A false color scanning electron micrograph (250,000-times magnification) shows gold nanoparticles created by the U.S. National Institute of Stan- dards and the National Cancer Institute’s Nanotechnology Characterization Laboratory for use as reference standards in biomedical research labs.
didn’t think it was possible to keep nanoparticles uniformly dispersed in molten metal as it undergoes solidification. “It was difficult to con- vince others that nanopar- ticles would be so effective [in metalcasting] because a lot of traditional scientific study showed that it would be difficult to trap a particle that is so small,” Li said. “Most nanotechnology in metals relies on powdered metal and sintering, not solidification. Tey think solidification will push nanotechnology out. Well, some particles will be pushed out, but some will stay.” In the U.S., more than $10 million has been budgeted for
research in nanocomposite casting technology through 2015 with a grant from the U.S. National Institute of Standards and Technology and matching funding from team partners. Te new commitment to nanocomposite research in metal- casting could mean the technology will be production-ready soon, according to Dave Weiss of research partner Eck Industries, Manitowoc, Wis. “We think this is something that could be reasonable to
go into production at least in some products in three to five years,” Weiss said. “It’s definitely not pie in the sky anymore.”
Particles Pack a Punch
Nanoparticles bridge bulk material with atomic or molecular structures. While bulk material, such as alumi- num, has constant physical properties regardless of size, at the nanoscale, size does matter. Te properties of a material change as it gets incredibly small. Researchers are studying ways to achieve specific properties, such as high strength, found in materials at the nano-scale while maintaining the properties inherent in the bulk material. According to
张伪彩色电子显微照片（放 大250000倍）显示被美国国 家标准技术研究所和美国癌 症研究所的纳米技术实验室 制备出来的黄金纳米颗粒被 用作生物医学研究实验室的 参照标准。
“很难说服其他人相 信纳米颗粒（在金属铸件 中）会如此有效，因为很 多传统学说认为纳米颗粒 太小了很难捕获，”李教 授说：“大部分应用于金
属上的纳米技术依靠粉末金属烧结，而不是凝固，他们 认为凝固将使纳米技术靠边站。是的，一些颗粒会被推 挤出来，但是一些颗粒会发挥作用”。截止到2015年， 美国国家标准技术研究所拨款超过1千万美元用于研究 纳米复合材料铸件，其他合作团队也提供了配套资金。 按照威斯康辛州Manitowoc的 Eck Industries公司Dave Weiss先生的说法，铸造中的纳米复合材料研究可能意 味着该技术很快将会投产。 Weiss先生说：“我们认为在三到五年内至少在一些 产品上该技术应该能够应用到生产中。这绝对不再是不 可奢望的事情了。”
颗粒块冲击
纳米颗粒连接成由原子或分子组成的块状材料。块 状材料，例如铝合金，它在尺寸变化时有恒定的物理性 能，在纳米级别，尺寸很重要。当材料变得很小时性能 会发生变化。研究人员正在想方设法将纳米颗粒中类似 高强度之类的优良性能转移到块状材料中。根据Weiss 的说法，现在通过在金属基复合材料中使用2%体积分 数的纳米颗粒已经使强度提高了100~120%。“很显
These cubes of cobalt (left), measuring about 50 nanometers wide, are showing scientists that on the nanoscale, a change in shape is a change in property. Unlike smaller spherical cobalt nanoparticles, nanocubes melt and fuse (right) when illuminated by a transmission electron mi- croscope and possess different magnetic characteristics than the nanospheres.
这些宽度在50纳米的钴立 方体（左）显示，在纳米级 别形状的改变将导致性能改 变。不像更小的球形钴纳米 颗粒，纳米立方体当被电子 显微镜点燃时熔化并融合， 它具有与纳米球体相比有更 好的磁性特性。
Fall 2011
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