Mass loss measurements

This parameter, the smoke parameter, is based on continuous mass loss measurements, since the specific extinction area is a function of the mass loss rate. A normal OSU calorimeter cannot, thus, be used to measure smoke parameter. An alternative approach is to determine similar properties, based on the same concept, but using variables which can be measured in isolation from the sample mass. The product of the specific extinction area by the mass loss rate per unit area is the rate of smoke release. A smoke factor (SmkFct) can thus be defined as the product of the total smoke released (time integral of the rate of smoke release) by the maximum rate of heat release [19], In order to test the validity of this magnitude, it is important to verify its correlation with the smoke parameter measured in the Cone calorimeter. 

Jenekhe et al. 140 Mass loss measured by TGA formal kinetics Pyrolysis — 0.3-lOKmin1, I m. = 550 "C 200-235, function of heating rate... 

Samples of the aluminium alloys obtained were analysed chemically to determine their transition-metal contents. Use was usually made of photometric methods. The results were then compared with those found from mass loss measurements. 

Calculated from mass loss measurements. b Found by chemical analysis of aluminium alloys after the runs. 

Measurement of mass lost is the conventional method for determining the corrosion rate. The mass loss of an Fe specimen immersed in a corrosion test potential is determined by weighing, (b) Convert the mass loss rate 2.34 x 102 g tf rrT2 into icon using the atomic weight 55.847. (c) What is the difference between the results of the mass loss measurement and the polarization resistance measurement (Numata)... 

The erosion yield of a polymer is typically measured by two methods (1) recession and (2) mass loss. Recession measurements are made by masking an area of a sample surface from attack and measuring the step height difference between exposed and unexposed areas. The thickness loss divided by the exposure fluence is the erosion yield. Mass loss measurements are made either by weighing a sample before and after exposure or by monitoring the mass loss in situ of a material that was coated onto a quartz crystal microbalance. Care must be taken in mass loss measurements to ensure that outgassing from the material in the vacuum of the exposure environment does not affect the results. The calculation of the erosion yield from a mass loss measurement requires knowledge of the density of the material and the surface area exposed, as well as the exposure fluence. 

Uncertainty of mass loss measurement. The standard method of the neutral salt spray test does not indicate the mass of RS. Mass loss was found as a difference between the RS prepared for the corrosion test and the RS after the corrosion test and corrosion product stripping as well as protective coating removal from the RS (Table 1). Such a mass loss determination is based on three components (1) mass loss determination by weighing (accuracy 0.5 mg and standard deviation 0.3 mg) before the neutral salt spray test and after it, (2) determination of difference and (3) cor-... 

Tanaka [45] used mass loss measurements to study the isothermal decomposition of NaHCOj between 383 and 397 K. Results fitted the Avrami-Erofeev equation, = 1.41. The value of , was 109 5 kJ mol, which was greater than the reaction enthalpy of 71.8 0.8 kJ mol. It was concluded that this is a nucleation and growth process. 

The incongruent vaporization of the compounds of the Ta-Al system and of WSCj (see Table 7) was studied by an apparatus combining Knudsen effusion mass spectrometry and mass-loss measurements. Schiffman et al. [240] obtained an enthalpy change of AH298 = 311 3 kJmoP for the reaction of evaporation 1/2 WSe Cs) 1/2 W(s) -h Se(g). 

Mass loss measurements do not detect melting or other phase changes. TG studies do not detect fusion. Melting may be a significant mechanistic feature of reaction and of importance in the interpretation of observations. TG has been widely used to study reactions that occur on heating reactants that are (at least initially) solid (21) it must be remembered that one of the possible consequences of heating is melting. 

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. 

The ablation rates calculated from mass loss measurements using a quartz crystal microbalance (QCM) [63] or mass spectrometry [64] reveal a so-called Arrhenius tail [63] (linear increase of products at low fluences, followed by a much faster increase). 

Photochemical volume models [56, 57, 72-74], reveal sharp ablation thresholds and lead to logarithmic dependence of the ablated depths per pulse. Such models may also result in a linear dependence if the movement of the ablation front is taken into account, and if the screening by ablation products is ignored. These models cannot explain the previously described Arrhenius tails observed in mass loss measurements. 

Scientists have used a wide arsenal of analytical techniques to monitor chemical and physical transformations of polymers following exposure to laser radiation, among which UV-Vis absorption, nuclear magnetic resonance (NMR) spectroscopy, electron spin resonance (ESR) spectroscopy for detection of free radicals, GC/MS analysis, FTIR for detection of various functional groups and bonds, X-ray photoelectron spectroscopy (XPS) for the chemical composition of surfaces, optical, and fluorescence microscopy, atomic force microscopy (AFM) for surface topography, quartz crystal microbalance (QCM) for in situ mass loss measurements, and so forth. 

The method applied to measure the depth of the ablated area or the removed mass can also have an influence on the ablation parameters. If profilometric measurements (optical interferometry, mechanical stylus [34], or atomic force microscopy [35]) are used to calculate the ablation rate, a sharp ablation threshold can be defined. This is also supported by reflectivity [36] and acoustic measurements [37], In mass loss measurements, such as mass spectrometry or with a quartz crystal microbalance (QCM), the so-called Arrhenius tail [38] has been observed for certain conditions. The Arrhenius tail describes a region in the very low fluence range, where a linear increase of detected ablation products is observed, which is followed by a much faster increase, that coincides with removal rates of the profilometric measurements [39]. 

Thermal stability/chemical structure correlations as reported by Van Krevelen [1] and Bicerano [2] are using and predicting the relative short-time, thermal stability values measured in an inert atmosphere. The mass losses measured under these (non-isothermal) conditions are caused by the damage of chemical bonds due to chain depolymerisation and/or random decomposition (see 2.2.1). Van Krevelen [1] distinguishes five experimental indices which characterise this non-isothermal decomposition process ... 

ISO CORRAG [23], the International Organization for Standardization (ISO) has implemented a classification system for evaluating atmospheric corrosivity and on the basis of variables that are fairly easy to obtain [24, 25]. This ISO classification has found several applications, for example, to predict the long-term corrosion behavior in different environments and to evaluate the effect of protective coatings. It contains two principally different approaches of assessing the corrosivity of any outdoor atmospheric environment. The first is based on exposure of standard specimens of steel, copper, zinc, and aluminum for one year whereby the corrosion effect is measured through mass loss measurements. One of five measured corrosivity classes... 

Sometimes, changes with time of the rate of corrosion call for a procedure with mass loss measurements at several intervals. Figure 4.15 shows the schedule for a planned interval test with four identical samples. Samples 1 to 3 are used to determine the evolution with time of the rate of corrosion. This provides information about a number of parameters, including the role of surface films formed during corrosion. On the other hand, a comparison of the corrosion rate of samples 1 and 4 reveals possible changes in the corrosivity of the solution during the test. 

At the start of a test, the specimen in the appropriate holder is placed on the load cell, which is located helow the heater. The load cell has a tare adjustment so that high accuracy mass loss measurements can he made, even if the mass of the holder and a possible substrate are much higher than that of the specimen. As soon as the pyrolysis products released by the specimen ignite, the electric spark plug is removed. All combustion products and entrained air are collected in the hood. An orifice plate at the entrance of the exhaust duct results in an almost imiform... 

The evaluation of the specimens in any corrosion test must be appropriate for the type of corrosion that actually occurs on the samples. In many cases, the actual sample evaluation requirements will not be known until the samples are retrieved and examined visually. This can complicate the administration of the testing program as the cost of specimen evaluation and the time to perform the evaluation cannot be planned in advance. For example, if general corrosion is the only form of corrosion experienced, the cost of sample evaluation by mass loss measurement is relatively inexpensive, whereas a form of corrosion such as stress corrosion cracking may require a high cost evaluation. 

These mass loss tests consist of preparing metallic coupons, cleaning them before testing, weighing them before exposure, exposing them to the corrosive media, post-test removal of visible corrosion products, and reweighing. The corrosion rate is calculated from the mass loss measured, converted to a volume of metal loss by the material density, and finally to a corrosion rate by dividing this volume by the material surface area and the test time. 

With respect to the chemical procedures described by ASTM G 1, the immersion time suggested for coupons in the alternative chemical baths should be used as a guideline only. There are many times when tenacious corrosion products can take significandy longer to remove than that expressed by the standard. AU corrosion products must be removed without resulting in additional corrosion of the metallic substrate for an accurate mass loss measurement. 

If the different materials can be disassembled after testing, mass loss measurements can be performed. In some... 

Mass loss measurements established high rates of corrosion for steel and copper. Potentiodynamic polarization measurements showed that in SRB environment, copper becomes anodic to steel. 

As most gels shrink during drying, it is essential to determine their surface area evolution to calculate the drying flux from mass loss measurements. With appropriate image analysis, very accurate shrinkage curves (as in Fig. 5.34) can be obtained from X-ray transmission images and reconstructed cross-sections (Fig. 5.12). The... 

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