Inorganic Mn-Based Core–Shell Pigments by Solution-Combustion Synthesis with Citric Acid as a Fuel

Core–shell pigments of a beige–brown gamut were produced by solution-combustion synthesis (SCS) from Mg, Mn, and Al nitrates using citric acid as a fuel and characterized by XRD, FTIR spectra, and SEM. Marshalite powder particles were used as a core, while SCS-produced solid solution of alumina-magnesia spinel served as a colored shell. SCS from acidic solution (pH 2) favored the formation of galaxite MnAl2O4 in resultant white pigment. Brown pigment was prepared similarly with the only difference that Mn3O4 was added to the black powder formed just upon gel combustion. Brown pigments represent solid solutions of alumina-magnesia spinel МgAl2O4, galaxite MnAl2O4, and hausmannite Mn3O4. The method is facile and rather scalable. The use of natural marshalite as a core affords for reducing the production cost of inorganic pigments.