فهرست مطالب leila ehrambaf

Strontium titanate (SrTiO3) was synthesized by mechanochemical processing of a mixture of purified celestite concentrate and titanium dioxide. First, SrCO3 was prepared from a mixture of purified celestite concentrate and sodium carbonate via a mechanochemical method, then SrTiO3 synthesizes from a stoichiometric mixture of SrCO3 and TiO2 powder. After isothermal heating of a 5-h milled mixture of SrCO3-TiO2 powder at 900 ℃ for 2 h, a single phase of SrTiO3 with a cubic structure was produced. The synthesized SrTiO3 powders were sintered at different temperatures for 2 h. The produced SrTiO3 samples were characterized using SEM micrographs, and the phase changes were evaluated using XRD analyses. The changes in the density and dielectric constant of the sintered samples were also determined. The results showed that the properties of SrTiO3 highly depended on the sintering temperature. Owing to the microstructure and grain size of the produced SrTiO3 in the milled samples, the dielectric constant of the milled sample was lower than that of the un-milled sample.

In this research perovskite phase of strontium titanate was produced from celestite concentrate (strontium sulphate). At first stage, the precursor of strontium carbonate was prepared from celestite-sodium carbonate mixture using mechanochemical process. Strontium titanate was synthesized using strontium carbonate-TiO2 mixture in the second stage. The results indicated that high energy ball milling plays a significant role in the chemical reaction and results in decreasing the temperature of post-heat treatment for producing of strontium titanate. Although some traces of rutile phase were overlapped with strontium carbonate, however no sign of chemical reaction observed in the10 hours milled mixtures of strontium carbonate-TiO2. TGA results showed that milling results in decreasing the formation temperature of perovskite strontium titanate phase in the milled mixtures. Although the traces of strontium titanate phase were revealed in the 5 hours milled mixture after isothermal heating at temperature of 600℃, the signs of un-reacted raw materials (TiO2 and SrCO3) were observed in un-milled mixture at this temperature. The traces of SrTiO3 were observed in un-milled and milled mixtures after heating at temperature of 900℃. XRD and FT-IR results indicated that strontium titanate can be synthesized form celestite concentrate (SrSO4) at lower temperatures using mechanochemical process. SEM micrographs showed that the ultrafine particles of strontium titanate (SrTiO3) can be formed in the milled samples.