The project proceeded regularly as foreseen. In a first stage, the activity of collection, characterisation and preparation of the slag was completed. This was done mainly by MicroEnergy, albeit with the support of Fondovalle and of the university partners (UNIMORE and UNITN) for defining the necessary characteristics for using this waste material. After a stage consisting of selection among various suppliers of slag, an Austrian company able to supply material with a particle size smaller than 200 µm, without variations in its physical and mechanical properties, was identified. This facilitates the stage of preparation of the slag, since a preliminary screening stage enables separation of the fraction containing particles smaller than 150 µm (about 80% of the total). Thanks to a milling system purchased by MicroEnergy, it is then be possible to process the remaining amount to obtain particle sizes of up to 60 µm.
The project then continued at the laboratory of Trento University, in order to define the most suitable forming and sintering techniques for obtaining specific prodotto ucts. This activity started out from a first characterisation of the milled material, made up mainly of Fe and Si (at a more or less constant concentration, even in various different batches), plus small quantities of Ca, Cu, Al, Zn, K and S, in addition to very minor quantities of impurities (Na and Mg). The first result was the elimination of tape casting technology, due to the rapid sedimentation of the metal particles due to their weights, unless these are milled to a particle size smaller than 10 µm, which would increase the environmental impact of the process. The activity continued with uniaxial pressing and sintering tests, in a normal atmosphere and in argon, finding different sintering and vitrification temperatures (ranging from 900°C to 1150°C), with considerable variations in the characteristics of the end prodotto uct. Further tests were then carried out using SPS (Spark Plasma Sintering) technology, with consolidation of the dust at considerably lower temperatures (ranging from 600°C to 700°C) and a high density of the samples obtained. The next stage took place both care of Fondovalle and care of MicroEnergy, with the construction of sub-systems for forming and sintering the new prodotto ucts and with the manufacturing of the first prodotto ucts. Specifically, MicroEnergy created a small but complete laboratory consisting of a mill, a press and one roller hearth furnace and one static oven for firing the prodotto ucts in an inert-gas atmosphere, while Fondovalle adapted its plants for preparing the raw materials, its presses, its grit- deposition system, its dryer and the firing kiln. The tests carried out gave rise to several different samples of new prodotto ucts, in particular:
to be used in high-power industrial microwave systems. A first stiff version was created with a slag content of 90% in weight of the tiles. Some initial samples of panels with a rubbery matrix were also created. These were flexible and lighter, with a slag content of up to 60% in weight.
CASSEROLE DISHES FOR MICROWAVE OVENS
with a slag content of 45% in weight; while normal containers are microwave-transparent, these oven dishes can reach a temperature of 250°C inside a microwave oven, enabling the food to be cooked conventionally through heat transfer, while the microwaves heat the food from inside.
to be used as replacements for tubular heating elements made of silicon carbide or molybdenum disilicide, which have a high embodied energy. The elements made, which measured 20 cm, have a very high resistivity and can reach temperatures of up to 1000°C rapidly due to the Joule effect simply by applying conventional voltages (0-100 V).
UNDER-FLOOR HEATING TILES
first of all small-sized samples were manufactured using a laboratory press. Then they were made on a semi-industrial scale, in two different ways. The first procedure consisted of introducing the slag into the mixture, then carrying out pressing, drying and subsequent sintering (firing) inside a roller hearth furnace. The second procedure consisted of creating a conventional ceramic backing and depositing a layer of grit made up of suitably selected slag on the surface of the unfired tile, followed by a second pressing, drying and sintering. In the meantime, the University of Modena and Reggio Emilia, jointly with an important manufacturer of ceramic glaze, proceeded with melting tests of the slag in order to obtain frit and glaze. These were carried out at a temperature of 1550°C using different types of crucible and adding different types of powder for facilitating melting and increasing the dielectric properties of the samples. The bulk material obtained in this way proved to have a microwave absorption capacity and dielectric properties suitable for going ahead with the project. The activity then continued with the tests for preparing and applying the frit and the glaze, carried out by Fondovalle and UNIMORE. The tests were carried out first on laboratory scale, in four different ways (a single layer of glaze, two layers of glaze, one layer of engobe and one of glaze, one layer of engobe and two of glaze), after which the item was fired in the industrial kiln. Then several samples of glazes and engobes were applied using a deposition system based on silk-screen printing rollers with especially designed screens. Again in this case, the results of the tests were more than satisfactory. After the realization, with the systems made, of samples for each type of prodotto uct, subsequent activities have focused on the functional characterization of the prodotto ucts themselves. The results were important, though not always met the initial expectations:
Microwave absorber tiles were tested and an insertion loss around 6 dB/cm at 2,45 GHz was measured. They were presented to many European stakeholders with the aim to enhance their interest towards the prodotto uct and to finely characterize the prodotto uct performance in industrial working conditions. For this reason ceramic absorbers with 60%wt. slag content were prepared to be installed on microwave conveyor oven walls. A drastic reduction of microwave leakage was measured. Their performance are equal or better than current shielding/attenuation solutions (water, silicon carbide, ferrite tiles), which are less versatile and much more expansive.
Microwave heating properties and cooking performances of microwave plates were tested in common microwave home appliances. Thanks to the hybrid absorbent/transmissive characteristics of the slag/ceramic composite, the position of the microwave inlet only slightly affects the heating pattern. Therefore this technology is very adaptable because the plate fits well with several ovens from different manufacturers with replicable results. To achieve sufficient cooking results the container should be preheated for 2-3 minutes at 900W to reach 150°C. In comparison to Crisp Plate this preheating times are quite longer because the ceramic plate weighs more (1000 g) than a conventional metallic Crisp Plate (600 g). On the other hand, the high thermal mass and thermal retention of ceramic allows the plate to remain warm for a double time than a Crisp Plate after cooking. Furthermore some cooking advantages were evidenced: slag-activated plates show a level of browning/crisping that is comparable or better than Crisp Plate. In addition, slag plates provide strong heat generation also on the lateral sides, while Crisp Plate don’t.
It was not possible to carry on the functional characterization of heating resistances because of the problems encountered during the development, as after 10-15 cycles samples brake: the heating resistances are not performant enough; we demonstrated that it is possible to obtain the resistances, they work, but they have too few activity cycles for applications.
UNDER-FLOOR HEATING TILES
glazed tiles have been prodotto uced. The frit has been mixed with water and Kaolin as clay and milled in order to obtain a slurry. Subsequently the slurry has been deposited on the support and subjected to the traditionalheating treatment. The support has been previously engobed. The engobe can be used for different purposes: to give color; to improve the surface texture, to provide a ground to do further decoration; to add textures in order to avoid some defects. One of the most frequently defect in the glaze are bubbles due to gas generated during transformation of the body. In particular, engobe eliminates gas bubbles large enough to prodotto uce holes, craters or depression. Another function it is to prevent direct contact between the tile body and the glaze. This avoids the risk of contamination of the glaze by the body transformation. The aesthetic properties has been evaluated considering the presence of defects such as bubbles and cracks. The final materials have been also characterized by X-Ray diffraction, scanning electron microscopy and Raman spectroscopy by UNIMORE. Other treatments have been performed changing the time of the heating process in order to promote the sinterization of the entire ceramic body. Through the pilot systems, various kinds of samples to be analysed have been prodotto uced and the characterizations get to the complete definition of the mechanical properties and chemical and mineralogical composition of the different prodotto ucts obtained with the project will be achieved. The electric and dielectric properties of the optimized samples have been, then, measured. All the samples show interesting conductivity values due to the presence of high percentages of iron in the glass matrix as well as due to the presence of magnetite as crystalline phase. By MW heating tests, the samples have been also subjected to heating cycles, suggesting that the samples can be used as selective materials for microwave heating applications. An assessment of the environmental impact due to the life cycle of the prodotto ucts obtained compared with the impacts due to the life cycle of traditional prodotto ucts having the same functions has been made as well. Analysis was conducted with the Life Cycle Assessment methodology (LCA), in order to consider the whole life cycle of the prodotto ucts, from the raw materials extraction, to the use and the end of life phase, including transports and all the stages of the prodotto uction processes, obtaining a “cradle to grave” overview. The comparison between the frit containing copper slags and a traditional one, showed that the former is 15,35% less impacting of the latter, and that the difference is bigger in the global warming category. The comparison between 1 m2 of slags tile and 1 m2 of a traditional stoneware tile shows a disadvantage from an environmental point of view. Slags tile damage is 18,30% higher than the damage prodotto uced by the traditional one. The comparison shows that it’s not advantageous to use this formulation for the prodotto uction of tiles. The innovative material is more sustainable than the traditional one, as microwave absorber, because of the high percentage of material of recovery that contains. In fact, the microwave absorber with copper slags has an environmental load, which is for 87% less to that of the traditional tile.