Temperature aging

Fig. 2. Tensile strength and elongation retention after aging of FZ. Aging temperature D, 150°C A, 175°C O, 200°C. To convert MPa to psi, multiply by...

Fig. 10.10. Detailed TTT diagram for the Al-4 wt% Cu alloy. We get peak strength by ageing to give 8". The lower the ageing temperature, the longer the ageing time. Note that GP zones do not form above 1 80°C if we age above this temperature we will foil to get the peak value of yield strength.

Table 1 Effect of Stabilizer Concentration on Film Polyethylene Aging (temperature 120 C, thickness 0.2 mm)...

The effect of thermal aging on polyethylene and isotactic polypropylene have been studied by Konar et al. [49]. They used contact angle, contact angle hysteresis, and XPS to characterize the modified surfaces of the polymers. Hysteresis increased with aging temperature. In the case of polyethylene, thermal aging led to a significant increase in adhesion strength of polyethylene with aluminium, but the increase in the case of polypropylene was much less marked. 

Fig.2. Amount of the plate-like phases of AlZn78 alloy versus cooling rate (left) and ageing temperature for 10 hours (right).

The rate at which ageing occurs depends on the ageing temperature. At very low ageing temperatures, over-ageing is not observed in a realistic time... 

In other instances, reaction kinetic data provide an insight into the rate-controlling steps but not the reaction mechanism see, for example, Hougen and Watson s analysis of the kinetics of the hydrogenation of mixed isooctenes (16). Analysis of kinetic data can, however, yield a convenient analytical insight into the relative catalyst activities, and the effects of such factors as catalyst age, temperature, and feed-gas impurities on the catalyst. 

FIGURE 3.24 Plots of volume fraction of the filled rubber in the swollen gel (Vrf) against aging temperature for acrylic rubber (ACM)-silica and epoxidized natural rubber (ENR)-silica hybrid nanocomposites. (From Bandyopadhyay, A. and Bhowmick, A.K., Plastic Rubber Comp. Macromol. Eng., 35, 210, 2006. Courtesy of Money Publishers.)... 

The activity of the Au/metal oxide catalysts is extremely sensitive to the method of preparation. The Au/metal oxide catalysts were prepared by the co-precipitating method [1]. During the course of this study, we have determined that the activity and the stability of the catalyst for room temperature CO oxidation were a function of Ph of the solution, temperature of precipitation, aging temperature and time, catalyst wash procedure, and calcination. 

Sometimes, properties are measured at the ageing temperature, which is a more severe method. 

Figure 4.118 shows three examples, for three different polyimide grades, of the half-lives (50% mechanical performance retention) in hours versus the air-ageing temperature indicated in °C. 

In subsequent aging studies the polyol component showed virtually no change In acid number at any of the aging temperatures (ambient, 60 , 71 C) over 13 months. The Isocyanate was shown to age similarly to the Isocyanate In Formulation 2. As a result, the above formulation Is being employed In the field ... 

Finally, a third formulation was devised which excluded the use of Freon 11 In the polyol component. Freon 11 was placed In the Isocyanate component and both Isocyanate and polyol components were changed to meet viscosity considerations. Subsequent aging studies showed the Isocyanate to age similarly to the previously aged (Formulation 2) Isocyanate. The polyol showed virtually no Increase In acid number at any aging temperature over 13 months. Thus, at ambient temperature we would expect a 6-8 year system lifetime on the Isocyanate before a 10% change In analytical properties would dictate a material change-out. The polyol appears to have a greater lifetime, but would probably be replaced at the same time. 

Figure 45. Age-temperature plot of the data from Figure 44. T = Terres Noires data (Dunoyer de Segonzac, 1969) v/here no depth information is available and where the temperature is estimated from the stability of fully expandable montmorillonite. Symbols as in Figure 44.

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