【正文】 Hirata et al., 1994。nH2 O had disappeared, but traces of water persisted to about 1000 ? C (4). The crystalline inversion of stabilized oxides at about 1200 ? C lead to failures when ceramic objects are heated or cooled above and below this temperature. The phase transformation is acpanied by a 9% volume expansion. The crystallite sizes of the produced mZrO2 nanopowders given from the most intense peaks [1 1 1] plane were temperature depending. The crystallite sizes were increased from nm at calcina tion temperature 1000 ? C to nm for the powder produced at calcination temperature 1200 ? C for CP technique and they were increased from to nm for the ZrO2 powders produced by CGC route at the same conditions. On the other hand, the tetragonal ZrO2 form changed to cubic phase for the powders produced using MRP technique when the anneal ing temperature increased from 700 to 1000 ? C. The change from tetragonal to cubic phase may be attributed to high tem perature that led to exothermic bustion deposition of the carbonaceous residue produced from triton X100 and npentanol. This phenomenon facilitates the solid phase reac tion among the constituent ions. Roy and Ghose (2022) showed that the formation of cubic phase when prepared zirconia in polyacrylamide matrix is attributed to the crystallite size resulting from polymer coprecipitation method is smaller than that of aqueous coprecipitation method which leads to considerable oxygen vacancies located in the bulk and on the surface. Presence of oxygen vacancies is believed to play an important role in stabilizing the metastable tetragonal/cubic phase of ZrO2 . Also, when the polymer deposed creates a reducing atmosphere, which can increase the oxygen vacan cies already present in the samples. This may be identi?ed in the present studies when the deposition of the surfactant and oil was occurred at 1000 ? C for 1 h. 7 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 ) 178–185 183 Fig. 5 – UV–visible absorption spectrum of the produced ZrO2 powders at calcined temperature 1000 ? C for 1 h by the three different techniques (a) CP, (b) CGC and (c) MRP. After annealing the ZrO2 precursors to 1200 ? C for 1 and 3 h, the crystallinity of the produced mZrO2 was increased. Increasing the calcination time up to 3 h had insigni?cant change on the crystallinity. In addition, weak peaks of tetrag onal phase were obtained. It is well known that cubicZrO2 phase is stable at all temperatures up to its melting point at 2680 ? C. Stabilization to the cubic phase is favored which undergoes no inversion. Scanning electron microscopy (SEM) investigations of the ZrO2 nanopowders produced by the three different process ing routes were given in Fig. 4. SEM photomicrograph of the precipitated ZrO2 powders and heated at 700 ? C showed that tetragonal form appeared as aggregations of ?ne to very ?ne grains. The grains were varied from spherical to elongated and from angular to subrounded (Fig. 4a). Two grains types represented the monoclinic phase were obtained with increas ing the calcination temperature up to 1000 ? C. The elongated, tabular and spherical shapes were characterized by rounded aggregates of larger size in some instances (Fig. 4b). On the other hand, the SEM image of ZrO2 powders produced by CGC technique and heated temperature to 700 ? C showed that tetragonal form appeared as dense, uniform, ?ne to medium grains and rounded in general (Fig. 4c). Monoclinic ZrO2 phase formed at 1000 ? C as aggregation of very ?ne rounded grains (Fig. 4d). In contrast, the SEM photomicrographs of ZrO2 pow ders processed through MRP method at 700 ? C showed that tetragonal phase appeared as elongated and tetragons. Aggre gation of small grains gave larger grains in some instances (Fig. 4e). Cubic ZrO2 powders processed at calcined tempera ture 1000 ? C showed that the ?owerlike texture of ?aky grains Fig. 6 – FTIR spectrum of the produced ZrO2 powders at calcined temperature 1000 ? C for 1 h by the three different techniques (a) CP, (b) CGC and (c) MRP. 8 184 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 was obtained. In general, they were larger in size pared to the tetragonal phase (Fig. 4f). The ZrO2 powders samples produced by the three synthe sized techniques and thermally treated at 1000 ? C for 1 h were pared using UV–visible absorption spectrum ranging from 100 to 900 nm. The results were given in Fig. 5 indicating ZrO2 have absorption in UV region. Two main peaks formed for the three techniques at 190–220 nm and the second peak at 360–370 nm for mZrO2 and cZrO2 nanopowders processed by different three syntheses routes. Other weak peak produced at equal nm related to cZrO2 phase. The absorbance of the UV spectrum for the cZrO2 processed through MRP tech nique was higher than the absorbance spectrum of mZrO2 powders processed by the CP and CGC methods. This could be attributed to the higher symmetry in cubic system pared with the monoclinic one. It is well known that ZrO2 is a direct band gap insulator with two band to band transitions. The spectrum has relatively weak absorption in the nearUV and visible region. The absorption behavior could arise from transitions involving extrinsic states such as surface trap state or defects. The energy values corresponding to the forbidden energy levels (Eg ), band gap energy of the cZrO2 powder is higher than mZrO2 powders, respectively. The obtained data agree with the information of Botta et al. (1999) that showed that the band gap energy for cZrO2 (– eV) is higher pared with mZrO2 (– eV) and tZrO2 (– eV). It is well known that the FTIR spectrums are very use ful