Material-corrodent combination

Active-passive behavior is dependent on the material-corrodent combination and is a function of the anodic or cathodic polarization effects, which occur in that specific combination. In most situations where active-passive behavior occurs, there is a thin layer at the metal surface that is more resistant to the environment than the underlying metal. In stainless steels, this layer is composed of various chromium and/or nickel oxides, which exhibit substantially different electrochemical characteristics than the underlying alloy. If this resistant, or passive, layer is damaged while in an aggressive environment, active corrosion of the freshly exposed surface will occur. The damage to... 

Incompatible Waste (1) A hazardous waste unsuitable for placement within a specific portion of a landfill because it may cause containment material to corrode or decay or, when combined with other wastes, might produce heat, pressure, fire, explosion, violent reaction, toxic dusts, mists, fumes, or gases. (2) Hazardous wastes which, if mixed, would become more hazardous than either waste individually. 

Tungsten is a relatively inactive metal. It does not combine with oxygen at room temperatures. It does corrode (rust) at temperatures above 700°F (400°C). It does not react very readily with acids, although it does dissolve in nitric acid or aqua regia. Aqua regia is a mixture of hydrochloric and nitric acids. It often reacts with materials that do not react with either acid separately. 

The thickness of the liner is a factor affecting permeation. For general corrosion resistance, thicknesses of 0.010-0.020 in. are usually satisfactory, depending on the combination of lining material and the specific corrodent. When mechanical factors such as thinning to cold flow, mechanical abuse, and permeation rates are a consideration, thicker linings may be required. 

CoCr/CoCr combinations and was proportional to the duration of implantation, as seen in Figure 9.5 (Gilbert et al, 1993b). A larger percentage (34.5%) of cases of corrosion was found with mixed CoCr/TiAlV systems than with CoCr/CoCr systems (7%) (Cook et al, 1994). Corrosion occurred at the interface between head and neck of modular components. No correlation between the presence or extent of corrosion with the time in situ was found. In another study the percentage of corroded tapered connections between titanium-alloy stems and cobalt-alloy heads was found to be about 57% (Collier et al, 1991). Titanium-titanium and cobalt-cobalt alloy combinations did not result in interfacial corrosion. 85% of prostheses made of dissimilar materials exhibited corrosion 24 months or more postoperatively. The data indicate that a correlation exists between corrosion and time of implantation. 

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