Effect of MeV protons on the phase behaviour and thermal stability of polytetrafluoroethylene

Thermomechanical spectroscopy analysis was used to study the influence of accelerated protons on the molecular-topological properties of polytetrafluoroethylene (PTFE). The study showed changes in a wide number of polymer parameters as a result of bombardment with 1, 2 and 4 MeV protons at fluences up to 2 × 10¹⁵ protons/cm². The basic topological process occurring under proton bombardment is amorphicity, as found for γ-irradiation of PTFE. The flow temperature of bombarded PTFE significantly decreases with increasing the fluxes and energy of the accelerated protons. The general process resulting from proton bombardment is cleavage of C-F bonds, leading to formation of “centered” radicals ～CF₂CF · CF₂～ and HF. The thermal stability of bombarded PTFE is below than that of virgin polymer. The rate of thermal destruction noticeably increases and the temperature of the initiation of effective thermal decomposition decreases after bombardment. The gaseous products generated during thermal destruction of the bombarded and virgin PTFE are similar.     

Gaseous products of the bombardment of a tetrafluoroethylene–hexafluoropropylene copolymer with accelerated MeV protons

The action of 1- to 4-MeV protons on a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP) in a vacuum is accompanied by the release of more than 25 gaseous products and a decrease in its thermal stability. During the course of proton bombardment, the predominant rupture of lateral C–CF₃ bonds with the release of CF₃ particles occurs along with the detachment of fluorine and hydrogen atoms yielding H₂ and HF. Unlike polytetrafluoroethylene, a distinctive feature of the radiolysis of FEP is a decrease by a factor of 5 in the probability of fluorine detachment from the FEP macromolecule by accelerated protons.     

The site of gas phase cation attachment. The protonation,methylation and ethylation of morpholine,thiomorpholine and 1,4-thioxane

The attachment of gaseous positive ions ([H]⁺, [CH₃]⁺ and [C₂H₅]⁺) to morpholine, thiomorpholine and 1,4-thioxane, through chemical ionization, has been studied by collision spectroscopy. The daughter ion spectra of the ion/molecule reaction products were compared to those of model ions, generated by fast-atom bombardment of corresponding quaternary ammonium salts, in order to determine the preferred site of reaction for the protonation and alkylation of these multifunctional nucleophilic compounds. For novel entities with no model precursors, the site of cation attachment was postulated on the basis of characteristic fragmentations and trends established by the study of other bifunctional heterocycles. The site of protonation followed predicted trends in proton affinity differences for the various heteroatoms (N>S>O), and the alkyl ion reactivities followed differences in electronegativity or nucleophilicity (S>N>O).     

Thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O: II. Identification of the gaseous products

The main goal of the presented work was to verify the previously assumed decomposition stages of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O (HACOT) [Thermochim. Acta 354 (2000) 45] under different atmospheres (inert, oxidising and reducing). The gaseous products of the decomposition were qualitatively and quantitatively analysed by mass spectrometry (MS) and Fourier-transformed infrared spectroscopy (FT-IR). It was confirmed that the gaseous products of HACOT decomposition under studied atmospheres there were H₂O (stage I) and NH₃, CO₂ (stage II). The main gaseous products in the third stage in argon and hydrogen (20 vol.% H₂/Ar) were CO and CO₂, whereas in air (20 vol.% O₂/Ar) only CO₂ was identified. Under the oxidising as well as reducing atmospheres the influence of secondary reactions on the composition of both, solid and gaseous products was found particularly strong during the third stage of the process. The studies of the multistage decomposition of HACOT, additionally complicated by many secondary reactions, required application of the hyphenated TA-MS or TA-FT-IR techniques combined with the pulse thermal analysis PTA^® allowing quantification of the spectroscopic signals and investigation of gas-solid and gas-gas reactions in situ.     

Heterogeneous reactions of gaseous methanesulfonic acid with NaCl and sea salt particles

Methanesulfonic acid (MSA) has been identified as one of the most important intermediate products of DMS reactions in the atmosphere. Although considerable amounts of MSA have been found in the marine boundary layer, little is known about the interaction of gaseous MSA with sea salt particles. To understand the fate of MSA in the atmosphere and its potential importance in atmospheric chemistry, the heterogeneous reactions of gaseous MSA with micron-scale NaCl and sea salt particles were studied using diffuse reflectance infrared Fourier transform spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. The CH₃SO₃Na and CH₃SO₃ ⁻ were the major products of the condensed phase of the reaction of gaseous MSA with NaCl and with sea salt particles. The steady-state uptake coefficient was determined to be (5.94±2.32)×10⁻⁷ (1 σ) for the reaction of gaseous MSA with NaCl particles and (2.23±1.25)×10⁻⁷ (1 σ) for the reaction of gaseous MSA with sea salt particles. The heterogeneous reaction of MSA with NaCl particles was found to be first-order for MSA. The reaction mechanisms were discussed. Supported by the National Natural Science Foundation of China (Grant No. 40490265) and the National Basic Research Priorities Program (Grant No. 2002CB410802)     

Tandem mass spectrometry of aminated fullerene derivatives

The products of the reaction between fullerenes (C₆₀/C₇₀) and dimethylamine were investigated by fast atom bombardment (FAB) mass spectrometry and tandem mass spectrometry (MS/MS). The FAB mass spectrum shows peaks corresponding to the addition of up to eight dimethylamine species, exclusively to C₇₀. MS/MS reveals an unusual fragmentation pattern. The mass spectrum of the reaction products, together with a number of tandem mass spectra, are shown.     

Kinetics and mechanism of degradation of Co(II)–<Emphasis Type="Italic">N</Emphasis>-benzyloxycarbonylglycinato complex

The kinetics of multi-step thermal degradation of Co(II) complex with N-benzyloxycarbonyl glycinato ligand [Co(N-Boc-gly)₂(H₂O)₄]·2H₂O, in non-isothermal conditions was studied using isoconversional and non-isoconversional methods. The degradation of complex occurs in three well-separated steps involving the loss of water molecules in first step followed by two degradation steps of dehydrated complex. The dependence of Arrhenius parameters on conversion degree showed that all observed steps of thermal degradation are very complex, involving more than one elementary step, as can be expected for most solid-state heterogeneous reactions with solid reactants and solid and gaseous products. It was shown that step 1, corresponding to the dehydration, involves a series of competitive dehydration steps of differently bound water molecules complicated by diffusion. Second step involves two parallel reactions related to the loss of two identical C₆H₅CH₂O– ligand fragments complicated by the presence of products in gaseous state. Further degradation in step 3 corresponds to complex process with a change in the limiting stage, in this case from the kinetic to the diffusion regime, connected with the presence of gaseous products diffusing through the solid product.     

整体式担载型Pt基催化剂上航空煤油的裂解:助剂SrO和BaO的影响

考察了整体式担载型Pt基催化剂上国产3号航空煤油(RP-3)的常压裂解反应,着重探讨了添加BaO和SrO助剂对裂解效果的影响,以及裂解时间对积炭量的影响.采用全自动吸附仪、程序升温还原、X射线光电子能谱以及X射线衍射和扫描电镜等方法对催化剂进行了表征.结果表明,在整体式担载型Pt基催化剂上RP-3裂解的总产气量比热裂解提高了39.7%;BaO或SrO助剂的添加又使其总产气量又分别提高了25.6%和37.0%;同时添加BaO和SrO的催化剂,其催化裂解总产气量则提高了96.5%.BaO和SrO助剂均可有效地抑制积炭的生成,而两者间的协同作用,进一步抑制了RP-3催化裂解过程中积炭的生成.     

The catalytic effect of NiO on thermal decomposition of nitrocellulose

The catalytic effect of NiO on thermal decomposition of nitrocellulose (NC) has been investigated via thermogravimetry–mass spectrometry (TG–MS) coupling technique, and the residue of NC with 20% NiO reacted in tubular furnace was analyzed by X-ray diffraction (XRD). TG–MS analysis showed that adding 2% NiO to NC accelerated the thermal decomposition process and promoted the generation of gaseous products. The catalytic mechanism was based on the accelerated generation of NO₂, which further reacted with the radical to produce other gaseous products. XRD analysis of catalyst residue showed that Ni was formed during the catalytic reaction.     

Conversion of hydrocarbon gases in dielectric barrier discharge in the presence of water

The conversion of C₁–C₄ hydrocarbons into gaseous and liquid products in a dielectric barrier discharge plasma in the presence of water has been studied. The formation of a deposit on the electrode surface is prevented by introducing water in the liquid state into a gaseous hydrocarbon stream, a finding that has been confirmed by IR spectroscopic study of the electrode surface. Hydrogen and C₂₊ hydrocarbons have been detected among the gaseous products of conversion, the liquid products being represented by C₆–C₁₀₊ alkanes. The total liquid products have amounted to 13.4, 26.0, or 36.6% for the methane, propane, or n-butane conversion, respectively. A 10% propane or butane admixture to methane increases the yield of the liquid products to make 22.0 and 31.7% for the methane–propane and the methane–butane mixture, respectively.     

Gas-phase reactions of free phenylium cations with C3H6 hydrocarbons

Free, unsolvated phenylium ions formed by the spontaneous β decay of a constituent atom of multitritiated benzene have been allowed to react with gaseous propene and cyclopropane in the pressure range from 10 to 700 torr. Phenylium ions attack efficiently both the C-H and the C-C bonds of cyclopropane, yielding respectively tritiated cyclopropylbenzene and indane as the major products. Selective attack of phenylium ions on the π bond of propene is suggested by the composition of tritiated products, isomeric phenylpropenes and isopropylbenzene. The different behavior of propene and cyclopropane toward gaseous phenylium ions is consistent with the results of related radiolytic investigations concerning gaseous systems at nearly atmospheric pressure. The reactivity pattern of the isomeric C₃H₆ hydrocarbons toward gaseous phenylium ions is discussed and compared with pertinent mass spectrometric data.     

Synthesis of carbon nanofibers by catalytic pyrolysis of ethylene in the presence of vapors of volatile components

Catalytic pyrolysis of ethylene was carried out at 700 °C in the presence of vapors of H₂O, EtOH, NH₄OH, PCl₃, (MeO)₃P, Me₂SO₄, (MeO)₃B, and HCl. The composition of solid pyrolysis products was studied using the elemental analysis, X-ray diffraction analysis, and electron microscopy. The composition of the gaseous pyrolysis products was studied using mass spectrometry. The processes in the gas phase were characterized, and the relationship between conditions of ethylene pyrolysis and the structure of formed carbon nanofibers was revealed. The introduction of gaseous additives has a substantial effect on the formation, growth, and structure of the carbon nanofibers formed.     

Monitoring of the Gas Phase Composition: A Prerequisite for Unravelling the Mechanism of Decomposition of Solids. Thermal decomposition of cobalt oxalate dihydrate

The complexity of the processes occurring during cobalt oxalate dihydrate (COD) decomposition indicates that an interpretation of the mechanism based only on the TG curve is of little value. Mass change alone does not allow deeper insight into all of the potential primary and secondary reactions that could occur. The observed mass changes (TG) and thermal effects (DTA/DSC) are a superposition of several phenomena and thus do not necessarily reflect COD decomposition alone. Investigation of the mechanism of decomposition requires the application of different simultaneous techniques that allow the qualitative and quantitative determination of the composition of the gaseous products. Composition of the solid and gaseous products of COD decomposition and heats of dehydration and oxalate decomposition were determined for inert, oxidizing and hydrogen-containing atmospheres. Contrary to previous suggestions about the mechanism of cobalt oxalate decomposition, the solid product formed during decomposition in helium contains not only metallic Co_met, but also a substantial amount of CoO (ca 13 mol%). In all atmospheres, the composition of the primary solid and gaseous products changes as a result of secondary gas-solid and gas-gas reactions, catalyzed by freshly formed Co_met. The course of the following reactions has been investigated under steady-state and transient conditions characteristic for COD decomposition: water gas shift, Fischer-Tropsch, CO disproportionation, CoO reduction by CO and H₂, Co_met oxidation under rich and lean oxygen conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

m-nitrobenzyl alcohol electrochemistry in fast atom bombardment mass spectrometry

The efficacy of m-nitrobenzyl alcohol (NBA) as a solvent (matrix) for fast atom bombardment (FAB) mass spectrometry of a group of pyrazolate-bridged dirhodium A-frame complexes has been assessed. Although NBA is frequently used to mitigate the formation of artifacts in FAB/MS of organometallics and other materials susceptible to bombardment-induced reactions, substantial evidence indicates that such reactions cause the formation of artifacts in the spectra obtained here. Parallel absorption spectroscopic studies have established that NBA is capable of inducing both oxidation and reduction reactions independent of ion bombardment, depending on analyte reduction half-wave potential (E_1/2). From the known electrochemistry of the complexes studied, it can be estimated that 1020 mV > E_1/2 > 500 mV for the reaction of NBA serving as a reducing agent, while 500 mV > E_1/2 > 424 mV for the reduction potential of NBA. However, in the presence of bombardment the former E_1/2 must be at least as low as 356 mY, and the latter E_1/2 must be at least as high as 1188 mY. The kinetics of redox reactions involving NBA, and therefore their influence on the appearance of FAB mass spectra, will be highly sample-dependent. However, this study illustrates an important potential role for redox reactions when NBA is used as a solvent, especially in the presence of bombardment in FAB/MS. Although analyte reaction products could be identified, substantial efforts aimed at identifying NBA oxidation and reduction products did not yield any definitive results due to the complexity of product mixtures.     

Identification of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) pyrolysis products by simultaneous thermogravimetric modulated beam mass spectrometry and time-of-flight velocity-spectra measurements

The pyrolysis products formed during the isothermal decomposition of HMX at 211°C are H₂O, HCN, CO, CH₂O, NO, N₂O, methylformamide, C₂H₆N₂O, octahydro-1-nitroso-3,5,7-trinitro-1,3,5,7-tetrazocine, and a nonvolatile residue. The temporal behaviors of these products during the decomposition are presented. The method for using time-of-flight (TOF) velocity spectra to assist mass-spectrometry measurements in identifying the different gaseous products formed from the pyrolysis of a material by determining the approximate molecular weights of the different gaseous products contributing to the different m/z values in the mass spectrum of the mixture is described. The ion fragmentation of HMX as a function of electron energy shows complete fragmentation of the HMX molecular ion for electron energies ≥ 12.4 eV. No fragments from the pyrolysis of HMX other than those mentioned above are observed.     

STUDY ON THE GASEOUS PRODUCTS OF HIGH TEMPERATURE PYROLYSIS OF ACRYLONITRILE POLYMERS BY ON-LINE FTIR METHOD

The gaseous products of high temperature pyrolysis (300℃ to 960℃) of aerylonitrile polymers were measured continuously under nitrogen atmosphere by on-line Fourier Transform Infrared Spectroscopic method (FTIR). From the variations of characteristic peaks it was found that the nitrogen of macromolecules evolved were mainly in the form of hydrogen cyanide and ammonia. During the pyrolysis amorphous carbonaceous element was formed, and crosslinked to form network structure. Three kinds of samples were used for comparison. The experimental results show that the gaseous products of volatile small molecules were HCN, NH_3, CH_4, C_2H_6 and cyanide. CO and CO_2 were also formed when copolymers of PAN were thermally pyrolyzed.     

Study of the thermal decomposition of flame-retarded unsaturated polyester resins by thermogravimetric analysis and Py-GC/MS

The thermal degradation behaviours of flame-retarded unsaturated polyester resin formulations containing ammonium polyphosphate (APP), Cloisite 25A nanoclay and zinc based smoke suppressants have been studied using thermogravimetric analysis (TGA) combined with infrared analysis of the evolved gases (EGA) and pyrolysis/gas chromatography-mass spectrometry (GC/MS). In TGA-EGA experiments, the mass loss as a function of temperature has been correlated with the evolution of carbon monoxide (CO) and carbon dioxide (CO₂) and oxygen (O₂) consumption as measured by an oxygen analyser. The effect of APP, Cloisite 25A and the smoke suppressants on the evolution of CO and CO₂ has been examined. The decomposition behaviour of flame-retarded polyester resins under isothermal pyrolytic conditions was investigated and the evolved gaseous products were collected and qualitatively and semi-quantitatively analysed via GC/MS. The addition of APP does not yield many new gaseous products relative to the unmodified polyester resin neither does the presence of zinc borate (ZB) and zinc stannate (ZS) together with APP. Possible chemical interactions are discussed in an attempt to explain the observed results.     

Thermal behavior of the highly luminescent poly(3-hydroxybutyrate):Eu(tta)3(H2O)2 red-emissive complex

The aim of this study has been to gain a fundamental understanding of the mechanisms governing thermal degradation of luminescent poly(3-hydroxybutyrate) (PHB). PHB was doped with diaquatris(thenoyltrifluoroacetonate) europium(III) complex, [Eu(tta)₃(H₂O)₂], and different luminescent systems were obtained. The thermal-stability of the luminescent films was discussed and the products of decomposition were analyzed. Thermal degradation of PHB:Eu(tta)₃ x % systems (x = 0, 1, 5, 10, and 15 %) was elucidated by means of thermogravimetric analysis (TG), the thermal-stability decreases with the increase of europium complex concentration. The PHB polymer decomposed with evolution of carbon dioxide and 2-butenoic acid molecules. The TG–FTIR results, of the gaseous degradation products of PHB in nitrogen atmosphere, indicated that the polymer is stable at temperatures up to 200 °C. Polymer matrix at concentrations above 5 % decomposed with evolution of water molecules among the other gaseous products, which implied the presence of a hydrated complex in the system. The luminescent films showed more flexibility due to a loss in crystallinity, which suggested a potential usefulness in technical applications.     

Kinetic formation of CO,CO2, H2, and light hydrocarbon gases from cellulose pyrolysis

The formation of gaseous products has been examined for cellulose over the temperature range of 360–595°C. The evolution of CO, CO₂, H₂, CH₄, C₂H₄, and C₂H₆ was determined as a function of time. The overall kinetic rate constants for decomposition were determined from the formation rates for each gas, as well as the rate constants for the formation of each specific gas. It has been verified that CO and CO₂ are both primary products of decomposition, and further emanate from the same kinetic pathway. By increasing the residence time of the reactor, the production of all gaseous products, including both CO and CO₂, further increased, indicating production by a secondary reaction mechanism. None of the gaseous products, save CO and CO₂, were detected in measurable quantities except at temperatures above which transport limitations had affected the measurement of the kinetic rates.     

Synthesis of HCN Polymer from Thermal Decomposition of Formamide

Prolonged heating of formamide (HCONH₂) at 185°C or 220°C produces a black insoluble product. The FT-IR spectroscopy and the X-ray photoelectron spectroscopy (XPS) suggest that the product has the chemical structure of a polymer of hydrocyanic acid: (HCN)_x. The pyrolysis of (HCN)_x prepared from formamide produces a large amount of gaseous HCN in a wide range of temperatures together with ammonia (NH₃) and isocyanic acid (H─N─C═O).

During the thermal decomposition of formamide to produce (HCN)_x, the volatile products evolved were monitored with gas phase infrared spectroscopy. At 185°C, the gaseous product released were CO₂, CO and NH₃ while at 220°C, also HCN was detected. In both cases, a white sublimate was collected in the upper part of the reaction vessel. It consists of ammonium carbamate and its hydrolysis products ammonium carbonate and hydrogen carbonate. It is therefore possible to synthesize the polymer of hydrocyanic acid (HCN)_x starting from formamide avoiding to handle the dangerous hydrocyanic acid.