Mauro Marangoni

Strong and chemically inert sinter crystallised glass ceramics based on Estonian oil shale ash

Abstract In heat and power production, oil shale combustion forms substantial amounts of solid waste, including fly ash. The present paper is dedicated to the manufacturing of frit derived glass ceramics from melting high amounts of this waste (65–67 wt-%) combined with inexpensive minerals, such as rhyolite (33–35 wt-%). Owing to a surface mechanism of crystallisation, fine powders led to glass ceramics with high strength and reliability, even for rapid treatments (fast heating, at a rate of 40°C min−1, followed by 30 min holding stage). To minimise the presence of pressing and demoulding induced defects, the tiles were prepared by incorporating binders, i.e. polyethylene glycol or kaolin, to the frit mixtures. Finally, the stabilising effect of recycled borosilicate glass powders, mixed with waste derived glass powders, was also investigated with promising results for the production of a chemically stable material.

Recycling of inorganic waste in monolithic and cellular glass-based materials for structural and functional applications.

Abstract The stabilization of inorganic waste of various nature and origin, in glasses, has been a key strategy for environmental protection for the last decades. When properly formulated, glasses may retain many inorganic contaminants permanently, but it must be acknowledged that some criticism remains, mainly concerning costs and energy use. As a consequence, the sustainability of vitrification largely relies on the conversion of waste glasses into new, usable and marketable glass‐based materials, in the form of monolithic and cellular glass‐ceramics. The effective conversion in turn depends on the simultaneous control of both starting materials and manufacturing processes. While silica‐rich waste favours the obtainment of glass, iron‐rich wastes affect the functionalities, influencing the porosity in cellular glass‐based materials as well as catalytic, magnetic, optical and electrical properties. Engineered formulations may lead to important reductions of processing times and temperatures, in the transformation of waste‐derived glasses into glass‐ceramics, or even bring interesting shortcuts. Direct sintering of wastes, combined with recycled glasses, as an example, has been proven as a valid low‐cost alternative for glass‐ceramic manufacturing, for wastes with limited hazardousness. The present paper is aimed at providing an up‐to‐date overview of the correlation between formulations, manufacturing technologies and properties of most recent waste‐derived, glass‐based materials.

Shielding effectiveness of construction materials

Shielding effectiveness measurement, up to the GHz range, of construction materials with different compositions is an important issue. In this paper a coaxial waveguide, originally developed for thin films, is proposed as a simple device able to perform measurements on test samples with a thickness of a few millimetres. A calibration of the test system, with length extended of 5 mm, has been done both with a theoretical evaluation and an experimental measurement. Data obtained with construction materials of current interest for research are presented. With respect to similar systems reported in literature, where data up to 1.5 GHz are shown, this system has proven to be appropriate for measurements up to 3 GHz without too stringent tolerances in the sample geometry and without contact problems. Moreover, with inorganic polymers test samples, a clear relation between shielding effectiveness and heating temperature of the material has been observed.

Double-layer waste-derived glass-ceramics prepared by low temperature sintering/sinter-crystallisation

Lightweight glass-ceramics with a dense surface layer were produced by a novel sintering approach. The surface porosity of a glass-ceramic body from the direct sintering of an engineered mixture of fly ash from thermal power plants, recycled soda-lime glass and boron waste (residues of the mining and purification of valuable boron containing minerals) was sealed by a glaze, deriving from the sinter-crystallisation of glass powders produced from the same mixture. The use of boron waste, providing B2O3, allowed a substantial viscous flow, for the substrate, even at the relatively low temperature (850–950°C) adopted for a single firing treatment (simultaneous sintering of substrate and sinter-crystallisation of glaze). The dense sinter-crystallised layer, besides imparting improvements in the mechanical properties, was found to feature an enhanced chemical stability.

Glass-ceramic proppants from sinter-crystallisation of waste-derived glasses

ABSTRACT The present investigation aims at evidencing the feasibility of glass-ceramic spheres by sinter-crystallisation of fine glass powders (<100 μm), in turn obtained by the melting of inorganic waste, such as red mud from Bayer process or municipal solid waste incinerator fly ash, or low-cost minerals. While dense and highly crystallised monoliths may be achieved by sintering pressed glass powders just at the glass crystallisation temperature (TC), applying fast heating and short holding times, dense glass-ceramic beads could be obtained only by firing well above Tc (Tc + 100°C). An increased sintering temperature was applied in order to enhance the viscous flow and promote the spheroidisation of powder clusters, previously formed by casting fine powders on a rotating drum. The high degree of crystallinity and the uniform microstructure were found to contribute positively to the mechanical properties (compressive strength exceeding 120 MPa, for beads with a diameter of 1 mm, approximately).