Development and dispensing of a nickel nanoparticle ink for the diffusion brazing of a microchannel array
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A process was developed for producing nickel nanoparticle (NiNP) films for use in diffusion-brazing stainless steel 316L microchannel laminae at 800 °C and 1 MPa of bonding pressure. NiNPs were synthesized in 45 s at 80 °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 4.2 ± 0.6 nm. Using TGA and DSC, phase change behavior was observed at temperatures as low as 720 °C. A continuous and uniform NiNP film with a thickness of 18.1 ± 2.3 μm and a roughness of 3.1 ± 0.5 μm was dispensed using a fluid pressure of 0.6 psi, a dispense gap of 1.5 mm, and a head speed of 0.5 mm/s. A microchannel array was bonded and hermetically tested up to a pressure of 120 psi with no leakage. The ultimate lap shear strength of the joint was found to be 341 ± 29 MPa. Migration of Ni into the stainless steel 316L laminae was confirmed using SEM and EDS.
KeywordsNickel nanoparticle synthesis Ink dispensing Stainless steel Diffusion brazing Microchannel array
The authors would like to acknowledge the financial support of the US Army (W15P7T08CV201) and the National Science Foundation under grant CBET-0654434. The authors would also like to acknowledge the financial support of the Murdock Charitable Trust (2010004) which was used to procure necessary equipment within the Microproducts Breakthrough Institute.
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