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[en] Highlights: ► 5 nm AgNPs showed size dependent melting behavior. ► 3003 Al alloy was brazed well below the Al–Ag eutectic (567 °C) temperature. ► Heating rate influenced the microstructural/phase changes at the bond interface. ► A 7 μm Ag interlayer resulted in shear stress of 69.7 MPa when brazed at 570 °C. ► Diffusion zone of ∼25 μm (one side) is a potential candidate for precision joining. -- Abstract: In the current study, we investigated the effect of braze filler particle size and various processing parameters on vacuum diffusion brazing of thin foils of 3003 Al using a Ag nanoparticle (AgNPs) interlayer. All samples were brazed at 550 °C and 570 °C at heating rates of 5 °C/min and 25 °C/min under a pressure of 1 MPa. Differential scanning calorimetric results, involving 5 nm AgNPs, showed significant reduction in phase transformation temperature. Microstructures of brazed cross-sections revealed that nanoparticles aid formation of the joint at temperatures below the Al–Ag eutectic temperature of 567 °C. X-ray diffraction analysis of the interface showed the presence of δ-phase (Ag2Al) and μ-phase (Ag3Al). This was confirmed with energy dispersive spectroscopic analysis. A tensile strength of 69.7 MPa was achieved for a sample brazed at 570 °C with an interlayer of approximately 7 μm in thickness.
[en] Growth in the potential applications of nanomaterials has led to a focus on the development of new manufacturing approaches for these materials. In particular, an increased demand due to the unique properties of nanomaterials requires a substantial yield of high-performance materials and a simultaneous reduction in the environmental impact of these processes. In this paper, a high-rate production of phosphine-stabilized undecagold nanoclusters was achieved using a layer-up strategy which involves the use of microlamination architectures; the patterning and bonding of thin layers of material (laminae) to create a multilayered micromixer in the range of 25-250 μm thick was used to step up the production of phosphine-stabilized undecagold nanoclusters. The continuous production of highly monodispersed phosphine-stabilized undecagold nanoclusters at a rate of about 11.8 (mg s-1) was achieved using a microreactor with a size of 1.687 cm3. This result is about 500 times over conventional batch syntheses based on the production rate per reactor volume.
[en] A critical barrier to the routine use of nanomaterials is the tedious, expensive means of their synthesis. Microreaction technology takes advantage of the large surface area-to-volume ratios within microchannel structures to accelerate heat and mass transport. This accelerated transport allows for rapid changes in reaction temperatures and concentrations leading to more uniform heating and mixing which can have dramatic impacts on macromolecular yields and nanoparticle size distributions. Benefits of microreaction technology include higher yield and reactant conversion, better energy efficiency and less by-product generation. Microreactors can help minimize the environmental impact of nanoproduction by enabling solvent free mixing, integrated separation techniques and reagent recycling. The possibility of synthesizing nanomaterials in the required volumes at the point-of-use eliminates the need to store and transport potentially hazardous materials and provides the flexibility for tailoring complex functional nanomaterials. Recognizing these benefits for nanosynthesis, continuous flow microreactors have been used by several research groups to synthesize and characterize nanomaterials. An overview of these efforts and issues related to scale up and other post synthesis processes such as separation and deposition are presented in this paper.
[en] Continuous microreactor-assisted solution deposition is demonstrated for the deposition of CdS thin films on fluorine-doped tin oxide (FTO) coated glass. The continuous flow system consists of a microscale T-junction micromixer with the co-axial water circulation heat exchanger to control the reacting chemical flux and optimize the heterogeneous surface reaction. Dense, high quality nanocrystallite CdS thin films were deposited at an average rate of 25.2 nm/min, which is significantly higher than the reported growth rate from typical batch chemical bath deposition process. Focused-ion-beam was used for transmission electron microscopy specimen preparation to characterize the interfacial microstructure of CdS and FTO layers. The band gap was determined at 2.44 eV by UV–vis absorption spectroscopy. X-ray photon spectroscopy shows the binding energies of Cd 3d3/2, Cd 3d5/2, S 2P3/2 and S 2P1/2 at 411.7 eV, 404.8 eV, 162.1 eV and 163.4 eV, respectively. - Highlights: ► CdS films deposited using continuous microreactor-assisted solution deposition (MASD) ► Dense nanocrystallite CdS films can be reached at a rate of 25.2 [nm/min]. ► MASD can approach higher film growth rate than conventional chemical bath deposition