Oxygen access

In the corrosion protection of marine structures, it is often found that the corrosion rate decreases strongly with increasing depth of water, and protection at these depths can be ignored. Investigations in the Pacific Ocean are often the source of these assumptions [7], However, they do not apply in the North Sea and other sea areas with oil and gas platforms. Figure 16-1 is an example of measurements in the North Sea. It can be seen that flow velocity and with it, oxygen access, is responsible for the level of protection current density. Increased flow velocity raises the transport of oxygen to the uncoated steel surface and therefore determines the... 

Nail sickness Nail sickness is chemical decay associated with corroded metals in marine situations. Chemical degradation of wood by the products of metal corrosion is brought about by bad workmanship or maintenance, or unsuitable (permeable) timber species, all of which permit electrolyte and oxygen access which promotes corrosion. Chemical decay of wood by alkali occurs in cathodic areas (metal exposed oxygen present). Softening and embrittlement of wood occurs in anodic areas (metal embedded oxygen absent) caused by mineral acid from hydrolysis of soluble iron corrosion products. 

Figure 1.5(a) shows as a typical example a computer-tomography-like atomic mono-layer representation of a bulk model for diisopropyldimethyl PEEK WC (DIDM-PEEK). In this case the oxygen-accessible free volume is obviously organized in relatively small isolated holes and the respective size distribution (cf. Figure 1.5(b)) is monomodal and extending only to hole radii of about 5 A. 

Fig. 7. Cross-sectional view of a pit. A, metal dissolution reaction, e.g. A1 -> Al3t + 3e, acid chlorides form, which produce hydrochloric acid and aluminium hydroxide on hydrolysis B, 2 Hh +2e- H2 C, porous corrosion product restricting oxygen access D, passive layer on the metal surface and E, inclusion acting as a local cathode.

When lubrication failure finally occurs, the surface film contains large quantities of molybdic oxide and sulphate, and very little molybdenum disulphide. Presumably the disordered nature of the products causes a volume increase, which leads to the formation of the blisters if the nature of the contact permits it. Kinner considered that blister formation was unlikely to be a cause of failure in conformal contacts because the presence of uniform loading over the surface prevents any vertical development. The same oxidation process takes place in conformal sliding, except to the extent that conformal contact inhibits oxygen access, and even if blisters are physically prevented from forming, there must be a slow increase in friction and film break-up. 

At this juncture, it is presumed that the regeneration order and kinetic constant or in general, the regeneration behavior changes due to significant transport resistance or oxygen accessibility limitation. 

After 10 months of storage, several small smoldering seams (about 100 x 100 cm in cross-section) of pellets became obvious on the sides of the pile and caused ignition of the plastic sheeting and of the tires used as anchors. The pellets themselves did not ignite, perhaps because of their close packing and limited oxygen access. The seams ran deep into the pile the affected pellets were black and brittle, presumably partially oxidized or pyrolyzed. The seams were in both the old and new parts and adjacent to both wet (>130 wt% moisture) and dry (<4 wt%) d-RDF. 

The temperature at which an incongruent phase is formed in Y Ba2Cu30 is much higher than the Er Ba Cu OQ compound. This fact and the difference in the grains sizes of these two compounds can be expected to alter their respective oxygen access and absorption. This may explain the differences in the resisitive behavior upon cooling of these compounds. 

Figure 9. Effect of processing time on the melt-flow index (MFI) of LDPE. (1) open chamber (excess air) (2) closed chamber (limited oxygen access) (3) closed chamber purged with argon (inert atmosphere).

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