MicroChannel plates fabrication

In this study, we developed microchannel PrOx reactor to control CO outlet concentrations less than 10 ppm from methanol steam reformer for PEMFC applications. The reactor was developed based on our previous studies on methanol steam reformer [5] and the basic technologies on microchaimel reactor including design of microchaimel plate, fabrication process and catalyst coating method were applied to the present PrOx reactor. The fabricated PrOx reactor was tested and evaluated on its CO removal performance. 

The fabricated microchannel plates were stacked together and tightened by end-plates to prevent the leak and mixing of gases as shown in Fig. 2. The dimensions of the reactor excluding fittings were about 60 mm x 40 mm x 3 mm respectively. 

MCPs operate on the same principle as CDEMs. A microchannel plate is essentially a monolithic array of miniaturized CDEMs fabricated in a single wafer or disk of glass. The disk contains pores extending from the upper surface to the lower surface. These pores are known as channels and perform the same function as the interior of the tube in a CEM, but in contrast to a typical CEM, the entrance ends of the channels are not flared. The channels are typically 3 to 30 micrometers in diameter depending on the design. The length of the channels is set by the thickness of the disk, typically 200 to 1000 micrometers. MicroChannel plates can be fabricated in areas measured in cm, and because the disk-shaped profile forms a nearly flat stopping surface for ions, they are ideal detectors for TOE mass spectrometers. Burle and Hamamatsu are the major suppliers of these devices. 

Fabrication of MicroChannel Plate Heat-Exchanger Reactors ... 

Aravamudhan, Rahman, and Bhansali. [70] developed a micro direct ethanol fuel cell with silicon diffusion layers. Each silicon substrate had a number of straight micropores or holes that were formed using microelec-tromechanical system (MEMS) fabrication techniques. The pores acted both as microcapillaries/wicking structures and as built-in fuel reservoirs. The capillary action of the microperforations pumps the fuel toward the reaction sites located at the CL. Again, the size and pattern of these perforations could be modified depending on the desired properties or parameters. Lee and Chuang [71] also used a silicon substrate and machined microperforations and microchannels on it in order to use it as the cathode diffusion layer and FF channel plate in a micro-PEMFC. 

Initially, the reactor was to be built using silicon wafers, 92 but more recent efforts have focused on a stainless steel reactor. The reformer, 7.5 x 4.5 x 11.0 cm (371 cm ), houses up to 15 stainless steel plates (0.5 mm thick) with chemically etched microchannels and heating cartridges. Conventional and laser micromachining techniques were used to fabricate the reformer body. The microchannel dimensions are 0.05 x 0.035 x 5.0 cm . The reactor inlet was carefully designed to allow uniform flow conditions. ... 

This chapter illustrates basic concepts, instrumental aspects, and modes of separation of electromigration techniques performed in capillary format. It shonld be noted that most of the fundamental and practical aspects of the electromigration techniqnes performed in capillary tubes also apply when the techniques are carried out in microchannels fabricated on plates of reduced dimensions, communally referred to as chips. 

Zhu et al. [76] designed and fabricated microfluidic devices on polymethylmethacrylate (PMMA) substrates for electrochemical analysis applications using an improved UY-LIGA process. The microchannel structures were transferred from a nickel mold onto the plastic plates by the hot embossing... 

Only very few studies with alternative materials and fabrication methods have been published. Ekstrom et al. [35] demonstrated the feasibility of structuring inexpensive polymeric materials by means of a microfabricated master for the production of microchannel systems. The structured polymer film was mechanically clamped between two glass plates to form a closed channel system. Recently, a similar route for the fabrication of microchannel chips that relies on casting of an elastomeric polymer material against a microfabricated master has been presented by Effenhauser et al. [36] (see Sect. 3.4). 

Microchannels have also been directly patterned on SU-8 photoresist [232-234,892]. Multilevel structures were fabricated using the SU-8 photoresist [232]. In another report, the SU-8 photoresist was spun (1250 rpm for 30 s) on an ITO-coated glass plate, which was first treated by an 02 plasma to increase the adhesion of SU-8 on ITO. The photoresist channel was of ribbon-like structure with triangular ends (40 pm height, 10 mm width and 90 mm length). The channel was bonded by hot-pressing to another ITO glass on top of the photoresist structures [892]. SU-8 photoresists have also been used to create multilayered... 

Figure 14 Fabrication procedure for the pile-up microreactor. (1) Photolithography Conventional photolithography/wet etching methods were applied. The back side of the glass plate was covered with polyolefin tape during the HF treatment. (2) Drilling Penetrating holes were drilled at the inlet and outlet ports of the micro-channel circuit. (3) Thermal bonding The required number of glass plates with microchannels and one cover plate were laminated and bonded thermally at 650°C.

Some of these will be discussed here with various attributes that they possess. Aside from the conventional substrates, others that are currently under development are short contact time (SCT) reactors that consist of screens, mesh, or expanded metal that are typically fabricated from high-temperature FeCrAl alloys. Reticulated foams that combine the very low pressure drop of monoliths with the improved transport of SCT reactors are often used. There are flat plate and microchannel reactors and recently microelectromechanical system (MEMS) reactor geometries that have been fabricated. In comparison to monolith or pellet beds, SCT substrates seem to allow Prox reactors to operate at significantly lower water concentrations before the onset of the hydrogen oxidation reaction, that is, the high-temperature steady state. 

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