Passive materials

Other passivating materials suffer pitting corrosion by chloride ions [62] in a way similar to stainless steels (e.g., Ti [63] and Cu [64]). The pitting potential for aluminum and its alloys lies between = -0.6 and -0.3 V, depending on the material and concentration of chloride ions [10,40-42]. 

We have observed that such proteins as CaM and bovine serum albumin (BSA) can be developed at the air-water interface to form monolayer protein films. In previous works, the developed BSA monolayer was stabilized by cross-linking with a bifunctional reagent immediately after the preparation of protein monolayer. The BSA thin film thus prepared can be employed as a passive material, e.g., an ultrathin protein film for a matrix of enzyme-linked immunosorvent assays. 

Intumescent fireproofing— A passive material that undergoes a chemical reaction when exposed to high heat or direct flame impingement that protects against the heat from a fire without additional intervention. 

Thin films (qv) of vitreous silica have been used extensively in semiconductor technology. These serve as insulating layers between conductor stripes and a semiconductor surface in integrated circuits, and as a surface passivation material in planar diodes, transistors, and injection lasers. They are also used for diffusion masking, as etchant surfaces, and for encapsulation and protection of completed electronic devices. Thin films serve an important function in multilayer conductor insulation technology where a variety of conducting paths are deposited in overlay patterns and insulating layers are required for separation. 

Materials of construction selected should be compatible with control measures such as sanitizing, cleaning, and passivation. Materials selected should be able to handle elevated operating, sanitization temperature, and chemicals or additives to be used to clean, control, or sanitize the system. 

Active or passive material transfer, with a low degree of induced shear... 

The hydration layer model more or less fits the behavior of all oxides and of silicon oxynitride. The latter has a great advantage over other pH-sensitive layers because it is an excellent passivation material itself that can be prepared virtually pinhole-free. On the other hand, even thermally grown Si02 has pinholes and cracks that form a leakage path. It is that leakage path that apparently served as a... 

Polyurethanes have also been employed as outer sensor membranes. Yu et al. evaluated the biocompatibility and analytical performance of a subcutaneous glucose sensor with an epoxy-enhanced polyurethane outer membrane.15 The membrane was mechanically durable and the resulting sensors were functional for up to 56 days when implanted in the subcutaneous tissue of rats. Despite the improved sensor lifetime, all of the polyurethane-coated sensors were surrounded by a fibrous capsule, indicating an enduring inflammatory response that is undesirable due to the aforementioned effects on analytical sensor performance. To date, the clinical success of most passive approaches has been rather limited. It is doubtful that one passive material alone will be capable of imparting long-term (i.e., weeks to months) biocompatibility for in vivo use due to the extremely dynamic nature of the wound environment. 

In the process proposed, the surface of an HgCdTe material is treated to remove and/or prevent formation of surface contaminants including oxides. A layer of passivating material is formed in direct contact with the semiconductor surface, the direct contact allowing the passivating material to tie up dangling semiconductor bonds. Furthermore, it is shown how the... 

As discussed in detail in Chapter 2, the corrosion potential is determined by the intersection of the sum of the anodic Evans lines and the sum of the cathodic Evans lines. For active-passive materials, the only new wrinkle is the increased complexity of the anodic line. Since the anodic line is not single-valued with respect to current density, three distinct cases can be considered. In all cases, the condition E /a = X Ic determines the position of the corrosion potential, and the condition im = z a - ic determines the appearance of the polarization curve... 

The cathodic reaction kinetics thus play an important role in determining the corrosion state for an active-passive material. The introduction of additional cathodic reactions to an environment or the change in the kinetics of one already present can dramatically affect the state of the material s surface. Figure 11 shows... 

Figure 15 Applied current densities required for different applied potentials for an active-passive material in acid. If there is a dissolution rate of 1 pA/cm2, cathodic protection to Ec would require an applied current density of 10,000 pA/cm2, while anodic protection to E4 would require only 1 pA/cm2. (After Ref. 21.)...

Localized corrosion is the direct result of the breakdown of passivity at discrete sites on the material surface. As was stated above, once passivity is established on a surface, one might expect either that it would remain passive or that a complete activation of the surface would occur. However, what is often observed in practice is the appearance of discrete areas of attack that begin to corrode actively while the vast majority of the surface remains passive. These isolated regions of attack are more than mere annoyances the local penetration rates can be on the order of 10 mpy or higher, leading to rapid perforation of any reasonably sized container. Since the original intent in using passive materials (e.g., CRAs) in any application is to exploit their low dissolution rates, localized corrosion can be a major operational problem. 

The different PEC VD film/substrate systems are schematically presented in Figure 6a. The substrates correspond to 99.99% pure Al, mechanically polished with a 0.3 pm alumina powder, then finally electrolytically in a 70% methanol-30% nitric acid solution. When exposed to air, a native aluminum oxide of about 3 nm is produced. The substrates were coated with a dielectric film of a passivation material either SijN or Si02 4.5 wt.% P. These systems are, respectively, denoted as system A and system C. The SijN films were produced by plasma enhanced chemical vapor deposition at a temperature of 360°C, while the SiO 4.5 wt.% P films were chemically vapor deposited at a temperature of 420°C. For both passivation materials, the thickness of the films was 0.8 pm. 

Yet, for systems A and C, the measured fracture energies remain low compared with the critical fracture energy of the bulk aluminum 10 J Moreover, we do not observe islands of passivation material on the A1 fracture surface and, inversely, we do not observe A1 on debonded surfaces of the passivation films. This suggests that the loss of interfacial adhesion is close to a brittle fracture process despite the influence of plasticity of the A1 substrate and crack blunting at the interface. This sort of brittle mode of interfacial failure, including plastic flow in a ductile material (the substrate), has been observed or discussed for a sapphire/Au interface. ... 

The relative velocities between the component and the media can have a direct effect on the corrosion rate. In some instances, increasing the velocity of the corrodent over the surface of the metal will increase the corrosion rate. When concentration polarization occurs, the increased velocity of the media will disperse the concentrating species. However, with passive materials, increasing the velocity can actually result in lower corrosion rates. 

A direct consequence of Lagrangian chaos is the exponential growth of passive scalar gradients and material fines [1, 4] A (passive) material fine of initial length q for large times grows as... 

Fig. 5. Transfer characteristics of a-Si H TFTs as passivation materials SiNx and acrylic polymer. The size of TFT is W = 30 //m and L = 6 ym.

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