Alloys doping effect

Dilute binary alloys of nickel with elements such as aluminium, beryllium and manganese which form more stable sulphides than does nickel, are more resistant to attack by sulphur than nickel itself. Pfeiffer measured the rate of attack in sulphur vapour (13 Pa) at 620°C. Values around 0- 15gm s were reported for Ni and Ni-0-5Fe, compared with about 0-07-0-1 gm s for dilute alloys with 0-05% Be, 0-5% Al or 1-5% Mn. In such alloys a parabolic rate law is obeyed the rate-determining factor is most probably the diffusion of nickel ions, which is impeded by the formation of very thin surface layers of the more stable sulphides of the solute elements. Iron additions have little effect on the resistance to attack of nickel as both metals have similar affinities for sulphur. Alloying with other elements, of which silver is an example, produced decreased resistance to sulphur attack. In the case of dilute chromium additions Mrowec reported that at low levels (<2%) rates of attack were increased, whereas at a level of 4% a reduction in the parabolic rate constant was observed. The increased rates were attributed to Wagner doping effects, while the reduction was believed to result from the... 

AlGaN alloys doped with Si have been grown by electron cyclotron resonance (ECR) MBE at temperatures between 700 and 800°C [23,24], These layers were found to have net carrier concentrations of 1016 to 1019 cm 3 as measured by the Hall effect technique. The carrier concentration varies only slightly on alloying up to 25% Al. The samples were found to be smooth and free from cracks. Murakami et al also reported crack-free surfaces of Si doped Alo.1Gao.9N with a carrier concentration of up to 2 x 1018 cm 3 [25],... 

Figure 11.7. A. NMR spectra of an Al-Mg alloy containing zinc, showing the signal from the matrix (upper) and from the precipitate, represented by stoichiometric MgnAli2 (lower). The 2 middle spectra show the effect of aging time at 200°C on the relative amounts of matrix and precipitate phases. B. Knight shift of the matrix of binary Mg-Al alloys as a function of aluminium content. C. Knight shift of the precipitate phase in Mg-Al alloys doped with zinc as a function of the Zn content. From Celotto and Bastow (2001) by permission of Elsevier Science.

In a recent paper, sulfidation kinetics of Mn—li and Mn—Cr alloys have been studied [61], and the doping effects have... 

Study of the doping effects is an important step in the description of the mechanisms through which the structure and properties of more complicated systems - composite alloys - are formed. 

It is important to stress once again the fact that the sulfidation rate of the discussed Al-Mo alloys is more than one order of magnitude lower than that of pure molybdenum (Fig. 20.26). This rather unexpected situation results from the doping effect. The inner barrier scale layer on these alloys, constituting the main part of the scale, is composed mainly of the M0S2 phase doped with... 

It is interesting to explain the lower sulfidation rate of Al-Mo alloys as compared to pure molybdenum in terms of the doping effect. The predominant defects in M0S2 scale growing on pure molybdenum are singly ionized interstitial sulfide ions and electron holes (MoS2+ f). The formation of these defects may be described by the following quasi-chemical reaction ... 

Alloy Rayons. It is possible to produce a wide variety of different effects by adding materials to the viscose dope. The resulting fibers become mixtures or aUoys of ceUulose and the other material. The two most important types of aUoy arise when superabsorbent or flame retardant fibers are made. 

Like sulphur, phosphorus appears to have little effect on the overall scaling of iron alloys in air. It may, however, play a role in suppressing breakaway oxidation in carbon steels in CO/CO2 environments. Donati and Garaud " found that the tendency for breakaway was lower over ferrite, where P segregates. To confirm this, the authors doped pure Fe with P and found that... 

Endohedral doping (encapsulation) of other materials within carbon nanostructures can be carried out by nano-capillary effects or during synthesis (Fig. 4.3(b)). A great variety of halides, oxides, metals and alloys have been encapsulated within CNTs [36-41]. When transition metals are encapsulated, the entire sample can exhibit high magnetic coercivities ca. 0.22 T [42,43]. The encapsulation of C60 molecules can also be accomplished and if the material is heat treated at high temperatures... 

The preliminary plastic deformation considerably effects on the phase formation, structure, microhardness and thickness of nitrided layers in -Fe and Fe-Ni alloys. The high microhardness of the diffusion layers results from the formation of the s- and y- nitrides. Iron doping with Ni leads to changing of the s-, f-phases composition. The existence of narrow intervals of deformations of 3-8 % and 20-30 %, in which the considerable (about 2 times) rise of microhardness of surface nitrided layers due to accelerated formation of s- and f-phases, was found. 

A. Andreasen, Effect of Ti-doping on the dehydrogenation kinetic parameters of lithium aluminum hydride , J. Alloys Compd. 419 (2006) 40-44. 

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