Use of inorganic materials to enhance thermal stability and flammability behavior of a polyimide

While a great variety of high temperature polyimide materials exist, these materials are being subjected to higher and higher use temperatures in oxidative and environmentally aggressive environments. There is a limit to the extent one can take a polyimide before it will oxidize and subsequently suffer property degradation, thermal decomposition, and structural failure. Therefore, we instead sought to use materials which do not oxidize (inorganic materials) to enhance the polyimide composition and perhaps move the properties of the organic polymer more into the realm of ceramics while maintaining polyimide composite weights and processing advantages. In this paper we present results of the combination of inorganic micron sized particles with and without carbon nanofibers to produce a variety of highly inorganic particle filled polyimides. These polyimides were tested for thermal stability and flammability in resin pellet form and as a protective coating for a carbon-fiber composite structure. Our results demonstrate that the resin with inorganic particles exhibited significant reductions in flammability by themselves, but minimal flammability reduction when used as a thin coating to protect a carbon-fiber composite. Further, the gains in thermal stability are limited by the thermal stability of the polyimide matrix, suggesting that more work is needed in measuring the limits of inorganic fillers to improve thermal stability. Still, the results are promising and may yield polyimide systems useful for providing resistance to damage from high heat flux exposures/fire risk scenarios.     

One-pot hydrothermal synthesis of reduced graphene oxide/zinc ferrite nanohybrids and its catalytic activity on the thermal decomposition of ammonium perchlorate

Reduced graphene oxide/Zinc ferrite (rGO/ZnFe₂O₄) nanohybrids are successfully decorated on the surface of the rGO sheets through a simple, one-step hydrothermal method. ZnFe₂O₄ nanoparticles (NPs) are homogeneously anchored on the rGO sheets. The rGO/ZnFe₂O₄ hybrids are characterized by XRD, FT-IR, XPS, TEM, Raman, BET. The rGO/ZnFe₂O₄ hybrids demonstrate amazing catalytic activity on thermal decomposition of ammonium perchlorate (AP), which is better than that of bare ZnFe₂O₄ NPs. TG-DTA results indicate that the ZnFe₂O₄ NPs in the hybrids with increasing ratio (1%, 3%, 5%) could decrease the second decomposition temperature of AP by 42.7?°C, 55.0?°C, 68.1?°C, respectively, and reduce the apparent activation energy of AP from 160.2?kJ?mol^?1 to 103.8?kJ?mol^?1. This enhanced catalytic performance is mainly attributed to the synergistic effect of ZnFe₂O₄ NPs and rGO.     

Comparison of the thermal decomposition behavior for members of the hydroxylamine family

In the present work the thermal stability of some members of the hydroxylamine family was studied using adiabatic calorimetry. The study included aqueous solutions of hydroxylamine free base, hydroxylamine hydrochloride, hydroxylamine sulfate, and hydroxylamine-o-sulfonic acid of concentrations typically used in industry. Also, the catalytic effect of metal surfaces of stainless steel, carbon steel, and titanium was studied. From the solutions studied HA is the most reactive with higher maximum temperature, pressure, non-condensable pressure, and lower time to maximum rate. HA maximum heat rate is at least ∼3 times higher than that of the other solutions studied, and the pressure generation rate is ∼13 times higher. All decompositions were catalyzed by stainless steel, but only HA was catalyzed significantly by titanium metal. Solid hydroxylamine hydrochloride, hydroxylamine sulfate, and hydroxylamine-o-sulfonic acid exhibited stability up to ∼60 °C. Hydroxylamine 100% was not studied because it is not readily available, is not used industrially, and is known to be unstable at room temperature. A violent reaction was measured for solid hydroxylamine sulfate that generated a heat rate >500 °C/min and pressure rate >5200 psia/min before the sample cell was completely destroyed by the generated pressure.     

Influence of oxidation state of phosphorus on the thermal and flammability of polyurea and epoxy resin

The focus of this study is an investigation of the effect of oxidation state of phosphorus in phosphorus-based flame retardants on the thermal and flame retardant properties of polyurea and epoxy resin. Three different oxidation states of phosphorus (phosphite, phosphate and phosphine oxide) additives, with different thermal stabilities at a constant phosphorus content (1.5 wt.%) have been utilized. Thermal and flame retardant properties were studied by TGA and cone calorimetry, respectively. The thermal stability of both polymers decreases upon the incorporation of phosphorus flame retardants irrespective of oxidation state and a greater amount of residue was observed in the case of phosphite. Phosphate was found to be better flame retardant in polyurea, whereas phosphite is suitable for epoxy resin. Phosphite will react with epoxy resin by trans-esterification, which is demonstrated by FTIR and ³¹P NMR. Further, TG–FTIR and XPS studies also provide information on flame retardancy of both polymers with phosphorus flame retardants.     

Self-assembled CuO nanoarchitectures and their catalytic activity in the thermal decomposition of ammonium perchlorate

CuO shuttle-like and flower-like nanocrystals were synthesized through a one-step, low-temperature solution-phase method in the presence of a cation surfactant, hexadecyl trimethyl ammonium bromide. These nanocrystals were studied as an additive for promoting the thermal decomposition of ammonium perchlorate (AP). With the addition of CuO shuttle-like and flower-like nanocrystals, the thermal decomposition temperature of AP decreased. The structure, particle size, and morphology of resulting CuO powders were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis technique was applied to investigate the thermal decomposition of mixtures of AP and as-prepared CuO nanocrystals.     

The thermal decomposition of N,N-dimethyl-3-oxa-glutaramic acid and the kinetics of its second-stage thermal decomposition reaction

N,N-dimethyl-3-oxa-glutaramic acid was purified and characterized by 1H-NMR, Fourier transform in-frared spectroscopy (FT-IR) and elemental analysis. The thermal decomposition of the title compound was studied by means of thermogravimetry differential thermogravimetry (TG-DTG) and FT-IR. The ki-netic parameters of its second-stage decomposition reaction were calculated and the decomposition mechanism was discussed. The kinetic model function in a differential form, apparent activation energy and pre-exponential constant of the reaction are 3/2 [(1-α) 1/3-1]-1, 203.75 kJ-mol-1 and 1017.95s-1, respec-tively. The values of ΔS≠, ΔH≠ andΔG≠ of the reaction are 94.28 J-mol-1-K-1, 203.75 kJ-mol-1 and 155.75 kJ-mol-1, respectively.     

Polytypic transformations during the thermal decomposition of cobalt hydroxide and cobalt hydroxynitrate

The isothermal decomposition of cobalt hydroxide and cobalt hydroxynitrate at different intervals of temperature leads to the formation of Co₃O₄. The phase evolution during the decomposition process was monitored using powder X-ray diffraction. The transformation of cobalt hydroxide to cobalt oxide occurs via three phase mixture while cobalt hydroxynitrate to cobalt oxide occurs through a two phase mixture. The nature of the sample and its preparation method controls the decomposition mechanism. The comparison of topotactical relationship between the precursors to the decomposed product has been reported in relation to polytypism.     

Dispersive kinetic models for isothermal solid-state conversions and their application to the thermal decomposition of oxacillin

The authors recently published works in which the use of two novel equations for modeling the dispersive kinetics observed in various solid-state conversions are described. These equations are based on the assumptions of a ‘Maxwell-Boltzmann (M-B)-like’ distribution of activation energies and a first-order rate law. In the present work, it is shown that it may be possible to expand the approach to include mechanisms other than first-order, i.e. some of those commonly encountered in the field of thermal analysis, thus obtaining ‘dispersive versions’ of these kinetic models. The application of these dispersive kinetic models to the slightly sigmoidal, isothermal conversion-time (x-t) data of Rodante and co-workers for the degradation of the antibiotic, oxacillin, is described. This is done in an effort to test the limitations of the proposed dispersive models in describing kinetic data which is not clearly sigmoidal (i.e. as shown in previous works). Finally, it is demonstrated that, using graphical analysis, the typically sigmoidal x-t plots of first-order dispersive processes are the direct result of (asymmetric) activation energy distributions that are either ‘∩-shaped’ (for heterogeneous conversions) or ‘∪-shaped’ (for homogeneous conversions) in appearance, i.e. when the activation energy is plotted as a function of conversion. This finding lends support to the founding hypothesis of the authors’ approach for modeling dispersive kinetic processes: the existence of ‘M-B-like’ distributions of activation energies.     

Thermal degradation and flame retardance in copolymers of methyl methacrylate with diethyl(methacryloyloxymethyl)phosphonate

Methyl methacrylate (MMA) has been free radically copolymerized, both in bulk and in solution, with diethyl(methacryloyloxymethyl)phosphonate (DEMMP), to give polymers which are significantly flame retarded when compared with PMMA, as indicated by the results of limiting oxygen index (LOI) measurements, UL 94 tests, and the results of cone calorimetric experiments. The physical and mechanical properties of the copolymers are similar to those of PMMA, except that the bulk copolymers are slightly crosslinked, and are better than those of PMMA flame retarded to a similar extent by some phosphate and phosphonate additives. Examination of the some of the gaseous products of pyrolysis and combustion, and of chars produced on burning, show that flame retardation occurs in the copolymers by both a condensed-phase and a vapour-phase mechanism. The condensed-phase mechanism is shown to involve generation of phosphorus acid species followed by reaction of these with MMA units giving rise to methacrylic acid units. The methacrylic acid units subsequently form anhydride links, which probably impede depolymerization of the remaining MMA sequences, resulting in evolution of less MMA (the major fuel when MMA-based polymers burn). By undergoing decarboxylation, leading to interchain cyclisation and, eventually, to aromaticisation, the anhydride units are probably also the principal precursors to char.     

Studies on the intercalation of naproxen into layered double hydroxide and its thermal decomposition by in situ FT-IR and in situ HT-XRD

Layered double hydroxides, novel anionic clay, meet the first requirement as inorganic matrices for encapsulating functional drugs or biomolecules with negative charge in aqueous media. In this study, naproxen has been intercalated into Mg-Al layered double hydroxide by the methods of ion exchange. The structure and composition of the intercalated material have been studied by X-ray diffraction (XRD), UV-vis spectroscopy and inductively coupled plasma emission spectroscopy. A schematic model has been proposed. Furthermore, in situ Fourier transform infrared spectroscopy, in situ high-temperature XRD, and thermogravimetry (TG) have been used to characterize the thermal decomposition of the hybrid material. It has been found that the thermal stability of the intercalated naproxen is significantly enhanced compared with the pure form before intercalation, which suggests that this drug-inorganic layered material may have prospective application as the basis of a novel drug delivery system.     

Effect of water vapor on the thermal decomposition process of zinc hydroxide chloride and crystal growth of zinc oxide

Thermal decomposition process of zinc hydroxide chloride (ZHC), Zn₅(OH)₈Cl₂·H₂O, prepared by a hydrothermal slow-cooling method has been investigated by simultaneous X-ray diffractometry and differential scanning calorimetry (XRD-DSC) and thermogravimetric-differential thermal analysis (TG-DTA) in a humidity-controlled atmosphere. ZHC was decomposed to ZnO through β-Zn(OH)Cl as the intermediate phase, leaving amorphous hydrated ZnCl₂. In humid N₂ with P_H2O=4.5 and 10 kPa, the hydrolysis of residual ZnCl₂ was accelerated and the theoretical amount of ZnO was obtained at lower temperatures than in dry N₂, whereas significant weight loss was caused by vaporization of residual ZnCl₂ in dry N₂. ZnO formed by calcinations in a stagnant air atmosphere had the same morphology of the original ZHC crystals and consisted of the c-axis oriented column-like particle arrays. On the other hand, preferred orientation of ZnO was inhibited in the case of calcinations in 100% water vapor. A detailed thermal decomposition process of ZHC and the effect of water vapor on the crystal growth of ZnO are discussed.     

Effect of the modification of silica on thermal properties and flammability of cross-linked butadiene-acrylonitrile rubbers

The paper presents the results of testing the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified silica. The test results were obtained with the use of a derivatograph, measurements of flammability by the method of oxygen index, in air and also with the use of a cone calorimeter. The effect of the modification on the zeta potential was also examined. A considerable reduction in the flammability of nitrile rubber vulcanizates filled with silica can be obtained by the modification of filler with bromine or iodine. All the vulcanizates containing modified silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates with bromine-modified silica makes it possible to obtain non-flammable polymeric materials. They neither ignite nor glow under the action of a flame source for 30 s. The findings can be a rational basis for the synthesis of modified silica that can act as active filler and effective flame-retardant agent at the same time.     

The effect of MWNTs on the microstructure of resin carbon and thermal conductivity of C/C composites

Multi-walled nanotubes were added into furan resin. Unidirectional carbon/carbon preforms were densified with the nanotube-doped furan resin by impregnation–carbonization cycle. The effects of Multi-walled nanotubes on the microstructure of resin carbon and thermal conductivity of carbon/carbon composites were investigated. The results show that Multi-walled nanotubes can induce the ordered arrangement of planar carbon microlites in resin carbon during high-temperature treatment and enhance the graphitization degree of resin carbon. Small amount of Multi-walled nanotubes in resin carbon can enhance the thermal conductivity of C/C composites evidently, especially the thermal conductivity vertical to the direction of fiber axis, due to the improvement of microstructure of resin carbon. Excess Multi-walled nanotubes in resin are disadvantageous to the enhancement of thermal conductivity instead, because they are difficult to disperse and easy to agglomerate, resulting thermal resistances in carbon matrix.     

Effects of the thermal decomposition of surface oxygen species on the chemical and catalytic properties of activated carbon supported Pt catalysts

Several carbon supported Pt catalysts were prepared by varying surface properties of support and tested for methylene chloride oxidation. They were investigated by BET, TPD, pH analysis and XPS. The Pt species would stabilize when the surface carbon was pregraphitized due to the π sites of basal plane. This revised version was published online in June 2006 with corrections to the Cover Date.     

Computational analysis of some possible initial steps in the unimolecular thermal decompositions of 1,3-diazacyclobutane and its 1,3-dinitramine derivative

Summary We have investigated some possible initial steps in the unimolecular thermal decompositions of 1,3-diazacyclobutane and its 1,3-dinitramine derivative, the latter being selected as the simplest example of a symmetric cyclic nitramine. Vibrational analyses were used to identify normal modes that, in the extreme limits, would correspond to bond rupture and molecular decomposition. The energy requirements for ring fragmentation and N-N bond-breaking were computed at the MP4/6-31G level, using SCF 3-21G optimized structures. It was concluded that ring-fragmentation is a probable initiating step in the decomposition of the unsubstituted molecule, and that it is roughly competitive with N-N bond scission for the dinitramine. The nitronitrite rearrangement is predicted, on the basis of SCF calculations, to be less likely than either of the other two processes. It is proposed that N-N bond-breaking may be of primary importance for nitramine stability, but that energetic performance may be determined more by decomposition pathways having energy barriers.     

Pure CuCr2O4 nanoparticles: Synthesis,characterization and their morphological and size effects on the catalytic thermal decomposition of ammonium perchlorate

In the present paper a pure phase of the copper chromite spinel nanoparticles (CuCr₂O₄ SNPs) were synthesized via the sol–gel route using citric acid as a complexing agent. Then, the CuCr₂O₄ SNPs has been characterized by field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). In the next step, with the addition of Cu–Cr–O nanoparticles (NPs), the effects of different parameters such as Cu–Cr–O particle size and the Cu/Cr molar ratios on the thermal behavior of Cu–Cr–O NPs + AP (ammonium perchlorate) mixtures were investigated. As such, the catalytic effect of the Cu–Cr–O NPs for thermal decomposition of AP was evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA/DSC results showed that the samples with different morphologies exhibited different catalytic activity in different stages of thermal decomposition of AP. Also, in the presence of Cu–Cr–O nanocatalysts, all of the exothermic peaks of AP shifted to a lower temperature, indicating the thermal decomposition of AP was enhanced. Moreover, the heat released (ΔH) in the presence of Cu–Cr–O nanocatalysts was increased to 1490 J g⁻¹.     

Preparation and characterization of NiO nanoparticles from thermal decomposition of the [Ni(en)3](NO3)2 complex: A facile and low-temperature route

NiO nanoparticles with an average size of 15 nm were easily prepared via the thermal decomposition of the tris(ethylenediamine)Ni(II) nitrate complex [Ni(en)₃](NO₃)₂ as a new precursor at low temperature, and the nanoparticles were characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), UV-Vis spectroscopy, BET specific surface area measurement, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and magnetic measurements. The magnetic measurements confirm that the product shows a ferromagnetic behavior at room temperature, which may be ascribed to a size confinement effect. The NiO nanoparticles prepared by this method could be an appropriate photocatalytic material due to a strong absorption band at 325 nm. This method is simple, fast, safe, low-cost and also suitable for industrial production of high purity NiO nanoparticles for applied purposes.     

Preparation and characterization of pure single-phase BiFeO3 nanoparticles through thermal decomposition of the heteronuclear Bi[Fe(CN)6]·5H2O complex

The heteronuclear Bi[Fe(CN)₆]·5H₂O complex was synthesized and single-phase perovskite-type BiFeO₃ nanoparticles with an average size of 30 nm were obtained by its decomposition at 600 °C. The complex and its decomposition products were analyzed using elemental analysis, thermal analysis (TGA/DTA/DSC), X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), UV–Vis spectroscopy, BET specific surface area measurement, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and magnetic measurements. The magnetic measurement confirms that the product shows a ferromagnetic order at room temperature, which may be ascribed to the size confinement effect. The DTA and DSC results confirm the multiferroic nature of the BiFeO₃ nanoparticles with Neel and Curie points at 372 and 825 °C, respectively. The BiFeO₃ prepared by this method could be an appropriate visible-light photocatalytic material due to its strong absorption band in the visible region. This method is simple, low-cost, safe and also suitable for industrial production of high purity perovskite-type BiFeO₃ nanoparticles for electromagnetic applications.     

Simple and low-temperature synthesis of NiO nanoparticles through solid-state thermal decomposition of the hexa(ammine)Ni(II) nitrate, [Ni(NH3)6](NO3)2, complex

NiO nanoparticles with an average size of about 12 nm were easily prepared via the thermal decomposition of hexa(ammine)Ni(II) nitrate complex, [Ni(NH₃)₆](NO₃)₂, at low temperature of 250 °C. The product was characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), UV-Vis spectroscopy, BET specific surface area measurement, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and magnetic measurement. The magnetic measurement revealed a small hysteresis loop at room temperature, confirming a superparamagnetic (weak ferromagnetic) nature of the synthesized NiO nanoparticles. Indeed, the NiO nanoparticles prepared by this method could be an appropriate semiconductor material due to the optical band gap of 3.35 eV which shows a red shift in comparison with the previous reports. This method is simple, fast, safe, low-cost and also suitable for industrial production of high purity NiO nanoparticles for applied purposes.     

The role of anhydrous zinc nitrate in the thermal decomposition of the zinc hydroxy nitrates Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O

The steps associated with the thermal decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O and ZnOHNO₃·H₂O are re-examined. Previous reports have suggested that Zn₅(OH)₈(NO₃)₂·2H₂O decomposes to ZnO via two intermediates, Zn₅(OH)₈(NO₃)₂ and Zn₃(OH)₄(NO₃)₂ whereas ZnOHNO₃·H₂O has been reported to decompose to ZnO via a Zn₃(OH)₄(NO₃)₂ intermediate. In this study, we demonstrate using TG, mass spectral analysis of evolved gases and in situ variable temperature powder X-ray diffraction analysis that, in fact, in the decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O an anhydrous zinc nitrate intermediate is also involved. We, additionally, show that the decomposition of ZnOHNO₃·H₂O to ZnO also involves the formation of an anhydrous zinc nitrate intermediate. The anhydrous zinc nitrate formed in both cases is poorly crystallised and this observation may explain why this phase could not be observed by PXRD analysis in the previous studies.