Influence of alkoxide molar ratio on rheological study of alumina sol for fiber preparation

Article abstract of DOI:10.1080/15533170802023569

Various molar ratio of aluminium isopropoxide (ALP) to aluminium nitrate nonahydrate (ALN) ranging from 1 to 5 were studied to determine suitable molar ratio in producing alumina fiber. Spinnability characteristics obtained only from intermediate molar ra

Full text of DOI:10.1080/15533170802023569

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:322–324, 2008
Copyright # 2008 Taylor & Francis Group, LLC
ISSN: 1553-3174 print/1553-3182 online
DOI: 10.1080/15533170802023569
Influence of Alkoxide Molar Ratio on Rheological Study
of Alumina Sol for Fiber Preparation
M. Hasmaliza, M. N. Ahmad Fauzi, and A. Zainal Arifin
School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering
Campus, Pulau Pinang, Malaysia
points as well as the high viscosity of melts. Some advantages
Various molar ratio of aluminium isopropoxide (ALP) to alu- of the sol-gel method over the conventional melting method are
minium nitrate nonahydrate (ALN) ranging from 1 to 5 were
studied to determine suitable molar ratio in producing alumina
fiber. Spinnability characteristics obtained only from intermedi-
ate molar ratio, 3, where the rheological shows Newtonian
behavior. The spinned gel fiber were calcined at different temp-
better homogeneity and purity from raw material, lower prep-
aration temperature, which save energy cost and the ability to
form unique composition.[3]
EXPERIMENTAL
Alumina sols were prepared by using aluminium isopropox-
.
ide, Al (OC3H7)3 (Merck, German) and 0.5 M aluminium
eratures ranging from 5008C to 12008C. The rheological studies
were carried out using Haake VT550 Rheometer. Calcined
fibers characterized using SEM showed well-developed grains of
alumina was formed and XRD analysis on calcined fibers at
12008C shows that the most stable phase, alpha were completely
occurred.
.
nitrate nonahydrate, Al (NO3)3 9H2O (Merck) as a starting
material. According to David[4] metal alkoxide in powder
form is not suitable for producing gel due to their low solubi-
lity; therefore, the use of 0.5 M aluminium nitrate nonahydrate
is to assist the solubility of this material.
Keywords alkoxide, alumina fiber, sol-gel
Alumina sol were prepared in 5 different molar ratios, alu-
minium isopropoxide (ALP): aluminium nitrate nonahydrate
(ALN) ¼ 1, 2, 3, 4 and 5 in order to get the viscous and spin-
nable sol that are important characteristics to produce fiber.
The rheological studies were carried out using Haake VT550
Rheometer. Spinnable sol were then spun using spinnerette
with hole diameters of 0.4 mm, and then the gel fibers from
spinnerette drum were collected and calcined to 12008C at a
heating rate of 58C/min (to observe the phase occurred using
XRD analysis). The experimental procedures are shown in
Figure 1.
INTRODUCTION
Alumina fiber is an important engineering material because
of its high strength and modulus, resistance to attack by molten
metals and non-oxide materials, chemical inertness in both oxi-
dizing and reducing atmosphere up to 10008C, low thermal
conductivity and good electrical insulation.[1] Distinct prep-
aration routes have been developed to achieve spinnable pre-
cursor of both structure and functional alumina fiber using
aqueous oxide sols and filament forming polymers as well as
metal, metal salts, metal alkyls, alkoxide or carboxylates.[2]
Among the ways to produce alumina fiber, the sol-gel
method has been used for the synthesis of ceramic fibers pre-
cursor since refractory oxide have extremely high melting
RESULTS AND DISCUSSION
Table 1 shows the effect of different ALP/ALN molar ratio
on the initial state and the spinnability of the sols where viscous
and spinnable sols were obtained from Sol 3 as shown in
Figure 2. Figure 3 shows the rheological behavior of Sol 3
where the sol was exhibited Newtonian behavior for as-
prepared, during evaporation process and spinning condition.
It has been shown that spinning sol should be linearly polymer-
ized and exhibit Newtonian behavior, i.e., viscosity should be
independent of shear rate in order to generate continuous
fiber,[1] whereas sol with lower molar ratio, Sol 1 and Sol 2
(Figure 4), gave the clear and very dilute sol where almost
the entire sol was evaporated during the evaporation process
Received 2 March 2008; accepted 3 April 2008.
The author would like to express their thanks to Malaysian
Ministry of Science, Technology & Environment for funding this
project under the Intensification of Research in Priority Area (IRPA)
grant 03-02-05-8003.
Address correspondence to M. Hasmaliza, School of Materials and
Mineral Resources Engineering, Universiti Sains Malaysia, Engineer-
ing Campus, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau
Pinang, Malaysia. E-mail: hasmaliza@eng.usm.my
322

INFLUENCE OF ALKOXIDE MOLAR RATIO
323
FIG. 3. Rheological studies of Sol 3 shows Newtonian behavior at as-
prepared, during evaporation process and spinning condition.
FIG. 1. Experimental flowchart.
TABLE 1
Effect on ALP/ALN molar ratio
ALP/ALN
molar ratio
State of the sol after
stirring process
Sol
Spinnability
Sol 1
Sol 2
Sol 3
Sol 4
Sol 5
1
2
3
4
5
Clear and dilute
Clear and dilute
Clear and viscous
Gel
No
No
Yes
No
No
FIG. 4. Sol 1 and Sol 2.
Gel with
precipitation
without obtaining suitable spinnability characteristics. This
result is shown in Figure 5. The sol with higher molar ratios,
Sol 4 and Sol 5 (Figure 6), shows the gelation during stirring
process due to three-dimensional polymerization. The
FIG. 5. Graph shows the decreasing of the volume for Sol 1 and Sol 2 during
evaporation process.
rheological studies cannot be done due to faster solidification
of the gel. The spinnable sols were then subjected to
spinning process followed by calcinations process to obtain
oxide fiber. Scanning electron microscopy (SEM) analysis
(Figure 7) showed well-developed grains of alumina was
formed at calcinations temperature of 12008C. The XRD
FIG. 2. Spinnable sol obtained from Sol 3.

324
M. HASMALIZA ET AL.
FIG. 8. Confirmation of alpha phase (ICDD 10-173) occurred in alumina
fiber calcined at 12008C, using XRD analysis.
analysis showed the transformation of alumina phases where
the most stable phase, a-Al2O3, occured at 12008C
(Figure 8). It has been stated by Hyuk-Joon and co-
workers[5] that the completion of a phase formation occurs at
the same temperature.
FIG. 6. Sol become gel, Sol 4 and Sol 5.
REFERENCES
1. V. Ramanan and R.R. Sutapa, Effect of Organic Additives on the
Properties of Sol-Gel Spun Alumina Fibres, Journal of European
Ceramic Society, 2000, 20, p. 2543–2549.
2. W. Glaubitt, et al. Sol-Gel Processing Of Functional And Structural
Ceramic Oxide Fibres, Journal of Sol-Gel Science & Technology,
1997, 8, 29–33
.
3. J.D. McKenzie, Glasses From Melts and Glasses from Gels, A
Comparison, Journal of Non-Crystalline Solid, 1982, 48, 1–10.
4. W.J. David, Jr., Sol-Gel Processing of Ceramic & Glass, American
Ceramic Society Bulletin, 1985, 64 (12), 1597–1602.
5. Y. Hyuk-Joon, W.J. Jin, T.K. Iu, and S.H. Kug, Temperature For-
mation of a-Alumina By Doping of an Alumina Sol, Journal Of
Colloid And Interface Science, 1999, 211, 110–113.
FIG. 7. SEM micrograph showed well-developed grains for fiber calcined at
12008C.