Weight Loss Measurement Technique

In random degradation molecular mass decreases early, while in chain degradation the molecular mass of the polymer remains almost constant. Characterisation methods for molecular mass are thus very sensitive methods to follow random degradation. In contrast, as monomer is produced in chain depolymerisation, weight loss measurement techniques are the best methods to follow this kind of degradation. (Chapters 10-12, in Section IV, of this book focus on the methods used in the molecular characterisation and analysis of polymer degradation and polymer degradation mechanisms.)... 

Potential measurement This technique has provided valuable information as to the condition of passive/active materials, particularly in the chemical industryAlthough quantitative weight loss measurements are not obtained, measurements can be on-line and more importantly, can be monitored using the actual plant material in situ) as a sensor. 

Electrochemical impedance, weight loss, and potentiodyne techniques can be used to determine the corrosion rates of carbon steel and the activities of both sulfate-reducing bacteria and acid-producing bacteria in a water injection field test. A study revealed that the corrosion rates determined by the potentiodyne technique did not correlate with the bacterial activity, but those obtained by electrochemical impedance spectroscopy (EIS) were comparable with the rates obtained by weight loss measurements [545]. 

In a later study by the Schmidt group (27), electron microscopy was used to characterize morphological changes in microspheres (<0.6 cm in diameter) of Pt, Rh, Pd, and Pt-Rh alloy in a number of reaction environments the reactions were ammonia oxidation, ammonia decomposition, and propane oxidation. No other experimental techniques, such as weight-loss measurements, were employed. After prolonged exposure to reaction mixtures of ammonia and air at temperatures less than 727°C, the surfaces of the spheres were reconstructed to favor specific crystal planes. The structure of the facets was found to be a function of the reaction mixture, temperature, and metal (Fig. 13). In the same reaction mixtures, as well as in pure ammonia at higher temperatures... 

The methods of measuring corrosion rates in the course of testing corrosion inhibitors are conventional weight loss, electrochemical techniques such as linear polarization resistance, potentiodynamic polarization, AC impedance, and electrochemical potential or current noise. 

The linear polarization technique estimates instantaneous corrosion rates under various process conditions. The corrosion current, according to the Stem-Geary equation, is inversely proportional to polarization resistance, which allows the measured polarization resistance to be normalized directly into corrosion rates. Because the current follows the appHed overvoltage, the polarization resistance curve is plotted automatically. Because this technique accurately measures corrosion rates <0.1 mpy, it is of a great importance in water distribution systems and food industries that face problems with traces of impurities and contamination. It can be used to measure the corrosion rates in civil engineering structures that cannot be subjected to weight loss measurements. Usually, Hnear polarization measurements are executed in 10 min. As shown in Fig. 5.3, the current as a... 

Specific studies of the vapor pressures of rare earth metals were not carried out until the late 1940 s. However, various earlier manipulations of rare earth metals, including vacuum melting of cerium and lanthanum gave a clear indication that these metals had relatively low vapor pressures, compared to the alkaline earth metals for instance. The first concerted study of the vapor pressure of a rare earth metal was that of Ahmann (1950) who used a radioactive tracer modification of the Knudsen technique to show that cerium had a vapor pressure of 10" Torr at 1735 C. Daane (1951) measured the vapor pressures of lanthanum using a direct weight loss Knudsen technique to show that lanthanum has a vapor pressure of... 

FIGURE 14.34. Corrosion rate of various materials in 30% NaOH solutions at 117 C as a function of the nickel content. Solid lines Electrochemical technique in solutions exposed to ain Dashed line Weight loss measurements in hydrogen-saturated solutions [36]. 

However some of the weight loss can be masked by the incorporation of oxygen into the material. To make residual weight loss measurements more accurate and convenient, the solvent extraction techniques for the retrieval of polymer incubated in soil have been applied. However, for some polyethylene based materials these techniques give erroneous results because of PE crosslinking (partially insoluble in 1,2,4-trichlorobenzene). Ideally, different measurements for biodegradation should correlate molecular weight determination when applied to the same polymer [120]. 

The combination of immersion, hydrogen collection and weight loss measurement is an easy corrosion evaluation method, particularly for magnesium alloys. The method, first established and used by Song et al. [5] to estimate and monitor the corrosion rate of magnesium in a NaCl solution, has been widely adopted as a common corrosion rate measurement technique for magnesium alloys in various aqueous solutions. The reliability of the method has been theoretically and experimentally demonstrated [24,25] and the details will not be repeated here. 

Cerresien Properties. The corrosion behavior of cast Al-2%Mg, Al-2%Mg-3.5% mica and Al-4%Cu-1.5%Mg-2.5% mica in nondearated 3.5% NaCl solution, under simple immersion, erosion-corrosion, and corrosive wear conditions has been evaluated using weight-loss measurements, electrochemical techniques, and scaiming elecuon microscopy. The composites were found to corrode faster than the matrix... 

The definition of polymer thermal stabiUty is not simple owing to the number of measurement techniques, desired properties, and factors that affect each (time, heating rate, atmosphere, etc). The easiest evaluation of thermal stabiUty is by the temperature at which a certain weight loss occurs as observed by thermogravimetric analysis (tga). Early work assigned a 7% loss as the point of stabiUty more recentiy a 10% value or the extrapolated break in the tga curve has been used. A more reaUstic view is to compare weight loss vs time at constant temperature, and better yet is to evaluate property retention time at temperature one set of criteria has been 177°C for 30,000 h, or 240°C for 1000 h, or 538°C for 1 h, or 816°C for 5 min (1). 

Thermal gravitational analysis (TGA) Chemical testing technique that precisely measures weight loss (due to gas forming reactions) as a function of temperature and time. 

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