Materials Sciences and Applications, 2011, 209-214
doi:10.4236/msa.2011.23026 Published Online March 2011 (http://www.scirp.org/journal/msa)
Synthesis, Acid and Base Resistance of Various
Copper Phosphate Pigments by the Substitution
with Lanthanum
Hiroaki Onoda1, Kenichi Okumoto2
1Department of Informatics and Environmental Sciences, Faculty of Life and Environmental Sciences, Kyoto Prefectural University,
Kyoto, Japan; 2Taihei Chemical Industrial Co., Ltd., Nara, Japan
Received November 30th, 2010; revised February 16th, 2011; accepted February 25th, 2011.
ABSTRACT
Transition metal phosphates are used as inorganic pigments, however these materials have a weak point for acid or
base resistance. Because lanthanum phosphate is insoluble in acidic or basic solution, the addition of lanthanum was
tried to improve the acid or base resistance of copper phosphate pigment. Various cooper – lanthanum phosphates
were synthesized in wet (H3PO4, Cu(NO3)2, La(NO 3)3) or dry (H3PO4, CuCO3Cu(OH)2H2O, La2O3) processes. The
additional effects of lantha num were studied on the chemical co mposition, particle shape and size distribution, sp ecific
surface area, color, acid and base resistance of the precipitates and their thermal products.
Keywords: Copper Phosphate, Pigment, Powder Properties, Acid and Base Resistance
1. Introduction
Phosphates have been used for ceramic materials, cata-
lysts, fluorescent materials, dielectric substances, metal
surface treatment, detergent, food additives, fuel cells,
pigments, etc [1-3]. In these applications, transition met-
al phosphate is suitable as a pigment because of high
anticorrosion properties [4-7]. However, there is a weak
point that is a certain degree of solubility for acidic and
basic solution.
It is well known that rare earth phosphates are insolu-
ble for acidic and basic solution in the groups of phos-
phate materials. In general, the addition of rare earth
elements gives higher functional properties to the mate-
rial [8]. Consequently, the addition of rare earth cation
had the anticipation to improve the acid and base resis-
tance of inorganic phosphate pi gments. In p revious wo r k ,
the addition of rare earth cation was studied in so lid state
syntheses and powder properties, acid and base resis-
tance of cobalt orthophosphate, pyrophosphate, and cyc-
lo-tetraphosphate [3]. The chemical composition and
powder properties of thermal products were changed by
the addition of rare earth cation. Furthermore, this addi-
tion improved the acid and base resistance of phosphate
materials synthesized in solid state reaction.
For the syntheses of inorganic phosphates, there are
some methods, one is based on the solid state reaction,
another one is on the cation exchange reaction in aque-
ous solution. The method by the solid state reaction had
some merits to be easy to form condensed phosphate and
to control the molar ratio of cation/phosphorus, on the
other hand, had a demerit to be difficult to keep the ho-
mogeneity of materials. The preparation of transition
metal phosphate in aqueous solution had an advantage to
obtain the homogenized materials and various kinds of
metal phosphates. However, it had a weak point to be
difficult to control the molar ratio of cation/phosphorus.
The synthetic method had much influence on the proper-
ties of phosphate materials. There are some cases that the
phosphate prepared in aqueous solution has the different
properties with the phosphate synthesized in solid state
reaction. It is important to clear the additional effects of
rare earth cation on syntheses of inorganic phosphate
materials prepared in wet process and their properties.
The addition of rare earth cation causes the change of
chemical composition, powder, and functional proper-
ties.
The substitution with lanthanum in nickel and cobalt
phosphate materials prepared in wet process was studied
on the chemical composition, powder condition, color,
acid and base resistance [9,10]. Specific surface area of

Synthesis, Acid and Base Resistance of Various Copper Phosphate Pigments by the Substitution with Lanthanum 210
phosphates increased and particle size became larger by
the substitution with lanthanum. The substitution with
lanthanum on acid and base resistance was effective for
design of inorganic phosphate pigment.
In this work, various copper – lanthanum phosphates
were synthesized in aqueous solution or by solid state
reaction. The obtained products were evaluated by their
particle shape and size distribution, specific surface area,
color, acid and base resistance.
2. Experimental
2.1. Synthesis of Various Copper—Lanthanum
Phosphates
The 0.1 mol/l of copper nitrate solution was mixed with
0.1 mol/l of phosphoric acid solution in the molar ratio of
Cu/P = 1/1 (wet process). This ratio is settled from the
chemical composition of copper orthophosphate, Cu-
HPO4. A part of copper nitrate was substituted with lan-
thanum nitrate in the molar ratio of La/Cu = 0/10 and 2/8.
The solutions were mixed in the molar ratio of P/(Cu +
La) = 1/1. Then, the mixed solution was adju sted to pH 7
by ammonia solution. The precipitate was filtered off and
heated at 700˚C for 1 hour. These preparation ratios are
shown in Table 1.
Basic copper carbonate (CuCO3Cu(OH)2H2O) was
mixed with 85 wt% phosphoric acid (H3PO4) at a mole
ratios of P/Cu = 2/3 and 1/1 (dry process). Copper or-
thophosphate, Cu3(PO4)2, and pyrophosphate, Cu2P2O7,
were expected by heating the mixture at 700˚C for 1 hour
via the following reaction.
3CuCO3Cu(OH)2H2O + 4H3PO4→
2Cu3(PO4)2 + 3CO2 + 12H2O (1)
CuCO3Cu(OH)2H2O + 2H3PO4→
Cu2P2O7 + CO2 + 5H2O (2)
At the same time, basic copper carbonate was mixed
with 85 wt% phosphoric acid in a mole ratios of P/Cu =
2/1. Copper cyclo-tetraphosphate, Cu2P4O12, was obtain-
ed by heating the mixture at 420˚C for 1 hour via the
following reaction.
CuCO3Cu(OH)2H2O + 4H3PO4→
Cu2P4O12 + CO2 + 8H2O (3)
A part of basic copper carbonate was substituted with
lanthanum oxide, La2O3, in the molar ratio of La/Cu =
0/10 and 2/8. These synthetic conditions are also sum-
marized in Table 1.
2.2. Evaluation of Phosphate Materials
A part of the precipitates was dissolute in hydrochloric
acid solution. The ratios of copper, lanthanum, and
phosphorus in the precipitates were calculated from In-
ductivity Coupled Plasma – Atomic Emission Spec-
trometry (ICP) results of these solutions. The ICP esti-
mation was measured with Shimadzu ICPS-8000.
The chemical composition of these phosphates was
analyzed by X-ray diffraction (XRD) and Fourier trans-
form infrared spectroscopy (FT-IR). X-ray diffraction
patterns were recorded on a Rigaku Denki RINT2000M
X-Ray diffractometer using monochromated CuKα ra-
diation. The IR spectra were recorded on a Shimadzu
FT-IR spectrometer FT-IR8600 with a KBr disk method.
The powder properties of thermal products were char-
acterized by particle shape, particle size distribution,
specific surface area, and their color. Particle shapes
were observed by scanning electron micrographs (SEM)
using VE8800 from Keyence Co. Ltd. Particle size dis-
tribution was measured with laser diffraction/scattering
particle size distribution HORIBA LA-910, which can
measure samples in the range of 0.02 to 1000 µm at one
time. Specific surface areas of phosphates were calcu-
lated from the amount of nitrogen gas adsorbed at the
temperature of liqu id nitrogen by BET method with Bel-
sorp mini from BEL JAPAN, INC. The color of phos-
phate pigments was estimated by ultraviolet-visible
(UV-Vis) reflectance spectra with a Shimadzu UV365.
Furthermore, the acid and base resistance of materials
was estimated in following method. The 0.1 g of thermal
products was allowed to stand in 100 ml of 0.1 wt% sul-
phuric acid or 0.1 wt% sodium hydroxide solution for 1
day. Then, solid was removed off by filtration. The fil-
tered solution was diluted with nitric acid. The concen-
trations of phosphorus, copper, lanthanum cation were
calculated by ICP results. As a resistance estimation, the
solubility (%) of target elements was calculated for the
concentration that thermal products were completely
dissolved by warming hydrochloric acid.
3. Results and Discussion
3.1. Chemical Composition of Copper —
Lanthanum Phosphates
Table 1 shows ICP results of samples synthesized in
various conditions. The preparation sections were the
expected ratios calculated from experimental conditions.
Samples prepared in wet process had lower ratio of
P/(2Cu + 3La) than the expected ratios (Table 1(a,b)).
The obtained precipitates were considered to be phos-
phorus-poor compounds. Because copper and lanthanum
cations were easy to react with phosphoric acid in these
ratios, a certain degree of phosphate anion was filtered
off [11]. In dry process, the ratio of P/(2Cu + 3La) in
precipitates was generally a little lower than those in
preparation process (Table 1(c-h)). Small amount of
phosphorus was considered to volatilize in heating proc-
ess. Samples substituted with lanthanum indicated wide
range of La/(Cu + La) ratio (Table 1(b,d,f,h)), however
the average of these ratios was near with the preparation
ratio.

Synthesis, Acid and Base Resistance of Various Copper Phosphate Pigments by the Substitution with Lanthanum
211
Table 1. ICP results of samples prepared in wet (H3PO4 + Cu(NO3)2 + La(NO3)3) and dry (H3PO4 + CuCO3Cu(OH)2H2O +
La2O3) processes.
expected Preparation Precipitate
composition P/(2Cu + 3La) La/(Cu + La) P/(2Cu + 3La) La/(Cu + La)
a wet CuHPO4 1/2 0 0.263 0
b wet CuHPO4-La 1/2.2 1/5 0.261 0.149
c dry Cu3(PO4)2 1/3 0 0.333 0
d dry Cu3(PO4)2-La 1/3 1/5 0.317 0.237
e dry Cu2P2O7 1/2 0 0.395 0
f dry Cu2P2O7-La 1/2 1/5 0.522 0.232
g dry Cu2P4O12 1 0 0.960 0
h dry Cu2P4O12-La 1 1/5 0.845 0.188
Figure 1 shows XRD patterns of samples synthesized
in various conditions. Samples prepared in wet process
indicated the peak patterns of Cu3(PO4)2 (JCPDS No.
21-0298) and Cu4O(PO4)2 (JCPDS No.31-0471) (Figure
1(a)). Because sample was the mixture of Cu3(PO4)2 and
Cu4O(PO4)2, the ratio of P/(2Cu + 3La) became lower
(Table 1(a)). By the substitution with lanthanum, these
XRD peaks became much weaker (Figure 1 (b)). The
lanthanum cations caused the strain and defects in crys-
talline structure of copper phosphates. Samples synthe-
sized in dry process were copper orthophosphate (Cu3
(PO4)2, JCPDS No.21-0298), pyrophosphate (Cu2P2O7,
JCPDS No. 21-0880), and cyclo-tetraphosphate (Cu2P4O12,
JCPDS No. 29-0572) corresponding with preparation-
condition (Figures 1(c,e,g)). By the substitution with
lanthanum, XRD peaks of copper phosphates became
weak and no peak related with lanthanum compound
appeared.
Figure 2 shows IR spectra of samples synthesized in
various conditions. Samples with and withou t lanthanum
had similar spectra in IR analyses. The substitution with
lanthanum had less influence on phosphate structure in
materials. Samples prepared in aqueous solution (Fig-
ures 2(a,b)) indicated common absorption peaks with
copper orthophosphate synthesized in resemble solid
state reaction (Figures 2(c,d)). The adsorption at 770
cm–1 was due to the P-O-P bonding in condensed phos-
phates. Copper cyclo-tetraphosphate (Figures 2(g,h))
had larger peak at 770 cm–1 than copper pyrophosphate
(Figures 2(e,f)).
3.2. Powder Properties of Copper—Lanthanum
Phosphates
Figure 3 shows typical SEM images of samples synthe-
sized in various conditions. All sa mples had no specified
shape. Random shape of phosphate particles covered the
surface of stage. Figure 4 shows the particle size distri-
bution of samples synthesized in various conditions.
Copper condensed phosphates, pyrophosphate and cyc-
lo-tetraphosphate, had larger size of particles than copper
orthophosphate. By the substitution with lanthanum, the
ratio of smaller particles than 100 µm increased.
Table 2 shows the specific surface area of samples
synthesized in various conditions. Specific surface area
has influence on the particle size, color, and solub ility of
phosphate materials. All samples had smaller specific
surface area than 10 m2g–1. The substitution with lantha-
num improved the specific surface area of phosphate
materials. Specific surface area became small with the
10 20 30 40 50 60
Intensity
2 /deg.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
θ
○
○
○
○
○
○
○
○○
○○○
○○ ○
△
△
◇
◇
◇◇◇
◇◇
◇
◇
◇◇
□
□□
□□
□
□
□
□□
□
□
Figure 1. XRD patterns of samples prepared in wet (H3PO4
+ Cu(NO3)2 + La(NO3)3) and dry (H3PO4 + CuCO3
Cu(OH)2H2O + La2O3) processes, (a) Wet, P/(2Cu + 3La) =
1/2, La/Cu = 0/10, (b) Wet, 1/2.2, 2/8, (c) Dry, 1/3, 0/10, (d)
dry, 1/3, 2/8 (e) Dry, 1/2, 0/10, (f) Dry, 1/2, 2/8, (g) Dry, 1,
0/10, and (h) Dry, 1, 2/8, ○; Cu3(PO4)2, ; Cu△4O(PO4)2, ; ◇
Cu2P2O7, □; Cu2P4O12.

Synthesis, Acid and Base Resistance of Various Copper Phosphate Pigments by the Substitution with Lanthanum 212
Table 2. Specific surface area of samples prepared in wet (H3PO4 + Cu(NO3)2 + La(NO3)3) and dry (H3PO4 +
CuCO3Cu(OH)2H2O + La2O3) processes /m2g–1.
Preparation ratio P/(2Cu + 3La) Main composition Non La La
wet 1/2 Cu3(PO4)2 + CuO 5.82 6.25
dry 1/3 Cu3(PO4)2 3.26 4.77
dry 1/2 Cu2P2O7 1.25 2.66
dry 1 Cu2P4O12 0.03 0.31
increasing of conde nsat i o n de gree of phosph at e anion.
The color of samples prepared in wet process was the
middle of light blue and green. Samples synthesized in
dry process were light blue. By the substitu tion with lan-
thanum, samples synthesized in wet and dry processes
whitened a little. Figure 5 shows UV-Vis reflectance
spectra of samples synthesized in various conditions.
Samples prepared in wet process had broad reflectance at
520 nm (Figures 5(a,b)). No novel adsorption appeared
by the substitution with lanthanum. Samples prepared in
dry process indicated the broad reflectance peak from
390 to 600 nm (Figures 5(c-h)). The structure of phos-
phate had less influence on color of materials.
3.3. Acid and Base Resistance Estimation of
Phosphates
Table 3 shows the acid and base resistance of samples
synthesized in various conditions. The small number of
400800120016002000
Transmittance
Wavenumber /cm-1
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
Figure 2. IR spectra of samples prepared in wet (H3PO4 +
Cu(NO3)2 + La(NO3)3) and dry (H3PO4 + CuCO3
Cu(OH)2H2O + La2O3) processes, (a) Wet, P/(2Cu + 3La) =
1/2, La/Cu = 0/10, (b) Wet, 1/2.2, 2/8, (c) Dry, 1/3, 0/10, (d)
Dry, 1/3, 2/8 (e) Dry, 1/2, 0/10, (f) Dry, 1/2, 2/8, (g) Dry, 1,
0/10, and (h) Dry, 1, 2/8.
(a) (b)
(c) (d)
Figure 3. SEM images of samples prepared in wet (H3PO4 +
Cu(NO3)2 + La(NO3)3) and dry (H3PO4 + CuCO3Cu(OH)2H2O
+ La2O3) processes, (a) Wet, P/(2Cu + 3La) = 1/2, La/Cu =
0/10, (b) wet, 1/2.2, 2/8, (c) Dry, P/(2Cu + 3La) = 1/3, La/Cu
= 0/10 and (d) Dry, 1/3, 2/8.
0
2
4
6
8
10
12
0.1110100 1000
(a)
(b)
(c)
(d)
(e)
(f)
Number of particles /%
Particle size /µm
Figure 4. Particle size distribution of samples prepared in
dry (H3PO4 + CuCO3Cu(OH)2H2O + La2O3) process, (a)
Dry, P/(2Cu + 3La) = 1/3, La/Cu = 0/10, (b) Dry, 1/3, 2/8, (c)
Dry, 1/2, 0/10, (d) Dry, 1/2, 2/8, (e) Dry, 1, 0/10, and (f) Dry,
1, 2/8.

Synthesis, Acid and Base Resistance of Various Copper Phosphate Pigments by the Substitution with Lanthanum
213
Table 3. Acid and base resistance of samples prepared in wet (H3PO4 + Cu(NO3)2 + La(NO3)3) and dry (H3PO4 + Cu-
CO3Cu(OH)2H2O + La2O3) processes.
dry/ Preparation ratio Acid (solubility) Base (solubility)
wet P/(2Cu + 3La) La/(Cu + La) P /% Cu /% La /% P /% Cu /% La /%
a wet 1/2 0 100 100 - 11.7 0.6 -
b wet 1/2.2 1/5 100 100 0.3 7.9 0 0
c dry 1/3 0 100 100 - 3.7 0 -
d dry 1/3 1/5 98.0 100 34.9 6.9 0 0
e dry 1/2 0 100 100 - 4.5 0.2 -
f dry 1/2 1/5 63.8 79.0 9.2 1.7 0 0.2
g dry 1 0 32.9 33.9 - 9.3 0 -
h dry 1 1/5 16.3 22.2 3.5 8.1 0.9 0
400 500600 700 800
Reflectance
Wavelength /nm
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
Figure 5. UV-Vis reflectance spectra of samples prepared in
wet (H3PO4 + Cu(NO3)2 + La(NO3)3) and dry (H3PO4 +
CuCO3Cu(OH)2H2O + La2O3) processes, (a) Wet, P/(2Cu
+ 3La) = 1/2, La/Cu = 0/10, (b) Wet, 1/2.2, 2/8, (c) Dry, 1/3,
0/10, (d) Dry, 1/3, 2/8 (e) dry, 1/2, 0/10, (f) dry, 1/2, 2/8, (g)
Dry, 1, 0/10, and (h) Dry, 1, 2/8.
solubility means high acid and base resistance. Samples
prepared in wet process with and without lanthanum
(Table 3(a,b)) solved perfectly in acid solution. The
solubility of samples prepared in dry process became
small by the substitution with lanthanum. The solubility
of phosphorus became lower than those of copper. In base
resistance, some samples indicate higher solubility b y th e
substitution with lanthanum. However, generally, the sub
stitution with lanthanum improved the base resistance of
copper phosph at es.
4. Conclusions
The chemical composition of samples prepared in wet
process was the mixture of Cu3(PO4)2 and Cu4O(PO4)2.
On the other hand, in dry process, copp er orthop hosphate,
pyrophosphate, and cyclo-tetraphosphate were obtained
corresponding to the synthetic ratio of phosphorus and
copper. Specific surface area of phosphate materials be-
came larger by the substitution with lanthanum. The
color of samples whitened a little. Acid and base resis-
tance of copper phosphates improved by the substitution
with lanthanum.
REFERENCES
[1] H. Onoda, H. Nariai, A. Moriwaki, H. Maki and I. Mo-
tooka, “Formation and Catalytic Characterization of Var-
ious Rare Earth Phosphates,” Journal of Materials Che-
mistry, Vol. 12, No. 6, 2002, pp. 1754-1760.
doi:10.1039/b110121h
[2] H. Onoda, T. Ohta, J. Tamaki and K. Kojima, “Decom-
position of Trifluoromethane over Nickel Pyrophosphate
Catalyst s Containing Metal Cation,” Applied Catalysis A;
General, Vol. 288, No. 1-2, 2005, pp. 98-103.
doi:10.1016/j.apcata.2005.04.028
[3] H. Onoda, K. Yokouchi, K. Kojima, and H. Nariai, “Ad-
dition of Rare Earth Cation on Formation and Properties
of Various Cobalt Phosphates,” Materials Science and
Engineering B, Vol. 116, No. 2, 2005, pp. 189-195.
doi:10.1016/j.mseb.2004.10.002
[4] D. M. Lenz, M. Delamar and C. A. Ferreira, “Improve-
ment of the Anticorrosion Properties of Polypyrrole by
Zinc Phosphate Pigment Incorporation,” Progress in Or-
ganic Coatings, Vol. 58, No. 1, 2007, pp. 64-69.
doi:10.1016/j.porgcoat.2006.12.002
[5] M. Mahdavian and M. M. Attar, “Investigation on Zinc
Phosphate Effectiveness at Different Pigment Volume
Concentrations via Electrochemical Impedance Spec-
troscopy,” Eletrochimica Acta, Vol. 50, No. 24, 2005, pp.
4645-4648. doi:10.1016/j.electacta.2005.02.015

Synthesis, Acid and Base Resistance of Various Copper Phosphate Pigments by the Substitution with Lanthanum 214
[6] M. A. Hernandez, F. Galliano and D. Landolt, “Mecha-
nism of Cathodic Delamination Control of Zinc – Alu-
minum Phosphate Pigment in Waterborne Coatings,”
Corrosion Science, Vol. 46, No. 9, 2004, pp. 2281-2300.
doi:10.1016/j.corsci.2004.01.009
[7] M. C. Deya, G. Blustein, R. Romagnoli and B. del Amo,
“The Influence of the Anion Type on the Anticorrosive
Behaviour of Inorganic Phosphates,” Surface and Coat-
ing Technology, Vol. 150, No. 2-3, 2002, pp. 133-142.
doi:10.1016/S0257-8972(01)01522-5
[8] N. E. Topp, “Chemistry of the Rare Earth Elements,”
Kagakudojin, Kyoto, 1974.
[9] H. Onoda, H. Matsui and I. Tanaka, “Improvement of
Acid and Base Resistance of Nickel Phosphate Pigment
by the Addition of Lanthanum Cation,” Materials Science
and Engineering B, Vol. 141, No. 1-2, 2007, pp. 28-33.
doi:10.1016/j.mseb.2007.05.009
[10] H. Onoda, K. Tange and I. Tanaka, “Influence of Lan-
thanum Addition on Preparation and Powder Properties
of Cobalt Phosphates,” Journal of Materials Science, Vol.
43, No. 16, 2008, pp. 5483-5488.
doi:10.1007/s10853-008-2831-7
[11] J. Liu, F. Wang, K. Sun and X. Xu, “Creation of a Mo-
nomeric Ruthenium Species on the Surface of Micro-Size
Copper Hydrogen Phosphate: An Active Heterogeneous
Catalyst for Selective Aerobic Oxidation of Alcohols,”
Advanced Synthesis and Catalysis, Vol. 349, No. 16,
2007, pp. 2439-2444. doi:10.1002/adsc.200700187