Chemical vapor impregnation

Fitzer E, Fritz W, Schoch G (1991) The chemical vapor impregnation of porous solids, modeling of the CVI-process. J de Physique IV 2 C-2-143-150... 

Chemical Vapor Deposition (CVD) is a technique of deposition of a solid on a heated substrate, from gaseous precursors. It has been used for many years to produce wear resistant coatings, coatings for nuclear fuels, thin films for electronic circuits ceramic fibers, etc. .. When the CVD technique is used to impregnate ratiier large amounts of matrix materials in fibrous preforms, it is called chemical vapor impregnation or infiltration... 

Chemical vapor impregnation (CVl) is a method of infiltrating fiber architectures with matrix particles via the vapor phase. Although this is a similar process to chemical vapor deposition (CVD) in terms of gas reaction, decomposition conditions in CVl are chosen for in-depth decomposition rather than coating the surface of the substrate. 

Multiwall carbon nanotubes (MWCNTs) have been synthesized by catalytic chemical vapor deposition (CCVD) of ethylene on several mesoporous aluminosilicates impregnated with iron. The aluminosilicates were synthesized by sol-gel method optimizing the Si/Al ratios from 6 to 80. The catalysts are characterized by nitrogen adsorption, X-ray diffraction, 27A1 NMR, thermogravimetric analysis (TGA) and infrared. The MWCNTs are characterized by TGA and transmission and scanning electron microscope. 

For this purpose, all three catalyst supports were initially synthesized by a chemical vapor deposition (CVD) process and thereafter, using a wet impregnation method, loaded with cobalt as the active component for FTS. The as-synthesized Co/nanocatalysts were then characterized by applying electron microscopic analysis as well as temperature-programmed desorption, chemi- and physisorption measurements, thermogravimetric analysis, and inductively coupled plasma... 

Transihon metal carbonyls are easily soluble in organic solvents. For this reason, the impregnation method can be used in the preparation of catalysts. In some cases their properties allow the preparation of catalysts by chemical vapor deposition (CVD) on the support [11]. 

Zeolite-supported Re catalysts have been synthesized by chemical vapor deposition (CVD) ofMTO (CH3Re03) (3) on various zeolites such as HZSM-5, H-Beta, H-USY and H-Mordenite. HZSM-5 samples with different A1 contents were prepared by a hydrothermal synthesis method. For comparison, conventional impregnated catalysts were also prepared by an impregnation method using an aqueous solution of NH4Re04. All catalysts were pretreated at 673 K in a flow of He before use as catalyst. 

In this section, some of the most important methods for catalyst preparation including impregnation, grafting, precipitation, and chemical vapor deposition (CVD) are discussed [6-18],... 

Figure 11, Schematic mechanisms of pore filling and pore blocking by liquid impregnation and by chemical vapor deposition (26).

Multidimensional BN fiber infiltrated (matrix) composites are analogous to carbon-carbon composites and overcome the brittleness and low to moderate thermal shock resistance of hot-pressed BN. With the availability of BN fibers (see 17.3.5.4), a weave of three or more dimensions is possible. Chemical vapor deposition may produce a turbostatic BN matrix that is sensitive to H2O, while liquid impregnation requires multiple reimpregnation cycles h One scheme is to impregnate a BN woven fiber preform with H3BO3, dry, sinter in NH3, and hot-press. 

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