• Journal of the Korean Ceramic Society
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• v.27 no.5
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• pp.625-630
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• 1990

Cordierite powders were prepared from Si(OC2H5)4, Al(OC3H7i)3 and Mg(OC2H5)2 by the sol-gel method. Two different methods were applied for producing fine and homogeneous powders. One is that Si(OC2H5)4 with a lowr rate of hydrolysis was partially hydrolyzed and then Al(OC3H7i)3 and Mg(OC2H5)2 were mixed and reacted. The other is based on the simultaneous hydrolysis of these metal alkoxides using i-C4H9OH which retards the rate of hydrolysis of Al(OC3H7i)3 and Mg(OC2H5)2. It was confirmed that ifne and homogeneous powders were obtained from both methods. Also these powders were calcined at four different temperatures during two hours. X-ray diffraction patterns show only ${\mu}$-cordierite phase at 1000$^{\circ}C$, ${\mu}$-cordierite and ${\alpha}$-cordierite phases at 1100-1200$^{\circ}C$ and ${\alpha}$-cordierite phase at 1300$^{\circ}C$ respectively.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.663-669
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• 2004

Mullite and cordierite, which were stable oxides having excellent thermal and chemical characteristics, were widely used as an engineering and electronic materials. However, thermal shock resistance of the mullite was detriorated, and strength of the cordierite was also reduced at high temperatures. The mullite-cordierite composite powders were synthesized for solving these problems in this study. The mullite-cordierite composite powders were manufactured by the solution-polymerization method using mixtures of fused silica, aluminium nitrate, magnesium nitrate, and PVA. Crystallinity, phase formation, density, and surface area of the synthesis powders were characteristics. Fine mullite-cordlerite composite powders were successfully synthesized at 1300$^{\circ}C$ and their surface areas were about 20㎡/g after planetary milling for 1h. With increasing the milling time, surface area increased to 23 ㎡/g for 4h ana 24㎡/g for 8h.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.55-62
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• 1995

Cordierite powders were prepared by a controlled hydrolysis of metal alkoxides with ethanol and distilled water. HC1 was used as a catalyst. The amount of HCI catalyst used was in range of 0.1-0. 5mol per lmol of TEOS. Effects of HC1 catalyst on the characteristics of cordierite powder were examined. $\alpha$-Cordierite powder prepared with HCI/TEOS mol ratio of O.lmol/mol was crystallized at $1050^{\circ}C$. On the other hand, $\alpha$-cordierite powders prepared with HCI/TEOS rnol ratio of 0.3 and 0.5rnol/mol were crystallized at $950^{\circ}C$. Spinel( mA120a) phase remained up to $1300^{\circ}C$ in the cordierite powder prepared with HCI/TEOS rnol ratio of 0.lrnolirnol. On the contrary, spinel phase was absent, and mordierite was the only phase remalned at $1300^{\circ}C$ in the cordierite powder prepared with HCI/TEOS mol ratio of 0.3 and O:5mol/mol.

• Journal of the Mineralogical Society of Korea
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• v.12 no.2
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• pp.55-65
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• 1999

Spotted cordierite occurs as the result of intrusion of Wolaksan Granite of Cretaceous age in the northern part of the Ogcheon Metamorphic Belt, forming a contact metamorphic zoning in accordance with the distance from the granite body: a cordierite-muscovite-biotite-quartz assemblage and the higher-temperature cordierite-biotite-quartz-(cummingtonite). These quartz-ubiquitous mineral assemblages identified in the cordierite spot seem to reflect Al-deficient condition of the protolith. TEM observations of textural relations between the cordierite and mica within the cordierite spot clearly reflect that cordierite was formed at the expense of micaceous matrix. A structure refinement of the poikiloblastic cordierite was performed by the Rietveld refinement method. Unit cell of the cordierite was determined to be as follows : lower-temperature type: a=17.1480(9)${\AA}$, b=9.7743(6)${\AA}$, c=9.3184(5)${\AA}$, V=1561.9(4)${\AA}$3, higher-temperature type: a=17.136(2)${\AA}$, b=9.751(1)${\AA}$, c=9.322(1)${\AA}$, V=1557.7(4)${\AA}$3. They show a remarkable difference in the unit cell dimension. The refinement results indicate that structural sites of lower-temperature cordierite are wholly occupied by appropriating ions. Compared to this, tetrahedral sites of the higher-temperature type exhibit an order/disorder ranging about 5-8% as the result of substitution between Si4+ and Al3+, except for T26 site occupied wholly by Al3+. These structural differences seem to be related to the formation temperatures of both cordierite types.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.48-52
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• 2014

The Mg-enriched magnesium aluminum silicate (MAS) glass is known for its higher mechanical strength and chemical resistance. Among such glasses, cordierite ($Mg_2Al_4Si_5O_{18}$) is well known to have a low thermal expansion and low melting point. Polycrystalline engineering ceramics such as alumina can be strengthened by a surface modification with low thermal expansion materials. The present study involves the synthesis of cordierite by a sol-gel process and investigates the effect of glass penetration on the surface of alumina. The cordierite powders were prepared from $Al(OC_3H_7)_3$, $Mg(OC_2H_5)_2$ and tetraethyl orthosilicate by hydrolysis and condensation reaction. The cordierite powders were characterized by X-ray diffraction (XRD, Rigaku), scanning electron microscope (SEM, JEOL: JSM-5610), energy dispersive spectroscopy (EDS, JEOL: JSM-5610), and universal testing machine (UTM, INSTRON). The X-ray diffraction patterns showed that the synthesized particles were ${\mu}$-cordierite calcined at $1100^{\circ}C$ for 1 h. The shape of synthesized cordierite was changed from ${\mu}$-cordierite to ${\alpha}$-cordierite with increasing calcination temperature. Synthesized cordierite was used for surface modification of alumina. Cordierite powders penetrated deeply into the alumina sample along grain boundaries with increasing temperature. The results of surface modification tests showed that the strength of the prepared alumina sample increased after surface modification. The strength of a surface modified with synthesized cordierite increased the most, to about 134.6MPa.

• Journal of the Korean Ceramic Society
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• v.42 no.3 s.274
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• pp.155-164
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• 2005

The characteristics of sintering for Mullite-Cordierite (MC) composites and the effect of $TiO_2$ addition were studied. The MC composites were manufactured by a solution-polymerization method using PVA as a polymer carrier, and $TiO_2$ was used as a sintering agent. They were calcined at $1300^{\circ}C$, planetary milled for 4 h and sintered at $1450^{\circ}C$. As cordierite content increased, relative density of materials was increased up to $98\%$ and sinterability was improved. In case of $50\;wt\%$ mullite/$5\;wt\%$ cordierite composition sintered for 16 h, the flexural strength and thermal expansion coefficient were 190 MPa and $3.07{\times}0^{-6}/^{\circ}C$, respectively. However, mechanical properties were decreased with the cordierite contents higher than $50\;wt\%$ because of the excess liquid-phase amount. As the addition of $TiO_2$ is increased, columnar crystal of mullite and liquid-phase contents were increased. In particular, the flexural strength and thermal expansion coefficient decreased in case of $5\;wt\%\;TiO_2$ addition.

• Journal of the Korean Ceramic Society
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• v.44 no.4 s.299
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• pp.230-234
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• 2007

Cordierite ceramics were fabricated via a reaction sintering process using ceramics-filled polysiloxane as a precursor for cordierite ceramics. In this study, the effects of the additive composition, additive content, and sintering temperature on the sintered density and compressive strength of cordierite ceramics have been investigated The sintered densities of reaction-sintered cordierite ceramics containing $TiO_2$ as an additive were insensitive to the additive composition, additive content, and sintering temperature and ranged from $1.92g/cm^3\;to\;2.06g/cm^3$. In contrast, the cordierite ceramics containing $Y_2O_3$ showed a maximal density of $2.21g/cm^3$ at 5 wt% addition and at a sintering temperature of $1400^{\circ}C$. The compressive strength of cordierite ceramics showed the same tendency with the density. Typical compressive strength of cordierite ceramics containing 5 wt% $Y_2O_3$ as a sintering additive and sintered at $1400^{\circ}C\;was\;{\sim}480MPa$.

• Korean Journal of Materials Research
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• v.25 no.7
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• pp.330-335
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• 2015

A low thermal expansion ceramic, cordierite ($2MgO{\cdot}2Al_2O_3{\cdot}5SiO_2$), was synthesized using pyrophyllite. Pyrophyllite usually consists of $SiO_2$ and $Al_2O_3$, which are the main components of cordierite. $MgCO_3$ and $Al(OH)_3$ were added in various amounts to pyrophyllite and fired for synthesis and sintering. ${\alpha}$-cordierite crystallized from $1000^{\circ}C$ with mixing of 20 wt% $MgCO_3$ and 1.7 wt% $Al(OH)_3$, and un-reacted cristobalite was also detected with the cordierite. As the temperature was increased to $1400^{\circ}C$, the cordierite yield was gradually increased. Powder compacts of the synthesized cordierite were sintered between $1250^{\circ}C{\sim}1400^{\circ}C$; the sintered samples showed a low thermal expansion coefficient of $2.1{\times}10^{-6}/^{\circ}C$ and typical sintering behavior. It is anticipated that it will be possible to synthesize cordierite ceramics on a mass production scale using the mineral pyrophyllite.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.151-157
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• 2004

Because of the excellent thermal and chemical properties of mullite and cordierite as the stable oxide ceramic materials, they were widely used from engineering materials to electronic materials. Notwithstanding of their high demands, mullite was synthesised because it is not existed in nature. It is also difficult to produce cordierite of fine powder with high purity due to the narrow range of synthetic temperature. Mullite was synthesised by solid state reaction. However, synthesized mullite has been inhomogeneous. Because of the facts, various synthetic methods have been studied so far including sol-gel method. The purpose of this study is to synthesis mullite and cordierite of fine powder with high purity at the lower temperature by solution-polymerization route using PVA as a polymer carrier, which is an economical method by using low cost materials. As a result, mullite and cordierite were produced with mono crystal phase at 1200$^{\circ}C$ and 1250$^{\circ}C$, respectively, and their surface area over 20 ㎡/g.

• Journal of the Korean Ceramic Society
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• v.43 no.6 s.289
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• pp.344-350
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• 2006

Porous cordierite was synthesized by the mechano-chemical processing using fly ash. The phase evolution of cordierite was investigated as a function of processing variables such as milling time and sintering temperature. In this study, the phase transition path of cordierite from fly ash was followed by sapprine/spinel ${\to}$ mullite/spinel ${\to}{\alpha}$-cordierite. Porous cordierite fabricated after 32 h of milling time and sintering at $1150^{\circ}C$ showed relatively low thermal expansion coefficient ($2.5{\times}10^{-6}/^{\circ}C\;(25{\sim}1000^{\circ}C$)) and high porosity (75%).