b for more than 3 5 and not more than 4 it was taken to be adequate c and for more than 4 it was taken to be poor d after the above mentioned boiling test disks of 0 5 mm thickness and 13 mm diameter were made of the columnar sintered product samples both sides of the disks were coated with a platinum paste on an area of 0 5 cm 2 each which was baked onto the samples and the ion conductivity was measured in this experiment the conductivity was calculated from the resistance with the alternating current impedance method in air the measurement temperature was 500 u00b0 c the resistance of the leads of the measurement device was subtracted when the conductivity in s cm was at least 0 007 it was taken as a for at least 0 001 and less than 0 007 it was taken as b and for less than 0 001 it was taken as c fig3 is an arrhenius plot showing the conductivity of materials in accordance with the present invention when the sintered product was single phase it was taken as a when it was multi phase it was taken as b and sintering failures were taken as.