Laser Heated Gradient NMR Studies of Ceramic Liquids

陶瓷在技术上的重要性日益增加，这突出表明有必要对陶瓷熔体的基本物理和化学性质进行新的研究，因为温度非常高（高达2,000摄氏度以上），而且需要进行许多工业加工。 我们已经建立了所需的设备，在超高温下的绝缘材料的性能的光谱和时域NMR测量，并到目前为止，确定了化学位移和核自旋弛豫时间27铝在几个熔融陶瓷之间的1700和2600 C。 该设备将用于在已知的耐火系统中扩展这些测量，例如二氧化硅-氧化铝，钙-氧化铝和钇-氧化铝，以及正在研究的新系统。 此外，我们计划通过将磁场梯度并入我们的NMR探针来进一步开发超高温NMR测量技术。 这有两个目的，提高我们的理解样品的温度梯度的装置，并实现直接测量的扩散率。 随着这些创新的加入，众所周知的基本测量的储备，NMR的应用有可能显着增加我们的了解液相在广泛的陶瓷系统。 然而，在熔融陶瓷中，测量特别具有挑战性。 典型陶瓷液体成分的高温和强反应性排除了样品容器的使用。 在我们的实验中，一个直径约为3毫米的小球悬浮在向上流动的氩气中，并用CO2激光器加热到2000 ℃以上。 对于NMR测量，样品还必须位于超导磁体中心的大磁场中。 样品的温度和成分可以变化，NMR数据提供了关于这些变化对液体中不同核的平均化学环境的影响的直接信息。 也可以得到扩散率。从这些信息中可以更清楚地了解熔融陶瓷的原子尺度结构和动力学特性。 有了这个，我们可以更好地了解熔体的宏观性质，例如它的粘度，并更好地控制许多应用中所得陶瓷材料的性质。该项目与AFOSR（6.1）共同资助。

The growing technological importance of ceramics has highlighted the need for new studies of the fundamental physical and chemical properties of ceramic melts, where temperatures are very high (up to and beyond 2,000 Celsius) and where much industrial processing is performed. We have built the apparatus required for both spectroscopic and time-domain NMR measurements of the properties of insulating materials at ultra-high temperatures, and have to date determined both chemical shifts and nuclear spin relaxation times of 27Al in several molten ceramics between 1700 and 2600 C. This apparatus will be used to extend these measurements in well-known refractory systems, e.g. silica-alumina, calcium-alumina and yttrium-alumina, as well as in new systems under investigation. In addition, we plan to further develop the technique of ultra high-temperature NMR measurements by incorporation of a magnetic field gradient into our NMR probe. This has the twin purposes of improving our understanding of sample temperature gradients in the apparatus, and of implementing the direct measurement of diffusivities. With the addition of these innovations to the well-known repertory of basic measurements, the application of NMR has the potential for significantly increasing our understanding of liquid phases over a broad range of ceramic systems. In molten ceramics, however, measurements are particularly challenging. The high temperatures and strong reactivities of a typical ceramic liquid's constituents preclude the use of sample containers. In our experiments a small sphere of material, about three mm in diameter, is levitated in an upward flow of argon gas and heated above ~2000 C by a CO2 laser. For NMR measurements the sample must also be located in a large magnetic field, at the center of a superconducting magnet. Sample temperature and composition may be varied, and the NMR data provide direct information about the effect of these variations upon the average chemical environments of different nuclei in the liquid. Diffusion rates can also be obtained. From this information a clearer understanding emerges, of the atomic scale structural and dynamic properties of molten ceramics. With this, we can better understand the macroscopic properties of a melt, for example its viscosity, and better control the properties of the resulting ceramic material for many applications.This project is co-funded with AFOSR (6.1).