Wet-processing techniques

Wet processing techniques, with usually 2 ml. of benzene per gram, are essential. 

For the past 2 years the output of analyses has been increased greatly, particularly with penetration studies, by utilization of wet-processing techniques and development of several new pieces of apparatus. This equipment includes the revolving drum-type stripping machine and especially adapted drill press used also for parathion studies. A detailed description of this press has been published ( ), and the stripping machine and accessory equipment have been described (5). 

Figure 2. Flow diagram for preparation of purified fiber, starch and proteinate from field pea and fababean by wet processing techniques.

FIGURE 20.25 Schematic representation of the direct transfer method and the electrochemical replacement method. (Reprinted with permission from Uemura, S., Sakata, M., Taniguchi, I., Kunitake, M., and Hirayama, C., Novel Wet process technique based on electrochemical replacement for the preparation of fuUerene epitaxial adlayers, Langmuir, 17, 5-7, 2001. Copyright 2001 American Chemical Society.)... 

The dry-processing techniques (VDP and E-CVD) have some merits over wet-processing techniques however, only a few polymers have now been formed by these methods, and further research is necessary. 

Chemical precipitation and solvent extraction are the main methods of purifying wet-process acid, although other techniques such as crystallisa tion (8) and ion exchange (qv) have also been used. In the production of sodium phosphates, almost all wet-process acid impurities can be induced to precipitate as the acid is neutralized with sodium carbonate or sodium hydroxide. The main exception, sulfate, can be precipitated as calcium or barium sulfate. Most fluorine and siUca can be removed with the sulfate filter cake as sodium fluorosiUcate, Na2SiFg, by the addition of sodium ion and control of the Si/F ratio in the process. 

A variation on the wet-spinning technique involves extruding into a heated gas environment. In this dry-spinning process, the temperature and composition of the gas control the extraction process. 

Once the structural support layers have been fabricated by extrusion or EPD for tubular cells or by tape casting or powder pressing for planar cells, the subsequent cell layers must be deposited to complete the cell. A wide variety of fabrication methods have been utilized for this purpose, with the choice of method or methods depending on the cell geometry (tubular or planar, and overall size) materials to be deposited and support layer material, both in terms of compatibility of the process with the layer to be deposited and with the previously deposited layers, and desired microstructure of the layer being deposited. In general, the methods can be classified into two very broad categories wet-ceramic techniques and direct-deposition techniques. 

Both wet-ceramic techniques and direct-deposition techniques require preparation of the feedstock, which can consist of dry powders, suspensions of powders in liquid, or solution precursors for the desired phases, such as nitrates of the cations from which the oxides are formed. Section 6.1.3 presented some processing methods utilized to prepare the powder precursors for use in SOFC fabrication. The component fabrication methods are presented here. An overview of the major wet-ceramic and direct-deposition techniques utilized to deposit the thinner fuel cell components onto the thicker structural support layer are presented below. 

Grain legumes have also been processed into refined starch (10,11) and protein isolates (12,13,14) by procedures derived from the traditional corn starch and soybean protein industries (15). However, comparative data on product yields, composition and losses have not been published. A commercial plant for the wet processing of field pea into refined starch, protein isolate and refined fiber has been established in Western Canada. Little is known about the characteristics of the protein isolate or refined fiber product. Water-washed starch prepared from the air-classified starch fractions of field pea (16,17) and fababean (6) have been investigated for certain physico-chemical and pasting properties. Reichert (18) isolated the cell wall material from soaked field pea cotyledons and determined its fiber composition and water absorption capacity. In addition, the effects of drying techniques on the characteristics of pea protein Isolates have been determined (14). 

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