【作者】 张岱宇；

【导师】 经福谦；

【作者基本信息】 西南交通大学 ， 固体力学， 2008， 博士

【摘要】 氧化铝单晶（蓝宝石）在常温常压下具有优异的力学强度和光学透明性,在冲击作用下也具有较高的冲击阻抗,因此它常在冲击测温和激光速度干涉实验技术中被用作窗口材料。经掺杂铬离子后,它还常被用作静高压DAC实验中的压力标定材料。研究蓝宝石在高温高压下物理性质对于高压技术的发展和对其地学应用具有重要意义。在冲击压缩状态下蓝宝石的光学性质,一直受到动高压研究领域的广泛关注,因为它在冲击测温实验中直接关系到对实测热辐射信号的正确解读。在冲击压力低于85GPa的低压区,前人曾经报道过蓝宝石的热辐射发光效应,但在100GPa以上压力区,蓝宝石的发光性质还未见到比较系统的研究报道。本文采用无氧铜作为基板对蓝宝石在124-172GPa压力区的热辐射进行了较为系统的实验研究。并取得了以下有意义的结果:1、在所研究压力区间内均发现蓝宝石材料具有明显的冲击发光效应。实测的光谱辐亮度与波长的关系表现为灰体辐射特征,辐射温度基本上不随压力而变化,其值约为4000K,分析后,认为这种“异常”的高温辐射效应源自受压蓝宝石中的不均匀绝热剪切带中的高温区热辐射,与前人根据P≤85GPa实验结果对蓝宝石热辐射机理的分析意见一致。2、实测光谱辐亮度随蓝宝石样品中冲击压缩厚度增加而增强的趋势表明,在本文实验条件下的蓝宝石具有较大的光学厚度,其光吸收系数值较小。根据实验结果拟合得到的光吸收系数α_W与加载压力P的关系式为:式中α_W单位为cm^-1,P的单位为GPa。并发现同一压力下α_W不随波长而变。3、与静高压实验和理论研究确定的蓝宝石相图相对照,发现本文测得的124-172GPa区的蓝宝石冲击辐射温度明显低于前人在P≤85GPa区测量的蓝宝石辐射温度值（约低1000K）,而且呈突然下降趋势,在P-T图上的位置大致对应于蓝宝石相图中从Rh₂O₃),（Ⅱ）相变化到CaIrO₃相的相边界上,故推测在冲击压缩下蓝宝石中不均匀生成的局域绝热剪切带结构及其热性质与它的固相结构类型有关。4、对由铜基板和蓝宝石两个热辐射源组成的实验测量复合热辐射场中提取出铜基板热源温度和发射率的信息做了尝试,得到了初步的结果。此项研究对发展金属材料的冲击温度测量技术有重要意义。更多还原

【Abstract】 The monocrystalline alumina （sapphire） has excellent mechanical and optical transparent properties at ambient condition, and relative high impedance under shock compression, thus it is commonly used as optical window for shock temperature measurement or velocity measurement by laser interference. In static high pressure experiments, alumina doped with Cr³⁺ is also used as pressure calibrant, and in some engineering applications it is one of important ceramic materials. In addition, alumina is believed to be one of the major constituent in the Earth’s mantle. Therefore, research on the high-pressure properties of sapphire is significant for further achievements in the high pressure science and technology, for the constraint of the Earth’s model, and for concerned engineering applications.Optical properties of sapphire under shock compression, such as optical absorption and emission, have been especially focused by the researchers working on the subjects of dynamic high pressure science and technology, because they will directly affect the interpretation for the shock-induced radiation from the contact interface of metal/sapphire. At the low pressure range of several tens of GPa, people had observed obvious emission of shocked sapphire, however, the transparency or emission properties of sapphire under strong shock compression is still an open question. In this thesis, in virtue of the low emission property of the oxygen-free copper baseplate, the self-emission effects of monocrystalline alumina under Mega bar pressures are investigated, and some advances are made in the following aspects:1、Obvious shock-induced emission from c-cut sapphire has been found in the pressure range of 124-172GPa, the wavelength dependence of the radiance is relating to the gray body’s radiation character, and the apparent temperature of the emission is fitted to be about 4000K. In this thesis, the high-temperature thermal radiations are attributed to the local melt shear banding induced by one-dimensional shock compression;2、The correlation between the observed temperature of the heterogeneous thermal radiation and the phase diagram of sapphire is founded. The temperatures of alumina in CaIrO₃ phase region at 124-172Gpa are lower by about 1000K than those inα-phase below 85GPa, this discrepancy is attributed to the phase transition induced by shock compression. Combining with the characteristics of P-T equilibrium curve for the solid-solid transformation, we supposed a three-phase point at 4000K and 80-125GPa in alumina’s phase diagram;3、The intensity of apparent radiation linearly rises with the thickness of the shocked part of sapphire sample; It shows that the c-cut sapphire under shock still has a considerable optical transparent thickness or a relative small absorption coefficient. The values of absorbance at different wavelengths are determined by use of the time-dependence radiance curves, and they are found insensitive to the radiation wavelength. Therefore, the sapphire’s optical emission induced by shock waves in our experiments can be treated by the gray-body model. The relationship between the absorption coefficient and shock stress is obtained by fitting the emission history curve, which is described by:α_W=0.503-0.022P+1.829*10^-4*P² (α_W in cm^-1, P in GPa)According to this formula, the effect of sapphire’s optical transparency on the temperature measurement can be quantitatively accessed.In summary, the characteristics of shock-induced emission in the crystalline alumina are systemically studied in this thesis, and the obtained results are of great importance. The present work shows that sapphire gives off obvious thermal radiation from heterogeneous shear banding at 120-172GPa, with a color temperature of about 4000K, and the temperature is found to be related to the structural transition of sapphire. Therefore, when the sapphire is used as optical window to measure the shock temperature, the optical emission and the structural transformation of sapphire will affect not only the observed intensity but also the history of the radiation signal. The functional relationship between the absorption coefficient and shock pressure can be applied to make a correction to the measurement temperature.更多还原