Annealing temperature effect

Figure 25 shows the annealing temperature effect on the thermal stability factor KuV /kBT [49] and anisotropy field Hk for the FePt C films with 45 vol. %C. Hk was calculated from Ho = 0.48 Hk, Ho was obtained from the Sharock fitting parameter. Hk increases rapidly with annealing temperature TA between 600 and 625 °C, then increases slowly and to saturation for TA > 625 °C. KuV /kBT increases linearly with TA except for the point at 675 °C that might be caused by either experimental error or the activation volume V being unusually small. Since Ka would be constant after the completion of L 0 ordering, the further increase of KuV /kBT with Ta is mainly due to the increase of V. As shown in Fig. 26, Ku is about 1.2 x 107 erg/cm3 for TA > 625 °C V increases slowly initially and then increases more rapidly with TA, which results in the quasi-linear increase of KuV /kBT.

Among arsenic, bismuth, lead, antimony, and sulfur in the concentration range of 5—26 ppm, bismuth had the greatest unit effect (59). A decrease in the annealing temperature prior to cold deformation led to a decrease in the measured unit effectiveness, indicating that at low temperature bismuth is not in sohd solution. Lead lowered the recrystaUization temperature, provided that the samples were aimealed at 700°C or lower. A precipitation reaction between lead and sulfur was proposed (60). 

In a detailed study the dissolution kinetics of shock-modified rutile in hydrofluoric acid were carefully studied by Casey and co-workers [88C01], Based on the defect studies of the previous sections in which quantitative measures of point and line defects were obtained, dissolution rates were measured on the as-shocked as well as on shocked and subsequently annealed powders. At each of the annealing temperatures of 200, 245, 330, 475, 675, 850, and 1000 °C, the defects were characterized. It was observed that the dissolution rates varied by only a factor of 2 in the most extreme case. Such a small effect was surprising given the very large dislocation densities in the samples. It was concluded that the dissolution rates were not controlled by the dislocations as had been previously proposed. 

For similar samples on alumina, these effects are not observed, as Indicated In Table I. Mo migration of aluminum or oxygen species Is observed In AES, and the capacity of the film to adsorb carbon monoxide Is not altered by changing the annealing temperature from 525 to 760 K. 

The effect of annealing temperatures (65 - 250 °C) and blend composition of Nafion 117, solution-cast Nafion , poly(vinyl alcohol) (PVA) and Nafion /PVAblend membranes for application to the direct methanol fuel cell is reported in [148], These authors have found that a Nafion /PVAblend membrane at 5 wt% PVA (annealed at 230 °C) show a similar proton conductivity of that found to Nafion 117, but with a three times lower methanol permeability compared to Nafion 117. They also found that for Nafion /PVA (50 wt% PVA) blend membranes, the methanol permeability decreases by approximately one order of magnitude, whilst the proton conductivity remained relatively constant, with increasing annealing temperature. The Nafion /PVA blend membrane at 5 wt% PVA and 230 °C annealing temperature had a similar proton conductivity, but three times lower methanol permeability compared to unannealed Nafion 117 (benchmark in PEM fuel cells). 

The effect of the annealing temperature on the initial modulus is also presented in Figure 20.8. The moduli of monofilaments annealed at 160 °C for 30 min are higher than those of normal monofilaments, because the matrix polymers are recrystallized with a low PHB content, and the LCP molecules in the domain are reoriented with a high PHB content. The thermal treatment of the PHB/PEN/PET fibers can be an effective way to improve the tensile properties, especially the tensile modulus, and high-speed winding may be a promising way to obtain fibers... 

In physical vapor-deposited as well as sputter-deposited films, incorporated gases can also increase stress and raise annealing temperatures. Similar effects are present in electron beam-evaporated films. 

Figure 18 Free carrier (electron) concentration in SiC samples implanted with P ions at RT (circles) and 1200 ° C (squares) as a function of annealing temperature. Annealing was performed for 20 min in Ar atmosphere. The electron concentration was obtained from Hall effect measurement at RT.

In many spinel systems, substitution for iron may result in a distribution of the solute on both A and B sites that varies strongly with temperature. In this case it is possible to vary the physical properties by quenching from different annealing temperatures. In each of the examples chosen to illustrate this effect, there is a point of additional interest to be introduced. 

Each of these effects are described in the following sections, with the discussion limited to the case where the B concentration does not exceed solid solubility at the annealing temperature. 

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