UDC 666.2.01

GLASS CERAMICS OF b-SPODUMENE COMPOSITION

WITH CONTROLLED DIELECTRIC CONSTANT

E. I. Suzdal’tsev1

Translated from Ogneupory i Tekhnicheskaya Keramika, No. 5, pp. 15 – 17, May, 2002.

A new class of heat-resistant, radio-transparent glass ceramic materials of �-spodumene composition is deve-loped. Modifying Li – aluminosilicate glasses with TiO2 addition allows preparation of materials with con-trolled dielectric constant in the range of 7 – 12 units.

It has been reported earlier [1 – 5] that ceramic techno-logy for fabrication of glass ceramic has a number of advan-tages over the traditional glass technology. The traditionaltechnology requires strict observance of the chemical com-position of precursor glasses, which, in turn, places limita-tions on the preparation of glass ceramic materials with agiven dielectric constant. Under modern conditions of thefrequent design modification of components and different re-quirements placed on radio-engineering characteristics, theuse of traditional technologies becomes less effective in bothtechnical (development of new compositions, melting, crys-tallization, etc.) and economical aspects.

It was shown in [6] that the dielectric constant as a func-tion of the material composition is best described by theLichtenecker equation

log � = c log �1 + (1 – c) log �2 ,

where � is the dielectric constant of the composite material;�1 is the dielectric constant of the material of addition; �2 isthe dielectric constant of the material of the matrix; and c isthe volume concentration of the material of addition.

An analysis of TiO2-modified materials has shown thatthe dielectric constant of these materials can effectively becontrolled by varying the concentration of TiO2 (Fig. 1) oncondition that the material of addition does not react with thematerial of the matrix and that the addition is uniformly dis-tributed over the composite’s bulk.

The data in Fig. 1 show that modifying a matrix of glassceramic material provides a way toward compositions whosedielectric constant can be varied over a wide range.

In this work, a glass ceramic of lithium aluminosilicatecomposition modified by TiO2 in the solid-phase state wasstudied.

The procedure was as follows. Granulated lithium alumi-nosilicate glass (SiO2 = 65%; Al2O3 = 25%; Li2O = 4%; andTiO2 = 6%) was ground in water to yield a high-density sus-pension (� = 1.97 – 2.05 g�cm3 ). TiO2 modifier was intro-duced into the stabilized suspension at a concentrationneeded for the required value of dielectric constant. The mix-ture was thoroughly homogenized and then cast into gypsummolds to prepare preforms with specified dimensions. The

Refractories and Industrial Ceramics Vol. 43, Nos. 5 – 6, 2002

1761083-4877/02/0506-0176$27.00 © 2002 Plenum Publishing Corporation

1 Tekhnologiya Federal State Unitary Production and Research En-terprise (FGUP ONPP), Obninsk, Kaluga Region, Russia.

�

100

90

80

70

60

50

40

30

20

10

0 10 20 30 40 50 60 70 80 90 100

TiO concentration, %2

Fig. 1. Dielectric constant of ceramic materials plotted as a functionof TiO2 concentration: 1 ) quartz ceramic; 2 ) glass ceramic; 3 ) alu-minum oxide ceramic.

preforms were heat-treated under appropriate conditions to

obtain a sintered, apparently pore-free material and to allow

the process of matrix crystallization from lithium alumino-

silicate glass to proceed to completion.

Titanium dioxide was chosen as a modifier because of its

high dielectric constant that would allow the dielectric pro-

perties of the main material to be varied without degrading

its strength characteristics. It was thought that, using this

method, the dielectric constant of a modified glass ceramic

can be varied from 7.0 to 18.0, which would allow a range of

radio-engineering applications using the same precursor ma-

terial and the same technology.

Glass Ceramics of b-Spodumene Composition with Controlled Dielectric Constant 177

TABLE 2. Properties of TiO2-Modified Glass Ceramics

Property

TiO2 concentration, %

0 5 10 15 20

Material grade

SK-1 SK-2 SK-3 SK-4 SK-5

1. Density, g�cm3 2.50 2.56 2.61 2.67 2.71

2. Water uptake, % � 0.1 � 0.1 � 0.1 � 0.1 � 0.1

3. Bending strength (20°C), MPa 100 – 120 100 – 120 100 – 120 100 – 120 100 – 120

4. Bending strength (20 – 1150°C), MPa 100 – 120 100 – 120 100 – 120 100 – 120 100 – 120

5. Compressive strength (20°C), MPa 250 – 350 270 – 360 250 – 410 240 – 380 250 – 400

6. Modulus of elasticity (20°C) � 10 – 3, MPa 55 – 60 53 – 60 57 – 60 56 – 60 55 – 57

7. CLE, � � 107, K – 1 (20 – 900°C) 5.0 – 13.0 7.0 – 15.0 8.0 – 16.0 11.0 – 21.0 13.0 – 23.0

8. Heat conductivity (20 – 700°C), W�(m � K) 1.6 – 1.8 1.7 – 1.9 1.8 – 2.0 2.1 – 2.4 2.2 – 2.5

9. Heat capacity (20 – 700°C), kJ�(kg � K) 0.8 – 1.1 0.9 – 1.2 0.9 – 1.2 0.9 – 1.2 0.9 – 1.2

10. Impact toughness (20°C), kJ�m2 2.5 – 3.0 2.1 – 3.1 2.0 – 2.5 2.0 – 2.4 1.9 – 2.3

11. Poisson’s ratio 0.28 0.28 0.29 0.29 0.30

12. Spectral semi-spherical emissivity (blackness) at � = 0.65 �m

(20 – 1200°C), % 22 – 25 27 – 36 30 – 42 33 – 45 35 – 48

13. Dielectric constant at f = 1010 Hz (20°C) 6.9 – 7.2 7.8 – 8.1 8.8 – 9.0 10.2 – 10.5 11.5 – 12.5

14. Dielectric constant increment at f = 1010 Hz (20 – 700°C), % � 6.0 � 5.0 � 4.5 � 4.0 � 3.0

15. Loss-angle tangent at f = 1010 Hz (20 – 700°C), tan � � 104 130 – 700 130 – 700 130 – 650 130 – 700 130 – 700

TiO2,

%

Properties of TiO2-modified slips and castings

slips castings

den-

sity,

g�cm3

visco-

sity,

sec

pH

electro-

kinetic

potential,

mV

0.063 –

0.5 mm

particle

concen-

tration,

%

mois-

ture

content,

%

den-

sity,

g�cm3

poro-

sity,

%

0 2.006 34.6 8.975 – 134.9 9.86 15.60 2.116 12.92

1 2.014 42 8.994 – 136.1 – – 2.125 13.21

2 2.024 44 8.995 – 135.6 – – 2.134 13.48

3 2.032 50 8.971 – 134.8 – – 2.134 13.76

4 2.048 53 9.002 – 136.0 – – 2.139 14.55

5 2.053 53 8.993 – 136.0 – – 2.144 14.97

6 2.061 55 9.012 – 137.1 – – 2.162 14.88

7 2.070 65 9.036 – 138.3 – – 2.167 15.29

8 2.076 67 9.030 – 138.1 – – 2.164 16.01

9 2.089 76 9.026 137.7 – – 2.167 16.48

10 2.089 59 – – 10.44 14.91 2.169 17.00

TiO2,

%

Properties of TiO2-modified slips and castings

slips castings

den-

sity,

g�cm3

visco-

sity,

sec

pH

electro-

kinetic

potential,

mV

0.063 –

0.5 mm

particle

concen-

tration,

%

mois-

ture

content,

%

den-

sity,

g�cm3

poro-

sity,

%

11 2.090 58 9.058 – 142.8 – 14.68 2.186 16.92

12 2.098 64 9.047 – 142.2 – 14.60 2.184 17.57

13 2.108 70 9.021 – 140.9 – 14.55 2.192 17.84

14 2.125 77 9.015 – 140.4 – 14.40 2.169 18.25

15 2.133 68 9.070 – 143.4 7.24 14.73 2.190 19.02

16 2.137 72 9.066 – 143.2 – 14.47 2.204 19.05

17 2.145 79 9.051 – 142.4 – 14.24 2.211 19.34

18 2.151 84 9.027 – 141.2 – 14.20 2.218 19.62

19 2.155 89 9.024 – 140.9 – 14.14 2.216 20.40

20 2.176 88 9.055 – 142.6 7.03 13.94 2.230 20.24

TABLE 1. Properties of Suspended and Cast Lithium Aluminosilicate Glasses Modified with Titanium Dioxide

In all cases, the modifier was added at concentrations notexceeding 30%. It should be noted that the increase in TiO2concentration caused an increase in density and viscosity ofthe suspension as well as an increase in porosity of themolded preforms. These effects are typical of conventionaltechnologies for preparation of other materials in which thestarting suspension is saturated by adding a solid phase. Inour case, the TiO2-modified Li-aluminosilicate suspensionhad both high density and viscosity, which preventeddemixing and allowed a uniform distribution of TiO2, despiteits density being higher than that of the glass, over the bulkof the preform material (Table 1).

The sintering of preforms molded from TiO2-modifiedLi-aluminosilicate suspensions was analogous to that of un-modified preforms. The shrinkage of apparently pore-freeglass ceramic with TiO2 of up to 20% was within 6 – 7%,which was much smaller than the shrinkage of glass ceramicprepared by powder technologies using organic or organo-silicon binder added to the precursor powder.

Structural and phase analyses of glass ceramics withTiO2 of up to 20% sintered at 1200 – 1240°C provided no

evidence of a reaction between the Li-aluminosilicate matrixand the modifying additions. The addition material was uni-

formly distributed over grain boundaries. �-Spodumenecrystals that form in this process incorporate the extraneousinclusions thereby cementing the matrix, which allows thematerial to maintain its high strength properties. As is seenfrom the data in Table 2, the use of TiO2 allows the dielectricconstant of glass ceramic to be controlled over a range of7 – 12 units (Table 2).

The data in Fig. 2 show good agreement between experi-mental and calculated dielectric constants as a function of theTiO2 concentration. Based on this evidence, one can predictdielectric properties in glasses of constant chemical compo-sition, which simplifies substantially the manufacturing tech-nology of components issued in small batches with frequentvariations in nomenclature.

REFERENCES

1. E. I. Suzdal’tsev, M. A. Suslova, N. I. Ipatova, et al., A Method

for Molding Components from a Sintered Glass Ceramic Mate-

rial of Lithium Aluminosilicate Composition, RF Patent

No. 2170715 [in Russian] (1999).2. R. Ya. Khodakovskaya, “State of the art and prospects in the sci-

ence of glass ceramics,” in: Catalyzed Crystallization of Glasses:

Coll. of Res. Papers [in Russian], Izd. MPSM SSSR, Moscow(1986), pp. 3 – 15.

3. V. I. Solov’ev, E. S. Akhlestin, É. P. Sysoev, and A. A. Tryapkin,“Prospects for the development of powder technology of glassceramics,” Steklo Keram., No. 3, 12 – 15 (1992).

4. L. K. Bondareva, N. M. Pavlushkin, G. A. Stupina, R. Ya. Khoda-kovskaya, and G. A. Éllern, “Crystallization and sintering ofglass powders in the Li2O – Al2O3 – SiO2,” Izv. Akad. Nauk

SSSR, Neorg. Mater., 22(9), 1487 – 1492 (1986).5. E. I. Suzdal’tsev, “A new direction in the synthesis of heat-resis-

tant, radio-transparent glassy crystalline materials,” Inzh. Fiz.Zh., 74(6), 121 – 130 (2001).

6. E. I. Suzdal’tsev, “Properties of a quartz ceramic,” Neorg. Mater.,20(2), 330 – 335 (1984).

178 E. I. Suzdal’tsev

TiO concentration, %2

�

12

11

10

9

8

70 5 10 15 20

Fig. 2. Dielectric constant of a glass ceramic plotted as a function ofTiO2 concentration: �) calculated values of �; �) experimental va-lues of �.