Synthesis, stability and coloring properties of yellow–orange pigments based on Ni-doped karrooite (Ni,Mg)Ti2O5

Synthesis and coloring performance of Ni-geikielite (Ni,Mg)TiO3 yellow pigments: Effect of temperature, Ni-doping and synthesis method

“…On the other hand, ilmenite Mg 1−x Ni x TiO 3 compositions (x = 0, 0.1, 0.2 and 0.4) were also prepared in aqueous media by a citrategel metalorganic decomposition route (MOD), following the same preparation steps previously reported for Ni-MgTi 2 O 5 pigments [10]. Mg(NO 3 ) 2 ·6H 2 O (98%, Panreac), Ni(NO 3 ) 2 ·6H 2 O (99%, Aldrich) and Ti n-butoxide (Ti[O(CH 2 ) 3 CH 3 ] 4 , 97%, Aldrich) were used as precursors, and citric acid (C 6 H 8 O 7 , 99.5%) was added as chelating agent, this time with a 2:1 molar ratio (citric acid:ilmenite).…”

“…In most cases, however, a much better understanding of the crucial role played by crystal chemical aspects is still needed to modulate or improve the coloring performance of already known or even new ceramic pigments. By an accurate knowledge and control of chromophore metal-oxygen distances [3], local environment distortions [6][7][8], cation order-disorder phenomena [9,10], structural relaxation or covalence effects [11] etc., the band gap energies [12][13][14], metal-ligand charge transfers [8] and crystal field intensities and energies on chromophore ions in a particular coordination environment can be tuned [11,12,15], and this is of paramount importance to optimize the coloring properties or to discover new ceramic pigments [16].…”

“…As an illustrative example, aiming to develop new yellow ceramic pigments we recently investigated the solid solubility of Ni 2+ in MgTi 2 O 5 pseudobrookite (karrooite) [10], and observed a noticeable increase of the yellowish orange color (chroma and intensity) with firing temperature (from 1200 to 1400 • C) and Ni content up to a certain amount (40-50 mol%). However, the partial cation disorder of Ni 2+ between both distorted octahedral sites of karrooite (M1 and M2) gave rise to rather broad absorption bands [9,10], and a relatively too-high amount of Ni (40 mol%) was required to obtain acceptably intense orange colors.…”

“…However, the partial cation disorder of Ni 2+ between both distorted octahedral sites of karrooite (M1 and M2) gave rise to rather broad absorption bands [9,10], and a relatively too-high amount of Ni (40 mol%) was required to obtain acceptably intense orange colors. Since pure and intense yellow colors were not achieved in this Ni-karrooite system, we thought it could be interesting to analyze the effect on coloring properties of accommodating Ni 2+ ions in the octahedral sites of other closely-related Mg titanate structures of the same MgO:TiO 2 system, namely the ilmenite (MgTiO 3 geikielite) and spinel (Mg 2 TiO 4 qandilite) compounds, with 1:1 and 2:1 Mg:Ti molar ratios respectively (1:2 in karrooite) [17,18].…”

“…), metal titanates have been synthesized through a plethora of wet-chemistry methods, such as coprecipitation [31], Pechini [45], citrates [46], sol-gel [25,37,47], solution combusting [35] or stearic acid gel [48] routes. Herein, as an alternative to the solid-state method, we employed a more homogeneous and reactive citrate-gel route (or metalorganic decomposition, MOD), which enables the formation at lower temperatures of more homogeneous multicomponent powders (mixed oxides) with finer-grained submicronic morphologies [10,[49][50][51][52].…”