CONTROL OF THE GAS CONTENT AND TEMPERATURE OF FOAMING OF GLASS IN THE PRODUCTION OF GLASS FIBEI K.V. Nagulevich, Yu. I. Kolesov UDC666.19921 and m.s. aslanova It is known that the gases dissolved in glass behave in different ways on reheating [1, 2]. It is as sumed that the presence in the glass of water, sulfur dioxide, and carbon dioxide may facilitate foaming of the glass while oxygen and nitrogen are retained in the glass on heating up to higher temperature [1, 3] According to the latest ideas, H2O, SO2, and O2 are found in glass as complex gas ions of dissolved salts or as ions directly bonded to the silicon-oxygen framework of the glass [4],i. e, their solubility in glass is due to the chemical interaction with the glass and obeys the law of mass action. It has been established that their physical solubility in glass is insignificant. On the other hand the solubility of nitrogen and the inert gases obeys the solution laws and depends mainly on the fining temperature of the glass batch and on the partial pressure. The dissolution of carbon dioxide depends to a great extent on chemical interaction with the components of the glass and on the physical conditions of the solution gas,The essence of the foaming phenomena [5] in the reheating of glass consists of the fact that the complex ions, OH",so?, and CO3 are bonded in the glass and with a change in the external conditions(second Fig 1. The dependence of the gas content of glass on the amount of sodium sulfate batch:1)total gas content; 2)foaming temperature; 3)carbon dioxide; 4) water; 5) Fig. 2. The dependence of the gas content of glass on the amount of sodium sulfate and 0.3% ar senic trioxide added to the batch (legend as in Fig. 1) All-Union Scientific-Research Institute of Glass Plastics and Glass Fiber, Translated from Stekle i Keramika, No 11, pp 23-27, November, 1970 0 1971 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New york, N. Y. 10011. Al rights reserved. This article cannot be reproduced for any purpose whatsoever without permission of the publis her. A copy of this article is available from the publisher for $ 15.00
CONTROL OF THE GAS CONTENT AND TEMPERATURE OF FOAMING OF GLASS IN THE PRODUCTION OF GLASS K.V. Nagulevich, Yu. I. Kolesov, and M.S. Aslanova FIBER UDC 666.199.211 It is known that the gases dissolved in glass behave in different ways on reheating [1, 2]. It is assumed that the presence in the glass of water, sulfur dioxide, and carbon dioxide may facilitate foaming of the glass while oxygen and nitrogen are retained in the glass on heating up to higher temperature [1, 3]. According to the latest ideas, H20 , SO2, and 02 are found in glass as complex gas ions of dissolved salts or as ions directly bonded to the silicon-oxygen framework of the glass [4], i.e., their solubility in glass is due to the chemical interaction with the glass and obeys the law of mass action. It has been established that their physical solubility in glass is insignificant. On the other hand the solubility of nitrogen and the inert gases obeys the solution laws and depends mainly on the fining temperature of the glass batch and on the partial pressure. The dissolution of carbon dioxide depends to a great extent on chemical interaction with the components of the glass and on the physical conditions of the solution. The essence of the foaming phenomena [5] in the reheating of glass consists of the fact that the complex gas ions, OH-, SO 2", and CO 2- are bonded in the glass and with a change in the external conditions (second t, foam, Vgas/Vbatch' ~ t, foam, Vgas/Vbatch, nzo ,~oo~ I deg,,zo _ ,ooo t 3OO ~300 b ~ t300 r {280- ~300 f260 t200 | l t260 - 1200 ( t200 r [ r - /#00 r goO I 1r H60 HSO ~ 900 tt#O 800 [ H48 - 800 HE0 7001 tr /tOO HOO ~ 7O0 r 60el tOaO - ~00 fO60 fO$O - 1040 f#'~O- 500 t020 ~Ot- 1020 - 400 1000 - /ON 300 980 9O0- 300 g20 r 920 - IO'a ''- v Q 0.o gz ~ o,e 0,a bo Na20, % o,o o,2 0,r o,e o,o ~,o NazO, % Fig. 1 Fig. 2 Fig. 1. The dependence of the gas content of glass on the amount of sodium sulfate added to the batch: 1) total gas content; 2) foaming temperature; 3) carbon dioxide; 4) water; 5) sulfur dioxide; 6) oxygen. Fig. 2. The dependence of the gas content of glass on the amount of sodium sulfate and 0.3% arsenic trioxide added to the batch (legend as in Fig. 1). All-Union Scientific-Research Institute of Glass Plastics and Glass Fiber. Translated from Steklo i Keramika, No. 11, pp.23-27, November, 1970. O 1971 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $15.00. 666
TABLE 1 heating, changes in the partial gas pressure over the melt) Fartial pressure of gases over the glass, may be de composed with the separation of these gases and Gas oxygen in their molecular forms. Since the physical solubi ank furnace glass-melting vessel lity of these gases in the batch is insignificant they form a free gas phase in the glass, as bubbles or even as continu CO, 3 From the law of chemical equilibrium it can be as sumed that an increase of oxygen in the batch will impede the decomposition of the complex ions leaving them in a chem- ically bonded state and will prevent the foaming of the glass. The purpose of this work therefore was to study the effect of various oxygen-containing additives on the character and total amount of gas in the glass and on its foaming temperature. In parallel with these additions arsenic trioxide, an oxide of a variabl valency metal, was added to the batch thus facilitating the solution of oxygen in the glass Specimens of glass to which various amounts of sodium sulfate, calcium nitrate, and arsenic tr oxide had been added, were melted in platinum crucibles in an electric resistance-heated muffle furnace temperature were determined using the method recommended by the All-Union Scientific-Research Insti tute of Glass Plastics and Glass Fibers [6] The change in the foaming temperature of the glass and the character and magnitude of its gas con tent are shown in Figs. 1 to 3 as a function of the type and quantity of the additives. The introduction of each additive, As2O3, Na2 SO4, Ca(NO3)2. 4H2O; Na2 SO4+ As2O3, Ca(NO3)2 4H2O+ As2O3, at first decreased the gas content in the glass, reduced the amount of CO2 and H,O, and increased the oxygen and sulfur dioxide content with a simultaneous increase of the foaming temperature of the glass. At this stage, when the quantity of the additives, expressed in terms of Cao and NaO, is less than 0.4% Cao or Na,O, they act both as fining additives decreasing the gas content in the glass and also as additives which increase the O2 content and stabilize the chemical bond between the gas ions and the components of the glass when it is which separates from the glass as bubbles, decreases the partial pressure of the residual gases in the The role of the oxygen as a fining agent in this case confirms the generall bubbles and enables other gases to flow from the glass into the bubbles and so to escape from the glass i. e, the gas content of the glass is decreased. With such a relatively low oxygen content introduced with the additives its role in the formation of a large quantity of complex gas ions chemically bonded to the glass when the glass is made, is clearly insignificant, but it is completely adequate for their stabilization in the glass on reheating. In these cases, therefore, the oxygen-containing additives decrease the amount of all the gaseous components in the glass(apart from oxygen) and increase the temperature at which the complex ions decompose, i. e, the foaming temperature be seen from Figs. I to 3)leads to an increase in the formation of complex ions of triatomic gases whlch p When the concentration of oxygen-containing additives is further increased, the excess oxygen(as significantly increases the total content of all the gaseous components in the glass. Nevertheless, the values of the foaming temperature remain at the former high value and only decrease slightly when there is a sufficiently large amount of oxygen-containing additives( Cao and Na,O content greater than 0.6 to 0.8% and still remain above the foaming temperature of the glass made without additives The dependences shown in Figs. l to 3 also indicate that under similar conditions the efficiency of the effect on the gas content and foaming temperature of the glass is not the same for different oxygen- containing additives. Thus, the greatest decrease in the total gas content in the glass and the highest value of the foaming temperature is reached after reheating when Ca(NO3)2 4H2O together with As,O3 is added to the glass. The solubility of oxygen in the glass is also greatest in this case As an approximate description of the processes involved in the solution of gases in glass on melting fining, and decomposition of the chemically bonded gaseous complexes on reheating, the following equili brium equation
TABLE 1 Eartial pressure of gases over the glass, Gas mm Hg tank furnace glass-melting vessel CO~ Ne H20 02 S02 73,6 522,0 151,0 13,4 0,2 ~2 36 152 heating, changes in the partial gas pressure over the melt) may be decomposed with the separation of these gases and oxygen in their molecular forms. Since the physical solubility of these gases in the batch is insignificant they form a free gas phase in the glass, as bubbles or even as continuous foam. From the law of chemical equilibrium it can be assumed that an increase of oxygen in the batch will impede the decomposition of the complex ions leaving them in a chemically bonded state and will prevent the foaming of the glass. The purpose of this work therefore was to study the effect of various oxygen-containing additives on the character and total amount of gas in the glass and on its foaming temperature. In parallel with these additions arsenic trioxide, an oxide of a variable valency metal, was added to the batch thus facilitating the solution of oxygen in the glass. Specimens of glass to which various amounts of sodium sulfate, calcium nitrate, and arsenic trioxide had been added, were melted in platinum crucibles in an electric resistance-heated muffle furnace. The fining time for all the glasses was kept constant and was 1 h at 1500~ The gas content and foaming temperature were determined using the method recommended by the All-Union Scientific-Research Institute of Glass Plastics and Glass Fibers [6]. The change in the foaming temperature of the glass and the character and magnitude of its gas content are shown in Figs. 1 to 3 as a function of the type and quantity of the additives. The introduction of each additive, As203, Na2SOr Ca(NO3) 2.4H20; Na2SO4+ As203, Ca(NO3) 2-4H20+ As203, at first decreasedthe gas content in the glass, reduced the amount of CO 2 and H20 , and increased the oxygen and sulfur dioxide content with a simultaneous increase of the foaming temperature of the glass. At this stage, when the quantity of the additives, expressed in terms of CaO and Na20, is less than 0.4% Ca(9 or Na20 , they act both as fining additives decreasing the gas content in the glass and also as additives which increase the 02 content and stabilize the chemical bond between the gas ions and the components of the glass when it is reheated. The role of the oxygen as a fining agent in this ease confirms the generally accepted view. Oxygen, which separates from the glass as bubbles, decreases the partial pressure of the residual gases in the bubbles and enables other gases to flow from the glass into the bubbles and so to escape from the glass, i.e., the gas content of the glass is decreased. With such a relatively low oxygen content introduced with the additives its role in the formation of a large quantity of complex gas ions chemically bonded to the glass when the glass is made, is clearly insignificant, but it is completely adequate for their stabilization in the glass on reheating. In these cases, therefore, the oxygen-containing additives decrease the amount of all the gaseous components in the glass (apart from oxygen) and increase the temperature at which the complex ions decompose, i.e., the foaming temperature. When the concentration of oxygen-containing additives is further increased, the excess oxygen (as can be seen from Figs. 1 to 3) leads to an increase in the formation of complex ions of triatomic gases which significantly increases the total content of all the gaseous components in the glass. Nevertheless, the values of the foaming temperature remain at the former high value and only decrease slightly when there is a sufficiently large amount of oxygen-containing additives (CaO and Na20 content greater than 0.6 to 0.8%) and still remain above the foaming temperature of the glass made without additives. The dependences shown in Figs. 1 to 3 also indicate that under similar conditions the efficiency of the effect on the gas content and foaming temperature of the glass is not the same for different oxygencontaining additives. Thus, the greatest decrease in the total gas content in the glass and the highest value of the foaming temperature is reached after reheating when Ca(NO3) 2.4H20 together with As203 is added to the glass. The solubility of oxygen in the glass is also greatest in this case. As an approximate description of the processes involved in the solution of gases in glass on melting, fining, and decomposition of the chemically bonded gaseous complexes on reheating, the following equilibrium equations can be used: . [so, Kso~-= Pso~- Po, '~/~ [o ~- l, ' 667
deg""batch' K [OH]2 After fining, the solubility of CO2, H2O, and so, in the glass and therefore the total content of these gases in the glass as sO4, Cos and oH- ions, will depend direct ly on the oxygen introduced into the glass and on the partial pressure of these gases. In the case in which the oxygen is introduced as sodium sulfate, with or without As,O3, the total gas content will be greater than when the oxygen is introduced as calcium nitrate. This is due to the fact that the solution of gases in the glass occurs at the same time from all three reactions and the gas content is due to the Fig 3. The dependence of the gas content of when Ca(NO3)2 4H2O is introduced into the batch, but also t solution in the gla ot only of H,o and CO, which occu Class on the amount of calcium nitrate and 0.3% arsenic trioxide added to the batch (le The role of oxygen as a factor which affects the solu- end as in Fig. 1) tion of other gases in the glass becomes quite clear if Figs and 2 are compared. The introduction of Na?, with As2O3 into the batch, as shown in Fig. 2, more than doubles the O2 content of the glass compared with the addition of Na2 SO4 alone (as in Fig. 1). As the same time there is also an increase in the total gas content of the glass This confirms that it is possible to use the equations above to describe the process of gas solution in glass on melting and fining The equilibrium equations may also be used to describe the decomposition of the gas ions which are chemically bonded to the glass, i.e., the foaming process. The foaming temperature in this case will also be a direct function of the oxygen, water, sodium dioxide, and carbon dioxide content of the glass. The complex interconnection between the foaming temperature and the O2 content in the glass explains the fact that the temperature does not increase indefinitely with an increase in the quantity of O2(Figs. 1-3).With an increase in the oxygen content of the glass the content of H2O, SO, and cO, increases abruptly, i.e., with a large amount of oxygen-containing additives in the batch the oxygen enables a large quantity of H O, Co and SO, to dissolve in the glass and they have the opposite effect on the foaming temperature(they lower it The partial pressure over the melt also clearly has an effect on its foaming temperature, The lower the partial pressure the greater is the probability of the gas ions decomposing (see Eqs. (1))and the glass foaming. The partial pressures of CO2, H,O, and SO, above the glass on reheating, for example in the glas melting vessel, are considerably lower than above the glass in the tank furnace(see Table 1). Therefore a second foaming is observed after heating the glass in the vessel. The foaming is particularly strongly affected by a decrease to zero in the partial pressure of so2 in the melting vessel and by a sudden decrease in the partial pressure of water vapor. Indeed, the foaming temperature of glasses containing SO, (Figs. 1 and 2)is significantly lower than that of glasses which do not contain SO,(Fig 3) Thus, the experimental studies show that by a trial-and-error selection of the batch composition it s possible to regulate the residual gas content of the glass and its foaming temperature. The results con firm the view held by several research workers of the chemical nature of the solubility of such gases as H2O, SO2, O2, and CO2 in glass and indicate the extremely important part played by the oxygen in the glass which affects the control of gas dissolution and gas separation from the glass. The experimental data cor firmed that the chemical equilibrium equations may be used to describe the dissolution in, and separation from the glass, of triatomic gases LITERATURE CITED 1. K. V. Nagulevich and Yu. I Kolesov, Steklo i Keramika, No 6(1969) 2. J. Budd et al.. Glass Technol., 3, No 4(1962)
t, foam, Vgas/Vbatch, degr " ~[ z /300 " r ,280- [~/r ,2ooty / "~ - 9 -'- tf40- 800 / r 7001- r162 I t080 - 6OO tObO- 500 /O#O - t000- 300 980 - . # 8 #60 - 2O0 #2O - too Fo~,~ O,o 0,2 o,z~ 0,6 0,8 CACAO, % Fig. 3. The dependence of the gas content of glass on the amount of calcium nitrate and 0.3% arsenic trioxide added to the batch (legend as in Fig. 1). K oP- eco, [o ~-] [OH]= Ko. -- PH,O [0 ~-] " (1) After fining, the solubility of CO2, H20 , and SO 2 in the glass and therefore the total content of these gases in the glass as SO~-, CO 2-, and OH- ions, will depend directly on the oxygen introduced into the glass and on the partial pressure of these gases. In the case in which the oxygen is introduced as sodium sulfate, with or without As203, the total gas content will be greater than when the oxygen is introduced as calcium nitrate. This is due to the fact that the solution of gases in the glass occurs at the same time from all three reactions and the gas content is due to the solution in the glass, not only of H20 and CO 2 which occurs when Ca(NO3) 2.4H20 is introduced into the batch, but also of SO 2 . The role of oxygen as a factor which affects the solution of other gases in the glass becomes quite clear if Figs. 1 and 2 are compared. The introduction of Na2SO 4 with As203 into the batch, as shown in Fig. 2, more than doubles the 02 content of the glass compared with the addition of Na2SO 4 alone (as in Fig. 1). As the same time there is also an increase in the total gas content of the glass. This confirms that it is possible to use the equations above to describe the process of gas solution in glass on melting and fining. The equilibrium equations may also be used to describe the decomposition of the gas ions which are chemically bonded to the glass, i.e., the foaming process. The foamingtemperature inthis case will also be a direct function of the oxygen, water, sodium dioxide, and carbon dioxide content of the glass. The complex interconnectionbetween the foaming temperature and theO 2 content in the glass explains the fact that the temperature does not increase indefinitely with an increase in the quantity of 02 (Figs. 1-3). With an increase in the oxygen content of the glass the content of H20 , SO 2 and CO 2 increases abruptly, i.e., with a large amount of oxygen-containing additives in the batch the oxygen enables a large quantity of H20, CO2, and SO 2 to dissolve in the glass and they have the opposite effect onthe foaming temperature (they lower it). The partial pressure over the melt also clearly has an effect on its foaming temperature. The lower the partial pressure the greater is the probability of the gas ions decomposing (see Eqs. (1)) andthe glass foaming. Thepartialpressures of CO2, H20, and SO 2 above the glass on reheating, for example in the glass melting vessel, are considerably lower than above the glass in the tank furnace (see Table 1). Therefore, a second foaming is observed after heating the glass in the vessel. The foaming is particularly strongly affected by a decrease to zero in the partial pressure of SO 2 in the melting vessel and by a sudden decrease in the partial pressure of water vapor. Indeed, the foaming temperature of glasses containing SO 2 (Figs. 1 and 2) is significantly lower than that of glasses which do not contain SO 2 (Fig. 3). Thus, the experimental studies show that by atrial-and-error selection of the batch composition it is possible to regulate the residual gas content of the glass and its foaming temperature. The results confirm the view held by several research workers of the chemical nature of the solubility of such gases as H20 , SO2, O2, and CO 2 in glass and indicate the extremely important part played by the oxygen in the glass which affects the control of gas dissolution and gas separation from the glass. The experimental data confirmed that the chemical equilibrium equations may be used to describe the dissolution in, and separation from the glass, of triatomic gases. 1, 2. LITERATURE CITED K. V. Nagulevich and Yu. I. Kolesov, Steklo i Keramika, No. 6 (1969). J. Budd et al., Glass Technol., 3, No.4 (1962). 668
J. P. Roberts and R. J. Roberts, Phys. Chem. Glass, No 5 (1964) 4. M. Mahicux, Verres et Refract. 10, Nos. 5, 6(1956); M. Boffe, Silikates Industrieles, No 28 (1963) S. Holmquist, J. Am. Ceram. Soc., No 9, 467(1966); M. Pearce, J. Am. Ceram. Soc., No. 7, 342 (1964) 6. K. V. Nagulevich, V. P. Polyakov, and Yu. I Kolesov, Steklo i Keramika, No 5 (1968)
3, 4. 5. 6. J. P. Roberts andR. J. Roberts, Phys. Chem. Glass, No. 5 (1964). M. Mahicux, Verres et Refract., i0, Nos. 5, 6 (1956); M. Boffe, Silikates Industrieles, No.28 (1963). S. Holmquist, J.Am. Ceram. Soc., No. 9, 467 (1966); M. Pearce, J. Am. Ceram. Soc., No. 7,342 (1964). K. V. Nagulevich, V. P. Polyakov, and Yu. I. Kolesov, Steklo i Keramika, No. 5 (1968). 669