Year 2011, Volume 31

Abstract

Iron ore tailing is a by-product generated during washing of iron ore & its amounts to be around 18-20 million tones per year in India. Storage of this huge amount of iron ore tailing in massive ponds pose environmental hazards. This study considers two Indian sources of iron ore tailings (marked as A1 and A2) & their structural evaluation utilizing X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). XRD analysis shows that A1 sample contains much more iron hydroxide oxide (hydrohematite) than the A2 sample. FESEM study also reveals that the A1 sample is less porous and denser than the A2 sample. The compacts of a mixture of 60 wt % iron ore tailings (A1 & A2 separately) and 40 wt% ferrogeneous type of kaolinitic clay were heated in the temperature range of 850-1000 °C. The heated samples were characterized in terms of bulk density, water absorption and cold crushing strength (CCS). The results revealed that such mixture can be used to produce building materials such as bricks (solid & hollow) & pavement blocks. Energy economy & lower production costs are some major benefits. The structural character of iron ore tailing has as important role on the strength development of heated compacts.

Abstract

The aim of the present work is to study effect of doping two MgO-enriched dolomite batches with 0.0-4.0% of 1:1 mole pure Al₂O₃/Fe₂O₃ (A/F) mixture on thermal equilibrium, microstructure and properties of their co-clinkered bodies fired up to 1600 °C. These batches were firstly prepared by adding 25 and 50% of fine Chinese magnesite to Egyptian raw dolomite powder, in order to process refractory MgO-dolomite dense bodies containing 55-60 and 70-75% MgO, respectively. For comparison, these bodies were processed along with dense dolomite and magnesite bodies, containing about 35 and 95% MgO, respectively. Bulk density, refractoriness-under-load and hydration resistance of all bodies were assessed in relation to their thermal equilibrium and microstructure. Selected co-clinkers were applied for processing unfired tar-bonded MgO-dolomite briquettes parallel to similar of the dolomite and magnesite types. The properties of the processed briquettes were also evaluated in relation to their phase composition and microstructure. It is concluded that the addition of 2.0% of the Al₂O₃/Fe₂O₃ mixture is sufficient to obtain dense and hydration resistant dolomite and MgO-dolomite refractory co-clinkers, after firing for 2 hours at 1600 °C, without appreciable deterioration of their loadbearing capacity. Also, enrichment of the dolomite with MgO up to 60 and 75% leads to improve bulk density, cold crushing strength, load-bearing capacity and hydration resistance of the MgO-dolomite co-clinkers. This is mainly attributed to development of the direct-bonded periclase network, which encloses most of the free CaO as well as C₃S and C₄AF phases within its interstitial spaces. So, these co-clinkers were selected to process dense and hydration-resistant tarbonded MgO-dolomite briquettes along with those of the dolomite and magnesite. All properties of the prepared MgO-dolomite briquettes were improved rather than those of the dolomite type. Accordingly, the processed tar-bonded MgO-dolomite briquettes can be recommended for lining the Egyptian basic oxygen steel furnaces instead of the currently used tar-bonded dolomite.

Abstract

Mullite forming sol was prepared by proper selection of hybrid precursors having both organic and inorganic origins. X-ray diffraction (XRD) and infrared spectroscopy (IR) were performed to distinguish between the two sets of precursors. Refractory grade flaky graphite was coated by the sol, dried and heat treated for microstructural analysis. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) studies with energy dispersive spectroscopy (EDS) were carried out to illustrate the characteristics of mullite forming aluminosilicate coating over graphite. The stability of this surface-modified graphite was also evaluated in comparison with the uncoated one by thermogravimetric analysis (TGA). The amount of casting water required for a monolithic refractory composition prepared by these graphites was also examined. Finally, the increase of the performance of castable containing coated graphite has been estimated by determining its physical properties such as bulk density and apparent porosity.

Abstract

The effect of alumina content on the mechanical strength of electrical porcelain manufactured by green machining of isostatically pressed blanks was examined with a view to attaining optimal mechanical properties at low sintering temperatures. Porcelain compositions were formulated with four different alumina contents, maintaining the same proportion of the other materials (kaolin, clay and feldspar). Test specimens were isostatically pressed at 70 MPa and machined at high speed into cylindrical test specimens using controlled machining parameters. These specimens were sintered at several temperatures to determine the optimal sintering temperature for each composition, after which their mechanical properties were analyzed by the flexural bend test. The results indicated a correlation between the alumina content and the sintering temperature, and between the flexural strength and its influence on the green machining conditions. An average tensile strength of 186 MPa was attained for the composition with an added content of 30 wt% of commercial alumina sintered at 1250 °C, pressed and machined under industrial conditions.

Abstract

By analogy with the development of nuclear power and photovoltaics, the position of MCFC technology is evaluated in the context of today’s energy supply. A brief review is presented of the technical status of MCFC materials and challenges left open. At system level, a number of more or less niche applications prove to be promising for approaching early markets and an update is given of some important figures on construction and deployment of MCFC systems worldwide.

Abstract

Pyrophyllite is largely an overlooked raw material available in huge quantities in nature. This is mainly due to the fact that other comparable aluminosilicate raw materials like china clay are available in much purer form. However, fast depleting reserves of standard raw materials necessitated renewed attention on so far sparingly used raw materials like pyrophyllite. Investigative work on pyrophyllite is also insignificant in comparison to other ceramic raw materials. Available information are scattered and it is felt that a comprehensive review is needed for effective dissemination of the information already generated and available in the public domain. In the present article salient points on the material including structure, chemistry of heating and possibility of future applications particularly in triaxial ceramic system is discussed. In a case study one Indian pyrophyllite was incorporated (15%) in a triaxial body composition replacing both china clay and quartz. The changes in fired properties was tried to correlate with phase development and microstructure.

Abstract

Mineralogical, microstructural, and firing characteristics of dead burned magnesia produced from hydrothermal magnesite deposits of eastern Iran have been evaluated. The ore bodies are highly pure crystalline magnesite with only trace amounts of impurities such as quartz, calcite, and dolomite. Ratio of CaO/SiO₂ in the bulk ore is variable. It was shown that the composition of dead burned magnesite from these deposits, calcined at different temperatures and durations, is predictable from phase equilibria. Textures of the calcined magnesite were studied by SEM; results show that the principal impurities produced during calcination are forsterite (F₂S), monticellite (CMS), merwinite (C₃MS₂), dicalcium and tricalcium silicates (C₂S, C₃S) and that these are located primarily at triple junctions of the periclase crystals. The size of periclase crystals increased with temperature and duration of calcination and the amount of periclase-periclase grain contacts was reduced by increasing the concentration of impurities in the starting ore EPMA analyses revealed that CaO and FeO contents in periclase increase steadly with an increase in the CaO/SiO₂ ratio and FeO content of the bulk ore, respectively. Moreover, it was found that limited solid solution exists between impurities. This study demonstrates that high quality dead-burned magnesia refractories with low CaO, SiO₂ and FeO contents can be produced from the studiedmagneiste deposits.

Abstract

Agacli-Kemerburgaz area, NW of Istanbul, is one of the most important underclay deposits of Turkey. This area is composed of Paleozoic sedimentary sequence, Upper Cretaceous volcanic rocks, Neogene sediments and Quaternary alluvium deposits. The calc-alkaline volcanic rocks are the parent rocks of the underclays in this area. In this work, mineralogical and chemical analyses and relevant technological tests were conducted in order to assess the potential of selected underclays of this region. The technological properties were characterized by firing shrinkage, water absorption and breaking strength after firing. The chemical analyses generally showed the characteristics of typical kaolinized materials. Underclays containing (up to 33 wt. %) porcelain stoneware formulations were prepared and standard tests were applied to the porcelain tiles after single fast firing under industrial conditions. The densification behaviour and phase evolution of the bodies upon firing were evaluated. Physical, thermal and optical properties and chromatic coordinates were also measured. The results revealed that it was possible to employ the underclays to replace more expensive clay in porcelain tile production without deterioration of the required properties.

Abstract

The successful design of mixers is known to depend primarily on the mixed fluids properties as well as the geometry of both impeller and vessel. A classical approach commonly used to predict the power requirements in the mixing process is to make use of the relation between the Power number (N_p) and the Reynolds number (Re). Here, Re = ρ.n.D² /μ, where ρ is the density of the liquid mixture, μ its viscosity, n the rotational speed of the impeller (rps), and D its diameter. On the other hand, N_p = P / ρ.n³.D⁵, where P is the power required for mixing. This approach has been conventionally applied to Newtonian fluids and suspensions but not to pastes. In the present paper, relationships were developed for mixing of ceramic pastes used in the manufacture of sewer pipes. A standard mix was chosen and the effect of the following variables on the power number - Reynolds number relation was investigated: water content, grog content and particle size of clay. All paste mixes investigated followed a relation of the type: N_p = a / Re^b, where a and b are constants that depend essentially on the fraction of grog used and to lesser extent on the water fraction and clay particle size. The values of the constant b were close to unity in all cases, emphasizing the fact that the laminar regime mixing relation N_p = a / Re, applicable for Newtonian fluids is also valid for pastes.

Abstract

Suitability of using limited additions of three solid waste by-products; homra (H), granulated slag (GS) and fly ash (FA), with Egyptian clay, belonging to Dakhla formation in south western desert, in the conventional red brick batches fired at different temperatures was assessed in comparison with a blank batch. The results showed that as the firing temperature increases, the densification parameters as well as the mechanical properties are improved. Fired brick bodies, containing 10% (FA), exhibit higher densification and mechanical properties at all firing temperatures than those of the other batches. The firing shrinkage was also increased slightly between 750 to 800 °C and sharply from 850 to 950 °C. The XRD and EDAX analyses illustrate that during firing, the main clay constituents of the brick batch react with those of the FA, GS and H additions, forming calcium-rich silicate phases.

Abstract

The aim of this work was to evaluate the use of the Bornova shale (BS) from Bornova-Izmir, west Turkey, as a raw material in the production of red fired ceramics. The Bornova-Izmir area is a convenient region for establishing a ceramics factory in terms of climate and proximity to Izmir harbour. The BS consists of phyllosilicates (illite, chlorite, and smectite), quartz, feldspar, and calcite. The dominant clay minerals are either illite or chlorite with smectite making up 0-7%. Differential thermal analysis (DTA) reveals that an amorphous phase occurs above 918°C. For the production of red fired ceramics, we used illiteand chlorite-rich BS in the following proportions: addition of 40% Fe-rich Eymir (Havran) kaolin (EK) to the BS, addition of EK (40%) and 2% Bigadiç Borate Concentrator Waste (BBCW), addition of EK (40%) and 3% BBCW, and addition of only 2% BBCW. Representative samples were prepared by pressing clay bodies at 15 MPa, which were then fired at temperatures between 850 and 1200 °C. The physical properties of the representative samples (e.g., water absorption and bending strength) were obtained from specific tests. Based on the desired colour and physical characteristics, the optimum batch was that with 98% BS +2% BBCW fired at 1100 °C. Addition of BBCW to the BS imparts binding and fluxing properties during the production process. These properties, in turn, improve mechanical strength and reduce energy usage.

Abstract

Three different mullite precursors were prepared from Al(OH)3 and silica sol with variation in the calcination temperature of Al(OH)3. These precursors were added to high alumina low cement castable composition to an extent of 6 wt%. The castables were conventionally processed and fired at 1000, 1200 and 1500 °C. Dried and fired castables were characterized for various properties for the comparative study of the effect of different mullite precursors on the castables. No strength degradation was observed at the intermediate temperature due to the formation of mullite phase in the castable matrix.