Titanium Sheet Fabricated from Powder for Industrial Applications

In collaboration with Ametek and Commonwealth Scientific and Industrial Research Organization (CSIRO), Oak Ridge National Laboratory has evaluated three different methods for converting titanium hydride?Cdehydride (HDH) powder into a thin-gauge titanium sheet from a roll-compacted preform. Methodologies include sintering, followed by cold rolling and annealing; direct hot rolling of the roll-compacted sheet; and hot rolling of multiple layers of roll-compacted sheet that are encapsulated in a steel can. Fabrication of fully consolidated sheet has been demonstrated using all three methods, and each processing route has the ability to produce a sheet that meets ASTM B265 specifications. However, not every method currently provides a sheet that can be highly formed without tearing. The degree of sintering between powder particles, postprocessing density, and the particle-to-particle boundary layer where compositional variations may exist have a significant effect on the ability to form the sheet into useful components. Uniaxial tensile test results, compositional analysis, bend testing, and biaxial testing of the titanium sheet produced from hydride?Cdehydride powder will be discussed. Multiple methods of fabrication and the resulting properties can then be assessed to determine the most effective and economical means of making components for industrial applications.     

Adaptive VN/Ag nanocomposite coatings with lubricious behavior from 25 to 1000 °C

A two-phase nanocomposite coating that consists of inclusions of silver in a vanadium nitride matrix (VN/Ag) was investigated as a potential adaptive coating with a reduced friction coefficient from 25 to 1000 °C. This nanocomposite structure was selected based on the premise that silver and silver vanadate phases would form on the surface of these coatings, reducing their friction coefficient in the (i) room to mid-range and (ii) mid-range to high temperatures, respectively. Silver and vanadium were expected to react with oxygen at high temperatures and create a lubricious silver vanadate film on the coating. The VN/Ag coatings were deposited using unbalanced magnetron sputtering and their elemental composition was evaluated using X-ray photoelectron spectroscopy. The tribological properties of the materials against Si₃N₄ balls were investigated at different temperatures. The lowest friction coefficients recorded for samples with identical compositions were 0.35, 0.30, 0.10 and 0.20 at 25, 350, 700 and 1000 °C, respectively. Post-wear testing Raman spectroscopy and X-ray diffraction (XRD) measurements revealed the formation of silver vanadate compounds on the surface of these coatings. In addition, real time Raman spectroscopy and high temperature XRD revealed that silver vanadate, vanadium oxide and elemental silver formed on the surface of these coatings upon heating to 1000 °C. Upon cooling, silver and vanadium oxide were found to combine at about 400 °C, leading predominantly to the formation of silver vanadate phases on the surface of these materials.     

Pd nanoparticle enhanced re-oxidation of non-stoichiometric TiO2: STM imaging of spillover and a new form of SMSI

We have used STM imaging in situ to demonstrate two fundamental steps in catalytic processes on model catalysts at elevated temperature. We show that Pd nanoparticles on sub-stoichiometric TiO₂(110) dissociatively adsorb O₂ at 673 K which spills over onto the support where further reaction takes place. The spillover oxygen re-oxidises the surface by removing Tiⁿ⁺ interstitial ions trapped in the crystal lattice, preferentially re-growing TiO₂ around and over the particles. The identification of the metal enhanced re-oxidation mechanism may have important and general consequences for the understanding of catalysis and gas sensing.     

Lattice misfit during ageing of a polycrystalline nickel-base superalloy

The temporal evolution of the lattice parameters and lattice misfit of an advanced polycrystalline nickel-base superalloy have been studied in situ during an ageing heat treatment using synchrotron X-ray diffraction. During ageing, the γ and γ′ lattice parameters were both observed to decrease, a trend that cannot be attributed to a loss of coherency alone. Phase-extracted γ′ replicated this behaviour. Atom probe tomography was used to measure the compositional changes between the start and end of the ageing heat treatment. Using these data, a thermodynamic assessment was made using the software ThermoCalc of the structural change across the interface between γ and γ′. Subsequently, the unconstrained lattice parameters were estimated and were shown to be in good agreement with the X-ray diffraction measurements. Thus, the observed anomalous lattice misfit behaviour was concluded to be dominated by elemental exchange between the γ and γ′ phases during ageing.     

Apportionment of primary and secondary organic aerosols in southern California during the 2005 study of organic aerosols in riverside (SOAR-1)

Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionmenttechniques. The secondary organic aerosol (SOA) mass is estimated by elemental carbon and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each ofthese methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SOA/OA contributions of 70-90% were observed during midday periods, whereas minimum SOA contributions of approximately 45% were observed during peak morning traffic periods. These results are contraryto previous estimates of SOAthroughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed.     

MESOZOIC MAGMATISM IN THE FALKLAND ISLANDS (SOUTH ATLANTIC) AND THEIR OFFSHORE SEDIMENTARY BASINS

Recent mineral and hydrocarbons exploration in and around the Falkland Islands has provided data that allows correlation of the onshore and offshore histories of magmatism. New Ar‐Ar age dating of onshore dykes in East Falkland has extended their Cretaceous age range back to ca. 135 Ma (Valanginian – Hauterivian) from the previously reported age of ca. 121 Ma (Aptian). Widespread onshore, ca.188–178 Ma, Jurassic dykes are generally considered a part of the regional Karoo‐Ferrar magmatism linked to the initial break‐up of Gondwana, but we relate the Early Cretaceous dykes, with their characteristic north‐south orientation, to extension of the Falklands Plateau during initiation of spreading in the South Atlantic Ocean. The onshore dykes demonstrate east‐west Early Cretaceous extension, whilst to the north of the archipelago the offshore North Falklands Basin extended between north‐south boundary fault systems from the Late Jurassic onwards. Intrusion of Valanginian – Hauterivian dykes onshore was penecontemporaneous with the intrusion of sills and the extrusion of lavas in the Falkland Plateau Basin. This magmatism, more extensive than previously supposed, may be linked to regional uplift associated with initial opening of the South Atlantic Ocean. The uplift can be demonstrated from seismic data and DSDP boreholes to have occurred during the Berriasian – Hauterivian interval. The thermally‐driven uplift of the platform region played a crucial role in elevating potential sediment source areas and providing the large volumes of sand that were shed intermittently into the surrounding basins from the Valanginian to the Aptian or Albian.     

Investigation of wear of knee prostheses in a new displacement/force-controlled simulator

The performance of two knee simulators designed by ProSim (Manchester, UK) was evaluated by comparison of the wear seen in the press-fit condylar (PFC) Sigma (DePuy) knee prosthesis. Twelve specimens of the same design and manufacturing specification, were subjected to a wear test of 2 x 10(6) cycles duration using bovine serum as a lubricant. The anterior/posterior displacement and internal/external rotation inputs were based on the kinematics of the natural knee. International Standards Organization (ISO) standards were used for the flexion and axial load. The wear rates and wear scar areas were compared across all stations. The mean wear rates found were 17.6+/-5 mm3/10(6) cycles for stations 1 to 6 and 19.6+/-4 mm3/10(6) cycles for stations 7 to 12, resulting in an overall mean wear rate of 18.1+/-3 mm3/10(6) cycles. The differences between the two simulators were not significant. The average wear scar area seen on inserts from stations I to 6 was calculated at 32.4+/-1 per cent of the intended articulating surface. Similarly on stations 7 to 12 the average wear scar area was 30.7+/-3 per cent. The wear scars seen were a good physiological representation of those found from clinical explant data. This study has shown good repeatability from the simulator, both within and between the simulators.     

Laminar burning velocity measurements of liquid fuels at elevated pressures and temperatures with combustion residuals

The laminar burning velocity is a fundamental property of a fuel that affects many aspects of its combustion behaviour. Experimental values are required to validate kinetic simulations, and also to provide input for models of flashback, minimum ignition energy and turbulent combustion.A constant volume vessel (rated at 3.4 MPa) in conjunction with a multi-zone model was used to calculate burning velocity from pressure and schlieren data, allowing the user to select data uncorrupted by heat transfer or cellularity. Using the pressure rise data allows measurements to be derived for much higher pressures and temperatures than when the constant pressure data are used. A 12 term correlation for burning velocity was fitted to the data.n-Heptane, iso-octane, toluene, ethylbenzene and ethanol were tested over a wide range of initial pressures (50, 100, 200 and 400 kPa), temperatures (310, 380 and 450 K) and equivalence ratios (0.7–1.4), along with tests using combustion residuals at mole fractions of up to 0.3. The results compared favourably with the limited data already published, especially at high pressures. Conditions at the onset of cellularity are given for iso-octane.