The effects of boron addition in kaolin-CaCO3 mixture

Abstract

The effects of boron addition (0–5) wt.% on a crystallization of high-temperature phases in kaolin-CaCO3 mixture is studied. The porosity, bulk density, water absorption, and thermal expansion of ceramic samples are determined. Input materials are prepared according to the anorthite stoichiometry composition. Mixtures are wet milled, dried, and then crushed to obtain fine powders. These mixtures are pressed in a stainless steel die with the compression pressure of ∼40 MPa. Samples during temperature interval from 780 °C to 1150 °C are analyzed using differential scanning calorimetry and thermodilatometry. The porosity and bulk density of samples are determined using helium pycnometry and the Archimedes method after firing at 1150 °C. The addition of boron oxide into the ceramic mixture broadens the temperature crystallization range and decreases the crystallization temperature of anorthite from 966 °C to 899 °C. The relative expansion also decreases, from 7.5 % to 2.5 %. A porous anorthite body was obtained. The highest bulk density is observed in the sample without boron (1.83 g/cm3) and the lowest in the sample containing 5 wt.% of B2O3 (1.53 g/cm3). The addition of boron oxide increases the porosity of samples by ∼15 %.