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

Abstract—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.