characterization and phase evolution of cordierite based glass

Transcription

JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 6, No. 1, Special Edition, 2009
30
CHARACTERIZATION AND PHASE EVOLUTION OF CORDIERITE
BASED GLASS SYNTHESIS FROM PURE OXIDE AND MINERALS
Banjuraizah Johar1, Hasmaliza Mohamad2, Zainal Arifin Ahmad2.
1
2
School of Materials Engineering, Universiti Malaysia Perlis
School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia
Engineering Campus, 14300 Nibong Tebal
[email protected]
ABSTRACT
α Cordierite is very important phase in MgO-Al2O3-SiO2 system because of their very
outstanding thermal, chemical and electrical properties. In this presents study nonstoichiometry cordierite (MgO:Al2O3:SiO2 = 3:1.5:5) using 2 different initial raw materials (
(i)mixture of pure oxide, and ii) mainly mixture of minerals) were fabricated and compared in
terms of phase transformation and physical properties. Cordierite was prepared by glass
method at low melting temperature (1350oC). Low melting temperature has resulted in partly
crystalline glass which has possesses higher hardness, required longer milling time and result
in contamination from grinding media. However, α-cordierite has successfully crystallized and
fully densified at 850oC/2h. Activation energy for densification was investigated from thermal
expansion coefficient (TCE) results. Other properties that were discussed included thermal
properties using DTA/TGA.
ABSTRAK
α Cordierite amat peringkat penting dalam sistem MgO-Al2O3-SiO2 disebabkan oleh mereka
sangat terma cemerlang, kimia dan sifat-sifat elektrik. Dalam hadiah-hadiah ini mengkaji tidak
stoikiometri kordierit (MgO:Al2O3:SiO2 = 3:1.5:5) menggunakan 2 bahan-bahan mentah
permulaan berbeza ( (i) campuran oksida tulen, dan (ii) terutamanya campuran mineral) telah
dibuat dan dibandingkan dalam syarat-syarat penjelmaan fasa dan sifat fizikal. Kordierit telah
bersedia dengan kaca kaedah pada suhu lebur rendah (1350oC). Suhu lebur rendah telah
menghasilkan dalam sebahagiannya kaca habluran yang telah memiliki kekerasan lebih tinggi,
dikehendaki lebih panjang masa pengilangan dan mengakibatkan pencemaran daripada media
pengisaran. Bagaimanapun, α-cordierite telah dengan jayanya mengkristalkan dan sepenuhnya
densified di 850oC/2h. Tenaga pengaktifan untuk penumpatan telah disiasat daripada pekali
pengembangan terma (TCE) keputusan-keputusan. Sifat-sifat lainnya yang telah dibincangkan
termasuk sifat terma menggunakan DTA / TGA.
Keywords: Nonstoichiometric cordierite glass ceramic, characterization, kaolin, talc,
INTRODUCTION
Indialite or α cordierite materials are extensively used in broad range of applications, including
automobile exhaust systems, as substrate material for integrated circuit boards and as kiln
furniture, carriers for purifying exhaust emission, filter for liquid at high temperature
(Gonzalez-Velasco, Ferret, Lopez-Fonseca, & Gutierrez-Ortiz, 2005; Goren, Gocmez, & Ozgur,
2006; Shi, Liang, & Gu, 2001; Yalamac & Akkurt, 2006). There are several methods use to
237
syntheses α cordierite such as solid state reaction, sol-gel and crystallization from glass (Goren
et al., 2006).
Although many researchers was conducted to lower the sintering temperature of α cordierite
either by mechanical activation before solid state reaction, combination of mechanical
activation and sintering aids, or even by sol-gel methods using various precursor and various
sintering aids, however only a few of them successful in decreasing the sintering temperature of
α cordierite and the value of crystallization temperature is still above 1000°C. It is widely cited
in the literature on the difficulty to produce dense α cordierite ceramic by solid state reaction
because of its sintering temperature is near the incongruent melting point of α cordierite
(1350oC).
Recently, dense cordierite ceramics that were fired at <1000oC have been produced via glass
crystallization method or via sol-gel method using alkoxide (Katsuhiro Sumi, Yuichi
Kobayashi, & Kato, 1999). Lower sintering temperature (less than 1000°C) is necessary for
electronic application packaging in order to be co-fired with copper (1083°C), silver (961°C), or
gold (1061°C). Among these methods, crystallization of glass powders had much higher
potential to decrease the sintering temperature of α cordierite to lower than 1000oC. Since there
has been no report on synthesis cordierite from talc and kaolinite via glass method using non
stoichiometric ratio (3:1.5:5) to produced α cordierite, therefore in the present investigation, α
cordierite was synthesized from mainly talc and kaolin using glass crystallization method. As a
comparison, α cordierite was also prepared using high purity metal oxide using the same
stoichimetric and processing technique. Above stoichiometric have been proved by Chen et. al
(Chen, 2008) can obtained single phase α cordierite at 950oC/2h and give better result in
dielectric properties.
Beside to compare the properties of cordierite glass ceramic from high purity oxide grade and
mixture of minerals, the purpose of this work is to get general idea to setup experimental
parameter in order to achieve low sintering temperature and high purity of α cordierite phase
using mainly minerals talc and kaolin.
METHODOLOGY
The starting raw materials for oxides samples (Sample A) were MgO, Al2O3, SiO2, CaO,
whereas, for second sample (Sample B), compositions were mainly from minerals talc and
kaolin which has higher MgO, Al2O3 and SiO2 content. CaO, MgO, Al2O3, SiO2 were added in
this second composition to compensate the chemical formulation. Composition of oxides for
both samples was taken from Chen et. al (Chen, 2008). The stoichiometric composition used in
this present work is 3MgO. 1.5 Al2O3. 5SiO2. The weight percent of minerals powder (Sample
B) used was calculate base on chemical formulation of talc and kaolin. The homogenized
mixture of raw ingredients was melted in alumina crucibles at 1500oC for 4 hours. The molten
glass was quenched in distilled water to form frit. The frits were then crushed and dry milled for
6h using zirconia ball mill to obtain particle size with the average 1-3 μm. The glass powder
than were sieved to less than 45 μm, followed by uniaxially pressing at 400 MPa to form a
pellet with 10 mm diameter. Dimension and initial weight were recorded. The green pellets
were then sintered at 850oC with heating rate of 5oC/min for 2 hours soaking time. The
FSEM/EDX analyses were carried out in a VP FESEM-Supra 35VP microscope.
The X-ray diffractometer diffraction (XRD) patterns of the milled products were obtained using
a Bruker D8 Advanced operated in Bragg–Brentano geometry, with Cu Kα radiation, in the 10°
≤ 2θ ≤to 90° range. A differential thermal analyzer (DTA/TG) (Model Linseis) was used to
record the themograms of codierite glass powder. During DTA/TG runs, the samples were
heated from 25oC to 1000oC at heating rate of 5oC/min with α Alumina as reference. Thermal
expansion coefficient were performed using Linseis dilatometer at heating rate 5oC/min in the
temperature range room to 1000oC on sample 20 mm x 8 mm x 8mm pressed at 150 MPa. The
238
average linear expansion coefficient from 2 different ranges was calculated following usual
method.
RESULTS AND DISCUSSION
Physical observation of glasses
Sample from mineral precursor was green in color and appeared in opaque. Both samples seem
to be partly crystalline and hard. However, sample from pure oxide is less glassy than sample
from minerals. Based on the observation, it seems sample from pure oxide required high
temperature for melting compared to sample from minerals. XRD pattern of glass sample as
shown in Figure 1, clearly indicate that both samples are partly crystalline and sample A has
higher crystalline phase compared to sample B.
Figure 1: XRD pattern of glass powder. Diffraction pattern of sample A is
a curve with black in color while sample B is a curve with red in
color. Q-Quartz, O-olivine, C-α-cordierite
Table 1: Phases present in heat treated samples
Sample
A
Sample
Phase present after sintering
Amorphous, α cordierite, forsterite, zircornia-cubic,
zircornia- monoclinic, zircornia-cubic
Amorphous,α cordierite, forsterite, zircornia-cubic,
239
B
zircornia- monoclinic, zircornia-cubic
Crystallization behavior
The XRD pattern of a crushed pellet sintered at various temperatures was properly indexed
using standard JCPDS files. Figure 1 show XRD pattern for both glass samples after quenching
and underwent intensive grinding for 6 hours. Figure 2 shows diffraction pattern of both type of
cordierite glass heat treated at 900oC, and the results is summarized in Table 1.
The X-ray diffraction measurements on the sintered samples clearly indicate that α
cordierite (PDF#48-1600) as the prevailing phase along with a significant amount of forsterite
(PDF#88-1000), zirconia-cubic (PDF#89-9069), zircornia tetragonal(PDF#89-9068),, and
zircornia-monoclinic (PDF#89-9066). α cordierite has successfully crystallize at 850oC for both
sample and glass crystallization method has been proved to be a method to synthesized α
cordierite at such lower temperature. The intensity of diffraction peak for α cordierite is higher
for sample A as compared to sample B. This indicates that the concentration of α cordierite is
higher in sample A, compared to sample B.
Forsterite phase was presence and not anorthite phase as what has been obtained by
Chen et. al (Chen, 2008) using the same composition. The possibility of forsterite to
crystallized is higher using this formulation (3MgO.1.5Al2O3.5SiO2), since excess MgO and
less alumina from exact stoichiometric of cordierite (2MgO.2Al2O3.5SiO2) will cause excess
MgO and SiO2 to react and form forsterite (MgSiO4). XRD pattern for both samples also
indicate the presence of all three type of zircornia polymorph at 850oC. Zirconia that was
presence in both samples coming from milling media. This contamination may come from wear
mechanism which caused by collision between the powder and the ball. Due to partly
crystalline the samples tend to be very hard. Hardness test was carried out to investigate the
hardness of samples and zircornia ball. The results are tabulated in Table 2 indicates that the
hardness of quenched sample is just slightly lower than the hardness of zircornia ball.
Therefore, from this observation, we can decide that the sample should be melting at much
higher temperature until fully glass phase is obtained. This is because the glass will exists in
meta-stable state and has free energy higher than that corresponding crystalline phase of the
same composition. In addition, during melting, the bonding between the atoms was disturbed
and it may exist in a single atom or disordered form. Therefore it will be easy to break the
sample. Secondly, milling media should be choose from hard and high wear resistance to avoid
the presence of other phases from grinding media.
240
Figure 2: Comparison on XRD pattern between sample from pure oxide
and minerals after heat treated at 900oC/ 2h. a-α cordierite, Fforsterite, M-zirconia monoclinic, t-zirconia tetragonal, c-zirconia
cubic
Table 2: The hardness of milling media and as-quenched sample.
Zircornia
glass from sample B
Average Hardness, Hv (GPa)
9.725
8.665
DTA & TGA
Figure 3 demonstrates DTA/TG results for both samples. Thermogravimetric analysis of all
cordierite glass powders show three distinct temperature ranges of weight loss. The first weight
loss occurred in the temperature range 30-200oC is due to removal of physically adsorbed
water. The second weight loss appears in the temperature range 400-450oC is probably
associated with the removal of chemical bonded water (Pal, 1996). It is clear from these results
that sample B materials undergo greater weight loss on heating compared to sample A. Total
percent weight loss for sample A when heated up 1000oC is about 2.4% while 4% for sample B.
DTA scan of both samples show only single exothermic peak present in each sample. An
endothermic peak signifying the glass transition temperature, Tg is not present in all
thermograms under the condition of this experiment. The absence of an endothermic peak may
result from the high activity of the fine glass powder (Kim, 1994). The exothermic peak
indicates the crystallization of certain phase. The exothermal peak can be assigned to the
241
crystallization α cordierite. An intense and sharp peak corresponding to α cordierite has been
observed in the diffragtogram of the powders obtained by heat treated the cordierite glass within
that temperature. DTA results indicate that crystallization began between 865.3 and 886.9oC for
sample A and between 842.9 and 879.8oC for sample B. This shows that the crystallization of α
cordierite can be obtained at lower temperature when using mineral precursors compared to
high purity of metal oxides.
A
B
Figure 3: DTA/TG curves of glass powder (a) sample A and (b) sample B
Microstructural characterization
Figure 4 shows microstructure of both glasses. Sample B has low porosity than sample A, and
likely more compact. This explain why sample B posses higher hardness compared to sample
A, and as a result it tends to worn out at much higher degree. This indicates that why sample B
has higher contamination from grinding media compared to sample A. EDX analysis that was
done on glass sample as show in Figure 5, indicated that sample A is highly pure, whereas
sample B contain carbon as impurities. Elemental composition of metal oxide on both samples
also differed. Although chemical has been received as pure, detail characterization of kaolin and
talc is necessary. Compositions design based on chemical equation between stoichiometric
kaolin and talc has resulted in difference metal oxide contents in the sample. Figure 6 clearly
shows that sample B has lower grain size as compared to sample A.
242
A
B
Figure 4: Micrograph of cordierite glass before milling showing dense
structure a) sample A glass b) sample B
A
B
Figure 5: EDX analysis of glass sample a) sample A b) sample B.
243
B
A
Figure 6: SEM micrograph etched sample a) sample A and b) sample B
Coefficient of thermal expansion
Dilatometry was performed to track the linear shrinkage of cordierite samples as a function of
temperature with a heating rate 5oC/min. Table 3 present the results of the dilatometric test.
Sample B shows negative TCE, while sample A gives TCE value equal to 5x10-8 oC-1 which is
much lower from what commonly report for high purity α- cordierite (2x10-6 oC-1). This is may
be due to existing of micro crack in the microstructure of sample. From dilatometry curve, large
densification rate occurred at 735oC for sample B and 803oC for sample A. This is related to the
formation of a glassy phase. The starting materials (kaolinite and talc) that were used to
synthesized cordierite glass contains many impurities in which may contribute in decreasing the
sintering temperature and increased the densification rate of cordierite. Densification occurs
before the formation of α cordierite phase, as expected for reaction sintering process. This can
be seen from DTA graphs where crystallization occurs at slightly larger than the densification
temperature. Densification has occurred before the crystallization of cordierite, as expected for
a reaction sintering process. This statement was confirmed through DTA and dilatometry
analysis. The activation energy for densification, Q can be calculated from the shrinkage data
on Figure 7a and 7b (in the temperature range 735-889oC for sample B and 803 to 907oC for
sample A). A linear relationship of ln (ΔL/Lo T2) and T-1 was plot in Figure 7 to calculate
activation energy.
Results of linear thermal expansion coefficient and activation energy for densifications are
shown in Table 3. From activation energy data, it can be concluded that sample B is more
effective in enhancing the densification of the cordierite glass during the initial period of
densification.
Table 3: Result of CTE and activation energy for densifications.
Activation energy for densification
Sample
Sample A (oxide)
CTE
o
-1
(kJ/mol)
-8
354
-1 oC-1x 10-7
269
5 C x 10
Sample B
(minerals)
244
Figure 7: Dilatometric curve and plot of ln (dl/lo.T2 vs 1/T)
245
CONCLUSION
α cordierite has been successfully synthesized using mainly minerals talc, kaolin with small
amount of MgO, Al2O3 , CaO and SiO2 to compensate the formulation, and P2O5 and B2O3 as
nucleating agent below 900oC. Therefore this sample has an ability to be co-fired with
electrode such as Cu. It also has relative density higher than 90%, better hardness and negative
cte. Microstructure reveal that micro cracks were physically observed in several samples, load
for compaction of pellet should be decrease during compaction. Contaminations which come
from grinding media exist due to the higher hardness of quenched glass. The glass is partly
crystalline and therefore high melting temperature is needed to obtain fully glass so as to
decrease the hardness of glass powder and consequently decrease the contamination from
grinding media. Furthermore hardened milling media should be used to avoid this
contamination. Further characterization of minerals talc and kaolin is necessary since EDX has
demonstrated different metal oxide contents in both samples.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the financial supports from Islamic Development Bank
(IDB) and Fundamental Research Grant Scheme (FRGS 9003-00171) Universiti Malaysia
Perlis and technical assistants from Universiti Sains Malaysia (USM).
REFERENCE
B. H. Kim, K. H. L. (1994). Crystallization and sinterability of cordierite-based glass powders
containing CeO2. J. Mater. Sci., 29, 6592-6598.
Chen, G.-h. (2008). Sintering, crystallization, and properties of CaO doped cordierite-based
glass-ceramics. J. Alloys Compd., 455(1-2), 298-302.
D. Pal, A. K. C., Suchitra Sen. (1996). The synthesis, characterization and sintering of sol-gel
derived cordierite ceramics for electronic applications. Journal of Materials Science, 31,
3995-4004.
Gonzalez-Velasco, J. R., Ferret, R., Lopez-Fonseca, R., & Gutierrez-Ortiz, M. A. (2005).
Influence of particle size distribution of precursor oxides on the synthesis of cordierite by
solid-state reaction. Powder Technol., 153(1), 34-42.
Goren, R., Gocmez, H., & Ozgur, C. (2006). Synthesis of cordierite powder from talc,
diatomite and alumina. Ceram. Int., 32(4), 407-409.
Katsuhiro Sumi, Yuichi Kobayashi, & Kato, E. (1999). Low-Temperature Fabrication of
Cordierite Ceramics from Kaolinit and Magnesium Hydroxide Mixtures with Boron Oxide
Additions. J. Am. Ceram. Soc., 82(3), 783-785.
Shi, Z. M., Liang, K. M., & Gu, S. R. (2001). Effects of CeO2 on phase transformation towards
cordierite in MgO-Al2O3-SiO2 system. Mater. Lett., 51(1), 68-72.
Yalamac, E., & Akkurt, S. (2006). Additive and intensive grinding effects on the synthesis of
cordierite. Ceram. Int., 32(7), 825-832.
246

characterization and phase evolution of cordierite based glass

Transcription

Similar documents

Glass instructions

Large Auction - Don Guthery and Associates Auctioneers

custom chandeliers

Decor Rentals - The White List

SoftEtch™ SoftEtch™ Colour

Ideation to Integration: Smart Glasses for Enterprise

Vertec - CMS CZ

Borosilicate Glass Art Trade

CONSTGLASS: Annex: Final object report

October 2010 Newsletter