The container materials (glass and Teflon) employed for reflux- digesting ZrO(OH)_2 gel in basic (NH_4OH: pH= 11.5, NaOH and KOH: pH = 13) solutions were shown to dramatically affect the texture, crystal phase and thermal stability of the ZrO(OH)2 and its calcined (600～800 °C) ZrO_2 products. Digestion in the glass container (G-preparation) led to prominent enhancement of the surface area, porosity and thermal stability of Zr0(OH)_2/ZrO_2 samples. And, the crystallization temperature on the sample DTA (differential thermal analysis) curves was shifted from ca. 460 t of the undigested ZrO( 0H)_2 to 800 ～840 ° C of the digested ones. These effects were independent of the nature of the employed bases (NH_4OH, NaOH and KOH), and small tetragonal crystallites (5～7 nm) were always obtained after the calcination at 800 °C . In comparison, little effects were observed for the samples digested in the Teflon container (T-preparation). Elemental analysis revealed that incorporation into ZrO(OH)_2 gel of SiO_2 impurity from the glass container happened during the digestion. The surface area and pore volume of the ZrO(OH)_2 and ZrO_2 samples increased linearly with the amount of Si~(4+) -ions in the solids. The incorporated Si4+ - ions prevented the crystallization of ZrO(OH)_2 up to temperature higher than 600 °C , but they induced a stabilization of very small (5-7 nm) tetragonal crystallites after the calcination at 800 t. This role of the Si~(4+) -impurity was further confirmed with authentic SKVeontaining ZrO(OH)_2 gels prepared by coprecipitation of ZrOCl_2 and Si(OC_2H_5)_4 in the Teflon container (ZS-preparation) , When there was no incorporation of Si~(4+)-ions (i. e. in the T- preparation), the incorporation of alkali ions from NaOH or KOH solution could result in formation of low surface area (65～70 m /g) ZrO(OH)_2 crystallites (ca. 20 nm) with mixed monoclinic and tetragonal phases. But, the incorporated alkali ions showed little effect on the texture and crystal size of the calcined (600～800 X,) ZrO_2. In addition, dehydration and dissolution-reprecipitation of ZrO (OH)_2 gel during the digestion also affected the texture and crystal size of ZrO_2 but the effect was much less important than the incorporation of Si~(4+) -ions.

Key words: HYDROGEL, ZIRCONIUM OXIDE, NANOPHASE MATERIALS, SILICON, DOPE, TEXTURE