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Title: Using state of the art engineering modelling and manufacturing techniques for developing instrumentation for high-pressure research
Author: Jin, Haoxiang
ISNI:       0000 0004 8497 8371
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2019
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The study of matter at extreme conditions is of great interest for modern science. Pressure, which is one of the important thermodynamic parameters, has a strong influence on the physical properties of matters, such as magnetic properties, electrical properties and optical properties. Apart from its fundamental importance in terms of understanding interactions on the atomic level, pressure is also important in practical applications such as synthesis of new materials. The demand for novel high-pressure instruments is constantly growing for high-pressure researches in physics, chemistry, geology, biology and engineering. However, conventional manufacturing methods cannot always satisfy the design requirements and high pressure achievements of the high-pressure cells. The main topic of this thesis focuses on design and construction of several high-pressure instruments using recent developments in rapid prototyping and finite element analysis techniques for high-pressure research. The first development presented in this thesis is a novel miniature high-pressure diamond anvil cell constructed using 3D micro selective laser sintering technique. This is the first application of 3D metal printing technology to construct high-pressure apparatus. The cell is compact and specifically designed for the use as an X-ray diffraction cell that can be fitted with commercially available diffractometers and open-flow cryogenic equipment to collect data at low temperature and high pressure. During its use, it is fully enclosed by the flow of cryogenic gas and the frost does not form on the optical windows of the cell because of its small size and full enclosure by the gas flow, which enhances the data quality from X-ray diffraction. The cell is clamped using a customized miniature buttress thread of 7 mm diameter and 0.5 mm pitch enabled by 3D micro selective laser sintering technique. Such dimensions are not attainable using conventional machining. The buttress thread was used as it has favourable uniaxial load properties allowing for higher pressure and better anvil alignment. A finite element analysis study has been conducted to simulate the stress distribution in buttress threads and to compare the performance of the cells with the customized buttress thread and the standard triangle thread. It demonstrates that stress is distributed more uniformly in the former. This FEA modelling was used to custom-design the dimensions of the thread. Rapid prototyping of the pressure cell by the laser sintering resulted in a substantially higher tensile yield strength of the 316L stainless steel (675 MPa compared to 220 MPa for the wrought type of the same material), which increased the upper pressure limit of the cell. The cell is capable of reaching pressures of up to 15 GPa with 600 μm diameter culets of diamond anvils. Sample temperature and pressure changes on cooling were assessed using X-ray diffraction on samples of NaCl and HMT-d12. The second development presented in this thesis is a 3D printed tungsten collimator which improves the data quality in the X-ray diffraction (XRD) experiments at synchrotron radiation facilities. The data processing is challenging due to the low signal-to-noise ratio with the use of diamond anvil cells. The main background noise in diffraction data is the Compton scattering from opposed diamond anvils. It is difficult to distinguish such noise and subtract it from the diffraction spectrum profile because its profile varies with changing pressures and temperatures. Besides, the signal from samples is quite weak due to the small sample volume in diamond anvil cells. In order to improve the signal-to-noise ratio for high-pressure synchrotron XRD experiments, a novel multi-channel collimator has been designed and constructed using the selective laser melting technique. This is the first 3D printed multi-channel collimator for high-pressure synchrotron XRD research. This device can block most of the noise from surrounding materials and improve the signal-to-noise ratio significantly. A mathematic model has been developed in this thesis to evaluate the signal-to-noise ratio with the use of the collimator, by calculating the solid angle integration across the defined diffraction volumes. Based on the mathematic model, a series of simulations have been conducted to clarify the influences of key parameters on the performance of the collimator and find out the optimum multi-channel collimator design. In addition to the XRD studies, some significant information about the material properties can also be obtained from neutron scattering, e.g. the magnetic properties. In order to obtain information from high-pressure neutron scattering research, a piston cylinder high-pressure cell with an electrical feed-through plug has been developed and tested in this thesis. The design of the electrical feed-through allows the use of manganin pressure gauge, which enables the pressure measurement in the sample volume in situ during the cell loading. This pressure measurement method, instead of the use of transitions, is quite convenient to save time during the neutron scattering experiments. The accuracy of the pressure measurements with the use of manganin pressure gauge is excellent for both room- and low-temperature high-pressure neutron scattering experiments. A FEA model has been built to simulate the stress distributions in the cell parts. The sample volume of the cell is as large as 400 mm3 and the maximum load of the cell is designed for the pressure generation up to 1.2 GPa.
Supervisor: Kamenev, Konstantin ; Mill, Frank Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: high-pressure instrumentation ; additive manufacturing ; 3D printing ; x-ray diffraction ; inelastic nuetron scattering