**5. Conclusions**

584 Sintering of Ceramics – New Emerging Techniques

Quartz has thus been shown to decrease the TCLR of feldspathic rocks, as indicated by the absence of rapid changes in the curves (Fig.3) in the range 600 – 700 <sup>о</sup> С. High concentrations of feldspathic minerals (microcline, plagioclase - 95 – 97.5 mass. %), which form a less

pH is a parameter showing the acidity of feldspathic rocks and the engineering properties of clay slurry (viscosity, the density of clay slurry, tixotropy for molding ceramic products. As рН rises, the tixotropy of the clay slurry increases. Interacting with water, feldspathic minerals change the acidity of ceramic shlicker, depending on their constituent cations and anions. The optimum viscosity of clay slurry for refractory products is achieved at рН 5.5 and that for porcelain at рН 7.5–9. According to GOST 21119.3-91 for feldspathic fillers in

The рН of suspensions was measured using the potentiometer method on an I-120.1-type ionometer. Suspensions were prepared from из finely dispersed samples (grain size 0.063 mm) at solid:fluid ratio of 1:2.5 in accordance with the procedure described in [6,7]. The results of measurements of the рН of feldspar rock suspensions are presented in Table 1, and Figure 4 shows the dependence of рН on total microcline and plagioclase concentration

Our results have shown that a common pattern of variations in the рН of feldspathic rock

suspensions is a rise in рН with increasing alkaline oxide concentration.

Fig. 4. Dependence of variations in pH on microcline and plagioclase.

viscous glass phase, increase the TCLR of feldspathic rocks.

**4. рН of feldspar suspension** 

varnish and paint production, рН is 6-9.

in the rock.

The electrical properties ε , lg ρ, tg δ of the cakes of nonconventional types of feldspathic rocks and conventional types, such as pegmatite, are basically affected by alkaline oxides and quartz. Dielectrical permeability depends more on microcline and quartz concentrations in rocks. The angle tangent of dielectrical loss and electrical resistance depend on total microcline and plagioclase concentration. Elisenvaara syenites, which contain high microcline and plagioclase concentrations (97 mass.%), typically show lower tg δ values (0.025) and higher electrical resistance (2.0◌ּ 10-12 Ohm◌ּ cm) than other rocks. Their TCLR is consistent with that of microcline pegmatite. The рН of the suspensions of nonconventional feldspathic raw material depends on total microcline and plagioclase concentration and quartz concentration. Elisenvaara alkaline syenites are a promising feldspathic raw material for electrical porcelain production.
