Theory of Emanation Thermal Analysis IX. Inert gas release during thermal decomposition of solids

In the Emanation Thermal Analysis the release of inert gas atoms previously incorporated in the sample is measured. Results of the statistical modelling of the inert gas release during thermal decomposition of solids are presented. The updated model supposing three components in the solid-state reaction system including the formation of an intermediate metastable component on the surface of the newly formed component was proposed for the modelling of the ETA curves. The release of inert gas atoms previously incorporated into the sample is used as a probe of microstructure changes. The random nucleation mechanism was considered in the modelling. The model can be used in modelling ETA curves of solid-solid, solid-gas and solid-liquid interactions where the existence of metastable intermediate component is supposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pyrolysis of rapidly growing grass biomass under isothermal conditions

The pyrolysis of rapidly growing grass biomass in an inert atmosphere was studied by thermogravimetric analysis using sorghum as an example. Pyrolysis was performed under isothermal conditions at temperatures from 250 to 400°C. To describe the reaction kinetics, a single-component model including six first-order reactions was proposed. A special feature of this model is the occurrence of a step of the formation of an intermediate carbonaceous substance from the volatile products of biomass decomposition.     

The role of molecular diffusion in the adhesion of elastomers

Butyl rubber (polyisobutylene-co-isoprene) mixed with polyisobutylene was crosslinked to yield elastomeric macromolecular networks containing dissolved linear macromolecules. Adhesion of these materials to themselves (self-adhesion) and to an inert substrate was investigated over a wide range of peel rates and test temperatures. Greatly enhanced self-adhesion was found when linear polyisobutylene molecules of high molecular weight were present, but the strength of adhesion to a rigid inert substrate was hardly affected. The enhancement of self-adhesion is attributed to interdiffusion of polyisobutylene molecules. It was greatest at intermediate peel rates and temperatures, becoming insignificant at extremely low rates, probably because the diffusing species can then migrate readily, and at high effective rates of peel when the polymer approaches the glassy state and the strength of adhesion is high in all cases. A transition to somewhat lower levels of adhesion at relatively high rates of peel is tentatively ascribed to the onset of molecular fracture in place of pullout. The presence of large amounts of low-molecular-weight polyisobutylene (M?_v = 50,000 g/mol) increased the level of self-adhesion and of adhesion to an inert substrate to a similar degree, over a broad range of peel rates. This effect is attributed primarily to enhanced viscous losses in the elastomeric layer during separation. Application of these results to crack and weld-line healing in glassy plastics is discussed.     

Sodium halide clusters: evidence for direct electronic fragmentation

Sodium halide clusters are generated by inert gas condensation and probed by electron and photon induced dissociation. The dependence of fragmentation on electron energy and initial cluster temperature indicates a direct electronic fragmentation process without an intermediate state of vibrationally hot clusters.     

Complex Surface Chemistry of an Otherwise Inert Solvent Molecule: Tetrahydrofuran on Si(001)

The reaction of tetrahydrofuran (THF), an otherwise inert solvent molecule, on Si(001) was experimentally studied in ultra‐high vacuum. Using scanning tunneling microscopy (STM) and photoelectron spectroscopy at variable temperature, we could both isolate a datively bound intermediate state of THF on Si(001), as well as the final configuration that bridges two dimer rows of the Si(001) surface after ether cleavage. The latter configuration implies splitting of the O?C bond, which is typically kinetically suppressed. THF thus exhibits a hitherto unknown reactivity on Si(001).     

A non-linear equilibrium analysis of blowdown policy in pressure—swing—adsorption separation

Using the local non-linear equilibrium approach, we investigated pressure—swing—adsorption (PSA) cycles directed toward the removal of an adsorbable impurity present in large amounts in an inert substance. Three blowdown policies are compared (the blowdown is the part of the PSA cycle in which the pressure of a column is released by rejecting gas). In one such policy, the gas resulting from blowdown is rich in the impurity and is rejected as waste. In a second policy in contrast, the production is adjusted so that the blowdown gas is pure and is considered as a product or is reused to recompress or purge another column. The third policy is intermediate, in the sense that part of the blowdown gas is pure and recovered, and part is impure and rejected.The equilibrium approach presented neglects mass-transfer and dispersion effects, but accounts for non-linear equilibria and variations in gas velocity. It thus allows analytical or semi-analytical expressions to be obtained for quantities such as the inert recovery ratio, and hence an easy qualitative discussion of the effects of operating parameters on the recovery. It is shown that the intermediate policy (partial recovery of the blowdown gas) is optimal. The adsorption of methane and ethane on activated carbon from helium or hydrogen are presented as illustrations.     

The fluoro analogue of Wilkinson's catalyst and unexpected Ph-Cl activation

The fluoro analogue of Wilkinson's catalyst, [(Ph3P)3RhF] (1), was synthesized and fully characterized. Both solution behavior and solid-state geometry parameters of 1 were found to be surprisingly similar to those of Wilkinson's catalyst. Unlike Wilkinson's catalyst however, 1 exhibited most unusual reactivity toward the notoriously inert C-Cl bond of nonactivated chloroarenes. The novel Ph-Cl activation with 1 includes fluorine transfer from the metal to a phosphine ligand and evidently phenyl transfer from the phosphine to Rh to produce an electron-rich sigma-phenylrhodium intermediate.     

Synthesis of 10-aminophenothiazines and derivatives

In this paper it is shown that 2-nitro-2′-(β-acetyl) hydrazinodiphenyl sulfides cyclize, via a Smiles rearrangement, to 10-acetylaminophenothiazines, which are inert to alkalis and suffer a strong decomposition by acids. 10-Aminophenothiazine has been obtained by ring closure of 2-bromo-2′-hydrazinodiphenyl sulfide via an assumed benzyne intermediate.     

Formation Mechanism of Polyaniline: Evidence from the Post-Reactions of Isolated Intermediates

The formation mechanism of Polyaniline was derived from the post reactions of the polymerization intermediate. The intermediate, RPAN, (3000 Å thickness film, purplish-blue in color) was isolated on silane modified substrates after polymerization for 10 minutes. Under air, RPAN converts to emeraldine salt within a couple of seconds. In the inert atmosphere, the conversion occurred at a relatively low speed. In acidic media, the intermediate was believed to be a very reactive radical cation, which oxidized then coupled with aniline oligomers to start the auto-catalytic chain growing process. When the radical cation was quenched in water or acid, a violet species, IPAN, with a structure composed mostly of pernigraniline units, was formed. IPAN reacts slowly with aniline oligomers in the presence of protons and oxidants to emeraldine. The conversion processes were monitored by IR and Uv/Vis/NIR spectroscopy.     

Cyclopolymerization of (E,E) - [6.2]paracyclophane-1,5-diene

Polymerization of (E,E)-[6.2]paracyclophane-1,5-diene proceeds by an intra–intermolecular mechanism to give a polymer containing a [3.2]paracyclophane in the repeat unit. Polymerization occurs with either free radical or cationic initiation; anionic initiation was unsuccessful. Cationic polymerization is favored and appears to proceed through a stabilized carbonium ion intermediate. Spectroscopic and model compound studies are consistent with the proposed polymer structure. Thermal analyses of the polymer indicate a complex thermooxidative behavior in the presence of oxygen, while depolymerization occurs above about 400°C in an inert atmosphere.     

On the solid state reactions in the system MnSiN

The reaction processes involving the formation and decomposition of manganese silicon nitride MnSiN₂ have been investigated. Thermochemical analysis in nitriding, inert and oxidizing atmospheres was carried out for this nitride and the appearing intermediate phases. The investigation was performed using TG, DTA and DTG techniques in the temperature range 25–1500°C.     

A pyrolysis/gas chromatography—mass spectrometry and thermogravimetry/differential thermal analysis study of bis(diethyldithiocarbamato)diphenyl tin (IV)

The P/GC—MS and TG/DTA analysis, in an inert atmosphere, of bis(diethyldithiocarbamato)diphenyl tin (IV) indicates that the thermal decomposition proceeds in two consecutive stages. Loss of the dithiocarbamate ligands and the phenyl groups occurs within the temperature range of 210–380°C leaving tin (II) sulphide as residue. The stability of the phenyl radical as a reactive intermediate, together with the unidentate bonding of the dithiocarbamate ligand, dramatically influence the major mode of thermal decomposition.     

Rearrangements in the haloalkoxy(mercapto,amino)-sym-triazine series

It is shown by means of an O¹⁸ label that the thermolysis of 2-methoxy-4-(2-chloroethoxy)-6-dialkylamino-sym-triazines to give oxazolo-sym-triazines in an inert medium proceeds without the formation of intermediate N-2-chloroethyl derivatives. In contrast to this, the thermolysis of 2-ethoxy(propoxy)-4-(2-chloroethoxy) derivatives gives N-2-chloroethyl derivatives, which upon prolonged heating are converted to oxazolo-sym-triazines. Triazinium salts are formed when both 2-chloroethoxy and N-2-chloroethyl derivatives are heated in water. The triazinium salts undergo rearrangement to N-2-chloroethyl derivatives when the water is removed. On the basis of the data obtained it is assumed that the thermolysis of 2-chloroethoxy-sym-triazines in an inert medium proceeds via a concerted mechanism, whereas thermolysis proceeds via an ionic mechanism in water. Data from the UV, IR, and PMR spectra are presented.See [1] for communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 124–127, January, 1979.     

CO oxidation over the Pt-Rh system. 2. Reaction on an alloy

The oxidation of CO over thin films of a Pt-Rh alloy prepared by sequential vacuum evaporation of the metals on an inert support has been investigated at low pressures (P < 2'10^-5 mbar). The results are compared with the data on the individual surfaces of Pt and Rh. It is found that the activity of the alloy is intermediate between the activities of the individual metals. The effect of alloy formation on the catalytic activity in CO oxidation is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetics of chemical ionization in shock waves: III. Inert diluent gas effect on the chemical ionization rate

An experimental study of ionization in hydrogen azide decomposition and methane oxidation in shock waves is reported. In both cases, the kinetics of chemical ionization changes significantly upon the replacement of argon with helium as the inert diluent gas. The diluent effect is explained in terms of the hypothesis that the reactions responsible for chemical ionization proceed via the formation of an excited intermediate complex. Calculations using kinetic schemes of the ionization processes are carried out.     

Studies on lanthanoid sulfites: Part VI. Thermogravimetric study of scandium sulfite pentahydrate

Scandium sulfite was found to crystallize as a pentahydrate both at 25 and 90 °C when precipitated by the action of sulfur dioxide on aqueous suspensions of Sc(OH)₃. Thermogravimetric analysis showed that the anhydrous sulfite is formed by 200 °C but it starts to decompose immediately after its formation. The decomposition leads to an intermediate phase which is stable up to 700 °C in inert (nitrogen) and air atmospheres but decomposes earlier in reductive (hydrogen) environment. The weight remaining, which corresponds to the intermediate level, varies between 58 and 43 %, depending on experimental conditions and thus cannot be assigned to a single compound such as Sc₂O₂SO₄ or Sc₂O₂SO₃. The intermediate phase is amorphous to X-rays but IR spectra indicate the presence of both sulfite and sulfate ions pointing to a mixture. In all atmospheres studied the final decomposition step is the formation of scandium sesquioxide.     

Use of a membrane reactor to improve selectivity to intermediate products in consecutive catalytic reactions

Through modeling it has been shown that a concentric-tube catalytic membrane reactor can be used to increase the selectivity for the intermediate products of a consecutive reaction scheme. The reactants are fed to the tube-side of the reactor where the catalyst is also located. The wall of the tube is permeable, allowing the intermediate products to pass through to the annular space instead of undergoing further reaction. The annular space is swept by an inert gas flow and contains no catalyst. Both permselective and non-permselective membranes have been considered in both co-current and counter-current flow regimes. In contrast to most catalytic membrane reactor applications where reactions are reversible and thermodynamically limited, in the present study the reactions considered are irreversible and are under kinetic control.     

Acid-catalyzed rearrangement of 1-benzyl-2-methyl-3-piperidone to 1-benzyl-2-acetylpyrrolidine

We report that 1-benzyl-2-methyl-3-piperidone, conveniently prepared from 3-hydroxy-2-methylpyridine, undergoes rearrangement to 1-benzyl-2-acetylpyrrolidine in aqueous 6 N HCl at reflux. Studies showing that the 2,2-dimethyl analog is inert under the same conditions support a mechanism of reversible tautomeric equilibria via ring-opened intermediates, one of which was independently synthesized and shown to be a kinetically competent intermediate to product.     

Computer study of the hydrogen atom recombination reaction under high pressure conditions

The hydrogen-atom recombination reaction has been simulated using a molecular dynamics technique recently formulated by the authors [1]. The rate of recombination has been calculated over a range of temperatures and inert gas concentrations (He and Ar) and agrees well with available experimental data. The calculations reproduce the negative activation energy characteristic of an atom recombination process. Over the range of conditions studied recombination was found to proceed via the energy transfer mechanism only, no evidence of bound HAr or HHe species was observed. Recombination was found to occur through an intermediate metastable diatomic molecule which is in equilibrium with its environment and from which there is a bottleneck to the formation of a stable molecule. The initial formation of a metastable species is sensitive to the hydrogen-inert gas potential, but relaxation of the total energy is primary determined by the mass of the third-body and the collision frequency.     

Investigation of thermal properties of double complex salts [M(NH3)5Br][AuBr4]2·nH2O, M?=?Rh, Ir

Novel double complex salts [M(NH₃)₅Br][AuBr₄]₂·nH₂O, M?=?Rh, Ir, have been synthesized and examined. The processes of thermal decomposition of the compounds in inert and reductive atmospheres have been studied and intermediate products identified. Simultaneous thermal analysis with parallel mass-spectrometric analysis of evolved gases (STA-EGA) has been employed for identification of main gaseous products of thermolysis in inert atmosphere. It has been revealed that the final products of decomposition in inert or reductive atmospheres are fine powders of gold and the corresponding platinum metal with sizes of crystallites 4?C40?nm. The possibility of preparation of the metastable solid solution Au_0.05Ir_0.95 on thermolysis of [Ir(NH₃)₅Br][AuBr₄]₂·H₂O in inert atmosphere has been demonstrated.