Ceramic capillaries

Figure 4.13 Ceramic capillary pin in holder. (From George, R. A. et al.. Genome Res., 11, 1780-1783, 2001. With permission.)...

The mechanical properties of the membrane are essential in operation and module design. For instance, hollow carbon fibers fabricated by pyrolysis of polymers are seemingly too brittle for practical applications [111]. Ceramic capillaries prepared by extrusion are much stronger, but appear limited in maximum length due to... 

Manttari, M. and Nystrom, M., Influence of flocculants on the performance of a ceramic capillary filter . Filtration Separation, January, 75-80 (1996)... 

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

Capillary Suction Processes. The force needed to remove water from capillaries increases proportionately with a decrease in capillary radius, exceeding 1400 kPa (200 psi) in a 1-p.m-diameter capillary. Some attempts have been made to use this force as a way to dewater sludges and cakes by providing smaller dry capillaries to suck up the water (27). Sectors of a vacuum filter have been made of microporous ceramic, which conducts the moisture from the cake into the sector and removes the water on the inside by vacuum. Pore size is sufficiently small that the difference in pressure during vacuum is insufficient to displace water from the sector material, thus allowing a smaller vacuum pump to be effective (126). 

Vitreous ceramics are made waterproof and strengthened by glazing. A slurry of powdered glass is applied to the surface by spraying or dipping, and the part is refired at a lower temperature (typically 800°C). The glass melts, flows over the surface, and is drawn by capillary action into pores and microcracks, sealing them. 

Slip casting is common in the ceramics industry. The material to be cast is milled to a mean particle size of a few microns. A slip is made by mixing the finely divided material with a liquid suspending medium. The slip is then poured into a suitable mold (e.g., of plaster of pans). The liquid in the slip is drawn into the mold by capillary forces and the solids are deposited in a coherent form. For TiBj, ZrBj and CrBj a suspending medium of 5-7 wt% cyclopentadiene in xylene is recommended. A 3 wt% aqueous solution of carboxymethylcellulose is the best dispersing medium... 

For silica, much of the work in this area was carried out in the 1980s and the reader is referred to the series of proceedings volumes from the Materials Research Society entitled Better Ceramics through Chemistry. 63 To illustrate typical precursor structures, and the role of reaction chemistry on precursor structure, Fig. 2.3 presents capillary gas chromatography results for the hydrolysis of tetramethoxysilane [TMOS Si(OCH3)4].72 Typical polymeric species formed (Fig. 2.3a) include linear and cyclic structures. 

The sample block cell 13 h consists of an aluminum oxide block which can be removed from the base plate. The thermocouples serving for DTA and temperature measurement are reinforced up to the hot junction by ceramic oxide capillary tubes. The sample cell can be mounted in either of two alternative positions, according to the quantity of test substance used. The DTA thermocouples extend into either the large or the small hole. 

A common method to slip-cast ceramic membranes is to start with a colloidal suspension or polymeric solution as described in the previous section. This is called a slip . The porous support system is dipped in the slip and the dispersion medium (in most cases water or alcohol-water mixtures) is forced into the pores of the support by a pressure drop (APJ created by capillary action of the microporous support. At the interface the solid particles are retained and concentrated at the entrance of pores to form a gel layer as in the case of sol-gel processes. It is important that formation of the gel layer starts... 

Radiation nozzle system for high-tem-peiatuie election diffiaction experiment for compounds with low volatility (1 - filament, 2 - supporting rod, 3 — ceramic supporter, 4 — sample container, 5 - nozzle capillary, 6 - thermocouple)... 

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