abstract
Inorganic pigments are substances that develop colour in organic solids such as ceramics and glazes, and are usually a complex mixture of oxides, and relatively low-cost. Their chromatic properties have been extensively studied, yet surprisingly the magnetic and electrical properties of these economic and common materials have been neglected, despite the fact many are based on ferrite spinels. Therefore, we investigated these properties in commercial black and brown pigments, to assess their potential as magnetic materials. The brown and black pigments were found to be spinel ferrites, with estimated formulas of Fe1.34Cr0.62Mn0.66Zn0.22Ni0.10Co0.06O4 and Fe1.02Cr0.97Co0.57Mn0.23Ni0.21O4, respectively. The brown pigment also contained a higher amount of SiO2 compared to the black pigment (similar to 7 mol% vs. similar to 2 mol%), which appeared as a second phase of crystalline quartz, and adversely affected its porosity, magnetisation and electrical ac conductivity, compared to the black pigment. However, both were very magnetic and very soft ferrites. The brown pigment had M-s=11.7 A m(2) kg(-1) and H-c of 1.5 kA m(-1), with a high electrical conductivity (sigma) of 4 x 10(-4)-7 x 10(-3) Omega(-1) m(-1) between 100 Hz and 1 MHz. The black pigment was equally magnetically soft, but had a much greater magnetisation and lower electrical conductivity, with M-s=18.7 A m(2) kg(-1), H-c=2.4 kA m(-1), and sigma=5 x 10(-6)-8 x 10(-5) Omega(-1) m(-1) between 100 Hz and 1 MHz. This work has revealed the potential hidden value of low-cost commercial inorganic pigments based on spinel ferrites as magnetic materials. This demonstrates their potential at low-cost alternative materials for applications such as in power supply transformers, switching materials and sensors, where soft magnetisation is especially important. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
keywords
SUBSTITUTED COBALT FERRITES; BLACK CERAMIC PIGMENTS; AUTO COMBUSTION METHOD; ELECTRICAL-PROPERTIES; CHROMATIC PROPERTIES; HEXAFERRITE
subject category
Materials Science
authors
Novais, RM; Seabra, MP; Amaral, JS; Pullar, RC
our authors
João Cunha de Sequeira Amaral
Assistant Researcher
Maria Paula Seabra
Assistant Professor
Rob Pullar
Collaborator
Rui Miguel Novais
Assistant ProfessorGroups
G2 - Photonic, Electronic and Magnetic Materials
G4 - Renewable Materials and Circular Economy
acknowledgements
This work was developed in the scope of the project CICECO-Aveiro Institute of Materials (Ref. FCT UID /CTM /50011/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. R. C Pullar wishes to thank FCT Grant SFRH/BPD/97115/2013 for supporting this work. The authors acknowledge GRESIEL for providing the inorganic pigments.