CRYSTALLIZATION I.
K.
KINETICS
IN G L A Z E
COATINGS UDC 666.3.053:666.295.5
Galushko
Two methods are usually employed for determining the crystallization p r o p e r t i e s of glasses, glazes, and enamels: gradient heating of the specimen [1], and chilling [2]. Using these techniques c r y s t a l l i z a t i o n is mainly studied on n o n c r y s t a l l i z e d specimens (rods or powdered glass, glazes, or enamels) and using heating c y c l e s that cause crystallization. P r a c t i c e has shown that basalt glazes are easily c r y s t a l l i z e d during the final (glost) firing of the goods. Their crystallization is due to the chemicomineralogical composition of the basic component - b a salt. The kinetics of crystallization were studied by the chilling method on chemically r e s i s t a n t basalt glazes whose composition is shown in Tables 1 and 2. The author designed an electric furnace for the experiments (see Fig. 1) with which, using a special attachment, it is possible to remove all specimens simultaneously at any time. The tests were done with fully molten glaze on porcelain tiles m e a s u r i n g 2 x 2 cm at 1350~ using a subsequent reduction in t e m p e r a t u r e every 50~ At the same time in each t e m p e r a t u r e range f r o m 1250 to 700~ we applied an i s o thermal soaking for 5, 10, and 30 min. The resulting glaze melts were cooled suddenly in water down to 18-20~ This yielded "frozen" melt with the appropriate structure. The cooling rate of all specimens was the same, and the firing a t m o s p h e r e was slightly oxidizing. The structure of the glaze coatings was studied with the MIM-7 m i c r o s c o p e and the URS-50I attachment; the m i c r o h a r d n e s s was determined on the P M T - 3 instrument. Microscopic analysis showed that the "frozen" g l a z e - m e l t s BSK-1 at 1350 and 1300~ BSK-3 at 1350 TABLE 1 and-1250~ BSK-4 at 1350-1150~ all consist of dark n o n t r a n s p a r e n t Content in %in glaze Material
~
r
r
,~
F~T~--
Basa i 98718 ~o
r~
r.,9
r~
r.o
4.9
ChPKhooy
Chromite ore Quartz sand Dolomite
2
2
---
--
Kablin
6
~220V~
g l a s s e s of the marblite type. Glazes BSK-2, BSK-5, and BSK-6, also in the 1350-1300~ region, contain fine c r y s t a l s of c h r o m i u m oxide m e a s u r i n g 0.3-0.5 it, since this is not readily dissolved in s i l i cate melts. Various opinions exist about the effect of c h r o m i u m oxides on the crystallization p r o c e s s . L. M. Blyumen notes that in their p r e s ence the glazes show no signs of crystallization [3]. According to N. A. Toropov's data c h r o m i u m oxide in optimum amounts leads to volume c r y s t a l l i z a t i o n of g l a s s e s [4].
i/
Roven Building Materials Combine. April, 1974.
Fig. 1. Electric furnace for studying the c r y s t a l l i z a t i o n of glazes. 1) Cover; 2) frame; 3) thermocouple; 4) glaze specimen; 5) silicon carbide heaters; 6) millivoltmeter M-64; 7) voltage r e g ulator; 8) c e r a m i c i n s e r t 60 • 70 ram; 9) wooden support; 10) water bath.
Translated f r o m Steklo i Keramika, Vol. 31, No. 4, pp. 23-25,
9 1974 Consultants Bureau, a division o f Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher. A copy of this article is available from the publisher for $15.00.
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