Precursors Ti

Not only has the Ti precursor been investigated, but also the structure of the molecular sieve has been heavily investigated. Thus we now have an array of silica and silica-alumina molecular sieve supported Ti catalysts. These include Ti on amorphous Si02,10,11 Ti on a variety of Si02 mixed oxides,12 Ti-0 (titanium-beta),13"17 Ti-MCM-48,18 Ti-MCM-41,19 Ti-HMS,18 titanium-... 

In some instances, this approach has proven successful, with comparatively low crystallization temperatures being observed. For example, Eichorst and Payne in the synthesis of LiNb03 noted crystallization temperatures of 400-500 °C for a mixed-metal alkoxide precursor.111 In other instances, these attempts have proven less successful. Numerous attempts have been made to synthesize Pb-Zr and Pb-Ti precursors, each with the 1 1 cation stoichiometry of the desired PbZr03 and PbTi03 compounds.83,84 Unfortunately, 1 1 stoichiometric ratio compounds have not always been obtained, with crystalline compounds of other stoichiometries precipitating from the solution, as illustrated in Fig. 2.11.83 This figure shows the crystal structure of PbTi2[p(4)—... 

Developing Ti-precursors that do not degrade hydrogen storage capacity (SNL, UH, SRTC)... 

Arrhenius plot of desorption rates of NaAIH4 doped with different Ti-precursors (K. Gross, et al, SNL)... 

The most commonly used hard templates are anodic aluminum oxide (AAO) and track-etched polycarbonate membranes, both of which are porous structured and commercially available. The pore size and thickness of the membranes can be well controlled, which then determine the dimension of the products templated by them. The pores in the AAO films prepared electrochemically from aluminum metals form a regular hexagonal array, with diameters of 200 nm commercially available. Smaller pore diameters down to 5 nm have also been reported (Martin 1995). Without external influences, capillary force is the main driving force for the Ti-precursor species to enter the pores of the templates. When the pore size is very small, electrochemical techniques have been employed to enhance the mass transfer into the nanopores (Limmer et al. 2002). 

It is reported that ammonium sulfate can produce the negatively charged oligomers through sulfate bridges, which induced the electrostatic interaction with the surfactant and therefore facilitate the formation of zirconia/CTAB mesophase [9]. Since Ti(S04)2 was used as Ti precursor in the present study, a various amounts of (NH4)2S04 was added into the CTAB solution in order to investigate the sulfate effect... 

Recently, one more Ti precursor has been introduced, Ti(MPD)(thd)2 (MPD = methyl-pentanedioxide), but its effects on the BST film deposition are not yet well known. It is generally understood that the optimum Ti precursor must have chemical compatibility with the Ba and Sr precursors, such as non-interaction in solution or in the gas phase and similar decomposition characteristics to the Ba and Sr precursors, in addition to volatility. Most of the Ti precursors discussed above have much better volatilities and thermal stabilities than those of the precursors of the group II elements but are still lacking appropriate chemical compatibility with them. It is known that the thermal decomposition of Ti(thd)2(i-0-P )2 is quite different from that of the Ba(thd)2 and Sr(thd)2 from the increasing Ti concentration in the BST film with increasing temperatures.It is believed that the thermal decomposition of Ti(thd)2(i-0-P )2 requires more... 

However, in region A, the chemical composition of the deposited thin films is very sensitive to the minute variation of temperature because in this region the thermal decomposition rate of the Ti precursor is very sensitive to temperature i.e. surface chemical reaction controls the deposition. The variation of mass concentration of the constituent ions estimated by x-ray fluorescent spectroscopy (XRF) is... 

An interesting observation results from the comparison between the Ti concentrations in Figures 15 and 17. When the Ti precursor input rate is increased by a factor of 2.93 (4.92/1.68) the Ti concentration of the film is increased by a factor of only 1.6 for a wafer temperature of 470°C, whereas it is increased by a factor of 2.73 when it is 420°C. This implies that as the deposition temperature increases, a type of selfregulating mechanism of film composition to the stoichiometric one is present, as in the case of Pb incorporation into PZT thin films. This kind of self-regulating mechanism can not generally be understood from simple thermodynamic calculations which usually predict formation of... 

From the above observations, it can be assumed that the formation of protrusions is due to incomplete thermal decomposition of the Ti precursors in the relatively low temperature region. The non-cracked ligands incorporated into the film hinder the formation of a uniformly crystallized thin film. It is reasonable to assume that the protruded region contains some carbonate material even though the crystallographic analysis did not detect any carbonate phase due probably to the fact that the carbon containing phase has non-crystalline structure. 

Numbers of experiments have been recently carried out to understand the mechanisms for hydrogen desorption and the role of Ti precursors play in the process. There are mainly three explanations ... 

Equation (9) proceeds in the presence of Et20/CCl4 and Eq. (10) in the presence of CH2CI2. Similarly, Ti-sol can be prepared using (i—PrO)4Ti or i— Pt20 as the oxygen donor and T1CI4 as the Ti precursor. 

F3CS03)2 were obtained from triflic acid hydrolysis of the appropriate Ti precursor.548,657... 

Influence of the Ti-precursor used for the grafting of Si02 on the catalytic properties of Rh/Ti-Si02 in the Partial Oxidation of Methane. 

---