Academia Journal of Scientific Research 4(10): 316-326, October 2016

DOI: 10.15413/ajsr.2016.0604
ISSN: 2315-7712
©2016 Academia Publishing

Research Paper

Synthesis of CoCuMnOx Pigments for Solar Collectors Absorbent Enamels

Accepted 19th May 2016

ABSTRACT

This aim of this research is to produce Co, Cu and Mn mixed oxides by means of
M.C. Gardey Merino1*, J.A.Alonso2, G.E.Lascalea3 one-step solution novel combustion methods using aspartic acid, lysine or
and P.Vazquez4
ethylenediaminetetraacetic acid as fuels. The pigments were characterized using
1Grupo CLIOPE, National Technological x-ray diffraction, scanning and transmission electron microscopy, infrared
University, Reg. Mendoza, Rodríguez 273, spectroscopy with Fourier transform, Brunauer–Emmett–Teller techniques and
Mendoza (M5502AJE), Argentina. the crystal structures refined by the Rietveld method. Finally, an enamel of
2Instituto de Ciencia de Materiales de Madrid

(CSIC), Cantoblanco, 28049 Madrid, Spain. alkyd- resin base was prepared with the pigment obtained and applied on an
3Laboratorio de Química Ambiental (LQA)- aluminum substrate (coating). In this coating, the solar spectral absorbance was
IANIGLA- CONICET-Mendoza Av. Ruiz Leal s/n determined. The obtained powders showed a CoCuMnO4 composition with spinel
Parque Gral. San Martin, CC. 131, M5502IRA, structure. An extraordinary value of absorption on the coatings between 95 and
Mendoza, Argentina.
4CINDECA, CCT CONICET - La Plata, 47 Street 97% was noted. The temperature achieved by coating to the sun was higher than
N° 257, La Plata (B1900AJK), Buenos Aires, that obtained for commercial black coating. These results suggest the possibility
Argentina. of utilizing these oxides in absorbent solar enamels.
*Corresponding author. E-mail:
mcgardey@frm.utn.edu.ar. Tel/fax: +54261- Key words: Oxides, optical materials, chemical synthesis, X-ray diffraction,
5244694/+542615244531. electron microscopy, optical properties.

INTRODUCTION

Electricity generation from renewable sources The efficiency of a solar thermal collector depends on
approximately tripled between 2010 and 2035 attaining the materials used as absorber coatings, especially on their
31% of the entire energy production. The use of renewable optical properties. As regards the absorption of the solar
sources is expected to reduce CO2 emissions by over 4.1 Gt spectrum, the oxides of transition metals (Co, Mn, Fe and
in 2035 contributing to the diversification of energy Cr) present a high absorbance owing to the existence of
sources, diminishing oil and gas import bills, and certainly numerous, allowed, electronic transitions between their
decreasing air pollution (Jebli and Youssef, 2015). In partially full “d” orbitals (Vince et al., 2003). These oxides
particular, solar energy can be used in industrial, are used as absorbents films in solar selective surfaces. For
commercial and domestic areas. In domestic applications, example, CuFeMnOx highly spectrally selective black films
households consume energy in air conditioning, heating, for solar absorbers can be made using sol–gel syntheses
water heating, lighting and other applications (Al-Khaffajy combined with dip coating or slip casting deposition
and Mossad, 2013). techniques (Kaluža et al., 2001); also, titanium-doped and
Solar thermal systems proved to be a valid way of undoped CuCoMnOx spinel films deposited on Al
utilizing the huge potential of the available solar energy. substrates from sols with their solar absorbance (αs)
Solar thermal collectors convert incident radiation through ranging between 85 and 91% that presents an infrared
photo thermal conversion into useful energy, that is, heat. emittance of 3.6% (Vince et al., 2003) and finally, selective
This is transferred to a working fluid and used in a variety absorber coatings with composition Cu1.5Mn1.5O4 can be
of ways such as space heating and electricity production successfully deposited on aluminum and stainless steel
(Trease et al., 2013). substrates by sol–gel dip-coating method (Pal et al., 2013).
 Academia Journal of Scientific Research; Merito et al. 317

Ternary spinel oxides powders are used as absorber glycine and urea as fuels was studied to obtain Co3O4
pigments in solar selective surfaces obtained by sol–gel through stoichiometric combustion syntheses and in
combustion method followed by air calcination at 500ºC studies for optimized combustion reaction to obtain Al2O3
for 1 h. A novel low-cost spectrally selective coating using with eight different fuels as lysine, glutamine and arginine
CoCuMnOx powders as solar-absorbing pigment is etc (Toniolo et al., 2010).
prepared by means of a spray-coating technique. By This work is aimed at the production of Co, Cu and Mn
optimizing the paint coating thickness, optical parameter mixed oxides by means of an original one-step
values of absorbance reached 92.8% and infrared stoichiometric combustion methods from Mn(NO3)2,
emittance showed a value of 19.8% (Geng et al., 2011). Co(NO3)26H2O, Cu(NO3)23H2O and aspartic acid (Asp),
By sol-gel techniques, it is possible to obtain thermally lysine (Lys) or ethylene diamine tetra-acetic acid (EDTA)
stable nano-structured pigments based on mixed metal as fuels. Once obtained by combustion processes, the ashes
oxides as CoCuMnOx (Fawzia et al., 2013: 231 - 236) that were calcined at 500°C in order to get the pigments with
could be used as absorber materials for heating collectors the desired crystalline structure. The powders were
due to their high absorption and moderate low reflectance characterized by x-ray diffraction (XRD), scanning electron
in the solar wavelength range. Similarly, cobalt and nickel microscopy (SEM), transmission electron microscopy
oxide nano-pigments were obtained with the same (TEM), infrared spectroscopy with Fourier transform (FT-
technique (Fawzia et al., 2015: 347 - 357). IR) and Brunauer–Emmett–Teller (BET) techniques and
Additionally, CuCr0.5Mn1.5O4 pigments were obtained the crystal structures refined by the Rietveld method.
through sol-gel self-combustion methods and then Then, alkyd-based enamel was prepared with the pigment
calcined at 700°C. These powders were subsequently used obtained through Asp-based process; the so-prepared
as pigment to prepare selective surfaces, achieving enamel was then applied on an aluminium substrate. The
absorbance (αs) values that ranged between 92 and 93% spectral absorbance plots of those substrates were
and emittance (εt) values ranging between 22 and 23% determined for the solar spectrum range of radiation.
(Geng et al., 2012: 293- 301). Besides, CuCr2O4 spinel Finally, prepared and commercial paint coatings were
powder with high quality black hue was synthesized by exposed to the sun and the temperatures measured to
sol-gel combustion process using citric acid as fuel and contrast with solar absorbance values.
metal nitrates as oxidizers (Geng et al., 2012: 281-288).
Similarly, throughout solution combustion syntheses, it
is possible to obtain Co3O4 absorbent pigment with the MATERIALS AND METHODS
recently proposed novel fuels like aspartic acid (Asp),
tris(hydroximethyl) aminomethane (Gardey et al., 2015: Synthesis of pigments
230 - 238) lysine (Lys) and ethylene diamine tetra-acetic
(EDTA) acid among others (Gardey et al., 2015). These CoCuMnOx powders were obtained by combustion
syntheses imply a low environmental impact because they syntheses using three different fuels; Asp, whose
are one-step processes; all use low quantities of reactive molecular formula is C4H7NO4; Lys, C6H14N2O2 and EDTA,
ashes obtained were always calcined at a relative low C10H16N2O8.
temperature of about 500°C. These processes are
consistent with the following principles of Green
Chemistry (Anastas and Warner, 1998): N°3 Design Synthesis with aspartic acid
synthetic methods to use and generate substances that
minimize toxicity to human health and the environment, In order to obtain a precursor, three different solutions
N°5 minimized the use of auxiliary substances wherever were prepared dissolving the following components in
possible and make them innocuous when used”, N°6 distilled water: First, 5 g Co(NO3)2.6H2O (Aldrich) and 1.43
minimize the energy requirements of chemical processes g Asp (C4H7NO4, Aldrich) getting a pH=3. Second, 5 g
and conduct synthetic methods at ambient temperature Cu(NO3)2.3H2O (Aldrich) and 1.83 g Asp getting a pH=2.
and pressure if possible and N° 8 minimize or avoid Third, 5 g of Mn(NO3)2 (10 ml) and 2.23 g of Asp, pH=3.
unnecessary derivatization if possible, which requires Afterwards, all the solutions were mixed achieving the
additional reagents and generate waste. precursor neededwhich did not show any precipitation.
By solution combustion syntheses, it is possible to obtain The result was concentrated on a hot plate (HP) at 250°C.
nanoparticles with homogenous crystalline structure by a When the remaining liquid was reduced enough, the
one step, simple route. The parameters influencing combustion ignited with sparks and flame. The resulting
combustion reactions include type of fuel, fuel to oxidizer ashes were placed at 200°C in a furnace for one hour to
ratio, use of an excess of oxidizer, ignition temperature and complete the reaction. Then, the black ashes were exposed
water content of the precursor mixture (Toniolo et al., to a two-hour-calcination at 500°C in air resulting in a
2012). The effect of fuel to oxidizer ratio in microstructure sample labelled as CoCuMnOx-Asp.
was studied in the synthesis of Co3O4 using urea as fuel The selection of quantities was carried out on the grounds
(Venkateswara and Sunandana, 2008); the influence of of the following reactions for obtaining Co3O4, Mn2O3 and
 Academia Journal of Scientific Research; Merito et al. 318

Table 1. Formulation of paint.

Ingredient Percentage by weight (%)

CoCuMnOx-Asp pigment 1
Alkyd resin 50
Ultrathin quartz 7
Aluminum powder 1
Solvent, xylene
22,5
Solvent, water
Black ferrite
Thickening agent
9,5
Dispersing agent
Wetting agent

CuO shown in reactions 1, 2 and 3 respectively. the aspartic acid, dissolving the elements in distilled water.
The first solution contained 5 g of Co(NO3)2.6H2O and
45Cu(NO3)26H2O + 28C4H7NO4 15CO3O4 + 59N2 + 112CO2 + 368H2O 1.17 g of EDTA (C10H16N2O8, Tetrahedron) ; for the second
(1) one, 5 g of Cu(NO3)2.3H2O and 1.51 g of EDTA; for the
third, 5 g de Mn(NO3)2 (10 ml) and 1.84 g of EDTA. Finally,
10Mn(NO3)2 + 6C4H7NO4 5Mn2O3 + 13N2 + 24CO2 + 21H2O the three solutions were mixed achieving a precursor
(2) which did not show any precipitation, getting a pH=3. After
HP heating, when the remaining liquid was reduced
15Cu(NO3)23H2O + 10C4H7NO4 15CuO +20N2 +40CO2 +80H2O enough, combustion ignited with sparks and flame.
(3) Afterwards, the process followed the same procedure as
earlier described. The resulting powders after calcination
was labelled CoCuMnOx-EDTA. The selection of quantities
Synthesis with lysine was carried out based on the reaction for obtaining Co3O4,
Mn2O3 and CuO shown in reactions 7, 8 and 9 respectively.
This synthesis was carried out with a similar process as in
the aspartic acid, dissolving the elements in distilled water.
The first solution contained 5 g of Co(NO3)2.6H2O and 0.85 (7)
g of Lys getting a pH=5; for the second one, 5 g of
Cu(NO3)2.3H2O and 1.11 g of Lys where pH=3; for the
third, 5 g de Mn(NO3)2 (10 ml) and 1.34 g of Lys with (8)
pH=3. Finally, the three solutions were mixed achieving a
precursor which did not show any precipitation. After HP
heating, when the remaining liquid was reduced enough, (9)
combustion ignited without sparks or flame. Afterwards,
the process followed the same procedure as earlier
described. The resulting powders after calcination was Paint coating production
labelled CoCuMnOx-Lys. The selection of quantities was
carried out based on the reaction for obtaining Co3O4, Paint coatings were obtained from alkyd paints applied
Mn2O3 and CuO shown in reactions 4, 5 and 6 respectively. over aluminium alloy substrate. First, a wash-primer
chromate based (Norm: SSPC-PT 3-64) was applied over
the substrate to eliminate surface natural aluminium
(4) oxide. After 48 h, absorbent paint was applied with a
brush. The absorbent paint was produced following the
formulation listed in Table 1 for 100 g. Solid ingredients
(5) were mixed in a mortar and then solvents were added.
This coating is named “absorbent paint coating”.

(6)
Pigments characterization

Synthesis with EDTA The phases contained in the resulting powders were
identified by XRD using a Pan Analytical X'PertPRO with a
This synthesis was carried out with a similar process as in copper anode. Additionally, it was determined at the
 Academia Journal of Scientific Research; Merito et al. 319

Table 2. Mean temperatures calculated for each period in both coatings.

Temperature (°C)
Pe Period
January March April
Coating type
Commercial Absorbent Commercial Absorbent Commercial Absorbent
Hour
9 24.53 24.61 20.40 20.25 15.61 15.63
10 34.15 33.85 25.04 23.59 19.84 19.13
11 47.41 49.90 35.97 36.04 31.10 31.31
12 58.18 60.59 43.26 44.02 39.33 39.81
13 64.73 67.06 48.98 49.94 46.34 46.89
14 64.53 66.96 50.85 51.88 48.80 49.63
15 59.96 62.23 52.87 53.77 48.35 49.39
16 57.48 59.65 50.99 51.85 46.67 47.80
17 56.39 58.44 47.08 48.03 40.77 42.05
18 50.52 52.32 40.43 42.09 33.54 35.19
19 41.91 43.31 31.44 32.57 25.45 26.64
20 33.92 34.71 27.69 28.38 21.86 22.45

average crystallite size from the width of Bragg peaks coating is named commercial coating. For each twenty-
using Scherrer equation in the peak at 2θ 36°. The two-day period, an hourly average was calculated to obtain
morphology of the powders was observed through a JEOL 24 mean hourly values. Table 2 shows these values
model 6610 LV microscope. The shape and size of the between 9 and 20 h. Additionally, differences of
particles were observed by TEM with a JEOL 100 CX II temperatures between prepared and commercial coatings
(JAPAN, 1983) microscope using a voltage of 100 kV. FT-IR are shown in Table 2 for the three periods. Finally, Figure
plots were obtained by a Bruker IFS 66 and textural 7 shows the mean temperature evolution for a day in
properties by BET technique with a Micromeritics January.
Accusorb 2100.

RESULTS AND DISCUSSION

Paint coating characterization
The diffraction diagrams of the obtained powders
The hemispherical reflectance spectra of paint coatings in correspond to the CoCuMnOx phase with a cubic spinel
the wavelength ranged between 0.32 to 2.5 µm were structure (Figure 1), according to the PDF card No. 47-
recorded with a UV/Vis/NIR Perkin–Elmer LAMBDA 900 0324. As previously reported in scientific literature, from
double beam spectrophotometer equipped with a standard sol-gel combustion synthesis of CoCuMnOx using citric acid
Lab sphere 150 mm integrating sphere. as fuel, the desired phase only appears at above 500°C
mixed with other phases (Geng et al., 2011). Another
segregated phase such as Mn2O3 appears together with
Temperature measurements CoCuMnOx phase- in the powders obtained by sol-gel
synthesis after calcination at 500°C (Kaluža et al., 2001).
A T-type thermocouple was placed underneath the Additionally, by solution combustion synthesis it is
absorbent paint coatings and exposed to the sun. The possible to stabilize the homogenous crystalline phase at
thermocouple was connected to a data logger HO-BO to 500°C, whereas by sol-gel route it is stabilized at 800°C
save the information. The measurements were carried out (Fawzia et al., 2013: 231 - 236). The advantage of the
taking data every 1 min during periods of 22 days, solution combustion synthesis presented here is,
resulting in 32500 values approximately for each period. therefore, the production of mixed oxides with a pure and
The periods considered were three: January, 13th to homogenous crystalline phase obtained at low-
February, 5th (Period of January), March, 3rd to 27th (Period temperature by means of a sustainable and simple method
of March) and April, 1st to 24th (Period of April). as compared with other methods (Kaluža et al., 2001; Geng
Measurements were carried out in Mendoza, Argentina. et al., 2011; Fawzia et al., 2013: 231 - 236). The Rietveld
With the objective to compare temperature analysis allowed the refinement of the spinel structure
measurements, a second coating was obtained from high- with a model assuming that Cu occupies the tetrahedral A
temperature aerosol black paint (Special purpose Krylon positions and Co and Mn are located at random at the
High Heat and Radiator) applied over the similar alloys octahedral B sites of the AB2O4 structure, that is,
substrate used in absorbent paint coating. This second Cu(CoMn)O4 as shown in Figure 2, with unit-cell
 Academia Journal of Scientific Research; Merito et al. 320

1600

[311] 1600
1400 CoCuMnOx-Edta
1400
1200
Cu(MnCo)O4, EDTA
1200 DRX, CuKa
1000
1000
Intensity (a.u)

800

intensity a.u.
800
[220]
600
600
[511]
[422] 400
400 [400]
[111]
[222] [440] 200
200
0

0 -200

10 20 30 40 50 60 70 10 20 30 40 50 60 70
2(°) 2 theta (deg)

Figure 1. Diffraction diagrams and Rietveld analysis of CoCuMnOx-EDTA sample.

Cu

(Co Mn)

Fd3m
Figure 2. Cubic crystal structure observed for all obtained powders. Cu occupies the tetrahedral A positions and
Co and Mn are located at random at the octahedral B sites of the AB 2O4 spinel structure, with crystallographic
formula Cu(CoMn)O4.
 Academia Journal of Scientific Research; Merito et al. 321

1600 1600

1400 CoCuMnOx-Asp
1400

CoCuMnOx-Lys
1200 1200

Intensity (a.u)
Intensity (a.u)

1000 1000

800 800

600 600

400 400

200 200

0 0

10 20 30 40 50 60 70 10 20 30 40 50 60 70
2(°) 2(°)

Figure 3. Diffraction diagrams of CoCuMnOx-Asp and CoCuMnOx-Lys samples.

Table 3. Average crystallite size and the specific surface area for all obtained powders

Surface specific area

Ingredient Crystalline phase Crystallite size (nm)
(m2/g)
CoCuMnOx- Lys 23 ± 2 11± 1
CoCuMnOx- Asp Cu(CoMnO4) 23 ± 2 7± 1
CoCuMnOx- EDTA 26± 3 3±1

parameters in the range 8.18 to 8.21 Å, as described in flameless and non-sparking synthesis. Similar polyhedral
literature for this composition. In Figure 1, the diffraction shapes were observed in nanoparticles of CuCrMnO4
diagram and the Rietveld plot for CoCuMnOx-EDTA powders synthesized by sol-gel routes (Geng et al., 2012:
powders showed the left and right panels, respectively, 293 - 301).
while Figure 3 showed other diffraction diagrams for Asp As estimated through TEM, the particle size ranges from
and Lys samples. 20 to 100 nm, (scale line = 20 nm), as shown in the right
In Table 3, the average crystallite size and the specific panels of Figure 4 (b, d y f), where TEM micrographs of all
surface area for all obtained powders are listed. The the obtained powders are displayed. The polyhedral shape
average crystallite size calculated by the Scherrer equation of particles is also evidenced. In gel combustion synthesis
ranged between 23 and 26 nm while the specific surface of CuCr2O4 powders calcined at 500°C reported a similar
areas values ranged between 3 and 11 m2/g. For these average particle size of 80 nm (Geng et al., 2012: 281-288).
powders, the influence of fuel type on the average Additionally, these authors studied the influence of
crystallite size and surface specific area resulted to be low. calcination temperature on optical properties of the
For powders obtained by sol-gel synthesis, the average pigments (Geng et al., 2012: 293 - 301).
crystallite sizes were smaller than or equal to 14 nm (Geng Figure 5 shows FT-IR spectra for the three selected
et al., 2011). powders. According to the literature, the bands of the
By SEM, it can be observed that all the samples exhibit a spinel oxide type in FT-IR plots was found in a region
high degree of agglomeration, as displayed in the left comprised between 400 and 700 cm-1 corresponding to
panels of Figure 4a, c and e. In particular, in CoCuMnOx- the vibration produced by metals and oxygen bonds. The
Lys Figure 3a, polyhedral particles can be clearly bands around 500 cm-1 were assigned to the vibration of
distinguished. Additionally, a high agglomeration of small the metallic atom in the tetrahedral environment of
nanoparticles is evidenced by comparison with the other oxygen atoms (A-O) and the band around 600 cm-1
samples, probably caused by the different characteristics corresponds to a vibration of B atom in the octahedral
of the combustion process produced in this particular, sites (Oh) of the spinel structure (Hosseini et al., 2013). In
 Academia Journal of Scientific Research; Merito et al. 322

A B

D
C

C
C
F
E F
E

Figure 4. SEM and TEM micrographs of: a) and b)CoCuMnOx- Lys; c) andd)CoCuMnOx- EDTA; e) and f)CoCuMnOx- Asp.

Figure 5, a first band at 568 cm-1 and a second one whilst the second one corresponds to the octahedral
between 630 and 660 cm-1 were evidenced in all cases. The cations Co and Mn. In particular for Asp powders, the
first band is associated to Cu cations located at the second band presents a lower intensity. Similar bands
tetrahedral positions according to the Rietveld analysis, around 502 and 601 cm-1 are observed for calcined
 Academia Journal of Scientific Research; Merito et al. 323

665 568

CoCuMnOx-Lys
Transmittance(a.u) 568
638

CoCuMnOx-Asp

636 568

CoCuMnOx-Edta

4000 3500 3000 2500 2000 1500 1000 500

.1
Wavenumber (cm )
Figure 5. FT-IR spectra a) CoCuMnOx- Lys b) CoCuMnOx- Asp c) CoCuMnOx- EDTA.

100,0
97,5
95,0
92,5 Surface 1
90,0
, Absorptance (%)

87,5
85,0
82,5
80,0
0 500 1000 1500 2000 2500

100,0
97,5
95,0
92,5
90,0 Surface 2
87,5
85,0
82,5
80,0
0 500 1000 1500 2000 2500
, Wavelength(nm)
Figure 6. Solar Absorbance- Average value 97%.

powders at 500, 700 and 900°C of CuCrMnO4 obtained by Figure 6 shows the spectral absorbance for painted
sol-gel combustion where Mn and Cr are found in surfaces. Solar absorption values are above 95% and the
octahedral positions (Geng et al., 2012: 293 - 301). average value is 97%. This absorption value is higher than
 Academia Journal of Scientific Research; Merito et al. 324

Table 4. Temperature difference between prepared and commercial coatings for each studied period.

T (ºC)
Hour
January March April
9 0.08 -0.15 0.02
10 -0.30 -1.45 -0.71
11 2.49 0.08 0.21
12 2.41 0.76 0.48
13 2.33 0.97 0.54
14 2.43 1.03 0.83
15 2.28 0.90 1.03
16 2.17 0.86 1.13
17 2.06 0.96 1.28
18 1.81 1.67 1.65
19 1.40 1.12 1.19
20 0.79 0.68 0.59

the one observed in other selective surfaces, for example, containing Al and Ni metallic alloys and b) coated with the
selective surfaces with CuCuMnOx or CuCr0.5Mn1.5O4 as same paint without any addition (Al-Shamaileh, 2010).
pigment only achieved 93% of the solar absorption (Geng Figure 7 displays a graphic of the mean temperatures in
et al., 2011; Geng et al., 2012: 293 -301). These absorption January for both coatings. The graphic makes evident that
ranges suggest the possibility of utilizing the so-prepared the temperature of our prepared coatings is significantly
combustion synthesized oxides as active pigments in higher than the commercial one in a time span of 11 to 20
absorbent solar enamels. Geng et al. (2011, (2012: 293 - h. The results showed the possibility of using these
301) focused on achieving a material with a solar pigments as solar absorbent paints.
absorption near to the 100% while keeping a low infrared
emittance, that is, with a higher optical selectivity. This
work is aimed to improve only solar absorption, for which Conclusions
high values have been achieved. Further researches will be
intended to reduce infrared emittance. The synthesis of nanoparticles of CuCoMnO4 was
As a further test of the performance of the pigments in performed by means of a one-step solution combustion
real working conditions, we aimed to corroborate the high method, using novel fuels such as Asp, EDTA or Lys. No
solar absorbance values. Table 2 illustrates the results segregated phases were observed. Previously, the
obtained in temperature measurements in coated nanoparticles were calcined at 500°C. These CuCoMnO4
aluminum solar radiation collectors. Our pigments are nanoparticles were incorporated as pigments in alkyd-
compared with a commercial coating. As the same resin enamels, utilized to coat aluminum solar radiation
substrates are utilized in this test, the differences observed collectors. A noticeable coating absorption value ranging
are directly related tothe solar absorbance of the different around 95 and 97% was evidenced. Additionally,
coatings. comparative tests with commercial coatings resulted in
Table 4 shows a higher temperature value for the significantly higher temperature values; these
prepared coating than for the commercial one in a time measurements were carried out both coatings exposed at
span of 11 to 20 h. The major difference between the two the sun in three different periods. These results suggest
coatings was 2.43°C at 14 h in January, while for March the possibility of advantageously utilizing these
and April were 1.67 and 1.65°C respectively. Regarding the nanostructured oxides as active pigments in absorbent
maximum temperature reached by the collector, the solar enamels.
highest value of 67°C was observed in January for our
absorbent paint coating, while for commercial coating it is
54°C and 50°C in March and April. The significant ACKNOWLEDGEMENTS
temperature increase observed for our coatings must be
attributed to the presence of spinel-type CoCuMnO4 mixed We want to acknowledge Sudipto Pal from the Department
oxide, a pigment used in absorbent paint coating which of Engineering for Innovation, University of Salento in
presents a higher level of solar absorption than Lecce, Italy for the measurements of optical properties of
commercial coatings. Another cause for the observed absorbents substrates. Also, we thank Ricardo Echazú
improvement could be the width of the painted coating, from No- Conventional Energy Institute, Salta National
which is thicker than the commercial one. University, Argentina for the measurements of optical
In solar collector, it can be observed at a variation of 5°C properties of absorbents substrates, to MSc. MaríaSilvina
in two different situations: a) coated with a paint Lassa, from MEByM-IANIGLA-CONICET for SEM images
 Academia Journal of Scientific Research; Merito et al. 325

January 13 th at February 5 th 2015

75

70 Commercial coating
Absorbent coating
65

60

55
Temperature(°C)

50

45

40

35

30

25

20

15
9h 10 h 11 h 12 h 13 h 14 h 15 h 16 h 17 h 18 h 19 h 20 h
Hour of a day ( h)
Figure 7. Temperature evolution of the solar collectors during the January period.

and to MateoPáezfrom Center for Research and Geng Q, Zhao X, Gao XH, Liuw G (2011). Sol–Gel Combustion-Derived
CoCuMnOx Spinels as Pigment for Spectrally Selective Paints. J. Am.
Development of Paint Technology in La Plata-Argentina for
Ceram. Soc. 94(3): 827-832.
the paint formulation. Finally, we want to acknowledge Geng Q, Zhao X, Gao X, Yang S, Gang L (2012). Low-temperature
granting number MSUTNME0002318 from National combustion sinthesys of CuCr 2O4 spinel powder for spectrally selective
Technological University for their support. paints. J. Sol-Gel Sci. Technol. 61 (I1): 281-288.
Geng Q, Zhao X, Gao X,Yu H, Yang S, Liu G (2012). Optimization design of
CuCrxMn2-xO4 based paint coatings used for solar selective
applications, Solar Energy Mater. Solar Cell. 105: 293–301.
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Absorber coatings based on CoCuMnO x spinels prepared via the sol-gel
http://www.academiapublishing.org/journals/ajsr
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