Oxygen consumption, measurement parameters

Oxygen consumption calorimetry with E = 13.1 kJ/g is used to measure heat release rate as a function of time. The specific heat release rate, Q(t), in W/g is equal to the heat release rate divided by the initial specimen mass, mG. The following live parameters are calculated when... 

This mechanistic scheme leads to a system of differential equations expressing the build-up or consumption rate of the reactive species. P°, P02°, POOH, O2 and PH concentrations can be derived from the above mechanistic scheme in which the only adjustable parameter is the initial hydroperoxide concentration. Oxygen diffusion and consumption can be coupled (see Colin et al. in the same Issue) but in the case under study here, the low sample thickness (70 pm) leads to a quasi uniform oxidation within that thickness. POOH build up (5) and oxygen consumption (7) can be measured, allowing us to partially verify this model. Carbonyl build-up can also be simulated by assuming that carbonyls result mainly from rearrangements of P0° radicals and by using a new adjustable parameters 72, that accounts for the yield of carbonyl buil-up in initiation and termination steps of the mechanistic scheme. 

One of the most important parameters that can be used to characterise an unwanted fire is the rate of heat release. It provides an indication of the size of the fire, the rate of fire growth, and consequently the release of smoke and toxic gases, the time available for escape or suppression, the types of suppressive action that are likely to be effective, and other attributes that define the fire hazard. Methods based on the oxygen consumption principle are now available to measure the rate of heat release reliably and accurately. The principle depends upon the fact that the heats of combustion of organic materials per unit of oxygen consumed are approximately the same. This is because the processes in the combustion of all these products involve breaking of G-C and C-H bonds (which release approximately the same amount of energy) with the formation of carbon dioxide and water. 

The chemical oxygen demand (COD) test requires less time and results are more reproducible than that for BOD determination. It is a parameter established for the assessment of the amount of both organic and inorganic matter contained in a water body and measures the ultimate oxygen consumption of a sample, being widely employed in analytical laboratories for monitoring water quality. 

The evaluation of the flammability properties of PMMA and its composites with AlOOH was done using a cone calorimeter (Fire Testing Technology). A 100 x 100 x 4 mm sheet was exposed to a radiant cone (35 kW.m ). The HRR was calculated from the oxygen consumption as measured with an oxygen analyzer. Table 12.1 gathers the parameters obtained in comparison with the pure PMMA sample. 

As before, with biosensors, the rate of oxygen consumption is measured, but the sample solution is not continuously aerated. Microorganisms are adsorbed on the electrode surface, supported by different kinds of materials. The electrode is then introduced into the water sample and DO is measured. Many works on this topic have been published (Table 13.1), with encouraging results. Unfortunately, BOD5 cannot yet be substituted by the parameter supplied by these electrodes (i.e., BODS). 

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