R. Rajeev

Thermal decomposition studies. Part 19. Kinetics and mechanism of thermal decomposition of copper ammonium chromate precursor to copper chromite catalyst and correlation of surface parameters of the catalyst with propellant burning rate

Abstract The thermal decomposition of copper ammonium chromate (CAC), which is a precursor of copper chromite (CC) catalyst (used as a ballistic modifier in solid propellants), has been thoroughly studied. The DTG curves show that there are three main peaks at about 286, 440 and 740°C, whereas DTA gives peaks at 254 (endo), 278 (exo), 408 (exo) and 699°C (endo). The kinetic parameters for the prominent and clear-cut first stage in TG (DTG peak at 286°C) are E = 236 kJ mol−1, A = 1.51 × 1021 s−1, and Δ = 136 J K−1 mol−1. The mechanism of this decomposition reaction is identified as a phase boundary reaction with spherical symmetry, as per the equation g(α) = 1 − (1 − α) 1 3 . The surface parameters of the CC samples obtained by calcination of CAC, at different temperature regimes compatible with TG data, have been determined. The surface area of the CC decreases when the calcination temperature increases. The surface area also decreases when CC samples are washed with acetic acid. X-ray diffraction (XRD) patterns of CC samples obtained from higher temperature calcinations of CAC differ from those obtained at lower temperatures. The propellant burning rate is enhanced by the addition of CC and increases when the Lewis acid amounts of the catalyst sample increase. These correlations have been established for the first time for CC catalysts used in propellant technology.

TG–MS study on the kinetics and mechanism of thermal decomposition of copper ethylamine chromate, a new precursor for copper chromite catalyst

Abstract Copper chromite is a well-known burn rate modifier for the combustion of composite solid propellants. In this study, basic copper ethylamine chromate (CEC), a new precursor for copper chromite catalyst, was synthesized by precipitation method. The thermal decomposition of the precursor was followed by thermogravimetry–mass spectroscopy (TG–MS) and X-ray diffraction techniques and compared with that of copper ammonium chromate, a conventional precursor for copper chromite catalyst. TG–MS analysis for the decomposition of CEC revealed that the decomposition starts with the liberation of ethylamine. The change in enthalpy for the decomposition reaction of copper ethylamine chromate was higher than that of copper ammonium chromate due to the oxidation of ethyl group. The reducing atmosphere created by the presence of carbon during the decomposition of CEC produced a mixture of Cu, CuCr2O4, CuCrO2 and CuO, while the oxidizing atmosphere of copper ammonium chromate produced a mixture of CuCr2O4 and CuO. Mechanistic study based on Criado and Coats–Redfern methods showed that CEC follows random nucleation (F1) mechanism as the rate-determining step for the thermal decomposition process.

New insights into the spectral, thermal and morphological analysis of time dependent structural changes during open end functionalization of single walled carbon nanotubes

Even though several authors have investigated the chemical derivation of single walled carbon nanotubes (SWCNTs) through their treatment with concentrated nitric acid (conc. HNO3), this paper reports hitherto unaccounted for insights in this field of study that can be achieved through a spectral, thermal and morphological evaluation of SWCNTs, functionalized at a fixed temperature for different time intervals. In this study, multiple techniques were employed to systematically evaluate the structural changes on SWCNTs with refluxing time. Furthermore, the nanotubes, specifically functionalized for different extents of time, were characterized using a combination of analytical techniques including Raman spectroscopy, thermogravimetry-mass spectroscopy (TG-MS), X-ray photoelectron spectroscopy (XPS) and ultra violet near infrared spectroscopy (UV-Vis-NIR). To arrive at an optimum reflux point, an analysis of the changes in Radial Breathing Mode (RBM), D-band & G-band of Raman spectra, TG-MS profile and Zeta potential measurements was carried out. TG-MS (of the evolved carbon dioxide) and XPS were employed, respectively, to quantify the acid groups in the functionalised SWCNTs (F-SWCNTs) and the type of functional groups attached onto the SWCNTs. While the electronic nature of the SWCNTs was analysed through the line-shape of the G-band, the 2D band of the Raman spectra and the UV-Vis-NIR spectra, their morphological characterisation was done using a high resolution transmission electron microscope (HRTEM). Exploiting the advantages of each characterization techniques, the reflux time for the effective functionalization of SWCNTs, without any compromise of their quality, was converged down to 4 h. This paper proposes a new mechanism to account for the multistage oxidation with the extension of reflux time and explain the type of functional groups attached onto the surface of SWCNTs as functionalization proceeds with time. It is also claimed that the changes in the relative concentration of functionalized groups on the SWCNT surface are directly proportional to the increase in the extent of functionalization. Significantly, this paper reports that the introduction of any desired ratio of functional groups on the surface of carbon nanotubes can be achieved by tuning the extent of functionalization.