Browsing by Author "Pedraza, A. J."

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Characterization of sputter-deposited 316L stainless steel films
(1992-01) Godbole, M. J.; Pedraza, A. J.; Allard, L. F.; Geesey, Gill G.
Sputter-deposited 316L stainless steel films deposited on various substrates were characterized using transmission electron microscopy and X-ray diffractometry. The deposits were found to be fine-grained and the phases present in the films depended on the nature of the substrate. Films of various thicknesses deposited on microscope slides or oxidized stainless steel substrates contained a mixture of two phases: a body centre cubic (b c c) and a modified hexagonal ε-phase. The hexagonal phase appeared to be an ordered phase, as suggested by the aO value of the structure, which is twice that for the ε-martensite found in many deformed stainless steels. These films were hard and brittle, as indicated by microhardness measurements. Films deposited on oxide-free austenitic stainless steel substrates, on the other hand, were mostly b c c and exhibited a dominant 〈2 00〉 texture. These films were softer and less brittle than those deposited on oxidized substrates. In situ high-temperature X-ray diffractometry revealed that the ε-phase transformed to b c c when the films were annealed at 773 K. On annealing at 873 K, the b c c phase transformed to face centre cubic, which remained stable on cooling to room temperature. These results agree with published data which suggest stability of the b c c phase up to 840 K. Some discrepancies from earlier published reports are discussed in the light of the present results.
The crystal structures of stainless steel films sputter-deposited on austenitic stainless steel substrates
(1993-05) Godbole, M. J.; Pedraza, A. J.; Park, J. W.; Geesey, Gill G.
Stability in aqueous media of 316l stainless steel films deposited on internal reflection elements
(1993-02) Pedraza, A. J.; Godbole, M. J.; Bremer, Philip J.; Avci, Recep; Drake, B.; Geesey, Gill G.
Thin films of 316L stainless steel were sputter-deposited on cylindrical internal reflection elements (IREs) made of germanium. These films are intended for use in Fourier transform infrared (FT-IR) spectroscopy studies on the stability of stainless steel in aqueous media. In these deposits the films tend to peel off the substrate when immersed in water, probably due to galvanic corrosion at the metal/substrate interface. Deposition of a 2-nm-thick layer of chromium oxide on the substrate prior to the deposition of the steel was beneficial on three counts. It provided an electrically insulating layer, it enhanced adhesion, and it solved the steel/germanium incompatibility problem. It was also found that annealing the substrate prior to deposition remarkably enhances the film adhesion and improves the optical properties of the substrate. The microstructure, the topography, and the chemical composition of the films were characterized by scanning and transmission electron microscopy, Auger electron spectroscopy, and atomic force microscopy. The only significant difference between the austenitic stainless steel target material and the film is that the crystalline structure of the film is body-centered cubic. The optical properties of the system germanium/metallic film/water were studied and calculated with the help of a computer program. The absorbance of the water bands in the IR range was measured in coated Ge-IRE.
Use of sputter-deposited 316l-stainless steel ultrathin films for microbial-influenced corrosion studies
(1992-01) Suci, Peter A.; Pedraza, A. J.; Godbole, M. J.; Geesey, Gill G.
Ultra thin films (12nm) were sputter deposited onto cylindrical germanium internal reflection elements pre-coated with a thin (2nm) layer of Cr2O3. Two crystals were inserted into Circle cell flow-through chambers and mounted on the optical bench of an Fourier Transform Infrared (FT-IR) spectrometer. One chamber was maintained as a sterile control while the other was sequentially inoculated with four bacterial species: Pseudomonas aeruginosa, Bacillus subtillis, Hafnia alvei, and Desulfovibrio gigas, in that order. The water absorption band (1640cm−1) was monitored and used to follow the deterioration of the ultra thin films. In this respect, the sterile control and inoculated films exhibited only slight differences during the 1000h course of the experiment. Assay of the visible biofilm that had accumulated on the surface of the inoculated crystal after 1000h revealed that the film incorporated viable cells from all four strains.