Year 2006, Volume 26

Abstract

Five Saudi Arabia kaolin-bauxite representative samples were assessed for ceramic industries. Chemical and mineralogical composition of these samples were investigated using XRF, XRD, DTA and TG methods. Plasticity, physical and optical properties as well as firing characteristics were followed after firing up to 1500°C.The solid phase composition of the vitrified samples was also investigated using XRD method.All kaolin samples are mainly composed of the kaolinite clay mineral, in addition of variable amounts of gypsum, calcite and/or microcline and anatase non-clay minerals.They are classified as low grade type and belonging to Seger 2 Category, which is not suitable for manufacturing white ware ceramics. The more pure types are recommended for the production of fireclay refractories, while the other types are suitable for manufacturing heavyclay products, e.g. vitrified ceramic tiles and pipes. On the other hand, bauxite-rich samples are mainly composed of gibbsite and kaolinite as well as high amounts of goethite, gypsum and anatase.They are recommended for manufacturing aluminous fireclay refractories as well as Bayer's precipitated aluminium hydroxide, after subjecting to proper selective mining and physical beneficiation processes.

Abstract

Rice husk can be an interesting source of raw material for obtaining silica, due to its composition, availability and cost.The extraction process of silica from rice husk can be divided in two parts. First some components of rice husk are removed by acid leaching, using HCl, H₂SO₄, or a mixture of them, followed by calcination for burning out carbon compounds.The residue obtained after calcination is composed of about 95% amorphous silica. In this work, silica was produced from rice husk following the steps previously described, using leaching solutions of 10% HCl, 10% H₂SO₄ and a mixture of 10% HCl and 10% H₂SO₄. Calcination of leached materials was carried out at 600 or 700ºC for 3 h.The silica powder obtained presented a mean particle size of 18 mm, around 98% amorphous SiO₂ with a specific surface area of about 300 m²/g.

Abstract

The gelcasting technique in shaping sanitary ceramics is very complex and difficult to control. The use of a modified artificial neural network (ANN) was proposed to model the non-linear relationship between gelcasting parameters and dry strength and dry shrinkage of the green body. The improved model for processing dataset and selecting its topology was developed using the Levenberg-Marquardt training algorithm and trained with comprehensive dataset of ceramic sanitaryware collected from experimental data.A basic repository on the domain knowledge of gelcasting process for ceramic sanitaryware is established via sufficient data mining by the network.With the help of the repository stored in the trained network, the influence of monomer content, cross-linker content, initiator content and catalyzer content on the dry strength and dry shrinkage can be analyzed and predicted.The results show that the ANN system is effective and successful in analyzing the influence of organic additives contents for gelcasting processes in shaping ceramic sanitaryware.

Abstract

In waterworks large amounts of sludge have to be discarded.This waste is usually destined to rivers, lakes and landfills, resulting in economic and environmental problems. This work reports on the use of waste (sludge) of a waterworks from South-Eastern Brazil as a raw material in red ceramic.The waste sample was characterized regarding crystalline phases, chemical composition, morphology, cation exchange capacity and particle size. In addition, leaching and solubilization tests were performed. Ceramic pieces containing up to 15 wt.% of waterworks waste powder were prepared by uniaxial pressing and sintered at 950 ºC.The effects of the waste addition on linear shrinkage, water absorption, apparent density, and flexural strength have been determined.The sintered microstructure was evaluated by scanning electron microscopy.The results showed that the municipal waterworks waste could be used for red bricks production, resulting in a new possibility for the recycling of this waste as well as natural resources conservation.

Abstract

Properties of a refractory castable bonded with sol-gel-routed nanostructured spinel (MgAl₂O₄) additive have been found to be much better than the same bonded by spinel synthesized via a fast coprecipitation method. The sol-gel additive also sets aside the conventionally coprecipitated spinel which is agglomerated. The microstructural studies (SEM and EDS) of the fired matrix of the castable indicates that the reactive sol-gel fines can improve the thermal shock and slag corrosion resistances.The results of XRD, IR, DTG,TEM and particle size distribution experiments of the rapidly coprecipitated spinel shows that this agglomerated additive also suffers from incomplete spinel formation with a huge amount of residual groups associated to its structure. Consequently it is not suggested as a suitable matrix powder for the refractory material investigated in this work.

Abstract

The Egyptian refractory raw materials available for application in the production of acidic and basic refractories are reviewed. Quartz and quartzite as well as fireclay and kaolin deposits suitable for the production of shaped and unshaped acidic products; namely, silica and aluminosilicate refractories exist at some localities in Aswan, Sinai and Eastern Desert. More than 60 thousand ton of high grade shaped and unshaped semi–silica, fireclay and aluminous fireclay refractories are locally produced from these raw materials for lining some Egyptian and Arabian industrial furnaces. Meanwhile , shaped and unshaped silica refractories are annually imported for lining coke ovens as well as ductile-iron induction furnaces. On the other hand,more than 70 thousand ton of shaped and unshaped basic refractories, i.e. MgO- based products are annually imported for lining and repairing of steel and cement furnaces due to the shortage of pure magnesite deposits in Egypt. However, some basic raw materials; namely, limestone, dolomite, dolomitic-magnesite and serpentinite rocks were assessed for the production of high quality lime, dolomite, MgO-dolomite, forsterite and cordierite refractories. It is concluded that Egyptian quartz and quartzite raw materials can be utilized in the production of shaped and unshaped silica refractories for lining coke ovens and ductile–iron induction furnaces, respectively.Also, the semi-silica and fireclay bricks currently produced from the available kaolinitic clays can be economically applied for lining steel ladles and tundishes, beside the aluminous fire clay bricks. On the other side, dense and hydration resistant shaped and unshaped lime, dolomite and MgO-dolomite refractories for lining and repairing of steel and cement furnaces can be produced from their available raw materials. In addition, shaped cordierite bodies can be produced as furniture for tunnel kilns used in firing white ware ceramics and forsterite bricks for lining the lower courses of the glass tank heat exchangers from varieties of serpentinite rocks.

Abstract

Mullite-zirconia-silicon carbide composites were synthesized from zircon flour, reactive alumina powder and a-SiC grains with Al powder and CeO₂ additives with variable proportions of SiC and reactive alumina.The different physico-mechanical properties of the powder compacts after firing like, firing shrinkage, apparent porosity, bulk density and true density along with the phase composition and microstructure varied with the change in composition and the firing temperature.Al powder influenced the sintering of the composites positively and the proportion of mullite in the fired compacts increased with the increase in firing temperature.

Abstract

A glass composition based on the Li₂O-Al₂O₃-SiO₂ (LAS) ternary diagram was prepared utilizing blast furnace slag (a by-product from steel plant) and china clay. The batch was modified by the addition of lithium carbonate, hydrated alumina, boric acid and titania (TiO₂).Titania was used as a nucleating agent. The batch was melted at 1400 oC followed by casting in the form of bars and annealed at 510 oC for 4h.The annealed specimens were subjected to heat treatment at predetermined temperatures, selected from DTA study of the parent glass.The specimen nucleated at 520 oC for 1 h and crystallised at 620 oC for 2h resulted a very low coefficient of thermal expansion [0.064 to 10.19X10^-7/ oC] in the temperature range of 30 to 500 oC due to the formation of b-eucryptite, g-eucryptite and LiAlSi₃O₈ crystalline phases, while other heating schedules showed the formation of spodumene and associated lithium aluminium silicate phases. All the samples showed excellent flexural strength value and varied in the range of 118-200 MPa. The micro-structural features were also examined through SEM study. Formation of dense microstructure was noticed in the sample nucleated at 520 oC for 4 h and crystallized at 620 oC for 2 h.

Abstract

The possible use of trachyte as an alternative fluxing agent in a commercial floor tile body was investigated. The experiments were carried out in two parts: In the first part, standard tests were applied to the products obtained from the experimental tile bodies modified with varying amounts (0-40 wt. %) of non-magnetic trachyte following single fast-firing under industrial conditions. The results indicated that 20 wt. % of trachyte (TRA2 formulation) as a substitute of albite completely and pegmatite partially in the standard formulation (STD) was satisfactory to carry out further experiments. In the second part, both STD and TRA2 formulations were further fired at different peak temperatures under laboratory conditions in order to establish their vitrification ranges and optimum firing temperatures. Consideration was also given to the phase and microstructural evolution of the tile bodies using x-ray diffraction (XRD) and scanning electron microscopy (SEM) in combination with energy dispersive x-ray spectroscopy (EDS), respectively. The preliminary results showed that it was possible to incorporate trachyte into a floor tile formulation as a fluxing agent and to obtain meaningful technological properties.

Abstract

The physical and mechanical properties of triaxial compositions involving the rock-type porcellanite, clays and volcanic ash (as flux) have been investigated.Two systems composed of (i) porcellanite/ash/low-plasticity clay (P-A-V) and (ii) porcellanite/ash/high-plasticity clay (P-A-G) were studied. In both systems the ash and clay proportions were alternatively held constant at 10% while varying the other and the porcellanite content such that for any given composition the porcellanite constituted the major body composition by weight (50 - 80%). In the P-A-V system it was found that essentially the same degree of total linear shrinkage (drying plus firing) was acheiveable over a range of compositions by keeping the ash constant and appropriately varying the clay/porcellanite ratio. With clay content constant, increased amount of ash enhanced strength, decreased porosity and increased bulk density in both triaxial systems, but at the trade-off cost of increased firing shrinkage.

Abstract

A multipurpose single body composition was utilized for producing tiles for various applications viz., wall, floor or high abrasion resistant vitrified product only by controlling the firing schedule. A body composition containing 90% pyrophyllite may be utilized for producing wall tiles at 1100°C with 0.86% linear shrinkage, 14.2% water absorption and 16.2 MPa flexural strength while the same composition when fired at 1175°C exhibited properties like 4.0% linear shrinkage, 4.0% water absorption and 38.7 MPa flexural strength which conform to the requirements of floor tiles. Similarly a composition containing 50% pyrophyllite on firing at 1175°C exhibited 5.75% linear shrinkage, 0.23% water absorption and 60.0 MPa flexural strength which conform to the requirements of synthetic vitrified tiles.The same composition at 1125°C may be utilized for producing floor tiles. XRD analysis of sintered samples confirms the presence of quartz and mullite.The latter phase increases with increasing pyrophyllite content. Presence of mullite in higher proportion was responsible for the development of higher flexural strength. Microstructural features were also observed through SEM.

Abstract

In the county of Campos dos Goytacazes, north of the State of Rio de Janeiro, Brazil, there is a large production of sugar, in which the sugar cane bagasse is used to generate power in boilers.This work has for objective to incorporate sugar cane bagasse ash into clay bricks, another important industrial activity of the county. Characterization of the ash was done by chemical composition, particle size distribution, X-ray diffraction and scanning electron microscopy. Ceramic mixtures with 0, 5, 10 and 20 wt.% of ash were prepared. Specimens were fabricated by extrusion and then fired in an industrial furnace at 970°C.Technological properties such as plasticity, water absorption, linear shrinkage and flexural strength were evaluated. Microstructural evaluation was also performed by X-ray diffraction and SEM. The results showed that the bagasse ash is predominantly composed of quartz.The ash addition made the workability easier and increased the porosity after firing. It was concluded that the incorporation of sugar cane bagasse ash into clay bricks fired at 970°C can be done up to a limit of 5 wt.%.