Gd-Mg alloy

The modifications in the hydrogen induced optical, electronic and structural properties of Gd-Mg alloy films have been studied by utilizing both the gas phase loading as well as electrochemical loading. The Gdi Mg alloy films (200 nm) with 0.1 < z < 0.9, capped with... 

GITT and the corresponding normalized transmittance as a function of concentration for some representative Pd capped (10 nm) Gd-Mg alloy films (200 nm), deposited by con-... 

Table 4.1 The fitted electrochemical parameter for the cathodic polarization curve of Mg-Gd-Y alloy under various thin layer thicknesses...

Table 4.1 demonstrated that the open circuit potential of Mg-Gd-Y alloy shifted to the noble direction with the decrease in TEL thickness. Generally, the increased corrosion potential attributed to the acceleration of cathodic process or the inhibition of anodic process. The polarization curve results implied that the cathodic process was significantly inhibited under the TEL condition. So, it could be predicated that the inhibition of anodic process under TEL might be the proper explanation for the increasing of corrosion potential. 

The LIS was carried out at open circuit potential (Fig. 4.13), which was aimed at confirming the results of cathodic polarization curve and at demonstrating the ohmic drop between working and reference electrode. The EIS of Mg-Gd-Y alloy under TEL consisted of two capacitive loops in the high and low frequency ranges. 

When the thickness of TEL was as low as 37 [im, the R( value increased from 1345 to 4096 Qcm, which revealed that there was a protecting film formed on the surface of Mg-Gd-Y alloy and the corrosion resistance of the film enhanced with the decreasing of TEL thickness. It was likely that this had to do with faster accumulation of corrosion products. In other words, the corrosion of Mg-Gd-Y alloy was inhibited under TEL condition, which agreed with the polarization results. 

According to the cathodic polarization curve and EIS results, it was clear that the cathodic process of the corrosion of Mg-Gd-Y alloy was dominated by the hydrogen evolution reaction in the case of TEL. With the decreasing of TEL thickness, the corrosion of Mg-Gd-Y alloy was retarded. 

The corrosion morphology of Mg-Gd-Y alloy after the immersion time... 

The cumulative probability F(f ) is plotted against the frequency of events fn in Fig. 4.16 for Mg-Gd-Y alloy under various TEL thicknesses. The procedure for determining the cumulative probability F(Jf) from / data is described as follows first, all calculated / data are arranged in order from the smallest and then the cumulative probability F(Jn) is calculated as... 

It was found that the distribution of/ shifted to a lower frequency region with the decrease in TEL thickness. Considering that high-frequency events would tend to occur all over the alloy surface, the corrosion of Mg-Gd-Y alloy would be less localized as high-frequency events became dominant. In contrast, the corrosion would be rather localized over the surface as low-frequency events were dominant. 

The above discussion revealed that TEL had significant influence to the pit susceptibility of Mg-Gd-Y alloy. In case of TEL, both the pit initiation rate and the pit growth probability were decreased. 

Van der Sluis et al. (1997) first demonstrated the possibility to attain color neutrality (constant transmittance in the fully hydrogenated state) by alloying R metals (Y, Sm, Gd, and Lu) with Mg. It was shown that by varying the Mg concentration in the R-Mg alloy, one could fine-tune... 

Fig. 150. Log (transmittance) as a function of wavelength fa- Gd-Mg multilayers (with constant average composition 40% and varying periodicities) along with those of Gdo,8oMgo.20 and Gd0.40Mg0.60 alloy films in the fully...

Fig. 151. Variation of switching time (defined as 90% of the optical effects from metal to high hydrogen state) for the Gd-Mg multilayers with constant average composition [25 x (1.68 nm Gd + 1.12 nm Mg)] and varying periodicities. The inset compares the transmittance as a function of the hydrogen exposure time for a 25 x (1.68 nm Gd -I-1.12 nm Mg) multilayer with composition close to Gdo.6oMgo.40 that of a 100 nm alloy film of same composition,...

Figure 5.14. Compound formation capability in the binary alloys of Sc, Y, light trivalent lanthanides (as exemplified by La), heavy trivalent lanthanides (exemplified by Gd) and of the actinides (exemplified by Th, U and Pu). The different partners of the 3rd group metals are identified by their position in the Periodic Table. Notice that a sharper subdivision between compound-forming and not forming metals will result from a shifting of Be and Mg from their position in the 2nd group towards the 12th group (see 5.12.3). The behaviour of the divalent lanthanides Eu and Yb is shown in Fig. 5.7 where it is compared with that of the alkaline earth metals.

---