Amit P. Srivastava

Manufacturing microstructured tool inserts for the production of polymeric microfluidic devices

Tooling is critical in defining multi-scale patterns for mass production of polymeric microfluidic devices using the microinjection molding process. In the present work, fabrication of various microstructured tool inserts using stainless steel, nickel and bulk metallic glasses (BMGs) is discussed based on die-sinking EDM (electrical discharge machining), electroforming, focused ion beam milling and thermoplastic forming processes. Tool performance is evaluated in terms of surface roughness, hardness and tool life. Compared to stainless steel, nickel and BMGs are capable of integrating length scales from 100 to 10−8 m and are good candidates for producing polymeric microfluidics. Selection of tool materials and manufacturing technologies should consider the end-user requirements of actual applications.

Investigation of medium range order and glass forming ability of metallic glass Co69Fe x Si21−x B10 (x = 3, 5, and 7)

Metallic glass of composition Co69Fe x Si21−x B10 (x = 3, 5, and 7) was studied using spatially resolved x-ray diffraction and positron annihilation spectroscopy. It was observed that the solute centered clusters forming the metallic glasses were connected to a fractal network of a reduced dimension of 2.18. The medium range order in the present system is described with a correlation function and its validity is discussed. A theoretical estimation of its glass forming ability (GFA) complimented the observations made on the local structural changes due to variation in Si content. The distribution of open volume defects in the metallic glasses during processing was found to be related to the relative GFA of the alloy compositions.

Palladium Nanoparticles Hosted on Hydrazine-Grafted Magnetite and Silica Particles to Catalyze the Reduction of Oxymetal Ions with Formic Acid

A new synthetic route has been developed to anchor a large amount of Pd nanoparticles (NPs) on the surface of hydrazine‐grafted and (3‐glycidyloxypropyl)trimethoxysilane‐coated inorganic host particles such as Fe3O4 and SiO2. The hydrazine‐grafted inorganic particles reduce Pd2+ ions spontaneously under ambient conditions. This results in the production of Pd0 seeds and their nucleation, which leads to the growth of Pd NPs on the surface of the host particle itself. These anchored Pd NPs on Fe3O4 and SiO2 have been characterized by elemental analysis, microscopy, and elemental mapping. Spherical Pd NPs of ≈0.3 and 1 nm are formed uniformly on Fe3O4 (25 nm) and SiO2 (100 nm) particles, respectively. Their concentration on the host particles was 12 mg g−1 for Fe3O4 and 20 mg g−1 for SiO2. These host particles loaded with Pd NPs have been investigated for their catalytic activity in the reduction of representative oxymetal ions such as UO22+ and Cr2O72− ions with formic acid. NP‐loaded SiO2 exhibited a good catalytic activity in both these reductions, whereas Pd NPs on Fe3O4 could reduce Cr2O72− ions only.

Nanocrystallization of Cobalt Based Metallic Glass

Effect of copper addition in a Metallic glass 2714A on the nanocrystallization characteristics have been examined in this study. Amorphous ribbon of the alloy composition Co64.5 Fe3.5 Si16.5 B13.5 Ni1Cu1 were prepared by melt spinning technique. Nanocrystallization kinetics was studied using differential scanning calorimeter technique. The kinetic parameters such as activation energy and Avrami exponent were determined using two different non-isothermal analysis methods. The kinetic behavior of individual crystallization event has been rationalized on the basis of these results. The role of addition of copper on the crystallization behavior has been understood by comparing with Metallic glass 2714A. The isothermally annealed nanocrystallized microstructures were characterized by X-ray diffraction.

Positron Annihilation Spectroscopy of Nanocrystallized Iron Based Metallic Glass

Amorphous ribbons of composition Fe68.5Cu1Nb3Si18.5B9 were produced by melt spun unit. Positron annihilation technique along with DSC and XRD studies has been employed to characterize the nanocrystallization process. XRD results confirmed presence of Fe3Si and Fe2B phases. Two life time components could be fitted to life time spectra of amorphous and heat treated samples. Life time of positron in amorphous matrix was found to be 163.3 ps. Small life time components in nanocrystallized samples could be ascribed to positron annihilation within amorphous and nanocrystalline particles. Larger life time component could be attributed to positron annihilation in interfaces associated with primary and secondary phase particles.

A Kinetics study on modified V‐doped FINEMET metallic glass

A new alloy composition of Vanadium doped FINEMET alloy has been synthesized by planer flow casting method. Vanadium doped FINEMET alloy has been reported to show better soft magnetic properties compare to unmodified FINEMET alloy. Constant heating rate experiment using Differential Scanning Calorimetry (DSC) was performed on amorphous ribbon in order to study the crystallization kinetics and predict the growth mechanism of the crystallizing events.

Effect of Cu Addition on Nanocrystallization Behavior in a Co-Based Soft Magnetic Metallic Glass

Microstructure and magnetic properties of a nanocrystalline soft magnetic material having composition Co64.5 Fe3.5 Si16.5 B13 Ni1.5 Cu1 has been studied. Amorphous ribbon could be produced by melt spinning unit. DSC analysis showed four distinct crystallization events. Heat treated samples were characterized using XRD and TEM techniques. Co2B, and CoB phases were found to crystallize before magnetic phase a−Co. Addition of copper was proved to have adverse effect on soft magnetic properties.