Citation: Safronova, T.; Chichulin, S.;
Shatalova, T.; Filippov, Y. Powder
Mixture for the Production of
Microporous Ceramics Based on
Hydroxyapatite. Ceramics 2022, 5,
108–119. https://doi.org/10.3390/
ceramics5010010
Academic Editors: Margarita A.
Goldberg, Elisa Torresani and Gilbert
Fantozzi
Received: 31 January 2022
Accepted: 16 February 2022
Published: 18 February 2022
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ceramics
Article
Powder Mixture for the Production of Microporous Ceramics
Based on Hydroxyapatite
Tatiana Safronova
1,2,
* , Stepan Chichulin
1
, Tatiana Shatalova
1,2
and Yaroslav Filippov
2,3
1
Department of Chemistry, Lomonosov Moscow State University, Building, 3, Leninskie Gory, 1,
119991 Moscow, Russia; chichulinsn@my.msu.ru (S.C.); shatalovatb@gmail.com (T.S.)
2
Department of Materials Science, Lomonosov Moscow State University, Building, 73, Leninskie Gory, 1,
119991 Moscow, Russia; filippovyy@my.msu.ru
3
Research Institute of Mechanics, Lomonosov Moscow State University, Michurinsky Pr., 1,
119192 Moscow, Russia
* Correspondence: safronovatv@my.msu.ru; Tel.: +7-916-3470-641
Abstract: Powder mixtures with a given molar ratio of Ca/P = 1.67 were prepared under mechanical
activation conditions from hydroxyapatite powder Ca
10
(PO
4
)
6
(OH)
2
and a 1M aqueous solution of
oxalic acid H
2
C
2
O
4
at a molar ratio of Ca
10
(PO
4
)
6
(OH)
2
/H
2
C
2
O
4
= 1:4. The phase composition of
obtained powder mixture included brushite (calcium hydrophosphate dihydrate) CaHPO
4
·2H
2
O,
calcium oxalate monohydrate CaC
2
O
4
·H
2
O in form of whewellite and weddellite, and some quantity
of quasi-amorphous phase. This powder mixture was used to produce microporous monophase
ceramics based on hydroxyapatite Ca
10
(PO
4
)
6
(OH)
2
with apparent density of 1.25 g/cm
3
after firing
at 1200
◦
C. Microporosity of sintered ceramics was formed due to the presence of particles with
plate-like morphology, restraining shrinkage during sintering. Microporous ceramics based on
hydroxyapatite Ca
10
(PO
4
)
6
(OH)
2
with the roughness of the surface as a consequence of the created
microporosity can be recommended as a biocompatible material for bone defects treatment and as a
substrate for bone cell cultivation.
Keywords: hydroxyapatite; oxalic acid; powder; whewellite; weddellite; calcium oxalate
monohydrate; brushite; calcium hydrophosphate dihydrate; heterophase reaction; ceramics;
microporosity
1. Introduction
The creation of ceramic materials based on calcium phosphates is one of the inten-
sively developing areas of modern materials science for medicine [1]. These materials
are biocompatible and can be used in medicine as porous matrices for replacing lost or
damaged bone tissue or as substrates for cell cultivation. Ceramics based on hydroxyapatite
Ca
10
(PO
4
)
6
(OH)
2
(HA) are widely used as material for bone implants creation due to its
stability and the similarity of chemical and phase compositions of inorganic part of natural
bone [2,3].
Ceramics for bone implants have to be porous with at least two levels of porosity to
mimic the natural bone. Macro pores have to be no less than 100 μm, and the dimension of
micropores should be about 10 μm[4,5]. Microporosity of ceramics producing roughness
on the surface can improve biointegration and osteoconductivity of material and ensure
effective fixation and reproduction of bone tissue cells, as well as a fusion of the implant
with the body [6].
Ceramics based on hydroxyapatite are very often prepared from HA powder previ-
ously synthesized by various methods. Among them, the following two big groups of
methods should be noted: syntheses in the presence of water and anhydrous syntheses [7].
Aqueous syntheses include synthesis by precipitation from aqueous solutions [8], hydrol-
ysis [9], hydrothermal synthesis [10], synthesis in aqueous suspensions and pastes [11].
Ceramics 2022, 5, 108–119. https://doi.org/10.3390/ceramics5010010 https://www.mdpi.com/journal/ceramics