Accelerated aging experiments

A Thermotron programmable humid oven was employed for the accelerated aging experiments. The temperature of the oven was held steadily at 90 0.2°C throughout this series of experiments. The... 

In principle, if values of at could be determined n times throughout an accelerated aging experiment in which the empirical rate constant, k, is determined, then n simultaneous equations could be solved to yield the chemical rate constants, kt. However, in practice this is not feasible, and Equation 13 is of little analytical value. Nevertheless, our assumption that the property kinetic constant, k, is related linearly to chemical rate constants is verified. Thus, the apparent linearity of the empirical rate constant, kT in Equation 9, with respect to oxygen and acidity suggests the occurrence of chemical processes that are first order in oxygen and acidity. 

The C-F approach treats AH(oo, TJ as an adjustable parameter as it is considered that the linear Cp extrapolation is inaccurate. The data are analyzed by curve fitting plots of AH(ta, TJ against log ta, to assess the thermodynamic aspects from the AH(oo, Ta) parameter, and the kinetic aspects, embodied in />(<<,). both of which are obtainable from this approach. Also considered in the C-F approach is the prediction of t, which is the time to reach 99.9 % of the thermodynamic equilibrium state of the infinitely aged glass, from accelerated aging experiments. 

The example above suggests that the simple mapping of experimental and real times can be obtained only in the simplest case of a uniform in space reaction. A concerted action of species diffusion and reaction makes the mapping problem much more difficult. The situation of simultaneous diffusion and reaction, however, is typical of ageing processes. One thing is obvious accelerated ageing experiments should always be preceded by a theoretical analysis. 

Accelerated ageing experiments are carried out on an NR vulcanisate exposed to air and to seawater. Failure strain, shown to correlate well with the fatigue lifetime, is used to monitor the extent of degradation. The effect of temperature on the rate of ageing follows an Arrhenius law, with activation energies equal to 90 + or -4 and 63 + or -3 kJ/mol for air and seawater ageing, respectively. The difference can be accounted for by the difference in oxygen concentration for the two environments. 35 refs. USA... 

In addition to the stabilizing effect of cathode particles on the electrolyte solutions at elevated temperatures, graphite-like carbon electrodes (anodes) were also foimd to reduce the thermal decomposition of bulk LiPFe electrolyte solutions. However, the reduction of bulk electrolyte decomposition coincided with reactions of the electrolyte with the anode. The surface of the carbon electrode was covered with the products of the electrolyte reduction, which formed a protective solid electrolyte interface (SEl) layer [35-37], The stabilizing effect of these anodes (e.g., based on lithiated mesocarbon microbeads, MCMB) on the electrolyte was proposed to relate to the degradation of the solid-electrolyte interphase (SEl) in LiPFe-based electrolytes at elevated temperatures [32,38], The loss of capacity and power from lithium-ion cells undergoing accelerated aging experiments has been attributed to the presence of thermal decomposition products of the electrolyte in the anode SEl [32],... 

During the accelerated aging experiment the resistance of the Nafion membrane did not change, but that of the grafted membrane increased substantially (Fig. 11, plot d). This suggests that the grafted polymer looses ion-exchange... 

The loss of antioxidants by migration was first observed in the 1960s for both elastomers [16,17] and polyethylene [ 18]. In a 1973 paper, Bair ]19] described a microscopy study of surface buildup of a hindered phenol antioxidant at a 0.08 percent level in a low-density polyethylene. Seventy percent of the antioxidant in antioxidant-polymer compounds was expelled in three days at 70 °C. He notes the danger of accelerated aging experiments, which do not account for this exudation. 

Wolf C, Macho C, Lederer K. Accelerated ageing experiments with crosslinked and conventional ultra-high molecular weight polyethylene (UHMW-PE) stabilised with alpha-tocopherol fat total joint arthroplasty. J Mater Sci 2006 December 17(12) 1333-40. 

For the purposes of the current investigation, durability of FRP composites is characterized by the results of accelerated aging experiments. Predictions for FRP-composite tensile modulus and tensile strength for both CFRP and GFRP composites in this analysis are modeled with an Arrhenius rate relationship derived from results for wet lay-up CFRP composites immersed in deionized water at 23 °C for approximately 2 years (Karbhari and Abanilla, 2007). The time-dependent functions for tensile modulus and tensile strength for FRP composites are as follows ... 

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