【摘要】 通过考察回流老化所用的碱液 (NH4OH ,NaOH和KOH)介质和容器材质 (玻璃和Teflon)对ZrO(OH) 2 凝胶及其焙烧产物ZrO2 的织构 /结构和热稳定性的影响 ,研究了杂质元素掺杂和凝胶溶解 -再沉淀等因素在形成高表面积纳米晶ZrO(OH) 2 /ZrO2 过程中的作用 .在Teflon容器中 ,以NH4OH为介质 (pH =11.5 )的回流老化对ZrO(OH) 2 /ZrO2 的性质无明显影响 .而使用玻璃容器则可显著提高ZrO(OH) 2 /ZrO2 的表面积、孔容和抗烧结性质 ,并在 80 0℃获得小晶粒 (5～ 7nm)四方晶相ZrO2 纳米晶材料 ;在DTA曲线上ZrO(OH) 2 转变成ZrO2 晶体的温度由回流老化前的 463℃提高到 810～ 840℃ .在以KOH和NaOH为介质 (pH =13 )的实验中 ,使用玻璃容器得到与以NH4OH为介质时相类似的结果 ;但在Teflon容器中只形成低表面积和较大尺寸 (约 2 0nm)以单斜相为主的混合晶相ZrO(OH) 2 ,其在 80 0℃焙烧后形成大晶粒 (3 5nm)单斜相ZrO2 .样品的元素分析结果清楚地揭示出使用玻璃容器时有SiO2 从器壁溶解掺杂进入ZrO(OH) 2 凝胶 .样品的表面积和孔容与杂质Si4+ 含量之间有顺变关系 ,表明Si4+ 掺杂是形成高表面积和大孔容ZrO(OH) 2 /ZrO2 、提高ZrO2 晶化温度以及稳定小晶粒四方晶相ZrO2 的最主要因素 .在不发生Si4+ 掺杂前提下 ,K+ 和Na+ 的?更多还原

【Abstract】 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 ℃) ZrO 2 products. Digestion in the glass container (G preparation) led to prominent enhancement of the surface area, porosity and thermal stability of ZrO(OH) 2/ZrO 2 samples. And, the crystallization temperature on the sample DTA (differential thermal analysis) curves was shifted from ca. 460 ℃ of the undigested ZrO(OH) 2 to 800～840 ℃ 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 ℃. 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 Si 4+ ions prevented the crystallization of ZrO(OH) 2 up to temperature higher than 600 ℃, but they induced a stabilization of very small (5～7 nm) tetragonal crystallites after the calcination at 800 ℃. This role of the Si 4+ impurity was further confirmed with authentic SiO 2 containing 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 2/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 ℃) 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.更多还原