Extension of conventional solid state methods: Microwave synthesis of transition metal carbides

在拟议的项目中，我们将探索将微波加热作为一种合成工具来获得各种二元和更复杂的过渡金属碳化物。固态微波反应已被广泛应用于制备许多甚至具有更好性能的无机化合物。根据我们在使用家用微波炉进行微波反应方面的经验(例如，半-Heusler金属间化合物和氧化物荧光粉)，我们将把我们的努力扩展到另一类化合物，即过渡金属碳化物。在这里，实验室级微波反应堆是该项目过程中将使用的核心设备。虽然国产微波炉已经取得了可喜的成果，但只有研究级的微波炉才能让我们充分利用微波加热技术。与家用微波炉相比，它具有许多优势，最重要的是可以监控反应过程中的温度，以及更高的安全标准。这两个方面对这里提议的项目都非常重要，因为它们将使合成的重复性很高，并在实验室中进行安全的反应程序。由于不同形式的碳与微波辐射的良好耦合行为，导致快速升温，碳化物是利用微波加热合成它们的理想候选者之一。将研究二元过渡金属碳化物，如Fe3C，Co2C，以评估各种可能的合成方法，从元素直接反应和各自氧化物的碳热还原。然后我们将转向六方MAX相，它是更复杂的碳化物，通式为Mn1AXn，其中M是早期过渡金属，A是A族元素(主要在第13和14族中)，X是碳或氮。其中许多化合物都是已知的，研究得也很好。然而，没有太多的工作致力于寻找更多的MAX相与后来的过渡金属，如锰，铁和钴。因此，我们将集中在已知的MAX化合物与后来的过渡金属的可能的固溶体，并对它们的磁性特别感兴趣。此外，还将对所谓的MXene化合物进行研究。它们是MAX相的剥离版本，其中A层已经被蚀刻掉。由于其中一些化合物表现出半导性而不是金属行为，它们有望显示出良好的热电性能。

In the proposed project, we will explore microwave heating as a synthesis tool to access a variety of binary and more complex transition metal carbides. Solid state microwave reactions have been widely used to prepare a multitude of inorganic compounds that often even exhibit improved properties. Based on our experience with microwave reactions using a domestic microwave oven (e.g. half-Heusler intermetallic compounds and oxide phosphors), we will extend our efforts to an additional class of compounds, namely transition metal carbides. Here, a laboratory-grade microwave reactor is the central piece of equipment that will be used during the course of this project. Although promising results can already be achieved with a domestic microwave oven, only the research-grade microwave will allow us to take full advantage of the microwave heating technique. It offers a number of advantages in contrast to the domestic microwave oven, most importantly the possibility to monitor the temperature during the reaction as well as much higher safety standards. Both aspects are of major importance for the here proposed project because they will enable highly reproducible syntheses as well as safe reaction procedures in the laboratory.Due to the excellent coupling behavior of different forms of carbon with the microwave radiation leading to rapid heating rates, carbides are among the ideal candidates to exploit microwave heating for their synthesis. Binary transition metal carbides, such as Fe3C, Co2C, will be studied to evaluate the various possible synthesis methods, direct reaction from the elements and carbothermal reduction of the respective oxides. We will then move towards the hexagonal MAX phases that are more complex carbides with the general formula Mn+1AXn, where M is an early transition metal, A is an A-group element (mostly in groups 13 and 14) and X is either carbon or nitrogen. Many of these compounds are known and well studied. However, not that much work has been devoted to finding additional MAX phases with later transition metals, such as Mn, Fe and Co. We will therefore focus on possible solid solutions of known MAX compounds with later transition metals and are particularly interested in their magnetic properties. Besides, so called MXene compounds will be also be investigated. They are an exfoliated version of the MAX phases where the A layer has been etched away. Since some of these compounds exhibit semiconducting instead of metallic behavior, they are expected to show promising thermoelectric properties.