Ceramics in Asia

18 Vol. 56 (2007) [1]

Synthesis, Properties and Applications of Cordierite Ceramics, Part 1A. Chowdhury, S. Maitra, S. Das, A. Sen, G.K. Samanta, P. Datta

1 Introduction

Cordierite (2MgO·2Al2O3·5SiO2) is an impor-

tant naturally occurring ceramic material,which

is popular especially for its unusually low ther-

mal expansion coefficient, low thermal mass,

low dielectric loss factor, low density, volume

resistivity and high thermal shock resistance.

Cordierite is isostructural with beryllium. It is

found in two structural forms, namely, the or-

thorhombic (low temperature form) symme-

try, which is more common, and the hexagonal

symmetry, which is also known as “indialite”.

The structure of cordierite is characterized by

six-membered rings and is built up from SiO4

and AlO4 tetrahedra. These tetrahedra form six

(cation) membered or four (cation) membered

rings [1], as shown in Fig. 1.

Anirban Chowdhury is apost-graduate research stu-dent working in the area ofsol gel ferroelectrics for hisPhD at the Institute for Ma-terials Research, University

of Leeds, UK. He earned his BTech in Ceramicsfrom the College of Ceramic Technology, Uni-versity of Calcutta and MTech in Materials Sci-ence from IIT Kanpur. He received the presti-gious ORS award and a Tetley & Lupton Schol-arship for 2005–2008.

AbstractAs an engineering material, cordierite has manyapplications in different fields exploiting itsunique electrical, mechanical and thermal prop-erties. The synthetic aspect of cordierite is ofconstant interest to researchers. Elucidation ofits structure and establishing the properties ofits structure has always been considered a fas-cinating subject by researchers. In the presentpaper these different aspects of cordierite arebriefly reviewed.

Keywords:

Cordierite, processing, properties, applications

Interceram 56 (2007) [1]

Some properties of this multiphase oxide are

given below [2–4]:

Density 2.0–2.53 g/cm3

Melting point 1470 °C

Thermal expansion coefficient from 25 to

1000 °C 1.4–2.6 � 10–6/K

Young’s modulus 139–150 GPa

Flexural strength at room temperature

120–245

Relative dielectric constant

5.0 (K and tanδ at 1 MHz)

Typical thermal expansion curves are shown in

Fig. 2. The expansion is small and anisotropic.

The “c”axis expansion is negative, while the “a”

axis expansion is positive and therefore the re-

sultant volume expansion is negligibly small

(with an aggregate thermal expansion of about

0.9 � 10–6/K from room temperature to 800 °C).

With elevated temperatures, the increased ther-

mal motion of the atoms of cordierite is accom-

modated primarily by twisting and rotation of

the rings. The relationship between thermal ex-

pansion and crystal structure of cordierite has

been discussed by Hochella and Brown [5].

Cordierite is widely used in the whiteware in-

dustries as kiln furniture because of its above-

mentioned properties. It also has advanced ap-

plications as electrical insulators, high perform-

ance resistors, heating element supports, burn-

er tubes, feed-through insulators,special furnace

shapes, exhaust catalyst supports, filters and

many more that are discussed here. For engi-

neering applications, it is usual to control puri-

ty and reproducibility by utilizing synthetic

cordierite.

2 Mineralogical aspects

Cordierite is a magnesium aluminium silicate

(Mg2Al4Si5O18) mineral. It belongs to the class

of silicates and the subclass of cyclosilicates (an-

dalusite-sillimanite-kyanite group).Although,

it is not a very popular mineral from the geo-

logical point of view, its gemstone variety, which

is called iolite, is well known among gemstone

collectors and fanciers. Cordierite was known

and used as a gemstone

in Sri Lanka long before

the French geologist-

mineralogist Pierre

Louis Cordier accurate-

ly described it in 1809.

Cordierite was identi-

fied as a specific miner-

al and named in 1813.

Apart from iolite, the

other varieties of

cordierite found are

bloodshot iolite and

praseolite. The unusual

blue-violet colour of

cordierite is attractive

and can be compared

Fig. 1 • Structure of cordierite [5]

Fig. 2 • Typical thermal expansion curves of cordierite [5]

19Vol. 56 (2007) [1]

> > >

with a light blue sapphire of purplish tint. This

is the reason why cordierite is sometimes called

"water sapphire". Different colours of cordierite

crystal available are blue, greyish blue, violet

blue, grey, yellow, brown, green (rare), etc. One

of the most notable characteristics of cordierite

is its strong pleochroism, or colour changing

ability. Generally, it is strongly trichroic.When

viewed from one direction, the crystal or gem-

stone may appear blue or blue-violet. But as the

crystal or gemstone is rotated in another view-

ing direction, the colour will appear yellowish

gray to light blue. The Mg-rich variety shows as

pale yellow, pale blue, and violet blue and the

Fe-rich variety shows as colourless and violet.

Its index of refraction varies in between

1.52–1.57. Its birefringence ranges from 0.005

to 0.018 and dispersion is 0.017. Its optical char-

acter is biaxial positive, but often it is negative.

The crystals may be colourless or transparent

to translucent. It has some opalescence resem-

bling star sapphire. It has a vitreous lustre. The

cleavage is poor in one direction and the frac-

ture is subconchoidal. Its hardness is 7–7.5, spe-

cific gravity is approximately 2.3 and streak is

white. It reacts slightly with concentrated acids,

but more readily dissolves in HF. The crystal

habits include rare prismatic crystals that are

usually massive, or in compact grains embed-

ded in metamorphic schists and gneisses. They

are also found as pebbles and grains in alluvial

deposits.The minerals associated with cordierite

are almandine, corundum, andalusite, biotite

and feldspars. The inclusions in cordierite crys-

tals are clouds of very small zircon crystals sur-

rounded by interference colours rimmed with

intense yellow and hematite platelets in parallel

orientation. Its notable occurrences include Sri

Lanka; India; Burma; Madagascar; Middlesex

Co.,Connecticut and the Yellowknife area of the

Northwest Territories of Canada.It is a very com-

mon mineral in Sweden as it is a component in

many Swedish schists, found in central Sweden.

It is of relatively low cost, has good electrical in-

sulation properties,moderate mechanical prop-

erties and temperature resistance, and can read-

ily be formed into a variety of shapes. It can be

made in high volume through cost-effective ex-

trusion or dry-pressing methods.

3 Processing of synthetic cordierite

Many researchers have tried to synthesize

cordierite from different starting materials

through various routes. The effects of different

additives like TiO2, ZrO2, ZnO, SrO, B2O3, etc.

on the densification of cordierite have also been

studied extensively. During powder preparation

of cordierite the kinetics of heat treatment can

also have a significant effect on its densification.

Cordierite can be synthesized by firing tradi-

tional ceramic raw materials like clay, talc, sili-

ca and alumina at 1340–1450 °C.But this process

does not yield theoretically dense bodies as they

cannot be fired to maturity due to excessive for-

mation of glass from talc and clay and because

of the fact that cordierite incongruously melts

at 1460 °C to give mullite. To overcome this

problem, a cordierite composition is pre-cal-

cined to grog (talc + alumina) and then com-

bined with clay. Sometimes, the batch compo-

sition is melted and after fabrication of the de-

sired shape directly from the melt or glass, the

amorphous shape is devitrified to yield a

cordierite monolith [6].

The conventional formation of cordierite in-

volves two stages. Firstly, a small amount of

cordierite is formed at 1275 °C through the sol-

id-state reaction of mullite, protoenstatite and

cristoballite – the decomposition products of

talc and kaolinite. In the second stage, a glassy

phase appears at 1335 °C from the reaction of

previously formed cordierite and the remain-

ing cristoballite and protoenstatite. The bulk of

the cordierite is then formed by the reaction of

the melt with mullite. Cordierite forms at low-

er temperatures (1140 °C) when clinochlore and

kaolinite are reacted [7].

3.1 Synthesis from kaolin by solidstate reactions P. Grosjean [8] studied the talc-clay reaction of

different sources and he found 30 mass-% talc

and 70 mass-% clay to be an optimum compo-

sition as it showed minimum thermal expan-

sion at 1000 °C in all test samples fired at

1330 °C. Khabas et al [9] studied the synthesis

of cordierite in mixtures of magnesia and clay

raw materials recovered from deposits in Siberia.

The raw materials were mechanically activated

using a vibratory centrifugal mill. The synthe-

sis can be brought to completion at lower tem-

peratures under mechanical activation condi-

tions using a cordierite addition.

3.2 Synthesis by solution technique Han and Park [10] synthesized cordierite from

inorganic compounds like Mg(NO3)2·6H2O,

Al(NO3)3·9H2O and colloidal silica by co-pre-

cipitation method and studied its sintering. In

other works, Han and Park [11–12] synthesized

and sintered cordierite from metal alkoxides,us-

ing Si(OC2H5)4·Al(OC3H7)3·Mg(OC2H5)2 by

the sol-gel method. Densification of this pow-

der compact, which was studied by using the

precursor powders calcined at 900 °C for 2 h,

improved at the sintering temperature of

800–900 °C. An alkoxide sol-gel route was de-

veloped by Tsai [13] to prepare stoichiometric

cordierite fibers. X-ray diffraction analysis re-

vealed that non-aged and aged fibrous gels all

remained amorphous at 800 °C, but began crys-

tallizing into µ-cordierite and α-cordierite at

900 °C and 1050 °C, respectively. Single-phase

α-cordierite fibers were obtained at 1300 °C.

Heating the non-aged fibers yielded denser mi-

crostructures with fine grain sizes of 0.2 and

0.4 µm,whereas the aged fibers exhibited porous

microstructures following heating at 1300 °C.A

higher heating rate and aging treatment result-

ed in higher open porosity of the fired fiber.

Petrovic et al [14] synthesized alkoxy-derived

cordierite gels from tetraethylorthosilicate

(TEOS), aluminium isopropoxide and magne-

sium ethoxide. TEOS was partially hydrolyzed

at molar ratios H2O/TEOS = 1.2 in the presence

of HCl as catalyst.At first µ-cordierite crystal-

lized in a three dimensional growth at

950–1000 °C with a small amount of spinel.

The transformation of µ- to α-cordierite be-

gan at about 1100 °C and that of α- to β-

cordierite occurred at above 1300 °C. The over-

all activation energy of the crystallization of µ-

cordierite is 580 ±81 kJ/mol. Fukui et al [15]

studied the effect of prehydrolysis on the struc-

ture of a complex alkoxide as a cordierite pre-

cursor and its crystallization behavior. Here

complex alkoxides were synthesized as cordierite

precursors by reaction of pre-hydrolysed TEOS

with Al and Mg alkoxides and the effect of pre-

hydrolysis on alkoxide structure was analyzed

by IR,27Al and 29Si NMR spectroscopies. It was

observed that, for temperatures at the lower end

of the range of α-cordierite formation, an in-

crease in the water ratio of prehydrolysis was ef-

fective because Si-O-Al bondings were intro-

duced into the Mg-Al-Si complex alkoxides.

Moon and Kim [16] prepared a cordierite ce-

ramic with a thermally stable pore structure by

a simple modification of a sol-gel reaction of

alkoxide precursors, synthesized from Mg met-

al or Mg-acetate, Al(i-Opr)3 and partially pre-

Ceramics in Asia

20 Vol. 56 (2007) [1]

hydrolyzed Si(OEt)4. The crystallization of

µ-cordierite began at 900 °C and α-cordierite

formed in between 1050–1250 °C. Lee and Kriv-

en [17] synthesized homogenous and stable

amorphous type cordierite powder by a solu-

tion-polymerization route using polyvinyl al-

cohol (PVA) solution as polymeric carrier. The

bulky, long chain polymeric precursor changed

into a very soft and porous powder after calci-

nation at 800 °C for 1 h. The calcined powder

was attrition milled to get a 30 nm size amor-

phous cordierite powder with a high specific

surface area (181 m2/gm).A dense powder hav-

ing a relative density of 99 % and a CTE value

of 2.1 � 10–6/°C was found in the process.

Awano et al [18] studied the effects of grinding

on the synthesis of cordierite where a precur-

sor gel derived from colloidal processing was

ground. The calcined ground powder enhances

the homogeneity of the resulting powder and

causes the accumulation of internal energy as

crystal strength; consequently the densities of

the sintered bodies increase and the optimum

temperature range widens.

3.3 Synthesis of cordierite glass-ceramicsGeiss et al [19] showed that a glassy phase of

cordierite can be retained by a rapid quench

from the melt and then a fine powder can be

prepared by the granulation of the quenched

glass. The resultant powder compact can be ful-

ly densified by a viscous flow sintering mecha-

nism at a temperature between the glass transi-

tion temperature (810 °C) and the softening

point (860 °C). Furthermore crystalline

cordierite can be obtained by annealing at a

higher temperature. Diaz et al [20] described a

new route of cordierite synthesis from geother-

mic wastes, as the geothermic plants produce a

variety of waste materials, which can be puri-

fied and used as a non-conventional source of

raw materials for making glass ceramics. Two

cordierite materials were synthesized by means

of de-vitrification time-temperature treatment.

TiO2, ZrO2, ZnO, and SrO were used as addi-

tives. Boccaccini et al [21] fabricated cordierite-

glass matrix composites from fly ash and waste

glass. Commercial alumina platelets were rein-

forced to improve the wear resistance of the ma-

terial.For fly ash contents up to 20 mass-%,near-

ly fully dense compacts could be fabricated at a

low sintering temperature (650 °C). For higher

fly ash contents, the densification was hindered

by the presence of crystalline particles in the fly

ash, which jeopardized the viscous flow densi-

fication mechanism. These materials have good

machinability.

3.4 Effect of additives on cordieritesynthesisLow temperature synthesis of cordierite had

been tried by Sumi et al [22] from kaolinite and

magnesium hydroxide mixtures with boron

oxide addition. Boron oxide (B2O3) was added

in the form of magnesium borate (2MgO·B2O3).

The addition of B2O3 promoted densification

at 850–900 °C and accelerated the crystalliza-

tion of α-cordierite. The authors found that the

specimen with 3 mass-% B2O3, that was fired at

950 °C showed a linear thermal expansion co-

efficient of ~ 3 � 10–6 K–1, a bending strength

of >200 MPa, and a relative dielectric constant

of 5.5 at 1 MHz. Finally, they concluded that

these cordierite ceramics may be used as sub-

strate materials for semiconductor interconnec-

tion. Torres and Alarcon [23] reported that ad-

ditions of TiO2 as nucleant and B2O3 as flux to

a chosen glass in the cordierite primary phase

field of the CaO–MgO–Al2O3–SiO2 quaternary

system favoured the crystallization of cordierite

as the only crystalline phase with hexagonal

prismatic morphology.But the presence of Na2O

and K2O as fluxes suppresses its crystallization.

This can lead to new glazes for floor tiles with

improved mechanical and optical properties.

Jung et al [24] studied the effect of pure or sta-

bilized ZrO2 addition on the sintering of

cordierite-based ceramics. As ZrO2 content is

increased, MOR, fracture toughness, and bulk

density of the cordierite ceramics increased

along with a decrease in the thermal expansion

coefficient. El-Kheshen [25] studied the effect

of alumina addition (15 vol.-%) on cristobal-

lite formation in cordieritic glass-ceramic com-

posites prepared from pyrex borosilicate glass

and silica. The cristoballite formation decreased

with the addition of alumina due to a strong re-

action between Al3+ of alumina and K+ of pyrex

borosilicate glass. Hence, the material has a low

thermal expansion coefficient.A new route for

the solid-state reaction synthesis of cordierite

with and without the use of a flux was followed

by Malachevsky et al [26] by varying the sinter-

ing temperatures between 900 and 1400 °C.

Bi2O3 was proved to be a useful additive for low-

ering the temperature needed for the reaction

to take place.

3.5 Other synthetic techniques

Many researchers have worked on the synthe-

sis of cordierite honeycombs and foams through

different routes. Oliveira et al [27] fabricated

cellular cordierite foams using the polymer foam

replication process, where a polyurethane tem-

plate was infiltrated with slurries containing ap-

propriate binders and ceramic particles, fol-

lowed by the removal of excess slurry, burning

out of the polymer to leave a ceramic replica of

the polyurethane and, finally, high temperature

sintering. Rheological studies showed that op-

timum dispersion and stabilization conditions

were achieved for aqueous slurries containing

40 vol.-% solids, 2 mass-% bentonite and

0.8 mass-% dispersant. The struts had an angu-

lar cross-section and cracks were seen along the

cell edges and the cell walls. The density of the

sintered foams was 20 % of the struts density.

The volumetric shrinkage was approximately

30 % and the linear shrinkage appeared to be

isotropic. The synthesis of cordierite from var-

ious pre-cursor materials via different routes

such as solid-state reaction, solution technique,

and viscous flow densification has been reviewed

in this part. The sol-gel process has been proved

as the low temperature densification process.

Cordierite densification occurs gradually from

µ to α to β at 900, 1100 and 1300 °C respective-

ly. The prehydrolysis of the complex alkoxides

in sol-gel processing was effective. Geothermic

wastes have been shown as a non-convention-

al source of raw material for the synthesis of

cordierite glass-ceramics. The precursor com-

positions were altered in many cases by the ad-

dition of different additives – B2O3 as flux; TiO2

as nucleant,and ZrO2 have been used to improve

the fracture toughness. The relation between

thermal expansion and crystal structure has al-

so been discussed.

4 Properties of cordierite ceramics

The general properties of cordierite ceramics

have been discussed previously in this paper.

These key properties of cordierite have made it

suitable for various applications. Many re-

searchers have studied the effects of different

additives and their amount of additions during

the synthesis of cordierite ceramics on the de-

velopment of these properties. The properties

required for any particular application have been

developed through proper selection of raw ma-

21Vol. 56 (2007) [1]

> > >

terials, mixing them in definite proportions, us-

ing additives in definite amount, etc. Different

processes of synthesis will lead to the acquisi-

tion of definite properties in the cordierite ce-

ramics. Some of these have been discussed in

the previous section and will be discussed fur-

ther in this section.

4.1 Structural evolution Logvinkov et al [28] analyzed the thermody-

namic relation ΔG = f(T) for solid-phase reac-

tions between stoichiometric components of the

MgO–Al2O3–SiO2 system and considered the

thermodynamic conjugation of solid-phase re-

actions.It was shown that the structural changes

in the crystal lattice of cordierite should be con-

sidered as arising from compositional changes

in the corresponding solid solutions rather than

from polymorphous transformations. The au-

thors discussed the thermodynamic instability

of cordierite and proposed a diagram for phase

relations in the subsolidus of the

MgO–Al2O3–SiO2 system. Torres and Alarcon

[29] reported the structural evolution of loose-

ly compacted equimolar cobalt-magnesium

cordierite glass powder (MgCoAl4Si5O18) with

annealing time at temperatures between 900 and

1100 °C. The first crystalline phase formed was

µ-cobalt containing cordierite, which trans-

formed to α-cordierite with longer annealing.

The µ-cordierite grew by a dendritic mechanism

along the particle surface, and the nucleation

and growth of α-cordierite occurred within the

µ-cordierite dendrites. At the beginning of this

transformation, some mullite and cobalt-mag-

nesium aluminate spinels were detected which

disappeared on further annealing.After long an-

nealing at 1100 °C, some ordering for Al and Si

in tetrahedral sites had taken place, indicating

some transformation to β-cordierite (or-

thorhombic). After short annealing at 1100 °C,

the fully crystallized microstructure developed

was α-cordierite with columnar or linear fea-

tures.Below Tc,cordierite shows an unusual do-

main pattern consisting of walls, which are not

well oriented along elastic soft directions due to

a low spontaneous strain and low anisotropy en-

ergies.Hence,there is a competition between the

wall due to strain and the wall due to local inter-

actions, which leads to the formation of ‘sand-

wich walls’, an intermediate between these two

wall types.Blackburn and Salje [30] tried to sim-

ulate the formation of the sandwich walls using

an atomistic computer model. These walls are

shown to be chiral in nature and the chirality di-

rection is fixed. The sandwich ‘filling’appears in

two shapes – a thick,well-defined domain at low

temperatures and a thin layer of wetting at high

temperatures.Matos et al [31] studied the struc-

ture of polymeric and polymer-derived ceram-

ic cellular cordierite foams using two different

approaches, which were compared. The authors

measured the morphological aspects of both

structure from images acquired by optical and

electron microscopy. In what concerns the cell

structure, a relation was observed either in the

proportion of the closed faces or in the size dis-

tributions of the cells. Average cell diameters

ranged from 575 to 715 µm in the ceramic foams

and 715 to 920 µm in case of polymeric foams.

The size distributions of the ceramic cells were

narrower than those of the respective polymer

templates.The authors established a relation be-

tween the final ceramic structures and the re-

spective templates and also explained the me-

chanical behaviour of the foams obtained. Di-

az-Mora et al [32] investigated the activation en-

ergy and activation enthalpy for crystal growth

and viscous flow in a cordierite glass-ceramic by

using experimental growth rates and viscosity

data. They concluded that the bond breaking

and molecular reorientation required for crys-

tallization is comparable to the atomic transport

mechanism involved in viscous flow and hence

viscosity data may be used to estimate crystal

growth rates in glasses.

4.2 Phase transformation andmechanical properties Yue et al [33] reported that a small amount of

B2O3 and P2O5 was found to promote the µ-

cordierite to α-cordierite transition in low tem-

perature sintered cordierite glass-ceramics pre-

pared by a sol-gel-process.At the higher concen-

tration, the transition occurs at high tempera-

ture due to the formation of MgO-P2O5 based

compounds. The material has a dielectric con-

stant of less than 5.5 and low dissipation factor,

however, the amount of B2O3 and P2O5 has no

effect on these properties. Oh et al [34] studied

the reaction kinetics, melting endothermal, nu-

cleation and crystallization behaviour of

cordierite glasses containing up to 5 mass-% ni-

trogen by using combined heat flux differential

scanning calorimetry and thermo-gravimetric

analysis. The authors also discussed the effect of

AlN on the stability of the melt,microstructures

and the container materials. Jain et al [35] com-

pared the mechanical behaviour of cordierite-

mullite honeycombs with that of commercial

cordierite foam with and without rubber encap-

sulation. While impact testing, the energy ab-

sorption of both the honeycomb and the foam

increased upon rubber encapsulation. The rub-

ber-encapsulated honeycomb had shown a sub-

stantial decrease in energy absorbed parallel to

the channel walls, as opposed to an increase in

the perpendicular direction.The foam absorbed

less energy than the honeycomb. The critical

stress decreased in the honeycomb but increased

in foam upon rubber encapsulation.

4.3 Thermal properties Hasselman et al [36] studied the effect of

15 vol.-% particulate diamond reinforce-ment

on the thermal conductivity of a cordierite ma-

trix as a function of diamond particle size from

room temperature to 700 °C. The thermal con-

ductivity increases with increasing particle size

to a maximum of ~75 % for a mean particle size

of 50 µm. The particle effect was more pro-

nounced at lower than at higher temperatures.

The effect of particle size and temperature was

attributed to an interfacial thermal barrier, pos-

sibly resulting from interfacial phonon scatter-

ing, with a positive temperature dependence on

interfacial thermal conductance.

Garcia et al [37] applied the laser flash method

for measuring the thermal diffusivity of highly

porous cordierite materials. Errors in the calcu-

lation due to the surface roughness were reduced

by attaching two thin Cu layers to both surfaces

of the samples.Nandi [38] observed the thermal

expansion behaviour of boron doped cordierite

glass ceramics, where 1, 2, and 3 mass-% B2O3

showed negative expansion in the temperature

range of 100–300 °C. The expansion of the un-

doped cordierite was positive.A relative decrease

in the degree of negative expansion was ob-

served as the B2O3 concentration increased.

Johnson et al [39] tried to establish correlations

between the cordierite content, processing tem-

perature and CTE values of the samples.A max-

imum cordierite content of 90 % was achieved

for sintering at 1693 K (4 h soaking) correspon-

ding to a lowest CTE of 0.74 � 10–6 / K. The au-

thors also showed that the bulk thermal expan-

sion of cordierite honeycombs increases on CaO

doping due to the absence of micro-cracks, but

the axial anisotropy is reduced. Thermal shock

resistance is an important property that predicts

the life of cordierite ceramic products in ther-

Ceramics in Asia

22 Vol. 56 (2007) [1]

mal environments used for automobile pollu-

tion control as catalytic converters or as diesel

particulate filters.Das et al [40] presented a com-

parative study on the thermal shock resistance

of extruded cordierite honeycombs calculated

by using CTE, MOE, MOR, etc.

4.4 Electrical and dielectric properties Freer and Owate [41] studied some electrical

properties of certain cordierite glass ceramics in

the system SiO2–MgO–Al2O3–TiO2. High crys-

tallinity, good surface finish, and homogeneous

microstructure yielded high break down strength.

Sarkar et al [42] studied the effects of firing tem-

perature and test frequency on the dielectric prop-

erties of nickel-cordierite,silver-cordierite and ti-

tanium-cordierite samples after firing. The val-

ues of the dielectric constant and dielectric loss

decreased with increasing test frequencies and in-

creasing firing temperature.A low dielectric con-

stant of 2.2 was observed for the nickel-cordierite

samples.Wu and Huang [43] studied the effect of

crystallization on microwave dielectric proper-

ties of stoichiometric cordierite glasses contain-

ing B2O3 and P2O5,where two glasses containing

5 mass-% B2O3/ 5 mass-% P2O5 and 7.5 mass-%

B2O3/ 7.5 mass-% P2O5 were studied.Both glass-

es were sintered to nearly full density at temper-

atures as low as 860 °C. Finally the authors con-

cluded that cordierite glass containing α-

cordierite possesses better microwave proper-

ties than glassy phase and µ-cordierite.

Concerning the mechanical properties additions

of B2O3 and P2O5 in definite proportion have

shown an effect on the transition of cordierite

from µ to α form at different temperatures. The

effect of diamond reinforcement with varying

particle size on the thermal conductivity and the

alteration of thermal expansion co-efficient of

cordierite with the addition of B2O3 has been

discussed.In respect of electrical properties,high

crystallinity, good surface finish, and homoge-

neous microstructure yielded high break-down

strength. From the studies it can be seen that

cordierite glass containing α-cordierite possess-

es better microwave properties than glassy phase

and µ-cordierite.

References [1] Ikawa, H., Otagiri, T., Imai, O., Suzuki, M.,

Urabe, K., Udagawa, S.: J. Amer. Cer. Soc. 69

(1986) [6] 492–498

[2] Advanced Technical Ceramics, Edited by

Somiya, S., Academic Press, Tokyo, (1984)

31–36

[3] Salmang, H.: Ceramics, Physical and Chem-

ical Fundamentals, (Translated By Francis,

M. ), Butter Worths, London, (1961) 294–298

[4] Hlavaac, J.: The Technology of Glass and Ce-

ramics, An Introduction. Elsevier Scientific,

Amsterdam, (1983) 232–237

[5)] Hochella, Jr., M.F., Brown Jr., G.E.: J. Amer.

Ceram. Soc. 69 (1986) [1] 13–18

[6] Encyclopaedia of Materials Science and En-

gineering,Editor-in-Chief: Bever,M.B.(1986)

873–874

[7] Encyclopaedia of Materials Science and En-

gineering,Editor-in-Chief: Bever,M.B.(1986)

4153–4155

[8] Grosjean, P.: Cordierite ceramics. Interceram

42 (1993) [1] 11–15

[9] Khabas, T.A., Vereshchagin, V.I., Vakalova,

T.V., Kirchanov, A.A., Kulikovskaya, N.A.,

Kozhevnikova, N.G.: Refractories and Indus-

trial Ceramics 44 (2003) [3] 181–185

[10] Han, M.-H., Park, K.-C.: J. Korean Ceram.

Soc. 27 (1990) [7] 899–906

[11] Han, M.-H., Park, K.-C.: J. Korean Ceram.

Soc. 27 (1990) [5] 625–630

[12] Han, M.-H., Park, K.-C.: J. Korean Ceram.

Soc. 27 (1990) [6] 777–782

[13] Tsai, M.-T.: J.Amer. Ceram. Soc. 85 (2002) [6]

1637–1639

[14] Petrovic, R., Janackovic, D.J., Zec, S., Drman-

ic, S., Kostic-Gvozdenovic, L.J.: J. of Sol-Gel

Science and Technology 28 (2003) [1]

111–118

[15] Fukui,T.,Sakurai,C.,Okuyama,M.: J.of Non-

Crystalline Solids 162 (1993) [1–2] 178–187

[16] Moon, K.T., Kim, D.P.: J. of Sol-Gel Science

and Technology 26 (2003) [1–3] 229–234

[17] Lee, S.-J., Kriven,W.M.: J.Amer. Ceram. Soc.

81 (1998) [10] 2605–2609

[18] Awano, M., Takagi, H., Kuwahara,Y.: J.Amer.

Ceram. Soc. 75 (1992) [9] 2535–2540

[19] Geiss,E.A.,Fletcher,J.P.,Herron,L.W.: J.Amer.

Ceram. Soc. 67 (1984) [8] 549–552

[20] Diaz, C.,Valle-Fuentes, F.J., Zayas, M.E.,Ava-

los-Borja, M.: Amer. Ceram. Soc. Bull. 78

(1999) [3] 62–64

[21] Boccaccini, A.R., Bucker, M., Bossert, J.,

Marszalek, K.: Waste Management 17 (1997)

[1] 39–45

[22] Sumi, K., Kobayashi,Y., Kato, E.: J.Amer. Ce-

ram. Soc. 82 (1999) [3] 783–785

[23] Torres, F.J., Alarcon, J.: J. Europ. Ceram. Soc.

23 (2003) [6] 817–826

[24] Jung, H.-J., Oh,Y.-J., Lee, J.-K.: J. Korean Ce-

ram. Soc. 27 (1990) [2] 256–264

[25] El-Kheshen, A.A.: Industrial Ceramics 23

(2003) [2] 127–132

[26] Malachevsky,M.T.,Fiscina,J.E.,Esparza,D.A.:

J.Amer. Ceram. Soc. 84 (2001) [7] 1575–1577

[27] Oliveira, F.A.C., Dias, S., Mascarenhas, J., Fer-

reira, J.M.F., Olhero, S., Dias, D.: Fabrication

of cellular cordierite foams.Advanced Mate-

rials Forum II, Materials Science Forum 455-

456 (2004) 177–181

[28] Logvinkov, S.M., Semchenko, G.D., Kobyze-

va, D.A., Babushkin,V.I.: Refractories and In-

dustrial Ceramics 42 (2001) [11–12] 434–439

[29] Torres, F.J., Alarcon, J.: J. Europ. Ceram. Soc.

24 (2004) [4] 681–691

[30] Blackburn, J.F., Salje, E.K.H.: J.of Physics-

Condensed Matter 11 (1999) [24] 4747–4766

[31] Matos, M.J., Vaz, M.F., Fernandes, J.C.,

Oliveira, F.A.C.: Structure of cellular

cordierite foams.Advanced Materials Forum

II, Materials Science Forum 455–456 (2004)

163–167

[32] Diaz-Mora, N., Zanotto, E.D., Fokin, V.M.:

Physics and Chemistry of Glasses 39 (1998)

[2] 91–97

[33] Yue, Z.X., Zhou, J., Ma, Z.W., Bal, J.N., Gui,

Z.N., Li, L.T.: Ferroelectrics 262 (2001) [1–4]

1005–1010

[34] Oh, J.T., Hing, P., Fong, H.S., Chin, S.F., Zeng,

C.L.: J. of Materials Processing Technology

63 (1997) [1–3] 851–854

[35] Jain,V., Johnson, Ganesh, R.I., Saha, B.P., Ma-

hajan,Y.R.: Effect of rubber encapsulation on

the comparative mechanical behavior of ce-

ramic honeycomb and foam. Materials Sci-

ence and Engineering A – Structural Materi-

als Properties Microstructure and Process-

ing 347 (2003) [1–2] 109–122

[36] Hasselman, D.P.H., Donaldson, K.Y., Liu, J.,

Gauckler, L.J.: J.Amer. Ceram. Soc. 77 (1994)

[7] 1757–1760

[37] Garcia, E., Osendi, M.I, Miranzo, P.: J. of Ap-

plied Physics 92 (2002) [5] 2346–2349

[38] Nandi, A.K.: J. Amer. Ceram. Soc. 82 (1999)

[3] 789–790

[39] Johnson, R., Ganesh, I., Saha, B.P., Rao, G.V.,

Mahajan, Y.R.: J. Mater. Sci. 38 (2003) [13]

2953–2961

[40] Das, R.N., Madhusoodana, C.D., Panda, P.K.,

Okada, K.: Bull. Mater. Sci. 25 (2002) [2]

127–132

[41] Freer, R., Owate, I.O.: J. Mater. Sci. 25 (1990)

[12] 5291–5297

[42] Sarkar, G., Kulkarni, K., Lam, H.M.: J. Mater.

Sci. 38 (2003) [8] 1803–1807

[43] Wu, J.-M., Hwang, S.-P.: J.Amer. Ceram. Soc.

83 (2000) [5] 1259–1265

Received: 16.03.2005 (To be continued)

��