Fabrication of novel glasses and glass micro-spheres by acoustic levitation and laser heating.

氧化物玻璃几千年来一直是重要的材料。它们在光学波长上的透明性使它们在房屋和汽车的窗户上无处不在，它们在显微镜和望远镜的透镜中的使用一直是许多科学发展的关键。今天，它们仍然是关键的技术材料，还有其他应用，例如，用于手机屏幕的硬玻璃，支撑当前高速通信的光纤，以及用作激光主体材料等等。制造典型的氧化物玻璃的过程包括熔化材料，并允许其冷却(淬火)成原子具有无序、非晶态排列的形式。在实践中，除了那些含有大量二氧化硅、氧化硼或氧化磷的材料外，大多数材料都很难实现这种非晶态。为了制造性能更好的玻璃(如折射率、红外透过率、稀土离子含量……)这些成分需要避免，这对它们的玻璃形成能力有重大影响。因此，需要新的玻璃制造方法。一种材料可靠地形成玻璃的能力取决于它冷却的速度(冷却速度)、它所在的容器以及任何固体杂质的存在(促进结晶)。一种非常热的物质在空气中通过辐射自由冷却的速度取决于它的大小。因此，为了提高给定材料的猝灭率，我们需要使其尽可能地小。为了避免因容器而结晶，我们需要使用一个非常光滑的容器，或者根本没有容器。因此，为了发现和生产新的玻璃材料，理想的做法是在无容器的条件下处理小样品。在这个项目中，我们将开发声悬浮方法，使我们能够在不需要容器的情况下在高温下处理材料。在这个项目中，我们将利用布里斯托尔最近开发的新技术。特别是，我们将进一步开发“TinyLev”设备，允许中等密度(高达5 g·cm-3)的材料进行常规悬浮，并基于朗之万号角的自动调谐设备，用于高密度材料(超过12 g·cm-3)。为了实现高熔体温度，我们将使用对准二氧化碳激光系统将样品加热到超过2500K的温度。激光加热系统的使用意味着样品可以在几秒钟内加热并熔化，温度梯度很小。作为热源，激光器可以瞬间关闭，使得样品将以其最大速率自由冷却，从而对于小于1 mm直径的尺寸，将达到10,000开尔文/秒量级的猝灭速率。该系统非常适合于新型玻璃材料的快速加工/成型。声悬浮和激光加热系统将用X射线和中子衍射法研究基于氧化铝、氧化钛和氧化镓的新型无二氧化硅玻璃形成系统的结构。特别是，我们将使用该系统在原位跟踪液体结构在快速冷却时的演变，以形成玻璃或观察引起晶体成核的过程。这些实验将与最先进的计算机模拟相结合，为玻璃的形成过程提供新的见解。越来越多的人对使用直径在10-100微米左右的高质量玻璃球在回音廊模式(WGM)设备中的应用感兴趣，如生物传感器、温度传感器和激光。这种声悬浮和激光加热系统将是生产这些球的理想系统，本项目的最后部分将探索和评估这种生产这些应用的WGM球的方法。

Oxide glasses have been important materials for millennia. Their transparency at optical wavelengths makes them ubiquitous in windows for houses and cars and their use in lenses for microscopes and telescopes has been key to much scientific development. Today they remain key technological materials with additional applications in, for example, the hard glasses used in mobile phone screens, the fibre optics that underpin current high-speed communications and as laser host materials to name a few.The process of making a typical oxide glass involves melting the material and allowing it to cool (quench) into a form in which the atoms have a disordered, non-crystalline arrangement. In practice, this non-crystalline form is difficult to achieve for most materials, apart from those that contain significant quantities of silicon dioxide, boron oxide or phosphorus oxide. In order to produce glasses with improved properties (e.g. refractive index, infrared transmission, rare-earth ion content ...) these components need to be avoided which has a significant impact on their glass forming ability. Hence, new methods for glass fabrication are required. The ability of a material to form a glass reliably depends on how fast it can be cooled (the quench rate), the container it is in and the presence of any solid impurities (that promote crystallization). The rate at which a very hot material will cool freely in air by radiation depends on its size. Hence to improve the quench rate for a given material we need to make it as small as possible. To avoid crystallization due to a container we need to use either, a very smooth container, or no container at all. Hence to discover and produce new glassy materials it is ideal to work with small samples under containerless conditions.In this project we will develop acoustic levitation methods to allow us to process materials at high temperatures without the need for a container. In this project we will exploit new techniques that have been developed recently in Bristol. In particular, we will develop further the 'TinyLev' device that allows routine levitation of materials with moderate density (up to 5 g. cm-3) and auto-tuning Langevin Horn based devices for use with high density materials (in excess of 12 g. cm-3).To achieve high melt temperatures we will use an aligned carbon dioxide laser system to heat the samples to temperatures in excess of 2500K. The use of a laser heating system means that the samples may be heated and melted in a matter of seconds with small thermal gradients. As a heat source the lasers may be switched off instantaneously so that the sample will be free cooled at its maximum rate so that for a size of less than 1mm diameter, quench rates of the order of 10,000 Kelvin/second will be achieved. The system will be very suitable for rapid processing/prototyping of new glass materials.The acoustic levitation and laser heating systems will be used to study the structure of novel silica-free glass forming systems, based on aluminium oxide, titanium oxide and gallium oxide, by X-ray and neutron diffraction. In particular, we will use the system to follow, in situ, the evolution of the liquid structure as it is rapidly cooled, to form either a glass or to observe the processes giving rise to crystal nucleation. The experiments will be coupled with state-of-the-art computer simulations to give new insight into the glass forming process.There is increasing interest in the use of high quality glass spheres with sizes of the order 10-100 microns diameter for applications in Whispering Gallery Mode (WGM) devices such as biosensors, temperature sensors and lasers. This acoustic levitation and laser heating system will be ideal to produce these spheres and the final part of this project will be to explore and evaluate this method for producing WGM spheres for these applications.