Antonino Coglitore

Exploitation of Ceramic Wastes by Recycling in Alumina-Mullite Refractories

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.

15-15Ti(Si) austenitic steel: Creep behaviour in hostile environment

This work aims at studying the creep behaviour of 15-15Ti(Si) austenitic steel, under uniaxial stress (range of 300-560 MPa), and its interaction with liquid lead. The steel was tested to verify its sensitivity to Liquid Metal Embrittlement (LME) and to simulate its behaviour in operating thermal and mechanical stress conditions of the IV generation Lead-cooled fast reactor. The experimental results permitted to plot the time-strain creep curve and the characteristic Norton-based curve, simulating the creep behaviour at all stress values. The comparison between the creep curves in air and in lead showed that the LME produces a decrease of creep-rupture time, a reduction of creep strain and then the loss of steel ductility. Moreover, the raw material and fracture surfaces were analyzed by Optical Microscope and Scanning Electron Microscope (SEM). SEM micrographs highlighted that lead changes both the mode and the type of specimen fracture. In addition, it was analyzed the lead action time, as the time after which the corrosion appears with macroscopic effects. Although some tests are still ongoing, it can be assumed that at high stresses, LME takes place after a long time of steel/lead contact while at low stresses, LME tends to prevail on creep effect.