Fired properties of Vermiculite-Clay Insulating Materials

Abstract

The effect of an increased pyrophyllite component on the bulk specific gravity, compressive strength, linear shrinkage and thermal conductivity was mainly investigated for insulating materials of the system expanded vermiculite-bond clay. The vermiculite from Fukushima Pref. was expanded at about 1050°C, and was used as an aggregate. The bond clays used with the aggregate were Mitsuishi-pyrophyllite from Okayama Pref., kibushi-clay from Aichi Pref., bentonite from Gumma Pref. and acid clay from Niigata Pref. In hand mixing, the bond clays and vermiculite were mixed dry until the resultant mass had a uniform color; after the addition of water to the mass, a further mixing was made for about 5 min. until a uniform consistency was obtained; the mixture was shaped, dried at 110°C, and then fired at temperatures of 800, 1000 and 1100°C for 4 hours.The results obtained are as follows: (a) Short mixing time is preferable for the vermiculite-clay specimens. Long mixing time and intensive mixing action have the tendency to crush the vermiculite granules and to cause the increase in both bulk specific gravity and linear shrinkage. (b) The bulk specific gravity is little different between both groups of specimens predominantly including pyrophyllite and predominantly including plastic clays as bonding materials. (c) The compressive strength is largely increased by the firing operation at temperatures ranging from 800 to 1100°C for the group of specimens predominantly including pyrophyllite. (d) The linear shrinkage is decreased with increasing the pyrophyllite content of bonding material. (e) The thermal conductivity is increased with temperature for the specimens investigated here.From the data presented, the following ranges of batch compositions are recommended for general insulating purposes at temperatures near 1000°C: 75-80 parts of Mitsuishipyrophyllite, 10 parts of kibushi-clay, 10-15 parts of expanded vermiculite and 30-40 parts of water by weight. The characteristics of the specimens obtained by firing the batches of the above range of compositions at a temperature of about 1000°C were as follows: Thermal conductivity (kcal/m, hr, °C) at the mean temperature of 350°C, 0.121-0.146; bulk specific gravity, 0.71-0.97; compressive strength (kg/cm2), 14.9-18.4; linear shrinkage (%), 0.80-0.86.