Roughened graphite biointerfaced with P450 liver microsomes: Surface and electrochemical characterizations.

Low-cost, voltage-driven biocatalytic designs for rapid drug metabolism assay, chemical toxicity screening, and pollutant biosensing represent considerable significance for pharmaceutical, biomedical, and environmental applications. In this study, we have designed biointerfaces of human liver microsomes with various roughened, high-purity graphite disk electrodes to study electrochemical and electrocatalytic properties. Successful spectral and microscopic characterizations, direct bioelectronic communication, direct electron-transfer rates from the electrode to liver microsomal enzymes, microsomal heme-enzyme specific oxygen reduction currents, and voltage-driven diclofenac hydroxylation (chosen as the probe reaction) are presented.

Crystallization Mechanism in Spark Plasma Sintered Bulk Metallic Glass Analyzed using Small Angle Neutron Scattering.

Understanding the thermal stability of metallic glasses is critical to determining their safe temperatures of service. In this paper, the crystallization mechanism in spark plasma sintered Fe48Cr15Mo14Y2C15B6 metallic glass is established by analyzing the crystal size distribution using x-ray diffraction, transmission electron microscopy and in-situ small angle neutron scattering. Isothermal annealing at 700 °C and 725 °C for 100 min resulted in the formation of (Fe,Cr)23C6 crystals, measured from transmission electron micrographs, to be from 10 to 30 nm. The small angle neutron scattering intensity measured in-situ, over a Q-range of 0.02 to 0.3 Å-1, during isothermal annealing of the sintered samples, confirmed the presence of (Fe,Cr)23C6 crystals. The measured scattering intensity, fitted by the maximum entropy model, over the Q-range of 0.02 to 0.06 Å-1, revealed that the crystals had radii ranging from 3 to 18 nm. The total volume fraction of crystals were estimated to be 0.13 and 0.22 upon isothermal annealing at 700 °C and 725 °C for 100 min respectively. The mechanism of crystallization in this spark plasma sintered iron based metallic glass was established to be from pre-existing nuclei as confirmed by Avrami exponents of 0.25 ± 0.01 and 0.39 ± 0.01 at the aforesaid temperatures.

Quantification of Thermal Oxidation in Metallic Glass Powder using Ultra-small Angle X-ray Scattering.

In this paper, the composition, structure, morphology and kinetics of evolution during isothermal oxidation of Fe48Cr15Mo14Y2C15B6 metallic glass powder in the supercooled region are investigated by an integrated ex-situ and in-situ characterization and modelling approach. Raman and X-ray diffraction spectra established that oxidation yielded a hierarchical structure across decreasing length scales. At larger scale, Fe2O3 grows as a uniform shell over the powder core. This shell, at smaller scale, consists of multiple grains. Ultra-small angle X-ray scattering intensity acquired during isothermal oxidation of the powder over a wide Q-range delineated direct quantification of oxidation behavior. The hierarchical structure was employed to construct a scattering model that was fitted to the measured intensity distributions to estimate the thickness of the oxide shell. The relative gain in mass during oxidation, computed theoretically from this model, relatively underestimated that measured in practice by a thermogravimetric analyzer due to the distribution in sizes of the particles. Overall, this paper presents the first direct quantification of oxidation in metallic glass powder by ultra-small angle X-ray scattering. It establishes novel experimental environments that can potentially unfold new paradigms of research into a wide spectrum of interfacial reactions in powder materials at elevated temperatures.

Effect of vibration frequency and displacement on melt expulsion characteristics and geometric parameters for ultrasonic vibration-assisted laser drilling of steel.

Recently, the applications of ultrasonic vibration assistance to laser-based manufacturing processes are rapidly proliferating. Ultrasonic vibration-assisted laser drilling (UVLD) process involves simultaneous application of high frequency vertical vibrations to the workpiece while being irradiated with a continuous wave laser beam. In UVLD, the ultrasonic vibration assistance causes expulsion of droplets from the laser melted surface, resulting in the formation of deep holes. In this paper, systematic analysis of the effects of ultrasonic vibration frequency (20-40 kHz) and displacement (16-32 µm) on melt expulsion characteristics in early stages of drilling and geometric/quality features of the holes for UVLD of AISI 316 is presented. Based on the analysis of initiation of droplet ejection from the melt pool and particle size of the ejected droplets, mechanisms of droplet ejection based on capillary wave theory are proposed. It was observed that while increasing both ultrasonic vibration frequency and displacement resulted in reduction in droplet ejection initiation time and the formation of deeper holes for the given laser irradiation time (100 ms), the effect of vibration displacement was much more pronounced than the frequency on the variation.

Melt expulsion during ultrasonic vibration-assisted laser surface processing of austenitic stainless steel.

Simultaneous application of ultrasonic vibrations during conventional materials processing (casting, welding) and material removal processes (machining) has recently been gaining widespread attention due to improvement in metallurgical quality and efficient material removal, respectively. In this paper, ultrasonic vibration-assisted laser surface melting of austenitic stainless steel (AISI 316) is reported. While the application of ultrasonic vibrations during laser processing delays the laser interaction with material due to enhancement of surface convection, it resulted in expulsion of melt from the irradiated region (forming craters) and transition from columnar to equiaxed dendritic grain structure in the resolidified melt films. Systematic investigations on the effect of ultrasonic vibrations (with vibrations frequency of 20 kHz and power output in the range of 20-40%) on the development of microstructure during laser surface melting (with laser power of 900 W and irradiation time in the range of 0.30-0.45 s) are reported. The results indicate that the proposed ultrasonic vibration-assisted laser processing can be designed for efficient material removal (laser machining) and improved equiaxed microstructure (laser surface modifications) during materials processing.

Tribological behavior of plasma-sprayed carbon nanotube-reinforced hydroxyapatite coating in physiological solution.

Wear behavior of plasma-sprayed carbon nanotube (CNT)-reinforced hydroxyapatite (HA) coating is evaluated in the simulated body fluid environment. Apart from enhancing the fracture toughness and providing biocompatibility, CNT-reinforced HA coating demonstrated superior wear resistance compared with that of hydroxyapatite coating without CNT. Initiation and propagation of microcracks during abrasive wear of plasma-sprayed hydroxyapatite coatings was suppressed by CNT reinforcement. Surface characterization and wear studies have shown that in addition to acting as underprop lubricant, CNTs provide reinforcement via stretching and splat-bridging for enhanced abrasion resistance in vitro.