Sintering of Si3N4 compounds requires additives that promote densification through the dissolution-precipitation mechanism in liquid phase sintering. The sintering of the Si3N4 with the SiO2-Y2O3-Al2O3 system has been extensively studied. Nevertheless, because SiO2 depends on the natural amount on the Si3N4 surface, little has been studied about SiO2 control. A pre-sintering treatment can increase the content of SiO2 through controlled oxidation of Si3N4. In this work the effect of the additive content on the densification of Si3N4 composite ceramics was evaluated. For this purpose, powder mixtures of Si3N4, Y2O3 and Al2O3 were prepared. The Y2O3 and Al2O3 ratio were modified in percentages of 4, 8 and 12% by weight. The mixtures were compacted and pre-sintered at 1300°C for 1 hour. Then, these were sintered at 1450°C for two hours. The samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results showed that during pre-sintering, the Y5(SiO4)3N phase is formed; then, it's subsequently oxidized at the sintering stage. A second phase identified as Y3Al5O12 was found in samples with higher proportions of Al2O3. Composition and quantity of the observed phases depend of Y2O3 and Al2O3 proportion in the added additive.

The atomic structure, electronic structure, and physical properties of (TiZrNbCu)1−xNix (x ≤ 0.5) metallic glasses (MGs) were studied in both the high-entropy (0 < x < 0.35) and the higher Ni concentration range (x ≥ 0.35). Atomic structure studies performed with X-ray diffraction and synchrotron powder diffraction provided average atomic volumes, structure factors, radial distribution functions, coordination numbers, and packing densities. Electronic structure studies performed using photoemission spectroscopy and low-temperature specific heat provided information about the electronic density of states within the valence band and at the Fermi level and also about interatomic bonding and atomic vibrations [from the Debye temperature and the boson peak (BP)]. Variations of both atomic structure and electronic structure with x showed a clear change for x ≥ 0.35, which corresponds to a valence electron number ≥7.4. All physical properties, namely, thermal stability parameters, Debye temperatures, BPs, magnetic, elastic, and electronic transport properties, change their concentration-dependence for x ≥ 0.35. The results are compared with those for binary and ternary MGs of the same elements.