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

氧化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透镜中的应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，在手机屏幕上使用的硬玻璃，支撑当前高速通信的光纤以及作为激光主机材料等方面有其他应用。制作典型氧化玻璃的过程包括熔化材料，并使其冷却（淬火）成原子无序、非结晶排列的形式。实际上，除了那些含有大量二氧化硅、氧化硼或氧化磷的材料外，大多数材料很难实现这种非结晶形式。为了提高玻璃的性能（如折射率、红外透射率、稀土离子含量等），需要避免这些对玻璃形成能力有重大影响的成分。因此，需要新的玻璃制造方法。一种材料形成玻璃的可靠能力取决于它冷却的速度（淬火速率），它所在的容器和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率取决于它的大小。因此，为了提高给定材料的淬火速率，我们需要使其尽可能小。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，或者根本不用容器。因此，为了发现和生产新的玻璃材料，在无容器条件下使用小样品是理想的。在这个项目中，我们将开发声悬浮方法，使我们能够在高温下处理材料，而不需要容器。在这个项目中，我们将利用最近在布里斯托尔开发的新技术。特别是，我们将进一步开发“TinyLev”设备，该设备允许中等密度（高达5 g cm-3）的材料进行常规悬浮，并可自动调谐基于朗格万角的设备，用于高密度材料（超过12 g cm-3）。为了达到高熔体温度，我们将使用对准的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以很小的热梯度加热和熔化。作为热源，激光可以立即关闭，使样品以其最大速率自由冷却，因此对于直径小于1mm的尺寸，将实现10,000开尔文/秒的淬火速率。该系统将非常适合新型玻璃材料的快速加工/原型制作。声波悬浮和激光加热系统将通过x射线和中子衍射研究基于氧化铝、氧化钛和氧化镓的新型无硅玻璃形成体系的结构。特别是，我们将使用该系统在现场跟踪液体结构的演变，因为它迅速冷却，形成玻璃或观察引起晶体成核的过程。实验将与最先进的计算机模拟相结合，以提供对玻璃成型过程的新见解。人们对直径为10-100微米的高质量玻璃球的使用越来越感兴趣，这些玻璃球用于低语廊模式（WGM）设备，如生物传感器、温度传感器和激光器。这种声波悬浮和激光加热系统将是生产这些球体的理想选择，该项目的最后一部分将是探索和评估这种生产用于这些应用的WGM球体的方法。

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.