Containerless heating for extreme melts and glasses: determining the melting temperature of the lower mantle.

无容器加热是在极端温度下研究液体和合成极端玻璃成分的日益重要的工具。例如，对熔融耐火材料(如氧化铝)结构的中子和X射线衍射研究使用悬浮熔炉在2500 k1以上的温度下悬浮气体中的熔滴。无容器加热具有以下优点：-最高温度不受坩埚材料的限制-样品几乎不可能受到污染-熔体的整个表面都与载气接触，导致快速平衡并在淬火过程中抑制结晶。在地球科学中，这意味着可以在与行星吸积和撞击过程相关的极端温度下进行分馏研究，并在受控氧逸度下产生极少二氧化硅的玻璃(例如纯橄榄石)。然而，英国地球科学界并不存在这样的设施。我们建议开发一种激光加热的气体悬浮炉，它满足上述所有方面的要求。在这一小额拨款建议的范围内，我们将用它来合成橄榄岩玻璃成分，用于研究下地幔熔融和压力对橄榄岩熔体结构的影响。未来使用这里开发的提升炉的研究将包括极端温度下的同位素分馏和地球吸积过程中主体成分的演变，这方面的资金将单独申请。

Containerless heating is an increasingly important tool for studying liquids at extreme temperatures and for synthesising extreme compositions of glass. For example, neutron and X-ray diffraction studies of the structure of molten refractory materials (e.g. Al2O3) have used levitation furnaces to suspend molten drops in gas at temperatures of over 2500 K1. Containerless heating has the following advantages: - the maximum temperature is not limited by the crucible material - there is little chance of contamination of the sample - the entire surface of the melt is in contact with the carrier gas, leading to rapid equilibration and inhibition of crystallisation during quenching. Within the Earth Sciences, this means that studies of fractionation can be performed at extreme temperatures relevant to planetary accretion and impact processes, and extremely silica-poor glasses (e.g. pure olivine) produced at controlled oxygen fugacity. However, no such facility exists in the UK Earth Sciences community. We propose to develop a laser-heated gas-levitation furnace which fulfils all of the aspects mentioned above. Within the remit of this small-grant proposal we will use it for synthesis of peridotite glass compositions for studies of lower-mantle melting and of the effect of pressure on peridotitic melt structure. Future studies using the levetation furnace developed here will include isotopic fractionation at extreme temperatures and the evolution of the Earth's bulk composition during accretion, for which funding will be applied for separately.