RESEARCH PAPER Development and dispensing of a nickel nanoparticle ink for the diffusion brazing of a microchannel array Ravi Eluri • Brian Paul Received: 8 March 2013 / Accepted: 19 June 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract 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 NiCl 2 Á6H 2 O salt solution, a combination of NaBH 4 and N 2 H 5 OH as reducing agents and PVP-40K as a stabilizing agent. A minimum molar ratio of 8:1 [NaOH]:[NaBH 4 ] 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 lm and a roughness of 3.1 ± 0.5 lm 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. Keywords Nickel nanoparticle synthesis Á Ink dispensing Á Stainless steel Á Diffusion brazing Á Microchannel array Introduction Metallic microchannel arrays have been used in a wide range of applications including the thermal manage- ment of laser diodes, nanoparticle synthesis, and fuel synthesis among many others (Hyung Dae et al. 2010; Paulraj and Paul 2011; Paul 2006). Microchannel lamination (microlamination) techniques are well- known for the fabrication of these devices (Paul and Peterson 1999). In general, microlamination involves the patterning of microchannel and header features onto thin foils called laminae and the registration and bonding of these laminae into devices. In prior applications, the bonding step has been carried out by thermal adhesive (Paulraj and Paul 2011), solder reflow, diffusion bonding (Paul et al. 2006), internal convective heating (Paul et al. 2010), and diffusion- brazing (Tiwari and Paul 2010; Eluri and Paul 2009) largely depending on the lamina materials used and end application temperature. Typically for higher temperature applications ( \ 500 °C), stainless steel (SS) laminae are bonded via diffusion bonding or diffusion brazing in a vacuum hot press (VHP) under uniaxial pressure and a controlled atmosphere. Diffusion bonding requires high temperatures (*0.7 Tm) and high pressures (6–10 MPa) to insure good fit-up of faying surfaces by plastically deforming surface asperities. Cycle times can be quite long to eliminate voids at the interface caused by surface asperities and to avoid thermal buckling of fins (Paul and Lingam 2012) and other high temperature failure R. Eluri (&) Á B. Paul Mechanical, Industrial and Manufacturing Engineering, Oregon State University, Corvallis, OR 97330, USA e-mail: ravindranadhtagore@gmail.com 123 J Nanopart Res (2013) 15:1814 DOI 10.1007/s11051-013-1814-z