Thermal decomposition reactions

The thermal decomposition reactions of several other layer-lattice clay minerals have also been studied by Al NMR in conjunction with other nuclides. These include a montmorillonite which contained sufficient iron for a complementary study to also be made by Mossbauer spectroscopy (Brown et al. 1987), Fuller s Earth (another 

Aluminium titanate (tielite, Al2Ti05) has excellent thermal shock resistance but poor mechanical strength which can, however, be improved by reinforcing with whiskers of a related phase such as potassium hollandite (K2Al2Ti60i6). Such composites can be formed by thermal decomposition of sol-gel precursors, reaction sintering of the two phases or by thermal treatment of an appropriate glass-ceramic material. Al MS NMR has been used to study the co-formation of these two phases during thermal treatment, and indicates that hollandite crystallises as whiskers within the tielite matrix (Kohn and Jansen 1998). 

Portland cement and high-alumina cements contain, in addition to calcium silicate phases, calcium monoaluminate, CaAl204 (or CA in cement chemist s shorthand, where C = CaO and A = AI2O3). The Al NMR spectra of this compound, in which the Al is exclusively in tetrahedral coordination, and a number of other calcium alu-minates have been determined (Muller et al. 1986), and more recently, using satellite transition spectroscopy (SATRAS) which has allowed the multiple tetrahedral sites in the various calcium aluminates to be distinguished (Skibsted et al. 1993). The NMR parameters for the synthetic aluminates and a number of their hydration products are shown in Table 5.4. 

Cements often contain small amounts of heavy metals carried over from the raw materials from which they are produced. The location of these impurities in the hydrated cement phases may affect their subsequent teachability, and is therefore of environmental interest. A detailed analysis of the Al NMR sideband structure of C3A hydrated in the presence of chromium and zinc ions has proved useful in determining the way in which these species enter into the structure of the hydration products of C3A (Moulin et al. 2000). 

NMR spectrum of Al guest ions in CasSiOs with (inset) the expanded central transition for the Af resonance. The asterisk marks the Af resonance corresponding to a total Al intensity of 3%. From Skibsted et al. (1994), by permission of the Royal Society of Chemistry. 

The equilibrium constant for an organic reaction in the gas phase can be determined directly for a few favourable reactions but it can be calculated if sufficient thermodynamic data on all the reactants and products are available. If the standard enthalpy and entropy of each substance taking part in the reaction are known, then the equilibrium constant for the reaction may be calculated  

Standard entropies at 298.15 K are evaluated from measurements of heat capacities at constant pressure and enthalpies of phase changes from low temperatures to 298.15 K, assuming the third law of thermodynamics is applicable to the substance. The entropy at 298.15 K is given by an expression such as 

The entropy of the compound in the ideal gas state at 298.15 K and the standard pressure (101.325 kPa) is calculated from the entropy at 298.15 K of the condensed phase, the enthalpy of vaporization at 298.15 K, and vapour pressure and gas imperfection data, using the equation  

In practice, heat capacity measurements are usually made from about 10 K. Values of C, below the lowest temperature of the measurements are obtained by extrapolation. For organic compounds with melting temperatures below the highest temperature of the Cj, measurements, values for the enthalpy and entropy of fusion are obtained in the course of the measurements and it is usual to calculate the equilibrium temperature (Tm) in the 

As indicated above, many organic compounds exist in more than one crystalline form and the transition between crystalline forms is frequently manifested by an anomaly in the heat capacity. The enthalpy and entropy of the transition are obtained from measurements in the transition region. The experimental apparatus for low-temperature heat capacity measurements is often usable for measurements up to about 400 K. Heat capacities of organic compounds above 298 K are required for chemical engineering computations, e.g. for calculations using Kirchhoff s equation, of enthalpies of formation and reaction at temperatures other than those at which the thermodynamic data are available. 

Chapter 7 Powder Syntiiesis with Gas Phase Reactants 

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Solutions of these fire retardant formulations are impregnated into wood under fliU cell pressure treatment to obtain dry chemical retentions of 65 to 95 kg/m this type of treatment greatly reduces flame-spread and afterglow. These effects are the result of changed thermal decomposition reactions that favor production of carbon dioxide and water (vapor) as opposed to more flammable components (55). Char oxidation (glowing or smoldering) is also inhibited. 

An extension ot this reaction provides a number of other perfluorovinylic halides [54] The type of reaction products from the thermal decomposition reaction and the type of hydrocarbon Grignard reagent used in the exchange reaction are solvent-dependent When an excess ot phenylmagnesium bromide is used, a variety of phenylated products are formed depending on the excess amount used [4S (equation 23)... 

An intensely colored by-product of the photolysis reaction of methyl-2-azidobenzoate has been identified as the first known derivative of 3,3 -diazaheptafulvalene 70 (94LA1165). Its molecular mass was established by elemental analysis and mass spectroscopy as that of a formal nitrene dimer, whereas and NMR studies demonstrated the twofold symmetry as well as the existence of a cross-conjugated 14 7r-electron system in 70. Involving l-azido-2,3-dimethoxy-5,6-dimethoxycarbonylbenzene in thermal decomposition reactions, the azaheptafulvalene 71 could be isolated and characterized spectroscopically and by means of X-ray diffraction. Tliis unusual fulvalene can be regarded as a vinylogous derivative of azafulvalenes (96JHC1333) (Scheme 28). 

In addition to the evolution of water, the ignition of precipitates often results in thermal decomposition reactions involving the dissociation of salts into acidic and basic components, e.g. the decomposition of carbonates and sulphates the decomposition temperatures will obviously be related to the thermal stabilities. 

The thermal decomposition of a solid, which necessarily (on the above definition) incorporates a chemical step, is sometimes associated with the physical transformations to which passing reference was made above melting, sublimation, and recrystallization. Aspects of the relationships between physical transitions and decomposition reactions of solids are discussed in a book by Budnikov and Ginstling [1]. Since, in general, phase changes exert significant influence upon concurrent or subsequent chemical processes, it is appropriate to preface the main survey of the latter phenomena with a brief account of those features of melting, sublimation, and recrystallization which are relevant to the consideration of thermal decomposition reactions. 

The thermal decomposition reactions of KN3, T1N3, and AgN3 have been studied in the corresponding halide matrices [301]. The formation of NCCT from trapped C02 was described and labelling with ISN established that only a single end-N atom of the azide ion was involved in NCO formation. The photodecomposition of PbN6 and the effects of dopants have been followed [302] by the changes produced in the near and the far infrared. 

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 ... 

Many of the early workers who studied the thermal decomposition reactions of diazocarbonyl compounds found that the addition of copper metal or copper salts allowed the reaction to be achieved at a lower temperature,<63AG(E)565, 64CB2628, 73JOU431> although no detailed study of this catalytic effect was undertaken. Alonso and Jano studied the copper-salt reaction of ethyl diazopyruvate 26 with acetonitrile and benzonitrile. The... 

Investigations on the thermal decomposition of 32 revealed the continuous loss of CO with concomitant formation of the di- and tetranuelear Tc(I) clusters [TcX(CO)4]2 (62) and [TcX(CO)3]4 (63) respectively. The latter is assumed to have cubane structure comparable to [Tc(OHXCO)3]4 [76,77,78]. The thermal decomposition reactions are depicted in Scheme 13. 

The thermal decomposition of iron complexes leading to the formation of different ferrites (MFe204, M = Fe, Co, Mn, etc.) is one of the most commonly used protocols to obtain magnetic NPs with control of size and shape [39]. However, some of them cannot be considered as green processes since the iron precursor, the Fe(CO)5 complex, is expensive, toxic, and flammable. Therefore, researchers have looked for non-toxic and less expensive iron precursors to be used in the thermal decomposition reactions. The first precursor in substitution of Fe(CO)5 was the FeCup3... 

A thermal decomposition reaction is a reaction that is activated by heat or high temperatures and that generates simpler (i.e., containing fewer atoms and thus characterized by lower molecular weights) substances from a single complex substance. The overall balanced equation for the thermal decomposition of sodium bicarbonate reveals the simpler substances produced ... 

Calcium oxide can be produced from extensive heating of limestone. Primarily composed of calcium carbonate, limestone is extracted from both underground and surface mines and heated to temperatures exceeding 180°F to convert the calcium carbonate into calcium oxide. This thermal decomposition reaction also generates carbon dioxide gas. 

The mechanism of thermal decomposition (pyrolysis) of methane has been extensively studied [90,91]. Because C-H bonds in the methane molecule are significantly stronger than C-H and C-C bonds of the products, the secondary and tertiary reactions contribute at the very early stages of the reaction, which obscure the initial processes. According to Holmen et al. [92], the overall methane thermal decomposition reaction at high temperatures can be described as a stepwise dehydrogenation as follows ... 

The metal and ammonium salts of dithiophosphinic acids tend to exhibit far greater stability with respect to this thermal decomposition reaction, and consequently these acids are often prepared directly in their salt form for convenience and ease of handling. Alkali-metal dithiophosphinates are accessible from the reaction of diphosphine disulfides with alkali-metal sulfides (Equation 22) or from the reaction of alkali-metal diorganophosphides with two equivalents of elemental sulfur (Equation 23). Alternatively, they can be prepared directly from the parent dithiophosphinic acid on treatment with an alkali-metal hydroxide or alkali-metal organo reagent. Reaction of secondary phosphines with elemental sulfur in dilute ammonia solution gives the dithiophosphinic acid ammonium salts (Equation 24). 

Solvolysis studies - Aa11 reactivity 60 Nucleophilic substitution reactions - SN2 reactivity 70 Thermal decomposition reactions 90... 

The formation of anhydrides 101 in the thermal decomposition reactions of TV-acyloxy-TV-alkoxyamides in non-polar mesitylene (Scheme 21, pathway (ii)) can thus be attributed to HERON migration of acyloxyl groups. However, the similarity of Eas for the two isomeric transition states raises the possibility that in these reactions some, or all of the ester might be generated by HERON migration of the alkoxyl substituent (Scheme 21, pathway (iii)). 

Thermal decomposition reactions, of IV-acyloxy-lV-alkoxyamides, 90-96 free radical decomposition, 91-93 HERON reactions, 93-96 Thiazine dyes, 233... 

Decomposition reactions are reactions in which a compound breaks down into two or more simpler substances. Although not all decomposition reactions are redox reactions, many are. For example, the thermal decomposition reactions, such as the common laboratory experiment of generating oxygen by heating potassium chlorate, are decomposition reactions ... 

The result obtained for Af//°[Cr(CO)6, cr)] is some 50 kJ mol-1 more positive than the recommended value, -980.0 2.0 kJ mol-1 [149], a weighted mean of experimental results determined with several types of calorimeter. The large discrepancy is not due to an ill-assigned thermal decomposition reaction but to a slow adsorption of carbon monoxide by the chromium mirror that covered the vessel wall. This is an exothermic process and lowered the measured Ar//°(9.13). 

The reaction of (1.16) follows reverse path to the thermal decomposition reaction of (1.13) and proceeds at room temperature and only slight overpressure of hydrogen supply. This presents a new mechanical activation route to manufacturing of nanomaterials for hydrogen storage. 

An ab initio RHF/3-21 G study has shown that the decomposition of 3-hydroxy-3-methylbutan-2-one is a concerted process with hydrogen transfer and bond breaking via a five-membered cyclic transition state.AMI and PM3 methods using UHF calculations were applied to study the thermolysis of 2-cyanofuroxan. The reaction proceeds via a two-step pathway in which the second step is rate determining. The effect of solvent in the thermal decomposition reaction of fran -3,3-dimethyl-5,6-tetramethylene-l,2,4-trioxacyclohexane was studied. ... 

Thermal Decomposition, Reaction with Oxygen, Reducing Properties... 

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