Preparation and properties of calcium hexaluminate blue ceramics

The doping of nickel and titanium is evaluated with the goal of coloring calcium hexaluminate ceramic (CaAl_12−2xNi_xTi_xO₁₉) and improving mechanical properties. The samples prepared by solid-phase reaction are studied with X-ray diffraction, UV–Vis diffuse reflection, a Konica Minolta colorimeter, scanning electron microscopy, and an indentation test of hardness. The increase in dopant content increases the fracture toughness of CaAl₁₂O₁₉, enabling us to obtain a pure blue ceramic material with a doping amount of x = 0.8. With the increase of Ni²⁺ and Ti⁴⁺, the color of the sample changes. Among the samples, the most vivid blue hue is obtained for an x value of 0.8 with a reflection peak at 473 nm in the UV spectrum and a blueness value (− b*) of 49.2 in the CIE L*a*b* system, which is bluer than cobalt-doped ceramics. The emission spectra of CaAl₁₂O₁₉ in the visible region confirmed that Ni²⁺ replaces Al³⁺ in the tetrahedron and causes an electron transition. The results also indicate that the incorporation of Ni²⁺ and Ti⁴⁺ increases the hardness of the sample and the fracture toughness, with the hardness of pure calcium aluminate increased by 22.1%.