Study of the Thermal Stability of Soda and Sodium Sulfate Crystal Hydrates
Abstract Generated abstract
This study examines the thermal decomposition of soda and sodium sulfate decahydrate crystal hydrates, materials that influence the aggregate behavior of moistened glass batches. Prepared soda decahydrate and standard sodium sulfate decahydrate samples were held at 22, 45, and 60°C, periodically weighed to constant mass, and evaluated by percentage loss of crystallization water. The results show that increasing temperature accelerates decomposition, with sodium sulfate decomposing rapidly at both 45 and 60°C, while soda decomposes more uniformly at 45°C and reaches completion at 45 to 60°C after about 7 to 8 hours. The findings support practical control of granulated glass batch moisture and suggest raising batch temperature to about 45 to 50°C rather than using higher, economically unjustified temperatures.
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INVESTIGATION OF THE THERMAL STABILITY OF SODA AND SODIUM SULFATE CRYSTAL HYDRATES
L. G. Lyutova, V. M. Vityugin, V. A. Trofimov
(Presented by the scientific seminar of the Department of GCT)
Ordinary glass batches consist, for the most part, of materials that do not possess plastic properties: sand, dolomite, limestone, chalk, and others. In addition, approximately one fifth of the batch consists of alkali-containing materials that are chemically active with respect to water: soda and sodium sulfate. They are chiefly responsible for the specific aggregate properties of glass batches. It is known that calcined soda, when interacting with water, forms decahydrate crystal hydrates from supersaturated solutions; at temperatures above 32–35°C these rapidly release crystallization water, turning into a plastic, flowing mass.
Sodium sulfate behaves in a similar manner when interacting with water (1).
The technology for preparing the raw glass batch at modern plants provides for moistening it to 5–7 and even 10% in order to reduce segregation and dusting. Granulation of glass batches under ordinary conditions is carried out at still higher moisture contents (20–25%) (2). Knowledge of the processes of decomposition of soda and sodium sulfate crystal hydrates at various temperatures will make it possible to control the aggregate properties of glass batches more effectively.
Decahydrate crystal hydrates of soda and sodium sulfate were taken as the objects of investigation. The soda decahydrate crystal hydrates were obtained by us as follows. One part of soda was dissolved in five parts of hot water, filtered, and the solution was cooled to room temperature. The precipitated crystals were quickly suction-filtered, washed with ether, and placed in a closed vessel with a ground-glass stopper (3). Standard sodium sulfate decahydrate crystal hydrates of chemically pure grade were used.
| Substance | Weight of sample of dehydrated crystalline hydrate, g | Process temperature, °C | 1 h | 2 h | 3 h | 4 h | 5 h | 6 h | 7 h | 8 h | 9 h | 10 h | 12 h | 14 h | 15 h | 16 h | 18 h | 20 h | 22 h |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Soda | 1.4808 | 22 | 12.3 | 29.4 | 46.7 | 62.6 | 77.8 | 79.6 | |||||||||||
| Soda | 2.1792 | 22 | 15.5 | 28.8 | 43.4 | 59.6 | 74.2 | 78.3 | |||||||||||
| Soda | 0.7480 | 22 | 15.6 | 26.9 | 41.2 | 61.6 | 67.7 | 74.8 | |||||||||||
| Soda | 0.8987 | 45 | 12.57 | 52 | 67 | 91.2 | |||||||||||||
| Soda | 0.9637 | 45 | 14.2 | 42.5 | 61.3 | 91.9 | |||||||||||||
| Soda | 0.8103 | 45 | 14.5 | 44 | 64 | 90.3 | |||||||||||||
| Soda | 0.5608 | 60 | 42.7 | 65 | 74.1 | 80 | 81.2 | 84 | 99 | ||||||||||
| Soda | 0.4184 | 60 | 45.5 | 62.3 | 72.3 | 78.9 | 80.8 | 83.8 | 98.4 | ||||||||||
| Soda | 0.4438 | 60 | 43.8 | 64.1 | 68.1 | 76.3 | 77.8 | 83 | 97.8 | ||||||||||
| Sodium sulfate | 1.7931 | 22 | 25.9 | 36 | 51 | 61.2 | 72.3 | 80.3 | 84.7 | 89.5 | 95.1 | 98 | 100 | ||||||
| Sodium sulfate | 2.0867 | 22 | 21.3 | 33.2 | 49.6 | 62.2 | 73.7 | 83.3 | 87.5 | 91.6 | 95.7 | 99 | 100 | ||||||
| Sodium sulfate | 0.4167 | 22 | 26.6 | 40.1 | 53.4 | 65.5 | 78.2 | 90 | 94 | 97.5 | 100 | ||||||||
| Sodium sulfate | 0.8382 | 45 | 53.6 | 90.1 | 93.8 | 100.1 | |||||||||||||
| Sodium sulfate | 0.5886 | 45 | 58.2 | 93.3 | 96.2 | 100.3 | |||||||||||||
| Sodium sulfate | 0.4997 | 45 | 60.1 | 91.8 | 94.8 | 98.4 | |||||||||||||
| Sodium sulfate | 0.4814 | 60 | 79.4 | 88.7 | 95.9 | 99.9 | |||||||||||||
| Sodium sulfate | 0.2951 | 60 | 97.8 | 99 | 97 | ||||||||||||||
| Sodium sulfate | 0.1819 | 60 | 100 |
To investigate the decomposition kinetics, weighed portions of the crystal hydrates, placed in weighing bottles, were held at the given temperature for a prolonged time until a constant weight was reached. At specified time intervals, dictated by the rate of the process (1 hour, 2 hours, 3 hours), the weighed portions were weighed. From the difference in weights before and after drying, the amount of moisture removed was determined, and from this the percentage decomposition of the crystal hydrates was calculated. The data obtained as a result of the experiment are summarized in Table 1.
As can be seen from the table, decomposition of the crystal hydrates of soda and sodium sulfate proceeds over time. At the same time, an increase in temperature promotes more rapid and more complete (for soda) decomposition of the crystal hydrates. In practice, decomposition of the sulfate crystal hydrates at temperatures of 45 and 60°C proceeds equally rapidly. For soda crystal hydrates, decomposition proceeds more uniformly at 45°C; at 60°C it proceeds at a higher rate during the first three hours, but decomposition at both 45 and 60° ends at approximately the same time, after 7–8 hours.
Under production conditions, the time for which the batch exists from the moment it is prepared until it is charged into the furnace is determined mainly by the correspondence between the productivity of the batching department and the capacity of the reserve bunkers, and ranges within 8–10 hours. The temperature of the batch gradually decreases from 50° to 20° (in summer) and almost to 0° in winter, that is, to a temperature below the decomposition temperature of the crystal hydrates.
The results of the investigation are mainly of practical significance in preparing the batch by the granulation method. The moisture of the granulation process, that is, the active free moisture, will be determined by the temperature of the batch. The higher the batch temperature, the lower the moisture content of pelletizing. However, an excessive increase in temperature is economically unjustified. The temperature should be raised to 45–50°C.
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L. G. Mel’nichenko. Forming properties of glass batches.—Steklo i keramika, 1954, 11.
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M. F. Gur’yanova. Granulation of glass batch.—Steklo i keramika, 1959, 5.
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Yu. V. Karyakin. Pure Chemical Reagents. State Chemical Publishing House, 1947.