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Magnesium aluminate spinel with an initial MgO: Al2O3 molar ratio of 2:1 was prepared from its constituent oxides through a solid-state sintering process at temperatures ranging from 1550 to 1700 °C in a normal air atmosphere. The effect of varying amount (0.25–1.0 wt%) of TiO2 and Yb2O3 on densification, phase assemblage, mechanical, thermo-mechanical properties and microstructure of magnesia-rich spinel were investigated under static heating condition. The addition of TiO2 and Yb2O3 favours the densification of magnesia-rich spinel, which is discernible up to 1650 °C. This beneficial effect may be attributed to the development of the secondary phase and formation of solid solution due to the dissolution of the additive ions in the spinel structure. A marginal increase in the average grain size of the samples along with a narrower grain size distribution occurred with the incorporation of both the additives. Both the additives improved the mechanical properties of the magnesia-rich spinel; however, better room temperature flexural strength was achieved with Yb2O3 as compared to TiO2 addition. For the samples sintered at 1550 °C, 1.0 wt% Yb2O3 addition resulted in 30% increase in flexural strength; however, same amount of TiO2 addition increased the strength by 20%. In case of thermal shock resistance, 1.0 wt% TiO2 and 0.25 wt% Yb2O3 addition demonstrated promising result among all the samples.

The thermal conductivity of the matrix part of alumina – carbon unshaped refractory has been estimated to accurately interpret its thermophysical and thermomechanical behavior. The properties of precalcined composite matrix containing either as-received or surface-modified graphite in equal quantity (20.0 wt%) have been investigated at three different temperatures (110,550,900 °C). The thermal compatibility or degradation of both kinds of carbonaceous matrices had been correlated with respective scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analyses. The monolithic matrices were also subjected to X-ray diffraction (XRD) studies to distinguish between their phase evolution patterns. A synergestic study on an equivalent graphite-free formulation was also carried out. The thermal shock resistance profile of respective castables had been addressed to confirm the superiority of surface-treated graphites. Nanoengineering at graphite surface was conceived by Rietveld analysis of the (004) peak that substantiated the additional influence of calcium aluminate coating on selective clumping and partial exfoliation of graphite sheets.

The present contribution focused mainly on the fundamental understanding of the influence of surface-modified graphite on rheology of the matrix of a castable slurry in comparison to the same containing the uncoated one. A special observation on the rheology of a graphite-free matrix of similar high alumina castable has been described. The change in rheological behavior due to the presence of other microfine constituents has also been noticed with a particular attention to the refractory cement bond. The variation in viscosity and shear stresses with shear rate of castable matrices containing as-received and surface-modified graphites has been compared. The ‘ball-in-hand’ consistency test of respective castables had also been differentiated. The effect of coated and uncoated graphites on the loss and storage moduli of the respective suspensions has been explored. Zeta potential values of individual constituents as well as the slurries have also been measured and correlated with the flow characteristics of castable matrices. The X-ray diffraction (XRD), SEM (scanning electron microscope) and EDS (energy dispersive spectroscopy) studies of the coated graphite have been observed to substantiate the flow pattern of the slurry. The physical properties of refractory castables at different temperatures have been estimated to supplement the rheological pattern.

Role of three rare earth oxides, viz., La2O3, CeO2 and Yb2O3 on reaction sintering of magnesium aluminate spinel having molar ratio of MgO:Al2O3 = 1:2 from its solid oxide precursors was investigated in static and dynamic heating conditions. Effect of these additives (3 wt%) on densification behavior, phase assemblage and microstructure development were studied in the temperatures of 1500–1700 °C. Yb2O3 enhanced the sintering of spinel, while La2O3 and CeO2 negatively impacted the sintering of magnesium aluminate spinel which can be discerned from the shrinkage curve of TMA as well as from static firing regime. This is ascribed to the formation of secondary phases in La2O3 and CeO2 containing samples which have different crystalline structures to that of spinel. This anisotropy due to different crystallinity hindered the pore shrinkage and pore removal and thereby retarded the densification. Whereas, the cubic structure of the secondary phase formed in Yb2O3 containing sample which is isotropic with the crystalline orientation of the parental spinel phase assisted the densification.

This paper deals with the preparation and evaluation of a zeolite prototype developed from an aluminosilicate precursor for its possible application as a hydrocracking catalyst. Aluminium nitrate and tetraethyl orthosilicate at definite proportions were the primary reagents for the gel synthesis. Nickel loading and stipulated post-synthesis treatment of the material are also addressed in this paper. The characteristics of the calcined aluminosilicate gel were estimated using X-ray diffraction (XRD), scanning electron microscope (SEM) study with energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) with thermogravimetry (TG) and Fourier-transformed infrared spectroscopy (FTIR) at different temperatures. A preliminary laboratory-scale investigation of hydrocracking performance of this zeolite prototype was also conducted.

The thermophysical and thermomechanical behavior of graphite-containing refractory castable matrix with 20.0 wt% of graphite had been compared with graphite-free high alumina based castable matrix analogous to it. The thermomechanical properties of similar type of castables with and without 5.0% of graphite had also been evaluated. Graphite was incorporated both as coated and as-received forms, the former having a thin sol-gel derived calcium aluminate coating on graphite flakes. The influence of thermal conductivity, thermal diffusivity and pore size distribution had been critically estimated. The changes in flexural strength, porosity and density of the matrices had also been determined to interpret the castable performance, namely refractoriness under load (RUL), spalling resistance and conventional physical properties. The role of coated graphite on improved densification and thermal tolerance of refractories was further explored by microstructure and phase evolution studies of all kinds of fired samples at 1500 °C. It was further supplemented with the scanning electron microscope (SEM) studies of surface-modified graphites at uncalcined and calcined condition.

This investigation entails our continued research on calcium aluminate coated graphite for application in alumina-carbon monolithic refractories. Surface treatment of graphite flakes by a scalable sol-gel route has been utilized to develop stable bonds between ceramic phases with the functionalized graphite sheets. This study has been primarily conducted to differentiate between the coating evolution pattern at green and calcined conditions. In this regard, C-H-N analysis, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), x-ray diffraction (XRD) with Rietveld analysis, Fourier transformed infrared spectroscopy (FTIR) and zeta potential studies of three kinds of graphites had been compared and critically estimated. These results were supplemented with thermogravimetry (TG), pore size distribution, oxidation resistance and scanning electron microscopy (SEM) of selected samples. A schematic outline of the work has also been proposed. An appreciable improvement of bulk density, apparent porosity and crushing strength of the respective castable has been correlated with the compatibility of the coating to the reactive matrix constituents of the refractory in wide temperature region (110-1500 degrees C).

The performance of alumina- and magnesia-based carbon-containing refractory castables, suitable for different sectors of steel plants, has been compared. Natural flaky graphites have been modified by their surface treatment via sol-gel route. The sustainability of graphite in oxidizing atmosphere was noticeably increased by this method with a synergistic possibility of pollution abatement. The hydrophilic nanocoatings of ceramic oxides derived by inorganic precursors reduced the water demand of the composite batch and simultaneously enhanced its oxidation resistance. The oxide coating compositions together with the precursor chemistry have been varied to substantiate their common beneficial features. Scanning electron microscopy (SEM), Raman spectroscopy, Differential thermal analysis (DTA), Thermogravimetry (TG), X-ray diffraction, thermal conductivity, and zeta-potential studies have been carried out to compare the influence of heat treatment on as-received and surface-modified graphites. The properties of refractory castables, namely, bulk density, apparent porosity, and cold crushing strength have been measured within wide temperature region (110–1500°C), to confirm the positive influence of nanoengineering on graphite surface. The sequence of important phase reactions during sintering of both the composite materials has been discussed. Finally the slag resistance behavior at aggressively fired condition has been investigated to corroborate the improved matrix characteristics due to coated graphites.

The sintering characteristics, phase composition, microstructure and optical properties of 1:1 ZnAl2O4 spinel doped with Ti4+ from 1.125 to 4.5 mole-% synthesized through coprecipitation were investigated in this study. Effective densification was achieved at a low sintering temperature, 1350°C after 1 h. Powder XRD patterns revealed that, besides ZnAl2O4 spinel and rutile as major crystalline phases, minor Zn2Ti3O8 phase was present in the sintered system, with its extent depending on the TiO2 content and sintering temperature. SEM micrographs demonstrated a coherent and uniformly distributed fine-grained microstructure in the fracture surfaces of the sintered Ti4+ doped ZnAl2O4 spinel ceramics body. The Tauc plot of Ti4+ doped ZnAl2O4 spinel exhibited a leftward shift of the band gap from 3.79 to 3.48 eV with increase of Ti4+ content from 0 to 4.5 mole-%. Ti4+ was observed to function as a normal grain growth accelerator during ZnAl2O4 sintering. This was probably due to enhanced grain boundary diffusion.

Here, we report the preparation of nano silver (Ag) and nano Ag-erbium (Ag–Er) co-embedded potassium–zinc-silicate based monolithic glass nanocomposites by a controlled heat-treatment process of precursor glasses. The nanocomposites were characterized by differential scanning calorimeter, dilatometer, UV–Visible absorption spectrophotometer, X-ray diffractometer and transmission electron microscope and spectroflurimeter. A strong surface plasmon resonance (SPR) band is observed around 430 nm in all the heat-treated glass nanocomposite samples due to the formation of Ag0 nanoparticles (NP). The Ag-glass nanocomposite samples display nearly 2-fold enhanced photoluminescence (PL) at 470 nm upon excitation at 290 nm until the size of the NP increases to the value equals to the mean free path of conduction electrons inside the particles. On contrary to this, the photoluminescence spectra of Er3+ ions exhibit a gradual decrease of NIR emission at 1540 nm due to 4I13/2 → 4I15/2 transition under excitation at 523 nm in the heat-treated glass nanocomposites which happened due to excitation energy transfer of Er3+ ions to the Ag NP, acting as ‘plasmonics diluents’ for Er3+ ions. These nanocomposites have huge potential for various nanophotonic applications.

The transparent willemite, Zn 2 SiO 4 (ZS) glass–ceramic nanocomposites were prepared from melt-quench derived ZnO–Al 2 O 3 –B 2 O 3 –SiO 2 (ZABS) precursor glass by an isothermal heat-treatment process. The generation of willemite crystal phase, size and morphology with increase in heat-treatment time was examined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 80–120 nm. The decreased refractive index with increase in heat-treatment time attributed to partial replacement of ZnO 4 units of willemite nanocrystals by AlO4 units and simultaneous generation of vacancies in the Zn-site. Fourier transform infrared (FTIR) reflection spectroscopy exhibits the structural evolution of willemite glass–ceramics. The photoluminescence spectra of Sm 3+ ions exhibit emission transitions of 4 G 5/2 → 6 H J ( J = 5/2, 7/2, 9/2, 11/2) and its excitation spectra shows an intense absorption band at 402 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 14-fold with crystallization into willemite.

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.

The Eu3+-doped novel precursor glass in the K2O-SiO2-SrO-Bi2O3-Ta2O5 system was prepared using the melt-quench technique. The transparent SrBi2Ta2O9 (SBT) glass-ceramic nanocomposites were derived from this glass using a controlled crystallization process. The formation of SBT crystal phase, size, and morphology with increase in heat-treatment time was examined using X-ray diffraction, field emission scanning electron microscopy, and fourier transform infrared transmission spectroscopy. Vicker's hardness study indicates marked improvement of hardness in the glass-ceramics compared to precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of D-5(0)-> F-7(j) (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 467 nm. These spectra reveal that the Eu3+ ions are gradually entering into the SBT nanocrystals present in the glass-ceramics. This study indicates that the incorporation of Eu3+ ions into SBT crystal lattice enhances the photoluminescence performance of the glass-ceramics by two-fold. It is believed that this work would generate significant impact in the exploration of SBT glass-ceramic nanocomposites.

Highlights: Black-Right-Pointing-Pointer Phase pure La{sub 1.95}Ca{sub 0.05}Zr{sub 2}O{sub 7-{delta}} (LCZ) material is prepared by combustion synthesis. Black-Right-Pointing-Pointer LCZ and Ni-LCZ bulk samples are prepared with theoretical density close to 100%. Black-Right-Pointing-Pointer Bulk electrical conductivity {approx}400 S/cm is obtained for Ni-LCZ cermet at 750 Degree-Sign C. -- Abstract: La{sub 1.95}Ca{sub 0.05}Zr{sub 2}O{sub 7-{delta}} (LCZ) and Ni-LCZ cermet have been prepared by combustion synthesis and conventional solid state mixing methods respectively. Both the materials are sintered in air and controlled atmosphere (5% H{sub 2} in Ar). The density obtained for the material sintered at 1400 Degree-Sign C in controlled atmosphere is found to be more than 99.5%. This sintering temperature (1400 Degree-Sign C) is considered to be much lower compared to the conventional sintering temperature. The corresponding total conductivity for such Ni-LCZ cermet materials is {approx}400 S/cm measured at 750 Degree-Sign C having 40 vol% of Ni and 60 vol% LCZ.

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.

Oxidation resistance and water wettability of graphite flakes have been improved by a thin sol-gel film of magnesium aluminate spinel (MgAl 2 O 4 ) over its surface. The hydrosol has been synthesized by less expensive precursors and the spinel formation has been studied by scanning electron microscopy (SEM), supplemented with energy dispersive spectral analysis. After an easy-to-use mixing procedure, drying (110°C), and subsequent calcination (550°C), coated graphites were sieved to below 75 μm. The coating over the powder contained 1.5 wt% MgAl 2 O 4 , which enormously increased the oxidation resistance (performed at 600°, 900°, and 1200°C) and water wettability, as revealed by hydrophilic functional groups from infrared spectra. Defective, intermediate spinel structure of fine, lamellar Mg-doped γ-Al 2 O 3 has been considered to be significant for this improvement. An approximate (1:2) stoichiometry of (Mg:Al) in the coating composition was confirmed by an X-ray photoelectron spectroscopy test. Castables prepared by this graphite remarkably improved their bulk density and apparent porosity compared with those prepared by the as-received graphite. Casting water was reduced along with the amount of antioxidants. This also enhanced the resistance toward the basic slag by retaining the graphite in the refractory.

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 ...

Polymeric monolithic doped zirconia and zirconia-alumina stiff gels (via stable zirconia and zirconia-alumina sols respectively), derived from Zr-n-propoxide, acetyl acetone, aluminium chloride, di-methyl formamide etc with judicious time-temperature-pH selection, have been prepared by controlled hydrolysis and polycondepsation, and subsequently subjected to heat treatment at 1300°C. The crystallization behaviour of the gels was studied by X-ray powder diffraction and differential thermal analysis. For the dried (25°C) composite gels pore size distributions were estimated. FTIR spectra (at 25° and 200°C) and scanning electron microscopy (at 25° and 1300°C) of both types of gels revealed that low temperature sintering is influenced by the addition of alumina sol in doped zirconia sol matrix to result in a better monolithicity. The microhardness of the fired composite gel was also determined.

This paper deals with the performance of alumina bearing sol, prepared through sol-gel route, when used as a bonding agent in low cement refractory castable composition. The physical properties of the samples prepared by different processing technique (tapping and vibration) are compared. The results indicate that the simple tapping technique may be a cost-effective solution in order to achieve desired high temperature properties. Also the increase in solid content by heat treatment of a particular sol upgrades its reactivity and improves the properties of a castable at elevated temperatures. XRD and SEM studies confirm the presence of corundum as a major phase and mullite as a minor.

For the problem of estimation of all elementary treatment contraata, restrictina ourselves to PBIBD's with two clus association schemea under a mixed model we follow the approach of Sinha and Sinha (1969) to study the behaviour of tho average variance [Formula: see text] as a function of [Formula: see text] and also as a function of the auociation scheme to some extent. The functional form of [Formula: see text] turna out to be the Jame as that under fixed effects model and either [Formula: see text] for all admissible θ>0. We got that when a BIB dosian does not exist with tho alven parameters a GO design with [Formula: see text] if it exists, is A-optimal within the class of all PBIB designs with two associate class association schemes. This proves that in respect of A-optimality, the result of Chong (1978) can be extended to all GD designs with [Formula: see text] if we restrict ourselves to such PBIB dosigns.

In this paper, results relating to the optimality properties of (i) the Balanced Block Designs and the Linked Block Designs in the one-way elimination of heterogeneity set-up (ii) the Generalized Youden Designs in the two-way elimination of heterogeneity set-up, both under mixed effects models, are presented.