Blue pigments based on Co
x
Zn
1Àx
Al
2
O
4
spinels synthesized by the polymeric
precursor method
Luiz K.C. de Souza
a
, Jose
´
R. Zamian
a
, Geraldo N. da Rocha Filho
a
, Luiz E.B. Soledade
b
, Ieda M.G. dos
Santos
b
, Antonio G. Souza
b
, Thomas Scheller
c
,Ro
ˆ
mulo S. Ange
´
lica
c
, Carlos E.F. da Costa
a
,
*
a
Laborato
´
rio de Cata
´
lise e Oleoquı
´
mica, ICEN, UFPA, Bele
´
m, Para
´
, Brazil
b
LACOM, Departamento de Quı
´
mica/CCEN, Universidade Federal da Paraı
´
ba, Campus I, CEP 58059-900, Joa
˜
o Pessoa, PB, Brazil
c
Universidade Federal do Para
´
, Centro de Geocie
ˆ
ncia, Caixa Postal 1611, 66075-110 Bele
´
m, Para
´
, Brazil
article info
Article history:
Received 30 May 2008
Received in revised form
15 September 2008
Accepted 17 September 2008
Available online 10 October 2008
Keywords:
Spinel
Polymeric precursor
Ceramic pigment
Chromophore elements
UV–vis
Colorimetric coordinates
abstract
The Co
x
Zn
1Àx
Al
2
O
4
system (x ¼ 0; 0.1; 0.3; 0.5; 0.7; 0.9 and 1) was synthesized by the polymeric
precursor method and characterized by the techniques XRD, TG-DTA, IR, UV–vis and colorimetry. The
XRD patterns displayed the characteristic peaks of the spinel structure and a good crystallinity. The DTA
curves showed an exothermic peak corresponding to the enthalpy of the transition taking place at about
700
C. The infrared spectra displayed vibrations at about 650, 550, 540, 520, 500, 490 cm
À1
, which were
ascribed to the spinel structure. The UV–vis spectra presented three bands at 550, 580 and 620 nm
attributed to the Co
2þ
spin transitions in tetrahedral sites. The colorimetric data point out the formation
of blue pigments, corresponding to highly negative values of b
*
. The lightness, coordinate L
*
, increases
with the heat treatment temperature. These facts reveal that Co
x
Zn
1Àx
Al
2
O
4
is a promising system that
can be employed to obtain ceramic blue pigments.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
Spinel-type oxide materials have attracted a great deal of
attention from scientists and industry leaders because of their
relevant magnetic, refractory and semiconducting properties [1,2].
The spinel structure, featuring the general formula AB
2
O
4
displays
64 tetrahedral sites and 32 octahedral sites, of which only 8
tetrahedral sites and 16 octahedral sites are occupied by the cations
A
2þ
and B
3þ
, respectively. There are two ideal types of this struc-
ture: the first one is the normal spinel, in which the tetrahedral
sites are occupied by the cations A
2þ
and the octahedral sites by the
cations B
3þ
. The second ideal type is the inverse spinel, in which all
the tetrahedral sites are occupied by cations B
3þ
, while an equal
number of cations A
2þ
and B
3þ
share the octahedral sites [3,4].
Besides these ideal structures, spinels can display a partially
inverted structure, moreover with the presence of a T-dependent
cation. In this case the occupancy of tetrahedral and octahedral
cations will shift toward a random distribution with increasing
temperature [5].
Recently, a new application of the spinels as ceramic pigments
has been explored, owing to their high mechanical resistance, high
thermal stability, low temperature sinterability and the easy
incorporation of chromophore ions into the spinel lattice, allowing
for different types of doping, thus producing ceramic pigments
with different colors [1–6].
Blue pigments are widely used in industry to bring color to
plastics, paints, fibers, papers, rubbers, glass, cement, glazes,
ceramics and porcelain enamels [7]. The main source of ceramic
blue pigments is cobalt, in compounds such as Co
2
SiO
4
(olivine),
(Co,Zn)
2
SiO
4
(willemite) and CoAl
2
O
4
(cobalt spinel). But cobalt is
scarce and expensive, thus increasing the production costs of
cobalt-based ceramic pigments. Moreover, serious environmental
problems may occur from the manufacturing process of Co-based
ceramic pigments [6].
Therefore, the present paper aims at synthesizing ceramic blue
pigments from the Co
x
Zn
1Àx
Al
2
O
4
(x ¼ 0; 0.1; 0.3; 0.5; 0.7; 0.9 and 1)
system, synthesized by means of the polymeric precursor method.
Gouveia et al. [8], Kakihana [9] and Lessing [10] provide a descrip-
tion and discussion of such synthesis method. The Co
x
Zn
1Àx
Al
2
O
4
system allows for a reduction of the production costs and also for
minimizing the environmental damage, as the amount of Co is
reduced.
Several methods can be employed for the synthesis of simple
oxides oroxide-based systems.The mostcommonmethods are:solid
state reaction [11], sol–gel [12], micro-emulsion [4], co-precipitation
*
Corresponding author. Tel./fax: þ55 91 32017364.
E-mail address: emmerson@ufpa.br (C.E.F. da Costa).
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
0143-7208/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2008.09.017
Dyes and Pigments 81 (2009) 187–192