Advances in Science and Technology Vol. 70

Abstract: FIRE has been incorporated as a non-profit organization in Canada, in May 2005. It is by now a network of professors, researchers and industrial partners, representing eight different universities spread in six different nations and eleven multinational companies, who have gathered, to undertake well-defined precompetitive research projects, and to train highly-qualified personnel for the industry. The evolution of the refractory education arena, in an economically globalized world, caught in a maelstrom of technical changes, is presented. The changes of paradigm from the “information age society” to the “crowdsourcing” in background, the FIRE realization are highlighted in such a context of “conceptual age society” are considered, with the concept of “coopetition”.

Abstract: Alumina-mullite (AM) refractories are widely used as liners in gas turbines for power production, because of their peculiar properties, appropriate for the thermal insulation of combustion chambers, characterized by turbine inlet temperature around 1400 °C. The typical tiles are made with a mixture of alumina and mullite with different granulometries, including a coarse fraction. In this work the feasibility of recycling of ceramic wastes, which come from other industrial processes, into AM refractories was assessed. The effects of their addition on phase composition, microstructure and thermomechanical properties of AM refractories were investigated. MOR and Young’s modulus were determined at room temperature and up to 1500 °C by four point flexural tests; thermal shock resistance was evaluated by MOR measurements after quenching tests. The comparison with a typical AM refractory used as liners shows that thermomechanical properties and thermal shock resistance were not significantly compromised by ceramic waste additions up to 20%, and, on the contrary, were improved.

Abstract: The paper describes formation of the phases in magnesia-zirconia refractories due to reaction with the cement furnace charge in a form of pre-calcined meal or Portland clinker containing sulphur and chlorine in a different content at the temperature 1300°C and 1450°C. The studies were carried out by using the coating test. The microstructure changes of the contact zones between coating and the brick were studied by the scanning electron microscopy, SEM, coupled with EDS. The temperature dependence of reactivity the pre-calcined meal and Portland clinker in relation to the magnesia-zirconia bricks has been documented and discussed.

Abstract: Refractories cover a wide range of products. With the aim to precisely describe the key product properties, end-users and refractory producers have progressively developed a common language: refractory standards. After a brief description of refractory standards history, and a synoptic overview of the present status, future prospects are illustrated by an example. The Belgian Ceramic Research Centre (BCRC) has recently launched a pre-normative research in the field of unshaped refractories. It focuses on robust methods to assess the workability and setting of hydraulically bonded unshaped products. Among the investigated methods, the so-called “exothermic profile” appears to have a high potential to become a standard for refractory producers or end-users.

Abstract: The denomination ‘flexible’ is chosen in the professional jargon of refractories technology for materials able to bear relatively high strains without or with acceptable loss of strength. In many cases this term is equivalent to relatively low brittleness. Characterisation of brittleness based on fracture mechanical investigations may use figures of merit like brittleness numbers, a so called characteristic length or the R’’’’ parameter according to Hasselman. In many cases these figures show that brittleness reduction of refractories is achieved by decrease of strength with at the same time more or less unaffected specific fracture energy. Microscopic investigations of fracture paths aim to exhibit which peculiarities of crack microstructure enable this change of mechanical properties. A microscopical technique developed for this purpose separately evaluates the relative crack lengths along the grain/matrix interface, within the matrix and within the grain. Results obtained for several types of refractories show brittleness decrease is associated by an increase of the relative crack length along the grain/matrix interface and a decrease of transgranular fracture. Prefabricated microcracks and a relatively low grain/matrix bond strength may support this type of crack propagation.

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 mechanical behaviour of ceramic refractories formulated in the MgO-CaO-SiO2- ZrO2 system is analysed in terms of the room temperature Young´s modulus, the modulus of rupture and the work of fracture at 25 and 1100°C. The materials have been designed taking into account the phase equilibrium relationships to obtain MgO-CaZrO3-Ca2SiO4-Ca3Mg(SiO4)2 or MgO-CaZrO3-Ca3Mg(SiO4)2-c-ZrO2 as final crystalline phases. Different relationships between the proportion and sizes of the fines and the aggregates have been explored. The microstructure of the materials has been characterised in terms of density, crystalline phases and phase distribution and morphology. A combination of X-Ray diffraction (XRD) analyses and Reflected Light Optical Microscopy (RLOM) has been used. The relationships between the obtained phases and microstructures and the grain size distributions of the used raw materials have been established. The relationships between the mineralogical composition and the obtained microstructure and the mechanical behaviour are discussed.

Abstract: Alumina-mullite refractory tiles are used as liners in gas turbines for power production, for the thermal insulation of the combustion chambers. The typical microstructure is characterized by a coarse fraction, in order to increase porosity (and hence thermal insulation) and improve thermal shock resistance (by grain bridging mechanism). A mixture of alumina and ceramic wastes was optimized to manufacture prototypal components, by cold isostatic press (CIP). On sintering at 1600°C, a final composition of 40% mullite and 60% alumina was obtained. For the production of refractory tiles with dimensions similar to the commercial ones, an appropriate mould was CAD-CAM designed and produced, using aluminium and silicone. 115 x 95 x 30 mm3 tiles were obtained and utilized for thermal shock tests. Samples were heated up to 1000°C and quenched to 20°C: this cycle was repeated 30 times before inspecting the macroscopic cracks. The results were compared with those obtained with a standard test for advanced technical ceramics based on MOR measurements. Two different pressing conditions were tested (60 and 150 MPa) in order to get data about a possible industrial production by uniaxial pressing.