Issue No. 2, August

Abstract

This study evaluates the effects of adding waste bottle glass or boric acid as fluxing agents on the stain resistance of a porcelain stoneware tile body. Different amounts of waste bottle glass, 5, 10 and 15 wt. %, were replaced with the same amounts of sodium feldspar in body formulation. In addition, 0.1, 0.3 and 0.5 wt. % of boric acid were added to the standard body formulation. These new compositions were sintered at 1210 and 1220 °C with a thermal cycle of 45 min. The densification behaviour of the samples was investigated by determining the water absorption, linear shrinkage and bulk density of the fired samples. The results show that the presence of waste bottle glass or boric acid positively influences the sintering behaviour, increases shrinkage, decreases open porosity and improves the stain resistance with respect to standard bodies.

Abstract

Magnesium oxychloride cement (MOC) polishing bricks developed for fine polishing of porcelain stoneware tiles were produced and characterized with respect to MgO/MgCl₂ molar ratio of 6/1, 7/1, and 8/1. X-Ray diffraction analysis revealed that the main crystalline phase formed in the bricks was 5Mg(OH₎₂ .MgCl₂ .8H₂O. Density, abrasion resistance, compressive strength, and chemical durability in water of the MOC bricks were determined to provide information on polishing behavior. Polishing of the tiles was accomplished both in laboratory scale and in online industrial scale. Polishing performance of the bricks was evaluated in terms of average roughness and gloss of the tile surface and of abrasive brick consumption occurred during polishing. The roughness of the tile surface and abrasive brick consumption decreased but the gloss increased when MgO/MgCl₂ ratio in the MOC brick is increased. Scanning electron microscope examinations revealed that the MOC bricks composed of MgO/MgCl₂ ratio of 7/1 had the best qualifications in terms of polishing performance.

Abstract

The aim of this work is to study the possibility to use crockery ware scrap in floor tile engobe formulations. The scrap powder was added to engobe formulation in substitution of china clay and its influence on slip properties like density and fluidity was studied. Fired properties such as whiteness and thermal expansion were determined. The effect of these engobes on the fired properties of matt glazed floor tiles was also evaluated. Incorporation of 5-10wt. % scrap resulted in significant improvement in fluidity. Coefficient of thermal expansion was found to be increased slightly and no detrimental effect was observed in whiteness as well as in maturity of engobes. Fired glazed tiles do not show any defect in appearance and exhibit good glaze to body fit. Thus, this study demonstrates the possibility to reuse waste materials like crockery ware scrap in engobe formulations which have a well defined role in glazed floor tile manufacturing.

Abstract

This study investigates the migration of SO₄^–2 and Ca⁺² ions in a red-clay ceramic, simulating the process of efflorescence. Ceramic bodies were molded (70x27x9 mm³) by vacuum extrusion formulated with different contents of CaSO₄.2H₂O (0%, 4%, 8%, and 16% in weight) and burnt at different temperatures (800 °C, 850 °C, 900 °C, and 950 °C) for 12 h. Ceramic bodies were characterized in terms of water absorption, apparent porosity and pore size distribution. Efflorescence was evaluated according to the ASTMC67/2003 Standard and by testing the solubilization of SO₄^–2 and Ca⁺² ions after 1 h with the ceramic bodies immersed in hot water as well as after 7, 14 and 28 consecutive days immersion in cold water. In the quantification of efflorescence, a new image analysis methodology was developed by using the graphic software Image Tools 3.0. The results allowed in establishing a relationship between the efflorescence of the investigated ions, physical properties (water absorption and apparent porosity), pore size distribution and solubilization.

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.