The effect of composition and synthesis conditions on the structure of cobalt-bearing pigments of the spinel type

Abstract

The results of producing cobalt-bearing spinels of a blue-sky to blue color range by self-propagating high-temperature synthesis (SHS) are described. The effect of the conditions of synthesis and the mixture composition on the structure of compounds obtained is demonstrated. The SHS method makes it possible to obtain spinels that can be used as ceramic pigments.One of the methods for producing pigments of the spinel type for ceramic paints and glazes is self-propagating hightemperature synthesis (SHS). It is based on using the heat from exothermic reactions and is faster and more cost-efficient than traditional methods.The purpose of the present paper is to obtain pigments of the spinel type by SHS and to study the effect of the initial composition and conditions of synthesis on the structure formation processes.Pigments were synthesized using Al 2 O 3 , Co 2 O 3 , ZnO, MgO, and aluminum powder ASD-4. Synthesis was performed in a constant-pressure plant in an argon atmosphere and in air. The obtained pigments were identified by x-ray phase analysis on a DRON-UM1 diffractometer (filtered CoK a radiation) and infrared spectroscopy in the range of 1400 -400 cm -1 on a Nicolet 5700 IR-Fourier diffractometer with a diffuse reflection device in KBr. The microstructure of samples was studied using light microscopy (Axiovert 200M).Blue pigments were obtained in the CoO -Al 2 O 3 system. According to the x-ray phase analysis data, the products of synthesis performed in the argon atmosphere contain, besides aluminocobalt spinel CoAl 2 O 4 , also a substantial amount of corundum (Al 2 O 3 ). Furthermore, the products contain metallic cobalt and Co(AlO 2 ) 2 . The IR spectroscopic analysis 2 indicates the formation of a mixed spinel (Fig. 1, curve 1 ) in the system, since in addition to the octahedral aluminum atom [AlO 6 ] whose vibrations are manifested at 560.0 cm -1 , which is typical of normal spinels, we observed also absorption bands of the tetrahedral atom [AlO 4 ] at 624.5 cm -1 , which is present in inverse spinels. Moreover, there is an intense absorption band at 1088.9 cm -1 related to the vibrations of the ion (AlO 2 ) -[1 -3].Synthesis performed in the air atmosphere produces pigments with better color characteristics, which is directly related to their composition and structure. The modification of the structure is clearly visible in the IR spectra of the pigments. Thus, the absorption bands at 886.1, 979.5, and

Preparation and properties of the CoFe2O4–Nb–Pb(Zr,Ti)O3 multiferroic composites prepared in situ by gel-combustion method

“…Due to the stretching vibration of Fe 3+ -O 2− in tetrahedral sites [28], our Co-ferrite shows only one absorption band at around 590 cm −1 . In Co-ferrite, the absorption maximum at 670 cm −1 is due the presence of Co in tetrahedral centers [29]. The octahedral complexes may not be present within the experimental range, because the band position is nearly 400 cm −1 .…”

“…The band at 1640 cm −1 present in CoFe 2 O 4 sintered at 900 • C shows the existence of residues of organic compounds; in the xCF-(1 − x)PZTN after heating treatment at 1100 and 1200 • C this band disappears, indicating the absence of organic compounds in synthesized composites. In Co-ferrite, the absorption maximum at 670 cm −1 is due the presence of Co in tetrahedral centers [29].…”

In situ preparation of CoFe2O4–Pb(ZrTi)O3 multiferroic composites by gel-combustion technique

“…Due to the stretching vibration of Fe 3+ -O 2− for tetrahedral sites,21 all the systems containing the ferrite show an absorption band at ∼590 cm −1 . The presence of Co in tetrahedral centers is proved by the occurrence of the absorption maximum at ∼675 cm −1 , due to the vibration of CoO 4 22. The bands at ∼675 cm −1 and at ∼590 cm −1 present in the spectra of the calcined powders indicate the formation of metal oxide, also confirmed by the XRD analysis as being a spinel single phase.…”

Formation and Coloring Mechanism of Typical Aluminosilicate Clay Minerals for CoAl2O4 Hybrid Pigment Preparation

“…After being calcined at 1,100°C, the typical absorption bands of Kaol at 3,651, 3,684, and 911 cm −1 disappear due to the dehydroxylation of Kaol during calcination. After incorporating of CoAl 2 O 4 nanoparticles, the characteristic absorption bands of CoAl 2 O 4 at 668, 557, and 509 cm −1 were clearly observed, which correspond to the stretching vibration of Al-O of AlO 6 and Co-O of CoO 4 (Chapskaya et al, 2005), respectively. Furthermore, these characteristic adsorption bands also can be found in the FTIR spectrum of CoAl 2 O 4 pigments.…”