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.
268
TABLE 2 Oxide content, wt. %: Glazes
SiO~
BSK-1 BSK-2 BSK-3 BSK-4 BSK-5 BSK-6
TiO~
AI~O~ Fe~O~ Cr~Oa
49,35 1,22 18,65 ~48 56 1,19 18,50 !53:83 1,02 17,49 158,21 1,00 16,33 ,45 82 1,14 17,65 48,89 1,15 20,23
The author e s t a b l i s h e d that c h r o m i u m a c c e l e r a t e s the kinetics of c r y s t a l l i z a t i o n . tallized coatings of f i n e - g r a i n e d s t r u c t u r e . c r y s t a l l i z a t i o n of g l a z e s is hindered, and i s
,45 ,48 i~6 ,21 ,08 ,40 ,42 1,07
FeO
GaO
MgO
ReO
11,6i 11,29 10,30 9,05 10,41 10,41
7,24 7,07 6,54 5,80 9,37 6,57
6,65 6,93 5,95 5,21 8,71 6,45
3,85 3.96 3,67 3,33 3,84 3,71
oxide plays a big role in f o r m i n g the s t r u c t u r e of glaze, and ~ne addition of 2% c h r o m i t e to the glaze yields v o l u m e - c r y s Without the c h r o m i t e addition, other conditions being equal, r e t a r d e d with a r i s e in the SiO 2 concentration in the glaze.
Thus, glaze BSK-1 with 49.35% SiO 2 begins to c r y s t a l l i z e at 1250~ and glaze BSK-3 and BSK-4 with 53.83 and 58.21% SiO 2 c r y s t a l l i z e at 1200 and 1150~ r e s p e c t i v e l y . In this c a s e , glaze BSK-4 c r y s t a l l i z e s at 1200-1150~ only with an i s o t h e r m a l soak of at l e a s t 30 rain. It has the m i n i m u m c r y s t a l l i z a t i o n c a p a city. I s o t h e r m a l soaking positively affects the c r y s t a l l i z a t i o n kinetics of the glaze, leads to an i n c r e a s e in c r y s t a l size, and c a u s e s the f o r m a t i o n of new s t r u c t u r a l c o m p l e x e s . Crystallization in the glazes studied is c o m p l e t e d during cooling to 800~ The b a s a l t glaze m e l t s can be h a r d e n e d in the glassy state with a cooling r a t e of m o r e than 80~ p e r min. TABLE 3 Crystal sizes, g, in glazes Crystalliza- I 8oaking~ tion temp.~ rain BSK-1
BSK-2 BSK-3 BSK-4 BSK-5 BSK-6
--
t2501200
150 30
1,3--4,31,2--7 I 0,9--4,30,9--5 1,3--7,1 1,2--8,51
15 30
1,5--7 0,9--5 1,5--8 0,9--7 1,5--10 0,9--8
15 U 30
1,5--12 0,9--10 -1,5--14 0,9--10 0,6--12 1,2--15 0,9--13 1,2--12 0,6~30
150
1,5--15 1,5--9 0,9--12 0,6--5 0,3--6 0,9--7 0,3--15 0,9--12 0,9--13 0,6--20 0,3--7,6 0,6--7,6 0,6--15 0,9--t2 0,9--13 0,6--32 0,6--35 0,9--12
--
1300
1150
1100
30 150
I000
95O
9oo
800
7OO
0,3--31 0,3--3
--
--
]
0.3--4
0,3--5
1350
0,3--4
0,3--5
1,5--7 0,9--7 1,2--8 11,2--4 1,5--7,60,3--9,2 1,2--7 1,5--9 0,9----8 1,5--9 1,5--9,2 1,5--11 0,2-----7 1,8--14 1,2--11 0,6--10 0,6--24 0,6--30
1,2--9 1,5--15 1,5--23
30
0,6--16 0,9--9 0,9--9,! 0,9--6 0,6--8 0,6--6 0,6--16 0,6--12 0,9--13 0.6--20 1,6--8 0.6--7 0,9--16 0,6--13 0,6--13 0,6--30 0.9--15 0,9--12
150 30
0,3--15 0,6--8 0,6--12 0.3--5 11,5--5 0,9--15 1,5--12 0,9--14 0,9--20 ,5--6 0,9--25 1,5--18 1,5--15 1,2--30 1,5--7
0,9--5 0,9--5 0,6--8
1~
1,5_15
09_5
i1,5_9
5_12
09_18
11,5-5
30
1,5--15 ,5--12 1,5--15 0,9--25 ,5--14 0,9--5 1,5--30 1,5--30 1.5--15 0,9--25 1,5--14 1,5--8
5 l0 30
0,9--10 0,9--10 0,9--15 1--5 0,9--14 1,5--15 0,9--15 1--11 0,3--16 1,8--15 0,9--15 1--15
3O
0,3--10 0,9--14 0,9--15 0,9--15 1,5--10 0,9--15 0,9--14 1,5--15 0,9--15 0,9--13 1,3--12 0,9--15 1--15 1,5--i4 1,3--25 0,9--16 1,8--15 0,9--15
0,9--7 0,6--5 0,9--12 0,9--15 1,5--13 1,5--24
269
TABLE 4
~~7~ ~~%''z ~ '~r ~ll~-~ =" ~O'MIiP~-~-F~ca~r~~,~' ~ of~-,~~-,-~~z glazes'~ 1350 -1300 --
428 390 555 390 555 438 428 390 555 390 555 438
I~~ ~281489555 125030 ~ 555489555555555
555 555 555 555
1~ 474 5551555 5551 555 555 555] 628 555 555] 724 555
12oo 30
~ ~ ~
150 555[6281628 55516281628
'~~ 0281~ l 6~810~8 724 ~24
628 730 628 724 724 724 l l00 30 628 724 628 628 724 724
1~ 724[724] 628 628[ 724 724
15 724 724 628 628 7241774 8361 836
900 30
~ ;;~ ~ ~
83~1836
~ ;7~i 8361 ;241 724 8~01 8~6 724 724 836 836 700
Microscopic studies showed that the s t r u c t u r e of glazes with an addition of c h r o m i t e (BSK-2, 5, and 6) contain 75-90% c r y s t a l line and 10-25% vitreous phases. In the glazes without the c h r o m i u m oxide additions (BSK-1, 3, and 4) the crystalline phases amount to 40-60%. The crystalline phases in the glazes BSK-1, 3, and 4 f o r m such m i n e r a l s as magnetite, anorthite, and orthoclase, and in glazes with the c h r o m i t e addition (BSK-2, 5, and 6) also chrompicotite. The kinetics of c r y s t a l growth as a function of c r y s t a l l i z a t i o n t e m p e r a t u r e and i s o t h e r m a l soaking, are shown in Table 3, and the r e lationship between the m i c r o h a r d n e s s of basalt glazes and the degree of crystallinity in Table 4. During cooling of the molten glazes, with a reduction in the c r y s t a l l i z a t i o n t e m p e r a t u r e and an i n c r e a s e in i s o t h e r m a l soaking the size of the c r y s t a l s increase, and attain their m a x i m u m size d u r ing the final stages of crystallization. With an i n c r e a s e in the degree of crystallinity of the coating their m i c r o h a r d n e s s i n c r e a s e s . In the c r y s t a l l i z a t i o n t e m p e r a t u r e range of 1350-1200~ the glazes studied acquire a m i c r o h a r d n e s s typical of ordinary silicate g l a s s e s , and during the m o s t final p r o c e s s of c r y s t a l l i z a t i o n the m i c r o h a r d n e s s of the coating r e a c h e s a level inherent in g l a s s - c r y s t a l l i n e material. The study c o n f i r m e d that h i g h l y - c r y s t a l l i z a b l e coatings p o s s e s s b e t t e r chemical p r o p e r t i e s than l e s s c r y s t a l l i z a b l e glazes [5]. Thus glazes BSK-2 and 6 have a r e s i s t a n c e in concentrated sulfuric acid of 99-100%, and in HC1 98.5-99.6%. The alkali r e s i s t a n c e in 35% NaOH solution is 97 and 97.6% respectively. The least c r y s t a l l i z a b l e glaze (BSK-4) has a chemical r e s i s t a n c e as follows: in concentrated sulfuric acid 98%, in HC1 96.5%, and in 35% alkali solution 80%.
5 774 836 724 724 836 836
Thus, the glazes studied consist of g l a s s - c r y s t a l l i n e coatings, the c r y s t a l l i z a t i o n of which is due to the chemicomineralogical c o m position of the basic component - basalt. The molten basaltic glazes can harden in the glassy state with a cooling rate of more than 80 deg/min. An addition of chromite to the glaze increases the crystallization rate and yields a fine-grained structure with crystal sizes of 0.9-16/~. The structure containing 75-90% crystalline and 10-25% glassy phases ensures the optimum chemical properties in the glaze coatings. The mierohardness of the glazes increases with an increase in the degree of cry stallization. LITERATURE lo 2. 3. 4.
5.
270
CITED
Yu. Ya. ~,iduk, Steklo i Keram., No. 3 (1962). M. V. Okhotin et al., Steklo i Keram., No. 6 (1954). L. M. Blyumen, Glazes [in Russian], Moscow, P r o m s t r o i i z d a t (1954). N. A. Toropov et al., in: P r o b l e m s of Stone Castings, No. 2 [in Russian], Izd. Akad. Nauk, Ukrainian SSR (1968). I. K. Galushko et al., Steklo i K e r a m . , No. 9 (1971).