Study of the Effect of Temperature on the Rheological Properties of Structuring Pore Suspensions in Molded Capillary-Porous Bodies

A. V. Vitugin, V. M. Vitugin, T. G. Leont’eva

In the technology of adhesive granulation of dispersed materials, after the pelletizing operation, heat treatment is, as a rule, carried out. At the same time, the intensity of multi-tonnage production is determined to a considerable extent by the thermal stability of the green granulate. The latter, in turn, depends substantially on the nature of the change in the rheological properties of the granulate pore suspension during heating. This is explained by the fact that the strength of the green granulate and the development of shrinkage stresses in it are a function of the rheological parameters of the pore suspension.

A generalized indicator of the rheological properties of structured suspensions is plasticity. The plasticity index of pore suspensions may expediently be expressed, following the proposal of M. P. Volarovich /1/, as the ratio:

\[ \psi = \frac{\Theta}{\eta_{\mathrm{pl}}} \tag{I} \]

where \(\psi\) is the plasticity index, sec\(^{-1}\); \(\Theta\) is the limiting shear stress, dyn/cm\(^2\); \(\eta_{\mathrm{pl}}\) is the plastic viscosity, P.

Experimental determinations of the limiting shear stress and plastic viscosity of bentonite suspensions are carried out on a rotational viscometer of M. P. Volarovich design, RV-8, which makes it possible to force the effect of temperature.

Suspensions of the pink variety of bentonite from the Tagan deposit were used as the objects of the present study. The sample studied was characterized by a bentonite number of 44, swelling of 8.6, and a total ion-exchange capacity of 64.6. The weight concentration of the bentonite suspensions was 10%, which corresponds to the practical concentration of bentonite in the pore suspension of green pellets during pelletizing of iron-ore concentrates. Thermostatting of experimental samples of the pore suspension was carried out in the temperature range from 20 to 50°C. Because of the tendency of the samples studied toward considerable coagulation structuring, the conditions and time of preparation of the suspension were strictly regulated—

were maintained and were constant in all experiments.

The results of the determination are given in the table.

Table 1

Effect of temperature on the rheological properties of bentonite suspensions.

With increasing temperature, the limiting shear stress increases sharply. Evidently, this is a consequence of the intensification of coagulation structure formation, while the destructuring effect of temperature is manifested to a lesser degree. The reason for this, apparently, lies in the substantial influence of heating on surface dispersion, which predetermines the effectiveness of structure formation. It is interesting that the effect of temperature on the viscosity of the suspension is practically imperceptible. At the same time, it is known that the viscosity of water decreases sharply with increasing temperature. Thus, for example, when the temperature of water is raised from 20 to 50°C, its viscosity decreases from 1 to 0.55 cP. However, it should be taken into account that the viscosity of the suspension under study is more than two orders of magnitude higher than the viscosity of water, and the effect of the change in water viscosity lies within the experimental error of viscosity determination on a rotational viscometer. In accordance with the above-described character of the change in limiting shear stress and viscosity, the plasticity tends to increase sharply with rising temperature. In practice this appears as softening of the granulate at the first stage of drying.

The established regularities evidently apply only to structured disperse systems constituting a single pseudophase, differing from ordinary two-phase suspensions by an increased surface tension. The possibility of transi-

of two-phase bentonite suspensions, with increasing bentonite concentration, into a single pseudophase is experimentally confirmed by special studies carried out at the Department of General Chemical Technology of TPI.

The high sensitivity of the rheological properties of pore suspensions to the influence of various surface-active additives, which change the degree of colloidality and hydrophilicity of the raw mixture, makes it possible to readily regulate the plasticity of coking systems and thereby the thermal stability of molded capillary-porous bodies.

In addition, the results obtained can be used in the technology of granulation of dispersed materials as a basis for reducing the amount of plasticizing additives in coking raw mixtures. Thus, in particular, the use of the temperature effect of plasticization in the pelletizing of iron-ore concentrates makes it possible to substantially reduce bentonite consumption.

Literature

1. M. V. Volarovich, “Colloid Chemistry,” No. 6, 1966.

STUDY IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES. IONIZATION CONSTANTS OF CERTAIN AMINO DERIVATIVES OF 9-SUBSTITUTED CARBAZOLES

E. E. Sirotkina, V. P. Lopatinsky, L. F. Kovaleva, T. V. Kakalina

A series of amino derivatives of 9-alkylcarbazoles was synthesized in this work by the method described in /1/, and their apparent ionization constants were measured by potentiometric titration at the pH of half-neutralized solutions in 20% ethyl alcohol /2/.

The obtained values of the ionization constants for the amines agree well with the spatial and electronic influence of the substituents.

The basicity constants of 9-alkyl-3-(I-aminoethyl)carbazole and 9-ethyl-6-chloro-3-(I-aminoethyl)carbazole, presented in the table, show that electron-acceptor substituents in the 6-position of carbazole decrease the basicity of the amines.