Preparation and Characterization of Bioactive Silica-Based Ceramics Derived from Rice Husk Ash

By: Nayak, Jyoti PrakashContributor(s): Bera, Japes [Supervisor] | Department of Ceramic EngineeringMaterial type: TextTextLanguage: English Publisher: 2010Description: 160 pSubject(s): Engineering and Technology | Ceramic Engnieering | Ceramic MaterialsOnline resources: Click here to access online Dissertation note: Thesis (Ph.D)- National Institute of Technology, Rourkela Summary: This thesis deals with the preparation a nd characterization of amorphous silica based bioactive ceramics using rice husk ash (RHA) as silica source. Three types of silica precursors were prepared depending on impurity and forms. Ceramics were fabricated through conventional powder compaction, poly meric sponge replica tion and gelcasting methods. Bioglass-ceramics and mesoporous s ilica aerogel were also prepared using silica precursor. Mechanical, in vitro bioactivity and biodegradab ility properties of above ceramics were investigated. Brown ash (BA), obtained by burning husk at 700 o C, contains about 96 wt.% amorphous SiO 2 and the rest 4% impurities like CaO, Fe 2 O 3 , K 2 O, ZnO, and Mn 2 O 3 . White ash (WA), prepared by burning acid-le ached husk, and contains almost pure silica (99.86%). Silica gel (SG) powder was prepared from BA through the alkaline extraction of silica from ash followed by acid neutra lization. SG contains about 99.79% silica. During sintering, amorphous silica transforme d into cristobalite phase at 1000, 1200, and 1300 o C, respectively for BA, SG, and WA ceramic s. The earlier phase transformation in BA was due to its highest impurity content. There was a fall in compressive strength of all three (BA, SG and WA) sintered sili ca ceramics as and when amorphous silica transformed to cristobalite. This was due to the crack formation by the high-low displacive phase transfor mation of cristobalite. Amorphous silica based scaffolds were fabr icated by slurry impregnation process using polymeric sponge as the replica. The aqueous slurry with 40 wt.% solid loading showed good thixotropic behaviour in presen ce of polyvinyl alcohol (PVA) binder. The strength of scaffold decreased above a si ntering temperature where the amorphous silica transformed into cristobalite. In vitro bioactivity test showed the formation of apatite layer on silica scaffold surface. vi Amorphous silica-based porous ceramics was al so prepared by gel casting method using SG powder. The slurry with 42 vol.% solid loading in 1:30 (MBAM:AM) monomer cross-linker solution, showed good th ixotropic behaviour and generated a good casting. Casted body also showed good mach inability. Sintered gel-casted body having ~25% porosity showed a mechanical strength of 27.5 ± 0.2 MPa. In vitro bioactivity experiment showed the formation of apatite layer on silica body. Soda-lime-silica based bioglass-ceramics was synthesized via sol-gel route utilizing sodium silicate, derived from rice husk ash. Gel powder was calcined at 700 °C for 2 h to get a reactive glass-ceramic pow der. The calcined powder mainly contains combeite-I (Na 6 Ca 3 Si 6 O 18 ) crystalline phase dispersed in amorphous glass matrix. The material was sintered at differe nt temperatures ranging from 900-1050 o C for 2 h. Glass- ceramics sintered at 1000 o C showed better mechanical property among all. Strength of 1050 o C sintered body was low due to the formation of cracks in it. Crystalline combeite phase of the glass- ceramics was found to dissolve easily in TRIS buffer solution. Carbonated hydroxyapatite was formed on the surface of the glass- ceramics within 3-days of incubation in SBF. 900 o C sintered body showed better bioactivity and biodegradability than others. On increasing sintering temperature, both bioactivity and biodegradability of glass-ceramic decreased due to the transformation of glass into crystalline phases. Optimum sintering temperature for the material should be around 950-1000 o C with respect to strength and bioactivity. Silica aerogel was successfully prepared through ambient pressure drying method using sodium silicate that was derived fr om WA. Surface modification and strengthening of wet gel was obtained by agi ng it in tetraethylor thosilicate (TEOS) /ethanol solution. Low surface tension liquid n -heptane was used to suppress capillary stresses and associated shrinkage during ambient pressu re drying. Aerogel with low density (0.67), high porosity (80%) and a sp ecific surface area of 273 m 2 .g -1 was obtained. Mesoporous aerogel was tested for its bio-activity and degradability. Apatite was formed on aerogel surface within 7-days of incubation in SBF. Aerogel showed quick release of silicic acid in TRIS buffer solution duri ng biodegradabi lity test. vii All these results suggest that the rice hus k ash could be a promising low cost raw material for the preparation of bioactiv e amorphous silica, bioglass-ceramics and mesoporous aerogel. Reticulated and gelcaste d porous ceramics, bioglass-ceramics and aerogel can be used as novel lo w cost biomaterial for different clinical applications like; scaffold for Tissue engineering, biosensor, dr ug delivery, and protein encapsulations etc.
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Thesis (Ph.D)- National Institute of Technology, Rourkela

This thesis deals with the preparation a
nd characterization of
amorphous silica based
bioactive ceramics using rice husk ash (RHA)
as silica source. Three types of silica
precursors were prepared depending on impurity
and forms. Ceramics were fabricated
through conventional powder compaction, poly
meric sponge replica
tion and gelcasting
methods. Bioglass-ceramics and mesoporous s
ilica aerogel were also prepared using
silica precursor. Mechanical,
in vitro
bioactivity and biodegradab
ility properties of above
ceramics were investigated.
Brown ash (BA), obtained by burning husk at 700
o
C, contains about 96 wt.%
amorphous SiO
2
and the rest 4% impurities like CaO, Fe
2
O
3
, K
2
O, ZnO, and Mn
2
O
3
.
White ash (WA), prepared by burning acid-le
ached husk, and contains
almost pure silica
(99.86%). Silica gel (SG) powder was prepared
from BA through the alkaline extraction
of silica from ash followed by acid neutra
lization. SG contains about 99.79% silica.
During sintering, amorphous silica transforme
d into cristobalite phase at 1000, 1200, and
1300
o
C, respectively for BA, SG, and WA ceramic
s. The earlier phase transformation in
BA was due to its highest impurity content.
There was a fall in compressive strength of
all three (BA, SG and WA) sintered sili
ca ceramics as and when amorphous silica
transformed to cristobalite. This was due to the crack formation by the high-low
displacive phase transfor
mation of cristobalite.
Amorphous silica based scaffolds were fabr
icated by slurry impregnation process
using polymeric sponge as the replica. The
aqueous slurry with 40 wt.% solid loading
showed good thixotropic behaviour in presen
ce of polyvinyl alcohol (PVA) binder. The
strength of scaffold decreased above a si
ntering temperature where the amorphous silica
transformed into cristobalite.
In vitro
bioactivity test showed the formation of apatite
layer on silica scaffold surface.
vi
Amorphous silica-based porous ceramics was al
so prepared by gel casting method
using SG powder. The slurry with 42
vol.% solid loading
in 1:30 (MBAM:AM)
monomer cross-linker solution, showed good th
ixotropic behaviour and generated a good
casting. Casted body also showed good mach
inability. Sintered gel-casted body having
~25% porosity showed a mechanical
strength of 27.5 ± 0.2 MPa.
In vitro
bioactivity
experiment showed the formation
of apatite layer on silica body.
Soda-lime-silica based bioglass-ceramics
was synthesized via sol-gel route
utilizing sodium silicate, derived from rice husk ash. Gel powder was calcined at 700 °C
for 2 h to get a reactive glass-ceramic pow
der. The calcined powder mainly contains
combeite-I (Na
6
Ca
3
Si
6
O
18
) crystalline phase dispersed
in amorphous glass matrix. The
material was sintered at differe
nt temperatures ranging from 900-1050
o
C for 2 h. Glass-
ceramics sintered at 1000
o
C showed better mechanical property among all. Strength of
1050
o
C sintered body was low due to the formation of cracks in it.
Crystalline combeite phase of the glass-
ceramics was found to
dissolve easily in
TRIS buffer solution. Carbonated hydroxyapatite was formed on the surface of the glass-
ceramics within 3-days of incubation in SBF. 900
o
C sintered body showed better
bioactivity and biodegradability
than others. On increasing
sintering temperature, both
bioactivity and biodegradability
of glass-ceramic decreased due to the transformation of
glass into crystalline phases. Optimum sintering temperature for the material should be
around 950-1000
o
C with respect to strength and bioactivity.
Silica aerogel was successfully prepared
through ambient pressure drying method
using sodium silicate that was derived fr
om WA. Surface modification and strengthening
of wet gel was obtained by agi
ng it in tetraethylor
thosilicate (TEOS)
/ethanol solution.
Low surface tension liquid
n
-heptane was used to suppress capillary stresses and
associated shrinkage during ambient pressu
re drying. Aerogel with low density (0.67),
high porosity (80%) and a sp
ecific surface
area of 273 m
2
.g
-1
was obtained. Mesoporous
aerogel was tested for its bio-activity and
degradability. Apatite was formed on aerogel
surface within 7-days of incubation in SBF.
Aerogel showed quick release of silicic acid
in TRIS buffer solution duri
ng biodegradabi
lity test.
vii
All these results suggest that the rice hus
k ash could be a promising low cost raw
material for the preparation of bioactiv
e amorphous silica, bioglass-ceramics and
mesoporous aerogel. Reticulated and gelcaste
d porous ceramics, bioglass-ceramics and
aerogel can be used as novel lo
w cost biomaterial for different clinical applications like;
scaffold for Tissue engineering, biosensor, dr
ug delivery, and protein
encapsulations etc.

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