Microchannel process technology (MPT) offers several advantages to the field of nanomanufacturing: 1) improved process control over very short time intervals owing to shorter diffusional distances; and 2) reduced reactor size due to high surface area to volume ratios and enhanced heat and mass transfer. The objective of this thesis was to consider how nanomaterials, produced in part using MPT, could be used to solve problems associated with the fabrication of MPT devices. Specifically, many MPT devices are produced using transient liquid-phase brazing involving an electroplated interlayer consisting of a brazing alloy designed for melting temperature suppression. Unfortunately, these alloys can form brittle secondary phases which significantly reduce bond strength. In contrast, prior efforts have shown that it is possible to leverage the size-dependent properties of nanomaterials to suppress brazing temperatures. In this prior work, thin films of off-the-shelf elemental nanoparticles were used as interlayers yielding joints with improved mechanical properties. In the present investigation, efforts have been made to characterize the synthesis and deposition of various elemental nanoparticle suspensions for use in the transient liquid-phase brazing of aluminum and stainless steel. Advances were used to demonstrate the nanoparticle-assisted diffusion brazing of a microchannel array. In the first section, a silver nanoparticle (AgNP) interlayer was produced for the diffusion brazing of heat exchanger aluminum. Efforts are made to examine the effect of braze filler particle size (~5 nm and ~50 nm) and processing parameters (heating rate: 5ºC/min and 25ºC/min; brazing temperature: 550ºC and 570ºC) on thin coupons of diffusion-brazed 3003 Al. A tensile strength of 69.7 MPa was achieved for a sample brazed at 570°C for 30 min under 1 MPa with an interlayer thickness of approximately 7 μm. Further suppression of the brazing temperature to 500ºC was achieved by sputtering a 1 µm thick layer of Cu before depositing a 5 nm thick film of AgNPs resulting in a lap shear strength of 45.3±0.2 MPa. In the middle section of this thesis, several techniques are investigated for the synthesis of sub 10 nm diameter nickel nanoparticles (NiNPs) to be used in the diffusion brazing of 316L stainless steel. The average NiNP size was varied from 9.2 nm to 3.9 nm based on the synthesis technique, solvent and reducing agent used. Conventional wet-chemical synthesis using NiCl₂.6H₂O in ethylene glycol (solvent) and N₂H₄.H₂O (reducing agent) resulted in the formation of 5.4 ± 0.9 nm NiNPs. Continuous flow synthesis using a microchannel T-mixer (barrel diameter of 521µm) and a 10 second residence time of reactants in a bath temperature of 130ºC resulted in a particle size of with 5.3 ± 1 nm. To make the synthesis safer and less energy intense, microwave heating was used along with less toxic Ni(CH₃CO₂)₂·4H₂O (nickel salt), propylene glycol (solvent) and NaPH₂O₂ (reducing agent) yielding 3.9 ± 0.8 nm diameter NiNPs. For the final section, nickel nanoparticles were synthesized using NiCl₂.6H₂O (nickel salt), de-ionized water (solvent), NaBH₄ (co-reducing agent), N₂H₄.H₂O (reducing agent) and polyvinylpyrolidone (capping agent) yielding 4.2 ± 0.6 nm NiNP. Several deposition techniques were investigated for controlling film thickness and uniformity in the diffusion brazing of 316L stainless steel (SS). Using in-house prepared NiNP and automated dispensing, a hermetic joint up to 70 psi (tested pressure) was obtained in 316L SS substrates under brazing conditions of 800ºC, 2 MPa and 30 min. Throughout the course of this thesis, techniques used for characterizing nanoparticles, films and joints included FT-IR, XRD, SEM, TEM, HRTEM, EDS, EPMA, DSC, mass spectrometry, and lap-shear testing. / Graduation date: 2012

[pt] A síntese de nanopartículas (NP) de níquel metálico via rota solvotérmica foi estudada com o intuito de produzir estruturas híbridas destas NP ancoradas na superfície de titanatos nanoestruturados. Inicialmente os parâmetros ideais para a formação das NP com os menores e monodispersos diâmetros foram determinados com o auxílio das técnicas de difração de raios X e de microscopia eletrônica. Em seguida, nanotubos de titanatos foram sintetizados via rota hidrotérmica alcalina. Esses titanatos foram adicionados à rota solvotérmica já estudada, buscando a nucleação heterogênea das NP de Ni metálico em sua superfície. Os produtos das sínteses foram analisados por diversas técnicas de caracterização a fim de determinar a nanoestrutura dos produtos formados, a estabilidade térmica das NP, assim como identificar os subprodutos da síntese solvotérmica e medir as eficiências catalíticas e fotocatalíticas dos materiais. Os resultados permitiram concluir sobre as características estruturais dos materiais e a eficácia da ancoração, bem como os mecanismos envolvidos na síntese solvotérmica para a redução do Ni2, presente no precursor organometálico, para Ni0, apresentando uma nova rota para a produção destas NP. / [en] The synthesis of metallic nickel nanoparticles (Ni-NP) via a solvothermic route was studied to produce hybrid structures of these NP anchored to the surface of nanostructured titanates. Initially the ideal parameters for the formation of NP with the smallest and monodisperse diameters were determined with the aid of Xray diffraction and electron microscopy techniques. Then, titanate nanotubes were synthesized via alkaline hydrothermal route. These titanates were added to the studied solvothermic route, seeking the heterogeneous nucleation of Ni-NP on its surface. The synthesis products were analyzed by several characterization techniques to determine the nanostructure of the products, the thermal stability of the NP, to identify the by-products of the solvothermic synthesis and to measure the catalytic and photocatalytic efficiencies of the materials. The results include the structural characteristics of the materials and the anchoring efficiency, as well as the mechanisms involved in the solvothermic synthesis to reduce the Ni2 ion, a component of the organometallic precursor, to Ni0, introducing a new route for the synthesis of these NPs.