**2. Electrical characteristics of feldspathic raw material**

To measure electrical properties, we prepared specimens of cakes. They were 20 - 25 mm in diameter and 2 - 3 mm in height. ε-, lgρ- and tg δ-values were measured using a bridge with a capacity Е of 7-8 and a working frequency of 1000 Hz at 20°С.

Electrical properties were estimated by introducing an additional coefficient to account for additional capacity on the specimen zones not covered by electrodes using the formulas: dielectric permeability: ε = к<sup>1</sup> к<sup>2</sup> с, where к1 = 1.14 is the coefficient of the sensor, к2 is the coefficient of specimen thickness, с is specimen capacity; specific electrical resistance: lgρ = к/g·l, where к = 33.55 is the sensor coefficient, g is conductivity, l is specimen thickness; dielectrical loss: tg δ = 0.175·g/s, where с is specimen capacity and g is conductivity.

The results of the measurement of the dielectrical properties of feldspathic rocks are shown in Table 1, and the dependence of variations in ε, lgρ and tgδ on the quantities of microcline and plagioclase in the cake is shown in Figures 2.

Fig. 1. Cake from feldspathic raw material.

Dielectrical permeability, ε, is the electrical parameter of a mineral showing its ability to polarize in an electrical field. According to experimental data, the dielectrical permeability of the cakes of the rocks evaluated (Nos. 1 – 12) varies from 3.26 to 8.1. The dielectrical permeabilities of feldspathic rocks from other deposits (Nos. 13 – 18), shown in Table 1, range from 5.6 to 7.7, and according to E.V. Rozhkova's results presented in the literature [4,5] /(Golod et al., 1975), they vary from 5.6 – 6.3. This means that the variation range of ε of the cakes of nonconventional feldspathic rocks is within known values.

Analysis of the dielectrical permeability values obtained has shown that ε depends largely on mineralogical composition. Microcline and quartz were shown to have the greatest effect on dielectrical permeability. A high percentage of quartz (44 mass.%), in contrast to that of other rocks, in volcanics from the Roza-Lambi deposit (cake no. 7) contributes to a decline in ε of the cake to 5.4 dtn/cm2.

The ε dielectrical permeability of plagioclase rock cakes (Nos. 10 – 12, Table) is lower than that microcline cakes (3.26-4.02), which seems to be due to the presence of large quantities of quartz and Са2+ and Мg2+ ions in cakes 11-12 and Ва2+ ions in cakeв no. 10, because the electrical conductivity of К+ and Na+ ions in dielectrics is higher than that of Са2+, Мg2+ and Ва2+ ions [1,4].

To measure electrical properties, we prepared specimens of cakes. They were 20 - 25 mm in diameter and 2 - 3 mm in height. ε-, lgρ- and tg δ-values were measured using a bridge with

Electrical properties were estimated by introducing an additional coefficient to account for additional capacity on the specimen zones not covered by electrodes using the formulas: dielectric permeability: ε = к<sup>1</sup> к<sup>2</sup> с, where к1 = 1.14 is the coefficient of the sensor, к2 is the coefficient of specimen thickness, с is specimen capacity; specific electrical resistance: lgρ = к/g·l, where к = 33.55 is the sensor coefficient, g is conductivity, l is specimen thickness;

The results of the measurement of the dielectrical properties of feldspathic rocks are shown in Table 1, and the dependence of variations in ε, lgρ and tgδ on the quantities of microcline

Dielectrical permeability, ε, is the electrical parameter of a mineral showing its ability to polarize in an electrical field. According to experimental data, the dielectrical permeability of the cakes of the rocks evaluated (Nos. 1 – 12) varies from 3.26 to 8.1. The dielectrical permeabilities of feldspathic rocks from other deposits (Nos. 13 – 18), shown in Table 1, range from 5.6 to 7.7, and according to E.V. Rozhkova's results presented in the literature [4,5] /(Golod et al., 1975), they vary from 5.6 – 6.3. This means that the variation range of ε

Analysis of the dielectrical permeability values obtained has shown that ε depends largely on mineralogical composition. Microcline and quartz were shown to have the greatest effect on dielectrical permeability. A high percentage of quartz (44 mass.%), in contrast to that of other rocks, in volcanics from the Roza-Lambi deposit (cake no. 7) contributes to a decline in

The ε dielectrical permeability of plagioclase rock cakes (Nos. 10 – 12, Table) is lower than that microcline cakes (3.26-4.02), which seems to be due to the presence of large quantities of quartz and Са2+ and Мg2+ ions in cakes 11-12 and Ва2+ ions in cakeв no. 10, because the electrical conductivity of К+ and Na+ ions in dielectrics is higher than that of Са2+, Мg2+ and

of the cakes of nonconventional feldspathic rocks is within known values.

dielectrical loss: tg δ = 0.175·g/s, where с is specimen capacity and g is conductivity.

**2. Electrical characteristics of feldspathic raw material** 

a capacity Е of 7-8 and a working frequency of 1000 Hz at 20°С.

and plagioclase in the cake is shown in Figures 2.

Fig. 1. Cake from feldspathic raw material.

ε of the cake to 5.4 dtn/cm2.

Ва2+ ions [1,4].



Evaluation of Dielectric Properties from

in Table 1).

the Cakes of Feldspathic Raw Material for Electrical Porcelain Production 583

quartz in a glass phase. Figure 3 shows that curves 1, 2 and 5 for the cakes of the rocks studied exhibit a non-uniform course of thermal expansion. A rapid increase in TCLR in the range 600 – 700<sup>о</sup> С is typical of compositions with a minimum quartz concentration and high microcline and plagioclase concentrations which form a less viscous liquid phase. Large quantities of quartz in rocks are responsible for the rectilinear course of the TCLR curves (3, 4, 6 and 7). A minimum TCLE value (7.10◌ּ 10-6 1/deg) in the range 600-700<sup>о</sup> С is observed in cake 7 with a minimum quartz concentration (44.0 mass.%), and a maximum TCLR value

Fig. 3. Temperature dependence of the thermal coefficient of linear expansion: (numbers as

According to the literature [5] the dependence of TCLR on quartz concentration is due to a difference in the density of minerals. It is known that as mineral density increases, TCLR decreases. As the density of quartz (2.65 g/cm2) is higher than that of albite (2.61 g/cm2) and that of microcline (2.55 g/cm2), low TCLR values in cakes with high quartz concentrations can well be expected. The dependence of TCLR on microcline-plagioclase ratio shows a more complex pattern. As quartz concentration rises with a decline in feldspar concentration [1], also observed in Roza-Lambi quartz porphyry, the porcelain burning expansion interval

will expand to 100 <sup>о</sup> С without deformation of products upon burning.

(8.9◌ּ 10-6 1/deg) in cake 1 with a quartz concentration of 2.5 mass. %.

Figure 2 shows that high microcline and plagioclase concentrations in feldspathic rocks are responsible for a low angle tangent of dielectrical loss in cakes: (no. 8) potassic halleflinta - 0,050, (no. 10) syenite - 0,025 – 0.032, (no. 6) and pegmatite (Cjryla) – 0.027- and increases their electrical resistance (Fig.3) -(1,23, 2,0, 2,10◌ּ 1010 Ohm◌ּ cm), which is consistent with GOST parameters 2484-85 for electrical porcelain: dielectrical permeability not more than 7, the angle tangent of dielectrical loss – 0.030 and electrical resistance 1-2◌ּ 1012. Low dielectrical loss (0.025) and high electrical resistance (2.0◌ּ 1010 Ohm◌ּ cm) are characteristic of Elisenvaara syenites which have a high total percentage of microcline and plagioclase (97 mass.%).

Fig. 2. Dependence of dielectric properties on feldspathic rock composition.

Elisenvaara syenites and Kostomuksha volcanics are most efficient feldspathic raw materials for electrical porcelain production in terms of their electrical properties.
