Issue No. 3

Abstract

The present paper describes a research project carried out on the possible re-use of filterpressed mud (sludge) from waste water treatment plant of a local tile company in commercial wall, floor and porcelain tile formulations. In order to achieve this aim, firstly the complete characterisation of the mud was carried out. Then, the particular focus was given to the effect of the waste material in increasing amounts (up to 10 wt. %) on the thermal behaviour and physical and technological properties of the reformulated tile bodies. During the studies, a range of characterisation techniques, namely XRF, XRD, SEM in combination with EDS, DTA, TGA and non-contact dilatometry, were employed. The results showed that it was possible to use the waste material in tile production without deteriorating the relevant technological properties of the dried and fired bodies.

Abstract

Prototypal components of alumina-mullite (AM) refractory tiles were produced to evaluate their thermal shock resistance according to standard multiple-quench test. This test is usually applied for refractory material, used as liners for the thermal insulation of the combustion chambers in gas turbines for power production. AM refractory tiles were obtained employing a previously optimized mixture of alumina and ceramic wastes and were realized by cold isostatic press (CIP). Two different pressures of forming were tested (60 and 150 MPa). A proper aluminium-silicone mould, designed by CAD-CAM, was produced to obtain prototypal components with a volume comparable to that of commercial tiles. Thermal shock behaviour of the developed material was compared with a commercial AM refractory. Thermal shock resistance of prototypes realized at 150 MPa resulted higher than that of the commercial refractories, used for this application. The results of multiple quench tests, carried out on 115 x 95 x 30 mm3 tiles, were compared with those previously obtained with a standard test for advanced technical ceramics, carried out on 12 x 5 x 85 mm3 specimens. In this way it was demonstrated that process scale-up didn’t affect negatively properties of developed material, containing ceramic wastes.

Abstract

Basic bricks containing chromium based complex spinel are used in the non-ferrous industry due to their corrosion resistance against fayalite-type slags. Objective of this work is to replace Cr³⁺ with Me⁴⁺ ions that form complex spinel. The incorporation of iron oxide in the MgO-Al₂O₃-Me⁴⁺O₂ systems contributes to reactive sintering. The mixes contain 60 wt.% MgO similar to most basic refractories used in non-ferrous converters and thus called “magnesia-rich” compositions. The investigation shows that incorporation of nano-oxides reduces the temperature of spinel formation and activates both synthesis and sintering. Magnesia-rich compositions with Al₂O₃, Fe₂O₃, SnO₂ and TiO₂ containing less than 3 wt.% nano-oxides fired at 1450 °C for 3 hours have resulted in formation of complete spinel solid solution and less than 5% open porosity.

Abstract

This paper deals with the characterization of the thermomechanical behavior of monolithic refractory castables in a wide temperature range, up to 1200 °C. Different test types are considered: tensile tests, compression tests, bending tests and tests on more complex shapes and geometries. A particular attention is paid to the detailed characterization and interpretation of the non-linear behaviors of these materials. Monotonic, cyclic and creep tests are considered. In some cases, digital image correlation (DIC) methods can be coupled to mechanical tests to obtain strain fields. Such results are particularly interesting to observe and to understand damage processes. As damage is a major characteristic of the monolithic castable behaviors, links are established between the thermomechanical behavior and damage mechanisms. Two main scales are taken into account for damage characterization: the macroscopic and the microscopic ones. Main mechanisms that are considered deal with microcracking, macrocracking, debonding and cavitation. Two types of materials are considered: non-reinforced and fiber reinforced refractory castables.

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

The design of highly porous bioceramic scaffolds is a crucial issue for bone tissue engineering. The samples obtained by means of the commonly used “polymer burning out” technique, where organic particles are employed as pore formers, may suffer low porosity and/or clogged pores. In this work sodium chloride particles are used as pore generating agents in scaffolds based on a novel bioactive glass. The new glass, named BioK, was derived from the traditional 45S5 Bioglass® composition, where sodium has been replaced by potassium. BioK can be sintered to a temperature lower than the melting temperature of the sodium chloride, therefore the salt particles did not melt during the sintering process and remained into the green bodies; in this way, the original pore shape was preserved. At the end of the process, the salt particles were removed by immersing the scaffold in water. Thanks to this protocol, it was possible to obtain highly porous samples with remarkable mechanical properties (i.e. Young’s modulus between 3.4 and 3.7 MPa).