Pitting specimen preparation

Hitzig et al. have produced a simplified model of the aluminium oxide layer(s) to explain impedance data of specimens prepared under different layer formation and sealing conditionsThe model also gives consideration to the formation of active and passive pits in the oxide layer. Shaw et al. have shown that it is possible to electrochemically incorporate molybdenum into the passive film which, as previously noted, improves the pitting resistance. 

Figure 12. Cross-sectional view of a bordered pit-pair. A pit aperture B pit border T torus. Note the thick, nonperforated torus. Most of the thin mar go was destroyed during specimen preparation, and only portions of it remain (arrow). Liquid flow occurs through the pit aperture, around the torus through the margo, ana out the other pit aperture into the adjacent cell. 5,000X...

Figure 12. (a) LM photo of cavitation bacterial attack of Pinus radiata wood cell walls. The cavities are generally oriented perpendicular to the long axis of the fibers and frequently develop from bordered pit (BP) areas. Bar 5.0 pm. (b) LM photo showing appearance of the angular cavities (AC) of cavitation attack produced within the S2 cell wall of tracheids. Bar 5.0 pm. (c) SEM shows where the S3 has collapsed during specimen preparation, giving the impression of surface attack. BP = bordered pit. Bar 2.0 pm. 

The metal electrode to be studied must be carefully prepared, attached to an electrical lead and mounted so that a known surface area of one face is presented to the solution. Several procedures are used such as mounting in a cold setting resin (Araldite) or inserting into a close-fitting holder of p.t.f.e. In the case of metal-solution systems that have a propensity for pitting care must be taken to avoid a crevice at the interface between metal specimen and the mounting material, and this can be achieved effectively by mounting the... 

Recommended practice for examination and evaluation of pitting corrosion Test method for determining susceptibility to stress corrosion cracking of high-strength aluminium alloy products Test method for pitting and crevice corrosion resistance of stainless steels and related alloys by the use of ferric chloride solution Recommended practice for preparation and use of direct tension stress corrosion test specimens... 

Post-reaction examination of similarly prepared specimens that had been treated in a flow reactor at 1 atm in 10% l /Ar at 970 K showed many of the features observed during the in situ studies. A sample treated in the flow reactor at 970 K looked comparable to a sample that had been treated in 1 Torr H2 at 1070 K in the microscope, i.e., many of the nickel particles had unsymmetrical pits associated with them. Reduction at 1120 K in the flow reactor produced dramatic changes in the appearance of samples, with extensive pitting of the titania film observed. 

Corrosion test specimens are used to evaluate average corrosion rate over the exposure period and eire also useful for assessment of crevice corrosion, pitting, and end grain attack, and may be used for metallographic examination of the corrosion test specimen or analysis of any deposits. Special corrosion test specimens may be prepared with welds to assess corrosion problems particular to weld material or heat affected zones. SCC may be monitored with specially mounted and loaded corrosion test specimens. 

ASTM G 1, Practice for Preparing, deeming, and Eveiluating Corrosion Test Specimens G 46, Practice for Examination and Evaluation of Pitting Corrosion. 

Pitting corrosion will occur in most environments, particularly those containing the chloride ion. Pitting can be evaluated on virtually any specimen, but flat panels usually are used when this is the principal purpose of the test. ASTM G 1 describes surface preparation of specimens for pitting tests, while ASTM G 46 covers specimen evaluation after test. 

The g values and spin intensities of specimens from each context showed substantial variation, revealing that a range of carbonization conditions were experienced by kernels even when they were depositied together in a single feature. Figures 3 and 4 shows the data from ancient samples, in the form of plots which place each sample in the g value/intensity plane. The data are superimposed on plots of the standards that were prepared in evacuated, sealed tubes. Midden samples had all been recovered by flotation. The pit samples that were recovered by flotation are distinguished in Figure 4 from those that were recovered without use of flotation. 

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