STUDY OF THE VISCOSITY OF LOAMS DURING EXPANDED-CLAY FORMATION

A. V. PETROV

(Presented by the scientific seminar of the Department of Technology of Silicates, Inorganic Substances, and Electrochemical Industries)

During the heat treatment of loams into expanded clay, owing to the complexity of their chemical and mineralogical compositions, intensive softening occurs at the end of the temperature interval of bloating, and the specimens, deforming, melt.

The magnitude of the softening interval, within which the liquid phase increases and the material passes from the solid into the pyroplastic state, depends mainly on the chemical composition of the loams and on the quantity of flux minerals that promote the appearance of the liquid phase at lower temperatures.

The rate of the processes taking place, associated with the appearance of the liquid phase and the formation of new crystalline formations, has a substantial influence on the viscosity of the resulting pyroplastic mass.

Observations, as S. P. Onatskii [1] points out, have established that the best results in the bloating of clay masses are obtained at optimal ratios of their viscosity and of the pressure of the gaseous phase formed and finely distributed within the mass.

In this connection, the study of viscosity during the heating of loams—which determines the course of their softening and bloating process—is of considerable interest. We reported earlier [2] on the composition of the gaseous phase, its quantity, and the pressure it develops during the period of expanded-clay formation. The viscosity of various low-melting clays of the European part of the Union was studied by the method of twisting the specimen by V. F. Pavlov [3] and others.

To establish the magnitude of the viscosity of loams of Tomsk Province during their transition into the pyroplastic state, we used an apparatus for determining the deformation of clays under load [4]. Since clay rocks are multiphase systems in which complex physicochemical processes occur during heating, the apparent (structural) viscosity was measured.

The study was carried out on specimens having the form of rings with a height and outside diameter of 16 mm and a wall thickness of 2 mm. The wall thickness of the rings was taken as 2 mm in view of the smaller temperature difference within the material itself, which made it possible to investigate more accurately the temperature dependence of viscosity. Heating of the specimens at a rate of 17° per minute was carried out in a tubular electric furnace with automatic temperature control. The change in height of the deforming specimen was measured with an indicator having a scale division value of ...

…division of \(0.001\) mm. The viscosity was determined by a static method, i.e., the change in viscosity over time at a constant experimental temperature was studied; for its calculation the formula proposed by N. V. Solomin [5] was used:

\[ \eta=\frac{P\cdot z(l-\Delta l)\cdot 981}{3\cdot \Delta l\cdot q}\ \text{poise}, \]

where \(\eta\) is the viscosity at a given temperature, in poise;
\(P\) is the load, in g;
\(Z\) is the time, in sec, during which deformation occurs;
\(\Delta l\) is the deformation, in cm;
\(q\) is the cross-sectional area of the ring, in cm;
\((l-\Delta l)\) is the mean height of the specimen after testing.

Chemical composition

The curves of the apparent viscosity of loams from five deposits of Tomsk Oblast are shown in Fig. 1; their chemical composition is given in Table 1.

Analysis of the character of the structural-viscosity curves, plotted in coordinates of logarithm of viscosity versus temperature, shows that, as the temperature changes, the viscosity of pyroplastic masses of different loams changes in different ways; there is no linear dependence between temperature and viscosity, i.e., this dependence is apparently complicated by the different action of their chemical and mineralogical compositions. The initial points of the curves characterize the appearance of a liquid phase in an amount sufficient for the onset of plastic deformations; the final points characterize transition to a fluid state. Similar dependencies were established by us for all the clayey rocks of Tomsk Oblast studied.

Fig. 1. Curves of the apparent viscosity of loams.

Owing to the insignificant thickness of the rings…

during heat treatment they do not bloat; therefore the viscosity was measured up to a temperature of 1180–1200°C, i.e., up to the onset of the fluid state. At lower temperatures, plastic deformation occurs in the loams of the Inguza, Bakchar, and Vasyugan deposits; the loams of the Kolpashevo deposit and the clays of Brick Plant No. 10 begin to deform at a higher temperature.

Thus, we have established that for the rocks studied the range of optimum softening temperatures lies between 1100 and 1180°C; the apparent viscosity of the pyroplastic masses in this case corresponds on average to \(3 \cdot 10^9 \div 3 \cdot 10^8\) poise.

To establish more precise viscosity values at bloating temperatures, it is more convenient to use curves of the dependence of melt viscosity on temperature in coordinates of temperature—double logarithm of viscosity, which over fairly considerable intervals hardly differ from straight lines (Fig. 2).

Table 1

Loams

From the character of the viscosity curves, the role of natural organic impurities in creating the plastic state of the masses required for bloating is also established to a certain extent. Thus, for example, the loams of the Bakchar, Inguza, Vasyugan, and other deposits (Table 1), which contain larger amounts of organic impurities, pass into the fluid state at temperatures much lower than the loams of other deposits.

Fig. 2. Curves of the double logarithms of the apparent viscosity of loams.

The developed method for determining apparent viscosity is quite simple and reliable and gives only a slight scatter of results in repeated experiments; therefore, it can be recommended for determining the principal parameter of clayey rocks during their heat treatment for expanded clay.

LITERATURE

1. S. P. Onatskii. Production of Expanded Clay, Gosstroiizdat, Moscow, 1962.

2. A. V. Petrov. Use of loams of Tomsk Oblast for expanded clay. Proceedings of Higher Educational Institutions—Construction and Architecture, Novosibirsk, 9, 1966.

3. V. F. Pavlov. Glass and Ceramics, 5, 1959; 3, 1960.

4. P. G. Usov, A. V. Petrov. Deformation of products made of red clays during firing. Proceedings of TPI, 83, 1956.

5. M. A. Bezbоrodov. Application of modeling in chemical silicate technology for the case of determining pyroscopic viscosity. Reports of the Academy of Sciences of the USSR, IX, 6, 1948.