The reactivity of the Ti-Al system was investigated experimentally in the case of reactive laminated particles produced by High Energy Ball Milling. The ignition temperature for self-sustaining reaction was measured as a function of the heating rate. By means of the Kissinger analysis, two activation energies were evaluated. The first one is associated to the solid state transformation at interface below the melting point of Al. The second one corresponds to the exothermic dissolution of Ti into Al liquid together with the formation of TiAl 3 . A complementary microscopic approach was developed in order to detect all elemental processes associated the reactivity of the Ti-Al system in composite materials.Above the melting temperature of Al, the exothermic dissolution of Ti into the liquid layer starts and induces a self-sustaining behavior until the reaction is complete. The dissolution step is limited by the low solubility of Ti in Al. The formation of the intermetallic compound TiAl 3 was observed. The microscopic analysis of the dissolution at interface explains some specific features of reactive particles.
The densification of CaLa 2 S 4 (CLS) powders prepared by combustion method was investigated by the use of Field-Assisted Sintering Technique (FAST) and Hot Pressing (HP). CLS powders were sintered using FAST at 1000°C at different pressures and heating rates and sintered by HP under 120 MPa from 800°C to 1100°C for 6 hours with a heating rate of 10°C/min. Comparison of both techniques was further realized by use of the same conditions of pressure, dwell time, and heating rate. Complementary techniques (XRD, SEM-EDS, density measurements, FTIR spectroscopy) were employed to correlate the sintering processes/parameters to the microstructural/compositional developments and optical transmission of the ceramics. Both sintering techniques produce ceramics with submicrometer grain size and relative density of about 99%.Nevertheless, HP is more suitable to densify CLS ceramics without fragmentation and also reach higher transmission than FAST. Transmission of 40%-45% was measured out of a possible maximum of 69% based on the Fresnel losses in the 8-14 μm window when HP is applied at 1000°C for 6 hours under 120 MPa. In both techniques, ceramics undergo reduction issues that originate from graphitic sintering atmosphere.
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