Poster presented at the 11th Conference of the Materials Research Society of Serbia - YUCOMAT 2009, Herceg Novi, Montenegro, August 31 – September 4, 2009

Ignjatović, Nenad

Lukić, Miodrag

Marković, Smilja

Uskoković, Dragan

Ignjatović, Nenad L.

Repository of the Vinča Nuclear Institute (VinaR)

M. J. Lukić,  S. Marković, N. Ignjatović, D. UskokovićInstitute of Technical Sciences of SASA, Belgrade, SerbiaINTROUDCTIONHydroxyapatite, (HAp), Ca5 (PO4 )3 (OH), due to its  excellent biocompatibility and osteoconductivity as  well as close similarity to human bone structure,  represents a promising material for hard tissue  implantation. However, mechanical properties of  synthetic HAp are not as good as those of natural bones and that limits load-bearing applications. It was found that nanostructured ceramics have much better mechanical properties, but final stage of sinterinig is always accompained with accelerated grain growth. An elegant way to suppress accelerated grain growth during final stage of sintering is provided by two-step sintering technique (TSS). This type of sintering is based on difference in kinetics of desirable grain  boundary diffusion and undesirable grain boundary migration. The key elements in this method are: (1) heating to a high temperature T1 to conduct first step sintering and to achieve a critical density ρ* to render pores unstable; (2) decreasing the temperature to T2 to conduct sintering without grain growth at the lower temperature [1].   In this work, method of chemical precipitation was performed to prepare HAp nanopowder. Also, a few regimes of TSS were investigated to obtain best result and master sintering curve (MSC) for this powder was constructed to help in further improvement of  characteristics of this bioceramics.EXPERIMENTAL PARTHAp powder was prepared by chemical precipitation method [2]. Precursor chemicals used were Ca(NO)3 4H2 O, 85% H3 PO4 and 25% NH4 OH. Aqueous solutions of Ca2+ and PO43- ions were made attaining starting pH values of both solutins at 10 by adding NH4 OH. Then, solution of PO43- ions was dropwise added to solution of Ca2+ under vigorous stirring of 1000 rpm and such obtaiined milky slurry was kept at boiling for 10 minutes. The precipitate was washed, filtered, dried at 70 ºC for 6 h and finally grounded in agate mortar. Before sintering, ultrasound treatment of dried powder was performed in ultrasonic bath for 45 min to reduce the degree of agglomeration, followed by calcination on 500 ºC for 1h to evaporate moisture and again deagglomerated with ultrasound at the same conditions. Such obtained nanopowder was uniaxially pressed under 440 MPa into 13 mm ∅ pellets  and two- step sintered. Green density of the sample, determined by Archimedes’ principle, was 1,84 g/cm3.The sample was heated to the first temperature with 6 ºC/min. Temprature range found to give the highest density with this nanopowder was 1100 ºC for T1 and 1000 ºC for T2 with attainment times to be 30 min and 20 h, respectively. The sample has been coolled down naturally between two temperatures. In order to find the optimum heating regime for densification and to estimate activation energy, Ea, for sintering of this nanopowder, we have constructed MSC. Pellets with ∅ 4 mm were  nonisothermally sintered to 1200 ºC with constant heating rates of  5, 10 and 15 ºC/min, respectively. Experiment was conducted in heating microscope E. Leitz, Wetzlar, Germany. As-prepared nanopowder as well as sintered pellets were characterized in sense of particle size distribution (PSD) (Mastrsizer 2000, Malvern Instruments Ltd. ,UK), XRD (Phillips PW 1050 ) and SEM (JEOL model JSM 5300).Results and discussionFig.1a shows XRD pattern of as synthesized nanopowder. All reflections could be asignated to pure HAp. Due to high surface energy, obtained nanopowder was agglomerated and particle size distribution exhibits average particle size of 925 nm. After 45 min of ultrasoud dry deagglomeration of nanopowder, 1h of calcination at 500ºC in order to eliminate moisture which could make problems during sintering and finally one more time 45 min of ultrasound tretment, PSD was significantly changed with average particle size of 66 nm and very narrow PSD, Fig.1c. In our opinion, dry ultrasound deagglomeration treatment gave better results in decreasing of average particle size because that could irreversible break inter- and intra- aglomerate bonds, which is not completly possible into dispersion, because there exist closer contacts between particles. After TSS regime, which we found the best (1100 ºC for T1 and 1000 ºC for T2 with attainment times to be 30 min and 20 h) of that nanopowder density of ceramics was 2,73 g/cm3 which is 86,4% of theoretical density for HAp (3,156 g/cm3 ). Fig 2.a shows SEM micrograph of fracture surface of sintered sample and on Fig1.d. XRD pattern at which it can be seen that at mentioned temperatures β- TCP phase arises. This observation implies on consideration of applications of the particular samples ,which should determine  the best ratio of Ca/P in synthesized powders.From construction of MSC we found that the activation energy Ea for HAp is 333 kJ/mol and that slower heating rate is optimal for densification..a)b)c)Fig. 1: a) XRD pattern of as-prepared Hap and  its b) partcle size distribution; c) particle size  distribution of the same powder after cycle: 45min ultrasound / 1h calcination at 500 ºC / 45min ultrasound deagglomeration.a) b)Fig. 2: a) SEM micrograph of fracture surface of two-step sintered sample and b) XRD pattern of that sample.a) b) c)Fig. 3: Nonisothermally heated samples to 1200ºC with different heating rates:a) 5, b) 10 and c) 15 ºC/min.Fig. 4: ))(,(log)( tTtΘ=Φ ρ for different activation energies, Ea.Fig. 6: MSC for HApa)b)CONCLUSIONFrom our results can be concluded that  simple method of chemical precipitation followed by ultrasound deagglomeration of dried powder can successfully be used for synthesis of HAp nanopowder. However, to have high dense nanostructured ceramics particle size distribution sholud be completly uniform, because any local density gradient will seriously affect the final microstructure of ceramics. Also we estimated Ea for sintering of this HAp nanopowder to be 333 kJ/mol.Fig. 5: mean residual square versus EaEa=333 kJ/mol REFERENCES[1] Chen, I. W. And Wang, X. H., “Sintering dense nanocrystalline ceramics without final stage grain growth”, Nature,2000, 404, 168- 171.[2] N. Ignjatović, D. Uskoković, “Biodegradable composites based on nano-crystalline calcium phosphate and bioresorbable polymers”,Advances in Applied Ceramics, Nanoceramics special issue, 107, 3 (2008) 142-147 .

Precipitation Synthesis and Two-Step Sintering of Hydroxyapatite Nanopowders

Hydroxyapatite, (HAp), Ca5(PO4)3(OH), due to its excellent biocompatibility and osteoconductivity as well as close similarity to human bone structure, represents a promising material for hard tissue implantation. However, mechanical properties of synthetic HAp are not so good as those of natural bones and that limits load-bearing application. Recently it was found that nanostructured ceramics have much better mechanical properties. The nanostructured ceramics could be obtained by two-step sintering technique. Of course, to have such final product, nanopowder as starting material is necessary. In this work, method of chemical precipitation was performed to prepare hydroxyapatite (HAp) nanopowders. The synthesis parameters, like concentration of starting solutions, speed of stirring, time of ageing, as well as time of ultrasound treatment of as-precipitated powders, were investigated in terms of particle size and particles size distribution. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size measurements. In order to suppress accelerated grain growth during final stage sintering and to maintain bioceramics nanostructured, with the most uniform grain size distribution, was treated by two-step sintering technique. The samples were uniaxially pressed into pellets and were first heated to the higher temperature T1 and attained at this for a short time, just to render pores unstable. After that, the sample was cooled down to the temperature T2 and kept for prolonged time. At the latter temperature densification should occur without grain growth because of difference in kinetics of desirable grain boundary diffusion and undesirable grain boundary migration. The best temperature range was determined by try and error method and master sintering curve in order to reach the highest possible density.Poster: [https://hdl.handle.net/21.15107/rcub_dais_268

Lukić, Miodrag J.

Serbian Academy of Science and Arts Digital Archive (DAIS)

ELEVENTH ANNUAL CONFERENCE   YUCOMAT 2009 Hotel “Plaža”, Herceg Novi, Montenegro, August 31 - September 4, 2009 http://www.mrs-serbia.org.rs     Programme  and  The Book of Abstracts    Organised by: Materials Research Society of Serbia, and Institute of Technical Sciences of the Serbian Academy of Sciences and Arts, Belgrade   under the auspices of Federation of European Material Societies and Materials Research Society Title:  THE ELEVENTH ANNUAL CONFERENCE “YUCOMAT 2009” Programme and The Book of Abstracts    Publisher: Institute of Technical Sciences of the Serbian Academy of Sciences & Arts   Knez Mihailova 35/IV; P.O. Box 377, 11000 Belgrade, Serbia   Phone: +381 11 2185-437; Fax: + 381 11 2185-263   http://www.itn.sanu.ac.rs     Editor:  Prof. Dr. Dragan P. Uskoković  Technical editor:  Aleksandra Stojičić  Cover page:  Aleksandra Stojičić and Milica Ševkušić     Copyright © 2009 Institute of Technical Sciences of the Serbian Academy of Sciences & Arts   Acknowledgment:        Printed in: Printing office “Čigoja”   Studentski trg 15, 11000 Belgrade    Phones: + 381 11 2186-725; + 381 11 625-954   Circulation: 300 copies. The end of printing: July 2009. ELEVENTH ANNUAL CONFERENCE “YUCOMAT 2009” Herceg-Novi, August 31-September 4, 2009   187P.S.E.5. PRECIPITATION SYNTHESIS AND TWO-STEP SINTERING OF HYDROXYAPATITE NANOPOWDERS  M. Lukić, S. Marković, N. Ignjatović, D. Uskoković Institute of Technical Sciences of SASA, Belgrade, Serbia  Hydroxyapatite, (HAp), Ca5(PO4)3(OH), due to its excellent biocompatibility and osteoconductivity as well as close similarity to human bone structure, represents a promising material for hard tissue implantation. However, mechanical properties of synthetic HAp are not so good as those of natural bones and that limits load-bearing application. Recently it was found that nanostructured ceramics have much better mechanical properties. The nanostructured ceramics could be obtained by two-step sintering technique. Of course, to have such final product, nanopowder as starting material is necessary.  In this work, method of chemical precipitation was performed to prepare hydroxyapatite (HAp) nanopowders. The synthesis parameters, like concentration of starting solutions, speed of stirring, time of ageing, as well as time of ultrasound treatment of as-precipitated powders, were investigated in terms of particle size and particles size distribution. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size measurements. In order to suppress accelerated grain growth during final stage sintering and to maintain bioceramics nanostructured, with the most uniform grain size distribution, was treated by two-step sintering technique. The samples were uniaxially pressed into pellets and were first heated to the higher temperature T1 and attained at this for a short time, just to render pores unstable. After that, the sample was cooled down to the temperature T2 and kept for prolonged time. At the latter temperature densification should occur without grain growth because of difference in kinetics of desirable grain boundary diffusion and undesirable grain boundary migration. The best temperature range was determined by try and error method and master sintering curve in order to reach the highest possible density.  

Digital Repository of the Institute of Technical Sciences of SASA

M. J. Lukić,  S. Marković, N. Ignjatović, D. Uskoković
Institute of Technical Sciences of SASA, Belgrade, Serbia
INTROUDCTION
Hydroxyapatite, (HAp), Ca5
 
(PO4
 
)3
 
(OH), due to its
 
 
excellent biocompatibility and osteoconductivity as
 
 
well as close similarity to human bone structure,
 
 
represents a promising material for hard tissue
 
 
implantation. However, mechanical properties of
 
 
synthetic HAp are not as good as those of natural 
bones and that limits load-bearing applications. It was 
found that nanostructured ceramics have much better 
mechanical properties, but final stage of sinterinig is 
always accompained with accelerated grain growth. 
An elegant way to suppress accelerated grain growth 
during final stage of sintering is provided by two-step 
sintering technique (TSS). This type of sintering is 
based on difference in kinetics of desirable grain
 
 
boundary diffusion and undesirable grain boundary 
migration. The key elements in this method are: (1) 
heating to a high temperature T1
 
to conduct first step 
sintering and to achieve a critical density ρ* to render 
pores unstable; (2) decreasing the temperature to T2
 
to conduct sintering without grain growth at the lower 
temperature
 
[1].   
In this work, method of chemical precipitation was 
performed to prepare HAp nanopowder. Also, a few 
regimes of TSS were investigated to obtain best result 
and master sintering curve (MSC) for this powder was 
constructed to help in further improvement of
 
 
characteristics of this bioceramics.
EXPERIMENTAL PART
HAp powder was prepared by chemical precipitation method [2]. Precursor chemicals 
used were Ca(NO)3
 
4H2
 
O, 85% H3
 
PO4
 
and 25% NH4
 
OH. Aqueous solutions of Ca2+ 
and PO43-
 
ions were made attaining starting pH values of both solutins at 10 by 
adding NH4
 
OH. Then, solution of PO43-
 
ions was dropwise added to solution of Ca2+ 
under vigorous stirring of 1000 rpm and such obtaiined milky slurry was kept at 
boiling for 10 minutes. The precipitate was washed, filtered, dried at 70
 
ºC for 6
 
h 
and finally grounded in agate mortar. Before sintering, ultrasound treatment of dried 
powder was performed in ultrasonic bath for 45 min to reduce the
 
degree of 
agglomeration, followed by calcination on 500
 
ºC for 1h to evaporate moisture and 
again deagglomerated with ultrasound at the same conditions. Such obtained 
nanopowder was uniaxially pressed under 440
 
MPa into 13
 
mm ∅
 
pellets  and two-
 
step sintered. Green density of the sample, determined by Archimedes’
 
principle,
 
was 
1,84 g/cm3.
The sample was heated to the first temperature with 6
 
ºC/min. Temprature range 
found to give the highest density with this nanopowder was 1100
 
ºC for T1
 
and 1000 
ºC for T2
 
with attainment times to be 30 min and 20 h, respectively. The sample has 
been coolled down naturally between two temperatures. In order to find the optimum 
heating regime for densification and to estimate activation energy, Ea, for sintering of 
this nanopowder, we have constructed MSC. Pellets with ∅
 
4 mm were
 
 
nonisothermally sintered to 1200 ºC with constant
 
heating rates of  5, 10 and 15 
ºC/min, respectively. Experiment was conducted in heating microscope E. Leitz, 
Wetzlar, Germany. 
As-prepared nanopowder as well as sintered pellets
 
were characterized in sense of 
particle size distribution (PSD) (Mastrsizer 2000, Malvern Instruments Ltd. ,UK), XRD 
(Phillips PW 1050 ) and SEM
 
(JEOL model JSM 5300).
Results and discussion
Fig.1a shows XRD pattern of as synthesized nanopowder. All reflections could be asignated to pure HAp. Due to high surface energy, 
obtained nanopowder was agglomerated and particle size distribution exhibits average particle size of 925 nm. After 45 min of ultrasoud 
dry deagglomeration of nanopowder, 1h of calcination at 500ºC in order to eliminate moisture which could make problems during 
sintering and finally one more time 45 min of ultrasound tretment, PSD was significantly changed with average particle size of 66 nm 
and very narrow PSD, Fig.1c. In our opinion, dry ultrasound deagglomeration treatment gave better results in decreasing of average 
particle size because that could irreversible break inter-
 
and intra-
 
aglomerate bonds, which is not completly possible into dispersion, 
because there exist closer contacts between particles. 
After TSS regime, which we found the best (1100
 
ºC for T1
 
and 1000 ºC for T2
 
with attainment times to be 30 min and 20 h) of that 
nanopowder density of ceramics was 2,73 g/cm3
 
which is 86,4% of theoretical density for HAp (3,156 g/cm3
 
). Fig 2.a shows SEM 
micrograph of fracture surface of sintered sample and on Fig1.d.
 
XRD pattern at which it can be seen that at mentioned temperatures β-
 
TCP phase arises. This observation implies on consideration of applications of the particular samples ,which should determine  the best 
ratio of Ca/P in synthesized powders.
From construction of MSC we found that the activation energy Ea for HAp
 
is
 
333 kJ/mol and that slower heating rate is optimal for 
densification.
.
a)
b)
c)
Fig. 1: a) XRD pattern of as-prepared Hap and  its 
b) partcle size distribution; c) particle size
 
 
distribution of the same powder after cycle: 45min 
ultrasound / 1h calcination at 500 ºC / 45min 
ultrasound deagglomeration.
a) b)
Fig. 2: a) SEM micrograph of fracture surface of two-step sintered sample 
and b) XRD pattern of that sample.
a) b) c)
Fig. 3: Nonisothermally heated samples to 1200ºC with different heating rates:
a) 5, b) 10 and
 
c) 15
 
ºC/min.
Fig. 4: ))(,(log)( tTtΘ=Φ ρ for different activation energies, Ea.
Fig. 6: MSC for HAp
a)
b)
CONCLUSION
From our results can be concluded that  simple method of chemical precipitation followed by ultrasound deagglomeration of dried 
powder can successfully be used for synthesis of HAp nanopowder.
 
However, to have high dense nanostructured ceramics particle size 
distribution sholud be completly uniform, because any local density gradient will seriously affect the final microstructure of ceramics. Also 
we estimated Ea for sintering of this HAp nanopowder to be 333 kJ/mol.
Fig. 5: mean residual square versus Ea
Ea=333 kJ/mol 
REFERENCES
[1] Chen, I. W. And Wang, X. H., “Sintering dense nanocrystalline ceramics without final stage grain growth”, Nature,2000, 404, 168-
 
171.
[2] N. Ignjatović, D. Uskoković, “Biodegradable composites based on nano-crystalline calcium phosphate and bioresorbable
 
polymers”,
Advances in Applied Ceramics, Nanoceramics special issue, 107, 3 (2008) 142-147 .


Poster presented at the 11th Conference of the Materials Research Society of Serbia - YUCOMAT 2009, Herceg Novi, Montenegro, August 31 – September 4, 2009.Conference abstract: [https://hdl.handle.net/21.15107/rcub_dais_14836

English

http://vinar.vin.bg.ac.rs/bitstream/id/13992/7376.pdf

Precipitation Synthesis and Two-Step Sintering of Hydroxyapatite Nanopowders

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Serbian Academy of Science and Arts Digital Archive (DAIS)

Digital Repository of the Institute of Technical Sciences of SASA

Serbian Academy of Science and Arts Digital Archive (DAIS)