Insulating passive effect

Lead is characterised by a series of anodic corrosion products which give a film or coating that effectively insulates the metal mechanically from the electrolyte (e.g. PbS04, PbClj, PbjO, PbCrO<. PbO, PbO, 2PbC03.Pb<0H)z), of which PbS04 and Pb02 are the most important, since they play a part in batteries and anodes. Lead sulphate is important also in atmospheric passivation and chemical industry applications. 

The silvery, shiny, ductile metal is passivated with an oxide layer. Chemically very similar to and always found with zirconium (like chemical twins, with almost identical ionic radii) the two are difficult to separate. Used in control rods in nuclear reactors (e.g. in nuclear submarines), as it absorbs electrons more effectively than any other element. Also used in special lamps and flash devices. Alloys with niobium and tantalum are used in the construction of chemical plants. Hafnium dioxide is a better insulator than Si02. Hafnium carbide (HfC) has the highest melting point of all solid substances (3890 °C record ). 

The passive film itself could not be treated as purely insulating since the known thickness of the film should give rise to a capacitive effect that would easily be seen in the impedance diagram. In fact, the film is apparently relatively conducting, probably through proton migration. 

Following are some examples of passive safety systems to reduce the likelihood of explosions in storage units. The use of baffles in a high-pressure storage vessel can cool the tank wall above the liquid surface via liquid pumped around by vapor bubbles, extending the time for fire fighting. Fire resistant tank insulation is also effective in delaying a BLEVE. 

A special problem can be the passivation of the electrode surface by insulating layers, for example, formation of oxides on metals at a too high anodic potential or precipitation of polymers in aprotic solvents from olefinic or aromatic compounds by anodic oxidation. As a result, the effective surface and the activity of the... 

The success of CD CdS in photovoltaic cells has driven related research with potential applications in other semiconductor devices. Since the CD process seems to play a role in the favorable properties of the CdS windows by decreasing interface recombination, studies of its passivation properties on other interfaces and surfaces have been carried out, with considerable success. For example, when a very thin film (ca. 6 nm) was deposited between InP and SiOi, the resulting reduction of the interface state density led to improved electrical properties of metal-insulator-semiconductor capacitors and field effect transistors (FETs)... 

Anodic Ni oxides catalyze H2 evolution if they are not formed at too high potentials, otherwise they may depress the activity [93, 385, 449, 456]. Insulating layers are normally inefficient for hydrogen evolution [457, 458]. It is interesting to note that semiconductors can reduce the overpotential for hydrogen evolution on Hg and the effect increases as the semiconductor band gap decreases [459]. This is in line with the observation that a passivated Nb electrode is not an efficient electrocatalyst... 

To investigate the effect of passivation layer on the performances of a-Si H TFTs under mechanical stress, we stressed both TFTs by outward cylindrical bending at the radius of curvature R = 5 mm as shown in Fig. 6. Less than R = 4 mm, most of TFTs employing acrylic polymer or SiNx as passivation layer were failed. When the radius of curvature was 5 mm, the strain on the surface of aciyl and SiNx was 0.0082 (0.82 %) and 0.0077 (0.72 %), respectively. Eq. 1 considering single aciyl (3 jtan) or SiNx (substrate-insulation, te-insulation and backchannel passivation 0.9 jtan) layer calculated the strain. 

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