13This paper reports the first results of a robust, high performance, stainless-steel 14 microchip gas chromatography (GC) column that is capable of analyzing complex real 15 world mixtures as well as operating at very high temperatures. Using a serpentine 16 design, a 10 m column with an approximately semicircular cross section with a 52 µm 17 hydraulic diameter (Dh) was produced in a 17 cm x 6.3 cm x 0.1 cm rectangular steel 18 chip. The channels were produced using a multilayer chemical etch and diffusion 19 bonding process, and metal nuts were brazed onto the inlet and outlet ports allowing for 20 column interfacing with ferrules and fused silica capillary tubing. After deactivating the 21 metal surface, channels were statically coated with a layer of 0.16 µm (5%-phenyl)(1%-22 vinyl)-methylpolysiloxane (SE-54) stationary phase, and cross-linked with dicumyl 23 peroxide. By using n-tridecane (n-C13) as test analyte with a retention factor (k) of 5, a 24 total of 44,500 plates (≈4500 plates/m) was obtained isothermally at 120 °C. The 25 column was thermally stable to at least 350 °C, and rapid temperature programming (35 26 °C/min) was demonstrated for the boiling point range from n-C5 to n-C44 (ASTM D 2887 27 simulated distillation standard). The column was also tested for separation of two 28 complex mixtures: gasoline headspace and kerosene. These initial experiments 29 demonstrate that the planar stainless-steel column with proper interfacing can be a 30 viable alternative platform for portable, robust microchip GC that is capable of high 31 temperature operation for low volatility compound analysis. Since the introduction of silicon microchip gas chromatography (GC) columns by 34 Terry et al. (1) in 1979, there has been tremendous interest among researchers in 35 fabricating such columns in various substrates such as ceramics (2,3) glass (4), 36 polymers (5, 6) and metals (2, 7-9). Despite the wide variety of substrates employed, 37 silicon accounts for the majority at approximately 80% of all microchip GC columns 38 fabricated. The advantages of silicon include established micromachining technology, 39 capability of generating high aspect ratio features, cost effectiveness due to batch 40 processing, low thermal mass, high thermal conductivity, chemical inertness and 41 familiar silanol (Si-OH) chemistry to the popular fused-silica capillary column technology 42 (10). It is worth mentioning that although there are reports of all-silicon microcolumns 43 (both etched in and bonded with silicon wafers), in most cases, the channels are 44 microfabricated in a silicon substrate followed by anodically bonding to a Pyrex glass 45 top layer (1, 11,12). This design is not ideal as such silicon/glass hybrid systems exhibit 46 thermal expansion coefficient (CTE) mismatch (13), non-uniformity in temperature 47 91 column. After bonding the channels, stainless steel connection tubes were brazed to the 92 plate for connection to the inlet and detector. Unlike epoxy-based adhesives, since 93 brazing can handle high...
a b s t r a c tWe present two designs for metal compliant mechanisms for use as threshold accelerometers which require zero external power. Both designs rely on long, thin flexures positioned orthogonally to a flat body. The first design involves cutting or stamping a thin spring-steel sheet and then bending elements to form the necessary thin flexors. The second design uses precut spring-steel flexure elements mounted into a mold which is then filled with molten tin to form a bimetallic device. Accelerations necessary to switch the devices between bistable states were measured using a centrifuge. Both designs showed very little variation in threshold acceleration due to stress relaxation over a period of several weeks. Relatively large variations in threshold acceleration were observed for devices of the same design, most likely due to variations in the angle of the flexor elements relative to the main body of the devices.
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