FABRICATION OF NANOSTRUCTURED CALCUMITTANATE - FLUORAPATTE BULKS VATWOSTEP SINTERNG METHOD

Researchers have shown that a remarkable suppression of grain growth could be achieved by controlling the sintering temperature and taking advantage of sintering aids during the final stage of a two-step sintering (TSS) method. To find how important the temperatures at sintering steps might be, several TSS regimes have been conducted. In present work, nanostructured Calcium TitanateFluorapatite bulks with mean crystallite size of less than 100 nm was fabricated successfully by TSS. The results showed that the optimum regime consisted of heating the green bodies up to 1200 °C (first step) and then holding at 1100 °C for about 20 hr (second step). This yielded the finest microstructure with no deterioration of the densification. A nearly full-dense structure (> 97% theoretical density) with an average crystallite size of 65 nm was obtained when the temperature of the second step was increased to 1100 °C. Empirical results showed that not only the first step temperature has to be high enough to reach a structure containing unstable pores, but the second sintering temperature must also be high enough to activate the densification mechanism without grain growth. This means that a considerable densification at the first step does not imply enough second-step densification. The full dense structure of the prepared bulks could be seen at the SEM micrographs and XRD patterns showed that the desired phases of the fabricated bulks were stable during sintering steps. It was concluded that the TSS method can be used to fabricate improved nanostructured Calcium Titanate-Fluorapatite bulks.

کلیدواژه ها:

nanostructure ، ceramics ، two step sintering