Accelerating aging temperature

B. It is also necessary that activation energy be independent of temperature. This can be assessed by using several temperatures in the study, including an accelerated-aging temperature only slightly greater than room temperature. 

The popular accelerated aging temperature used to predict natural aging is 65°C (150°F), with the adhesive-coated products either in roll or sheet form independently supported in a controlled humidity environment, such that they occupy less than a quarter of the available space to ensure ample circulating air. Typical commercial products are exposed to an 80% humidity using a saturated reagent grade ammonium sulfate bath [24],... 

Notice that these principles do not explicitly define the test parameters. However, the guidance documents developed by CDHR do provide accelerated aging protocols for specific devices within their jurisdiction based on the Q,q theory for chemical reactions. So, the theory postulated by Von t Hof using the Qio value (which states that a rise in temperature of 10°C will double the rate of chemical reaction) is the most convenient method of estimating the approximate ambient storage time equivalent at a selected accelerated aging temperature, despite flie Imown limitations and concerns for use on complex and dissimilar material structures. 

For the example shown in the flowchart, using an accelerated aging temperature of 55 C, the equivalent ambient storage time for 1 year is 26 days. Caution must be taken not to accelerate the aging too much, since elevating the temperature of packaging materials could result in a mode of failure that might never be observed in real life (material roduct interaction, creep, defoimation, etc.) (Reich et al., 1988). 

These findings clearly illustrate how the results of so-called "accelerated-aging" tests can be affected by the high temperatures in ordinary xenon- and carbon-arc equipment and can, therefore, lead to erroneous conclusions regarding the photochemical behavior of materials at near-normal temperatures (23). 

Nalidixic acid is stable up to five years under reasonable conditions of temperature and humidity. Pawelczyk and Plotkowiakowa(17) subjected sodium nalidixate solutions to accelerated aging, but were unable to identify decomposition products. Detzer and Huber(lS) studied the photolysis and thermolysis of nalidixic acid in the presence of oxygen. Photolysis produced de-carboxylated nalidixic acid, structure A, and a diketone product, structure B, as well as carbon dioxide and ethylamine. 

The solution is made up from an aqueous solution 0.4 M in NaiSOs and 0.2 M in Se. This solution typically is stirred at 60°C for a couple of hours (the Se dissolves slowly, the reason a fresh solution is usually not made up every time). If this solution is prepared over a longer time (maybe 6 hours and/or at a higher temperature, even boiling), it will undergo accelerated aging. This results in more reproducible deposition conditions on one hand, but at the cost of reduced reactivity and a shorter lifetime of the solution. 

The use of quasi-solid-state electrolytes usually reaches the goal of a superior thermal stability with respect to liquid electrolytes cells can survive prolonged periods (accelerated aging of 1000 h) at relatively high temperatures (55-80°C) under... 

Vacuum-Steam-Pressure Test. A special aging test which has been used successfully in the USA to accelerate aging to produce the effects of 6-month tropical exposure on certain types of sealed fuzes. It is primarily a development test which can be used during production The test consists of subjecting bare fuzes to 1000 fifteen-minute consecutive cycles in a vacuum-steam-pressure environment. The 1000 cycles takes about 10 days of continuous running time. The basic cycle consists of temperature-humidity cycling superimposed on pressure cycling in a test chamber with a salt laden atmosphere. Representative curves of temperature and pressure are shown in Fig 1... 

The relationship between accelerated aging and real-time aging for packages has not been determined, and although the theory states that for every 10°C rise in temperature the reaction rate of material doubles, this should be applied with some caution for such materials as medical devices packaging. 

Here, the best way to accelerate aging is to decrease the sample thickness (when possible). Except in very highly hydrophilic materials, D is independent of the relative hygrometry or water activity, but is an increasing function of temperature ... 

Accelerated aging by a simple temperature variation not only increases the reaction rate but also modifies the spatial distribution of degradation events. Caution must be taken, therefore, in the interpretation of experimental results or in the comparison of data from various sources. 

The stability is another critical aspect for RM use it has to be verified in relation to the purpose of the study, e.g. over the duration of an interlaboratory study, or over long-term storage periods (for CRMs). The (in)stability should be studied or known before the RM is produced and should be monitored on the batch of RM. Studies may be performed under accelerated ageing conditions, e.g. elevated temperatures, or at various temperatures over defined periods of time. The BCR has developed a strategy with respect to stability assessment which has been successfully used for a wide variety of chemical species as described later in this chapter. Full details on the organisation of such studies are described elsewhere (Quevauviller et al., 1996a Quevauviller, 1998b). 

In the laboratory aging procedure (Johnson and Korcek, 1991), high temperature antioxidant capabilities were assessed at 160°C in a batch reactor using blow by components to accelerate oil degradation. The sample analyzed after five hours of accelerated aging of (MoDTC + ZDDP) without MPH, had lost its ability to reduce friction coefficient to below that which would be observed for a ZDDP - only system. The five hour sample from the mixture (MoDTC + ZDDP) containing added MPH still provided substantial friction reduction and the results are very similar to those observed for the fresh mixtures, p 0.05. 

---