Vycor process, glass

The Vycor process described in Chapter 8 uses the principle of phase separation. The resulting glass is 96% SiOz and 4% pores and is used as a filter and a bioceramic where porosity is important. It can be densified (after shaping) to allow processing of a pure SiOz shape at a lower temperature than for pure quartz glass. 

Besides etching of masked glass substrates, see Sect. 6.1, the leaching of phase-separated glasses, see for instance Figs. 1.14-1.16, is completely an other process and also allows for the fabrication of microstructured glass bodies. A schematic of the process to fabricate a porous glass membrane, which was developed from the classical VYCOR process, is shown in Fig. 6.4. 

Vycor glass (Corning, 7930) is porous silica processed in the same way as CPG except that the last step of base etching is missing. Therefore the surface is rough. Only a 40-A pore is available. When porous silica with a pore size smaller than 75 A is needed, Vycor glass is the choice. Bulk pieces of Vycor glass are available commercially and need to be crushed into small particles before use. 

The Vycor glass tube used in the membrane reactor experiments was filled with 3.2 g of catalyst. As the accessible area was ca. 30 cm2, the ratio of membrane area to catalyst mass is in the range specified by Eq. (35). Consequently, there should be sufficient membrane area available to remove significant amounts of hydrogen and, therefore, to have an effect on the reaction process. 

In addition, Vycor can be shaped and/or formed while in its borosilicate state before it is transformed into Vycor. Thus, molded, pressed, tapered, and other shapes that would otherwise be very difficult, expensive, and/or impossible in fused silica can be done (relatively) easily with the pre-Vycor material with much less energy. Once the manufacturing is complete, the glass can then be processed to Vycor. 

The pyrolysis reactors were similar to those used earlier (1,2) they were 1.1 to 1.26-cm i.d. tubes that were heated in an electrical resistance furnace over a length of about 48 cm. The materials of construction in the four reactors used in this investigation were as follows Incoloy 800, stainless steel 304, Vycor glass, and alonized Incoloy 800. The latter reactor was prepared by Alon Processing, Inc. of Tarentum, Pennsylvania. 

Mesoporous glass ("Vycor type") can be produced by a combined heat-treatment and leaching procedure as summarised by Burggraaf and Keizer [78] in an extended overview of synthesis methods. Modification of this process leads to microporous hollow fibres with interesting properties (see Chapter 9). Details of this modification process are not known to this author. 

Mesoporous glass (Vycor type) can be produced by a combined heat-treatment and leaching procedure [9]. Modification of this process can lead to microporous hollow-fibre systems with interesting properties as discussed by Shelekhin, Ma et al [56]. For further discussion see Sections 9.4.2 to 9.4.4. 

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