纳米Al_2O_3前驱体形貌对烧结温度的影响及转型机理分析

Impact of Nano Al_2O_3 Precursor Morphology Herphology on Sintering Temperature and Transformation Mechanism Analysis

为了揭示纳米Al2O3的转型机理,对水热中间产物γ-AlOOH进行了热失重分析及烧结试验。差热分析结果表明,前驱体形貌不同,发生转型所需要的温度也不同,其块粒状在发生γ-AlOOH转型时较须状和片状所需温度要低;烧结实验结果也表明,不同形貌的前驱体相变实际转型温度也存在一定出入。为了深入揭示烧结转型机理,运用先进的"RTO金属包埋切片微米-纳米表征法",对烧结产物做了单颗粒切片分析,观测了不同晶型的氧化铝的微观晶体结构,从原子迁移的角度揭示了烧结行为过程,推测了不同形貌的纳米氧化铝在转型过程中的晶格转换模式,阐明了各种形貌的前驱体在烧结过程中的晶体转型机理。分析结果表明,氧化铝由低温相变(如γ-AlOOH与γ相之间的转变)时,其过程只涉及到原子在晶体结构中的短程重排,得到的γ-Al2O3可以保持原来前驱体的纳米形貌。但当煅烧温度超过临界温度1 000℃时,也即发生高温转型时,须状或片状前驱体就会相互聚集,形成具有网状或蛭石状的α-Al2O3;而块粒状的则发生团聚,形成不规则的六方晶格的α-Al2O3;此外,烧结产物形貌也都存在不同程度的部分折断或粘连现象。

Thermogravimetic analysis and sintering test of intermediate products in earlier stage of hydrothermal γ-AlOOH were conducted.The result of differential thermal analysis shows that for precursors with different morphologies,the temperature required by transformation was also different.The transformation temperature of granular γ-AlOOH was lower than those of whisker and flake γ-AlOOH.And the result of sintering experiments also found the difference in sintering temperature.To explain this phenomenon,this paper used advanced ‘RTOmetal embedding sectioning micron and nanometer characterization method＇to analyse single particle section of sintering product,observed the micro crystal structure of alumina with different crystal form,revealed the process of sintering behavior fromthe angle of the atomic migration,speculated the lattice conversion mode of nanometer aluminium oxide with different morphologies in the process of transformation,and clarified the crystal transformation mechanism of precursor with different morphologies in the process of sintering.It can be concluded that γ-Al2O3 can preserve its nano morphology because the process of low temperature phase transition of alumina only involves atom＇s short-range rearrangement in the crystal structure.But when the calcination temperature is over a critical temperature of 1 000℃,fibrous or flaky nano alumina aggregates,forming meshy and Vermiculite α-Al2O3 ;and granular alumina reunites and forms irregular hexagonal lattice α-Al2O3.In addition,partial breaking and adhesion occur in sintering products.