Аннотация:Different calcium orthophosphates can
be obtained by precipitation by using a
definite precursor pair in the form of water
solutions of calcium salt and a salt
containing the orthophosphate ion, another
approach is to vary the conditions of
synthesis (temperature and pH). The
following calcium orthophosphates are of
interest for biomedical applications and can
be synthesized by precipitation or hydrolysis:
brushite (CaHPO4*2H2O), monetite
(CaHPO4), octacalcium phosphate
(Ca8(HPO4)2(PO4)4 *5H2O) and
hydroxyapatite (Ca10(PO4)6(OH)2 ). Ordinarily,
maintaining the pH at a definite level during
synthesis guarantees that a powder with a
prescribed phase composition will be
obtained. Sometimes the pH regulation
occurs within the system itself because the precursor pair determines the result of synthesis.
Biphase ceramic containing Ca10(PO4)6(OH)2 and β-Ca3(PO4)2 has been obtained from a
uniform nanocrystalline calcium phosphate powder with the structure of apatite, synthesized from
water solutions of calcium apatite and ammonium hydrophosphate with molar ratio Ca/P = 1.5 at
room temperature without pH regulation. After firing at 1100°C the material contained 75% β -
Ca3(PO4)2 and the grain size did not exceed 600 nm. It is suggested that the carbon formed in the
interval 200 – 500°C, as a result of the carbonization of the organic components of synthesis
adsorbed by particles of powder, be used as a physical barrier impeding intense mass transfer up
to 800°C, which makes it possible to obtain an ultrafine grained ceramic with grains smaller than 1
μm.