Pitting causes

Pitting had two distinct causes. Sulfate reducers had formed the large hemispherical pits. The more undercut pits were formed during a low-pH excursion involving mineral acid after the sulfate-reducing bacteria became inactive. It is likely the low-pH excursion deepened preexisting sulfate-reducer pits, causing final perforation. 

Suction lines are often partly filled by settled sand and by debris from the pits, causing the pump to hammer at abnormally low speeds. Frequent inspection and cleaning of the suction manifold is required. The suction strainer can also be a liability if it is not cleaned frequently. 

Pitting caused by the dissolution of non-metallic inclusions can increase the value. Consequently, the microstructures of specimens with a high value must be examined to identify the source of the elevated value. In general, P values below 0-10 are characteristic of unsensitised microstructures, while sensitisation is indicated if P, exceeds 0-4. Single loop tests are sensitive to mild degrees of sensitisation but do not readily distinguish between medium and severely sensitised materials. 

The restricted level of oxygen within the pit causes that area to become anodic while the external surfaces then become cathodic. Consequently, the metal at the base of the pit dissolves to form ions. These ions migrate to the mouth of the pit where they are hydrolyzed to form hydroxide deposits. As the hydroxyl ions are consumed at the mouth of the pit, the net acidity within the pit increases.1... 

Fig. 2. Etch pits produced by point-defect clusters. (A) pits beginning to form at small precipitates (B) pits become flat-bottomed when precipitates are gone (C) small pits caused by precipitates in LiF (D) same as (C) after more etching (large pits are at dislocations).

Since one desires only light reflections from etched facets, the entire surface of the sample should be covered with etch pits. This can be obtained by etching an abraded surface. Fig. 5 shows the results of the action of a preferential etch for germanium on an abraded and on a polished surface. The multitude of pits on a lapped surface raises an interesting question are these pits caused mainly by the multitude of Irregularities produced an the surface by abrasion or by the multitude of mechanically induced dislocations In an attempt to answer this... 

Thin films of -Ta205 with (111) orientation were prepared by Tominaga and coworkers using Ta(thd)4Cl as CVD precursor (source temperature 215 °C, reactive carrier gas 1 1 argon-oxygen, substrate quartz and Si(lOO) at 600-700°C, pressure 5 Torr, deposition rate 50-150 Amin ) °. The films are smooth but appeared to contain a number of pits caused by columnar growth perpendicular to the substrate. 

Fruit with faded or gray-white, sunken patches or pits. Causes Sunscald cold injury. Green or ripe fruit can be sunscalded. Damage shows up as a large, sunken patch on the exposed side. Patches turn dry and may develop black mold. Control leaf diseases to prevent defoliation, so fruit will be shaded and protected from direct sun. Stake plants. 

Potatoes with rough, rotted pits. Causes Pox nematodes. Plants with pox, a bacterial disease, may be pale and stunted, and roots often resemble a string of irregular beads. Destroy infected plants and use healthy roots as soon as possible. Prevent problems by planting disease-free plants. Adjust the soil pH to below 5.2 by adding sulfur if pox has been a major problem in the past. While this is below the optimal pH range for sweet potatoes, they will tolerate it and the bacteria will be inactive. 

TUBERCLE - A protective crust of corrosion products (rust) which builds up over a pit caused by the loss of metal due to corrosion. 

In the chemical process industry, GRP vessels are frequently used to store mineral acids and strong caustic solutions. It is of particular interest when chloride ion is present. There are very few metals or alloys which can offer the long term resistance to pitting, caused by the presence of chloride ion, which GRP can offer. The difficulty in the chemical process industry is that very few pure chemicals are used. Most of the time we are dealing with mixtures of a wide range of chemicals. A considerable body of knowledge on the subject of the corrosion resistance of metals to pure chemicals is available and a metal can always be found to resist a particular chemical, but very few can offer the broad range of resistance which GRP can offer. 

The most important pit in piping systems where leakage is a concern is the deepest pit. This pit causes the first tubing wall penetration and the first leak. The time between the first tube failure and subsequent failures depends upon the statistical distribution of these pits and the rate at which corrosion continues. 

Evaporation Corrosion Test Manufocturing aids evaluation (lubricants/coolant) Potential for pitting caused by fluid left to evaporate on machined alloy after 7 days Currently qualified fluid... 

Compound Semiconductors, Electrochemical Decomposition, Fig. 3 Etch pits caused by galvanic corrosion in a p-InP-based semiconductor laser (From... 

Source F. Mansfield, Pitting Caused by Chlorides or Sulfates in Organic Media, Galvanic and Pitting Conosion—Field and Latx)iatory Studies, ASTM STP 576,1976, p 18CV203... 

The passivity breakdown and pitting caused by Cl ions has been the subject of an enormous amormt of work. This area has been reviewed in Chapter 8. 

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