Nanostructured Metallic Alloys - Materials for the Future

Recent advancements in the field of nano-technology focused attention on developing materials with new and useful characteristics. In particular, there is interest in designing nanocomposite thermites for self-propagating high-temperature synthesis (SHS) applications. The composite material consists of nano-scale particles that are in nearly atomic scale proximity but constrained from reaction until triggered. Once initiated, the reaction will become self-sustaining and a new intermetallic alloy product will be produced¹。

这些材料由含亚博网站下载有纳米级金属，金属氧化物和/或有机和无机聚合物粘合剂的混合物组成，并用于重叠的技术，这些技术范围从材料合成范围¹to local energy generation applications²。For example, when a reactant mixture is ignited to produce a new material, the combustion synthesized product can be useful as a biomaterial³或反应物可以定制以合成耐腐蚀的高温金属合金⁴。When the reaction is significantly exothermic and results in rapid flame propagation, the reactant mixture can be tailored to generate energy for industrial, civil or military applications⁵。

这篇简短的文章重点是纳米结构金属合金中未来机会的例子，但是有相对较大的文献基础报道了纳米与微米（传统尺寸）颗粒的独特行为的观察结果yabo214^1-15。

While some of the fundamentally unique observations specific to nanoparticles are just now being realized, these developments can be exploited to help researchers address current critical issues such as energy generation applications, biomaterials for bone implants and skeletal repair, and the spread and transfer of infectious bacteria and molds.

当单个燃料和氧化剂颗粒接近纳米尺寸时，纳米颗粒的热和燃烧行为是独一无二yabo214的，因为启动反应所需的能量实际上可以存储并堆积在颗粒中。这些储能配方由燃料金属纳米颗粒组成，与金属或金属氧化物纳米颗粒组合，称为纳米气体yabo214¹⁶。

当颗粒保持在惰性状态时，纳米充电器将能量存储，并且在触发时，发生的缓慢反应由yabo214质量传输和彼此扩散反应物所需的能量控制。点火会导致缓慢控制的自我传播，高温化学能向热能的转化。纳米颗粒的独特的热，机械化学和燃烧性能是这种创新概念的基础：在纳米充电器中使用纳米颗粒燃料和氧化剂复合材料作为反应物，该反应物将储存和提供按需yabo214储存能源。

图1显示了来自IR摄像机的时间戳记的仍然框架的图像，表明纳米样品的能量储存的能量比微米复合材料长46秒。纳米充电器可以描述为电池和熔融盐之间的交叉。反应物获得了熔融盐的相似热惯性特性（启用储存），但能量输送基于化学反应，更类似于电池。延长热能可能对某些形式的可再生能源（例如太阳能热力）有用。这样，白天存储在纳米充电器中的热能很容易在傍晚时分传递，当太阳不发光时¹⁶。

图1: Infrared thermal images time stamped for nanometric particulate mixtures and micrometer particulate mixtures composed of Al/Mn. (Adapted from [16]).

In the field of combustion synthesis, much work has been done to generate porosity by adding blowing agents to the reactant matrix and Moore et al. provide a review of much of this literature^17-18。A foam-type product can be created when a mildly energetic composite includes a modest amount of gasifying agent (GA). During a reaction the gasifying agent generates nucleation sites that promote the formation of bubbles. As the reaction wave passes, the gas pockets within the bubbles escape leaving a porous structure.

在先前的燃烧合成研究中，可以将气化剂添加为单独的反应物，通常以粉末或颗粒状材料的形式添加¹⁹。This strategy was shown to be highly successful for synthesizing ceramic materials for biological applications¹⁵。但是，将吹剂掺入合成金属合金并未被广泛追求，但最近已证明使用纳米颗粒是可行的yabo214¹⁵。Control over properties of the final product, such as porosity, can be achieved by tailoring reactant composition. In 2006, combustion synthesis was used to form porous nickel aluminide and showed that the porosity of the final product is a function of the percentage of gasifying agent present in the reactant matrix¹⁵。

如今，这项工作已扩展以了解合成多孔钛合金（ALTI）合金的机制，以创建轴向分级的孔隙率分布。金属泡沫是通过自传播的高温反应来合成的，该反应产生具有可定制材料特性的高度多孔固体金属合金。纳米尺度铝和纳米级钛颗粒与用气体级铝制的纳米级铝混合，用气体量（如纯氟烷基羧酸）（C）（Cyabo214₁₃F₂₇COOH) or polytetrafluoroethylene (Teflon) (C₂F₄） 粒yabo214子。当压入颗粒并用激光点火时，它们会产生由具有高度多孔结构的Alti合金组成的反应产物。

这样，燃烧合成可用于创建功能分级的多孔Alti合金，并识别产品微结构与参数（例如反应物中存在的气化剂的类型和量）之间的相关性。摄影数据允许解释反应传播，而最终产物的表征表示孔隙度和形态。这些纳米结构的金属合金可能通过在整个基质中调整孔隙度来在生物材料开发中应用。图2显示了该Alti合金的扫描电子显微照片（SEM）。

图2：Alti纳米结构金属合金的SEM。

Bacterial contamination in hospitals, food industries, and public environments create a major public health issue. Despite considerable research and development efforts, the problem of contaminations related to biomedical devices and food preparation persists. Traditional cleaning methods, such as aerosolized disinfectant sprays or wipes have a limited effectiveness. There is a strong need to mitigate bacterial colonization by engendering materials with properties that include surface chemistry^20-22and surface roughness^23-25which are unfavorable for bacterial attachment and growth. Silver has been used for years in many bactericidal applications because of its strong toxicity to a wide range of micro-organisms^20-27。

Research has shown that the bactericidal properties of silver are size dependent, and only nanoparticles present a direct interaction with the bacteria²²。Titanium dioxide (TiO₂）has also become a popular agent for bacterial neutralization. Several commercial products have been developed that incorporate nanoparticles of TiO₂用于抗菌应用²⁸。

高度多孔的抗菌固体金属合金（或泡沫）可以通过燃烧合成产生。通过结合纳米级氧化银（Ag₂O) or TiO₂particles with Aluminum (Al) nano-scale particles, the reaction can produce a self-propagating heat wave that will synthesize metallic foams made of pores only nanometers wide that inherently exhibit antibacterial properties. The extraordinarily high surface areas these foams possess serve as an excellent platform for the neutralization of bacteria. These newly synthesized alloys present a novel approach to bacterial neutralization.

图3显示了在24和48小时接受细菌生长试验的纳米结构金属合金。。细菌生长以白色圆圈突出显示。图3D显示了暴露前后的对照样本。

图3：暴露后基于Al的金属泡沫A。Ag2o;B. Nano Tio2; C. micron Ag2o;D.控制。

Five important conclusions can be drawn from these results.

1. 燃烧合成可用于创建具有抗菌特性的纳米结构金属合金。
2. Bacteria growth kinetics are a function of reactant particle size.
3. 纳米级反应物在中和细菌方面更有效。
4. TIO₂particles can delay, but not prevent bacterial growth, and;
5. 由纳米级AL和AG组成₂O prevent growth of bacteria.

这些纳米结构的金属合金可以通过燃烧合成来轻松作为结构材料或金属涂层创建，并且在可再生能源，食品服务和医疗行业中具有深远的应用。纳米结构的金属合金确实是未来的材料。

参考

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