Abhijit Dey

Graphene-iron oxide nanocomposite (GINC): an efficient catalyst for ammonium perchlorate (AP) decomposition and burn rate enhancer for AP based composite propellant

A facile and ecofriendly method for the synthesis of nano-sized iron oxide (Fe2O3) decorated graphene (GINC) hybrid by ultrasonication via microwave irradiation has been developed. During this process, nano-sized Fe2O3 particles with a size of approximately 20–30 nm were uniformly decorated over a graphene sheet. The nanohybrid was characterized by XRD, HRTEM, Raman spectroscopy and Raman mapping. To study the enhancement of catalytic activity of iron oxide by preparing GINC, several AP based compositions containing 1–5 weight% GINC were made and characterized through simultaneous thermal analysis (STA). Along with this, formulations with other catalysts with 1–5 weight% concentrations were also prepared and evaluated. Experimental results showed that GINC with 5 weight% concentration was considerably more effective as compared to other compositions. To further extend this application as a burn rate enhancer in composite propellants, several formulations of composite propellants containing 1 part of different burn rate enhancers, such as Fe2O3, nano-sized Fe2O3 and GINC, were prepared and evaluated using theoretical prediction, viscosity, ballistic properties, sensitivity parameter and thermophysical properties. To quantify the burn rate enhancement in the presence of GINC, burn rate measurement, STA, DSC and activation energy calculation were performed. The results show that the burn rate of propellant increases from micron-sized Fe2O3 (30% increases) to nano-sized Fe2O3 (37% increase). In the presence of GINC, a significant increase (52%) in burn rate is achieved. In GINC, effective iron content is about 50% as compared to nano- and micron-sized Fe2O3. Hence, GINC was found to be an excellent burn rate modifier for an advanced AP based propellant system.

One pot green synthesis of graphene–iron oxide nanocomposite (GINC): an efficient material for enhancement of thermoelectric performance

We report for the first time, a green method for graphene–iron oxide nanocomposite (GINC) synthesis by dispersing graphene and nano iron oxide (Fe2O3) in ethanol via ultrasonication followed by micro-wave irradiation. This is a simple method of making a broader range of graphene–metal oxide nanocomposites with excellent dispersion of 3D nanoparticles over 2D graphene. In addition, we have also demonstrated the synthesis of highly conductive PVAc–GINC and PVAc–graphene composites by ultrasonication followed by hot compaction for thermoelectric application. Graphene and GINC concentration were judiciously varied and optimized for the sake of high electrical conductivity and Seebeck coefficient. The fabricated PVAc–GINC film exhibited a conductivity of 2.18 × 104 S m−1 with a Seebeck coefficient of 38.8 μV K−1. Hence, the power factor (PF) reaches 32.90 μW m−1 K−2, which is 27 fold higher than the thermoelectric material based on PVAc–graphene composite. This PF value is found to be the maximal ever reported without using conducting polymer.

A graphene titanium dioxide nanocomposite (GTNC): one pot green synthesis and its application in a solid rocket propellant

A green process was developed for a graphene–titanium dioxide nanocomposite (GTNC) synthesis by dispersing titanium dioxide (TiO2) nanoparticles and graphene nano-sheets (GNSs) in ethanol via ultrasonication followed by microwave irradiation. The synthesized GTNC was well characterized by various tools: viz. XRD, HRTEM, FTIR and Raman spectroscopy. Also, Simultaneous Thermal Analysis (STA) and Differential Scanning Calorimetry (DSC) techniques have been employed to study the enhancement of the catalytic activity of the GTNC for the decomposition of Ammonium perchlroate (AP). The GTNC with 5 wt% in AP was found to be a highly effective catalyst for the AP decomposition. The decomposition temperature decreases from 412.87 °C to 372.50 °C and ΔH increases from 2053 to 3903 J g−1. Furthermore, the GTNC was identified as an effective burn rate enhancer (i.e. combustion catalyst) for an AP based composite propellant for solid rocket propellants as confirmed by STA, DSC, activation energy calculations and burn rate measurements. The results show that the burn rate of the propellant increases by 24% for the TiO2 nanoparticle based composition compared to the base composition, whereas a significant increase of 50% is achieved in the presence of the GTNC. Hence, the performance is improved significantly for the solid rocket propellant.

PVAc/PEDOT:PSS/graphene–iron oxide nanocomposite (GINC): an efficient thermoelectric material

A green method for the synthesis of a graphene–iron oxide nanocomposite (GINC) and its PVAc based polymer nanocomposites was reported in an earlier communication. The fabricated PVAc–GINC film exhibited a conductivity of 2.18 × 104 S m−1 with a Seebeck coefficient of 38.8 μV K−1. Hence, the power factor (PF) reached a value of 32.90 μW m−1 K−2 which is 27 fold higher than a thermoelectric material based on a PVAc–graphene composite as reported in the contemporary literature. In continuation of the above mentioned study, PEDOT:PSS was used to further enhance the power factor (PT) and figure of merit (ZT) of the system. During evaluation, a PEDOT:PSS/GINC composite (5 : 95) showed a remarkable increase in various thermoelectric properties like electrical conductivity (8.0 × 104 S m−1) with a Seebeck coefficient of 25.42 μV K−1 and thermal conductivity 0.90 W m−1 K−1. Hence PF and ZT reach up to 51.93 μW m−1 K−2 and 0.017, respectively. To improve the mechanical strength of the polymer composite, cellulose fibre was also employed. By the addition of cellulose fibre, though the mechanical strength of the composite increases the PF reaches 5.6, which is 10 times lower than the PEDOT:PSS/GINC composite.

Band engineered p-type RGO–CdS–PANI ternary nanocomposites for thermoelectric applications

A ternary hybrid nanocomposite of RGO–CdS–polyaniline (PANI) is prepared by a simple two stage in situ method for its thermoelectric studies. For this purpose, CdS quantum dots were first prepared with varying concentrations in the presence of reduced graphene oxide to form RGO–CdS nanocomposites using 3-mercaptopropionic acid as a linker. Polyaniline was then prepared in situ in the presence of RGO–CdS nanocomposites to eventually obtain RGO–CdS–PANI nanocomposites. The electrical conductivity, Seebeck coefficient and power factor of the RGO–CdS–PANI nanocomposites were calculated with various loadings of RGO–CdS nanocomposites in PANI. The final RGO–CdS–PANI nanocomposites delivered a high electric conductivity in the order of 105 S m−1 and showed strong re-dispersion in DMF and ethanol. The effective band alignment and decreased thermal conductivity in RGO–CdS–PANI nanocomposites resulted in p-type behaviour and a high power factor value.

Calculation of enthalpies of formation and band gaps of polymeric binders

Enthalpies of formation and band gaps of polymeric binders are important parameters to consider when designing compositions of explosives and propellants. We have used computational methods to determine enthalpies of formation and band gaps of polymeric binders. Initially, we computed the enthalpy of formation of the known non-energetic binder hydroxy terminated polybutadiene (HTPB), and the value obtained is close to that of its experimentally determined enthalpy of formation. The applied computational methodology has also been validated by the calculation of enthalpies of formation for the known energetic binder glycidyl azide polymer GAP. Furthermore, enthalpy of formation of azido HTPB (AHTPB) was calculated, which indicates that the addition of the azido group helps produce an energetic, insensitive and compatible polymeric binder. In this study, enthalpy of formation of the polymer was determined by extrapolating the results of the calculations carried out on monomers and oligomers, whereas periodic boundary condition (PBC) computations were carried out on the dimers to obtain band gap values of polymers. Highly positive enthalpies of formation of oligomers of AHTPB compared to those of HTPB and GAP suggests that AHTPB can be a potentially energetic binder in explosive compositions. Analysis of periodic boundary condition (PBC) – frontier molecular orbital band gap studies suggests that stabilities or insensitivities of these polymeric binders are in the order: HTPB > GAP > AHTPB. A superior curable nature of AHTPB over HTPB is indicated by the calculation of interaction energies. These results are vital in the quest for molecular-based predictions of polymer properties in general, but they are in particular encouraging for the study of polymers with monomers of relatively large molecular weight.

Polymer based graphene/zinc oxide nano crystal (GZnNC): an outstanding thermoelectrical energy conversion material

This work presents the synthesis of a new material, graphene/zinc oxide nano composite (GZnNC) by employing ultrasonication techniques where nano-ZnO and graphene nano-sheet have been dispersed in ethanol followed by microwave irradiation. The GZnNC was well characterized by XRD, HRTEM, FTIR, and Raman spectroscopy. Also, polymer based GZnNC has been subjected to the measurement of energy harvesting/thermoelectric properties. Present study includes PVAc, PVAc/PEDOT: PSS, and PEDOT: PSS based compositions with concentration variation of GZnNC/graphene and measurement of thermoelectric properties like electrical conductivity, Seebeck coefficient, power factor (PF), thermal conductivity and figure of merit(ZT). PEDOT: PSS/GZnNC composite showed the twelvefold increase in electrical conductivity and two times increase in Seebeck coefficient as compared to the PVAc-graphene composite. Interestingly, the calculated power factor for PEDOT: PSS/GZnNC composite increases up to 50 times as compared to PVAc/graphene composite. Thermal conductivity gets reduced to 3.01 W/mK Hence, figure of merit is reached up to 0.0051. This value is comparatively very high compare to the existing nanocomposites. Correspondence to: Arun K. Sikder, EMR Division, High Energy Material Research Lab, Sutarwadi, Pune-411021, India, E-mail: ak_sikder@rediffmail.com