A. Mishra

Synthesis of Gold Nanoparticles by Leaves of Zero-Calorie Sweetener Herb (Stevia rebaudiana) and Their Nanoscopic Characterization by Spectroscopy and Microscopy

ABSTRACT In this research work, gold nanostructures with different shapes, such as octahedrons, hexagons and triangles, have been synthesized within 20 min by reducing gold chloride (HAuCl4) with dried, powdered Stevia rebaudiana, leaves, previously not exploited for the synthesis of gold nanoparticles. The nanoparticles were characterized and investigated by ultraviolet-visible (UV-Vis) spectrophotometry, high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD). The UV-Vis spectrum of the aqueous medium containing gold nanostructures showed a peak at 539 nm corresponding to the surface plasmon resonance band (SPR) of gold nanoparticles. HR-TEM micrograph showed the formation of well-dispersed octahedral gold nanoparticles of size 8–20 nm. XRD spectrum of the gold nanoparticles “exhibited Braggs pattern of reflection.”

Reverse Taylor Tests on Ultrafine Grained Copper

Reverse Taylor impact tests have been carried out on ultrafine grained copper processed by Equal Channel Angular Pressing (ECAP). Tests were conducted on an as‐received OFHC Cu rod and specimens that had undergone sequential ECAP passes (2 and 8). The average grain size ranged from 30 μm for the initial sample to less than 0.5 μm for the 8‐pass samples. The dynamic deformation states of the samples, captured by high speed digital photography were compared with computer simulations run in AUTODYN‐2D using the Johnson‐Cook constitutive equation with constants obtained from stress‐strain data and by fitting to an experimentally measured free surface velocity trace. The constitutive response of copper of varying grain sizes was obtained through quasistatic and dynamic mechanical tests and incorporation into constitutive models.