Total specimen area

If localized corrosion is occurring (e.g., pitting corrosion), and the experimentally determined value of Icorr is divided by the total specimen area, A, to determine icorr, then Faraday s law is used to calculate the corrosion intensity, Cl, or corrosion penetration rate, CPR, why are the resultant values to be regarded as minimum values (i.e., the actual local values will be considerably higher) ... 

Mixed potential theory also allows predictions of the dependence of the polarization resistance on the exposed area of a galvanically active substrate. With due consideration for the influence of the total specimen area, as well as the surface roughness, an expression for the polarization resistance may be derived ... 

A circular specimen of about 38-mm (I.5-iu) diameter is a convenient shape for laboratory corrosion tests. With a thickness of approximately 3 mm Vh in) and an 8- or Il-mm- (yi6- or Vifi-in-) diameter hole for mounting, these specimens will readily pass through a 45/50 ground-glass joint of a distiUation kettle. The total surface area of a circular specimen is given by the equation ... 

It should be noted that it is extremely difficult to predict service lives of buried pipelines from the results of controlled trials with small specimens, whether in the laboratory or in the field. For example a study on the comparative corrosion resistances of ductile and grey iron pipes carried out jointly by European pipemakers in 1964-1973 indicated a mean pitting rate of 0 -35 mm/y for uncoated ductile iron pipe exposed in a typical heavy Essex clay of 500-900 ohm cm resistivity for 9 years. This is clearly at odds with the rate of 1 mm/y normally found on a corroded service pipe from such a soil. The discrepancy appears to be due to the use of specimens that were only a third of a pipe length each and were buried separately. It may reflect the contribution of the total surface area of the pipe as a cathode to the corrosion current at the anodic area at the pitting site. 

The absorption property exhibited by active carbon certainly depends on the large specific surface area of the material, though an interpretation that it is based solely on this is incomplete. This is borne out by the fact that equal amounts of two activated carbon specimens, prepared from different raw materials or by different processes and having the same total surface area, may behave differently with regard to adsorption. Such differences can be partly explained in terms of the respective surface properties of the carbon samples and partly in terms of their relative pore structure and pore distribution. Every activated carbon particle is associated with at least two types of pores of distinctly different sizes. They are the macropores and the micropores. The macropores completely permeate each particle and act as wide pathways for the diffusion of material in and out of carbon, but they contribute very little to the total surface area. The micropores are more important since they... 

Eyring pre-exponential factor Effective cross-sectional area of specimen Total cross-sectional area of specimen Area strain... 

Why should the specimen surface be carefully examined for localized corrosion after an electrochemical corrosion-rate test before calculating the corrosion intensity or corrosion penetration rate based on the total exposed area of the specimen, the experimentally determined corrosion current, and Faraday s law ... 

When the elements of interest in a specimen occur at extremely low concentrations, or when the available amount of material in a specimen is very small, it is desirable to apply the special techniques of trace analysis. In most fluorescence spectrometers the analyzed area on the surface of the specimen is designed to be approximately 5 cm. If the specimen is larger in area than this sensitive region and is much thicker than the thickness yielding 99% of the emitted x-ray intensity, then it can be considered to be of infinite dimensions. Many of the quantitative models and analysis techniques have been developed for this type of specimen. Occasionally, it is necessary to analyze a specimen which is thin compared to the 99% yield thickness or a specimen which cannot cover the total sensitive area of the fluorescence spectrometer. This type of specimen is considered to be of limited quantity. More frequently, specimens of unlimited quantity are available, but several or all of the elements of interest are present at trace concentration levels. 

The volume of water shall be at least 8 mlVcm of the total surface area of the test specimen. No specifics given on the volume of water required. 

From the analysis it seems that there are two possible solutions, to increase the beam current or reduce the scan rate. Neither of these may be possible. At any resolution the beam current is limited by the brightness of the electron source, and the scan time is limited by practical concerns including the patience of the operator. It is difficult to adjust the focus or astigmatism of a slowly scanning image. For polymers there is also the real possibility that radiation damage of the specimen limits the total number of electrons that can be allowed to strike a given specimen area. 

A specimen is heated by electrical self-resistance in vacuum. Total hemispherical emittance is determined from the Stefan-Boltzmann law of radiation, knowing the power input, the total surface area, and the temperature. By using a solar simulator, as in method 3, the difference in electric power required to maintain a given temperature with the solar simulator on and off determines the solar absorptance. 

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