Showing papers on "Thermal decomposition published in 1999"
TL;DR: Kinetic control of crystal growth in the presence of a coordinating ligand is critical for the formation of a new structure of elemental cobalt (ε-cobalt, the unit cell with the two different types of cobalt atoms is shown), which was discovered upon analyzing the metallic powder produced by the thermal decomposition of [Co2 (CO)8 ] in solution in the absence of trioctylphosphane oxide.
Abstract: Kinetic control of crystal growth in the presence of a coordinating ligand is critical for the formation of a new structure of elemental cobalt (e-cobalt, the unit cell with the two different types of cobalt atoms is shown), which was discovered upon analyzing the metallic powder produced by the thermal decomposition of [Co2 (CO)8 ] in solution in the presence of trioctylphosphane oxide [TOPO, Eq. (1)].
482 citations
TL;DR: In this article, the authors investigated the thermal stability of prismatic Li-ion cells and their components and concluded that the heat generation from the decomposition of PE material and reaction of that with electrolyte initiates thermal runaway in a Li−ion cell, under thermally or abusive conditions.
Abstract: Thermal stability of fully charged 550 mAh prismatic Li‐ion cells (Sn‐doped carbon) and their components are investigated. Accelerating rate calorimetry (ARC) is used to determine the onset temperature of exothermic chemical reactions that force the cell into thermal runaway. Differential scanning calorimetry (DSC) and thermogravimetry analysis are used to determine the thermal stability of the cell's positive electrode (PE) and negative electrode (NE) materials from 35 to 400°C. The cell self‐heating exothermic reactions start at 123°C, and thermal runaway occurs near 167°C. The total exothermic heat generation of the NE and PE materials are 697 and 407 J/g, respectively. Heat generations of the NE and PE materials, washed in diethyl carbonate (DEC) and dried at ≈65°C under vacuum, are significantly lower than unwashed samples. Lithium plating increases the heat generation of the NE material at temperatures near the lithium melting point. Comparison of the heat generation profiles from DSC and ARC tests indicates that thermal runaway of this cell is close to the decomposition temperature range of the unwashed PE material. We conclude that the heat generation from the decomposition of PE material and reaction of that with electrolyte initiates thermal runaway in a Li‐ion cell, under thermally or abusive conditions. © 1999 The Electrochemical Society. All rights reserved.
374 citations
Book•
01 Jan 1999
TL;DR: The thermal decomposition of selected Ionic solids has been studied extensively in the literature as mentioned in this paper, with a focus on the role of temperature on reaction rate and its influence on reaction performance.
Abstract: Part A: Theory and Background. 1. Introduction. 2. Stoichiometry and extent of decomposition. 3. Kinetic models for solid-state reactions. 4. The influence of temperature on reaction rate. 5. Analysis and interpretation of experimental kinetic measurements. 6. Characterization of reactants, decomposition intermediates and products, and the formulations of mechanisms. Part B: Thermal Decompositions of Selected Ionic Solids. 7. Thermal hydration of hydrated salts. 8. Thermal dehydration of hydroxides. 9. The thermal dissociation of oxides. 10 Decomposition of other binary compounds. 11. Decomposition of azides. 12. Decomposition of carbonates. 13. Decomposition of metal perhalates, halates and halites. 14. Decomposition of metal salts of various oxyacids. 15. Decomposition of ammonium salts. 16. The thermal decompositions of metal salts of organic acids. 17. Decompositions of coordination compounds. 18. The present position and prospects for future progress in studies of thermal decompositions of solids. Glossary. Index.
360 citations
TL;DR: An overview of the literature together with selected authors' data on thermal and thermo-oxidative decomposition of commercial aliphatic nylons (nylon 6, nylon 7, nylon 11, nylon 12, nylon 6.6, nylon 8.10, nylon 9.12) is presented in this paper.
Abstract: An overview of the literature together with selected authors' data on thermal and thermo-oxidative decomposition of commercial aliphatic nylons (nylon 6, nylon 7, nylon 11, nylon 12, nylon 6.6, nylon 6.10, nylon 6.12) is presented. Despite the high level of research activity and the large number of publications in the field, there is no generally accepted mechanism for the thermal decomposition of aliphatic nylons. Polylactams (nylon 6, nylon 11 and nylon 12) tend to re-equilibrate to monomeric or oligomeric cyclic products. Diacid–diamine type nylons (nylon 6.6, nylon 6.10 and nylon 6.12) produce mostly linear or cyclic oligomeric fragments and monomeric units. Because of the tendency of adipic acid to fragment with elimination of CO and H2O and to undergo cyclization, significant amounts of secondary products from nylon 6.6 are reported in some papers.
Many authors have shown that the primary polyamide chain scission occurs either at the peptide C(O)NH or at adjacent bonds, most probably at the alkyl–amide NHCH2 bond which is relatively the weakest in the aliphatic chain. Hydrolysis, homolytic scission, intramolecular CH transfer and cis-elimination (a particular case of CH transfer) are all suggested as possible primary chain-scission mechanisms. There are no convincing results reported which tend to generally support one of these mechanisms relative to the others; rather, it seems that the contribution of each mechanism depends on experimental conditions. This conclusion is also supported by the wide spread of kinetic parameters measured under the different experimental conditions.
More uniform results are observed in the literature regarding the mechanism of thermo-oxidative decomposition of aliphatic nylons. Most authors agree that oxygen first attacks the N-vicinal methylene group, which is followed by the scission of alkyl–amide NC or vicinal CC bond. Alternatively, it is suggested that any methylene group which is β-positioned to the amide group methylene can be initially oxidized. There are few mechanisms in the literature which explain discoloration (yellowing) of nylons. UV/visible active chromophores are attributed either to pyrrole type structures, to conjugated acylamides or to conjugated azomethines.
Some secondary reactions occurring during the thermal or thermo-oxidative decomposition lead to crosslinking of nylons. Nylon 6.6 crosslinks relatively easily, especially in the presence of air, whereas nylon 11 and nylon 12 crosslink very little. Strong mineral acids, strong bases, and some oxides or salts of transition metals catalyse the thermal decomposition of nylons, but minimize crosslinking. In contrast, many fire retardant additives promote secondary reactions, crosslinking and charring of aliphatic nylons.
© 1999 Society of Chemical Industry
350 citations
TL;DR: The results revealed that HAP gradually releases its OH- ions and transforms into OHAP in the temperature of 1000-1360 degrees C, which indicates HAP decomposition and speculated that some oxyapatite (OAP) might be formed during dehydration with a great amount of OHAP still left in the system even up to theTemperature of decomposition.
347 citations
TL;DR: In this article, a new class of polyimide/silica composites with chemical bonds between the polyimides and silica network has been synthesized by the sol−gel reaction and characterized.
Abstract: A new class of polyimide/silica composites with chemical bonds between the polyimide and silica network has been synthesized by the sol−gel reaction and characterized. The hybrid composite films were obtained by the hydrolysis and polycondensation of (3-aminopropyl)triethoxysilane (APTES) and tetraethoxysilane (TEOS) in N,N-dimethylacetamide solution (DMAc), followed by heating at 100, 200, and 300 °C. The presence of chemical bonds between polyimide (PI) and silica has great effect on the properties of polyimide films, especially on their mechanical properties. The modulus and ultimate strength of the hybrid composite films increased and elongation at break decreased with increased silica content. These hybrid films showed no apparent decrease in thermal decomposition temperature.
325 citations
TL;DR: In this paper, a new computational technique (advanced isoconversional method) has been used to determine the dependence of the effective activation energy (Eα) on α for isothermal and nonisothermal TGA data.
Abstract: The methods of thermogravimetric analysis (TGA) and differential scanning calorimettry (DSC) have been used to study the thermal decomposition of ammonium perchlorate (AP). TGA curves obtained under both isothermal and nonisothermal conditions show a characteristic slowdown at the extents of conversion, α = 0.30−0.35. DSC demonstrates that in this region the process changes from an exothermic to an endothermic regime. The latter is ascribed to dissociative sublimation of AP. A new computational technique (advanced isoconversional method) has been used to determine the dependence of the effective activation energy (Eα) on α for isothermal and nonisothermal TGA data. At α > 0.1, the Eα dependencies obtained from isothermal and nonisothermal data are similar. By the completion of decomposition (α → 1) the activation energy for the isothermal and nonisothermal decomposition respectively rises to ∼110 and ∼130 kJ mol-1, which are assigned to the activation energy of sublimation. The initial decomposition (α → ...
240 citations
TL;DR: In this article, the perovskite-type oxide powders used for the preparation of the thick films have been tested in laboratory, in environments with different gases (CO and NO 2 ) in dry and wet air.
Abstract: Thick films of LaFeO 3 and SmFeO 3 were fabricated by screen-printing technology on alumina substrates with comb-type Au electrodes. The perovskite-type oxide powders used for the preparation of the thick films have been prepared by the thermal decomposition at 700°C of hexacyanocomplexes, Ln[Fe(CN) 6 ] · n H 2 O. These powders are ultrafine, homogeneous, and free of intragranular pores. The films have been fired at different temperatures in the 750–1000°C range, in N 2 and air atmospheres. The gas-sensitive electrical response of the thick films have been tested in laboratory, in environments with different gases (CO and NO 2 ) in dry and wet air. For field tests, the prototype sensors have been placed beside a conventional station for environmental monitoring. The electrical response of the thick films has been compared with the results of the analytical instruments for environmental monitoring. The same trend was observed for both systems, with very promising results.
221 citations
TL;DR: In this article, isothermal and dynamic measurements are performed by combined thermogravimetry mass spectrometry (TG-MS) and isothermal measurements are carried out with a new closed loop-type reactor.
209 citations
TL;DR: In this article, a novel method for preparing nanoporous polyorganosilicate films, which promise to satisfy the key requirements, via inorganic/organic polymer hybrid templating, was presented.
Abstract: Dielectric insulator materials containing nanometer-scale closed-cell pores with low dielectric constants (k < 2.2), good mechanical properties, and high dielectric breakdown strengths are required for future semiconductor devices. In this paper we present a novel method for preparing nanoporous polyorganosilicate films, which promise to satisfy the key requirements, via inorganic/organic polymer hybrid templating. The nanometer-scale inorganic/organic polymer hybrids are generated in situ upon heating mixtures of methylsilsesquioxane (MSSQ) prepolymer with star-shaped hydroxy-terminated poly(e-caprolactone) (PCL) to ∼250 °C, causing chain extension and cross-linking of MSSQ. Subsequent heating to 430 °C results in the thermal decomposition and volatilization of PCL components from the vitrified poly(methylsilsesquioxane) (PMSSQ) matrix, leaving behind porous PMSSQ films with pores with the size and shape of the original hybrid morphology. A dielectric constant as low as 2.1 has been achieved for closed-c...
208 citations
TL;DR: Using thermogravimetric analyses as well as isothermal gravimetric measurements, the thermal stability of the iron(III) nitrate nanohydrate has been determined in this article, where several decomposition stages are the result of melting, evaporation and hydrolysis processes occurring in the salt-water system in the temperature range of 20-400°C.
Abstract: Using thermogravimetric analyses as well as isothermal gravimetric measurements, the thermal stability of the iron(III) nitrate nanohydrate has been determined. Several decomposition stages are the result of melting, evaporation and hydrolysis processes occurring in the salt—water system in the temperature range of 20–400°C. Some of the intermediates and the final product (α-Fe2O3) are characterized by means of chemical analyses, X-ray diffraction patterns and IR spectra.
TL;DR: In this paper, the thermal degradation of poly(methyl methacrylate) (PMMA) has been studied in both pure nitrogen and oxygen-containing atmospheres, and the model-free isoconversional method has been used to determine the dependence of the effective activation energy on the extent of degradation.
Abstract: The thermal degradation of poly(methyl methacrylate) (PMMA) has been studied in both pure nitrogen and oxygen-containing atmospheres. The presence of oxygen increases the initial decomposition temperature by 70 °C. The stabilizing effect of oxygen may be explained by forming thermally stable radical species that suppress unzipping of the polymer. This assumption is supported by the experimental fact that introduction of NO into gaseous atmosphere increases the initial decomposition temperature by more than 100 °C. The model-free isoconversional method has been used to determine the dependence of the effective activation energy on the extent of degradation. The initial stages of the process show a dramatic difference in the activation energies that were found to be 60 and 220 kJ mol-1 for respective degradations in nitrogen and air.
TL;DR: In this paper, a cascade of well-s stirred reactors is used to perform stepwise pyrolysis of mixtures of poly(vinyl chloride), polystyrene and polyethylene, where the different components of the mixture are pyrolysed at different temperatures.
TL;DR: In this paper, a series of pendent hydroxyl groups ortho to the heterocyclic imide nitrogen were prepared via the solution condensation of aromatic dianhydrides with bisaminophenols.
Abstract: A series of hydroxy-containing polyimides, containing pendent hydroxyl groups ortho to the heterocyclic imide nitrogen, were prepared via the solution condensation of aromatic dianhydrides with bisaminophenols. The polyimides were found to undergo thermal conversion to polybenzoxazoles upon heating between 350 and 500 °C under nitrogen or vacuum. The thermal conversion was accompanied by loss of carbon dioxide. No other volatile byproducts were detected by IR or NMR. Structures were confirmed by IR, solid-state NMR, and elemental analysis. Polybenzoxazole films, obtained by the thermolysis of solvent-cast poly(amic acid) or polyimide solutions, displayed excellent solvent resistance and good thermal stability. Insolubility of the polybenzoxazoles in all solvents tested indicates possible cross-linking. No crystallinity was observed by X-ray diffraction. Due to the insolubility of the resulting polybenzoxazoles, model compound reactions were also investigated. In the vapor phase at 400 °C, N-(2-hydroxyphen...
TL;DR: In this paper, an octahedral geometry was proposed for 3-N-methylmorpholino-4-amino-5-mercapto-1,2,4-triazole with Co(II), Ni(II) and Cu(II).
TL;DR: In this paper, the authors reported the preparation of layered MnO2 and preliminary results on its cathodic performance in Li secondary batteries, where the success of synthesis is ascribed to the high population of K+ ions in the pyrolyzing media that act as pillaring cations to stabilize the layered framework.
Abstract: We report here the preparation of layered MnO2 and the preliminary results on its cathodic performance in Li secondary batteries. The thermal decomposition of KMnO4 powder at 250−1000 °C in air produces KxMnO2+δ·yH2O (x = 0.27−0.31, δ = 0.07−0.13, and y = 0.47−0.89) with a product yield of 67−79% based on the Mn molar quantity. It can be judged from the Rietveld refinement on the X-ray diffraction pattern that the 800 °C-prepared sample has a layered structure (hexagonal unit cell, space group = P63/mmc, a = 2.84 A, and c = 14.16 A), where the K+ ions and H2O molecules reside at the interlayer trigonal prismatic sites (P2-type structure). Contrary to the previous findings whereby the layered MnO2 transforms to α-/γ-MnO2 phases or manganese suboxides at >450 °C, such impurities are negligible in this synthesis even at higher temperatures. The success of synthesis is ascribed to the high population of K+ ions in the pyrolyzing media that act as pillaring cations to stabilize the layered framework. In additi...
TL;DR: A model for the thermal decomposition of gaseous N2O is developed and it is shown that atomic oxygen is present at the Si wafer, and that this removes previously incorporated nitrogen.
Abstract: The gas-phase chemistry of silicon oxynitridation in N2O has been investigated. From an evaluation of available kinetic data, we have developed a model for the thermal decomposition of gaseous N2O. To quantify heat transfer between the N2O gas and the wall of the furnace, we introduce the concept of referencing to an N2 gas-temperature profile, measured in an oxidation furnace. Using this model, we can account for the increase with flow rate and temperature of the NO concentration in the N2O decomposition product, and the self-heating during decomposition, for furnace processing. This change in gaseous NO concentration translates to a higher nitrogen content and lower growth rate for the silicon oxynitride. For rapid thermal and other short-gas-residence-time systems, we show that atomic oxygen is present at the Si wafer, and that this removes previously incorporated nitrogen.
TL;DR: In this article, the authors used high-intensity ultrasound (200 kHz, 6 W cm-2) for the preparation of platinum nanoparticles, which were stable, homogeneously spherical and relatively monodispersed with an average 2.6 nm diameter.
Abstract: Platinum nanoparticles were prepared in an aqueous system using high-intensity ultrasound (200 kHz, 6 W cm-2). The particles formed in the presence of a surfactant (sodium dodecyl sulfate, SDS) were stable, homogeneously spherical, and relatively monodispersed with an average 2.6 nm diameter. The rate of formation of the platinum nanoparticles was 26.7 μM min-1 in the Pt(II)−SDS system. Reducing species generated near and/or in the hot bubbles, which were sonochemically induced in the media, would react with the PtCl42- complexes to form the platinum nanoparticles. Three kinds of the reducing species were proposed to be formed in the sonicated system: (a) radicals formed from the thermal decomposition of SDS at the interfacial region between the cavitation bubbles and bulk solution; (b) radicals formed via reactions of the hydroxyl radicals or hydrogen atoms with SDS; (c) hydrogen atoms. During the reduction of the Pt(II) ion, (b) and (c) ((b) > (c)) may be effective while (a) is only slightly effective,...
TL;DR: In this article, pyrolysis and gas chromatography/mass spectrometry were applied to investigate the influence of some metals (aluminium, iron and zinc), metal oxides (aluminum, titanium, copper and iron) and carboxylates (zinc and tin) on the thermal decomposition processes of PVC.
TL;DR: The thermal decomposition pathways leading to the formation of volatile compounds and to char residue in poly(bisphenol A carbonate) (PC), poly(resorcinol carbonate), and poly(hydroquinone carbonate, PHC) have been investigated by mass spectrometry as mentioned in this paper.
Abstract: The thermal decomposition pathways leading to the formation of volatile compounds and to char residue in poly(bisphenol A carbonate) (PC), poly(resorcinol carbonate) (PRC), and poly(hydroquinone carbonate) (PHC) have been investigated by mass spectrometry. The structure of the volatile compounds obtained in the temperature range 300−700 °C, by direct pyrolysis mass spectrometry (DPMS), suggests that these polycarbonates undergo thermal decomposition by a number of different pyrolysis processes. In the initial stage of the thermal degradation are generated cyclic oligomers by an intramolecular exchange reaction, whereas the evolution of CO2 and H2O is spread over all the pyrolysis temperature range, being responsible for the formation of ether bridges (decarboxylation) and phenolic end groups (hydrolysis). A disproportionation reaction of the BPA isopropylidene bridges of PC itself takes place at higher temperature yielding phenyl and isopropylidene end groups, whereas pyrolysis products containing dibenzo...
TL;DR: In this article, a simple method of producing aligned carbon nanotube films and a mechanism for their formation are described, based on the self-organization by surface decomposition of a SiC wafer in a vacuum at a temperature between 1500 and 1700°C.
Abstract: A simple method of producing aligned carbon nanotube films and a mechanism for their formation are described. The alignment method is based on the self-organization by surface decomposition of a SiC wafer in a vacuum at a temperature between 1500 and 1700°C. From the results of cross-sectional observations by high-resolution transmission electron microscopy and analytical electron microscopy, the following formation mechanism is proposed: SiO gas molecules are generated by surface oxidation and graphite caps of 2-5 nm in size are formed by the bubbling of SiO gas on the surface, characterized by a (0001)SiC plane. Then carbon nanotubes grow in a vertical direction, eroding the SiC crystal during the continuous oxidation.
TL;DR: In this paper, the synthesis of mixed ZrO2-SiO2 oxides has been carried out using a new non-acid-base alkoxide route, where the chemical reactivity of Zirconium n-propoxide (ZP) is first modified with the chelating agent acetylacetone (acac) before it is brought in contact with tetraethoxysilane (TEOS), and a linear relationship between the IR absorption band shift of Zr-O-Si linkages and the Zr content is established to indicate the
Abstract: The synthesis of mixed ZrO2–SiO2 oxides has been carried out using a new non-acid–base alkoxide route. The chemical reactivity of zirconium n-propoxide (ZP) is first modified with the chelating agent acetylacetone (acac) before it is brought in contact with tetraethoxysilane (TEOS). It is found that the gelation rate of bi-component sols is much faster than those of the mono-components under similar preparation conditions. A self-catalytic effect of the resultant Zr–O–Si on Si–O–Si formation is thus identified. By employing FTIR/DTA/TGA/XRD techniques, the mixing level of the two oxides in terms of Zr–O–Si hetero-linkages has been investigated in detail. A linear relationship between the IR absorption band shift of Zr–O–Si linkages and the Zr content is established to indicate the amount of oxide mixing. Phase segregation and thermal decomposition of xerogels upon calcination are studied and factors responsible for good mixing are also discussed. Using this approach, a high level of mixing has been achieved for the ZrO2–SiO2 binary oxides (Zr up to 50 mol%) with an acac to ZP molar ratio in the range 0.2–0.4 in the absence of an acid or base catalyst.
TL;DR: Sulforaphane, a cancer chemopreventive agent identified from broccoli, was degraded in an aqueous solution at 50 and 100 degrees C and the major thermal degradation compound was determined as N, N'-di(4-methylsulfinyl)butyl thiourea.
Abstract: Sulforaphane, a cancer chemopreventive agent identified from broccoli, was degraded in an aqueous solution at 50 and 100 °C. The reaction mixtures were extracted with methylene chloride and analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Dimethyl disulfide, S-methyl methylthiosulfinate, S-methyl methylthiosulfonate, methyl (methylthio)methyl disulfide, 1,2,4-trithiolane, 4-isothiocyanato-1-(methylthio)-1-butene, and 3-butenyl isothiocyanate were identified as volatile decomposition products. After methylene chloride extraction, the aqueous layer was dried and silica gel column chromatography was used to separate and purify the nonvolatile decomposition products. The major thermal degradation compound was determined by 1H NMR, 13C NMR, and FAB-MS as N,N‘-di(4-methylsulfinyl)butyl thiourea. A possible mechanism for the formation of these products is proposed.‘ ‘‘ Keywords: Sulforaphane; isothiocyante; thermal decomposition; N,N‘-di(methylsulfinyl)butyl thiourea
TL;DR: In this paper, the mechanism and kinetics of thermal decomposition of injection molded HOA ceramics were studied over the temperature range of 1473-1758 K. At temperatures below 1473 K the sintering and transformation of HOA to hydroxyoxyapatite proceeded to a conversion degree of 0.4 to 0.5, while at temperatures between 1473 and 1758 K the HOA was decomposed to α-TCP, H2O and CaO.
Abstract: The mechanism and kinetics of thermal decomposition of injection moulded hydroxyapatite ceramics were studied over the temperature range of 1473–1758 K. At temperatures below 1473 K the sintering and transformation of hydroxyapatite to hydroxyoxyapatite proceeded to a conversion degree of 0.4 to 0.5. At temperatures between 1473 and 1758 K the hydroxyapatite was decomposed to α-TCP, H2O and CaO. The decomposition of HOA started on the surface of the HOA ceramics. The rate of increase in the thickness of the reaction products (α-TCP) was described by the parabolic law. The kinetic analysis of the time dependence of HOA conversion to TCP by means of the J-M-A-J-K equation also showed that the thermal decomposition of HOA ceramics was controlled by diffusion of water from the reaction zone to the surface of the ceramic sample. The activation energy of the thermal decomposition of HOA ceramics amounted to 283.5 kJ/mol.
TL;DR: In this paper, Fourier transform infrared spectroscopy was used for drying linseed oil and poppyseed oil at 60°C, and a broad vibration band centered around 3425 cm−1 was observed.
Abstract: The curing of drying oils at 60°C has been investigated by Fourier transform infrared spectroscopy and Fourier transform Raman analysis of linseed oil and poppyseed oil. In the first step, hydroperoxides are formed (broad vibration band centered around 3425 cm−1) with concomitant conjugation and cis-trans isomerization of the double bonds (disappearance of cis bands at 3011 and 716 cm−1, appearance of trans conjugated and trans nonconjugated bands at 987 and 970 cm−1). The subsequent decomposition of hydroperoxides in the presence of oxygen leads to the formation of alcohols (nitrite band at 779 cm−1 after nitrogen monoxide treatment), aldehydes (bands at 2810 and 2717 cm−1 in gas phase), ketones (saturated and unsaturated at 1720 and 1698 cm−1, respectively), carboxylic acids (saturated and unsaturated acid fluorides identified at 1843 and 1810 cm−1 after SF4 treatment), and peresters or γ-lactones (near 1770 cm−1). A rapid decrease in the double-bond concentration is recorded when curing continues, and the formation of epoxides, characterized by a vibration band at 885 cm−1, is observed. Thermolysis experiments have suggested the proposal of a reaction of addition of peroxyl radicals on the conjugated double bonds as a probable mechanism. This mechanism explains both the rapid disappearance of conjugated double bonds and the formation of epoxides as intermediate products observed in the initial step of curing.
TL;DR: In this paper, an Mg/Al and a mg/Ga layered double hydroxide (LDH) were synthesized by using the coprecipitation method and calcined at a variety of temperatures.
Abstract: An Mg/Al and a Mg/Ga layered double hydroxide (LDH) were synthesized by using the coprecipitation method and calcined at a variety of temperatures. The starting LDHs and their calcination products (mixtures of oxides and spinels) were characterized by X-ray diffraction, solid-state NMR and IR spectroscopies and thermogravimetric analysis. Based on the results, the LDHs studied possess a brucite-like structure where tervalent cations occupy octahedral positions. At moderate temperatures, calcination gives a mixture of oxides; at high temperatures, however, the corresponding spinels are obtained.
TL;DR: In this paper, the properties of HT-B depend on the ratio M2+:Al of the initial sample and the substitution Mg ↔ Ni does not influence the properties in the low temperature region.
Abstract: Synthetic hydrotalcite-like samples with composition [M1 − x2+Alx3+(OH)2](CO3)x/2 ·nH2O, where M = Mg, Ni, x = 0.25 and 0.33, n = 2x and 1.5x, are studied by XRD, DTA, TG and IR spectroscopy after heating in the temperature interval 120–260 °C and rehydration in air and water. Structural models of the two metaphases obtained are proposed. Metahydrotalcite-D (HT-D) is formed at 140–180 °C by the reversible dehydration of the interlayer. Metahydrotacite-B (HT-B) is formed at temperatures 240–260 °C as a result of the dehydroxilation of a part of OH groups of the brucite-like layer and inclusion of two oxygenes from the CO3-group in the same layer. The HT-B has a specific crystal structure. Rehydration does not restore the initial structural state but leads to the formation of a phase (HT-B-r) characterized with increased thickness of the interlayer, high content of water and a low temperature of dehydration. The properties of HT-B depend on the ratio M2+: Al of the initial sample. The substitution Mg ↔ Ni does not influence the properties of the metaphases in the low temperature region.
TL;DR: In this paper, a biphenyl-containing epoxy resin (Bis-EBP) was synthesized and confirmed by elemental analysis, infrared spectroscopy, and 1H-nuclear magnetic resonance spectrograph.
Abstract: A new type of epoxy resin containing a 4,4′-biphenylene moiety in the backbone (Bis-EBP) is synthesized and confirmed by elemental analysis, infrared spectroscopy, and 1H-nuclear magnetic resonance spectroscopy. In addition, to evaluate the influence of the 4,4′-biphenylene group in the structure, an epoxy resin having a 1,4-phenylene group in place of the 4,4′-biphenylene moiety (Bis-EP) is synthesized. The cured polymer obtained through the curing reaction between the new biphenyl-containing epoxy resin and phenol novolac is used for making a comparison of its thermal and physical properties with those obtained from Bis-EP and bisphenol-A (4,4′-isopropylidenediphenyl)-type epoxy resin (Bis-EA). The cured polymer obtained from Bis-EBP shows markedly higher fracture toughness of 1.32 MPa m1/2, higher glass transition temperature, lower moisture absorption, and higher thermal decomposition temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 690–698, 1999
TL;DR: In this paper, the thermal decomposition and isomerization processes of C3−C4 alkyl radicals, 1-C5H11, and 1-c6H13 have been investigated by using a shock-tube apparatus coupled with atomic resonance absorption spectrometry (ARAS).
Abstract: The thermal decomposition and isomerization processes of C3−C4 alkyl radicals, 1-C5H11, and 1-C6H13 have been investigated by using a shock-tube apparatus coupled with atomic resonance absorption spectrometry (ARAS). Isomeric alkyl radicals were generated by the thermal decomposition of respective alkyl iodides. Branching fractions for the competitive pathways (C−C bond cleavage, C−H bond cleavage, and isomerization) have been determined by following the hydrogen-atom concentration by ARAS. In the investigated temperature range (900−1400 K), for all alkyl radicals, the energetically favored C−C bond cleavage was found to dominate over the C−H bond cleavage. The 1,2 or 1,3 isomerization reaction was found to be minor in C3 and C4 alkyl radicals. On the other hand, the results for 1-C5H11 and 1-C6H13 radicals clearly show the occurrence of 1,4 and 1,5 isomerization reactions. From an RRKM analysis of the present result and the previous lower temperature data, with consideration of the tunneling effect, the ...
TL;DR: In this paper, a sol-gel process for silica/fluoride composites is described, where dry silica gels containing La3+ and trifluoroacetate ions (CF3COO−) were produced from tetramethylorthosilicate (TMOS), methanol, dimethylformamide, lanthanum acetate, triffluoroacetic acid, water and nitric acid.
Abstract: A novel sol–gel process for silica/fluoride composites is described. Crystallization of LaF3 in the sol–gel silica has been investigated. Dry silica gels containing La3+ and trifluoroacetate ions (CF3COO−) were produced from tetramethylorthosilicate (TMOS), methanol, dimethylformamide, lanthanum acetate, trifluoroacetic acid, water and nitric acid. By heating the gels at temperatures above 300°C, LaF3 microcrystals with a size of 10–30 nm were formed in the silica matrix. IR, XPS and TG-DTA analyses suggested that CF3COO− ions are coordinated to La3+ ions in the sols and the dried gels, leading to the formation of LaF3 by the thermal decomposition at elevated temperatures.