Issue No. 2, August

Abstract

The resistance to deep abrasion of porcelain stoneware tiles (standard ISO 10545-6) corresponds to a model of tribological behaviour for threebody abrasion, based on mechanical characteristics (hardness and fracture toughness) and wear conditions (applied load, contact area and size of abrasive particles).The mechanical properties are affected by the total porosity (2-8%) of porcelain stoneware; thus there is a certain dependence of the material removed by abrasion on the pore volume, that however does not explain the entire variance of the measurements of wear resistance.The phase composition plays a fondamental role and a simple predictive model has been developed, indicating that the larger is the content of mullite, zircon and quartz, the higher is the resistance to deep abrasion. In particular, mullite and zircon ensure the main contribution to the tribological properties, owing to both their hardness and a toughening mechanism originated by differences of thermal expansion and elastic moduli between glassy and crystalline phases, inducing a compression at grain boundaries. Other crystalline phases, such as quartz and corundum, have a less relevant effect on the wear resistance, for the unfavourable differences of thermal expansion with the vitreous matrix.To improve the resistance to deep abrasion of tiles, it is possible to act on the body formulation, in order to increase significantly the amount of "hard" phases, mainly mullite and zircon, without altering the amount of residual porosity, that influences heavily both hardness and fracture toughness of porcelain stoneware.

Abstract

An attempt has been made to develop a “Singular Blended Clay” (SBC) having plastic properties and dry strength required for the production of vitreous sanitary porcelain and tableware. A pre-determined mixture of a crude china clay, plastic ball clay and a plastic fire clay from Indian origin were crushed, blended together and impurities removed by wet processing including gravity settling, screening, deironing and filter pressing. The physico-chemical properties of feed raw materials have also been studied with emphasis on singular blended clay and its influence on the thermo-mechanical properties and microstructure of vitreous sanitary porcelain compositions. Progressive substitution of singular blended clay up to 60 wt % leading to almost complete replacement of traditional crude clays resulted in an increase of flexural strength (~ 32%) and a decrease in thermal expansion (~ 22.7%) due to decrease in residual quartz content in the compositions. The addition of SBC had although little effect on the mullite content of the fired bodies but decreased the vitrification temperature by 50°C and also enhanced the vitrification range.

Abstract

A municipal sewage sludge (MSS) from a traditional wastewater treatment plant and a paper mill sludge (PS) were incinerated and transformed into powders which were blended in different proportions to give powders with different composition. Blendings were performed by attrition milling in order to reduce the milling time with respect to the traditional wet milling process. Powders were then pressed into specimens which were submitted to thermodilatometric tests to evaluate their shrinkage and their softening temperatures on heating up to 1350°C. Samples were then air sintered by means of a muffle furnace and characterized by density, strength, hardness, fracture toughness measurements and XRD and SEM investigations.The mechanical properties of the sintered specimens are satisfactory for all compositions and this may be due to the formation of small grains that, in some cases, are surrounded by a vitreous phase. One binary composition (75% MSS and PS 25%) showed a strength over 150 MPa.A mixture containing 33 % wt MSS, 33 % wt PS and 33 % wt steelworks slag (SS) was also prepared, processed and characterized like the other blends. All sintered samples were finally aged in an acidic (HCl) water solution to evaluate the elution of the components. It was observed that it is possible to limit the release of many of the most hazardous metals contained in the starting powders by an appropriate sintering schedule.

Abstract

A new technology aimed at protecting Torpedo Car refractory lining through the Formation of a Protective Layer - FPL - was developed.The technique consists of doping the process slag, thereby leading to an increased resistance of Torpedo Car refractory lining wear. Preliminary laboratory simulations were run, with a view to streamlining slag doping elements concentration, followed by trials in a rotary oven to simulate Torpedo Car refractory wettability by means of doped slag. As a result, the FPL technology was implemented on an industrial scale, thus helping protect CSN Torpedo Car refractory lining.

Abstract

High performance composite fibre or platelet reinforced ceramics were widely expected to have been implemented into a relatively wide range of industrial applications but did not achieve the expected potential whilst for general high temperature refractory applications the vast majority of products have very anisotropic microstructures although they may actually behave as bulk isotropic. Finite element modelling of these complicated 3 dimensional microstructures is relatively difficult due to the very large model size and obtaining accurate material property data.This paper demonstrates the use of advanced parametric finite element analysis modelling techniques of composite ceramics and structures for industrial applications. The accurate modelling of these composite materials and related industrial refractory structures in a reasonable time scale would drastically reduce the materials technology development cycle for existing and new high temperature refractory applications compared to the historically empirical materials and industrial application development cycle.An industrial case study of this approach is demonstrated.

Abstract

Two different batches of zero-cement castables composed of 85 wt. % fused MgO-spinel aggregate with 10 wt.% hydratable alumina and 5 wt.% of either kaolin or alumina/silica fine powder mixture were prepared and compared with other two conventional castables of the same composition where hydratable alumina is replaced by high alumina cement. The densification parameters, cold crushing strength as well as refractory properties (thermal shock and creep resistance) were tested. Zero-cement castables, specially those containing kaolin showed a compromise between considerable mechanical properties and good refractory behaviour as compared with the corresponding conventional ones.This behaviour is strongly related to the absence of lime that causes many deleterious effects on the properties of conventional castables.

Abstract

Elimination of the physically bonded water and dehydroxylation take place simultaneously in the green electroceramic body during its firing for a diameter of the sample d >= 5 cm and heating rate >= 2 °C/min.The larger the sample diameter the wider the overlap of these processes and the higher the temperature of their completion.

Abstract

Zirconia-mullite composites containing 0-6 mol% yttria were prepared by the reaction sintering process.The main raw materials were Indian coastal sillimanite sand and zirconia and alumina.After milling, samples were isostatically pressed, sintered at 1500-1600°C for 2 h and characterized in terms of phase coexistance, martensitic start (Ms) temperature, thermal expansion coefficient, thermal shock resistance and microstructure.The addition of yttria improves the thermo-mechanical, thermo-physical and physical properties of the resulting composites. The thermal expansion coefficient and martensitic transformation temperature decrease with yttria content. The relative densities of yttria bearing samples are higher.