Two-stage Decomposition Process Research Articles

Copper-doped zinc tartrate (Cu-ZnT) nanocrystals: Exploring their physical and antimicrobial properties

This study investigates the growth and properties of pure zinc tartrate (ZnT) and copper-doped zinc tartrate (Cu-ZnT) nanocrystals synthesized via a sol-gel technique using double-distilled water, sodium metasilicate, and tartaric acid. Controlled pH gels were prepared with the subsequent addition of zinc chloride and copper chloride solutions to facilitate nanocrystal formation. The synthesized nanocrystals were characterized using various techniques, including Energy-Dispersive X-ray analysis, Fourier Transform Infrared Spectroscopy, Thermogravimetric analysis, UV–visible-near infrared spectral analysis, X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy. EDAX confirmed the elemental composition of Zn, Cu, C, and O in the crystals. FTIR spectra revealed the presence of functional groups corresponding to water of crystallization, tartaric acid moieties, and potentially other compounds. TGA analysis indicated a two-stage decomposition process for ZnT and the formation of zinc copper oxide in Cu-ZnT. UV–vis-NIR analysis yielded a low cut-off wavelength of 285 nm for both crystals, suggesting electronic transitions below 350 nm. Both ZnT and Cu-ZnT nanocrystals are transparent in visible and near-infrared light, absorbing strongly in the ultraviolet. Copper doping enhances Cu-ZnT light absorption. While both act as insulators, Cu-ZnT exhibits significantly higher conductivity due to copper doping. XRD analysis estimated an average crystalline size of 42 nm, while FE-SEM images revealed a quasi-spherical morphology. Refractive index, extinction coefficient, and optical bandgap were further determined, highlighting the potential suitability of these nanocrystals for optoelectronic applications. Antibacterial and antifungal assays demonstrated moderate effectiveness against tested microorganisms compared to standard drugs.

Study on the thermal decomposition reaction process and kinetics of SF6 and tungsten

The thermal reaction of SF6 with tungsten powder was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC), combined with the characterization of solid decomposition products of SF6 and tungsten by SEM, EDS, XPS and Raman. Based on above experiments, a two-stage decomposition process of SF6 with tungsten was proposed: the first stage is the surface vulcanization reaction W+SF6→S2, mainly taken place at 600 °C, with the activation energy valued at 152.8 kJ·mol-1, according to Avrami-Erofeev equation; the second stage is the endothermic fluorination reaction WS2+SF6 →WF6, mainly taken place at 750 °C,, with the activation energy valued at 126.0 kJ·mol-1 according to the Avrami-Erofeev equation.

A numerical and experimental study of the decomposition pathways of guanidinium nitrate

The thermal decomposition behaviour of guanidinium nitrate (GN), an energetic material, was analysed using a combined experimental and computational approach. Simultaneous thermogravimetric analysis, Fourier transform infrared spectroscopy and mass spectrometry (TG-FTIR-MS) experiments were carried out at three different heating rates under closed and open crucible conditions. A two-stage decomposition process was observed, and the major gases evolved were found to be NH3, N2O, NO2 and CO2. Quantum mechanics based ab initio computations were performed to evaluate the possible decomposition pathways available for GN. Results indicate that decomposition of GN is not initiated in the condensed phase as the guanidinium cation and the nitrate anion are highly stable. The most likely mechanism involves isomerization of GN followed by a proton transfer in the gas phase to yield nitric acid and guanidine. These products then further react to form nitroguanidine (NQ) and H2O. NQ dissociates via several competing pathways to yield NH3, N2O, H2O and CO2. HNO3 decomposition can help explain NO2 formation. The residue left towards the end of TG can be attributed to dimerization and trimerization reactions of cyanamide.

An integrated spectroscopic and wet chemical approach to investigate grass litter decomposition chemistry

The chemical transformations that occur during litter decomposition are key processes for soil organic matter formation and terrestrial biogeochemistry; yet we still lack complete understanding of these chemical processes. Thus, we monitored the chemical composition of Andropogon gerardii (big bluestem grass) litter residue over a 36 month decomposition experiment in a prairie ecosystem using: traditional wet chemical fractionation based upon digestibility, solid state 13C nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The goals of this study were to (1) determine the chemical changes occurring during A. gerardii litter decomposition, and (2) compare the information obtained from each method to assess agreement. Overall, we observed a 97 % mass loss of the original litter, through a two-stage decomposition process. In the first stage, within 12 months, non-structural, cellulose and hemicellulose fractions not encrusted in lignin were preferentially and rapidly lost, while the acid unhydrolyzable residue (AUR) and microbial components increased. During the second stage, 12–36 months, all wet chemical fraction masses decreased equivalently and slowly with time, and the AUR and the lignin-encrusted cellulose fractions decomposition rates were comparable to each other. Method comparisons revealed that wet chemical fractionation did not accurately follow the initial litter structures, particularly lignin, likely because of chemical transformations and accumulation of microbial biomass. FTIR and NMR were able to determine bulk structural characteristics, and aid in elucidating chemical transformations but lacked the ability to measure absolute quantities of structural groups. As a result, we warn from the sole use of wet chemical methods, and strongly encourage coupling them with spectroscopic methods. Our results overall support the traditional chemical model of selective preservation of lignin, but shows that this is limited to the early stages of decomposition, while lignin is not selectively preserved at subsequent stages. Our study also provides important evidence regarding the impact of chemically different litter structures on decomposition rates and pathways.

Kinetic analysis of the non-isothermal degradation of high-density polyethylene filled with multi-wall carbon nanotubes

The thermal stability and non-isothermal degradation kinetics of high-density polyethylene (HDPE)/multi-wall carbon nanotube (MWNT) nanocomposites were studied by thermogravimetric and derivative thermogravimetric analyses using multiple heating rates (5, 10, 15, 20 °C min−1) under nitrogen gas atmosphere. A series of HDPE/MWNT composites of various vol% concentration of nanotubes were fabricated using melt mixing process. The morphology and nanostructure of prepared nanocomposites was examined by field emission scanning electron microscopy (FESEM). The kinetic parameters were evaluated using multiple heating rate-based four different “model-free” methods (viz., Kissinger, Friedman, Flynn–Wall–Ozawa, and Kissinger–Akhaira–Sunose) and single heating rate-based one “model-fitting” method (Tang approach), and 18 kinetic model equations were used. FESEM images confirmed that the dispersion and distribution of the MWNTs in the HDPE polymer matrix was homogeneous. The kinetic parameters [E a, A, n, and k (Arrhenius constant at 600 °C)] for all the samples studied were calculated. The highest values of E a, A, and n were found for the composites filled with 0.25 vol% MWNTs. For various vol% concentrations of HDPE/MWNT nanocomposites, the dependence of the apparent activation energy (E a) on fractional conversion (α) showed two-stage decomposition process, within the conversion window (0.05 ≤ α ≤ 0.95). Invariant kinetic parameter method (IKP) has been employed for all investigated nanocomposite system. A linear dependence between ln(A i) and E a,i was observed, making use of so-called compensation effect. Using IKP method, the values of the artificial isokinetic temperature “T iso” and artificial isokinetic rate constant “k iso” have been also estimated for all heating rates and found increases with increase in the heating rate (β). In addition, the dependence of lnA α on α was evaluated, and it was found that the lnA α revealed the same dependence on α as the apparent activation energies (E a) versus α plot shown. In order to estimate the kinetic degradation mechanism(s) of investigated system, Criado method was employed. The thermal decomposition kinetics of HDPE/MWNT composites were found to be best described by kinetic equations of n th order (AnFn and Dn mechanisms) to be more precise A1F1 → D1 → D2 kinetic models.

Thermal behavior of furosemide

Data from theoretical, thermal, and spectroscopic methods were compared in order to map a possible mechanism for the thermal decomposition of furosemide, a diuretic compound, in solid state. TG/DTG curves suggested a two-stage decomposition process. The first product of decomposition is water (m/z = 18), released due to a dimerization resulting in the formation of an amide. Then carbon dioxide (m/z = 44), nitroxide (m/z = 30), and 2-methyl-furanyl ion (m/z = 81) are released in the second stage. The chlorine substituted benzene ring, due to the double bond conjugated system, being the last fraction to decompose. Theoretical calculations presented are in agreement with experimental results.

Thermal degradation kinetics of poly(aryl ether sulfone 1,3,5-triazine)s containing phthalazinone moieties

Thermal degradation of phthalazinone-based poly(aryl ether sulfone 1,3,5-triazine) copolymers (PPESTs) has been investigated under nitrogen flow in dynamic heating conditions. Model-free kinetic approaches were applied to data for decomposition processes of PPESTs with different molecular structure. The activation energy was calculated as a function of the degradation extent by using Kissinger–Akahira–Sunose and Vyazovkin method. The effect of polymer composition and structure on the characteristic temperatures and kinetic parameters of thermal degradation was also investigated. The replacement of sulfone by 1,3,5-triazine in polymer main chain significantly increases initial decomposition temperature and E a, and its stabilizing effect may be explained by the existence of two-stage decomposition process that suppresses unzipping of the copolymers. This assumption is supported by the experimental fact that the complete replacement of sulfone by 1,3,5-triazine increases the initial decomposition temperature by 31 °C and E a by at least 57 kJ/mol according to Vyazovkin method.

Rice straw as an alternative reinforcement in polypropylene composites

We studied the use of rice straw as reinforcement in maleated polypropylene (PP m ). Composites containing 20 and 30% by weight rice straw were successfully prepared by extrusion and compression molding. The samples were characterized by tensile tests, differential scanning calorimetry (DSC), thermogravimetry (TGA), dynamo-mechanical analysis (DMTA) and scanning electron microscopy (SEM). The results of the mechanical properties showed that rice straw can be used as an alternative reinforcement for polypropylene. Higher tensile moduli (E) were obtained for composites containing higher rice straw content. Thermogravimetric curves of the composites exhibit two-stage decomposition process and slightly higher thermal stability. Higher crystallization (T C ) and melting peak temperatures for composites were detected by DSC analysis (T cpp = 107.8 °C, T cRS/PP(20/80) = 114.5 °C). The renewability of rice straw and the recyclability of thermoplastic polypropylene provide an attractive eco-fnendly quality to the resulting composites.

Thermal degradation studies of methacrylonitrile polymers and copolymers. 1. Polymethacrylonitrile prepared using normal free radical initiators

Several polymer samples have been prepared and studied by TG, DTA and TVA (thermal volatilisation analysis). By separation and analysis of the degradation products from the TVA experiments, it has been verified that polymethacrylonitrile, when pure and initiated by normal free radical initiators such as azoisobutyronitrile and benzoyl peroxide, degrades almost quantitatively to monomer, with only trace quantities of isobutene and hydrogen cyanide also produced. The two-stage decomposition process under programmed heating and the presence of the above trace products have been explained in a proposed degradation mechanism.

Thermal decomposition of GAP and GAP-based double-base propellants

This paper reports the thermal decomposition pattern of GAP and GAP-containing double-base (DB) compositions. Dynamic and isothermal TGA reveal a two-stage decomposition process for GAP. At temperatures below 200°C reactant-product interface diffusion, while at higher temperatures nucleation-based diffusion processes appear to be operative. Inclusion of GAP resulted in a drop in temperature for the onset of freeradical reaction.

Inhibition reaction of LiF on the combustion of ammonium perchlorate propellants

Lithium fluoride (LiF) is known as a negative catalyst which acts to reduce the burning rate of ammonium perchlorate (NH 4 ClO 4 : AP) composite propellants. To elucidate the role of LiF, the thermal decomposition process of AP particles with and without LiF was examined using differential thermal analysis, thermogravimetry, photomicrographic observations, and x-ray analysis. A two-stage decomposition process was observed during heating of the mixture of AP and 10% LiF. LiF acts to form a solution of AP and LP (LiClO 4 ) accompanied by an endothermic reaction. In the first-stage decomposition process, the liquified AP decomposes rapidly to form gaseous NH 3 and HClO 4 which react with each other exothermally. In the second-stage decomposition process, the liquified LP decomposes to O 2 and solidified LiCl. The gas phase reaction of AP composite propellants with and without LiF was examined by a microthermocouple technique. For example, the gas phase reaction rate is reduced by as much as 40% by the addition of 0.5% LiF. Thus, the heat feedback from the gas phase to the condensed phase decreases by 10 to 20%. Consequently, the burning rate decreases by 20 to 35%. This reduced gas phase reaction rate is attributed to altered condensed-phase decomposition processes between AP and LiF.

The ?-phase in rapidly solidified ferrous alloys

An Fe-1.9 wt% Si-4.2 wt% C alloy has been rapidly quenched from the melt in a controlled-atmosphere “gun” splat-cooling device to produce material consisting predominantly of the hexagonal close-packede-phase. The techniques of X-ray diffraction, scanning and transmission electron microscopy, and differential thermal analysis have been used to study the nature of thee-phase and its decomposition during heat treatment. The presence of the metastablee-phase could not be accounted for as the transformation product of a low stacking-fault energy austenite, and it appears to be formed directly from the liquid state. It has a complex and variable microstructure, which ranges from elongated, relatively featureless grains in the most rapidly-cooled areas to highly-faulted and twinned structural units containing precipitate particles. Thee-phase undergoes a two-stage decomposition process upon heating, but the first stage does not appear to involve the formation of martensite ande-carbide, which has been the hitherto accepted reaction. As an alternative it is suggested that thee-phase may decompose by a spinodal reaction.

Decomposition of the metastable phase in the silver-germanium system

The decomposition behaviour of the metastable h.c.p. phase in a splatcooled silver-23 at. % germanium alloy was studied by differential thermal analysis, X-ray and electron metallographic techniques. A two-stage decomposition process was observed. The activation energies for the two stages were found to be 0·91±0·09 eV/atom and 1·95±0·19 eV/atom, respectively. The first stage is associated with the transformation from h.c.p. to metastable f.c.c. solid solution, the second stage represents the precipitation of germanium from this solid solution. The total enthalpy of transformation was found to be 2·21±0·22 meV/atom.