STUDY OF THE EFFECT OF THE METHOD OF PREPARATION OF STEATITE BODY ON ITS TECHNOLOGICAL PROPERTIES

P. G. USOV, Yu. I. NESTEROV

The physicotechnical properties of ceramic articles depend to a considerable extent on the phase composition and structure. Articles with a fine-grained structure, with a crystalline phase uniformly distributed in the glass, have the highest indices.

Steatite articles are characterized by high mechanical strength and high dielectric properties, but their production has a number of substantial shortcomings. They sinter within a short temperature interval, have a short interval of the sintered state, and are prone to bloating during firing. The short interval of sintering and of the sintered state is explained by the rapid increase of melt during firing, with a sharp decrease in its viscosity, and the bloating by the reaction of barium carbonate.

The aim of the study was to determine the influence of the rate of cooling of the body, from the final firing temperature (1320°), on the behavior of articles made from it during firing and on the final properties of the articles. The study was carried out on a body of the following composition: raw Onot talc—32%; calcined talc—48%; Chasov Yar clay—5%; and magnesium carbonate—15%. The wet preparation of the body was carried out according to the usual procedure. Sintered masses were obtained by cooling from a temperature of 1320°—together with the furnace, over 12 hours; by cooling in air—one hour; and by cooling in water—10 minutes. It was intended, by sharp cooling, to obtain a body with greater disordering of the lattices of the crystalline phase and, consequently, greater reactivity. Thermal-analysis data show (Fig. 1) that the behavior during firing of powders from such bodies is not the same. In all three bodies the crystobalite effect is recorded at temperatures of 370–400°, and at temperatures of 790–825° a precrystallization effect is recorded. In the body cooled together with the furnace it is barely noticeable; in the body cooled in air it is clearly noticeable; and in the body cooled in water it is large, caused by considerable regrouping of atomic groups. The reactivity of the bodies was evaluated by the rate of sintering and by the change in other ceramic characteristics caused by this process. All bodies were ground in the same way to a particle size of 0.063 mm. The articles were formed with a paraffin binder and fired according to the standard schedule.

The behavior of the bodies during firing is shown in the graphs of Figures 2, 3, and 4. Rapid cooling of the body during firing increases its reactivity. Articles made from it sinter more intensively during the firing process, but the interval of their sintered state remains, as before, short. The tendency of the articles to bloat is not reduced either. Rapid cooling of the body during firing has no noticeable effect on the phase composition of the articles or on their dielectric properties.

Fig. 1. Thermal curves of body P-5 with different methods of its preparation.

Fig. 2. Change in water absorption of articles made from body P-5 during firing.

![Graph: Change in bulk density of specimens made from P-5 body during firing. Vertical axis: bulk density, g/cm³; horizontal axis: temperature, °C. Curves labeled I, II, III.]

Fig. 3. Change in the bulk density of specimens made from P-5 body during firing.

![Graph: Change in diametral shrinkage during firing of specimens made from P-5 body. Vertical axis: diametral shrinkage, %; horizontal axis: temperature, °C. Curves labeled I, II, III.]

Fig. 4. Change in diametral shrinkage during firing of specimens made from P-5 body.