Alloying effect

Bimetallic particles of PdCu and PdCur were first prepared by simultaneous condensation of both metals on NaCl (100) single crystals cleaved in situ under UHV conditions.The same kind of particles have been produced by decomposition of Pd(acac)2 and Cu(acac)2 in solution, on previously cleaned MgO micro-cubes. It has been shown that small Pd particles ( 6 nm) prepared from solution in this manner had the same characteristics (shape, structure, and structure of the interface) as particles condensed under UHV conditions. 

After annealing between 350 and 400 °C in a reducing atmosphere of H2 at 400 torr, PdCu particles have the fee structure, but with undefined shape. Their size varies between 2 and 4 nm. Most are oriented (001) or (110) on MgO (001), as is apparent from Fig. 11. 

During annealing between 400 and 450 °C, the particles assume the f ordered structure of the bulk alloy (type CsCl). They are polyhedral and limited at the edges 

Depending on sample thickness, HRTEM images of p PdCu correspond to chemical images in which it is possible to differentiate between the atomic columns of Pd and the atomic columns of Cu in the [001] orientation, and the Pd layers or the Cu layers in the [110] orientation. The simulated images are given in Figs. 13a and 13b, respectively. In the HRTEM images of the interface PdCu-MgO, in the [100] and [110] directions of MgO, respectively, the contrast between Pd and Cu is 

The PdCu3 particles were obtained with the a ordered structure, (type AuCu3), after annealing at 500 °C in H2 for 5 days. Particles smaller than 20 nm are found in two main epitaxial orientations (001) and (110) on MgO (001), with a continuous structure and stacking faults. Larger particles had periodic anti-phase boundaries as observed in the bulk, with a modulation of 4 unit cells, corresponding to an atomic composition between 24.5 and 27% of Pd 

The reaction rate of ammonia synthesis depends on the rate of nitrogen chemisorption, the amoimt of adsorbed nitrogen (retardation), and the amount of adsorbed 

A number of bimetallic catalysts have been studied for their activity in ammonia synthesis. A Fe-Mo (1 1) catalyst exhibits a high activity, although it decreased remarkably for a prolonged run when the content of molybdenum is lower than 80%. This catalyst is prepared by calcining the mixtures of metal nitrate and 

The activity of the magnetite based catalyst is decreased by adding and enhanced by adding Co. The catalyst is prepared by burning a Fe-Co alloy in oxygen followed by adding the promoters. The alloy effect of Fe-Co and Fe-Ni has 

Catalyst Surface area (mVg) Rate at 588 K (mmol NH3/(g h)) Activation energy (kcal/mol) 

Transition metals can be activated by alloying with positive charges. Raney Ru prepared by the Al-Ru alloy has the higher activity than that of pure Ru in terms of the activity per unit area. The activity is even higher with the addition of K. The catalyst has activity even at 373K. Raney Ru is also very active when CsNOs acts as a promoter.  

---

F1 NMR of chemisorbed hydrogen can also be used for the study of alloys. For example, in mixed Pt-Pd nanoparticles in NaY zeolite comparaison of the results of hydrogen chemisorption and F1 NMR with the formation energy of the alloy indicates that the alloy with platinum concentration of 40% has the most stable metal-metal bonds. The highest stability of the particles and a lowest reactivity of the metal surface are due to a strong alloying effect. 

Table 3.10. Alloying Effects that Improve Creep Properties [14]...

Alloying effects that improve creep properties.67... 

We have used the basis set of the Linear-Muffin-Tin-Orbital (LMTO) method in the atomic sphere approximation (ASA). The LMTO-ASA is based on the work of Andersen and co-workers and the combined technique allows us to treat all phases on equal footing. To treat itinerant magnetism we have employed the Vosko-Wilk-Nusair parametrization for the exchange-correlation energy density and potential. In conjunction with this we have treated the alloying effects for random and partially ordered phases with a multisublattice generalization of the coherent potential approximation (CPA). 

To further discuss the underlying mechanisms that forces the phase stabilities we also did calculations where the alloying effects were treated within the so-called virtual crystal approximation (VGA) where the real alloy constituents are replaced by an atom with an average (noninteger) atomic number. 

However, for high-concentrated alloys it becomes important t.o l.reat the alloy effect,s outside the imirrrrity cluster. The use of CPA medium is strortgly suggested. 

Our work demonstrates that EELS and in particular the combination of this technique with first principles electronic structure calculations are very powerful methods to study the bonding character in intermetallic alloys and study the alloying effects of ternary elements on the electronic structure. Our success in modelling spectra indicates the validity of our methodology of calculating spectra using the local density approximation and the single particle approach. 

Zinc and zinc alloys Effective Ineffective Ineffective Effective — Reasonably effective Reasonably effective... 

Min M, Cho J, Cho K, Kim H. 2000. Particle size and alloying effects of Pt-based alloy catalysts for fuel cell applications. Electrochim Acta 45 4211-4217. 

Huges, R.C., Schubert, W.K. and Buss, R.J., Solid-state hydrogen sensors using palladium-nickel alloys Effect of alloy composition on sensor response, Journal of Electrochemical Society, 142, 249,1995. 

Copper-nickel alloys, 17 100 Copper-nickel-tin alloys, effect... 

H. Yukawa, M. Takagi, A. Teshima, M. Morinaga, Alloying effects on the stabUity of vanadium hydrides, J. Alloys Compd. 330-332 (2002) 105-109. 

To stress the localized character of chemisorption (a term surface pseudomolecules was introduced at that time), Sachtler introduced for the alloying effects discussed in paragraph (2) a term ligand effect (5). It was then a task for an experimentalist to establish how important—relatively—the effects (1) and (2) were. A general consensus now is that effect (1) is more essential than (2) in any case, but the discussion is still going on, on the reliability of some pieces of evidence which have been presented in the literature in favor of a role for effect (2). 

A. Classification of the Reactions on Metals and General Description of Alloying Effects... 

A quantitative analysis (like, e.g., determination of the exact size of ensembles required) of the alloying effect is impossible at this time. The surface composition, in particular that of small particles, under a running catalytic reaction is generally not known. Further, it is not known how metals and alloys differ in extent and composition of the carbonaceous deposits and in their influence on the reaction under study. Therefore, no reliable quantitative conclusions can be made on the number of metal atoms involved in the formation of individual complexes. For the sake of simplicity... 

CC-AI2O3 catalyst was attributed to a decrease in hydrogen coverage brought about by an alloying effect.396... 

---