Vol 27, No 3 (2018)

Cellulose-assisted combustion synthesis is a simple and effective continuous synthesis method that emerged almost a decade ago and now witnessing exponential growth in research interest and application. The simplicity of the process and easily scalable nature makes it appropriate for industrial scale synthesis of nanomaterials with high surface area and large porosity. Over the past few years, catalysis community has devoted considerable efforts in exploiting these properties borne naturally in combustion-synthesized materials such as complex surface structure and large porous volume providing suitable surface sites for catalytic reactions. In this review article, we plan to gather this development in the cellulose-assisted combustion synthesis and gain some insights related to possible future outlook and research needs.

Flameless combustion of 40% Fe₂O₃ – 40% RDX – 20% HDI (mix I) and 30% CoCO₃ – 15% iron formate – 40% RDX – 15% HDI (mix II) systems was explored by time-resolved X-ray diffraction (TRXRD). In case of mix I, the reaction was found to proceed via the formation of FeO intermediate: Fe₂O₃ → FeO → Fe₃O₄. Variation in the extent of iron reduction was associated with dynamic temperature change and a reductant content of the reaction zone. The reduction proceeded as a solid-state reaction, without amorphization of the structure. The process in system II involved the formation of CoO and FeO intermediates. Further reduction – up to metals – takes place behind the combustion front and yields a mixture of nanosized Co, Fe, and Co_0.7Fe_0.3 particles. Exposure of hot reaction products – nano-sized Co and Fe – to the air leads to their self-ignition and formation of Co₃O₄ and Fe₃O₄, respectively.

The effect of copper doping on cobalt ferrites Cu_xCo_1–xFe₂O₄ (x = 0, 0.4, 1.0) prepared by solid-state method was studied in detail. According to XRD results, the Co–Cu ferrites calcined at 800°C exhibited better crystallinity. Average crystallite sizes varied within the range 18–29 nm. The infrared spectra revealed two principal absorption bands, the high-frequency one ν₁ around 600 cm⁻¹ and the low-frequency one ν₂ around 400 cm⁻¹, attributed to stretching vibrations of the oxygen–metal bond in the tetrahedral (A) and octahedral (B) sites in the spinel lattice, respectively. The electrical properties of the material were semiconducting in their character. The results were used to obtain the following parameters: force constants for tetrahedral (K_t) and octahedral sites (K_o), Young’s modulus (E), rigidity modulus (G), bulk modulus (B), micro strain (ε), Debye temperature (Θ_D), X-ray density (ρ_X), dislocation density (ρ_D), transverse (V_t) and longitudinal (V_l) wave velocities.