In the past ten years the study of the mechanisms of chemical transformations on metal surfaces has advanced appreciably. Today complex reaction networks can be unraveled by combining several spectroscopies, derived principally from the practice of ultrahigh-vacuum surface physics. Of paramount importance in this field is the combination of mass spectrometric methods for the identification of reaction products with spectroscopies which help identify surface-bound reactive intermediates. This quasi-monograph highlights the progress in this field with studies which clearly exemplify such research and at the same time provide more general understanding of chemical reactivity at surfaces. This book was constructed to be a resource to all scientists interested in the chemical reactivity of metals, including those whose primary interest may lie in fields outside surface reactivity. The book is'intended to be an advanced case study text, not a "review" in the standard sense. Each chapter develops principles and illustrates the use of experimental methods. Consequently, more attention is given to experimentation than normally found in journal articles or review articles. My intent in organizing these chapters was to make this field accessible to professionals and graduate students in the fields of chemistry, material science, and physics. Even so, we hope that experts in the field of surface reactivity will also find these chapters informative. After the introduction (Chap. 1) the book consists of chapters on the mechanism of selective oxidation by silver (Chap. 2 by R.1. Madix and J.T.

Balloon-expandable coronary stents may be made of stainless steel conforming to ASTM or ISO specifications, referred to by ASTM as UNS S31673 alloys. A need exists for an alloy with enhanced radiopacity to make stents more visible radiographically and more effective clinically. A research program was initiated with the objectives of enhancing fluoroscopic radiopacity while maintaining adherence to the ASTM and ISO specifications. These objectives were ultimately achieved by adding a noble metal, platinum, to UNS S31673 by vacuum induction melting a commercially-available alloy. Freedom of the resulting microstructure from formation of harmful topologically close packed phases was ensured by use of phase computation methodology (New PHACOMP), and confirmed by X-ray diffraction and transmission electron microscopy. Platinum was chosen since it is over twice as dense as nickel and, with approximately half its effect as an austenitizer, allows nickel content to be reduced to a minimum level.

Dilation-balloon expandable coronary stents are made of implant grade stainless steels, UNS S31673, e.g., BioDur® 316LS. Boston Scientific/Interventional Technologies (BS/IVT) determined that addition of platinum to UNS S31673 could produce a stainless steel with enhanced radiopacity, which made such stents more visible radiographically. A goal of the program was to ensure the platinum additions would not adversely affect the corrosion resistance of the resulting 5-6 wt % PERSS® alloys. Corrosion resistance of PERSS and BioDur 316LS was determined using electrochemical tests for general, pitting, crevice and intergranular corrosion. Experimental methods included A262E, F746, F2129, and potentiodynamic polarization. The ~ 6 wt % PERSS alloy (IVT 78) had a resistance to pitting, crevice and intergranular corrosion similar to base materials. IVT 78 was a single-phase austenitic PERSS alloy with no evidence of inclusions or precipitates; it was more resistant to pitting corrosion than the ~ 5 wt % PERSS alloys. PERSS performance was not a function of oxygen content in the range 0.01 to 0.03 wt %.

A platinum-enhanced variant of UNS S31673 stainless steel has been eveloped for use in fabricating balloon-expandable coronary stents. PERSS® is sufficiently radiopaque to be detected by current radiographic methods and maintains compliance with ASTM requirements. Boston Scientific Corporation/Interventional Technologies (BSC/IVT) has implemented a pilot program for the development of PERSS with the intent of achieving vertical integration of the manufacturing process. PERSS ingots containing 5 wt% platinum were cast by vacuum induction melting, refined by vacuum arc remelting, upset in a forge, then hot and cold-rolled into sheet and foil. The sheet was cold-rolled on a 20-high cluster mill to a foil thickness of less than 0.25 mm (0.01 inches). While the final product otherwise meets the ASTM specification for UNS S31673 alloys, intentional addition of unspecified additional elements precludes its compliance with same.