MEASUREMENT AND MODELLING OF STRUCTURE AND PORE LEVEL PROCESSES IN FILTERS AND WICKS

Characterisation of new filtration and wicking materials through a 'wet-bench" testing process is a requirement for many filtration companies before new products can be released to market. A reduction in this testing commitment through the application of successful computational based models, requiring minimal empirical input, would undoubtedly result in huge financial savings and reductions in testing lead times. Such models could offer total media characterisation and could also aid further insights into many filtration and wicking processes which before would have required an expensive combination of different testing procedures. In this research, a depth filtration model has been developed, based on the three-dimensional void network model Pore-Cor, The geometry of the void network is fitted, by means of an 8-dimensional Boltzmann annealed amoeboid simplex, to the porosity and percolation characteristics of stainless steel sintered filters measured by mercury intrusion porosimetry (MIP). Preferential and critical flow paths through the network are calculated via a newly developed algorithm which allows a representation of net flow within individual pore/throat clusters. Particles from an experimental size distribution are fed along these flow-biased paths, using a newly developed random-particle-selection algorithm and, when straining occurs, the flow paths are re-calculated. The model is shown usefully to reproduce experimental filtration efficiencies as a function of pressure drop, measured by single pass tests. A critique of filtration efficiency measurements is given, suggesting use of a new 'alpha efficiency' rather than standard beta efficiency. The model is currently being adapted to accept porometry as well as porosimetry data, hence avoiding the use of mercury in future testing. Further to development of the filtration model the research associated with this thesis has also investigated two related areas. One is an investigation of a hydrophilic treatment of a series of polymeric sinters using oxidizing plasma. The investigation shows an improved method of data analysis of capillary rise measurements. An optimization process for determining the correct hydrophilic treatment parameters is proposed based on the variance across sample sets, and results are interpreted with respect to the Vyon® samples analysed. Secondly an investigation of anomalous compression characteristics found in the MIP of stainless steel Sinterflo® media is presented. Hypotheses were proposed for the observed increase in media compressibility and these were investigated using the Pore-Cor void network model for comparison with other investigations of porosity and compression analysis. Preliminary results suggest increased compressibility arises from microscopic material deformities and micro-fractures found in the media.Porvair Filtration Group Lt

Application of Image Analysis for the Identification of Prehistoric Ceramic Production Technologies in the North Caucasus (Russia, Bronze/Iron Age)

The recent advances in microscopy and scanning techniques enabled the image analysis of archaeological objects in a high resolution. From the direct measurements in images, shapes and related parameters of the structural elements of interest can be derived. In this study, image analysis in 2D/3D is applied to archaeological ceramics, in order to obtain clues about the ceramic pastes, firing and shaping techniques. Images were acquired by the polarized light microscope, scanning electron microscopy (SEM) and 3D micro X-ray computed tomography (µ-CT) and segmented using Matlab. 70 ceramic sherds excavated at Ransyrt 1 (Middle-Late Bronze Age) and Kabardinka 2 (late Bronze–early Iron Age), located in in the North Caucasian mountains, Russia, were investigated. The size distribution, circularity and sphericity of sand grains in the ceramics show site specific difference as well as variations within a site. The sphericity, surface area, volume and Euler characteristic of pores show the existence of various pyrometamorphic states between the ceramics and within a ceramic. Using alignments of pores and grains, similar pottery shaping techniques are identified for both sites. These results show that the image analysis of archaeological ceramics can provide detailed information about the prehistoric ceramic production technologies with fast data availability

Microstructural, mechanical and electrical characterisation of piezoelectric particulate composites with dielectric modelling

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Three-dimensional virtual microstructure generation of porous polycrystalline ceramics

Various numerical methods have been recently employed to model microstructure of ceramics with different level of accuracy. The simplicity of the models based on regular morphologies results in a low computational cost, but these methods produce less realistic geometries with lower precision. Additional methods are able to reconstruct irregular structures by simulating the grain-growth kinetics but are restricted due to their high computational cost and complexity. In this paper, an innovative approach is proposed to replicate a three-dimensional (3D) complex microstructure with a low computational cost and the realistic features for porous polycrystalline ceramics. We present a package, written in MATLAB, that develops upon the basic Voronoi tessellation method for representing realistic microstructures to describe the evolution during the solid-state sintering process. The method is based on a cohesive prism that links the interconnect cells and thus simulates the neck formation. Spline surfaces are employed to represent more realistic features. The method efficiently controls shape and size and is able to reconstruct a wide range of microstructures composed of grains, grain boundaries, interconnected (open) and isolated (closed) pores. The numerical input values can be extracted from 2D imaging of real polished surfaces and through theoretical analysis. The capability of the method to replicate different structural properties is tested using some examples with various configurations

Mass transport and electrochemical properties of La2Mo2O9 as a fast ionic conductor

La2Mo2O9, as a new fast ionic conductor, has been investigated widely due to its high ionic conductivity which is comparable to those of the commercialized materials. However, little work has been reported on the oxygen transport and diffusion in this candidate electrolyte material. The main purpose of this project was to investigate oxide ion diffusion in La2Mo2O9 and also the factors which could affect oxygen transport properties. Oxygen isotope exchange followed by Secondary Ion Mass Spectrometry (SIMS) measurements were employed to obtain oxygen diffusion profiles. A correlation between oxygen ion transport and the electrochemical properties such as ionic conductivity was built upon the Nernst Einstein equation relating the diffusivity to electrical conductivity. In-situ neutron diffraction and AC impedance measurements were designed and conducted to investigate the correlation between crystal structure and oxygen transport in the bulk materials. Other techniques, such as synthesis, microstructure studies, and thermal analysis were also adopted to study the electrochemical properties of La2Mo2O9. The results of the study on the effects of microstructure on oxygen diffusion in La2Mo2O9 revealed that the grain boundary component played a significant role in electrochemical performance, although the grain size seemed to have little influence on oxygen transport. The oxygen isotope exchange in 18O2 was successfully carried out by introducing a silver coating on the sample surface, which solved the main difficulty in applying oxygen isotope exchange on pure ionic conductors. The ionic conductivity obtained from the diffusion coefficients was consistent with the result from AC impedance spectroscopy. The number of mobile oxygen ions was estimated to be 5 per unit cell. There was a difference of oxygen self diffusion coefficient when the isotope exchange was conducted in 18O2 and H2 18O. The activation energy of oxygen diffusion in humidified atmosphere was higher than that measured in dry atmosphere. It indicated that the humidified atmosphere had affected oxygen transport in the material. The studies on hydroxyl incorporation and transport explained the decreased oxygen diffusion coefficients in wet atmosphere and also suggested proton conductivity in La2Mo2O9, which leads to further investigation on applications of La2Mo2O9 as a proton conductor. In-situ neutron diffraction and AC impedance measurement revealed a close relationship between crystal structure and ionic conductivity. The successful application of this technique provides a new method to simultaneously investigate crystal structure and electrical properties in electro-ceramics in the future

Post processing for nylon 12 laser sintered components

PhD ThesisThis research investigates the effect of post-processing on the mechanical characteristics and behaviour of laser sintered components produced by selective laser sintering (SLS). It aims to understand the material’s behaviour and to develop postprocessing methods that can be used to improve and maintain consistency in the mechanical properties of the layer manufactured material. Duraform Polyamide (Nylon 12) and a Sinterstation VanguardTM SLS machine were used to produce test specimens. The behaviour of the layer material characteristics was established using different fabrication orientations and tensile, compression, shear and flexure tests as benchmarking investigations. The results show that there are significant variations in mechanical properties, as well as divergences from previous results. In addition, section thickness in closed and open hollow structures was investigated in order to establish its effect on mechanical properties. The larger a sintered area, the greater the tensile properties gained when there is an increase of section thickness and when solid specimens are used. Moreover, when fill and outline scanning strategies were implemented in producing the specimens, the improvements were obtained in the tensile properties of nylon 12 laser-sintered material with no impact on geometry. To further improve the mechanical properties, a new post processing method that included heat treatment in air and vacuum environments was investigated. Experiments were conducted in air from room temperature to 140oC with a treatment time of 120 minutes and vacuum heat treatment was conducted from room temperature to 180oC with 16 hours and 100 hours treatment time. The material properties in both conditions were then analysed in terms of tensile properties, thermal characterisations, microstructure and geometrical changes. Heat treatment in air showed no significant improvement in mechanical properties. However, Nylon 12 SLS material heat-treated in a vacuum showed considerable improvement in crystallinity and peak melting point. Heat treatment for a longer period to approach the melting point, especially on material with the different section thicknesses and solid specimens and particularly in a vacuum, has a greater impact on mechanical properties, but this may not be sufficient to justify the cost and time involved.Government of the Republic of Indonesia, through the Ministry of Research, Technology and High Educatio

Direct Metal Laser Sintering of Titanium implant with Tailored structure and Mechanical Properties

Direct Metal Laser Sintering has attracted much attention over the last decade for producing complex parts additively based on digital models. The capability and reliability of this process has stimulated new design concepts and has widened the manufacturing perspective of product customisation. This research work is designed to gain a deep understanding of laser sintering processing parameters, the corresponding microstructures and the mechanical properties. The main purpose is to have a body of fundamental knowledge about the laser and titanium powder material interactions, thus establishing the factors that influence the process-structure-properties relationships of the Direct Metal Laser Sintering process. Finally, a route for manufacturing customised craniofacial implants was described. This is to evaluate the DMLS processing capabilities in medical areas, particularly those parts having porous and lattice design structures. The interaction between a laser beam and the powder bed creates a distinctive structure; a ball shaped (blob) consists of solid and porous regions. All the blobs have the same shape and morphology which may well suggest that there is a tendency for the powder particles to form a spherical droplet prior to a movingless laser beam. Surrounding the melted core is a sintered region of partially melted powder particles where the powder particles were fused together to form inter-particle necks. There is a linear relation between size, weight and density of a blob and the laser power. The surface temperature obtained exceeds the melting and vaporization temperature of the titanium and this creates a hole on the top part of a blob as a result of a massive temperature rise. Laser power of 140W gives a consistent structure and hardness in a blob. Metallographic analyses of a blob’s cross-section show an α+β structure with prior-beta grains. The morphology of the lamellar structure consisted of acicular needles with a basket-weave pattern. The pores were characterised as having flat and spherical features with the size ranging from 2µm to 6µm. The micro-porosity observed may be associated with shrinkage which occurs during solidification or with the presence of entrapped gases from the atmosphere or argon gas from the shrouding environment Laser power and scan speed are the two most crucial factor controlling the laser-powder interactions. Result shows that laser power is capable of widening the processing parameters particularly the scan speed. Increased laser power causes more powder to melt thus creating a bigger melt pool. Contrary to this, increasing the scan speed reduces the interaction time thus a smaller amount of powder melts. The right combination of these two parameters results in inducing an appropriate exposure time where continuously scanned tracks can be formed. Most of the parts were successfully built using a specific volume energy density of 50Jmm⁻³, which was considered to be the optimum processing parameter for this research work. The ideal laser-material interaction time was calculated at 0.0008secs. The microstructural analysis revealed a fully lamellar structure with acicular morphology. XRD analysis confirmed the presence of α’ martensite, which explains the thermal history of a high isothermal condition and rapid cooling. The cross section of a solid part exhibited an acicular, needle-like structure with a herring bone pattern, parallel to building direction, due to directional solidification. The microstructure had a high tensile strength but with low ductility. It is also worth mentioning that a slight change in scan speed, with the intention of providing more energy density to the powder, may cause instability in the melt pool and cause deterioration in the mechanical properties. It is therefore confirmed that there is an upper limit and allowable processing window where a good balance of tensile strength and hardness in a DMLS part is achievable. A framework prior to an implant’s fabrication was established and the associated design and manufacturing software are reported. The processing route required software like MIMICS and MAGICS to manipulate the medical images and design data and equitable skills must be acquired to handle the machine in order to successfully fabricate the desired parts. Employing MAGICS new lattice function proved to be more efficient, saving time compared to a manual procedure, especially when dealing with large medical data manipulation. In conclusion, the proposed method from this study is capable of producing a customised part with the highest degree of design complexity compared with other conventional manufacturing methods. This has proved to be very suitable for manufacturing titanium medical implants, particularly craniofacial implants which require a customised and lightweight structure and at the same time still provide good mechanical propertie