Direct Measurements of Shear and Longitudinal Wave Velocities of Iron and Iron Alloys at High Pressure and High Temperature by Laser Ultrasonics Technique

了解矿物在高压下的弹性行为是开发地球结构模型的关键因素，因为有关地球内部的大多数信息来自地震数据。因此，在高压和高温下直接测量矿物的速度和其他弹性特性是理解地震信息的关键，使我们能够将其转化为地球内部矿物的化学成分，矿物学和温度。铁被认为是地球核心的主要组成部分，人们已经做出了相当大的努力来了解它在高压和高温下的特性。然而，在高温高压条件下，铁的弹性行为的实验数据和理论之间存在差异。为了理解这一点的原因，应该直接测量铁和铁合金在高压和高温下的横波和纵波速度。该项目的主要目标是使用激光超声（LU）和金刚石砧室（LU-DAC）直接测量铁和铁镍合金在室温下100 GPa的高压和高达3000 K的高温下的纵向和剪切速度，LU-DAC是夏威夷大学新开发并成功测试的。该研究的成功对于地球物理科学和材料科学具有重要意义。对于地球物理科学而言，在类似于地球内部的升高条件下现场直接测量铁和铁镍合金的剪切和纵向速度对于解释观察到的地震异常和了解该地区矿物的物理特性至关重要。LU-DAC系统的主要思想是利用超短纳秒脉冲和连续波激光器在DAC中的高温高压下远程激发和检测材料中的声波。 LU-DAC点源点接收器技术用于非透明非晶固体和熔体的主要优点是它不需要任何额外的数据（例如高压下样品的厚度）来确定铁在高压下的弹性特性。LU-DAC技术的发展将为研究极端条件下非透明功能材料的弹性行为提供一种简单，廉价，非破坏性的技术;例如在高压和高温下合成的磁性，超硬或摩擦材料。从拟议的研究中获得的结果将提供扩展这样的测量研究的弹性和富铁矿物在高压高温条件下，当LU-DAC系统与激光加热相结合的部分熔体的基础。富含铁的矿物的弹性特性的知识将允许地球的核-幔界面的更现实的建模和阐明的性质和组成的D”层和地球的核心，并可能通过热点夏威夷群岛的形成。

Understanding of the elastic behavior of minerals under high pressure is a crucial factor for developing a model of the Earth's structure because most information about the Earth's interior comes from seismological data. Therefore, direct measurements of velocities and other elastic properties of minerals at elevated pressures and temperatures are keys to understand the seismic information, allowing us to translate it into chemical composition, mineralogy, and temperature of the minerals inside the Earth. Iron is thought to be the main constituent of the Earth's core and considerable efforts have been made to understand its properties at high pressure and high temperature. However, there are discrepancies between experimental data and theory on the elastic behavior of iron under high pressure and high temperature (HPHT) conditions. To understand the reason for this, the shear and longitudinal wave velocities of iron and iron alloys at high pressure and high temperature should be measured directly. The main goal of this project is to carry out direct measurements of both longitudinal and shear velocities of iron and iron-nickel alloys under high pressures to 100 GPa at room temperature and high temperature up to 3000 K using the laser ultrasonic (LU) coupled with a diamond-anvil cell (LU-DAC), which has been newly developed and successfully tested at the University of Hawaii. Success of the proposed research is of fundamental importance for geophysical science and materials science. For geophysical science, direct measurements of shear and longitudinal velocities of iron and iron-nickel alloys in-situ at elevated conditions similar to the Earth's interior are essential for interpreting the observed seismic anomaly and understanding physical properties of minerals in that region. The main idea of the LU-DAC system is to use ultra-short nanosecond pulse and continuous wave lasers for remote excitation and detection of acoustical waves in materials under high pressure and high temperature in DAC. The main advantage of the LU-DAC point-source-point-receiver technique for non-transparent amorphous solids and melts is that it does not require any additional data (such as thickness of the specimen under high pressure) to determine the elastic properties of the iron at high pressures. The development of the LU-DAC technique will provide a simple, inexpensive, non-destructive technique for studying the elastic behavior of non-transparent functional materials at extreme conditions; for instance magnetic, superhard, or tribological materials synthesized at high pressure and high temperature. The results obtained from the proposed research will provide the basis for extending such measurements to study the elasticity of melts and partial melts of iron-rich minerals at high pressure high temperature conditions when the LU-DAC system is combined with laser heating. The knowledge of the elastic properties of iron-rich minerals will allow a more realistic modeling of the Earth's core-mantle interface and shed light on the nature and composition of the D" layer and the Earth's core, and possibly on the formation of the Hawaiian Islands through the hot spot.