil & Gas > Upstream (0.35)
ABSTRACT The effect of the crevice former material on the evolution of localized corrosion-damage is determined in this study. A standard crevice corrosion test method is modified by the use of ceramic or polymer materials as the crevice former. Our overall focus is on the post initiation stage of crevice corrosion and to address factors that may limit the initiation of localized corrosion and also slow or stop the continued propagation of corrosion. Here the focus is on the measurement of damage evolution under controlled conditions. Crevice corrosion tests are performed under aggressive, accelerated conditions on Ni-Cr-Mo alloy C-22 and the less corrosion resistant 316 stainless steel (SS316). Under identical conditions in high temperature, concentrated chloride brines, the polytetrafluoroethylene (PTFE) Teflon tape covered ceramic is the most active crevice former on alloy C-22 while solid polymer crevice formers that are PTFE or polychlorotrifluoroethylene (PCTFE, Kel-F) are less active and ceramic crevice formers cause no crevice corrosion. The affects are important to the determination of the penetration rate and extent of corrosion damage by localized corrosion. INTRODUCTION Crevice corrosion is an important degradation mode to be evaluated for corrosion performance of passive metals exposed to high temperature brines over long exposure periods. A necessary condition for crevice corrosion is that a crevice former creates a sufficiently tight, restricted geometry on the metal surface to support the development of critical crevice chemistry. Crevice geometry factors, e.g. height, gap and length affect the initiation, propagation and stifling and arrest of crevice corrosion. Both modeling and experimental work has been performed on the effect of the crevice geometry on the initiation and propagation of crevice corrosion . Heppner coupled a transport model and an ionic interaction model to simulate the effect of a crevice gap on the initiation of crevice corrosion. The results showed that decreasing the crevice gap will increase the electrical potential along the crevice, increase the electrical conductivity of the solution and increase the severity of the crevice solution composition. As the gap size decreases, the charge density throughout the crevice solution and the severity of crevice increase. Akashi studied the effect of applied torque on the crevice repassivation potential of 304 stainless steel in NaCl solution. As the applied torque increased, the repassivation potential decreased, i.e. more severe corrosion with a tighter crevice. When the applied potential was above a certain value, the repassivation potential was stable and no longer decreased when the applied torque was increased . Factors that affected the crevice geometry could affect the crevice corrosion. Surface roughness and the mechanical properties of the crevice former could also affect the severity of crevice corrosion. Localized corrosion of alloy C-22 has been examined by a number of researchers . Different crevice formers were used to characterize the localized corrosion performance of alloy C-22. Commonly used crevice formers are PTFE Teflon tape covered ceramic 12 and PTFE Teflon .
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)