Laine R M, Marchal J C, Sun H P, Pan X Q
Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2136, USA.
Nat Mater. 2006 Sep;5(9):710-2. doi: 10.1038/nmat1711. Epub 2006 Aug 6.
Nanometre-sized particles of transition (t)-aluminas are important for the fabrication of high-quality alumina ceramics. Multiple tons are produced each year using a variety of gas-phase processes. The nanoparticles produced by these methods consist mainly of the undesired delta phase with some gamma- and theta-Al(2)O(3). Nano-t-aluminas should provide access to dense nano/submicrometre-grained alpha-Al(2)O(3) shapes offering significant advantages over micrometre-grained shapes. Unfortunately, polymorphism coupled with the high activation energy for nucleating alpha-Al(2)O(3) greatly impedes efforts to process dense alpha-Al(2)O(3) with controlled grain sizes, especially for submicrometre materials. Typically alpha-Al(2)O(3) nucleation within t-aluminas is sporadic rather than uniform, leading to exaggerated grain growth and vermicular microstructures without full densification (5). Thus, production of quantities of nano-alpha-Al(2)O(3) from multiple nano-t-aluminas for seeding or direct processing of alpha-Al(2)O(3) monoliths could greatly change how alpha-Al(2)O(3) components are processed. We report here that liquid-feed flame spray pyrolysis of nano-t-aluminas converts them to dispersible 30-80 nm alpha-Al(2)O(3) powders (50-85% phase transformed). Surprisingly, the powder surfaces are fully dehydrated. These powders pressureless sinter to more than 99.5% dense alpha-Al(2)O(3) with final grain sizes < or =500 nm without sintering aids.
纳米级过渡（t）-氧化铝颗粒对于高质量氧化铝陶瓷的制造至关重要。每年通过各种气相工艺生产数吨此类颗粒。这些方法生产的纳米颗粒主要由不希望有的δ相以及一些γ-和θ-Al₂O₃组成。纳米t-氧化铝应能制备出致密的纳米/亚微米级晶粒α-Al₂O₃形状，与微米级晶粒形状相比具有显著优势。不幸的是，多晶型现象以及α-Al₂O₃成核的高活化能极大地阻碍了制备具有可控晶粒尺寸的致密α-Al₂O₃的努力，尤其是对于亚微米材料。通常，t-氧化铝内的α-Al₂O₃成核是零星的而非均匀的，导致晶粒过度生长和蠕虫状微观结构，且无法完全致密化（5）。因此，从多种纳米t-氧化铝生产大量纳米α-Al₂O₃用于α-Al₂O₃整体材料的晶种或直接加工，可能会极大地改变α-Al₂O₃部件的加工方式。我们在此报告，纳米t-氧化铝的液体进料火焰喷雾热解将它们转化为可分散的30 - 80 nm的α-Al₂O₃粉末（50 - 85%相转变）。令人惊讶的是，粉末表面完全脱水。这些粉末在无烧结助剂的情况下无压烧结至密度超过99.5%的α-Al₂O₃，最终晶粒尺寸≤500 nm。
