Sintered Glass–Ceramics and Glass–Ceramic Matrix Composites from CRT Panel Glass

Abstract

Sintering with simultaneous crystallization of powdered glass represents an interesting processing route for glass–ceramics, especially originating from wastes. Highly dense glass–ceramic samples may be obtained from a simple and short treatment at a relatively low temperature. In addition, glass–ceramic matrix composites may be obtained by mixing glass with suitable reinforcements. In this work sintered nepheline glass–ceramics, based on panel glass from cathode ray tubes, are illustrated. A limited addition of Al2O3 platelets caused a significant improvement in the mechanical properties (elastic modulus, bending strength, microhardness, fracture toughness), already remarkable for the un‐reinforced glass–ceramic, compared with traditional nepheline glass–ceramics.

Sintered sanidine glass-ceramics from industrial wastes

“…The transition temperature, available from dilatometric analysis, is confirmed. Large exothermic and endothermic effects, which correspond, respectively, to crystallization and melting processes, are clearly evident at about 880 and 1100 • C. This thermal analysis constituted an essential reference point for glassceramics manufacturing since, like in previous experiences, 18,19 the processing temperature for achieving glass-ceramics was coincident with the crystallization temperature. This choice was suggested by the expected high nucleating activity of finegrained glass (maximum size of 37 m), and may represent a desirable feature from an economic point of view, due to the lower processing temperature than in other experiences of sintering with concurrent crystallization of glass.…”

“…Such observation is in a good agreement with the ability of nepheline crystals to separate, in powder processed glass-ceramics, after limited sintering times, reported in recent works. 19,32 The precipitated feldspathoids likely acted as nucleating agents for other alumino-silicate phases.…”

Micro- and macro-cellular sintered glass-ceramics from wastes

“…Precisely, for the monoliths, feldspathoid crystals (the first to be developed, according to Bernardo et al) 18 were susceptible to surface crystallization in limited times, like in another work, focused on nepheline glass-ceramics. 15 In the case of porous bodies, the precipitation of crystals is even accelerated, likely due to the high specific surface of cellular materials: in a monolith, the progression of sintering gradually reduces the "free glass surfaces", i.e. the nucleation sites; in a foam, every cell wall may be useful for surface crystallization.…”

“…Feldspar and feldspathoid crystals (like sanidine, trikalsilite, nepheline), known to give notably stable glasses, practically unable to crystallize, have been recently found as the main crystal phase of several sintered glass-ceramics. 15,17,18 Secondly, using fine glass powders may allow the incorporation of secondary phases, like alumina platelets, 14,15 useful for the preparation of strong glass-ceramic matrix composites. Finally, the fine powders may be useful for the preparation of cellular glass-ceramics, deposited on polymeric foams, by the so-called "replication process" (the polymeric foam models the solid fraction of the final cellular material), 19 or mixed with "foaming agents", i.e.…”

“…[11][12][13][14][15][16][17][18] The sintering approach has recently led to significant innovations, applied to fine glass powders (typically <37 m). 14,15,17,18 Firstly, the same enhancement of crystallization, provided by the high specific surface of fine powders, may lead to the development of phases which are hardly found by applying the traditional procedures. Feldspar and feldspathoid crystals (like sanidine, trikalsilite, nepheline), known to give notably stable glasses, practically unable to crystallize, have been recently found as the main crystal phase of several sintered glass-ceramics.…”