CALCIUM PHOSPHATE CERAMIC BASED ON POWDER …
Transcript of CALCIUM PHOSPHATE CERAMIC BASED ON POWDER …
BIOMATERIALS
UDC 666.3.022:542.65:546.41’33’18
CALCIUM PHOSPHATE CERAMIC BASED ON POWDER SYNTHESIZED
FROM A MIXED-ANIONIC SOLUTION
T. V. Safronova,1, 2 A. V. Knot’ko,1 T. B. Shatalova,1 P. V. Evdokimov,1 V. I. Putlyaev,1
and M. S. Kostin1
Translated from Steklo i Keramika, No. 1, pp. 27 – 34, January, 2016.
Ceramic based on calcium phosphates is obtained from powders synthesized from water solutions of calcium
nitrate, ammonium hydrophosphate, and ammonium pyrophosphate as well as from a mixed-anionic solution con-
taining simultaneously ammonium pyro- and orthophosphate in the molar ratio (NH4)2HPO
4�(NH
4)4P
2O
7= 1.
The ceramic obtained contains biocompatible bioresorbable phases and can be used to make implants used in
regenerative methods for the treatment of bone tissue defects. This represents the first time synthesis from
mixed-anionic solutions is used to obtain powders of calcium phosphates with significant quantities of each
anion.
Key words: brushite, monetite, amorphous calcium pyrophosphate, ceramic, thermo-hydrolysis, calcium
pyrophosphate, tricalcium phosphate, biomaterial.
Ceramic based on calcium phosphates for bone implants
remains at the focus of research in the field of medical inor-
ganic materials science [1]. Materials based on calcium
phosphates are of interest because the main component of an
inorganic constituent of bone tissue is hydroxyapatite
Ca10
(PO4)6(OH)
2. The advancement of regenerative ap-
proaches to the medical treatment of bone tissue in humans
makes it necessary to develop bioresorbable materials based
on calcium phosphates for the fabrication of porous matrices
in which osteogenesis could occur after implantation. Cal-
cium phosphates with molar ratio Ca�P < 1.67 can be
resorbed upon implantation, since they are soluble in water
[2]. The following phases can be present in ceramic material
after firing: hydroxyapatite Ca10
(PO4)6(OH)
2(Ca�P = 1.67);
tricalcium phosphate Ca3(PO
4)2
(Ca�P = 1�5); calcium pyro-
phosphate Ca2P
2O
7(Ca�P = 1.0); and, calcium polyphos-
phate Ca(PO3)2
(Ca�P = 0.5).
The production of ceramic materials presupposes the use
of highly disperse powders obtained by chemical methods,
predominately precipitation from solutions. Variation of the
conditions of synthesis of the powders, for example, varia-
tion of the ionic composition of the solutions, is widely used
to control the properties of ceramic materials.
A great deal of experience has been accumulated on the
cationic modification of the precipitated powders for obtain-
ing conventional oxide ceramic based on Al2O
3or ZrO
2[3]
and for ceramic based on calcium phosphates [4 – 6].
Coprecipitation from solutions has also been used to obtain
anion-substituted calcium phosphates, when teraethoxysilane
is used to introduce the anion SiO4
4�
[7, 8] and the interaction
of Ca(OH)2
and CO2
gas is used to introduce the anion CO3
2�
[9].
The synthesis of calcium phosphates from calcium ni-
trate and sodium, potassium, and ammonium hydro-ortho-
phosphates at pH = 9 in the presence of magnesium ions with
ratio Mg�Ca = 0.11 and pyro-phosphate ions (in the form
Na4P
2O
7) in the amount 15% of the total phosphorus content
has been investigated [10]. In this investigation the condi-
tions chosen for synthesis (short duration (30 sec) and rela-
tively low temperature (25°C)) promoted the formation of
amorphous precipitates. The ratio Ca�P = 1.67 set at synthe-
sis was not preserved in the material after firing; the forma-
tion of phases with the ratio Ca�P = 1.5 or even Ca�P = 1
was observed.
Glass and Ceramics, Vol. 73, Nos. 1 – 2, May, 2016 (Russian Original, Nos. 1 – 2, January – February, 2016)
25
0361-7610�16�0102-0025 © 2016 Springer Science+Business Media New York
1M. V. Lomonosov Moscow State University, Moscow, Russia.
2E-mail: [email protected].
DOI 10.1007/s10717-016-9819-6
Research on the synthesis of calcium phosphates from
solutions containing simultaneously the orthophosphate and
pyrophosphate ions in the ratio Ca�P = 1 for the components
of the initial solutions is not presented in the literature. At the
same time the experience gained in the production of ce-
ramic based on calcium pyrophosphate (Ca�P = 1) from
powders synthesized from ammonium pyrophosphate
(NH4)4P
2O
7and calcium nitrate is reflected in the literature,
specifically, in our research [11]. The use of soluble sodium,
potassium, or ammonium hydro-orthophosphates, depending
on the pH, in the reaction zone in the presence of interaction
with soluble calcium salts at the Ca�P ratio set for the initial
solutions makes it possible to obtain powders of basic or
acidic hydrated calcium phosphates with different Ca�P ra-
tios. The phase composition of the ceramic fabricated from
these powders can be represented by hydroxyapatite, �-tri-
calcium phosphate for the initial ratio Ca�P = 1.5 [12] as
well as �-tricalcium phosphate and �-calcium pyrophosphate
for the initial ratio Ca�P = 1 [13].
In summary, the aim of the present work was to investi-
gate the properties of ceramic based on calcium phosphate
powders synthesized with the ratio Ca�P =1 for the initial
components from a water solution of calcium nitrate and a
mixed solution containing ammonium hydro-orthophosphate
and pyrophosphate. An additional goal was to determined the
effect of the composition of a phosphate-containing solution
containing orthophosphate and�or pyrophosphate ions on the
properties of the powder after synthesis and on the properties
of ceramic fabricated from these powders.
EXPERIMENTAL PART
The powders were synthesized using calcium nitrate
tetrahydrate (GOST 4142–77, chemically pure), ammonium
hydro-orthophosphate (GOST 3772–74, chemically pure),
and ammonium pyrophosphate (TU 6-09-1288–76, chemi-
cally pure) from the Labtekh Company (Moscow). The fol-
lowing reactions were used to calculate the quantities of the
initial salts:
Ca(NO3)2
� 4H2O + (NH
4)2HPO
4=
CaHPO4
� 2H2O� + 2NH
4NO
3+ 2H
2O; (1)
3Ca(NO3)2
� 4H2O + (NH
4)4P
2O
7+ (NH
4)2HPO
4+
xH2O = CaHPO
4� 2H
2O� + Ca
2P
2O
7� xH
2O� +
10H2O + 6NH
4NO
3, 2 � x � 4; (2)
2Ca(NO3)2
� 4H2O + (NH
4)4P
2O
7+ xH
2O =
Ca2P
2O
7� xH
2O� + 4NH
4NO
3+ 8H
2O, 2 � x � 4. (3)
The conditions for synthesis of the powders are pre-
sented in Table 1. The synthesized powders were labeled as
follows: ortho — powder obtained via the reaction (1);
mix — powder obtained via the reaction (2); pyro — powder
obtained via the reaction (3). All syntheses were conducted
at room temperature. The solution containing Ca(NO3)2
was
added to the solutions containing phosphate ions.
The precipitate obtained was separated from the mother
liquor on a Büchner filter and dried at room temperature. The
dried powders were degassed in acetone in a planetary mill
with zirconium dioxide milling bodies and mass ratios mill-
ing bodies : powder : acetone = 5 : 1 : 1.
To obtain a ceramic and investigate the thermal evolution
of the obtained powders the samples pressed without using
an additional binder with specific pressing pressure 50 MPa
were fired in the interval 800 – 1000°C with step 100°C,
soaking time 2 h at the final temperature, and heating rate
5 K�min.
A Rigaku D�Max-2500 with a rotating anode (Japan)
was used to perform x-ray phase analysis (XPA) of the syn-
thesized powder and heat-treated samples. The ICDD PDF2
database was used for qualitative determination of the
phases. The photographs were obtained in reflection using
CuK�
radiation (angles 2� = 2 – 60° with steps 0.02°, acqui-
sition rates of the spectra 5 °�min). Thermal analysis (TA)
was performed with an STA 409 PC Luxx thermal analyzer
(NETZSCH, Germany) with heating rate 10 K�min in the
temperature interval 40 – 1000°C. The sample mass was at
least 10 mg. The microstructure of the synthesized powder
samples and the heat-treated ceramic samples was investi-
gated by means of scanning electron microscopy (SEM) per-
formed with a LEO SUPRA 50VP scanning electron micro-
scope (Carl Zeiss, Germany; auto-emission source); the pho-
tography was performed in a low-vacuum regime (40 Pa N2
)
with accelerating voltage 20 kV (VPSE secondary electron
detector) and voltages 3 – 20 kV (SE2 detector).
26 T. V. Safronova et al.
TABLE 1. Conditions for Synthesis of Powders and Sample Designations
No. Designation
Solutions containing Ca2+ ions Solutions containing phosphate and pyrophosphate ionsPlanned molar content of phases
in the synthesized powder, %
V, mlCa(NO
3)2,
mol�literV, ml
(NH4)2HPO
4,
mol�liter
(NH4)4P
2O
7,
mol�literCaHPO
4� 2H
2O Ca
2P
2O
7� xH
2O
1 ortho 250 1 250 1 0 100 0
2 mix 375 1 250 0.5 0.5 50 50
3 pyro 250 1 250 0 0.5 0 100
RESULTS AND DISCUSSION
XPA shows that the phase composition of the ortho pow-
der synthesized via the reaction (1) is represented by brushite
and ammonium nitrate, which is a co-product of the reaction.
The pyro powder synthesized via the reaction (3) contains an
x-ray amorphous product whose composition, based on the
fact that the qualitative and quantitative composition of the
solutions used, can comprise a mixture of hydrated calcium
pyrophosphate and the co-product ammonium nitrate. The
phase composition of the mix powder synthesized via the re-
action (2) includes brushite, an x-ray amorphous product,
and ammonium nitrate. The XPA data on the synthesized
powders after disaggregation in acetone are presented in
Fig. 1. After disaggregation brushite in the ortho powder
transforms into monetite (reaction (4)) via the action of ace-
tone under intense mechanical action:
CaHPO4
� 2H2O = CaHPO
4+ 2H
2O. (4)
The pyro powder remains x-ray amorphous after dis-
aggregation. The brushite in the mix powder transforms via
the reaction (4) only partially. Brushite, monetite, and an
x-ray amorphous product were found in the mix powder.
The phase composition of all synthesized powders after
disaggregation suggests the formation of calcium pyrophos-
phate after heat treatment at high temperature. This expecta-
tion relies on the data in [10, 12] and the fact that the compo-
sition of the initial components is known, and all products
found in the powders either decompose (NH4NO
3) or trans-
form upon heating via the reactions (4) – (7):
2CaHPO4
� 2H2O = Ca
2P
2O
7+ 5H
2O; (5)
2CaHPO4
= Ca2P
2O
7+ H
2O; (6)
Ca2P
2O
7� xH
2O = Ca
2P
2O
7+ xH
2O. (7)
Photomicrographs of the powders after synthesis are pre-
sented in Fig. 2. The particles of the brushite powder (ortho)
possess its characteristic plate-like morphology (Fig. 2a ).
The length and width of the plates lies in the interval
2 – 10 m. The thickness of the plates equals 200 – 500 nm.
The pyro powder particles (Fig. 2c ) of size 100 – 200 nm,
whose shape is close to isometric, are aggregated. It was
shown previously by means of transmission electron micros-
copy that the particles of such powder, which are close to
isometric, contain 20 – 40 nm mesopores [11]. The aggre-
gates of the particles appear in the image as large blocks
reaching 10 – 20 m in size. In the photomicrograph of the
mix powder (Fig. 2b ) it is hardly possible to find particles
with plate-like morphology characteristic for brushite,
though the XPA data show brushite to be present in the pow-
der. Individual sections where the particle aggregates are
similar to those found for the pyro powder can be found in
the photomicrograph. On the whole the mix powder is repre-
sented by aggregates reminiscent of carnation flowers and
consisting of small plates. The size of these aggregates is
6 – 10 m.
It can be supposed that the co-product, viz. ammonium
nitrate, crystallizes from the mother liquor filling the meso-
pores and voids between the particles in their aggregates.
The density of the samples after pressing falls into the
range 40 – 50% in terms of the density of �-calcium pyro-
phosphate (3.09 g�cm3 ) and increases from pyro to ortho
samples.
The thermal analysis data (Fig. 3) attest that the total
mass loss upon heating the powder to 1000°C equals 35% for
ortho and 40% for pyro powder. The total mass loss for the
Calcium Phosphate Ceramic Based on Powder Synthesized from a Mixed-Anionic Solution 27
2 , deg�
Fig. 1. XPA data on the synthesized ortho, mix, and pyro powders
after disaggregation in acetone: �) peaks corresponding to brushite
CaHPO4
� 2H2O, card PDF2 No. C11-293; +) monetite CaHPO
4,
card PDF2 No. C9-80; �) ammonium nitrate, card PDF2 No. C8-452.
2 m 2 m 2 m
a b c
Fig. 2. Photomicrographs of the synthesized ortho (a), mix (b ), and pyro powders (c).
mix powder equals 37.5%. Loss of physically bound ad-
sorbed water occurs for all powders in the interval from 40 to
220°C. The subsequent mass loss for brushite is associated
with successive transformation via monetite into pyrophos-
phate (reactions (5) and (6)); for the amorphous product,
which is most likely represented by hydrated calcium
pyrophosphate, it is associated with its transformation into
pyrophosphate via the reaction (7). The decomposition of the
co-product of the reaction — ammonium nitrate — also
makes its own contribution to the mass loss. The course of
the curve for mix powder suggests that the mass loss upon
heating of this powder is due to the dehydration of brushite
as well as hydrated calcium pyrophosphate.
The XPA data obtained after heating at 800°C attest that
the phase composition of the ceramic samples obtained from
the ortho, mix, and pyro powders is represented by the �-cal-
cium pyrophosphate (Fig. 4 – 6). The phase composition of
the ceramic obtained from ortho powder after heat-treatment
at 900 and 1000°C does not change, which agrees with the
previously obtained data [13, 14]. The phase composition of
ceramic obtained from pyro powder after firing at 900°C is
also represented by �-calcium pyrophosphate (Fig. 4c and d ).
However, after firing at 1000°C �-tricalcium phosphate was
found in the phase composition of ceramic obtained from
pyro powder; this contradicts the previously obtained data
[11]. The formation of �-tricalcium phosphate in ceramic ob-
tained from pyro powder in the present investigation can be
explained by the difference in the preparation protocol for
the powder used to obtain ceramic as compared with the pro-
tocol used in [8]. In the present work the synthesized and
disaggregated powders were used as quickly as possible after
synthesis and therefore contained large quantities of ad-
sorbed or occluded water, which during subsequent heating
permitted thermohydrolysis of calcium pyrophosphate via
the reaction
3Ca2P
2O
7+ H
2O = 2Ca
3(PO
4)2
+ 2HPO3. (8)
The phase composition of ceramic obtained from mix
powder after firing at 900 and 1000°C is represented mainly
28 T. V. Safronova et al.
m� 0, %m
Fig. 3. Thermal analysis data for the ortho, mix, and pyro powders
after synthesis: m) sample mass at the running temperature; m0
) ini-
tial sample mass.
2 , deg�
Fig. 4. XPA data after firing at temperature 800 – 1000°C of ce-
ramic samples fabricated from ortho powders:�) peaks correspond-
ing to �-Ca2P
2O
7(card PDF2 No. C9-346).
2 , deg�
Fig. 5. XPA data after firing at temperature 800—1000°C of ce-
ramic samples fabricated from mix powders: �) peaks correspond-
ing to �-Ca2P
2O
7, card PDF2 No. C9-346; �) peaks corresponding
to �-Ca3(PO
4)2, card PDF2 No. C9-169.
2 , deg�
Fig. 6. XPA data after firing at temperature 800—1000°C of ce-
ramic samples fabricated from pyro powders: �) peaks correspond-
ing to �-Ca2P
2O
7, card PDF2 No. C9-346; �) peaks corresponding
to �-Ca3(PO
4)2, card PDF2 No. C9-169.
by �-tricalcium phosphate (Fig. 4b, d, and e). The formation
of this phase in ceramic obtained from mix powder can also
be a consequence of the thermohydrolysis via the reaction (8)
upon heating. In addition, the appearance of �-tricalcium
phosphate even at 900°C can be due to the fact that the struc-
ture of the synthesized mix powder, which includes ortho-
and pyrophosphate ions, is capable of retaining water mole-
cules in its environment up to higher temperatures. The water
can also remain in closed mesopores upon heating to temper-
atures significantly above the boiling point.
Curves of the change in the linear dimensions (diameter)
of the pellets formed as a function of the heat-treatment tem-
perature reflect compaction processes that occur in the parts
pressed from ortho, mix, and pyro powders (Fig. 7). The
highest relative linear shrinkage (33% (�3)) and density
(2.32 g�cm3 (�0.1)) are observed for samples made from
pyro powder after firing at 1000°C. The lowest relative linear
shrinkage (7% (�3)) and density (1.83 g�cm3 (�0.1)) are seen
after firing after 1000°C for ceramic made from ortho pow-
der. For ceramic made from mix powder after firing at
1000°C the shrinkage was equal to 16% (�3)) and the density
2.15 g�cm3 (�0.1)). It was noted previously that during
sintering, because of its structural particularities the pyro-
phosphate anion, which is spatially larger, diffuses more
slowly than the orthophosphate anion [15]. The course of the
temperature dependences of the linear dimensions of the
samples and their relative arrangement in Fig. 7 most likely
illustrates the effect of the sintering activity of the powders,
which is also related with the particle size and morphology.
The photomicrographs of the ceramic samples fabricated
from ortho powder (Fig. 8) confirm grain growth and poros-
ity reduction with increasing firing temperature. For exam-
ple, the grain size of ceramic equals 1 – 2 m after firing at
800°C and 2 – 6 m after firing at 1000°C. No particles or
grains with plate-like morphology could be found in the
microstructure of ceramic samples fabricated from the ortho
powder after firing in the interval 800 – 100°C.
The evolution of the microstructure of the ceramic fabri-
cated from the mix powder is displayed in Fig. 9. After firing
at 800°C the particles of the powder blank are in the sintering
state, they are weakly confined next to one another, and the
particle size does not exceed 1 m. The microstructure of the
ceramic after firing at 900°C can be described as a three-di-
mensional network formed by particles whose contact with
one another is characterized by a larger area than at the tem-
perature 800°C. The grain size is about 1 m. After firing at
900°C the grains of the ceramic form a quite dense sinter.
The grain size equals 1 – 4 m.
The photomicrographs of the ceramic fabricated from the
pyro powder and fired at 800 – 1000°C also attest to the stan-
dard development of the microstructure of the ceramic with
increasing firing temperature. The grain size after firing at
800°C and 900°C is quite difficult to evaluate. It can only be
presumed that at 800°C the particle size is much less than
1 m. At 900°C we observe sintering in individual aggre-
gates of particles. The grain size of the ceramic after firing at
1000°C does not exceed 1 m.
It is evident that the material obtained from a solution
containing simultaneously the ortho- and pyrophosphate ions
possesses a more uniform microstructure than the material
obtained from the ortho powder. In all probability this fact is
associated with the influence of the pyrophosphate ion on the
Calcium Phosphate Ceramic Based on Powder Synthesized from a Mixed-Anionic Solution 29
Fig. 7. Relative diameter of the ceramic samples fabricated from
ortho, mix, and pyro powders versus the firing temperature: D) di-
ameter of the sample at the running temperature; D0
) initial diame-
ter of the sample.
2 m 2 m 2 m
a b c
Fig. 8. Photomicrographs of fracture surfaces of ceramic samples, fabricated from ortho powder, after firing for 2 h at 800°C (a), 900°C (b ),
and 1000°C (c).
character of the growth of brushite particles in the form of
plates when calcium nitrate interacts with ammonium hydro-
phosphate (see Fig. 2b ). At the same time the grain size of
such material is larger than that of the ceramic obtained from
pyro powder.
In summary, the use of a mixed anion solution in synthe-
sis, presupposing the ortho- and pyrophosphate ions to be
present simultaneously, can serve as a tool for controlling the
microstructure and phase composition of the ceramic ma-
terial.
CONCLUSIONS
The properties of biocompatible and bioresorbable ce-
ramic materials from powders synthesized from ammonium
orthophosphate, ammonium pyrophosphate, and their mix-
ture were investigated. It was shown that the composition of
the phosphate-containing solution affects the phase composi-
tion and microstructure of the ceramic after firing. In the
presence of the pyrophosphate ion it is possible to obtain
powders of calcium phosphate ions that at a prescribed value
of the initial ratio Ca�P = 1 in the ceramic material form after
firing at 800°C a phase with a large ratio Ca�P = 1.5, specifi-
cally, a �-tricalcium phosphate phase. The formation from
calcium phosphates with the ratio Ca�P = 1 of a phase with a
higher ratio Ca�P = 1.5 could be due to thermohydrolysis in
the presence of occluded water in closed mesopores when
the powdered material is heated. It should be noted that the
grain size tends to decrease in the sequence ortho, mix, and
pyro ceramic samples. Owing to the known properties of the
components of their phases the ceramic materials obtained
can be used as a biocompatible and bioresorbable structural
base for tissue engineering in order to restore lost bone tissue.
The equipment used in this work was acquired under the
development program at Moscow University.
The research was supported by the Russian Science
Foundation under Grant No. 15-19-00103.
REFERENCES
1. T. V. Safronova and V. I. Putlyaev, “Medical inorganic materials
science in Russia: calcium phosphate materials,” Nanosistemy:
Fiz., Khim., Matematika, 4(1), 24 – 47 (2013).
2. P. G. Koutsoukos, “Current knowledge of calcium phosphate
chemistry and in particular solid surface–water interface inter-
actions,” in: Proc. of the 2nd Intern. Conf. on Phosphorus Re-
covery for Recycling from Sewage and Animal Wastes, Institute
of Chemical Engineering and High Temperature Chemical Pro-
cesses, Univ. of Patras (2000), pp. 12 – 14.
3. S. Rajendran, M. V. Swain, and H. J. Rossell, “Mechanical
properties and microstructures of co-precipitation derived tetra-
gonal Y2O
3–ZrO
2–Al
2O
3composites,” J. Mater. Sci., 23(5),
1805 – 1812 (1988).
4. S. Kannan, A. F. Lemos, J. H. Rocha, and J. M. Ferreira, “Cha-
racterization and mechanical performance of the Mg-stabilized
30 T. V. Safronova et al.
2 m 2 m 2 m
a b c
Fig. 10. Photomicrographs of cleavage surfaces of ceramic samples, fabricated from pyro powder, after firing for 2 h at 800°C (a), 900°C (b ),
and 1000°C (c).
2 m 2 m 2 m
a b c
Fig. 9. Photomicrographs of cleavage surfaces of ceramic samples, fabricated from mix powder, after firing for 2 h at 800°C (a), 900°C (b ),
and 1000°C (c).
�-Ca3(PO
4)2
prepared from Mg-substituted Ca-deficient apa-
tite,” J. Am. Ceram. Soc., 89(9), 2757 – 2761 (2006).
5. S. D. Miao, W. J. Weng, K. Cheng, et al., “A low temperature
co-precipitation preparation of nano-sized zinc containing �-tri-
calcium phosphate powders,” Key Eng. Mater., 309, 565 – 568
(2006).
6. T. V. Safronova, V. I. Putlyaev, A. V. Kuznetsov, et al., “Pro-
perties of calcium phosphate powder synthesized from calcium
acetate and sodium hydrophosphate,” Steklo Keram., No. 4,
30 – 34 (2011); T. V. Safronova, V. I. Putlyaev, A. V. Kuznetsov,
et al., “Properties of calcium phosphate powder synthesized
from calcium acetate and sodium hydrophosphate,” Glass Ce-
ram., 68(3 – 4), 131 – 135 (2011) .
7. I. R. Gibson, S. M. Best, and W. Bonfield, “Chemical characte-
rization of silicon-substituted hydroxyapatite,” J. Biomed. Ma-
ter. Res., 44(4), 422 – 428 (1999).
8. A. M. Pietak, J. W. Reid, M. J. Stott, and M. Sayer, “Silicon sub-
stitution in the calcium phosphate bioceramics,” Biomaterials,
28(28), 4023 – 4032 (2007).
9. I. R. Gibson and W. Bonfield, “Preparation and characterization
of magnesium�carbonate co-substituted hydroxyapatites,” J.
Mater. Sci.: Mater. in Medicine, 13(7), 685 – 693 (2002).
10. E. D. Eanes, “Thermochemical studies on amorphous calcium
phosphate,” Calcified Tissue Res., 5(1), 133 – 145 (1970).
11. T. V. Safronova, V. I. Putlayev, K. A. Bessonov, V. K. Ivanov,
“Ceramics based on calcium pyrophosphate nanopowders,”
Proc. Appli. Ceram., 7(1), 9 – 14 (2013).
12. T. V. Safronova, V. I. Putlyaev, G. K. Kazakova, and S. A. Kor-
neichuk, “Biphase CaO–P2O
5ceramic based on powder synthe-
sized from calcium acetate and ammonium hydrophosphate,”
Steklo Keram., No. 2, 34 – 41 (2013); T. V. Safronova, V. I. Pu-
tlyaev, G. K. Kazakova, and S. A. Korneichuk, “Biphase
CaO–P2O
5ceramic based on powder synthesized from calcium
acetate and ammonium hydrophosphate,” Glass Ceram.,
70(1 – 2), 65 – 70 (2013).
13. T. V. Safronova, A. V. Kuznetsov, S. A. Korneychuk, et al.,
“Calcium phosphate powders synthesized from solutions with
[Ca2+
]�[PO4
3�
] = 1 for bioresorbable ceramics,” Cent. Eur. J.
Chem., 7(2), 184 – 191 (2009).
14. T. V. Safronova, V. I. Putlyaev, M. A. Shekhirev, and A. V. Kuz-
netsov, “Composite ceramic containing a bioresorbable phase,”
Steklo Keram., No. 3, 31 – 35 (2007); T. V. Safronova, V. I. Pu-
tlyaev, M. A. Shekhirev, and A. V. Kuznetsov, “Composite ce-
ramic containing a bioresorbable phase,” Glass Ceram.,
64(3 – 4), 102 – 106 (2007).
15. T. V. Safronova, V. I. Putlyaev, S. A. Kurbatova, et al., “Synthe-
sis and properties of amorphous calcium pyrophosphate pow-
der, synthesized using ion exchange, for obtaining biocera-
mics,” Neorg. Mater., 51(11), 1269 – 1276 (2015).
Calcium Phosphate Ceramic Based on Powder Synthesized from a Mixed-Anionic Solution 31