Phase Transitions In Bismuth Research Articles

Casting Octahedra for Reproducible Multi-Anvil Experiments by 3D-Printed Molds

Making consistent and precise octahedral pressure media is crucial for reproducible high-pressure experiments in the multi-anvil press. Here we report a new approach of casting octahedra using 3D-printed molds, and pressure calibrations for octahedra both with and without pre-existing gaskets (“fins”). The 3D-printed molds for casting octahedra from either Ceramacast 584-OF or 646 cement improve the reproducibility of the octahedra and allow for a pre-existing central hole (for the high-pressure cell assembly) in the final cast product. Pressure and temperature calibrations of the octahedra have been performed based on phase transitions in bismuth (Bi) and silica (SiO2), respectively, in order to determine the efficiency and reproducibility of pressure generation and thermal insulation for cast octahedra designed for use with 18/12, 14/8, and 10/5 multi-anvil assemblies. The pressure-generating efficiency of the 14/8 and 10/5 octahedra with pre-existing gaskets, cast from the 584-OF cement, is similar to that of the corresponding COMPRES (Consortium for Materials Properties Research in Earth Sciences) octahedra, and more efficient than pre-cast octahedra made from the same material but lacking pre-existing gaskets. The efficiency of pre-gasketed 18/12 octahedra made of the 646 cement is markedly lower than those of the 584 cement. However, the 18/12 large-volume octahedra, cast (with fins) from the ZrO2-based 646 cement, also provides efficient thermal insulation. Casting octahedral solid pressure media for multi-anvil experiments using 3D-printed “injection” molds is a low-cost and low failure-rate alternative for conducting reproducible experiments at high pressure in the multi-anvil apparatus.

Phase transitions in bismuth under rapid compression**Project supported by the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics (NSAF) (Grant No. U1530134), the Foundation of National Key Laboratory of Shock Wave and Detonation Physics, China (Grant No. 6142A0306010817), and the Chinese Academy of Sciences (Grant Nos. KJCX2-SW-N20 and KJCX2-SW-N03).

The structural phase transitions of bismuth under rapid compression has been investigated in a dynamic diamond anvil cell using time-resolved synchrotron x-ray diffraction. As the pressure increases, the transformations from phase I, to phase II, to phase III, and then to phase V have been observed under different compression rates at 300 K. Compared with static compression results, no new phase transition sequence appears under rapid compression at compression rate from 0.20 GPa/s to 183.8 GPa/s. However, during the process across the transition from phase III to phase V, the volume fraction of product phase as a function of pressure can be well fitted by a compression-rate-dependent sigmoidal curve. The resulting parameters indicate that the activation energy related to this phase transition, as well as the onset transition pressure, shows a compression-rate-dependent performance. A strong dependence of over-pressurization on compression rate occurs under rapid compression. A formula for over-pressure has been proposed, which can be used to quantify the over-pressurization.

A strip anvil apparatus with linear uniform pressure distribution

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.

Pressure calibration for the cubic press by differential thermal analysis and the high-pressure fusion curve of aluminum

Cell pressures in the cubic press have been determined by means of differential thermal analysis (DTA) based on the known fusion curve of aluminum. The results compared favorably with those of the well-known fixed-point method, based on pressure-induced phase transitions in bismuth (I–II, 2.55 GPa) and thallium (II–III, 3.68 GPa). The high-pressure fusion curve of lead was measured using our calibrated results, which agreed well with those of the previous work. All of this was made possible by the development of a successful cell assembly for the DTA analyses in the cubic press. Details of the design are described in the present work.

Phase Transitions in Bismuth

Phase Transitions in Bismuth

In situ pressure calibration for piston cylinder cells via ruby fluorescence with fiber optics

A fiber-optic measurement technique is developed for estimating the pressure inside a piston cylinder cell up to approximately 4 GPa, based on the pressure-induced R1 fluorescence line shift of ruby (ruby scale). Ruby scale and a conventional technique (calibration on phase transitions of bismuth) were simultaneously applied to the cell filled with a pressure transmitting medium of isopropyl alcohol. The pressure readings of the two methods were consistent with each other, and no pressure gradient was observed. The ruby scale has the advantages of real time estimation and easy installation in a small space. Because of these advantages, three fibers were simultaneously introduced in the sample space at the same time, and pressure distribution was measured for Fluorinert (FC70:FC77=1:1), Daphne oil 7373, and Fomblin oil (YHVAC 13014).

Influence of MgO on the growth of cubic boron nitride using the catalyst Mg3N2

Cubic boron nitride (cBN) may be synthesized under high pressures and high temperatures in the presence of a catalyst, provided that hexagonal boron nitride (hBN) is used as starting material. Typical catalysts are known to be the nitrides of the alkali and alkaline earth metals. Sato et al. [1] and Endo et al. [2] reported the effect the oxygen content ( B 2 0 3 ) of hBN on the growth of cBN. The present work investigated the influence of MgO content in the catalyst magnesium nitride (Mg3N2) on the growth of cBN. HBN powder and the sintered body used as starting material contained 0.6 wt % oxygen and had a graphitization index of 1.6. Mg3N2 was synthesized by heating magnesium metal under a nitrogen stream at 600°C for 4 h, and subsequently at 900 ° C for 8 h. Mg3N2 was mixed with MgO in the weight ratio Mg3Nz:MgO of 5:1. Oxygen contents were measured by neutron activation analysis and the graphitization index was determined by X-ray diffraction patterns. A belt-type high-pressure cell was used for the experiments. The catalyst Mg3N 2 was placed in the centre of the reaction cell and was surrounded by hBN. The pressure was calibrated at fixed points for the phase transitions in bismuth (2.55, 7.7 GPa), thallium (3.68GPa) and barium (5.5GPa). The temperature was determined from an electric power input against temperature plot, calibrated by thermocouples. The crystal habit and the surface structure of cBN samples were observed by optical and scanning electron microscopy. The conversion rate and the crystal growth rate of cBN were investigated in the temperature range 1600 to 2200 K at pressures from 6.5 GPa. The crystal growth rate had a maximum at Figure 2 MgO layers on the crystal surfaces.

Determination of the dynamic phase transitions in bismuth with in-material manganin gauges

We performed planar impact experiments with in-material manganin gauges in order to record the multiple wave structure resulting from the BiI-II and BiII-III phase transformations. Our values are somewhat higher than the static values (28 kbar for BiI-II and 32.5 kbar for BiII-III) but they agree with other dynamic measurements. The release portion of the stress signal shows a complicated structure which results from the multiplicity of waves in the target and their interactions. Our measured wave amplitudes and Lagrangian velocities are in good agreement with those obtained by free-surface velocity measurements, thus demonstrating the usefulness of manganin gauges in planar impact experiments.

The method of compression test under high pressures in a cubic press and the strength of granite

A cubic press was used for the triaxial test on rocks under very high confining pressures up to 4 GPa. For a specimen of 16 mm length and 8 mm diameter in a silver chloride sleeve with a pressure-medium of pyrophyllite, the axial and the confining pressures were calibrated by means of the phase transitions in bismuth, thallium and barium. The compressive strength of granite was determined up to 3 GPa of confining pressure in the cubic press. The results were compared with those from the ordinary triaxial testing machine with a pressure-medium of oil up to 450 MPa. For the whole pressure range, the compressive strength was expressed by : C/ C 0 = 1 + 4.33 ( P/ C 0) 0.47 where C is the differential compressive strength, P is the confining pressure and 0 is the uniaxial compressive strength which was 180 MPa for the Man-nari granite used in this work.

New device for generating ultra-high pressure

This paper describes a unique device for generating ultra-high pressures of the order of 300 kilobars (30 GPa). This is a variable lateral support, Bridgeman anvil device which utilizes the principle of a segmented cylinder to provide the lateral support and to apply the force to the anvils. The system has been calibrated to 212 kilobars using resistivity measurements to detect the known phase transitions in bismuth, iron, lead, and 10 and 20% cobalt alloys of iron.

Phase Transitions of Bismuth at Low Temperatures

Phase Transitions of Bismuth at Low Temperatures

Shock-Wave Compression of Iron and Bismuth

A helium gun was used to propel metal projectiles against targets of the same materials. Pressures produced by impact were varied by varying projectile velocities. The method produced pressures up to somewhat over 100 kbar, thus overlapping the lower part of the range of pressures which can be produced by detonation of high explosives. Of particular interest was the range of pressures intermediate between the highest which can be produced statically and the lowest which can be produced by explosives. A condenser micrometer was used to detect motion of the free surface of the target. This method permitted examination of the motion in greater detail than could reasonably be accomplished by other methods which have been used. Elastic and plastic waves were observed in iron and in bismuth. Assuming the Rankine-Hugoniot shock conditions, pressures and compressions were computed. Pressure-compression data for iron were obtained for intermediate pressures not previously investigated. Phase transitions in bismuth were observed for pressures up to about 40 kbar.