Two types of magnesium-aluminate spinels, one commercially available as preformed powder and the other prepared from cheaper precursors by the sol-gel route as a semidried reactive mass, were characterized in terms of particle size distribution, XRD phase evolution and chemical composition. These two were incorporated in a high alumina based refractory castable in different concentrations and fired at elevated temperatures. Those preformed and in situ spinel bonded castables were characterized in terms of bulk density, apparent porosity, cold crushing strength, thermal shock resistance, volume shrinkage, flexural strength, XRD, SEM, EDS and slag corrosion resistance test to understand the effect of both kinds of spinel in the castable composition. © 2003 Elsevier Ltd and Techna S.r.l. All rights reserved.

SUNANDA MUKHOPADHYAY

Chemical Technology

PODDAR P K DAS

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Effect of preformed and in situ spinels on microstructure and properties of a low cement refractory castable

Ceramics International

This study has been carried out on castable and matrix of a magnesia-based unshaped refractory system containing respectively 5.0% and 20.0% graphites. The graphite has been incorporated either as uncoated or surface-modified form, the latter containing a thin sol-gel calcium aluminate film over graphite surface. Surface modification of graphite has been confirmed by scanning electron microscopy, X-ray diffraction, Raman spectra, Fourier transformed infrared study and some other experiments. The sol-gel coating improved hydrophilicity and oxidation resistance of graphite. Sinterability, thermal and thermomechanical properties of castable matrices have been elaborately documented. From this work it is apparent that presence of coated graphite in matrix part of basic castable is not that encouraging as observed in alumina-carbon system. However, the castable properties as a whole are satisfactory due to protection of graphite and its less water demand for casting. © 2017 Indian Ceramic Society.

Transactions of the Indian Ceramic Society

Thermomechanical Characteristics of Low Carbon Magnesia-Based Monolithic Refractory Containing Nanostructured Surface-Modified Graphites in Matrix

Some newer insights had been reported in this paper on synthesis and application of calcium aluminate coated graphite in alumina–carbon refractory castables. The course of evolution of AlO4 (tetrahedral) and AlO6 (octahedral) units in the nanocoating was investigated by XRD (X-ray diffraction), Raman spectroscopy and FTIR (Fourier transformed infrared spectroscopy) studies. An extended research on the resemblance and disparity between sol–gel and conventional refractory cements were also explored. FESEM (Field Emission Scanning Electron Microscopy), XRD of coated and uncoated graphites had been revisited with a special study on ESEM (environmental scanning electron microscopy) of those two. The hydrophilic thin film containing Ca-doped γ-Al2O3 phases rendered a decisive influence on graphite retention in castable matrix. A comparison between pore size distribution and thermogravimetric analysis (TGA) of two fired castable refractories advocated the superiority of the one containing coated graphite. Determination of corrosion and penetration indices by the static slag corrosion test, supplemented with microstructural studies, confirmed that the less porous castable containing coated graphites excelled again in the harsh environment. © 2015 Elsevier Ltd and Techna Group S.r.l.

In depth studies on cementitious nanocoatings on graphite for its contribution in corrosion resistance of alumina based refractory composite

The synthesis and properties of high alumina castable containing nanostructured calcium aluminate coated graphite were studied in terms of slag resistance and overall physical characteristics. Raman spectroscopy, BET surface area and field emission scanning electron microscopy (FESEM) were performed to exclusively understand the coating characteristics and its compatibility in refractory composite. The coating not only secured graphite in castable for prolonged period but also noticeably improved matrix to aggregate contact. The microstructural aspects of castables were investigated, with special emphasis on a representative matrix prepared and infiltrated with slag at elevated temperature. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of fired composite containing surface-treated graphite was quite prospective. It circumvented the problems of incorporating as-received graphite in castables and should be in the attention of refractory researchers and producers. © 2013 Elsevier Ltd. All rights reserved.

Materials Research Bulletin

Nanoscale calcium aluminate coated graphite for improved performance of alumina based monolithic refractory composite

The performance of high alumina castables containing mullite and spinel coated graphites was investigated to explore their commercial application in carbon containing refractory composites. It was compared in terms of thermal shock resistance, refractoriness under load, static slag resistance test, pore size distribution, and physical properties, e.g., apparent porosity and cold crushing strength. The microstructures of these two castables, along with the other containing uncoated graphites, were also studied. Differential thermal analysis and X-ray diffraction patterns of heat-treated carbon-containing castable composites have also been noted. Castables containing mullite-coated graphite were found to be more resistant to repeated thermal shock cycles, whereas those containing spinel-coated graphites were more encouraging when slag resistance and overall physical properties are concerned. © 2012 Copyright Taylor and Francis Group, LLC.

Materials and Manufacturing Processes

Characteristics of refractory castables containing mullite and spinel coated graphites

Selected physical and thermal properties of conventional spinel-alumina castables were compared with those of castables produced using spinel fines prepared from a prepared gel. Limited numbers of hydroxyl groups created around the spinel precursor helped to improve thermal shock resistance. Micrographic examination confirmed that retained nanodimensional spinels firmly connected the hibonite and corundum grains in the castable, developing multiple interfaces after densification. Castable-containing spinel with excess alumina powder was found to have the best combination of bulk density, apparent porosity, and hot modulus of rupture. The reactive magnesia fine used to prepare in situ spinel-bonded castable was not found to give satisfactory results, owing to progressive disintegration of brucite-type compounds and abnormally grown spinels. Thermal characteristics of castables were assessed by differential thermal analysis (DTA), measurement of porosity, and percent linear change (PLC). Transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS) analysis of the gel-derived spinel and castable confirmed their differences, particularly with commercial spinel having comparable chemistry but lacking nanocrystalline structure.

Journal	Data powered by TypesetCeramics International
Publisher	Data powered by TypesetELSEVIER SCI LTD
ISSN	0272-8842
Open Access	No