Rita Khanna

The exploration, understanding and potential applications of ‘Carbyne’, the one-dimensional sp allotrope of carbon, have been severely limited due to its extreme reactivity and a tendency for highly exothermic cross-linking. Due to ill-defined materials, limited characterization and a lack of compelling definitive evidence, even the existence of linear carbons has been questioned. We report a first-ever investigation on the formation of carbyne-like materials during low temperature pyrolysis of biobased lignin, a natural bioresource. The presence of carbyne was confirmed by detecting acetylenic –C≡C– bonds in lignin chars using NMR, Raman and FTIR spectroscopies. The crystallographic structure of this phase was determined as hexagonal: a = 6.052 Å, c = 6.96 Å from x-ray diffraction results. HRSEM images on lignin chars showed that the carbyne phase was present as nanoscale flakes/fibers (~10 nm thick) dispersed in an organic matrix and showed no sign of overlapping or physical contact. These nanostructures did not show any tendency towards cross-linking, but preferred to branch out instead. Overcoming key issues/challenges associated with their formation and stability, this study presents a novel approach for producing a stable condensed phase of sp-bonded linear carbons from a low-cost, naturally abundant, and renewable bioresource.

Light-weight ferro-aluminium alloys are finding increasing application in the transport sector to reduce overall weights, energy costs and CO₂ emissions. As the primary production processes of both Fe and Al are among the most energy-intensive industrial processes in the world, there is an urgent need to develop alternate routes for producing Fe-Al alloys. Our group has successfully produced these alloys in the Fe₂O₃-Al₂O₃-C system by producing molten iron in situ, followed by the reduction of alumina at 1550 °C and pick-up of Al by Fe. In this article, we report on the influence of silica, a typical impurity present in iron oxide and reductant carbon, on the reduction reactions in this system, and on the formation of ferroalloys. In-depth investigations were carried out on the Fe₂O₃-SiO₂-C and Fe₂O₃-Al₂O₃-SiO₂-C systems at 1550 °C for times of up to 60 min. Detailed HRSEM/EDS and XRD analysis was carried on the quenched reaction products recovered after various heat treatments. A complete reduction of silica and alumina was observed in the Fe₂O₃-SiO₂-C system, along with the formation of FeSi and SiC. The reduction reactions were relatively slow in the Fe₂O₃-Al₂O₃-SiO₂-C system. While the formation of SiC, FeSi and mullite (Al₆Si₂O₁₃) was observed, even small amounts of Fe-Al alloys could not be detected. The presence of silica impurities reduced the formation of Fe-Al to negligible levels by depleting molten iron from the reaction zone, a key ingredient for the low-temperature carbothermic reduction of alumina. This study shows that some impurities can be highly detrimental to the reaction kinetics and the formation of ferroalloys, and great care needs to be exercised during the choice of reaction constituents.

Carbon bearing industrial/commercial waste is difficult to recycle and a significant fraction is generally landfilled. With an aim to utilize such waste as carbon resources for iron and steelmaking, high temperature pyrolysis investigations are carried out on three waste polymers: waste CDs (compact discs), carbon fiber reinforced polymers (CFRPs), and Bakelite. These materials are heat treated in the temperature range 1000–1550 °C for 15 min in argon atmosphere and are subsequently quenched. Detailed structural and compositional characterization is carried out on recovered chars using a variety of analytical techniques: LECO, X‐ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy, and BET surface area measurements. Significant differences are observed in various chars recovered from these three waste polymers under investigation. With carbon contents in chars from 65 to 98%, surface areas from 2.2 to 274 m² g⁻¹ and structural order from amorphous to graphitic, these chars present a wide spectrum of carbon characteristics. These properties are evaluated toward their utilization during lower temperature carburization of iron.

The degradation behavior of alumina (10–20 wt%) carbon refractories was investigated during high temperature (1 550 °C) contact with a ternary casting mould meniscus slag containing 50% MnO, 25% SiO₂, and 25% Al₂O₃ and a binary slag containing 40% MnO and 60% SiO₂. Using the sessile drop approach, the transient progress of corrosion reactions was investigated as a function of time and refractory composition. An in‐depth characterization and analysis of reacted assemblies was carried out using optical and scanning electron microscopy (SEM). Optical micrographs showed a significant penetration of both slags within the refractory substrate, with very little slag remaining behind after 15 min of contact. The depth of penetration of ternary slag was found to increase with carbon concentration in the refractory. An all‐round corrosion was observed with extensive refractory degradation over a period of time. Corrosion was determined to a great extent by dissolution reactions in the interfacial region; alumina dissolution from the refractory resulted in the formation of needle‐like corundum crystallites which transformed to a cohesive network of faceted corundum crystals on extended contact. A number of reaction products containing Mn and Si were also observed.

We report an investigation on the corrosion behavior of ZrO₂–graphite insert in submerged entry nozzles (SEN) during its high temperature interaction with the mould flux focused specifically on the role of glaze coating. A detailed metallographic examination of the representative samples collected at different stages of its usage was carried out to examine the transient progress of corrosion. The interaction between the glaze material and the base refractory at the typical preheating temperature of SEN initiated the degradation of the partially stabilized ZrO₂ grains due to the formation of reaction products. Clear evidence is presented to show that the reaction product and the original layer of glaze coating survived after 90 min of casting. Early stages of corrosion involved the progressive congruent dissolution of reaction products and the residual glaze phase into the mould flux. Due to the absence of the glaze layer in the later stages of operation (480 min), corrosion was caused by the fragmentation of the aggregate phase and structural damage. This work highlights the importance of compositional control and coating thickness of the glaze material on the ZrO₂–graphite refractory insert.