The equilibrium shape and surface energy anisotropy of clean platinum

Journal Article · Sat Dec 01 04:00:00 EST 1990 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(90)90028-I· OSTI ID:5533604

Lee, W H; Vanloon, K R; Petrova, V; Woodhouse, J B; Loxton, C M; Masel, R I ^[1]

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1. Univ. of Illinois, Urbana (USA)

The authors have measured the equilibrium shape of clean platinum by monitoring the changes in the shape of a series of micrometer-sized platinum droplets during annealing at 1200{degrees}C in 10{sup {minus}7} Torr of oxygen. The droplets start out with a rounded shape and a wavy surface. Upon annealing for 24 h or more, the particles are converted to nearly spherical shapes with distinct facets in the (100) direction and smaller facets in the (111) direction. At equilibrium, the facets only cover 16% of the particle's surface. The rest of the surface is stepped or kinked. The equilibrium particle shape is also independent of particle size for particles in the size range explored here (d > 1 micrometer). Initially, the particles show a series of hill and valley structures around to (100) facets. However, the hill and valley structures disappear after a long anneal. After a long anneal, the particles also assume an epitaxial relation with the support. From the data, the authors estimate that the surface energy of platinum only varies by about 92 erg/cm{sup 2} with crystal face, with Pt(100) having the lowest surface energy, Pt(111) having a slightly higher surface energy, and all of the other faces of platinum having essentially the same surface energy. By comparison, previous workers have shown that heats of adsorption of simple gases often vary by 350 erg/cm{sup 2} with crystal face. The implication, therefore, is that in platinum the variations in surface energy with orientation are small enough that particle shape control in supported metal catalysis is feasible. Consequences to the stability of various single crystal faces are also discussed.

• DOE Contract Number: AC02-76ER01198
• OSTI ID: 5533604
• Journal Information: Journal of Catalysis; (USA), Journal Name: Journal of Catalysis; (USA) Vol. 126:2; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
ADSORPTION HEAT
ANISOTROPY
ANNEALING
CATALYST SUPPORTS
CATALYSTS
CORRELATIONS
CRYSTAL STRUCTURE
ELEMENTS
ENERGY
ENTHALPY
FREE ENERGY
HEAT TREATMENTS
METALS
MORPHOLOGICAL CHANGES
PARTICLE SIZE
PHYSICAL PROPERTIES
PLATINUM
PLATINUM METALS
SHAPE
SIZE
SORPTIVE PROPERTIES
SURFACE ENERGY
SURFACE PROPERTIES
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS