The Precursor Method

Examples of ceramic (1.1 and 1.3) and precursor (1.2 and 1.4) reactions to produce some mixed oxides are as follows  

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As noted above, the synthesis of dimer involved a complicated synthetic procedure and produced very low yields. Alternative routes for deposting poly-(tetrafluoro-p-xylylene) thin film were studied the precursor method and a new... 

Accidently, using hexafluoro-p-xylene with the contaminated copper wire obtained from the precursor method experiments, a polymer film was deposited on the silicon substrates. Obviously, some dibromotetrafluoro-p-xylene from the precursor method that adhered to, or reacted with, the metal could somehow initiate this VDP process. However, a complete explanation of these results is not yet available. As an extension of this discovery, commercially available 1,4-bis(trifluoromethyl)benzene in conjunction with a catalyst/initiator has proved to be a potential alternative by which to deposit poly(tetrafluoro-p-xylylene) film successfully.23... 

It is possible to extract the nanocolloids from aqueous solution into an organic phase or to support them onto inorganic supports by what is called the precursor method (described in Section 3.5) to generate heterogeneous catalysts. Such catalysts find application in chemical catalysis, e.g., in selective hydrogenation of fatty acids. 

The precursor method achieves mixing at the atomic level by forming a solid compound, the precursor, in which the metals of the desired compound are present in the correct stoichiometry. For example if an oxide MM 204 is required, a mixed salt of an oxyacid such as an acetate containing M and M in the ratio of 1 2 is formed. The precursor is then heated to decompose it to the required product. Homogeneous products... 

However, for modern electronic circuits, it is important to have a product of controlled grain size and the precursor method is one way to achieve this. (Another way is the sol-gel method which has also been applied to this material.) The precursor used is an oxalate. The first step in the preparation is to prepare an oxo-oxalate of titanium. Excess oxalic acid solution is added to titanium butoxide which initially hydrolyses to give a precipitate which then redissolves in the excess oxalic acid. 

The products of the precursor method are usually crystalline solids, often containing small particles of large surface area. For some applications, such as catalysis and barium titanate capacitors, this is an advantage. 

In what form do you want the product to be You might choose, for example, vapour phase epitaxy because an application requires a single crystal. Alternatively, you might choose a particular method, such as the precursor method or hydrothermal synthesis, because you need a homogeneous product. 

The electron micrographs of no-matrix resins prepared by the precursor method show that there are discrete acidic and basic domains in which the acidic groups are in effect, embedded in a matrix of the polyamine. A possible mode of polymerization is one in which block copolymers are formed as a result of the formation, initially, of a macroradical. The marked dependence of the thermally regenerable capacity of a resin on the solvent suggests that a macroradical may be involved, since their formation and stability are also greatly dependent on the solvent. However, a study of some linear analogues suggests that this is an oversimplified picture. 

In addition the combustion process that modifies the precursor method is also attractive. It requires only a short duration of few minutes to produce metal oxides having fine size and large surface area. The required quantities of metal nitride are mixed with urea and the mixture is dissolved in a minimum amount of water. The content is transferred to a Pyrex dish and then is introduced into a preheated muffle furnace maintained at 773 K. The water evaporated in a few minutes to produce a fluffy powder. Ceria and Ccj Pr Oj fine powders have been synthesized by this method." ... 

The reaction temperature could be lowered by using the precursor method of preparation, e.g. dissolve cobalt acetate and aluminium acetate in acetic acid. Evaporate to dryness and heat the residue. 

A variation of the precursor method is that the mixed precursors are polymer complexes. A powder of composition Ceo,i2Zro,8802 has been synthesized at mild temperatures (873 - 1073 K) by a polymer complex solution method using polyvinylalcohol (PVA) and by a polymerizable complex method using ethylene glycol. In these methods, a solution of polyvinylalcohol (PVA) (or ethylene glycol), citric acid, and metal ions are polymerized to form a gel precursor with randomly distributed cations. Heating of these precursors at a mild temperature produces mixed oxides that are compositionally homogenous at an atomic level. 

A thiophene based polymer poly(2,5-thienylenevinylene) (PTV, 43b) has been synthesized using the precursor method.[242] The dimethylformamide solution of the PTV precursor polymer was spun-cast and then heated to 200°C for 5 min under a nitrogen stream containing a small amount of HCl gas. During the heat treatment, HCl effectively acts as a catalyst for the conversion of the precursor polymer to the PTV.[243] Mobilities as high as 0.22 cm V s were reported. The same polymer has been used for fabrication of integrated circuits, [244] with reported mobilities of... 

With 5 ttiM of the phenol, small PDls (< 1.2) were achieved from an early stage to a later stage of polymerization. Thus, the precursor method was confirmed to be useful. Other phenols were also effective (Figure 3 and Table 1 (entries 4-7)). They include a common antioxidant BHT, phenol itself, a natural compound vitamin E (VE), and also a vinyl alcohol vitamin C (VC). The use of BPB (instead of VRl 10) led to a faster polymerization as in the TT system (Table 1 (entries 8-12)). 

The precursor method allows the preparation of ferrites with a precise stoichiometry. It involves the synthesis of a compound, the precursor, in which the reactants are present in the required stoichiometry upon heating, the precursor decomposes yielding the ferrite. 

However, the precursor route to active catalyst is hindered by the cost of preparing the catalyst. Organic components, synthesis, can be costly, as can be disposal of waste products produced during decomposition. Nevertheless, catalysts prepared by the precursor methods provide interesting insight into important aspects of catalyst activity and selectivity. 

A variety of CPEs have been prepared by the precursor method, including those that feature polythiophene, polyfluorene and poly(phenylene ethynylene) backbones. In most cases the precursors feature ester (for anionic) and free amine (for cationic) functionality that can be easily converted to the ionic form in a high yield follow-up reaction. 

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