Amorphous ageing effect

The appearance of a perpendicular anisotropy in the mixed state of both amorphous and crystalline structure was reported by Miyazaki et al. (1997) for (Tbo.3Dyo.7)0.33Feo.67 films fabricated above 673 K (400°C) (see fig. 32). The thermal stability and the reproducibility of those films were studied also. For films prepared with substrate temperatures above 673 K (400°C), the magnetostriction changes remarkably after 3 months. This is due to ageing effects, related to the formation of the Laves phase (Tb,Dy)Fe2. 

Catalyst Aging Effects. The yields for most of the catalysts remain relatively stable with catalyst aging. In constant conversion runs such as these, the catalyst temperature is increased to maintain conversion and yield stability can be shown by a plot of yield versus average catalyst temperature. Figure 6 shows results for two amorphous catalysts. 

Struik showed furthermore that for amorphous and semi-crystalline polymers the ageing effect after complicated thermal histories is strikingly similar. In both cases high stresses can erase previous ageing and "rejuvenate" the material. 

A modulus value increase upon storage under ambient conditions is also reported for other semi-crystalline polymers like, for instance, polypropylene. Struik [11] measured for PP a continuously increasing dynamic stiffness at 20°C in combination with a decrease of the intensity of the glass-rubber (S) transition of PP (the temperature location of the S-transition did not change). Struik called this phenomenon an amorphous phase ageing effect a densification process of the amorphous PP phase due to a free volume relaxation effect. 

The solubility of amorphous silica in salt water solutions at 0 to 25 C has been the subject of much study in recent years, and it is interesting that determination of such an apparently simple nxunber can yield such a wide range of results (Table I). As an illustration of the problem, Willey ( 1) showed a plot of the solubility of amorphous silica in seawater at 0 C and at pressures from 1 to 1000 atmospheres pressure A later study using the same experimental apparatus ( ) reproduced the same plot. However, two months later during the next experiment with the same equipment and the same silica, a solubility decrease occurred at all pressures, and the pressure dependence became slightly different than in both previous studies. This aging effect caused a solubility decrease of approximately 20%. Two other pressure studies (3, , which used different experimental... 

Because PLA is a semi-crystalline polymer, thermal history affects the physical properties of PLA, inducing changes in the crystalline/amorphous ratio, as well as large physical aging effects on the glassy amorphous phase (Gelli and... 

The effect of physical aging on the crystallization state and water vapor sorption behavior of amorphous non-solvated trehalose was studied [91]. It was found that annealing the amorphous substance at temperatures below the glass transition temperature caused nucleation in the sample that served to decrease the onset temperature of crystallization upon subsequent heating. Physical aging caused a decrease in the rate and extent of water vapor adsorption at low relative humidities, but water sorption could serve to remove the effects of physical aging due to a volume expansion that took place in conjunction with the adsorption process. 

There appear to be no extrinsic field studies on the familiar amorphous chromia gel catalyst although it is known (24) to have only a slight indication of the zero field anomaly shown by a-Cr203 at TN. A gel catalyst aged in hydrogen has a small positive field effect at 323 K and a small negative effect at 273 K. 

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