Environmentally Benign Solution‐Based Procedure for the Fabrication of Metal Oxide Coatings on Metallic Pigments

Abstract

Aluminum pigments were coated with Fe2O3 and CuO by solution‐based thermal decomposition of the urea nitrate compounds hexakisureairon(III)nitrate and tetrakisureacopper(II)nitrate. The deposition process was optimized to obtain homogeneously coated aluminum pigments. The growth of the surface coatings was controlled by investigation with scanning electron microscopy, energy dispersive X‐ray spectroscopy and static light scattering as well as infrared, X‐ray diffraction and thermogravimetric analysis. The iron precursor showed an incomplete decomposition in solution, incorporating traces of urea molecules inside the coatings while the copper precursor showed complete dissociation accompanied by in situ formation of amine complexes. The amount of organic residues resulting from ligand fragments in the final oxide coatings could be reduced to 22 % for the iron oxide and 12 % for the copper oxide by further temperature treatment in solution (259 °C). Colorimetric investigations of the obtained pigments revealed an excellent hiding power, outperforming the pigments used in current state‐of‐the‐art formulations.

Hexakis(urea-O)iron Complex Salts as a Versatile Material Family: Overview of Their Properties and Applications

“…UV−vis Spectroscopy. Jørgensen determined the electronic transitions of the [Fe(urea) 6 ] 3+ complex cation 45,46 as 4 Γ 4 (G) ← 6∑ = 800 nm, 4 Γ 5 (G)← 6∑ = 584 nm, 4 Γ 1 (G) ← 6∑ = 433 nm, and 4 Γ 3 (G) ← 6∑ = 427 nm. Holt et al measured the UV−vis spectra of hexakis(urea)iron(III) perchlorate at both 298 and 20 K temperatures and with different polarizations (σ and π).…”

“…48 Carp et al measured the UV−vis spectra of hexakis(urea)iron(III) nitrate. 31 Two broad, low-intensity peaks with shoulders ∼600 and ∼850 nm, belonging to the 4 T 2g (G) ← 6 A 1 transition and the 4 T 1g (G) ← 6 A 1 transition, respectively. The 4 T 2g (G) ← 6 A 1 and 4 A g , 4 E g (G) ← 6 A 1 transitions of compound 7 were observed at 590 (very weak and broad band) and 432 nm, respectively, and both transitions are due to the degeneration of the octahedral symmetry of the [Fe(urea) 6 ] 3+ ion.…”

“…Yao et al and Gao et al used hexakis­(urea)­iron­(III) chloride (compound 2 ), while Bies et al , used the nitrate salt (compound 1 ) to prepare different γ-Fe 2 O 3 -containing pigments with direct thermal , and solvothermal , heat treatment reaction routes.…”

“…The urea complexes of iron with various anions have enormous importance from scientific and industrial points of view, e.g., in the preparation of selective oxidants for organic chemistry, iron oxide-based catalysts for converting CO 2 into hydrocarbons, nanotube–magnetite nanocomposites, various iron oxides, metallic pigments, and long-lasting trace element fertilizers . Furthermore, iron complexes with urea or urea-like linkages containing ligands ensure excellent potential to prepare bioactive complexes , or precursor materials of different kinds of metal–organic frameworks (MOFs). − …”