CN101778683A - 由阀金属和阀金属低氧化物组成的纳米结构及其制备方法 - Google Patents
由阀金属和阀金属低氧化物组成的纳米结构及其制备方法 Download PDFInfo
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Abstract
本发明描述了新型带状或板状阀金属和阀金属氧化物结构,其具有5-100nm的横向尺寸。
Description
技术领域
本发明涉及在一个方向上的尺寸小于100nm的阀金属(valve metal)和阀金属低氧化物的新型片层结构及其制备方法。
背景技术
由于具有大比表面积,粉末或较大金属基材的表面区域中存在的由金属和金属低氧化物组成的精细结构具有广泛应用,可用作催化剂、催化剂载体材料,用于膜和过滤器技术,在医学领域用作植入材料,在蓄电池中用作存储材料,用作电容器的阳极材料。
WO 00/67936披露了通过用气态还原性金属如Mg、Al、Ca、Li和Ba还原阀金属氧化物粉末制备精细阀金属粉末的方法。由于氧化物还原为金属时体积收缩,而还原性金属形成固体氧化物时引起体积增加,所以形成了具有高比表面积的高孔阀金属粉末,它特别适用于制备固体电解质电容器。
现在已经发现,在特定还原条件下形成纳米范围横向尺寸的片层结构,所形成的片层初始包含由被还原的阀金属氧化物和被氧化的还原性金属交替构成的层。
还原性金属的氧化物在无机酸中溶解和浸出,使纳米尺寸的阀金属结构能够脱离还原性金属的氧化物的束缚。
根据初始阀金属氧化物的几何结构情况,可得到具有片层结构的精细粉末,或者在具有较粗/大结构的金属基材上得到具有带状或片层表面结构的精细粉末,其中金属和/或低氧化物带或层具有小于100nm的宽度,间距(中间空隙)可达带宽的两倍,具体取决于阀金属氧化物及其所达到的氧化态。
因此,当使用初级结构的平均粒径为50-2000nm、优选小于500nm、更优选小于300nm的精细阀金属氧化物粉末时,可得到具有片层结构、金属或低氧化物带宽为5-100nm、优选8-50nm、特别优选最多30nm,横向尺寸为40-500nm,比表面积超过20m2/g、优选超过50m2/g的精细金属或低氧化物粉末。
当使用具有上述尺寸例如10μm的较大阀金属氧化物基材时,可在这些结构上得到宽度最多达100nm、优选5-80nm、特别优选8-50nm、更优选最多达30nm,间距1-2倍于带宽的金属或低氧化物带。带之间的凹槽深度可达1μm。
发明内容
先通过化学方法或阳极化方法氧化表面,再根据本发明还原表面,可得到具有带状表面的较大金属结构或基材,例如金属丝或箔,其中带深取决于初始产生的氧化层的厚度。
此外,本发明的结构可通过以下方式得到:提供包含例如另一种含阀金属氧化物层的金属或陶瓷的基材,例如通过气相沉积或电解沉积施涂阀金属层,然后氧化该涂层,根据本发明将其还原为金属或低氧化物。
满足本发明目的的阀金属氧化物可以是元素周期表中第4-6族过渡元素的氧化物,例如Ti、Zr、V、Nb、Ta、Mo、W和Hf的氧化物及其合金(混合氧化物),还有Al的氧化物,优选Ti、Zr、Nb和Ta的氧化物,特别优选Nb和Ta的氧化物。作为起始氧化物,特别优选的是Nb2O5、NbO2和Ta2O5。本发明的优选反应产物是起始氧化物的金属。作为还原产物,也可得到起始阀金属氧化物的低级氧化物(低氧化物)。特别优选的还原产物是具有金属导电性的铌低氧化物,其化学式为NbOx,其中0.7<x<1.3,除钽和铌外,所述还原产物也适合用作本发明电容器的阳极材料,特别适合在最高为10V、特别优选最高为5V、尤其是最高为3V的低活化电压范围使用。
根据本发明,可用的还原性金属有Li、Mg、Ca、B和/或Al及其合金。优选Mg、Ca和Al,只要这些金属没有起始氧化物中的金属那么贵。特别优选Mg或Mg与Al的低共熔体。
本发明的还原产物的一个特性是,由于还原过程中发生掺杂,还原金属的含量在高于10ppm、特别是50-500ppm的范围内。
可用来产生纳米级结构的本发明方法基于如WO 00/67936所述用气态还原性金属还原金属氧化物。在此,是在反应器中使粉状待还原阀金属氧化物与还原性金属蒸气接触。使还原性金属气化后,通过载气流如氩气将其传送到存在于网或舟上的阀金属氧化物粉末上,网或舟的温度通常为900-1200℃的较高温度,处理时间通常为30分钟至数小时。由于阀金属氧化物的摩尔体积是相应阀金属的体积的2-3倍,所以在还原过程中体积显著减小。因此,在还原中形成海绵状高孔结构,其中沉积有还原性金属的氧化物。由于还原性金属的氧化物的摩尔体积大于阀金属氧化物与阀金属的摩尔体积之差,所以它们结合到孔中,产生残余应力。通过溶解这些氧化物,可使所述结构摆脱还原性金属的氧化物的束缚,从而得到高孔隙金属粉末。对还原机理和孔的形成及其分布所进行的研究表明:在反应初始阶段,从阀金属氧化物微粒或基材表面上的细小反应核开始,在阀金属/阀金属氧化物反应前沿后面形成具有纳米尺寸的层状结构。所述层首先在微粒/基材靠近表面的区域以垂直于该表面取向。然而,当反应前沿深入氧化物微粒/基材时,片层的取向和尺寸取决于阀金属氧化物中初级微粒的晶体取向和尺寸以及反应条件。阀金属氧化物微晶中一定数目的晶格平面被在化学计量上相等数目的阀金属和还原性金属氧化物的晶格平面取代。由于存在高界面应力,这些纳米尺寸的层结构从能量角度看实际上是非常不利的,但由于还原过程是强放热过程,且至少部分过剩的能量没有以热的形式散失,而是“投入”结构的形成,使快速反应从动力学上成为可能,所以所述层结构的产生也变得可能,并且成为现实。层结构中的众多平坦界面成为还原性金属原子的“快速公路”,也就是说,它们使金属原子快速扩散,从而有利于反应动力学,使反应体系的总能量快速而有效地减少。然而,由阀金属和还原性金属氧化物组成的层状结构只是形成亚稳态,在引入热能后,它才形成具有更低能量的结构态。当在较长热处理时间和稳定反应条件(温度、还原金属的蒸气压力等)下“正常”进行还原过程时,此结构转变不可避免地发生,即纳米层结构转化为由阀金属区和还原金属氧化物区组成的大大粗化、互穿的结构。
现在已经发现,若谨慎行事,确保在发生结构转变之前,将还原产物冷却到片层结构可保持稳定的温度,就能将该片层结构冻结。因此,根据本发明,适当设定还原条件,使还原在短时间内非常均匀地进行,也就是说,若在氧化物粉末床内使用粉状起始氧化物,在还原完成之后尽可能立即迅速冷却还原产物。
因此,优选采用厚度较小的粉末床,以确保还原性金属蒸气从床中均匀透过。粉末床的厚度特别优选小于1cm,更优选小于0.5cm。
此外,通过为还原性金属蒸气提供长的自由路径长度,可确保还原性金属蒸气从粉末床中均匀透过。因此,根据本发明,还原优选在减压下进行,更优选在无载气的情况下进行。还原特别优选在10-2-0.4巴、更优选0.1-0.3巴的还原金属蒸气压和无氧条件下进行。在没有不利影响的情况下,最高0.2巴、优选小于0.1巴的低载气压力是可接受的。特别合适的载气是惰性气体如氩气和氦气和/或氢气。
由于沿着还原金属片层与在金属片层间形成的还原金属氧化物之间的界面的扩散路径越来越长,片层结构深度的增幅随着深度的增加而下降。已经发现,在还原过程中,当深入材料最高达1μm时,片层结构基本上不发生转变。
因此,根据本发明,优选使用初级结构微粒的最小横截面尺寸(微晶尺寸)不超过2μm、优选不超过1μm、特别优选平均不超过0.5μm的阀金属氧化物粉末。若初级结构大致具有较小的尺寸,则可以多孔烧结团聚体形式使用阀金属氧化物粉末。同样有利的是,将初级微粒强烈地烧结到一起,但在团聚的初级微粒之间存在分级结构化开孔网络,这样,开孔的孔径分布使还原性金属蒸气有可能直接接触很大一部分初级微粒表面,并将其还原。
相邻初级微粒之间的颗粒边界也可加速扩散,尽管它们不如孔道那么有效。因此,除形成细小的初级微粒和聚集的阀金属氧化物微粒中的开放孔隙外,在初级微粒之间形成很高比例的颗粒边界是有利的。这一点可通过以下方式实现:在氧化物前体以氢氧化物沉淀和焙烧该氢氧化物成阀金属氧化物时,优化初级微粒尺寸和烧结条件。焙烧优选在400-700℃的温度下进行。焙烧温度特别优选500-600℃。
在制备具有片层表面结构的金属箔或丝时,优选使用表面具有厚度小于1μm、优选小于0.5μm的氧化层的金属箔或丝。
根据所用还原性金属蒸气或金属蒸气混合物及其蒸气压力,在低于大气压的压力下还原数分钟至数小时、优选约10-90分钟之后,通过中断还原性金属蒸气的供应使还原停止,迅速将被还原的阀金属冷却到低于100℃,以稳定各层阀金属或阀金属低氧化物和还原性金属氧化物的纳米片层结构。烧结具有不同取向的相邻片层结构而带来稍许粗化是可接受的。冷却可通过例如快速增加压力来进行,加入保护性气体(冷却气体)、优选氩气或氦气可导致压力增加。优选在3分钟内冷却至300℃,然后在3分钟内进一步冷却至200℃,再在5分钟内进一步冷却至100℃。
根据本发明,优选在较低温度下进行还原,以最大程度减少纳米片层结构的粗化。待还原阀金属氧化物的温度优选为500-850℃,更优选低于750℃,特别优选低于650℃。在此,由于还原反应的放热特性,还原开始时的实际温度可能显著超出上述范围。
在本发明中,可采取多种措施避免由起初在还原过程中形成的反应产物和被氧化的还原性金属组成的纳米片层结构分解和粗化,这些措施可作为替代措施使用或者组合使用。
例如,在高还原温度下,通过例如使用小的起始金属氧化物粉末床和/或减小载气压力的方式提供快速、有效地接触还原性金属蒸气,即增长还原性金属蒸气原子的自由路径长度,足以确保较短的还原时间。
另一方面,在低还原温度下,较长的还原时间是可接受的。
若起始阀金属氧化物粉末团聚体具有有利的开放孔结构,为获得本发明的片层结构而所需的烧结处理条件就没那么严格。
在还原过程结束,且通过逐步加入氧气或空气来冷却被还原的阀金属氧化物并使其呈惰性之后,可借助例如无机酸如硫酸或盐酸或其混合物将被包封的还原性金属氧化物从所得纳米结构中浸出,并用软化水洗至中性,然后干燥。
在还原精细粉末的情况下,这些粉末包含具有片状初级结构的微粒,所述微粒部分以枝状形式相互融入。
还原性金属氧化物浸出之后,现在处于独立状态的阀金属的片层结构保持几何稳定,因为它们借助各层端部充分烧结到取向一般不同的相邻片层结构中。原来的(多晶)阀金属氧化物微粒由此转化为聚集的阀金属微粒,其初级微粒包含具有不同取向的多组层结构,它们相互烧结到一起。这样,总体上就形成了稳定的互穿的金属结构和“平”孔。
图1显示了实施本发明方法的装置的示意图。一般通过标记1表示的反应器具有还原室2。标记3表示包含加热盘管和冷却盘管的温度控制器。保护性气体或冲洗气体或冷却气体沿箭头4所示方向经阀引入还原室。沿箭头5所示方向抽空还原室或抽出气体。还原室2与蒸发室6连接,在蒸发室6中提供独立的加热装置7用于还原性金属。蒸发室和还原室借助阀区(valve region)8实现隔热。待还原的阀金属氧化物以薄粉末床形式装在舟10中。若使用阀金属氧化物箔或丝,或者使用其表面由阀金属氧化物组成的箔或丝,则它们优选垂直悬挂,并与还原性金属蒸气在还原室内的流动方向平行。将舟9中的还原性金属加热至一定温度,提供所需蒸气压力。
以高5mm的床的形式将氧化物粉末装在舟中。将装有镁屑的舟放入蒸发室。用氩气冲洗反应器。然后,将还原室加热至还原温度,并抽空至0.1巴的压力。随后将蒸发室加热至800℃。镁蒸气压(静态)约为0.04巴。30分钟后,停止加热还原室和蒸发室,将已通过从200巴减压而冷却的氩气通入,再通过还原室一段时间。同时,用水冷却还原室壁。
图2、3和4显示了钽粉的不同放大倍数的透射电子显微图,所述钽粉根据本发明通过聚焦离子束制备还原产品后已经还原。图中深色条纹是钽片层,浅色条纹是氧化镁片层。片层结构的不同取向对应于起始五氧化钽的不同微晶取向。
Claims (14)
1.带状或板状阀金属和阀金属低氧化物结构,其具有5-100nm的横向尺寸。
2.如权利要求1所述的阀金属和阀金属低氧化物结构,其特征在于,其具有粉末形式的板状或层状初级结构。
3.如权利要求1所述的阀金属和阀金属低氧化物结构,其特征在于,其形式为表面带结构。
4.如权利要求3所述的阀金属结构,其特征在于,其形式为具有带的箔或丝,带宽为5-100nm,带间距为带宽的1-2倍。
5.如权利要求1-4中任一项所述的阀金属和阀金属低氧化物结构,其特征在于,所述带或片层分组平行对齐。
6.如权利要求1-5中任一项所述的阀金属和阀金属低氧化物结构,其特征在于,所述横向尺寸或带宽为8-50nm。
7.如权利要求1-6中任一项所述的阀金属结构,其特征在于,其包含Ti、Zr、V、Nb、Ta、Mo、W、Hf或Al,特别是Nb或Ta,或其合金。
8.如权利要求1-6中任一项所述的阀金属低氧化物结构,其特征在于,其具有化学式NbOx,其中0.7<x<1.3。
9.如权利要求1-8中任一项所述的阀金属和阀金属低氧化物结构,其特征在于,至少一种还原性金属的含量为10-500ppm。
10.一种在足以进行还原的温度下,通过还原性金属蒸气将阀金属氧化物还原形成片层纳米结构的方法,其特征在于,在片层结构发生热分解和转化为粗化结构之前,冻结被还原的阀金属氧化物。
11.如权利要求10所述的方法,其特征在于,所述还原在小于0.2巴的惰性气体压力下、10-2-0.4巴还原性金属蒸气压力的条件下进行。
12.如权利要求10或11所述的方法,其特征在于,还原完成之后,立即在数分钟之内将还原产物冷却至低于100℃。
13.如权利要求10-12中任一项所述的方法,其特征在于,用Li、Al、Mg和/或Ca,特别是Mg作为还原性金属。
14.如权利要求10-13中任一项所述的方法,其特征在于,用Al、Hf、Ti、Zr、V、Nb、Ta、Mo和/或W的氧化物及其混合氧化物,特别是Nb或Ta的氧化物作为待还原氧化物。
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JP4788880B2 (ja) * | 2005-07-22 | 2011-10-05 | 独立行政法人物質・材料研究機構 | バルブ金属酸化物ナノ構造体の製造方法 |
US7988760B2 (en) * | 2007-03-13 | 2011-08-02 | Global Tungsten & Powders Corp. | Method of making nanocrystalline tungsten powder |
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2008
- 2008-07-23 US US12/673,559 patent/US20110123822A1/en not_active Abandoned
- 2008-07-23 WO PCT/EP2008/059659 patent/WO2009021820A1/en active Application Filing
- 2008-07-23 RU RU2010109437/02A patent/RU2493939C2/ru not_active IP Right Cessation
- 2008-07-23 JP JP2010520521A patent/JP5542672B2/ja not_active Expired - Fee Related
- 2008-07-23 CN CN201510198881.7A patent/CN104889381A/zh active Pending
- 2008-07-23 EP EP08786351A patent/EP2188081A1/en not_active Withdrawn
- 2008-07-23 MX MX2010001586A patent/MX2010001586A/es active IP Right Grant
- 2008-07-23 KR KR1020107003852A patent/KR101530727B1/ko not_active IP Right Cessation
- 2008-07-23 CN CN200880103432A patent/CN101778683A/zh active Pending
- 2008-08-15 TW TW097131058A patent/TWI477437B/zh not_active IP Right Cessation
Patent Citations (1)
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CN1892166A (zh) * | 2005-07-01 | 2007-01-10 | 松下电器产业株式会社 | 热交换器用铝箔、其制造方法及使用其的热交换器和空调 |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN106623980A (zh) * | 2016-09-18 | 2017-05-10 | 华南理工大学 | 一种金属钼纳米片的制备方法 |
CN106623980B (zh) * | 2016-09-18 | 2019-06-18 | 华南理工大学 | 一种金属钼纳米片的制备方法 |
Also Published As
Publication number | Publication date |
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RU2493939C2 (ru) | 2013-09-27 |
KR101530727B1 (ko) | 2015-06-22 |
TWI477437B (zh) | 2015-03-21 |
EP2188081A1 (en) | 2010-05-26 |
KR20100065280A (ko) | 2010-06-16 |
US20110123822A1 (en) | 2011-05-26 |
JP5542672B2 (ja) | 2014-07-09 |
TW200927641A (en) | 2009-07-01 |
MX2010001586A (es) | 2010-03-15 |
CN104889381A (zh) | 2015-09-09 |
JP2010537040A (ja) | 2010-12-02 |
WO2009021820A1 (en) | 2009-02-19 |
RU2010109437A (ru) | 2011-09-27 |
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