【正文】 techniques for the determination of the crystal phase for ZrO2 (Wang et al., 2022). Moreover, recent reports reveal that ZrO2 matrix is an ideal medium for preparation of highly luminescent materials because it is chemically and photo chemically stable with a high refractive index and low phonon energy (Wang et al., 2022). The FTIR absorption spectrum of recrystallized ZrO2 xH2 O Naturally dried ?→ [Zr16 O22 (OH)20 (H2 O)20 ] + xH2 O (2) Fig. 1 – XRD patterns of the produced ZrO2 powders by CP method at 120, 500, 700, 1000 and at 1200 ? C for 1 and 3 h. [Zr16 O22 (OH)20 (H2 O)20 ]?→ 16ZrO2 + 30H2 O heat (3) 5 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 5 ( 2 0 0 8 ) 178–185 181 Fig. 3 – XRD patterns of the produced ZrO2 powders by MRP method at 120, 500, 700, 1000 and at 1200 ? C for 1 and 3 h. When ZrO2 is the Bragg angle. The change in crystal morphologies of the ZrO2 particles produced at heated temperature 700 and 1000 ? C for differ ent processing routes were examined by scanning electron microscopy (JEOLJSM 5410 SEM). Speci?c surface area (SBET ) of 4 180 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 5 ( 2 0 0 8 ) 178–185 samples was determined by BET surface area analyzer (Nova 2022 series, Quantachrome Instruments, UK). UV–visible absorption spectrums of the processed ZrO2 powders using three processing routes at calcination temper ature 1000 ? C were measured using CECIL CE 7200 UV double beam spectrophotometer. Vibration spectrum of the crystalline ZrO2 powders at calcination temperature 1000 ? C for the different processing techniques in KBr were recorded on Fourier Transformer and PyeUnicam SP 300 instrument. 3. Results and discussion The XRD patterns of the ZrO2 nanopowders products syn thesized by precipitation (CP), citrate gel bustion (CGC) and microemulsion re?ned precipitation (MRP) techniques at different thermal treatment from 120 to 1200 ? C were shown in Figs. 1–3. It is clear that the processed samples synthe sized at temperature 120 ? C were amorphous in the three processing techniques and it was also nearly amorphous for the produced ZrO2 powders of the precursor sample pow der which treated at the temperature 500 ? C in case of CP method. XRD studies also showed that the transformation of ZrO2 precursors to the crystalline tetragonal phase (JCPDS 49 1642) occurred as the calcination temperatures were increased Fig. 2 – XRD patterns of the produced ZrO2 powders by CGC method at 120, 500, 700, 1000 and at 1200 ? C for 1 and 3 h. between 500 and 700 ? C for heating time 1 h. The crystallite sizes of formed singlephase tZrO2 nanopowders as calcu lated from XRD analyses using DebyeScherrer formula of the most intense peaks (1 1 1) plane were in the range of , and nm at 700 ? C for CP, CGC and MRP methods, respectively. The presence of tetragonal phase in as prepared ZrO2 and the powder formed at low temperature is attributed to the fact that the speci?c surface free enthalpy of tetragonal ( = J/m2 ) is smaller than that of mono clinic ( = J/m2 ). The large surface area of assynthesized nanopowders bees a thermodynamic barrier for tZrO2 to mZrO2 phase transformation. Consequently, tetragonal phase is remained. Liang et al. (Liang et al., 2022) explained the formation of tetragonal phase at low temperature is attributed to that the structure of zirconia precursor is regarded as hydrous zirconia (ZrO2 nH2 O calcined at different temperatures from 500 to 1200 ? C at a rate of 10 ? C/min and kept at the respective temperature for 1 h. To process ZrO2 powders by CGC method, 10 g of zir conium oxychloride octahydrate was dissolved in water. A stoichiometric amount of citric acid was added to the aque ous solution. The mixture was evaporated to dryness at 60 ? C. Then, the produced precursor was dried to 120 ? C overnight. The formed precursor was heated again to 500, 700, 1000 and 1200 ? C at a rate of 10 ? C/min and kept at the respective tem perature for 1 h. For the MRP method, the authors employed npentanol as the oil phase and triton X100 as the surfactant. One molar of Triton X100 (nonanionic surfactant) was prepared by dissolv ing in npentanol and the processed solution was divided into two parts, one part was added to 10 g zirconyl chloride octahy drate dissolved in small amount of water and the other part was used for preparation of 2 M sodium hydroxide. Both two solutions were mixed together to precipitate zirconia hydrate at pH 10. The precipitated solution was ?ltered, washed, dried at 120 ? C, then calcined at different temperatures from 500 to 1200 ? C. . Characterization The phase identi?cation and the crystallite size of the pro cessed ZrO2 nanopowders were characterized by Philips XRay Diffractometer PW 1730 with nickel ?ltered Cu K radiation ?( = A) at 40 kV and 30 mA. The crystallite sizes of ZrO2 nanopowders were determined for the most intense peak (1 1 1) plane of ZrO2 crystals from the Xray diffraction data using the DebyeScherrer formula: dRX = k cos 194。 Bhattacharjee et al., 1991). According to the change in thermal treatment, cZrO2 phase is stable at all temperature up to the melting point at 2680 ? C. mZrO2 phase is stable below 1170 ? C and inverted to tZrO2 phase by increasing tem perature over 1200 ? C. tZrO2 phase is stable between 1170 and 2370 ? C by adding stabilized oxides (Stefanc et al., 1999). From our knowledge, little information in literature is found about the change in the phase transformation and the mor phology of the formed ZrO2 nanopowders that are produced by CP, CGC and MRP techniques. The present work aims at paring the change in crystal structure, morphology, FT