Shaped samples were dried at laboratory conditions (21 1C, 40% relative humidity) for 72 h and then dried to constant weight at 105 1C in the oven. Dried samples were fired in laboratory type electrically heated furnace at the rate of 2 1C/min until 600 1C and then at the rate of 5 1C/min untill 900 1C. Furnace wasturned of after holding period of 30 min