The development of microreactors that operate under harsh conditions is always of great interest for many applications. Here we present a microfabrication process based on low-temperature co-fired ceramic (LTCC) technology for producing microreactors which are able to perform chemical processes at elevated temperature (>400°C) and against concentrated harsh chemicals such as sodium hydroxide, sulfuric acid and hydrochloric acid. Various micro-scale cavities and/or fluidic channels were successfully fabricated in these microreactors using a set of combined and optimized LTCC manufacturing processes. Among them, it has been found that laser micromachining and multi-step low-pressure lamination are particularly critical to the fabrication and quality of these microreactors. Demonstration of LTCC microreactors with various embedded fluidic structures is illustrated with a number of examples, including micro-mixers for studies of exothermic reactions, multiple-injection microreactors for ionone production, and high-temperature microreactors for portable hydrogen generation. IntroductionChemical microreactors are a type of meso-scaled reaction systems that have fluidic channels with characteristic dimensions in the sub-millimeter range. By combining process intensification concepts with microfabrication techniques, these microreactors have been rapidly developed to perform liquid/gas phase chemical reactions, particularly the quasiinstantaneous endothermic or exothermic ones.1,2 Ceramic materials in general feature high chemical and thermal stability. Hence they are very preferable to be used as reactor construction materials, especially for reactors involved with high temperature and/or harsh chemical reactions. be used as the embedded fluidic structures (e.g. channels or cavities) get easily damaged in the stacked LTCC tapes by the high lamination temperature and/or pressure, causing sagging, tearing and cracking issues. Several approaches have been proposed so far in order to reduce these deformations and improve the quality of integrated LTCC fluidic structures. One method is using temporary inserts to introduce mechanical supports to the LTCC cavities to avoid deformation and/or sagging during lamination. These inserts, usually solid flexible objects, 23 are removed right after lamination. However, the removal of inserts from the laminate can cause permanent damage to these fluidic structures. Besides, this method is not applicable for fabricating fully embedded fluidic channels. Alternatively, a chemical-assisted lamination process has been proposed that enables low-pressure and/or lowtemperature bonding of LTCC green tapes. Roosen et al. 24used double-sided adhesive tape that contains acrylate adhesives and a polyethylene terephthalate (PET) film to ensure temporary binding of green tapes under a low lamination pressure at ambient temperature. Upon heating (40-60°C), these adhesives, together with the binders in the LTCC green tapes, soften and join the laminates through capillary forces. Aside from adhesives, ...

This work introduces and investigates the a novel compact catalytic nanoparticle bed microfabricated reactor suitable for utilization in small-scale intermediate-temperature micro-SOFC systems. It is shown that the presented micro-reactor is able to produce syngas (CO + H 2 ) efficiently from n-butane and propane at temperatures between 550 -620 °C by means of catalytic partial oxidation (CPOX) using Rh-doped nanoparticles embedded in a foam-like porous ceramic bed as a catalyst. The novel micro-fabricated reactor system is experimentally tested using a carrier specially designed for heating the reactor as well as feeding the fuel and receiving the reaction product gases. Optimization of the syngas production is performed by varying fuel dilutions and reactor temperatures. The performance of the micro-reactor was investigated in two modes: (1) Continuous heating mode, in which two built-in heaters underneath the carrier are kept on throughout the reforming reaction. This simulates the operating state of a micro-SOFC system where the post-combustor provides heat to the microreformer continuously. (2) Thermally self-sustained mode, in which the heaters are turned off after the CPOX has been ignited. An estimation of the heat losses of both testing modes is also given. The present micro-reactor is able to achieve syngas yield as high as 60 % for nbutane and 50 % for propane in the continuous heating mode, which is a substantial improvement to state-of-the-art micro-reactors.

With growing public interest in portable electronics such as micro fuel cells, micro gas total analysis systems, and portable medical devices, the need for miniaturized air pumps with minimal electrical power consumption is on the rise. Thus, the development and downsizing of next-generation thermal transpiration gas pumps has been investigated intensively during the last decades. Such a system relies on a mesoporous membrane that generates a thermomolecular pressure gradient under the action of an applied temperature bias. However, the development of highly miniaturized active membrane materials with tailored porosity and optimized pumping performance remains a major challenge. Here we report a systematic study on the manufacturing of aerogel membranes using an optimized, minimal-shrinkage sol-gel process, leading to low thermal conductivity and high air conductance. This combination of properties results in superior performance for miniaturized thermomolecular air pump applications. The engineering of such aerogel membranes, which implies pore structure control and chemical surface modification, requires both chemical processing know-how and a detailed understanding of the influence of the material properties on the spatial flow rate density. Optimal pumping performance was found for devices with integrated membranes with a density of 0.062 g cm(-3) and an average pore size of 142.0 nm. Benchmarking of such low-density hydrophobic active aerogel membranes gave an air flow rate density of 3.85 sccm·cm(-2) at an operating temperature of 400 °C. Such a silica aerogel membrane based system has shown more than 50% higher pumping performance when compared to conventional transpiration pump membrane materials as well as the ability to withstand higher operating temperatures (up to 440 °C). This study highlights new perspectives for the development of miniaturized thermal transpiration air pumps while offering insights into the fundamentals of molecular pumping in three-dimensional open-mesoporous materials.