PERLITE BASED CERAMIC TILES.

Ludmil S. Bozadgiev, Efimia M. Popova

University “Prof. Asen Zlatarov” – Burgas, Bulgaria

 Received  21.07.01; Cited 14.08.01

Abstract

In a feldspar body for ceramic tiles, composed of (mass%) 35 refractory clay, 20 quartz sand and 45 sodium feldspar, the feldspar was partly and completely replaced by perlite. Increasing the perlite quantity the mechanical strength and the shrinkage of the tiles also increase and the water absorption decreases.

Double fired tiles, biscuit at 1050°C and glost fired at 950°C, have 40.30 – 48.62 MPa bending strength, 3.55 – 5.92 % water absorption and 3.59 – 4.94 % shrinkage.

The use of perlite instead of feldspar in the ceramic tile bodies improves the mechanical strength and decreases the water absorption.

Key words  - ceramic tiles, perlite.

Introduction

The perlite used as ceramic raw material don’t undergo structural modification during drying and firing and don’t have environmental pollution’s [1]. This explains the interest, perlite to be used for manufacture of ceramic tiles. A ceramic tile body containing 5-25% perlite, 50-85% waste rock materials obtained by cutting granite, marble and basalt and 10-25% low melting montmorilonite clay have 21.0 – 27.5 MPa bending strength, 13 – 15% water absorption and 0.5 – 0.7 % shrinkage. [2].

Ceramic tile bodies with 15 – 25 mass% perlite, 55 – 60 mass % refractory clay and the rest waste glass cullets, after firing at 950°C have 44.3 – 46.1 MPa bendimg strength, 7.5 – 8.1 % water absorption and 4.2 – 5.4 % shrinkage. [3].

With the aim to decrease the firing temperature by simultaneously decrease the water absorption following additives are proposed (mass %): 5 – 20 perlite, 10 – 15 glass cullets, 10 – 15 quartz sand, 20 – 40 phosphogypsum and 30 -  47% refractory clay. [4]. The tiles fired at 950°C have 2.9 – 3.2 % water absorption and 1.2 – 1.9 % shrinkage.

A composition for ceramic tiles containing (mass %): 25 – 30 perlite, 50 – 60 clay and 8 – 10 waste glass cullets, after firing at 980 - 1000°C ensures 48 – 66 MPa bending strength, 99 – 100 MPa compressive strength and 1-1,2 % water absorption.

Selfglazing ceramic tiles composed of (mass%): 18-44 perlite, 16-52 waste bricks material, 16-26 quartz sand, 8 – 12 calcium containing additives and 2-4 water glass after firing at 750-800°C and a thermal shock at 1030-1050 C, have 147-162 MPa compressive strength and 2.8-3.0 % water absorption.

The aim of the present work is to obtain ceramic tile bodies containing perlite and to investigate their properties.

Experemental

In ceramic tile bodies containing 45 mass% sodium feldspar, the feldspar was partly and completely replaced by perlite. The composition of the bodies is shown in the table 1 and the chemical composition of the used raw materials in table 2. Fig.1 and table 3 shows the diffractograms of the raw materials and fig.2 – the derivatogram of the body containing 45% perlite (Table 4.).

By preparation of the bodies the correlation material: mill balls: water was from 1:1.5:1 to 1:1.5:2 for compositions with higher perlite content. The bodies were milled up to 2% oversize return on 63 mm sieve. The slip were dried to 8 % water content and granulated on sieve 1 mm. The tiles were pressed on hydraulic press with 40 MPa pressure, dried at 110 °C, biscuit fired at 1050 and glost fired at 950°C. Some samples were single fired at 1150°C.

The composition of the used glaze with firing temperature 950°C was (mass%):67.3 SiO₂, 0.6 ZrO₂, 8.6 Al₂O₃, 0.2 Fe₂O₃, 9.0 B₂O₃, 2.2 CaO, 0.6 MgO, 0.9 BaO, 0.6 ZnO, 5.0 PbO, 3.8 Na₂O and 1.2 K₂O. The composition of the glaze with firing temperature 1150°C was (mass%): 59.4 SiO₂, 9.3 ZrO₂, 5.7 Al₂O₃, 0.1 Fe₂O₃, 12.8 B₂O₃, 5.3 CaO, 0.3 MgO, 1.0 ZnO,  5.5 Na₂O and 0.6 K₂O.

The properties of the fired ceramic tiles are shown in tables 3-4 and their diffractograms in fig.3 and table 7.

Discussion

In the bodies the nonplastic components are represented by quartz sand, sodium feldspar and perlite. The quartz sand consists of quartz (0.334-0.426-0.182 nm). The sodium feldspar contains albite and mixed potassium feldspar (0.321-0.325-0.411 nm). The perlite is build of volcanic glass – 90-95%, has porphiric structure and small admixtures of quartz (0.334 nm), crystobalite (0.405 nm) and sodium potassium feldspar (0.321 nm). By firing at 900°C the perlite has a weight loss of 5.0, which respond to the water contain of the perlite glass.

The plastic component of the body is 35 mass % and consists of refractory clay. The clay contains kaolinite (0.714-0.357-0.234 nm), quartz (0.334 nm) and calcite (0.304-0.228-0.209 nm). Typical for the refractory clay are two endothermic effects at 110 and 530°C, connected with the separation of the interlayer water and the OH – groups of the kaolinite. The weight loss of the refractory clay by firing at 900°C is 12.5 mass %, 6% in the 50-190°C and 6.5 % in 420-580°C intervals.

The bodies containing feldspar and perlite have endothermic effects at 110 and 530°C connected with the main plastic component – the refractory clay. The weight loss of the bodies vary from 5.5 to 6.5 mass %.

Tile specimens were pressed of the bodies. The tiles were biscuit fired at 1050°C and glost fired at 950°C. The initial body containing 45 % feldspar has 40.30 MPa bending strength, 5.92 % water absorption and 3.59 % shrinkage. By completely replacement the feldspar by perlite, the tiles have 48.62 MPa bending strength, 5.92 % water absorption and 4.94 % shrinkage. The single fired at 1150°C tiles of the feldspar body have 53.36 MPa bending strength, 1.88% water absorption and 5.56 % shrinkage. The tiles of the perlite body have 69.90 MPa bending strength, 0.21% water absorption and 8.81% shrinkage.

The double fired tiles contain: quartz (0.334 nm), feldspar (0.321 nm) and modified by the firing clay substance. After firing at 1150°C quartz is left and new phases: mullite (0.338-0.220-0.341 nm), crystobalite (0.405 nm) and glass appear. The appearance of glass explains the higher mechanical strength and the lower water absorption of the single fired tiles.

Conclusion

The investigation confirms, that the substitution of the sodium feldspar by perlite in the composition for ceramic tiles increases the  mechanical strength and the shrinkage and decreases the water absorption of the ceramic bodies. The double fired ceramic tiles (1050 and 950°C) containing 45 mass % perlite have 48.62 MPa bending strength, 3.55 % water absorption and 4.94 % shrinkage. The perlite containing single fired tiles (1150°C) have 69.90 MPa bending strength, 0.21% water absorption and 8.81 % shrinkage.

References

1. La perlite: un un materiau redecouvert. Ind.ceram. (1993),/6/ 402-403

2. Patent USSR N^o 1638131,1991

3. Patent USSR N^o 1689350,1991

4. Patent USSR N^o 1715766,1992

5. Patent USSR N^o 1675276,1991

6. Patent USSR N^o 1648926,1991

 Table 1

Composition of the tile bodies (mass.%)

Table 2

Chemical composition of the used raw materials (mass.%)

Table 3

Interplate distances (d) and relative intensity (I/I₁) of the raw materials