Solution Combustion Synthesis of Calcium …
181
2 Literature Survey on Solution Combustion Synthesis
of Hydroxyapatite and Calcium Phosphate Powders
and Coatings
The solution combustion method has been used for preparing calcium phosphate
bioceramics. Bovand et al. have prepared β-tricalcium phosphate by microwaveassisted solution combustion method using three different fuels such as glycine, urea
and citric acid. Citric acid as fuel facilitated the formation of high purity β-TCP
powders and small amounts of hydroxyapatite (HAp), calcium pyrophosphate and
calcium hydrogen phosphate were formed when glycine and urea were employed
as fuels [25]. Calcium phosphates (CaP) with whisker-like structures were synthesized through microwave-induced and salt-assisted solution combustion synthesis
employing urea as fuel and potassium chloride as an additive [26]. When potassium chloride was used, HAp and chlorapatite (ClP) were formed and in its absence
calcium pyrophosphate was a major phase [26]. Single and biphasic CaP nanoparticles with a high aspect ratio (5–20) were formed with microwave-assisted solution
combustion synthesis in presence of urea as fuel and the diameters and lengths were
ranging from 250 to 500 nm and 2–10 μm respectively [27]. HAp has been synthesized by utilizing nitrate ions and nitric acid as oxidizers and various fuels such as
citric acid, tartaric acid, sucrose, glycine and urea and a mixture of fuels [28, 29].
The mixture of fuels always resulted in the formation of TCP as a major product
while single fuel resulted in carbonated hydroxyapatite. It is interesting to note that
the solution combustion method was used to prepare single-phase HAp, β-tricalcium
phosphate (β-TCP) and biphasic calcium phosphates (BCP) by regulating Ca/P ratio
and annealing temperature [30].
Metal doped HAp is receiving a lot of attention for biomedical applications as
it enhances the biocompatibility of HAp. Nanopowders of hydroxyapatite (HAp)
and chromium (Cr
3+ ) doped HAp (Cr-HAp) have been synthesized using polyvinyl
alcohol as fuel and the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium
bromide) assay studies confirmed the compatibility with human blood [31]. The effect
of doping Al in HAp (Al-HAp) on the biocompatibility of HAp has been studied
under the physiochemical conditions [32]. The Al-HAp nanoparticles synthesized
by polyvinyl alcohol (PVA) assisted SCS was studied using L929 cell lines by MTT
assays up to 24 h and they did not exhibit any toxic effects for further possible in vivo
applications [32]. A hypothesis based on nucleation growth kinetics for the formation of one-dimensional strontium doped HAp (Sr-HAp) nanorods was proposed and
as-synthesized powders exhibited better structural and chemical homogeneity with
optimum crystallinity and thus satisfying the criteria for biomedical applications
[33]. Solution combustion synthesized nanosized Sr-HAp powders were synthesized with structural and chemical nature matching the bone mineral and hence is a
promising candidate material for hard tissue replacement and drug delivery systems
[34]. Highly crystalline europium-doped calcium phosphate nanowhiskers with high
aspect ratio suitable for multifunctional bioimaging probe applications were synthesized using a simple microwave-assisted SCS method [35]. They exhibited red and
181
2 Literature Survey on Solution Combustion Synthesis
of Hydroxyapatite and Calcium Phosphate Powders
and Coatings
The solution combustion method has been used for preparing calcium phosphate
bioceramics. Bovand et al. have prepared β-tricalcium phosphate by microwaveassisted solution combustion method using three different fuels such as glycine, urea
and citric acid. Citric acid as fuel facilitated the formation of high purity β-TCP
powders and small amounts of hydroxyapatite (HAp), calcium pyrophosphate and
calcium hydrogen phosphate were formed when glycine and urea were employed
as fuels [25]. Calcium phosphates (CaP) with whisker-like structures were synthesized through microwave-induced and salt-assisted solution combustion synthesis
employing urea as fuel and potassium chloride as an additive [26]. When potassium chloride was used, HAp and chlorapatite (ClP) were formed and in its absence
calcium pyrophosphate was a major phase [26]. Single and biphasic CaP nanoparticles with a high aspect ratio (5–20) were formed with microwave-assisted solution
combustion synthesis in presence of urea as fuel and the diameters and lengths were
ranging from 250 to 500 nm and 2–10 μm respectively [27]. HAp has been synthesized by utilizing nitrate ions and nitric acid as oxidizers and various fuels such as
citric acid, tartaric acid, sucrose, glycine and urea and a mixture of fuels [28, 29].
The mixture of fuels always resulted in the formation of TCP as a major product
while single fuel resulted in carbonated hydroxyapatite. It is interesting to note that
the solution combustion method was used to prepare single-phase HAp, β-tricalcium
phosphate (β-TCP) and biphasic calcium phosphates (BCP) by regulating Ca/P ratio
and annealing temperature [30].
Metal doped HAp is receiving a lot of attention for biomedical applications as
it enhances the biocompatibility of HAp. Nanopowders of hydroxyapatite (HAp)
and chromium (Cr
3+ ) doped HAp (Cr-HAp) have been synthesized using polyvinyl
alcohol as fuel and the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium
bromide) assay studies confirmed the compatibility with human blood [31]. The effect
of doping Al in HAp (Al-HAp) on the biocompatibility of HAp has been studied
under the physiochemical conditions [32]. The Al-HAp nanoparticles synthesized
by polyvinyl alcohol (PVA) assisted SCS was studied using L929 cell lines by MTT
assays up to 24 h and they did not exhibit any toxic effects for further possible in vivo
applications [32]. A hypothesis based on nucleation growth kinetics for the formation of one-dimensional strontium doped HAp (Sr-HAp) nanorods was proposed and
as-synthesized powders exhibited better structural and chemical homogeneity with
optimum crystallinity and thus satisfying the criteria for biomedical applications
[33]. Solution combustion synthesized nanosized Sr-HAp powders were synthesized with structural and chemical nature matching the bone mineral and hence is a
promising candidate material for hard tissue replacement and drug delivery systems
[34]. Highly crystalline europium-doped calcium phosphate nanowhiskers with high
aspect ratio suitable for multifunctional bioimaging probe applications were synthesized using a simple microwave-assisted SCS method [35]. They exhibited red and