Weight loss measurement, direct

Direct Weight Loss Measurement (method 1). In this method several containers were charged, each with 0.3 g of raw shale of known particle size and 50 ml of an HC1-KC1 solution with ionic strength of about 0.1 molar ions/1. and pH of 1.28. The reaction was allowed to progress after a specific period the shale from one of the containers was quickly separated from the acid by vacuum filtration and washed thoroughly with deionized water. The shale was then dried at 105 °C for at least 2 hr before weighing. The same process was repeated for a preweighted container, and the data were adjusted. 

The most common method of corrosion monitoring is the direct weight loss method, via small metal coupons. In addition, there are a number of electrical methods, including developed potential measurement,... 

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... 

The simplest form of direct atmospheric corrosion measurement is by coupon exposures. Subsequent to their exposure, coupons can be subjected to weight-loss measurements, pit density and depth measurements and to other types of examination. The main drawback associated with conventional coupon measurements is that extremely long exposure times are usually required to obtain meaningful data, even on a relative scale. It is not uncommon for such programs to run for 20 years or longer. 

In a chronic study in rats (Quast et al. 1980a), some changes in the blood parameters measured were observed at various intervals during the study, but the findings did not occur consistently and were not dose-related. Therefore, the authors concluded that these findings were not direct effects of exposure to acrylonitrile, but rather were a secondary response to other effects such as weight loss, tumor formation, or inflammatory reactions. 

No similar direct measurements of the rate of heat release seem to have been published. One related set of data at 180°C only by Topf (12,13) is based on measuring the weight loss versus time of powdered material together with the combustion value of the solid residuals. The heat released is then taken as the difference in combustion value to that of the original sample. 

This term is normally abbreviated to ERH. The ERH is deduced by extrapolating the weight loss values over a range of water activities greater and lesser than that of the product. Where the two lines intersect lies the water activity of the product. This extremely tedious and time consuming method has largely been superseded by instruments that measure the water activity directly. The ERH still has practical importance since it indicates the conditions under which the product can be stored without deterioration. 

The method by which an analyte is physically separated from the matrix varies depending on the nature of the sample and what form the analyte is in relative to its matrix. For example, the analyte or its matrix may be sufficiently volatile so that one or the other can be separated by evaporation at a temperature attainable by laboratory ovens or burners. In that case, the analyte weight is measured either by sample weight loss if the analyte has been evaporated or directly if the matrix has been evaporated. In either case, the weight of a container may also be involved. 

This is normally measured as a volume, and it is assumed that 1 ml liquid = 1 g. Obviously, for greater accuracy, the weight of the liquid could be determined. In some cases, one may also want to distinguish between aqueous weight/volume loss and lipid weight/volume. One could also measure the weight loss of the sample directly. 

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. 

Originally, water activity could not be measured directly. One method was to measure the weight loss of a product held at a range of controlled relative humidities, which also has the effect of holding the product over a range of water activities. If a product is held at its own water activity it neither gains nor loses weight, and this point is described as its equilibrium water activity. 

Bonding density cannot be measured directly the measured value is either (a) carbon content on modified material, (b) weight loss after ashing in the oven, or (c) thermogravimetric weight loss between 200°C and 700°C. Carbon... 

The efficiency of insect resist finishes can be determined by tests that measure the weight loss of the treated fabrics and/or the weight of insect excrement after exposure to insects under controlled conditions. The direct examination of exposed fabrics by microscopic methods to observe fibre damage is also useful. The typical half round bite traces of the moth larvae are observable. Standard methods for evaluating fabrics with insect resist finishes are given in AATCC Test Method 24. Procedures for cultivating the test insects are included in this method. 

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