Weight loss determination

If changes have been made to the process (e.g. if incoming water quality cannot be maintained or other uncertainties arise concerning the corrosion behavior of the construction materials) it is possible to incorporate coupons or probes of the material into the plant and monitor their corrosion behavior. This approach may be used to assist in the materials selection process for a replacement plant. Small coupons (typically, 25 x 50 mm) of any material may be suspended in the process stream and removed at intervals for weight loss determination and visual inspection for localized corrosion. Electrical resistance probes comprise short strands for the appropriate material electrically isolated from the item of plant. An electrical connection from each end of the probe is fed out of the plant to a control box. The box senses the electrical resistance of the probe. The probe s resistance rises as its cross-sectional area is lost through corrosion. 

The T values quoted in table III were obtained from elemental microanalysis determinations. In order to check the reliability of these values, thermogravimetric (TGA) studies were carried out on several of the Si02 g-PS samples. The weight (w) of the sample is followed as a function of temperature and hence a, the fractional weight loss, determined, where a is given by... 

Weight loss determinations associated with the loss of bound water were obtained in the course of gravimetric adsorption studies of various vapors on these surfaces. Quartz springs of 250-mg. capacity and sensitivities near 1 mg. per mm. were used in the above system. Outgassing in the 300° to 400° C. temperature range required 4 to 9 days to obtain the required low pressure measurement. 

The displayed temperatures are T. initial degradation temperature obtained at 2% weight loss T10 temperature for 10% weight loss Tmr temperature(s) of maximum rate of weight loss, determined from the peaks of the first derivative of TGA curve. 

The progress of the reduction is checked by periodic weight-loss determinations. The reduction is assumed to have gone to completion when the weight of the reaction product lies within... 

Table III. Comparison of Zn Corrosion Based on Weight Loss Determine ations and That Obtained by Analysis of Dew and Rain Rinse Samples...

The Zn corrosion products in the dew represent only the soluble corrosion products. Information on the insoluble corrosion products was obtained only in the C3H6/NOX experiment in which weight loss determinations were made. It was found that the total Zn corrosion determined by the weight loss method was larger than that found in the dew and rinse. The difference is equal to the amount of insoluble corrosion product formed. 

Upon conclusion of testing, every probe was removed from each soil box, followed by cleaning and weight loss determination. The weight loss was then converted into corrosion rate by applying Faraday s law. 

Figure 4 shows the results of MIC testing reproduced in the laboratory, wherein corrosion rate estimated from AC impedance measurements by applying Eq. (1) [4] was correlated to the corrosion rate converted from actual weight loss determination using Faraday s law. 

Use the data obtained after two and four hours of the exposure period, assume that the corrosion current decreases linearly with the time, and determine the corrosion contribution in percent of the total weight loss. Determine finally the average rate of thickness reduction in mm/year. 

If desired, the approach above may be adapted to semiquantitative analysis of black powder, Pyrodex, or flash powders. A weighed sample, 0.25 g or more, on a tared filter paper is treated several times with a few milliliters of hot water, the filter dried, and the weight loss determined. The loss represents the oxidizer concentration. The filter is treated with pyridine, dried, and reweighed. The weight loss represents sulfur concentration and the residue either charcoal or aluminum as appropriate. 

Exposed area pipes 2S mm diameter x 330 mm flats 250 mm x 380 mm. Weight loss determined after cleaning with acetic acid. Average of three specimens. 

The three steps in Figure 17 are (1) the loss of H2O to form anhydrous oxalate, (2) the loss of CO to form the carbonate, and (3) the loss of CO2 to form CaO. The observed weight losses, determined from the integral curve (TGA), may be compared with the theoretical values obtained from the known stoichiometry of the process. Potential differences in the sample temperatures indicated by the... 

Similar results were presented in [9]. In uninhibited CO2 environments it was observed that in general the P-factors were of the order of 15-20 mV for pH-statted test procedures. However, as soon as a corrosion product layer formed, the factors increased. It is for this reason that the original PAIR -meter by Petrolite pre-programmed a P-factor of 37 mV based on extensive laboratory and field calibrations [45]. Newer commercial instruments allow the user to dial in a value for the p-factor. However, this presupposes that the Tafel slopes are known, and since these cannot be reha-bly determined as indicated above, the user is still left to guess, unless calibration procedures are in place, such as weight loss determinations or iron counts. 

Table 4.4 Thermal stability (by TGA-FTIR coupling) and radical stability (by immersion of membranes for different times in Fenton s Reagent and subsequent weight loss and molecular weight loss determination) ofB4/S4a andB4/S4b...

Weight loss determination is a relatively sensitive method to determine mass change caused by microbial attack It is a very easily applicable method. 

There are several experimental techniques that may be used to test the performance of a candidate corrosion inhibitor. Electrochemical testing (e.g. AC impedance and DC polarisation) are the traditional and primary research techniques, whereas weight loss determinations (immersion [45], outdoor exposure, or salt fog/cyclic chamber tests) tend to be used in commercial appUcations [90]. 

Moisture content has been classically determined by Karl Fischer titration using semi-automated apparatus as described in ASTM E 203. This has been largely replaced in routine operations by weight loss determination using automated balances, often with microwave heat input (see Volatile Loss in the foregoing). Such operations are covered in ASTM D 6980. With suitable columns and detectors, GC methods can be used, particularly in combination with TGA loss of water. Proton NMR is also sensitive and can distinguish between water of hydration and physically adsorbed moisture. 

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