Gravimetric corrosion rates

Owing to the laborious task of obtaining corrosion rates from gravimetric measurements, data for the effect of exposure time on corrosion rates have been very limited. However, with the more recent use of polarisation resistance measurements it would appear that in the absence of macro-biofouling... 

In this expression, bd and bc refer to the appropriate anodic and cathodic Tafel constants. Comparison of weight loss data collected as a function of exposure time determined from R , Rf from EIS, and gravimetric measurements of mild steel exposure to 0.5 M H2S04 are often within a factor of two. This suggests that use of Rn in the Stern-Geary equation may be appropriate for the estimation of corrosion rate (147-150). However, Rn measurements may underestimate corrosion rates. / p is often measured at effective frequencies of 1(T2 Hz or less in linear polarization or EIS measurements, while Rn is measured at 1 Hz or greater. An example of this is provided in Fig. 57, which shows the corrosion rate of carbon steel in 3% NaCl solution as a function of exposure time determined by EIS, linear polarization, noise resistance, and direct current measurement with a ZRA. Among these data, the corrosion rates determined by noise resistance are consistently the lowest. 

In the case of uniform surface corrosion gravimetric measurements [DIN 50918] can be used to determine the linear specific rate of change of mass x (corrosion rate, Figure 2.104) ... 

Figure 9 indicates the corrosion rate per year at different wt % loading of ZMP nanocontainers in alkyd resin coatings. At first ZMP nanocontainers were incorporated in the alkyd resin with the help of pigment Muller and formidation was coated on MS plates for study corrosion rate analysis. Experimentation was carried out by dipping coated MS in HCl, NaCl and NaOH (5 wt % each) solutions for a period of 750 h The loss in weight of each species was measured by gravimetric analysis for the analysis of... 

Another source of error involves cases in which both the anodic and cathodic reactions are not charge transfer controlled processes, as required for the derivation of Eq 25. Modifications to Eq 25 exist for cases in which pure activation control is not maintained, such as in the case of partial diffusion control or passivation [35]. Other researchers have attempted to calibrate the polarization resist2ince method with gravimetrically determined mass loss [36], In fact, polarization resistance data for a number of alloy-electroljrte systems have been compared to the observed average corrosion currents determined from meiss loss via Faraday s law [28], A linear correspondence was obtained over six orders of magnitude in corrosion rates. 

In atmospheres with SO2 + NO2, the gravimetric data show greater zinc corrosion after its exposure to atmospheres with both gases compared to that found in atmospheres with only SO2. However, bearing in mind that the corrosion rates found in atmospheres with only NO2 are practically negligible, it may be stated that the presence of NO2 in combination with SO2 has a synergistic accelerating effect. 

Concepts of CP kinetic criteria were postulated from the beginning of the 1970s, but at that time no appropriate measurement method was available to put them into practice. Reliable corrosion rate measurements of metals in CP conditions were ensured by only two physical methods gravimetric and resistometric measurements. Both methods allow the determination of increasing corrosion losses over longer time intervals (due to relatively low sensitivity) however, they do not allow the determination of the instantaneous corrosion rate. Such information would be required by users of CP installations, allowing the regulation of protective parameters in a feedback system. 

Two-month measurements of the effectiveness of CP of water heaters carried out for comparison by the EIS and gravimetric techniques have shown good compliance of the corrosion rates obtained by two independent methods (Jankowski and Juchniewicz, 1994). Application of the EIS technique for the determination of the corrosion current of steel in a heterogeneous environment such as soil caused significantly greater difficulties. Usually, strongly flattened, dif-... 

Figure 9-7 shows the iron concentration of test solutions as a function of the HEDP concentration at the end of gravimetric measurements (24 h) (Kalman et al., 1994). The iron content was determined separately in dissolved and precipitated (rust) form. The variation of total iron content is in accordance with the corrosion rate of carbon steel, showing a minimum curve. At lower HEDP concentrations, high amounts of iron exist in the form of rust, indicating a corrosion protection effect of the oxide layer on the carbon steel surface. At higher concentrations (c> 10 M), HEDP keeps the total amount of iron in the solution phase. These results indicate that complex formation between HEDP and iron ions has an important effect on the inhibition effect of HEDP. The... 

Other tests are used to evaluate corrosion from nitridation by anhydrous ammonium (Sanctis, 1995), by treating the sanples at different temperature for different lengths of time. The extent of corrosion is determined gravimetrically and by metallographic microscopy, and the corrosion rate can be determined by kinetic tests. 

A comparison of the results using this method and the rate of electroless copper deposition determined gravimetrically shows that the best results are obtained with the Le Roy equation applied to the polarization data in the anodic range. It is interesting to note that here, in the metal deposition as in the corrosion (9), the partial reaction, which does not involve destruction or building of a crystal lattice of metal substrate, gives better results (this is hardly surprising, of course). 

The time required to determine Icorr by Tafel extrapolation is approximately 3 h, which corresponds to the approximate time required for experimental setup and generation of a cathodic polarization curve at a commonly employed, slow scan rate of 600 mV/h. In comparison, a comparable gravimetric evaluation (mass-loss measurement) on a corrosion-resistant metal or alloy could take months, or longer. A limitation of the Tafel extrapolation method is the rather large potential excursion away from Ecorr, which tends to modify the WE surface, such that if the measurement is to be repeated, the sample should be re-prepared following initial procedures and again allowed to stabilize in the electrolyte until a steady-state Ecorr is reached. Consequently, the Tafel extrapolation method is not amenable to studies requiring faster, or even continuous, measurements of Icorr. 

Table 6.5.8 The rates of corrosion (mm/year) determined from gravimetric and linear voltammetry measurements...

LED3A to inhibit the corrosion of bright mild steel was evaluated. Steel coupons were immersed in 15% HCl at 40°C for 96 hours. The progress of corrosion was followed gravimetrically. The data are presented in Figure 18. The control contained no corrosion inhibitor. The LEDS A reduced the rate of corrosion by a factor of 10. Na LED3A has also been found to passivate stainless steel under highly alkaline conditions. 

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