Pitting control methods

Corrosion control methods for copper corrosion are (i) improved production techniques that yield a clean inner bore and free from carbon films, which initiate pitting. The main practice is to use iron grit for blasting to remove carbon films this process reduces the frequency of pitting by 90%. Another technique is to preoxidize the inner bore that removes the carbon film and produces an oxide film that improves the resistance to corrosion. Chemical treatment of the water supply is also a method used to reduce the corrosive attack on copper pipes. 

Figure 3. Mixed potential diagram illustrating controls on the kinetics of corrosion at a pitted, oxide-covered metal. The potential range is from -700 to +300 mV/NHE. Arrows (B) corrosion current at the bottom of the pit, controlled by Fe Fe + (acid) and 2H - H2 (M) corrosion current at the mouth of the pit, controlled by the partial currents for Fe -> Fe2+ (passivated) and RX RH (Pit) corrosion current for the short-circuited pit, controlled by Fe Fe + (acid) and RX - RH. The three solid curves are generated using the Tafel equation and exchange current densities and Tafel slopes from reference (9). The dashed curve was measured at 5 mV s in pH 8.4 borate buffer, using methods described in reference (9).

Bradshaw, R., Brinson, L.C., A Sign Control Method for Pitting and Interconverting Material Functions for Linearly Viscoelastic Solids Mech. of Time-Dependent Materials, Vol. 1, No. 1 / March, 1997, p. 85-108. 

The forms of corrosion which can be controlled by cathodic protection include all forms of general corrosion, pitting corrosion, graphitic corrosion, crevice corrosion, stress-corrosion cracking, corrosion fatigue, cavitation corrosion, bacterial corrosion, etc. This section deals exclusively with the practical application of cathodic protection principally using the impressed-current method. The application of cathodic protection using sacrificial anodes is dealt with in Section 10.2. 

The critical pitting temperature (CPT) is widely used as a measure of the resistance of stainless steel against pitting attack. Various methods for determination of the CPT are described here, special attention being given to the choice of test potential for the control of stainless steel quality. 

There are other variations of this approach that involve the phase inversion temperature (PIT) (see Section 3.6.1). In one method an emulsion is formed at a temperature a few degrees lower than the PIT, where the interfacial tension is quite low and small droplets can be formed. The emulsion can then be quickly cooled. Another method uses a controlled temperature change to cause an emulsion to suddenly change from a coarse oil-in-water (O/W) emulsion, through a microemulsion phase, and into a fine water-in-oil (W/O) emulsion [432]. 

Cables via the powder-in-tube (PIT) method The approach is especially suited to processing Bi-2223 into leads and cables for power applications. A silver or silver alloy tube, filled with the partially reacted precursor powders formulated to yield Bi-2223, is drawn down to a wire 1-2mm diameter. The wire is rolled into a tape if that is the required form, usually with a width-to-thickness ratio of approximately 10 1. The composite is then heated to 800-900 °C when the powder partially melts. The recrystallization process is controlled and the pure Bi-2223 phase develops with large grains oriented so that the Cu-O planes lie parallel to the silver surface to optimize Jc. 

We will begin by reviewing methods of temperature measurement, furnace design, and temperature control. The instruments, how they work, what they measure, potential pit-... 

Corrosion control. Generally corrosion inhibitors, cathodic protection, anodic protection, and coatings are used for this purpose or combination of them. However, cathodic protection is the only method that avoids corrosion completely if the system is not sensitive to hydrogen embrittlement or alkaline medium. Anodic protection is a recent approach when the metal can be passivated in the corrosive solution. In this technique, a current can be applied using a potentiostat, which can set and control the potential at a value greater than the passive potential Ep or below the pitting potential Ep]l for environments containing corrosive species such as chlorides, bromides, etc. 

Ill) face quite slowly. The difference in etch rates is 300 1. The wafer is immersed in the etch and, by carefully controlling the etch time or using an etch stop method, a deep pit is generated. Depending on the thickness of the wafer and the size of the etch window, a thin membrane of single-crystal silicon can be formed at the bottom. 

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