Effects of Titania Addition on Sintering of Zircon Bodies

Abstract

Effects of TiO2 addition on sintering of ZrSiO4 at 1450°, 1500°, and 1600°C for 1 to 24 hrs. in air have been investigated. Shrinkage after sintering, bulk density, apparent density and apparent porosity of the sintered bodies were measured in relation with sintering time, temperature and TiO2 content. Mineral constitutions of the sintered samples were identified with an X-ray diffractometer. Microstructures of the sintered bodies were examined by means of an EMA and a reflected microscope.The results obtained were as follows:(1) Sintering of zircon was accelerated by addition of TiO2. Shrinkage and bulk density of the samples increased, and apparent density and apparent porosity decreased with increase of TiO2 content, sintering time and sintering temperature.(2) Zircon was decomposed to ZrO2 and SiO2 by addition of TiO2. A solid solution of TiO2 with ZrO2 was recognized at 1450° and 1500°C. The formation of a compound ZrTiO4 was recognized at 1600°C. SiO2 dissociated from ZrSiO4 coexisted as crystobalite at 1450° and 1500°C and changed into liquid at 1600°C. ZrO2 appeared in samples sintered at 1600°C.(3) Acceleration of sintering of ZrSiO4 was due to the formation of a solid solution, a compound ZrTiO4 and liquid. Especially, formation of liquid was one of the most important factors.(4) In the case of sintering of samples crushed and heated repeatedly, rapid reaction between ZrSiO4 and TiO2 was attained. Samples heated at 1600°C and contained TiO2 less than 5 wt% showed the increase of bulk density, while that of the other samples showed the decrease.