Precursor thermal decomposition

More complex (ternary and quaternary) nitride ceramics can also be formed from polymeric precursors. Thermal decomposition of [CH3Si(N = C = N)i.5]n has been shown by N NMR to form NSi3 units when the protons are lost from the system during heating at 600-800°C (Gabriel et al. 1999). The product is an amorphous mixture of Si3N4 and carbon which reacts to form an amorphous Si-C-N ceramic phase. Similar studies have been carried out on the formation of Si-B-N ceramics from single phase... 

The nanoparticles of non-linear optical material KTiOPO< (KTP) were synthesised through metal-organic precursors, prepared by reaction of alkoxides (RO)3P(0), Ti(OR)4, and KOR (R-Et, Pr, Bu) in alcohol solution. The precursor thermal decomposition (650-900°C) resulted in a single-phase KTP of different, preferably spherical, morphology. The dimension of produced particles is ranged from 45-50 up to 800-1500 nm. 

It was shown in [5 3,54] that there are two methods to fabricate the homogeneous polymer-immobilized dispersions of colloidal metal particles (Fe, Co, Cr, Mo, W, Mn, Re, Ni, Pd, Pt, Ru, Rh, Os, Ir) using the precursors thermal decomposition. In the former case an active polymer solution (containing amino-, amido-, imino-, nitrilo-, hydroxy-, and other functional groups) is used. In an inert solvent a labile metal compound is gradually added to the solution (this operation creates the favorable conditions for the chemisorption interaction) followed by the suspension thermal decomposition at 370-440 K or by radiation. 

An original method of metallopolymer production by precursors thermal decomposition is to localize the particles being formed due to a fast monomol-ecular decay of the solutions containing the metal compounds in polymer melts—that is, in the natural voids of the polymer matrix (as PE, PP, PTFE, etc.). Such materials are called cluspol [30, 63-65], and for their production it is necessary to provide the most possible melt temperature, which must be considerably above the temperature of the carbonyl decay initiation. For this purpose the carbonyl dilute solutions are used under these conditions, providing the ultimately fast and complete removal of the split out ligand from the reaction system. Such an approach has many advantages because the temperature rise from one side promotes the metal-forming precursor decomposition and from other side decreases the by-products yield. Furthermore, in a melt (as... 

The generic apparatus used in a vapor precursor process is very similar to that used in spray pyrolysis, except that the precursor material is introduced to the reactor as a vapor (see Figure 2.1, 2. la). If the precursor is a liquid, carrier gas is typically bubbled through it. If the precursor is a solid, then the carrier gas is often passed through a heated, packed bed of the material. The vapor-laden carrier gas then flows to a furnace reactor, where thermal decomposition of the precursor occurs and particle formation results. Product powder is collected or measured at the reactor outlet. Flame processes also fall into the vapor precursor/thermal decomposition category of gas-phase powder synthesis. The only difference is that the thermal energy is provided by combustion as opposed to an external source. 

Mixed oxides have the ability to form paracrystalline phases that represent an intermediate phase between the crystalline and the amorphous phase. Because of the disordered structure paracrystallinity causes defects that occur due to the inhibition of recrystallization and are initiated by the introduction of additional anions or molecules into the lattice structure. The formation of these deformed crystalline structures depends on the used synthesis method as well as the nature of the cation precursor. Thermal decomposition of the LDHs leads to the formation of the metastable phase that contains divalent and trivalent cations with densely packed configuration [2,32]. After the reduction, tri-valent ions are trapped inside the crystallites of divalent ions causing the formation of active centers. The centers that exhibit higher reactivity are believed to be formed on the surface of the paracrystalline crystals. After deactivation, the grain size of these mixed oxides increases due to the gradual removal of the defects in the crystal lattice [2]. 

Photolysis of dlazirines to nitrogen and carbenes is a general reaction and plays a greater role in carbene chemistry than photolysis of linear diazo compounds. Whereas the latter are often obtained only under the conditions of their thermal decomposition from suitable precursors, diazirines are obtainable in a pure state in most cases. Photolysis has the further advantage to permit nitrogen extrusion at atmospheric pressure, even with low-boiling materials. 

Tnmethyl(trifluororaethyl)tin can also be prepared via in situ formation and capture of tnfluorometbide by trimethyltin chlonde [13, 14] (equation 9) This tin analogue has been used as a precursor for difluorocarbene either by thermal decomposition or by reaction with sodium iodide m 1,2-dimethoxyethane This carbene generation procedure has been used to study difluorocarbene selectivity with steroidal olefins [75] (equation 10). 

The formation and stability of peroxoniobates and peroxotantalates can be used successfully in the technology of tantalum and niobium oxide production. Belov, Avdonina and Mikhlin [512] investigated processes of precipitation and thermal decomposition of high-purity ammonium tetraperoxoniobate and tetraperoxotantalate as precursors for the production of tantalum and niobium... 

The excited triplet states of quinones can be fairly readily populated by irradiation and nuclear polarization observed (Cocivera, 1968). Hydrogen atom abstraction leads to the relatively stable semiquinone radicals and, in alkaline media, radical anions. Recombination of radical pairs formed in this way can give rise to CIDNP signals, as found on irradiation of phenanthraquinone (20) in the presence of donors such as fluorene, xanthene and diphenylmethane (Maruyama et al., 1971a, c Shindo et al., 1971 see also Maruyama et al., 1972). The adducts are believed to have the 1,2-structure (21) with the methine proton appearing in absorption in the polarized spectrum, as expected for a triplet precursor. Consistently, thermal decomposition of 21 as shown in equation (61) leads to polarization of the reactant but now in emission (Maruyama... 

In thermal-decomposition reactions, a molecule is split into its elements and/or a more elementary molecule. Such reactions are the simplest since only one precursor gas is required. Typical examples are as follows ... 

SsO may also function as a precursor for S2O units. However, it should be noticed that free S2O has never been detected directly in liquid solutions and that the isolated products most probably arise from a reaction of the S2O precursor with the trapping reagent since the reaction temperature is always 20 °C (e.g., by a transition-metal-induced retro-Diels-Alder reaction) [52, 53]. An exception may be the thermal decomposition of the substituted tetrathiolane-2,3-dioxide shown in Scheme 2 this compound evidently... 

The preparation method of titania support was described in the previous paper [6]. Titanium tetraisopropoxide (TTIP 97%, Aldrich) was used as a precursor of titania. Supported V0x/Ti02 catalysts were prepared by two different methods. The precipitation-deposition catalysts (P-V0x/Ti02) were prepared following the method described by Van Dillen et al. [7], in which the thermal decomposition of urea was used to raise homogeneously the pH of a... 

Cyclopropenylidene [2] has been obtained from two different precursors, [3] and [4], by their thermal decomposition in the gas phase (Reisenauer et al., 1984 Maier et al., 1987, 1989a). The subsequent UV photolysis (A = 313 nm and 254 nm) of this carbene in an argon matrix led to its isomerization to propargylene [5] and further to vinylidencarbene [6]. It should be noted that the carbene [5] was independently obtained by... 

The bands of the SiCls radical (Milligan and Jacox, 1968b), have not been observed at all. Due to the high selectivity of its thermal decomposition within a wide temperature interval, Si2Cl6 has become one of the most suitable precursors of dichlorosilylene in preparative chemistry (Chernyshev and Komalenkova, 1990). 

Positive ion FAB mass spectra obtained with a double focusing mass spectrometer produced abundant molecular ions ([M] +) of carotenes and xanthophyUs with minimal fragmentation and no detectable thermal decomposition. Fragmentation of the precursor ion was enhanced by collision-induced dissociation (CID) using helium gas. ... 

The nitration of N,N -diethylurea gives nitrated products which are precursors for a new energetic plasticizer N,N -dialkyl-N,N -dinitrourea (DNDA). For macroscopic batch processing, this reaction is characterized by a lack of selectivity owing to mononitro derivative formation and thermal decomposition of the dinitro product due to increasing temperature during the course of reaction [37, 38]. 

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