A strip anvil apparatus with linear uniform pressure distribution

Abstract

Bridgman anvil is a useful and effective tool in high-pressure research. However, in this apparatus, the pressure distribution is essentially centrosymmetric. Thus, considerable pressure gradients exist in the gasket and in the sample chamber respectively, and the uniform pressure area is limited. To improve the pressure uniformity in flat face supported anvils, we design a strip face anvil instead of conventional round face anvil and adopt an assortive strip gasket. Principle analysis and a series of pressure calibration experiments are also presented in this paper.The construction of the strip anvil and relevant parts of the apparatus are shown in the diagrams and photos. The relationship between pressure and shearing stress in the strip gasket is investigated by using the model of M. Wakatsuki, which indicates that the pressure distribution should be uniform along the central line of the strip gasket.Pressure calibration experiments are conducted by using strip anvils made of tungsten carbide with a length of 20 mm and width of 5 mm and by using the assortive strip gasket of pyrophyllite. Pressures at different places of the central line are calibrated according to the known phase transitions of bismuth in the same loading process, and the samples are assembled with symmetrical, unsymmerical, and separated local collocations, respectively.Experimental results exhibit that the pressure reaches up to 10 GPa in the central line of the strip gasket, and the pressures are almost equal at least within the range of 12 mm on the central line. The bias errores of oil pressures measured at different places of the central line are all less than 2.0% at 2.55 GPa and 3.6% at 7.7 GPa, indicating only a small pressure gradient along the central line. The main reason for the measuring bias errors lies in the difficulty of the assembly technique. Specifically, the bismuth wire is difficult to adhere to the central line of the anvil during compression. Hence, further improvement of the process is expected in the future.In conclusion, the strip anvil is a unique high-pressure apparatus. The principle analysis and pressure calibration experiments confirm that the pressure is uniform in one-dimensional direction along the central line of the strip anvil. This feature is propitious to the accurate investigation of linear samples under high pressure.