Kinetic instability of nanocrystalline aluminum prepared by chemical synthesis; Facile room-temperature grain growth
Kinetic instability of nanocrystalline aluminum prepared by chemical synthesis; Facile room-temperature grain growth
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DOI：
10.1021/ja981972y
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发表时间：
1998-10-28
影响因子：
15
通讯作者：
Buhro, WE
中科院分区：
文献类型：
--
作者：
Haber, JA;Buhro, WE
采用两种化学方法合成了纳米铝（纳米铝）。方法A包括以下内容：LiAlH(4)和AlCl(3)在1,3,5-三甲基苯中164℃反应生成平均相干长度（晶粒尺寸）为160 +/- 50 nm的纳米al。副产物LiCl通过在-25℃或0℃下用MeOH洗涤去除。方法B包括以下内容：纳米Al通过在1,3,5-三甲基苯（约100-164℃）中回流分解H(3)Al（NMe(2)Et）产生，有或没有添加分解催化剂Ti(O-i-Pr)(4)。在这里，纳米al的平均粒径（40-180 nm）和聚集度取决于所使用的分解催化剂的摩尔百分比（0-1%）。A法制备的纳米铝中C、O、Cl各含3-4 wt %；而方法B制得的C、O和Cl各只含有小于或等于0.25 wt %的C， O和Cl各含有大于或等于99 wt %的al。两种方法制得的纳米al在250、100或300℃的单轴压力下，在350 MPa下压实1小时，可以观察到方法B制得的粉末在每个压实温度下都有快速晶粒生长。在25℃下，平均晶粒尺寸在1小时内翻倍，并在更长时间内继续增加到纳米级以上。化学合成的（方法b）纳米al的低温晶粒尺寸不稳定性与气体冷凝或机械摩擦制备的纳米al的高温稳定性（大于或等于300℃）形成明显对比。化学合成的纳米al（方法b）晶粒生长迅速，归因于更高的晶界纯度和聚集体结构，最大限度地减少了意外氧化。结果表明，纯纳米al的晶粒生长障碍本质上是低的。
Nanocrystalline aluminum (nano-Al) is synthesized by two chemical methods. Method A consists of the following: reaction of LiAlH(4) and AlCl(3) at 164 degrees C in 1,3,5-trimethylbenzene produces nano-Al with an average mean coherence length (crystallite size) of 160 +/- 50 nm. The byproduct LiCl is removed by washing with MeOH at -25 or 0 degrees C. Method B consists of the following: nano-Al is produced by decomposition of H(3)Al(NMe(2)Et) under reflux in 1,3,5-trimethylbenzene (ca. 100-164 degrees C), with or without added decomposition catalyst Ti(O-i-Pr)(4). Here the mean particle size (40-180 nm) and degree of aggregation of the nano-Al depend on the mole percent of decomposition catalyst used (0-1%). The nano-Al produced by method A contains 3-4 wt % each of C, O, and Cl; whereas that produced by method B contains only less than or equal to 0.25 wt % each of C, O, and Cl and is greater than or equal to 99 wt % Al. nano-Al produced by both methods has been consolidated by uniaxial pressing at 350 MPa for 1 h at 25, 100, or 300 degrees C Rapid grain growth is observed at each pressing temperature in method-B powders. The mean grain size doubles at 25 degrees C within 1 h and continues to increase beyond the nanometer-size regime over longer periods. The low-temperature grain-size instability of the chemically synthesized (method-B) nano-Al contrasts markedly with the high-temperature stability (greater than or equal to 300 degrees C) of nano-Al prepared by gas condensation or mechanical attrition. Facile grain growth in the chemically synthesized (method-B) nano-Al is attributed to higher grain-boundary purity and to aggregate structures that minimize adventitious oxidation. The results establish that barriers to grain growth in pure nano-Al are intrinsically low.