Inorganic Network Structures Exhibiting Unusual Negative Behaviours

表现出异常负面行为的无机网络结构

• 批准号: EP/C516591/2
• 负责人: Richard Walton
• 金额: --
• 依托单位: University of Warwick
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FC516591%2F2
• 关键词: Inorganic; Network; Structures; Exhibiting; Unusual

Most everyday materials will become thinner when stretched: for example, consider stretching an elastic band - you would picture the strip of rubber becoming narrower. Some, less common, materials behave rather differently, and when stretched actually become fatter: these materials are described as being auxetic. This is not just a scientific curiosity as auxetic materials have many technological applications in areas ranging from toughened engineering materials to nanotechnology (for example, an auxetic solid might act as a tuneable sieve on a molecular scale, because the network could expand to produce an open structure). Auxetic materials may be described as having 'negative behaviour': behaviour which is counterintuitive. A second type of negative behaviour is 'negative thermal expansion'. Here a material shrinks when it is heated, rather than expanding, as might be expected. As with auxetic behaviour, negative thermal expansion has many technological applications, for example, in making composite materials that show no expansion when heated. It is believed that the same fundamental processes can be responsible for these two negative behaviours. This, however, has not yet been proved, and in order to do so, experimental measurements must be made that probe both the structure of matter on an atomic scale, and the properties of large specimens, to relate the bulk properties of materials to atomic structure.Our proposal is to make these experimental measurements for the first time. We will focus upon one family of materials: the open-network silicates. These materials have been predicted by computer simulations to be auxetic, but this prediction has never been verified, although some also are known already to have negative thermal expansion properties. The silicates are commonly found as minerals in the Earth's crust, but in the laboratory we are able to make large crystals of the materials in a pure state; this is something that in the past has been difficult to do, but we have recently developed reliable methods to do so. The large crystals will be subjected to mechanical tests - literally stretching the specimens along different directions will allow us to measure their elastic properties and determine whether the proposed negative behaviour exists. Since we can study a large number of specimens with differing chemical compositions, we will be able to relate the chemistry of the material to the elastic properties, and then determine relationships between the of chemical composition of sample (that is atomic-scale properties) and its bulk elastic properties. We aim to use these results to verify computer predictions of auxetic behaviour and then understand why auxetic behaviour exists. The materials will also be studied for their thermal expansion properties: the question to address here is whether solids that possess auxetic behaviour also show negative thermal expansion. This has never been studied before. The proposed work is a collaboration between chemists and engineers and this interaction will be an ideal combination to achieve our aims: the chemists are experts in making new materials and understanding their structures, while the engineers study the elastic and mechanical properties of materials.

大多数日常材料在拉伸时会变得更薄：例如，考虑拉伸弹性带-你会想象橡胶条变得更窄。一些不太常见的材料表现得相当不同，当拉伸时实际上会变得更胖：这些材料被描述为拉胀材料。这不仅仅是一种科学好奇心，因为拉胀材料在从增韧工程材料到纳米技术的领域中具有许多技术应用（例如，拉胀固体可能在分子尺度上充当可调筛，因为网络可以扩展以产生开放结构）。化学物质可以被描述为具有“负面行为”：违反直觉的行为。第二种类型的负面行为是“负热膨胀”。在这里，材料受热时会收缩，而不是像预期的那样膨胀。与拉胀行为一样，负热膨胀具有许多技术应用，例如，在制造加热时不显示膨胀的复合材料中。人们认为，相同的基本过程可以负责这两个负面行为。然而，这一点还没有得到证实，为了做到这一点，必须进行实验测量，在原子尺度上探测物质的结构，以及大样品的性质，将材料的整体性质与原子结构联系起来。我们将集中在一个家庭的材料：开放网络硅酸盐。这些材料已经通过计算机模拟预测为拉胀的，但是这种预测从未被证实，尽管一些也已知具有负热膨胀性质。硅酸盐通常作为矿物存在于地壳中，但在实验室中，我们能够以纯净的状态制造出这种材料的大晶体;这在过去是很难做到的，但我们最近开发出了可靠的方法。大的晶体将受到机械测试-字面上拉伸试样沿着不同的方向将使我们能够测量其弹性性能，并确定是否存在所提出的负面行为。由于我们可以研究大量具有不同化学成分的样品，我们将能够将材料的化学成分与弹性性质联系起来，然后确定样品的化学成分（即原子尺度性质）与其体弹性性质之间的关系。我们的目标是使用这些结果来验证计算机预测的拉胀行为，然后了解为什么拉胀行为存在。还将研究这些材料的热膨胀特性：这里要解决的问题是，具有拉胀行为的固体是否也表现出负的热膨胀。这在以前从未被研究过。拟议的工作是化学家和工程师之间的合作，这种相互作用将是实现我们目标的理想组合：化学家是制造新材料和了解其结构的专家，而工程师则研究材料的弹性和机械性能。