Platinum structure-property studies

Among ordered bimetallic systems, the Pt-Sn one can be considered at present as the most in-depth studied not only for its surface structural properties, but also for its reactivity and catalytic properties. A comparable detailed knowledge exists only for a few other cases, among platinum alloys we can cite the Ni-Pt and Co-Pt systems, examined for their catalytic properties and the Pt-Ti system studied for their electrocatalytic properties [5]. Sparse data relative to the surface properties of several other Pt alloys exist (e.g. FeaPt and CuaPt -[3] and PtaMn [51]. All these data available pertain to fee phases either random substitutional or ordered compounds. Data exist also for other cubic ordered alloys which are isostructural with the PtaSn compound, e.g. NiaAl [52, 53] and AuaPd [28] and finally the Au-Cu system, which has been object of interest as the prototypical LI2 or Pm3m ordered system in the CuaAu composition [54, 55]. 

Model Networks. Construction of model networks allows development of quantitative structure property relationships and provide the ability to test the accuracy of the theories of mbber elasticity (251—254). By definition, model networks have controlled molecular weight between cross-links, controlled cross-link functionality, and controlled molecular weight distribution of cross-linked chains. Silicones cross-linked by either condensation or addition reactions are ideally suited for these studies because all of the above parameters can be controlled. A typical condensation-cure model network consists of an a, CO-polydimethylsiloxanediol, tetraethoxysilane (or alkyltrimethoxysilane), and a tin-cure catalyst (255). A typical addition-cure model is composed of a, co-vinylpolydimethylsiloxane, tetrakis(dimethylsiloxy)silane, and a platinum-cure catalyst (256—258). 

To determine the phase properties of the calcined bimetallic nanoparticles, a detailed x-ray diffraction (XRD) study was carried out. The XRD data of AuPt/C showed that the diffraction patterns for the carbon-supported nanoparticles show a series of broad Bragg peaks, a picture typical for materials of limited structural coherence. Nevertheless, the peaks are defined well enough to allow a definitive phase identification and structural characterization. The diffraction patterns of Au/C and Pt/C could be unambiguously indexed into an fcc-type cubic lattice occurring with bulk gold and platinum. We estimated the corresponding lattice parameters by carefully determining... 

---