Oxidation service lifetime

Oxidation. Oxidation reactions utilising supported catalysts usually present extraordinary challenges, because most oxidations are highly exothermic and may generate extremely high localized temperatures that the catalyst surface must survive to have an adequately long service lifetime. In addition, in many cases the desired product is subject to further oxidation, which must be prevented or minimized. 

The service lifetime of UV absorbers is prolonged in combination with phenolic antioxidants, protecting the ESIPT mechanism from depletion by preferential oxidation of the antioxidant. 

Material specifications for under-the-hood automotive applications require retention of mechanical properties for materials subjected to changes in ambient temperatures (-40-175°C) for prolonged periods of time. Besides temperature, the prolonged service lifetime of a molded part reflects material durability to extremes in environmental conditions that include moisture, thermo-oxidative degradation, exposure to sunlight, and creep resistance under high static stress loads. 

Under normal conditions, oxidative reactions progress extremely slowly. Correspondingly, the associated oxidative stabiliser consumption is also slow. However, not only oxidation, but other chemical degradation processes can also destroy antioxidants. For example, phosphates and other antioxidants are hydrolysis-sensitive (Gugumus 1990). In addition to such chemical antioxidant depletion , there are physical depletion processes The concentration of the added antioxidants is reduced by extraction and migration processes while the plastic is stored and used (Pfahler and Lotzsch 1988). Such processes are usually the main cause of gradual loss of stabilisers at application temperatures. All these depletion processes determine induction time t 2 and thus service lifetime of the plastic. They... 

However, none of these experiments were pursued to the end of the depletion process and oxidative degradation was not actually achieved, since this requires very long test times even at high temperatures. Therefore, the depletion rates have to be considered with caution because they have been estimated from short-term experiments, and the assumption that the antioxidant depletion time is the most relevant part of the service lifetime, needs experimental justification. 

What conclusion about service lifetimes can be drawn from these longterm test results For our discussion it is crucial that the change in OIT value provides at least a rough estimation for the depletion time t2. This assumption was established for the antioxidant package commonly used in HOPE geomembranes and it explains the oxidation behaviour in the OIT measurement itself as described in Sect. 3.2.7. In the following we will show that a consistent explanation of all our experimental results is possible within this interpretation scheme. 

This paper will outline performance validation testing that has been completed on the MCO coating to evaluate oxidation and chromium volatilization resistance that limit the service lifetime of coated metallic interconnects. 

Thomas Alva Edison invented the alkaline nickel-iron battery early in the 20 century. Iron is the negative pole of the battery, nickel oxide the positive. The cell has a terminal voltage of 1.15 V. In industrial applications and for local reserve power stations many cells are connected in series. The service lifetime for this battery type is re-... 

In a simplistic way, extrapolation of the curves in Fig. 3.13 to 20 years aUows to approximate oxidation development at the IHX end-of-Iife operating at 950°C. Provided that corrosion kinetics has not changed during the service lifetime, the aUoy microstmcture would be affected over hundreds of micrometers surface layer thickness of 50 pm, internal oxidation of A1 at grain boundaries up to 250 pm, carbide dissolution up to more than 0.7 mm. These dimensions are to be compared with the actual component wall thickness of a few millimeters for a compact design. And it is necessary to further investigate the effect of these microstmcture changes on the mechanical properties. 

Cyclic oxidation testing is a key method to aid material selection and to predict service lifetime of components. However, it is a complex procedure that has many possible variables. Hence it is often difficult to compare data from different laboratories unless either (i) the procedures in each laboratory are similar, or (ii) the influence of any differences in procedure on the resultant data is known. 

One important point is the combined action and effect of interface structure and interface reactions. The development of this kind of model could lead to a new approach to questions linked to the effect of impurities and their segregation, to the effect of reactive elements or to the coupling between mechanical and oxidation behaviour, which could be of major importance in the determination of service lifetime for high-temperature components. 

A1 concentration was <10A1 after only 6kh at 800°C. Many power generation applications desire 40 kh minimum service lifetimes (Pint et al., 2006b). In addition to interdiffusion and its effect on substrate mechanical properties (Dryepondt et al, 2006), other coating compatibility problems must be addressed, such as the formation of undesirable phases and surface crack nucleation. Thus, the notion that coatings are universally available to protect non-oxidation resistant compositions is limited to short lifetime applications at best. 

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