Sintering behaviour of spinel-alumina composites

Abstract

Study of alumina-magnesia binary phase diagram reveals that around 40-50 wt% alumina dissolves in spinel (MgAl 2 O 4 ) at 1600°C. Solid solubility of alumina in spinel decreases rapidly with decreasing temperature, which causes exsolution of alumina from spinel phase. Previous work of one of the authors revealed that the exsolution of alumina makes some interlocking structures in between alumina and spinel phases. In the present investigation, refractory grade calcined alumina and spinel powder were used to make different batch compositions. Green pellets, formed at a pressure of 1550 kg cm -2 were fired at different temperatures of 1500°, 1550° and 1600°C for 2 h soaking time. Bulk density, percent apparent porosity, firing shrinkage etc were measured at each temperature. Sintering results were analysed to understand the mechanism of spinel-alumina interactions. SEM study of present samples does not reveal the distinct precipitation of needle shaped α-alumina from spinel, but has some effect on densification process of spinel-alumina composites. Microstructural differences between present and previous work suggest an ample scope of further work in spinel-alumina composites.

Observation and partly characterisation of silver nanoparticles in X-ray irradiated radiophotoluminescent phosphate glass

“…A lattice fringe spacing of approximately 0.22-0.30 nm was observed in the precipitated particles as shown in Fig.6 (a), which is in good agreement with those of 0.24 nm (Ag (1 1 1)) and 0.28-0.3 nm (silver oxide) in soda-lime silicate glasses [25] and silica thin films [26] with Ag particles. A qualitative composition analysis using EDXS during TEM confirmed that these spherical particles were silver nanoparticles.…”

“…In the case of the GD-450 dosimeter used in this work, the peak intensity at 310 nm linearly increased up to 5 Gy for X-ray irradiation [24]. Similar investigations on phosphate-and silicate-based glasses containing silver have been performed by TEM analysis and various optical measurements to understand the origin of the induced bands and the mechanisms of nucleation and growth processes [18,[25][26][27][28]. Fig.…”

On the origin of the changes in color of Ag/Al2O3 catalysts during storage

“…Ag 0 nanoparticles smaller than 10 nm, such as silver colloids in water, are yellow, and exhibit a SPR absorption band at around 400 nm [63][64][65]. A yellow color has also been reported for Ag 0 particles interacting with a support [22,65,66]. Since no Ag particles are detected by XRD or TEM in our calcined samples, this means that they are smaller than 1 nm (i.e., containing less than 50 atoms).…”

“…Since no Ag particles are detected by XRD or TEM in our calcined samples, this means that they are smaller than 1 nm (i.e., containing less than 50 atoms). Accordingly, Pal and De [65] could not observe either any nanoparticles in a yellow Ag/porous silica film calcined in air at 450 °C. Hence, the band at 350 nm and the yellow color of our samples can result from the SPR of Agn clusters, neutral or slightly positively charged and containing a small number of Ag atoms.…”

“…Indeed, for silver, and in contrast with gold, even tiny Ag particles [20] or clusters of less than 20 atoms, whether they are neutral [61] or ionic [62], generate surface plasmon resonance like much larger metallic Ag particles. Ag 0 nanoparticles smaller than 10 nm, such as silver colloids in water, are yellow, and exhibit a SPR absorption band at around 400 nm [63][64][65]. A yellow color has also been reported for Ag 0 particles interacting with a support [22,65,66].…”