Alloys phase structure

Well-dispersed ternary PtRuSn catalysts of various atomic ratios (60 30 10, 60 20 20, and 60 10 30) were deposited onto carbon using a modified alcohol-reduction process by Wu et al. [303]. The alloy phase structure and surface morphology for each variation of the PtRuSn/C catalysts were determined by XRD and HR-TEM. In order to evaluate the contributions of Ru and Sn in the different stages of ethanol oxidation, electrochemical oxidations of adsorbed CO, ethanol, acetaldehyde, and acetic acid were performed on each PtRuSn/C catalyst. The results indicated that the Ru-rich PtRuSn/C catalyst (60 30 10) exhibited the lowest... 

An alloy is cooled from a temperature at which it has a single-phase structure (a) to a temperature at which the equilibrium structure is two-phase (a -i- ji). During cooling, small precipitates of the P phase nucleate heterogeneously at a grain boundaries. The nuclei are lens-shaped as shown below. 

Experimentally it is found that the Fe-Co and Fe-Ni alloys undergo a structural transformation from the bee structure to the hep or fee structures, respectively, with increasing number of valence electrons, while the Fe-Cu alloy is unstable at most concentrations. In addition to this some of the alloy phases show a partial ordering of the constituting atoms. One may wonder if this structural behaviour can be simply understood from a filling of essentially common bands or if the alloying implies a modification of the electronic structure and as a consequence also the structural stability. In this paper we try to answer this question and reproduce the observed structural behaviour by means of accurate alloy theory and total energy calcul ions. 

If neither the AC nor the BC component exhibits in any part of its (zero pressure) (x, T) phase diagram the structure a, which though exists in their solid solution, then the latter is of Type III . In this case, the alloy environment stabilizes a structure which is fundamentally new to at least one of its components. Such alloy-stabilized phases with no counterpart in the phase diagram of the constituent components can be formed in bulk equilibrium growth and may be distinguished from the unusual alloy phases that are known to form in extreme non-equilibrium growth methods and in epitaxial forms. 

We investigated on structure of CuPd (2 1) bimetallic nanoparticles by XRD [71]. Since the XRD peaks of the PVP-protected CuPd nanoparticles appeared between the corresponding diffraction lines of Cu and Pd nanoparticles, as shown in Figru e 11, the bimetallic alloy phase was clearly formd to be formed in CuPd (2 1) bimetallic nanoparticles. We also characterized Ag-core/Rh-shell bimetallic nanoparticles, which formed during simple physical mixing of the corresponding monometallic ones, by XRD coupled with TEM [148]. 

F. Laves, Crystal Structure and Atomic Size, p. 124 in Theory of Alloy Phases, Amer. 

The phase distribution observed in the alloys deposited from AlCb-NaCl is very similar to that of Mn-Al alloys electrodeposited from the same chloroaluminate melt [126 129], Such similarity may also be found between the phase structure of Cr-Al and Mn-Al alloys produced by rapid solidification from the liquid [7, 124], These observations are coincident with the resemblance of the phase diagrams for Cr-Al and Mn-Al, which contain several intermetallic compounds with narrow compositional ranges [20], inhibition of the nucleation and growth of ordered, often low symmetry, intermetallic structures is commonly observed in non-equilibrium processing. Phase evolution is the result of a balance between the interface velocity and... 

Fig. 25. Phases observed in electrodeposited Mn-Al alloys. The structural Strukturbericht designations are shown in parenthesis [126-129, 148-151].

Despic, A. R., Identification of Phase Structure of Alloys by Anodic Linear Sweep Voltammetry, in Electrochemistry in Transition, O. J. Murphy, S. Srinivasan, and B. E. Conway, Eds., 1992, New York Plenum Press. 453. 

Engel, N.N. (1969) Alloy phase stability criteria. In Developments in the Structural Chemistry of Alloy Phases, ed. Giessen, B.C. (Plenum Press, New York), p. 25. 

Selke, W. (1989) Long period structures in alloys-statistical mechanics in the ANNNI model and related concepts. In Alloy Phase Stability, eds. Stocks, G.M. and Gonis, A., NATO ASI Series, Series E Applied Sciences (Kluwer Academic Publishers, Boston, USA), Vol. 163, p. 205. 

N. Hanada, S. Orimo, H. Fujii, Hydriding properties of ordered-/disordered-Mg-based ternary Laves phase structures, J. Alloys Compd. 356-357 (2003) 429-432. 

Electrodeposited binary alloys may or may not be the same in phase structure as those formed metallurgically. By way of illustration, we note that in the case of brass (Cu-Zn alloy), x-ray examination reveals that apart from the superstructure of... 

The consequence of the positive interactions is that alloys which lie between xi and X2 can lower their Gibbs energy by forming two-phase structures. One phase which is y4-rich with composition Xi and the other which is B-rich with composition... 

X2- The lowering of Gibbs energy, by forming multi-phase structures rather than a series of continuous solutions, is the reason for some of the fundamental features of alloy phase diagrams and will be discussed later in section 3.7. 

The oxidation state of Ge atoms and linking metal atoms in the framework structure was probed by X-ray photoelectron spectroscopy (Fig. 15). The XPS spectra suggest that the Ge and linking metal atoms are in relatively low oxidation state and have electronic configuration similar to those observed in metal-alloy phases [57]. 

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