Crystal growth of metastable quartz solid solutions in MgO - Al2O3 - SiO2 glasses

Journal

of Crystal

Growth 2 (1968) 41 l-412

CRYSTAL

0 North-Holland

Publishing

LETTERS

TO THE

EDITORS

GROWTH OF METASTABLE QUARTZ SOLID SOLUTIONS MgO - AI,O, - SiOz GLASSES HANS-JOERG

Itwtitute

Co., Amsterdam

of Crystallography

and Petrography

SCHEEL*

of the Federal

Received

IN

25 July

Institute

of Technology,

Zurich,

Switzerland

1968

Crystals of metastable high-quartz solid solutions have been grown from MgO-A1203-Si02 glasses by initiating crystal interior of the glass. Transformation to the stable cordierite-phase is prevented by the high viscosity of the glassy

The metastable high-quartz phase is the first crystallization product from MgO-AI,O,-x SiO, glasses at low temperatures’). It is not possible to obtain crystals of this phase by normal crystal growing techniques.

Fig.

1.

Preferred

orientation

* Now with IBM Zurich

Research

of

the

metastable quartz-type into the glassy medium

Laboratory,

8803 Rtischlikon,

growth in the medium.

For instance Schreyer and Yoder’) did not find quartz solid solutions in the system 2MgO-2Al,O,-5SiO,H,O between 350 and 1300 “C and pressures up to 10000 atm, only pure low-quartz, cordierite, mont-

crystals (partially

which nucleated crossed nicols).

Switzerland.

411

at the wall

of the bore-hole

and

grew

412

HANS-JOERG

morillonite, etc. In the anhydrous system they observed crystallization of quartz solid solutions at low temperatures after short crystallization times. Crystallization of bulk glass samples,

with and with-

out flux, starts from the surface and results in the formation of small crystallites. If the crystallization could

SCHEEL

quartz-type phase was identified by X-ray Guinier photographs. In the microscope (crossed nicols) one sees the orientation of the c-axes parallel to the growth direction; this effect has been described and explained by Laves3) and by Kamb4). It should be possible to increase the crystal size by slowly traversing a suitable temperature gradient (a

start at some point in the interior of the glass the crystallites would have a better possibility of increasing

zone

their size in all directions. Therefore bore-holes of about l-2 mm diameter were drilled into bulk glass

molten zone in zone melting) gradient should prevent the

samples and filled with a flux of composition Li,O . 4 WO,. The samples were packed in platinum foil and annealed in a furnace of uniform temperature for three months. During this time the temperature was raised stepwise from 600 to 800 “C. The glass sample of composition MgO * Al,O, . 3Si0, (l/l/3) showed single crystals of the quartz solid solution of 0.2-0.3 mm diameter and 1.5-2 mm length (see fig. 1). The compositions l/l/2 and l/l/4 gave smaller crystals, and l/l/6 did not crystallize under these conditions. The

crystallized metastable quartz-type phase. The author thanks Prof. Dr. F. Laves for his interest in this work, and Owens-Illinois Inc., Toledo, for financial support.

of ideal

diffusion

constants

analogous

to the

through the glass; the transformation of the

References 1) W. Schreyer and J. F. Schairer, Z. Krist. 116 (1961) 60. 2) W. Schreyer and H. S. Yoder, Neues Jahrb. Mineral. Abh. 101 (1964) 271. 3) F. Laves, Naturwissenschaften 27 (1939) 705. 4) W. B. Kamb, J. Geology 67 (1959) 153.