Metals segregation

Many of these problems can be solved by using continuous casting (Fig. 14.3). Contraction cavities do not form because the mould is continuously topped up with liquid metal. Segregation is reduced because the columnar grains grow over smaller distances. And, because the product has a small cross-section, little work is needed to roll it to a finished section. 

Cations siting, distribution, mobility, and metal segregation have been found to strongly influence catalytic activity and the stability of Co,Ag-FER catalysts in lean CH4-SCR of NOx. 

Pt skin catalysts are prepared by high-temperature annealing and are therefore expected to be thermodynamically stable structures Thermochemical studies of the metal segregation energies of various metal alloys [114] suggest that Pt-rich alloys prefer to segregate Pt atoms to the surface and form Pt skins. 

Pt-Re First moments of formation of bimetallic cluster monitored. Controlled by A1203 network initially. Metal segregation occurs later after particle growth.35 ... 

It also should be noted that we have herein, in effect, turned the charging problem around and made it an auxiliary morphological tool. In order to demonstrate the versatility of this tool, we have employed the aforementioned negative shift with cluster formation not only to study metals dispersions, but also to assist in the study of the integrity of thin film interfaces (16), and metals segregation during alloying corrosion (H). 

If the iron and stony-iron meteorites came from fully differentiated asteroids, how did these asteroids heat to the point of partial melting and how did the metal segregate from the silicates Unlike large planets, where potential energy release triggers core formation, small asteroids require an additional heat source. The heat source(s) for asteroidal melting produced a wide range of products, from unmetamorphosed chondrites to fully molten asteroids, as well as partially melted asteroids. Samples from these latter asteroids provide us with a rare opportunity to observe core formation—frozen in place. 

Thibault Y. and Walter M. J. (1995) The influence of pressure and temperature on the metal/sihcate partition coefficients of nickel and cobalt in a model Cl chondrite and impheations for metal segregation in a deep magma ocean. Geochim. Cosmochim. Acta 59, 991 — 1002. 

Adams RD (2000) Metal segregation in bimetallic clusters and its possible role in synergism and bifunctional catalysis. J Organomet Chem 600 1... 

Adams et al. [78,79] have reported a series of synthesis of mixed-metal cluster compounds. One example, Pt2Ru4(CO)is, is depicted in Figure 1(b). This mixed cluster compound was investigated to study the effect of Pt-Ru nanoparticles developed after the precursor annealing on carbon [80]. In line with the spectroscopic and microscopic measurements, the authors demonstrated that mixed Pt-Ru nanoparticles, with an extremely narrow size distribution (particle size 1.4nm), reflect an interaction that depends on the nature of the carbon support. Furthermore, as revealed by EXAFS, the Pt-Pt, Pt-Ru, and Ru-Ru coordination distances in the precursor (2.66, 2.64, and 2.84 A) [79] changed to 2.73, 2.70, and 2.66 A, respectively, on the mixed-metal nanoparticles supported on carbon black, with an enhanced disorder [80]. Furthermore, some metal segregation could be... 

This effect of metal segregation is borne out by measurements of resistivity versus volume percent metal filler as shown in Figure 18.6. A threshold for... 

Abstract Monte Carlo simulations were carried out to study the different stmctures showed by bimetallic nanoparticles synthesized in microemulsions. It is observed that the difference in reduction rates of both metals is not the only parameter to determine the metals segregation, playing the interdroplet channel size a relevant role. The reduction rates difference determines nanoparticle structure only in two extreme cases when both reactions take place at the same rate a nanoalloy structure is always obtained if both reactions have very different rates, the nanoparticle shows a core-shell structure. But in the large interval between both extreme cases, the nanoparticle structure is strongly dependent on the intermicellar exchange, which is mainly determined by the surfactant film flexibility, and on reactants concentration. This result is very promising for the preparation of bimetallic nanoparticles with a given structure. 

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