Development of novel high pressure instrumentation
The application of pressure to chemical substances can change their physical properties (optical, magnetic, and electrical) and it can also be used to alter some chemical reactions. The need for compatible pressure generating instruments is constantly growing in various high pressure (HP) researches. The work described in this thesis is focused on development, construction, testing of several high pressure cells of novel design. These designs were developed to meet the requirements of different research collaborations. The main objective of this project is to develop high pressure cells for magnetic studies in the magnetic properties measurement system known as MPMS, which is the most popular commercial magnetometer nowadays. Three high pressure cells were designed and tested for different type of magnetic measurements. The first design presented in this thesis is a cylinder type pressure cell which is specially designed to measure the magnetic susceptibility of the pressure-sensitive material under pressure. The cell is driven by compressed helium gas which allows the internal pressure to be adjusted with small increments (1 MPa) through the regulator of the external gas cylinder. The cell was made of non-magnetic beryllium copper alloy and designed to work up to 100 MPa at 400 K temperature. The design was verified with finite element analysis (FEA) simulation and its sample volume was optimised to provide large sample capacity which allows high quality data to be collected in the MPMS. Modified from the earlier turnbuckle magnetic diamond anvil cell (TM-DAC) reported in Konstantin V. Kamenev (KVK) group, the second high pressure cell presented in this thesis is an opposed diamond anvil pressure cell. The working mechanism of this cell is based on the turnbuckle principle. The cell was specifically developed for iHelium3 system which is a add-on cryostat of the MPMS. The cell was coded TM-3He-DAC to distinguish with the original TMDAC. The cell is 6 mm in diameter and 7 mm in length, which are smaller than the dimensions of the predecessor (TM-DAC). Copper titanium alloy was used in building the cell to further reduce the magnetic background from the cell. The cell is capable of achieving close to 5 GPa sample pressure in the loading test and the magnetic background is significantly lower than the TM-DAC. The development of this cell enables high pressure magnetic measurements to be performed at extreme low temperature (0.5 K) in the iHelium3 system. The third high pressure cell developed for the MPMS is also a turnbuckle diamond anvil cell, however, all the material used in the cell is non-metallic to enable high-pressure ac magnetic measurement to be performed. An advanced high strength polymer was assessed using finite element analysis and experimental testing. The performance and failure modes for the key components of the cell working in tension and in compression were evaluated and the ways for optimising the designs were established. The cell is coded PTM-DAC in this thesis and the composite gasket was also developed and tested for the PTM-DAC. The cell is approximately 14 mm long, 8.5 mm in diameter and was demonstrated to reach pressures of 5.6 GPa. Ac susceptibility data collected on Dy2O3 and U6Fe demonstrated the performance of the cell in magnetic property measurement and confirmed that there was no screening of the sample by the environment which typically accompanies used of conventional metallic high pressure cells in oscillating magnetic fields. Based on the experience of from the development of above two turnbuckle diamond anvil cell, a turnbuckle sapphire anvil cell (T-SAC) was developed in this project for high-pressure neutron scattering. Commercial spherical sapphire were used as anvil in the cell as they are much more cost effective if compared to the diamond anvil. The developed T-SAC can generate and maintain sample pressures above 6 GPa with a sample volume 6 X 10-² mm³ which is 6 times that of conventional diamond anvil cell (DAC). Failure analysis was performed on the sapphire anvil to gain a better understanding of the failure mechanism of the spherical sapphire anvil. The cell had been used in measuring the crystal structure of single crystal niobium at 1.6 GPa through small angle neutron scattering (SANS) technique. The cell is less than 16 mm in length and 14 mm in diameter, it is the smallest sapphire anvil cell to date. The miniature feature allow it can be fit into most cryostat of modern scientific instrument without difficulties. Lastly, two piston-cylinder type high pressure cells were developed for high-pressure chemistry studies. These cells were designed to pressurise large amount of liquid sample (particular for water-based sample) up to 800 MPa in a controllable manner. Each design is presented separately with stress analysis in FEA and a description of the working mechanism. Hoop strain at the external surface of the cell was measured and then the internal pressure was calculated through the Lam´e equation. After that, the load and attainable internal pressure was calibrated for the users. These cells have been used in the high-pressure study of salicylaldoximes process, bio-diesels decomposition and crystallization, material polymerisation and pharmaceutical experiments.