Brian Paul

Synthesis of nickel nanoparticles by hydrazine reduction: mechanistic study and continuous flow synthesis

The continuous synthesis of nickel nanoparticles (NiNPs) in a static microchannel T-mixer by the reduction of NiCl2·6H2O in the presence of ethylene glycol without a stabilizing/capping agent was investigated. The nanoparticles were formed in accordance with the modified polyol process with hydrazine used as a reducing agent and NaOH as a catalyst for nanoparticle formation. The reaction mechanism for NiNP formation was investigated in batch with the help of Fourier transform infrared spectroscopy and X-ray diffraction (XRD) techniques. Parameters were found for reducing reaction times from 60 to 1xa0min. The effects of temperature (60–120xa0°C) and NaOH concentration (0.1 and 0.5xa0M) on batch-processed particle characteristics were also studied using XRD, transmission electron microscope and electron microprobe analysis. Average particle size was reduced from 9.2xa0±xa02.9 to 5.4xa0±xa00.9xa0nm at higher temperature and NaOH concentration. Adaptation of this chemistry to a static microchannel T-mixer for continuous synthesis resulted in smooth, spherical particles. Increases in the reaction temperature from 120 to 130xa0°C resulted in a narrow size distribution of 5.3xa0±xa01xa0nm and also resulted in magnetic properties of 5.1xa0emu/g (saturation magnetization), 1.1xa0emu/g (remanent magnetization), and 62xa0Oe (coercivity).

Microreactor-Assisted Solution Deposition for Compound Semiconductor Thin Films

State-of-the-art techniques for the fabrication of compound semiconductors are mostly vacuum-based physical vapor or chemical vapor deposition processes. These vacuum-based techniques typically operate at high temperatures and normally require higher capital costs. Solution-based techniques offer opportunities to fabricate compound semiconductors at lower temperatures and lower capital costs. Among many solution-based deposition processes, chemical bath deposition is an attractive technique for depositing semiconductor films, owing to its low temperature, low cost and large area deposition capability. Chemical bath deposition processes are mainly performed using batch reactors, where all reactants are fed into the reactor simultaneously and products are removed after the processing is finished. Consequently, reaction selectivity is difficult, which can lead to unwanted secondary reactions. Microreactor-assisted solution deposition processes can overcome this limitation by producing short-life molecular intermediates used for heterogeneous thin film synthesis and quenching the reaction prior to homogeneous reactions. In this paper, we present progress in the synthesis and deposition of semiconductor thin films with a focus on CdS using microreactor-assisted solution deposition and provide an overview of its prospect for scale-up.

The synthesis of cadmium sulfide nanoplatelets using a novel continuous flow sonochemical reactor

A continuous flow sonochemical reactor was developed capable of producing metastable cadmium sulfide (CdS) nanoplatelets with thicknesses at or below 10nm. The continuous flow sonochemical reactor included the passive in-line micromixing of reagents prior to sonochemical reaction. Synthesis results were compared with those from reactors involving batch conventional heating and batch ultrasound-induced heating. The continuous sonochemical synthesis was found to result in high aspect ratio hexagonal platelets of CdS possessing cubic crystal structures with thicknesses well below 10nm. The unique shape and crystal structure of the nanoplatelets are suggestive of high localized temperatures within the sonochemical process. The particle size uniformity and product throughput are much higher for the continuous sonochemical process in comparison to the batch sonochemical process and conventional synthesis processes.

Development and dispensing of a nickel nanoparticle ink for the diffusion brazing of a microchannel array

A process was developed for producing nickel nanoparticle (NiNP) films for use in diffusion-brazing stainless steel 316L microchannel laminae at 800xa0°C and 1xa0MPa of bonding pressure. NiNPs were synthesized in 45xa0s at 80xa0°C using a NiCl2·6H2O salt solution, a combination of NaBH4 and N2H5OH as reducing agents and PVP-40K as a stabilizing agent. A minimum molar ratio of 8:1 [NaOH]:[NaBH4] was required to obtain pure fcc-Ni with an average particle size of 4.2xa0±xa00.6xa0nm. Using TGA and DSC, phase change behavior was observed at temperatures as low as 720xa0°C. A continuous and uniform NiNP film with a thickness of 18.1xa0±xa02.3xa0μm and a roughness of 3.1xa0±xa00.5xa0μm was dispensed using a fluid pressure of 0.6xa0psi, a dispense gap of 1.5xa0mm, and a head speed of 0.5xa0mm/s. A microchannel array was bonded and hermetically tested up to a pressure of 120xa0psi with no leakage. The ultimate lap shear strength of the joint was found to be 341xa0±xa029xa0MPa. Migration of Ni into the stainless steel 316L laminae was confirmed using SEM and EDS.Graphical Abstract

Predicting the Force Needed to Create a Compression Seal in an Ultra-Thin Elastoviscoplastic Membrane

In this paper, a finite element model is developed, and experimentally validated, for predicting the force required to produce a compression seal between a polycarbonate sealing boss and a 25 μm thick elastoviscoplastic hemodialysis membrane. This work leverages previous efforts to determine the conditions for hermetic sealing in a microchannel hemodialyser fabricated using hot-embossed polycarbonate microchannel laminae containing sealing boss features. Methods are developed for mechanically characterizing the thin elastoviscoplastic hemodialysis membrane. Experimental data for assessing the depth of penetration into the membrane as a function of force show an R2 value of 0.85 showing good repeatability. The average percent error was found to be −8.0% with a range between −21.9% and 4.4% error in the strain region of interest.Copyright