On the Interaction of Components of a High-Boron Glass Batch during Granulation
Abstract Generated abstract
This paper examines chemical interactions among components of a high-boron glass batch during moist granulation and low-temperature drying, with attention to reducing boric acid and alkali volatilization during early glass melting. The authors compare granulated S49-1 glass batch with evaporated aqueous mixtures of individual batch components, using mass changes, carbonate analysis, calcination residues, and differential thermal analysis. The experiments indicate that, during moistening and drying near 65°C, boric acid and alkali salts partly dissolve and react to form less volatile borate-type compounds that coat quartz grains and promote earlier solid-state reactions. The study concludes that granulation can reduce the initial volatilization associated with hydrogen-containing boron compounds in high-boron glass batches.
Full Text
ON THE INTERACTION OF COMPONENTS OF A HIGH-BORON GLASS BATCH DURING GRANULATION
V. M. VITOGIN, A. V. PETROV, L. N. SERDYUK,
G. D. SPITSIN, N. I. LOZBINA
(Presented to the scientific seminar of the Department of General Chemical Technology)
It is known that, in the process of melting high-boron glasses, considerable volatilization of boric acid and alkali metals occurs, as a result of which the specified properties of the glass change sharply and, under production conditions, an enormous amount of rejects is formed. Moreover, the greatest volatilization is observed when the batch is charged into the furnace and at the first stage of preparation of the glass melt, as a result of the entrainment of light components by the outgoing gases and the dehydration of boric acid at relatively low temperatures.
Studies carried out by us with a granulated boron-containing batch for glass S49-1 show that when the batch is moistened (during granulation) to 10%, part of the boric acid and alkali-metal salts passes into solution and enters into interaction with the formation of compounds which, in dried granules (drying temperature 65°C), become less volatile upon heating in comparison with boric acid and alkalis in a loose batch. In addition, the compounds formed cover the grains of quartz sand with a thin film, promoting closer contact of the reacting batch components, owing to which the reactions begin to proceed in the solid state at lower temperatures than in a loose batch [1].
The interaction between the batch components during granulation and drying, and the formation of new compounds of the sodium borate type, is confirmed by the results of specially designed experiments.
Individual batch components were dissolved in water, mixed in various combinations and ratios, and the solutions thus obtained were evaporated at a temperature not higher than 65°C to constant weight. The choice of temperature is explained by the fact that above 70° $Na_2B_4O_7 \cdot 5H_2O$ precipitates from solution, while boric acid begins to decompose at this temperature [2].
Quantitative changes and analytical data for $CO_3''$ (for mixtures with soda) made it possible to establish the interaction between the batch components at low temperatures.
Part of the compounds formed in this process volatilizes, for example, the decomposition products of $H_2CO_3$, formed during the interaction of $H_3BO_3$ and $Na_2CO_3$.
The quantitative changes depend on the ratio in which the initial components are taken: a) if in a stoichiometric ratio, then after evaporation and subsequent calcination to 500°C (judging from stoichiometric calculations) sodium borate remains—$Na_2BO_3$; b) if in such
Table 1
| No. | Initial components | Amount, g (each) | Amount, g (total) | Amount after drying, g | Relative decrease, % | CO₂ content, % (before drying) | CO₂ content, % (after drying) | Residue after calcination | Relative decrease after calcination, % |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Boric acid Soda |
20.6 53 |
73.6 | 66.7 | 9.37 | 40.8 | 29.4 | 47.8 | 28.3 |
| 2 | Boric acid Niter |
15.5 63.8 |
79.3 | 73.85 | 6.88 | — | — | 60.04 | 18.7 |
| 3 | Boric acid | 50 | 50 | 50 | — | — | — | 34.85 | 30.3 |
| 4 | Batch | 50 | 50 | 44 | 12 | — | — | 40.88 | 7.08 |
| 5 | Boric acid Soda |
37 10.9 |
47.9 | 37 | 22.8 | 12.86 | 7.47 | 31.9 | 13.75 |
| 6 | Boric acid Niter |
37 9.7 |
46.7 | 37.5 | 19.7 | — | — | 34.16 | 8.9 |
| 7 | Boric acid Sodium chloride |
37 1 |
38 | 36 | 5.27 | — | — | 22.28 | 38.2 |
| 8 | Boric acid Alumina |
37 0.85 |
37.85 | 34.5 | 8.85 | — | — | 25.50 | 26.05 |
Fig. 1. DTA curves: 1 — boric acid, 2 — soda, 3 — boric acid and soda, 4 — granules, 5 — batch.
as in the batch (that is, with a considerable excess of boric acid), after evaporation there also remains boric acid, which then decomposes during calcination; moreover, up to 500°C its decomposition is not completed.
All components of the batch, with the exception of $\mathrm{SiO_2}$, proved to be active under the experimental conditions.
The amount of boric acid, when its solution was evaporated without the addition of other components, did not change, which confirms its thermal stability up to 65°C.
The identity of the processes occurring during granulation and drying of the granules, on the one hand, and during evaporation of solutions, on the other, is confirmed by comparison of the differential-thermal-analysis curves for the batch and granules, first, and for individual components and mixtures obtained by evaporating merged solutions of these components, second. Some of these curves are shown in Fig. 1. The greater thermal stability of sodium borate, as compared with boric acid, is confirmed by material calculations and by derivatograms for boric acid, for a mixture of boric acid with soda, and for the batch, according to which the weight loss at 250°C was: for boric acid, 34.1%; for the mixture, 7.65%; for the batch, 19.8%.
Thus, owing to granulation, the principal cause of volatilization in the first stage of glass melting—due to the presence of a hydrogen-containing boron compound—is eliminated.
REFERENCES
- I. I. Kitaigorodskii, Technology of Glass. Moscow, Gosstroiizdat, 1961.
- B. V. Nekrasov, General Chemistry. Moscow, Goskhimizdat, 1963.