Ni-doped Hibonite (CaAl12O19): A New Turquoise Blue Ceramic Pigment

A new structure for ceramic pigments was synthesized by a conventional solid state reaction process. It is based on Ni-doped hibonite, CaAl12O19, which assumes a turquoise-like blue colour similar to that of V-doped zircon. Hibonite is associated with anorthite, CaAl2Si2O8, acting like a fluxing agent in order to lower the synthesis temperature, and with cassiterite, SnO2, acting as a tin buffer to promote coupled Ni2+ + Sn4+ -> Al3+ + Al3+ substitution, in order to ensure the electric neutrality of the hibonite lattice. Since relatively low chromophore contents are required, this new system constitutes an interesting alternative to the common blue ceramic pigments based on cobalt aluminate spinel or vanadium-doped zircon, implying lower cost and environmental advantages. The pigments characterization was performed by X-ray powder diffraction, diffuse reflectance spectroscopy, CIELAB colourimetric analysis, and testing in ceramic glazes and bodies. The substitution of Al3+ by bigger ions, like Ni2+ and Sn4+, increases the cell volume compared to undoped hibonite and is responsible of the turquoise blue colour, as verified by UV-Vis analysis. The chromatic mechanism is due to incorporation of Ni2+ in tetrahedral coordination, likely occurring at the site M3 of the hibonite lattice, where it partially substitutes the Al3+ ion. While this product shows a strong hue as a pigment, it is not stable after severe testing in glazes and attempts to improve its colouring performance are now under development

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta