D.K. Mishra

Synthesis of β-SiC Powder from Bamboo Leaf in a DC Extended Thermal Plasma Reactor

Fine silicon carbide powder was synthesized from bamboo leaf in a DC thermal plasma reactor through a single step process. With an applying current of 300 amp and 50 V voltages, the optimum duration of conversion of silica rich bamboo leaf to silicon carbide is 20 minutes. X-ray diffraction (XRD) results reveal that the final product is identified as β-SiC having lattice parameter a = 4.295 Å, which is in close agreement with the reported value of 4.347 Å. The scanning electron microscope (SEM) micrograph clearly shows the formation of cubical particles of β-SiC. The micro-Raman and X-ray photoelectron spectroscopy (XPS) analysis also confirm the formation of β-SiC phase.

Oxygen vacancy mediated large magnetization in chemically synthesized Ni-doped HfO2 nanoparticle powder samples

A cost-effective solution based chemical method of synthesizing nanostructured Hf1−xNixO2 with 0 ≤ x ≤ 0.05 in powder form, from easily available laboratory reagents is presented. Production of uniformly shaped and sized (13–16 nm) nanoparticles with excellent crystallinity is demonstrated by transmission electron microscopy, x-ray diffraction (XRD) studies and Raman spectra. The origin of ferromagnetism in the Ni-doped HfO2 nanoparticle powder samples is investigated. Magnetization studies along with x-ray photoelectron spectroscopy (XPS) studies suggest that some of the Ni-ions are substitutionally incorporated in HfO2 host matrix. The XPS studies also show the presence of a small fraction of Ni metal (most likely Ni nanoclusters), undetected in standard XRD for lightly doped samples, suggesting that the observed room temperature ferromagnetism is at least partly due to Ni nanoclusters. The observed large value (∼6 emu/g) of magnetization, may not be entirely due to the presence of Ni metal cluster, can...

Structural and Microstructural Properties of Fused ZrO2-Mullites

Silimanite and zircon rich sea beach sand is taken with alumina powder for the synthesis of fused zirconia mullite (MUZ) composites by extended arc thermal plasma reactor. The bulk density value of fused MUZ (∼3.79 g/cm3) is well comparable to the density value of commercial available MUZ (∼3.6 gm/cm3). The electron probe microstructure analysis predicts that alumina is rich in mullite grains, whereas the grain boundary region is rich with zirconia. A small percentage of zirconia is also present in the intragrain region, which reveals that mullite compound is surrounded by well-structured and compacted zirconia. The X-ray photoelectron spectrum reveals the presence of mullite phase along with crystalline Si in the composites.

Correlation between properties of zirconia mullite and Y2O3 stabilised zirconia mullite derived by various processing techniques

Abstract Abstract Zirconia mullite (MUZ) and Y2O3–MUZ composites were synthesised by plasma melting, plasma sintering and conventional sintering techniques. Mixtures of tetragonal and cubic phases have been observed in all the processed Y2O3–MUZ composites. This observation infers that though the available temperature in plasma sintered and conventionally sintered MUZ specimens is not sufficient for the transformation of monoclinic to cubic zirconia, the addition of Y2O3 favours this transformation and also stabilises the cubic zirconia phase at room temperature. The optical absorption studies completely reflect the improvement in optical band gap of Y2O3–MUZ composites to prove it as a suitable candidate for refractory applications. The bulk density, hardness and higher crystalline nature of plasma sintered composites indicate that better quality of products can be synthesised by direct current extended arc thermal plasma heating technique within a short duration of time.

Lattice Defect Induced Ferromagnetism In Implanted ZnO Single Crystal

Room temperature ferromagnetism (RTFM) is observed in 5 and 7% Ar implanted ZnO single crystals after annealing the implanted ZnO single crystals at 750 °C for seven hours. The presence of oxygen vacancies in 5 and 7% Ar implanted ZnO samples is the main reason of showing RTFM. There is no contribution of magnetism from Ar ions. But Ar ions play a major role in creating lattice defects with the increase of incident ion fluencies.

Influence of ultrasonic cavitation on microstructure and mechanical response of an aluminum/alumina nanocomposite

Abstract Nanocomposites of Al and Al2O3 were synthesized by an ultrasonic full cavitation technique which is a novel route for synthesis of uniformly distributed nanoparticles in metal matrix composites. The transmission electron micrograph indicates the uniform arrangement of nanoparticles throughout the metal matrix and the average size of the nanoparticles are in the order of 5 nm. The selected area electron diffraction analysis shows the presence of both Al and Al2O3 phases, which is also evidenced from the X-ray photoelectron spectroscopy analysis. The significant improvement in hardness and Young’s modulus due to the addition of a low weight fraction of nano-sized Al2O3 in aluminium infers that alumina nanoparticulates are distributed uniformly throughout the aluminium metal matrix. Hence, this paper shows a new method for inexpensive fabrication of bulk light weight metal matrix nanocomposites (MMNCs) by the use of noncontact full cavitation method.

Optical and Micro-Raman Characterization of Fused Mullite Prepared from Beach Sand Sillimanite

Plasma-fused mullite compounds were prepared from beach sand sillimanite with varying sillimanite and alumina ratio (60:40 = MU1, 65:35 = MU2, and 75:25 = MU3) within five minutes of thermal plasma treatment. The X-ray diffraction (XRD) and micro-Raman studies indicate the presence of corundum phase in MU1 and MU2 compounds, whereas no signature of corundum phase is evident in MU3. This observation confirms that sillimanite and alumina taken in the ratio 75:25 (MU3) are exactly in the appropriate proportion for the complete conversion of mullite. The bulk density is higher in fused MU3 as compared to other two compositions. The optical band gap measured using UV-Visible spectrophotometer for this composition is found to be 3.37 eV.

Process integration for material synthesis from a deactivated catalyst: Studies on the interaction of metal ions between two immiscible phases

Present investigation deals with the treatment of deactivated Co-Mn bromide catalyst for the recovery of Co and Mn as Co metal powder and chemical manganese dioxide by an integrated process comprising of a selective metal ion transfer from an aqueous solution containing a mixture of metal ions with a saponified solution of di-2ethyl-hexyl phosphoric acid, followed by selective scrubbing and metal stripping. The pure metal solutions so obtained were subjected to precipitation and hydrothermal treatment to obtain a desired material. The deactivated catalyst was leached by H2SO4 in presence of H2O2 followed by removing Fe, Si etc. The purified leach liquor of composition: 6.9g/L Co, 9.4g/L Mn was used for detail study to optimize the best conditions for the separation of Co from Mn. Experimental observations show that the extraction of both increased with increasing equilibrium pH and the concentration of the organic, with a separation factor of about 10, at equilibrium pH of 3. A quantitative extraction of Mn was possible with 20% D2EHPA in three stage counter-current extraction. After Co scrubbing, Mn was stripped with dilute H2SO4 and high pure spherical shaped CMD was produced. Co in the raffinate was recovered as powder by hydrothermal H2- reduction.

Selective Production of Co and Ni Powders Through Hydrothermal Reduction of Leach Solutions of a Synthetic Matte Containing Cu-Ni-Co-Fe-S

Synthesis of metal powders with tailored characteristics, such as those of Cu, Ni & Co has been the subject of much attention during the past decades. This is due to their potential technological applications in several critical & emerging areas, e.g. in the manufacturing of energy storing devices, optoelectronic and magnetic recording media, high end catalysts, etc. etc. In recent years, nano particles of nickel have found applications as electrodes in multi layer ceramic capacitors (MLCC) due to their excellent electrical conductivity, high melting temperature & low cost [1–3]. Similarly, fine cobalt powders are one of the main constituent for manufacture of rare-earth based permanent magnets [4].

A Comparative Study of CaO-MUZ Composites Elaboration by Plasma Melting and Sintering Techniques

CaO doped zirconia mullite (CaO-MUZ) samples were synthesized through plasma melting, plasma sintering, and conventional sintering using plasma reactor and high temperature furnace as the heating sources. The compositional ratio (wt) of silimanite, alumina, and zircon were taken as 47:38:15, and 4 wt% of CaO was added to the above compositional ratio for the synthesis of CaO-MUZ. A mixture of tetragonal and cubic zirconia phases have been observed in all the processed CaO-MUZ composites. This observation infers that though the available temperature in plasma sintered and conventionally sintered MUZ specimens is not sufficient for the transformation of monoclinic zirconia to cubic zirconia, the addition of CaO favors this transformation. The arrangement of close compacted small and large crystal grains in conventionally sintered specimen increases the bulk density, while the hardness remains lower in comparison to the plasma-sintered CaO-MUZ. The optical bandgap measurements predict that the CaO-MUZ composites can be used as suitable refractory materials for ceramic industrial applications. We report the suitability of heating sources and the impact of melting and sintering techniques on the structural, microstructural, mechanical, and optical properties of CaO-MUZ, so that one can choose appropriate synthesis techniques to achieve the desired product at the industrial scale.