Passivation Techniques

During handling and processing operations, such as machining, forming, tumbling, and lapping, particles of iron, tool steel, or shop dirt may be embedded in or smeared on the surfaces of stainless steel 

These contaminants may reduce the effectiveness of the natural oxide (passive) film that forms on stainless steels exposed to oxygen at low temperatures. If allowed to remain, these particles may corrode and produce rust-hke spots on the stainless steel. To prevent this condition, semi-finished or finished parts are given a passivation treatment. This treatment consists of cleaning and then immersing stainless steel parts in a solution of HNOj or of HNOj plus oxidizing salts. The treatment dissolves the embedded or smeared iron, restores the original corrosion-resistant surface, and maximizes the inherent corrosion resistance of the stainless steel. 

contamination of the passivating solution (particularly with high levels of chlorides) can cause flash attack, which results in a gray or black appearance and deterioration of the surface. 

After cleaning, the work piece can be immersed in the passivating acid bath. As shown in Table 12.3, the composition of the acid batch depends on the grade of stainless steel. The 300 series stainless steels can be passivated in 20 vol% HNOj. A sodium dichromate (Na2Cr207.2H20) addition or an increased concentration of HNOj is used for less corrosion-resistant stainless steels to reduce the potential for flash attack. 

Even normally efficient water rinses can leave residual add trapped in these discontinuities after passivation. This acid can then attack the surface of the part unless it is nentralized or removed. For this reason, a special passivation process, referred to as the alkaline-acid-alkaline method, is 

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Perhaps the most precise, reHable, accurate, convenient, selective, inexpensive, and commercially successful electroanalytical techniques are the passive techniques, which include only potentiometry and use of ion-selective electrodes, either direcdy or in potentiometric titrations. Whereas these techniques receive only cursory or no treatment in electrochemistry textbooks, the subject is regularly reviewed and treated (19—22). Reference 22 is especially recommended for novices in the field. Additionally, there is a journal, Ion-Selective Electrode Reviews, devoted solely to the use of ion-selective electrodes. 

According to the definition, a passive technique is one for which no appHed signal is required to measure a response that is analytically usehil. Only the potential (the equiHbrium potential) corresponding to zero current is measured. Because no current flows, the auxiHary electrode is no longer needed. The two-electrode system, where the working electrode may or not be an ion-selective electrode, suffices. 

Because of its good performance in mineral acids, there is little need or incentive to invoke anodic passivation techniques for zirconium. The metal can be anodised in sulphuric acid, but, again in contrast to the behaviour of titanium, it does not form a stable anodic film in chloride solutions, and even in neutral sodium chloride, zirconium rapidly corrodes if an anodic potential of 2 V is applied. 

Malik, A.S., and Choi, T.S., Application of passive techniques for three-dimensional cameras, IEEE Trans. Cons. Elec. 53, 258, 2007. 

In this chapter the role of active and passive techniques as a support to homeland security is explored. The essentials of bistatic and netted radar are introduced which enables the relative strengths and weaknesses of these approaches to be outlined. In this way a foundation is provided against which a variety of potential applications may be explored. 

Heat transfer has been identified by Rlay 13 as an important area in which process intensification is expected to offer major benefits in terms of energy efficiency, pollution control and plant operating costs. So-called passive techniques including modifying the walls of a plant unit, for example, are routinely used to improve heat transfer coefficients in... 

Materials compatibility is the resistance of materials of system construction to chemical or physical attack by the propellants or the products of propellant combustion. In addition to destroying the integrity of the pertinent structural member, corrosion of the material by the propellant results in contamination of the propellant with the corrosion products, which in turn deteriorates the propellant s physical and chemical properties. As in storability, materials compatibility is related to usage temperatures, as well as to special materials handling, cleaning, and/or passivation techniques. Although limited materials compatibility of a... 

All oxidizers being evaluated for use in rocket engines are carefully examined to determine their compatibility with the materials with which they will be in contact. In some cases elaborate steps are necessary to develop passivation techniques that permit extended storage of these oxidizers. One of the classical cases in recent years was the development of inhibited red fuming nitric acid (IRFNA) for use in aluminum tanks. 

There are two categories of remote sensing, active and passive. Passive techniques utilise electromagnetic radiation emitted from or transmitted through the atmosphere, the radiation source being for example the black body emission from the earth s surface or solar and stellar irradiances. The most critical part of a passive remote sensing instrument is its detector. In contrast, active remote sensing systems have their own radiation source and a detector, for example, radar and lidar techniques. 

Passivation is needed to insulate the backplane from the OLED stacks everywhere except the ITO and bonding contact areas. Unlike poly-Si and a-Si H backplanes, on which both organic and inorganic passivation layers can easily work, the device passivation technique needs extra consideration for pentacene TFTs. We explored several different materials for passivation of pentacene TFTs, including poly(vinyl alcohol) (PVA), room temperature plasma-enhanced chemical vapor deposition silicon nitride (RT PECVD SiN), and vapor-deposited parylene. 

Enhancement of nucleate boiling heat transfer in large diameter ehannels is often used to augment flow boiling heat transfer. Enhancement teehniques can be elassified either as passive (without external power) or as active (with external power or external additives). Table 1 gives a short list of the various techniques used in the area of boiling heat transfer. From proeess industry perspective the passive techniques are more important than active techniques because of the benefit of simplicity. 

Some attack, but protective coaling form ) Using anodic passivation techniques ) Some attack/absorption/slow erosion Nol sulphate... 

Passive technique of capillary action movement of water... 

The use of SP surveys as an exploration tool has waned since the 1950s with the increasing sophistication of other electrical geophysical techniques such as induced polarisation (IP) and ground resistivity. Part of the reason is that the interpretation of these non-passive techniques is easier because electrical theory and electronics theory can be applied. Since the causes of natural SP above mineralisation are still widely misunderstood (Hamilton, 1998), the interpretation of the results of SP surveys is difficult. 

A good overview on the various passivation and deposition processes can be found in Refs. [267-269]. In Table 1.5 the resulting Dit trap densities for the various possible passivation techniques are shown. Thermal passivation yields the highest interface quality, that is the lowest Dit can be achieved. Quality wise the electrochemical passivation is next. However, electrochemical reactions at a semiconductor surface are only possible in the accumulation mode. Therefore, anodic reactions only take place at p-type doped Si electrodes (accumulation of majority charge carriers, i.e. holes), whereas on n-Si only reduction reactions are possible. Consequently, only p-type doped Si can be anodically passivated. This can be changed by an illumination... 

Figure 24.16 O-CMOS inverter stage transfer characteristic. The inverters have been realised using (a) the Si02 Ca passivation technique and (b) the UV modification approach of a PMMA dielectric. For plot (a) a max. gain of 24, and for plot (b) a max. gain of 17 was obtained.

As mentioned, non-invasive or passive techniques have been added to many multidimensional and multinuclear pulse sequences such as the 2D edited-HSQC up to more complicated 3D and 4D heteronuclear-based NOESYs. The basic principle is to use a relatively long selective pulse to manipulate water. 

In order to control combustion efficiency, intensity, flame signatures, emissions of trace pollutants, and combustion instability, the flame structure must be controlled. Combustion characteristics can be controlled using either active or passive techniques. Even though the active control techniques may be more effective than passive, the active techniques are more expensive, complicated, and... 

Surface defects such as dangling bonds and vacancies may, in principle, be removed by chemical passivation techniques. A successful passivation procedure should result in the disappearance of defect luminescence and the appearance of strong exciton luminescence. Many chemicals have been tried for this purpose but with few successes. The two most successful passivation techniques developed so far involve the use of ammonia [50] and hydroxide ion [35]. In both cases, defect luminescence is greatly reduced with the... 

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