T.G. Zocco

Transformation of selenate and selenite to elemental selenium byDesulfovibrio desulfuricans

SummaryDesulfovibrio desulfuricans (DSM 1924) can be adapted to grow in the presence of 10 mM selenate or 0.1 mM selenite. This growth occurred in media containing formate as the electron donor and either fumarate or sulfate as the electron acceptor. As determined by electron microscopy with energy-dispersive X-ray analysis, selenate and selenite were reduced to elemental selenium which accumulated inside the cells. Selenium granules resulting from selenite metabolism were cytoplasmic while granules of selenium resulting from selenate reduction appeared to be in the periplasmic region. The accumulation of red elemental selenium in the media following stationary phase resulted from cell lysis with the liberation of selenium granules. Growth did not occur with either selenate or selenite as the electron acceptor and13C nuclear magnetic resonance indicated that neither selenium oxyanion interfered with fumarate respiration. At 1 μM selenate and 100 μM selenite, reduction byD. desulfuricans was 95% and 97%, respectively. The high level of total selenate and selenite reduced indicated the suitability ofD. desulfuricans for selenium detoxification.

Preservation of biomolecules in cancellous bone of Tyrannosaurus rex

ABSTRACT An exceptionally well preserved specimen of the tyrannosaurid dinosaur Tyrannosaurus rex Osborn shows little evidence of permineralization or other diagenetic effects. It appears that the cancellous bone tissues of the specimen may have been protected from water infiltration or mineral deposition by the very dense cortical bone which surrounds them. The cancellous tissues provided an opportunity to test the hypothesis that indigenous biomolecules might be preserved over the course of millions of years under the appropriate conditions. HPLC analysis of extracts from the bone tissues revealed the presence of molecules with light absorbance maxima consistent with nucleic acids and peptides/proteins. Analyses of bone extracts for amino acid content yielded ratios similar to those found for modern ostrich and horse bone. A high molar glycine ratio and the presence of hydroxylysine peaks in bony tissue samples from the T. rex suggests the presence of collagen type I remnants. Results indicate that the ...

Characterization of the surface oxide formed by excimer laser surface processing of AISI 304 stainless steel

Abstract We have used excimer laser processing in air to grow thick oxide layers on AISI 304 stainless steel and have characterized the resulting oxide layer using a variety of techniques including Mossbauer, Auger, and Rutherford backscattering spectroscopy, X-ray and electron diffraction, transmission electron microscopy, and nuclear reaction analysis. The resulting oxide, which is grown under rapid quenching conditions, has a spinel structure and a complex composition. In particular, a Cr to Fe ratio of approximately one was observed to persist throughout the oxide. Carbon incorporation at approximately 13 at%, presumably from surface contamination, and N at approximately 5 at% were also found.

Tribological effects of excimer laser processing of tool steel

We examined the effects of excimer laser surface processing and of laser alloying with titanium on the mechanical and tribological properties of A-7 tool steel. We found that laser processing and alloying had no discernible effect on the mechanical properties of tempered steels. However, the dry, sliding friction coefficient of both laser processed and alloyed surfaces was reduced. Substantial but transient reductions in the friction are consistent with formation of a low friction transfer film. Long-lived reductions of friction in the laser processed case are associated with an absence of the adhesive wear which is conspicuous in the untreated case.

Microstructure and mechanical properties of ion‐beam‐produced Fe‐Ti‐(N), Fe‐Ti‐(C), and Fe‐Ti‐(C,N) surface films

Ion‐mixed films of Fe53 Ti47 were produced by ion irradiating a Fe‐Ti multilayer structure on AISI 304 stainless steel. The ion‐mixed films were subsequently implanted with nitrogen, carbon, or both carbon and nitrogen. The microstructure following nitrogen implantation consisted of a bcc solid solution of iron and titanium and finely dispersed TiN precipitates. In the cases of carbon or carbon and nitrogen implantation, a two‐phase structure consisting of an amorphous matrix with TiC or Ti(C,N) precipitates was found. All these films initially possessed improved tribological properties as revealed by lowered friction and increased wear resistance. However, after an extended test of 1000 wear cycles, a reduced friction was only observed for the carbon or carbon and nitrogen implanted samples. The wear track on the dual implanted surface was extremely smooth, while the surface of the nitrogen‐implanted sample was partly worn through, causing the friction to increase to the level of the untreated sample. The improved tribological properties of the implanted films are attributed to an increase in surfacehardness. However, the surfacehardness is unable to explain differences between different implantations. In the case of the dual carbon and nitrogen implantation, improvements appear to be in part the result from an increased capability to accommodate plastic deformation. These conclusions are supported by transmission electron microscope studies of the wear tracks as well as by nanoindentation measurements.

Metabolism of Metals and Metalloids by the Sulfate-Reducing Bacteria

The bacteria and archaea that reduce sulfate to sulfide can transform a variety of metal(loids). The latter include metalloids (As, Se and Te), transition metals (Au, Co, Cr, Fe, Hg, Mo, Mn, Ni, Pb, Pd, Pt, Re, Rh, Tc, V, and Zn), and actinides (Pu and U). The conversions are achieved via (1) use of metal-specific enzymes, (2) cometabolism, i.e., use of non-substrate-specific enzymes, (3) biomethylation, (4) inorganic precipitation, (5) oxidation-reduction reactions in the growth medium; or (6) oxidation/cathodic depolarization of the elemental form. Respective examples are (1) the respiration of arsenate by Desulfosporosinus auripigmenti; (2) reduction of selenate and selenite to elemental selenium by enzymes involved in sulfate respiration or assimilation; (3) methylation of mercury; (4) precipitation of zinc sulfide in the supernatant; (5) reaction of sulfide and selenite forming selenium sulfide (SeS2) in the supernatant; and (6) the anaerobic corrosion of iron. Some of these processes yield valuable commodities, e.g., the precipitation of gold by Desulfovibrio desulfuricans. The understanding of anaerobic corrosion can lead to the prevention of corrosion of pipelines. The formation of selenium nanoparticles has potential applications in the design of drug-delivery systems. The formation of insoluble precipitates facilitates the design of bioremediation technologies. While some metals, e.g., Fe, Co, Mo, Mn, Ni, Se, V and Zn, are essential nutrients for bacterial growth, this review focuses on detoxification processes and not on trace metal assimilation into cellular materials.

Excimer laser surface processing of Ti-6Al-4V

We have examined the effect of surface processing in air, using excimer laser light at 248 nm wavelength, on the oxygen content, microstructure, and surface hardness of Ti-6Al-4V. Processing with a single pulse results in the transformation of theα +β material toα′ martensite. Multiple pulse processing results in rapid incorporation of oxygen in the material. Oxygen initially dissolves in the material in the liquid phase. As the concentration exceeds the solid solubility limit during solidification, TiO particles precipitate. In contrast to equilibrium oxidation processes in Ti, only TiO is observed as an oxidation product; further processing results in increased oxygen incorporation and an increased volume fraction of TiO but no other oxides of Ti. The TiO particle size is a function of the oxygen concentration and the number of pulses, with some grain growth occurring after many pulses. The effects of solution hardening by dissolved oxygen and precipitation hardening by the TiO are identifiable as functions of oxygen concentration and mean free path between particles, respectively. A maximum surface hardness almost twice that of electropolished Ti-6Al-4V is observed.

Initial electron backscattered diffraction observations of a plutonium alloy

Abstract In this work, the first electron backscattered diffraction patterns (EBSPs) were captured for a plutonium–gallium (Pu–Ga) alloy. The experimental techniques used for EBSP acquisition are described in detail. This demonstrated sample preparation and characterization technique is expected to be a powerful means to further understand phase transformation behavior, orientation relationships, and texture in the complicated Pu and Pu-alloy systems.

Electron backscatter diffraction of a plutonium–gallium alloy

Abstract An experimental technique has recently been developed to characterize reactive metals, including plutonium (Pu) and cerium, using electron backscatter diffraction (EBSD). Microstructural characterization of Pu and its alloys by EBSD had been previously elusive primarily because of the extreme toxicity and rapid surface oxidation rate associated with Pu metal. The experimental technique, which included ion-sputtering the metal surface using a scanning Auger microprobe (SAM) followed by vacuum transfer of the sample from the SAM to the scanning electron microscope (SEM), used to obtain electron backscatter diffraction Kikuchi patterns and orientation maps for a Pu–gallium alloy is described and the initial microstructural observations based on the analysis are discussed. The phase transformation behavior between the δ (face-centered cubic) and e (body-centered-cubic) structures is explained by combining the SEM and EBSD observations.

Formation of stable nanoscale iron carbide particles by laser breakdown chemical vapor deposition

Abstract We have used laser breakdown chemical vapor deposition to produce nanocrystalline particles predominantly of Fe 3 C with some α-Fe. Air exposure results in oxidation of the Fe to Fe 3 O 4 . Transmission electron microscopy and diffraction techniques were used to characterize the materials. The particles can be suspended in de-ionized water and sorted magnetically.