CVD-prepared

Figure 28. Comparison of the IR spectra of the (a-C H) obtained by CVD preparation and from the high-pressure transformation of benzene. Asterisks indicate the absorption bands of unreacted benzene.

We illustrate the CVD preparation of thin films with some examples. The selected materials are ferromagnetic [Fe+ (Cp )2][TCNE] and the solvent-free V(TCNE) c phase. [Ee+ (Cp )2][TCNE] is a ferromagnet with Tq = 4.8 K (Miller etal, 1988) and V[TCNE] c orders magnetically above 350 K (Manriquez et al., 1991), as previously discussed in Section 1.5. Table 3.2 summarizes the CVD conditions for growth of the thin films. V(TCNE) c and [Fe+ (Cp )2][TCNE] correspond to type I and II, respectively. 

Finally, the molecular approach, which has been adopted for many years by research groups in heterogeneous catalysis, appears to be a powerful concept to tackle the CVD preparation of nanostructures. 

Figure 7 shows the morphology of the thermal CVD prepared membrane. The size of deposited silica particles was mostly not exceeding 11 nm, and the thickness of deposited layer was about 2 pm. Figure 8 shows an EDX analysis of the interface between the support and CVD deposited layer. A silica layer was uniformly fonned on the top of the support with or without evacuation through the porous support. It is supposed that the growth of the deposited silica occurred towards the horizontal and the vertical directions in the pore. 

Packed-bed reactor operation was used to test the stability of the CVD-prepared Ti/Si02 catalysts. For simplification, the reaction used was the epoxidation of 1-ocfene with TBUP. It is much easier and simpler to carry out 1-octene epoxidation (than propylene epoxidation) in a packed-bed reactor because 1-octene (boiling point, b.p. = 122 °C) is a liquid under the reaction temperature (110 °C). No decay of 1,2-epoxyoctane yield was observed during 12 h of continuous operation with the packed-bed reactor, therefore, the CVD-prepared Ti/Si02 catalysts were stable under continuous operation conditions. 

Table 14.1 also presents the turnover frequencies (TOF) of the CVD-prepared Ti/Si02 catalysts. For 1-octene epoxidation with TBHP in a batch reactor at 110 °C... 

Daub, K., Wunder, V.K., Dittmeyer, R., 2001. CVD preparation of catalytic membranes for reduction of nitrates in water. Catalysis Today 67,257-272. 

Chemical Vapor Deposition. In chemical vapor deposition (CVD), often referred to as vapor transport, the desired constituent(s) to be deposited are ia the form of a compound existing as a vapor at an appropriate temperature. This vapor decomposes with or without a reducing or oxidizing agent at the substrate— vapor interface for film growth. CVD has been used successfully for preparing garnet and ortho ferrite films (24,25). Laser-assisted CVD is also practiced. 

Fluoroall l-SubstitutedTitanates. Tetraliexafluoroisopropyl titanate [21416-30-8] can be prepared by the reaction of TiCl and hexafluoroisopropyl alcohol [920-66-17, in a process similar to that used for TYZOR TPT (7). Alternatively, it can be prepared by the reaction of sodium hexafluoroisopropoxide and TiCl ia excess hexafluoroisopropyl alcohol (8). The fluoroalkyl material is much more volatile than its hydrocarbon counterpart, TYZOR TPT, and is used to deposit titanium on surfaces by chemical vapor-phase deposition (CVD). 

Boron Trichloride. Approximately 75—95% of the BCl consumed iu the United States is used to prepare boron filaments by CVD (7). These high performance fibers are used to reinforce composite materials (qv) made from epoxy resius and metals (Al, Ti). The principal markets for such composites are aerospace industries and sports equipment manufacturers. 

Alternative Thin-Film Fabrication Approaches. Thin films of electronic ceramic materials have also been prepared by sputtering, electron beam evaporation, laser ablation, chemical beam deposition, and chemical vapor deposition (CVD). In the sputtering process, targets may be metal... 

The technical problem in die high teiiiperamre application of Si3N4 is that unlike the pure material, which can be prepared in small quantities by CVD for example, die commercial material is made by sintering the nitride with additives, such as MgO. The presence of the additive increases the rate of oxidation, when compared with the pure material, by an order of magnitude, probably due to the formation of liquid magnesia-silica solutions, which provide short-circuits for oxygen diffusion. These solutions are also known to reduce the mechanical strength at these temperatures. 

In spray pyrolysis, very fine droplets are sprayed onto a heated substrate. The limitations of this process are the same as for spin-on coating. The same is often the case for preparing solid electrolytes by chemical vapor deposition (CVD) processes, which in addition are more expensive, and the precursors are often very toxic. 

PF3A11CI, prepared from Au2C16 and PF3 in SOCl2 has a vapour pressure of 10 4mbar at room temperature and has been suggested as a laser CVD precursor [80],... 

Metal carbonyls form a large and important group of compounds which are used widely in the chemical industry, particularly in the preparation of heterogeneous catalysts and as precursors in CVD and metallo-organic CVD (MOCVD). 

Carbonyl Nitric Oxides. Another group of metal-carbonyl complexes, worthy of investigation as CVD precursors, consists of the carbonyl nitric oxides. In these complexes, one (or more) CO group is replaced by NO. An example is cobalt nitrosyl tricarbonyl, CoNO(CO)3, which is a preferred precursor for the CVD of cobalt. It is a liquid with a boiling point of 78.6°C which decomposes at 66°C. It is prepared by passing NO through an aqueous solution of cobalt nitrate and potassium cyanide and potassium hydroxide. ... 

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