Ramani Venugopalan

Preoxidation and hydrogen reduction of ilmenite in a fiuidized bed reactor

Studies on preoxidation and hydrogen reduction of Quilon-grade ilmenite have been carried out in a fluidized bed reactor. During preoxidation, the effect of various parameters such as temperature, gas flow rate, and period of reaction has been studied. Hydrogen reduction studies have been carried out both for raw and preoxidized ilmenite. Results obtained on the conversion rate of iron oxide to metallic iron for the preoxidation as well as the reduction period showed three distinct stages: (1) initial slow induction stage; (2) intermediate acceleratory stage; and (3) final slowing down process. Kinetic data plot on -In (1 -x) vs time for metallization of iron oxide showed a linear trend for preoxidation and hydrogen reduction.

Morphological study of SiC coating developed on 2D carbon composites using MTS precursor in a hot-wall vertical reactor

Abstract Silicon carbide coating was developed using chemical vapor deposition on carbon substrate as a protective coating. The present studies were carried out with methyl trichlorosilane as the SiC precursor, at 1673 K along with hydrogen and argon as carrier gas using a high-temperature vertical graphite reactor. The SiC coatings were characterized by means of X-ray diffraction for phase identification. Scanning electron microscopy analysis with energy dispersive X-ray spectrometer was also carried out for microstructure and elemental analysis. From the morphological study of different SiC deposits obtained at varying operating parameters it was observed that methyl trichlorosilane feed rate and hydrogen flow rate play a major role in deciding the nature of deposits and the argon percentage in the mixed gas also plays a vital role.

Study of properties of SiC layer in TRISO coated particles grown using different alkyl-silicon compounds

The silicon carbide (SiC) layer used for the formation of Tri-isostatic (TRISO) coated fuel particles is normally produced at high temperatures via fluidized bed chemical vapor deposition from methyltrichlorosilane (MTS) in a hydrogen environment. In this work, we show the deposition of uniform SiC layers using different organosilicon precursors such as MTS and hexamethyldisilane (HMDS) via spouted bed chemical vapor deposition. From the X-ray diffraction pattern it could be inferred that the SiC deposits obtained through different precursors have the β-SiC phase. The microstructure and mechanical properties of the fabricated SiC coating were studied. The hardness and fracture toughness of the fabricated SiC coatings using MTS and HMDS were nearly the same and close to the theoretical value for pure silicon carbide.

Studies on nickel nanoparticle attachment on surface modified carbon nanotubes by wet chemical method

Wet chemical method is a relatively simple technique, which has been used for attaching nickel nanoparticles homogeneously on multi-walled carbon nanotubes (MWCNT). The MWCNT was synthesised by catalytic chemical vapour deposition (CCVD) method. The surface of MWCNT was modified by treating with boiling conc. nitric acid. Carbon nanotubes dispersed in nickel nitrate solution were heat treated with particular heating rate of 8°C/min from room temperature to 100°C under argon atmosphere and soaked at this temperature for 1 h before heating to 500°C at 4°C/min. The resultant product is found to be nanostructured nickel oxide attached to MWCNT. Subsequent reduction of the metal oxide in hydrogen atmosphere yielded nickel nanoparticles anchored to the surface of nanotubes. Chemical impregnation resulted in homogeneously dispersed nickel particles on the surface of oxidised MWCNT whereas in the case of unoxidised MWCNT uneven dispersion of nickel particle was observed. Results obtained on the characterisation of the products from XRD, SEM, TEM and EDX are presented. This simple method could allow large-scale production of functionalised MWCNT, which can be used as catalyst supports with high stability.

Mathematical modelling of a ternary particle system for determining the critical size ratio in a chemically reacting condition

The paper discusses the effect of particle size ratios in a chemically reacting condition for a typical case of the preparation of vanadium carbide by aluminothermic reduction followed by in situ carburization. The ternary particle system involved in this preparation is comprised of vanadium oxide, aluminium (Al) and carbon (C). A mathematical model has been developed to predict the critical particle size ratio of the oxides of vanadium and Al, which would give the best possible arrangement of the reductant and oxides of vanadium to satisfy the stoichiometry as well as the monolayer formation of fines over the carrier (coarse) particle for the efficient reduction reaction. This model also helps the selection of the C particle size, which is the third component of the ternary system chosen in this study.

The development and characterisation of carbon nanotubes grown on conductive substrate for field emission application

The CNT-inconel interface exhibhits good electrical contact as well as strong adhesion to be used directly as electrodes for super capacitors and field emitters without any post growth processing with respect to other metal substrate. Carbon nano tubes were synthesized on inconel substrate over the 10*10 mm2 area by catalytic decomposition of ferrocene - Xylene mixture at 800°C. The growth process involved injecting a solution of particular concentration of ferrocene in xylene at a particular flow rate into a preheating zone of reactor. A mixture of argon and hydrogen was used to carry the xylene containing catalyst vapors upto substrate. Scanning electron microscopy (SEM) and Raman Spectroscopy investigations reveal that the nanotubes are multi-wall CNTs having about 40-70 nm diameter. The possibility of growing CNTs on the metal substrates other than silicon has been confirmed from the above results.