Mass loss

After the determination of the decomposition model, the mass transfer during decomposition can be obtained according to Eq. (4.16)  

As only resin decomposes to gases when the temperature exceeds the decomposition temperature, most of is composed of fibers. The TGA above also evidenced that about 86% of the remaining materials are fibers. Accordingly, Eq. 4.16 can be expressed as  

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DTDP > DIDP > DINP > DOP > DIHP > DBP. Higher molecular weight esters such as trimeUitates are even more thermally stable and trimeUitate esters find extensive use in the demanding cable specifications which have strict mass loss requirements. 

The actual time required for poly-L-lactide implants to be completely absorbed is relatively long, and depends on polymer purity, processing conditions, implant site, and physical dimensions of the implant. For instance, 50—90 mg samples of radiolabeled poly-DL-lactide implanted in the abdominal walls of rats had an absorption time of 1.5 years with metaboHsm resulting primarily from respiratory excretion (24). In contrast, pure poly-L-lactide bone plates attached to sheep femora showed mechanical deterioration, but Httie evidence of significant mass loss even after four years (25). 

A final type of measurement is the detection of localized corrosion, such as pitting or crevice attack. Several corrosion-measuring probes can be used to detec t localized corrosion. Some can detect locahzed corrosion instantaneously and others only its result. These types of corrosion may contribute little to the actual mass loss, but can be devastating to equipment and piping. Detec tion and measurement of localized corrosion is one of the areas with the greatest potential for the use of some of the newest electrochemicaUy Based corrosion monitoring probes. 

Corrosion Rate Measurements Determining a corrosion rate from measured parameters (such as mass loss, current, or electrical potential) depends on converting the measurements into a corrosion rate by use of relationships such as Faradays law. 

A plot of mass loss versus time can provide information about changes in the conditions under which the test has been run. One example of such a plot comes from the ASTM Standard G96, Standard Gmde. ... 

In given work the possibilities enumerated above of varieties of thermal analysis used to reseai ch of solid solutions of hydrated diphosphates with diverse composition. So, for example, the results of differential-thermal analysis Zn Co j P O -SH O showed, that it steady in the time of heating on air to 333 K. A further rise of temperature in interval 333 - 725 K is accompanied with the masses loss, which takes place in two basic stages, registered on crooked TG by two clear degrees, attendant to removal 4,0 and 1,0 mole H O. On crooked DTA these stages dehydration registers by two endothermic effects. In interval 603 - 725 K on crooked DTA is observed an exothermal effect. 

Anodes for boilers can be tested by such methods. Good-quality magnesium anodes have a mass loss rate per unit area < 30 g m d", corresponding to a current yield of >18% under galvanostatic anode loading of 50 /xA cm" in 10 M NaCl at 60°C. In 10 M NaCl at 60°C, the potential should not be more positive than t/jj = -0.9 V for the same polarization conditions [27],... 

Six iron anodes are required for corrosion protection of each condenser, each weighing 13 kg. Every outflow chamber contains 14 titanium rod anodes, with a platinum coating 5 /tm thick and weighing 0.73 g. The mass loss rate for the anodes is 10 kg A a for Fe (see Table 7-1) and 10 mg A a for Pt (see Table 7-3). A protection current density of 0.1 A m is assumed for the coated condenser surfaces and 1 A m for the copper alloy tubes. This corresponds to a protection current of 27 A. An automatic potential-control transformer-rectifier with a capacity of 125 A/10 V is installed for each main condenser. Potential control and monitoring are provided by fixed zinc reference electrodes. Figure 21-2 shows the anode arrangement in the inlet chamber [9]. 

FIRAC is a computer code designed to estimate radioactive and chemical source-terms as.sociaied with a fire and predict fire-induced flows and thermal and material transport within facilities, especially transport through a ventilation system. It includes a fire compartment module based on the FIRIN computer code, which calculates fuel mass loss rates and energy generation rates within the fire compartment. A second fire module, FIRAC2, based on the CFAST computer code, is in the code to model fire growth and smoke transport in multicompartment stmetures. 

ISO EN 9886 presents the principles, methods, and interpretation of measurements of relevant human physiological responses to hot, moderate, and cold environments. The standard can be used independently or to complement other standards. Four physiological measures are considered body core temperature, skin temperature, heart rate, and body mass loss. Comments are also provided on the technical requirements, relevance, convenience, annoyance to the subject, and cost of each of the physiological measurements. The use of ISO 9886 is mainly for extreme cases, where individuals are exposed to severe environments, or in laboratory investigations into the influence of the thermal environment on humans. 

Body mass loss, gross The reduction in body mass over a given period of time, mg, in kg. 

Body mass loss, respiration The loss of body mass due to respiratory evaporation, in kg. 

Body mass loss, sweat The body mass loss due to sweating, in kg. 

Aggregate Epoxy binder compositions Mass loss after abrasion (g)... 

The main characteristic of attack by halogens at elevated temperatures is that most reaction products are volatile compared with the solid products that form in all cases considered hitherto in this chapter. Thus, in cases where metals are exposed to pure halogen gases large mass losses are usually reported with very little external scale formation. Li and Rapp " showed that internal chloridation occurred when nickel-chromium alloys were exposed to Ni + NiClj powders at 700-900°C. However, where oxide scales can also form, as in combustion gases, the oxide layer was usually highly... 

Alloy Mass loss (%) Depth of subsurface attack (mm)... 

Mass loss (S ) = ML(i) - Mt.(0/ML(i) x 100 Internal attack exiusivc of corrosion mass losses... 

Probably the most frequently made observation is the change in mass of a test-piece. This may take the form of a mass gain or a mass loss. 

Expression of mass loss in terms of a percentage of the original mass of a test-piece is usually meaningless except for comparing specimens of the same size and shape, since it does not take into account the important relationship between surface and mass. 

Since it is often difficult to visualise the extent of attack in terms of depth from such mass-loss units as mdd, it is common practice to convert these mdd figures into others to indicate depth of penetration, i.e. inches per year (ipy), mils or mm y" . Such calculations suffer from the same defects as the mdd figures in that they take into account neither changes in corrosion rates with time nor non-uniform distribution of corrosion. However, since such conversions are often made it is desirable for the initial reporter of the test results to make the calculations accurately and to report corrosion rates in both mdd and mm y or similar units. 

The characteristic mode of corrosion of some alloys may be the formation as a corrosion product of a redeposited layer of one of the alloy constituents, as in the case of the brasses that dezincify, or of a residue of one of the components, as in the case of the graphitic corrosion of cast iron. Particularly in the case of the dezincified brass, the adherent copper is not likely to be removed with the other corrosion products, and therefore the mass-loss determination will not disclose the total amount of brass that has been corroded. This is especially important because the copper layer has very little strength and ductility and the extent of weakening of the alloy will not be indicated by the mass loss. In these cases, also, the mass-loss determinations must be supplemented by, or replaced by, mechanical tests or metallographic examination, or both, to reveal the true extent of damage by corrosion. Difficulties in obtaining accurate mass losses of heavily graphitised specimens have been reported... 

Sample no. Alloy Mass loss after 1 0(X) h (g) Penetration of impingement pit (% of cross-section) Appearance... 

It is evident from previous considerations (see Section 1.4) that the corrosion potential provides no information on the corrosion rate, and it is also evident that in the case of a corroding metal in which the anodic and cathodic sites are inseparable (c.f. bimetallic corrosion) it is not possible to determine by means of an ammeter. The conventional method of determining corrosion rates by mass-loss determinations is tedious and over the years attention has been directed to the possibility of using instantaneous electrochemical methods. Thus based on the Pearson derivation Schwerdtfeger, era/. have examined the logarithmic polarisation curves for potential breaks that can be used to evaluate the corrosion rate however, the method has not found general acceptance. 

Stern and Weisert " by taking arbitrary values of the Tafel constants showed that corrosion rates determined by the polarisation resistance techniques are in good agreement with corrosion rates obtained by mass loss methods. 

The controversy that arises owing to the uncertainty of the exact values of and b and their variation with environmental conditions, partial control of the anodic reaction by transport, etc. may be avoided by substituting an empirical constant for (b + b /b b ) in equation 19.1, which is evaluated by the conventional mass-loss method. This approach has been used by Makrides who monitors the polarisation resistance continuously, and then uses a single mass-loss determination at the end of the test to obtain the constant. Once the constant has been determined it can be used throughout the tests, providing that there is no significant change in the nature of the solution that would lead to markedly different values of the Tafel constants. 

An obvious method for studying galvanic corrosion either with or without supplementary electrical measurements is to compare the extent of corrosion of coupled and uncoupled specimens exposed under identical conditions. Such measurements may use the same techniques for estimating corrosion damage, such as mass-loss determinations, as have been described in connection with ordinary corrosion tests. 

A relationship was also established between the oxide-reduction time and time of exposure, and the results for a mild steel and a lCu-3Ni weathering steel were similar to those obtained by mass loss. The authors give various expressions that relate oxide-reduction time (min) with corrosion rate (mm/y), and claim that a short exposure to a laboratory SO2 atmosphere followed by determining the E vs. time and oxide-reduction time provides a rapid method of evaluating weathering steels. 

Nitric acid test t 65 wt.% HNOj Five 48 h exposures to boiling solution refreshed after period Average mass loss per unit area of five testing periods -1- 0-99 to -1- 1-20 1. Chromium-depleted areas 2. <7-phase 3. Chromium carbide... 

Acid ferric- sulphate (Streicher) test n 50wt.% H2SO4 -1-25 g/l ferric sulphate 120 h exposure to boiling solution Mass loss per unit area -1- 0-7 to -1- 0-9 1. Chromium-depleted areas 2. <7-phase in some alloys... 

Nitric-hydrofluoric acid test 1 10% HNO3 -1- 3% HF 4 h exptosure to 70° C solution Comparison of ratio of mass loss of laboratory annealed and as-received samples of same material Corrosion potential of 304 steel = -l-O-14 to -I-0-54 1. Chromium-depleted areas 2. Not for 0-phase 3. Used only for Mo-bearing steels... 

Hydrochloric acid test 1 10% HCl 24 h in boiling solution 1. Appearance of sample after bending around mandril 2. Mass loss per unit area (a) Redox pxjtential = -I-0-32 (b) Corrosion potential = -0-2 0-1 1. Alloy-depleted area 2. Not for 0-phase... 

Nitric acid Cr II 5 N H2SO4 -1- 0-5 N Boiling with solution 1. Mass loss per unit (a) Redox potential Solute segregation to... 

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