Combination of Imaging Infrared Spectroscopy and X-ray Computed Microtomography for the Investigation of Bio-and Physicochemical processes in Structured Soils

Soil is a heterogeneous mixture of various organic and inorganic parent materials. Major soil functions are driven by their quality, quantity and spatial arrangement, resulting in soil structure. Physical protection of organic matter (OM) in this soil structure is considered as a vital mechanism for stabilizing organic carbon turnover, an important soil function in times of climate change. Herein, we present a technique for the correlative analysis of 2D imaging visible light near-infrared spectroscopy and 3D X-ray computed microtomography (mCT) to investigate the interplay of biogeochemical properties and soil structure in undisturbed soil samples. Samples from the same substrate but different soil management and depth (no-tilled topsoil, tilled topsoil and subsoil) were compared in order to evaluate this method in a diversely structured soil. Imaging spectroscopy is generally used to qualitatively and quantitatively identify OM with high spatial resolution, whereas 3D X-ray mCT provides high resolution information on pore characteristics. The unique combination of these techniques revealed that, in undisturbed samples, OM can be found mainly at greater distances from macropores and close to biopores. However, alterations were observed because of disturbances by tillage. The correlative application of imaging infrared spectroscopic and X-ray mCT analysis provided new insights into the biochemical processes affected by soil structural changes

Polyaniline membranes for use in organic solvent nanofiltration

Imperial Users onl

Polymeric properties and metal extraction performance of poly (vinyl chloride)/Aliquat 336 polymer inclusion membanes and electrospun fibres

This thesis aimed to investigate the polymeric properties and the metal extraction performance of polyvinyl chloride (PVC) and Aliquat 336 polymer inclusion membranes (PIMs) and electrospun fibres. The PIMs and the electrospun fibres were prepared using PVC and Aliquat 336 as the base polymer and extractant, respectively. The results showed that PVC/Aliquat 336 PIMs were non-homogenous and phase separated at sub micrometre scale even though all PIMs were transparent and homogenous to the naked eye or upon microscopic examination by scanning electron microscopy. The surface morphology of PIMs showed smooth surface with no apparent pores for PIMs with less than 30 wt.% Aliquat 336. Above 30 wt.% Aliquat 336, the PIMs showed some wrinkles and it became obvious as the Aliquat 336 content reach 40 wt.% suggesting that it might contain two separate domains. The phase separation was confirmed by the DMA results where the glass transition (Tg) and the melting temperature (Tm) of separated PVC and Aliquat 336 rich phases was clearly identified. This two phases is assigned to the α transition and β transition respectively. But, the later transition was not detected by DSC due to small changes in heat capacity where it could only be used to determine the Tg of PIMs with low Aliquat 336 content. For the PIMs observed here, the Tg was independent of Aliquat 336. This result indicates that Aliquat 336 does not act as a plasticising reagent in PIMs even though it has successfully produced a transparent and flexible thin film. The phase separation nature of PVC/Aliquat 336 PIMs has important implication towards the metal ion extraction performance in which the metal ions extraction could only occur when the proportion of Aliquat 336 exceeded 30 wt.%. This Aliquat 336 content of 30 wt.% also coincide with the appearance of Aliquat 336 rich phase observed by DMA. In addition, results from impedance study showed that PIMs with less than 30 wt.% Aliquat 336 were far out from the ideal plot and were not suitable to be used as a solid state polymer-electrolyte for metal ions extraction. This is due to the high resistance and low conductivity of the PIMs film. However, the metal extraction rate can also be improved by increasing the extraction temperature which increases the diffusivities in Aliquat 336 phase. The impact of aging on PVC/Aliquat 336 PIMs was also investigated in this thesis work. The results showed that freshly prepared PIMs contain residual tetrahydrofuran (THF) which was used as solvent for membrane manufacture. Removal of some residual THF by membrane aging resulted in notable changes in the thermomechanical properties of the PIMs where the PIMs exhibited two thermal transitions over the same range temperature. Although there is a clear impact of aging on membrane properties, there is no significant impact on the extraction of Cd(II) by PVC/Aliquat 336 PIMs. The preparation of electrospun fibres from PVC and Aliquat 336 was also demonstrated in this study. A detailed thermomechanical characterisation revealed that key characteristics and properties of PVC/Aliquat 336 PIMs and electrospun fibres differ significantly. The PVC/Aliquat 336 electrospun fibres were homogenous at sub micrometre scale. The homogeneity of PVC/Aliquat 336 electrospun fibres was confirmed by a single transition that is an α transition observed using DMA. Furthermore, the Aliquat 336 in electrospun fibres could function as a plasticizer. This was confirmed by the appearance of a single Tg that decreased with the increasing of Aliquat 336 content. In terms of metal ion extraction, the extraction of Cd(II) increased with the increasing of Aliquat 336 content. There was a significant extraction even at low Aliquat 336 content (i.e., 6 wt.%). In contrast, the extraction of Cd(II) in PIMs needs to exceed the percolation threshold of 30 wt.% Aliquat content. Besides, results from extraction capacity showed that electrospun fibres have higher absorption capacity compared to PIMs which clarify why they have better extraction. On the other hand, it appears that the applied voltage might influence the formation of beads and fibres diameters of PVC/Aliquat 336 electrospun mats but the level of significance may varies with the polymer concentration and tip distance or in this case Aliquat 336 concentration

Development of Ti-Fe-based powders for laser additive manufacturing of ultrafine lamellar eutectics

Years of academic research has gone into developing Ti-Fe-based ultrafine eutectic and near-eutectic alloys with remarkable mechanical properties. Cast ingots (few mm in dimensions) have demonstrated high compressive strengths (> 2 GPa) similar to bulk metallic glasses (BMGs), while retaining more than 15 % plasticity at room temperature [1–3]. However, conventional casting methods are incapable of providing uniform and high cooling rates necessary for growing such ultrafine microstructures over large dimensions without introducing significant heterogeneities. On the other hand, laser-based Additive Manufacturing (AM) techniques with inherently very high cooling rates like Selective Laser Melting (SLM) (ranging 106 K/s) or Laser Metal Deposition (LMD) (ranging 104 – 105 K/s) are appropriate for such microstructural growth and their track and layer-wise building approach maintains an almost constant cooling rate throughout bulk. This strongly motivates the development of high-quality powders for SLM and LMD trials. In this work, pre-alloyed powder of Fe-rich near-eutectic composition Fe82.4Ti17.6 (at %) was developed for LMD, while powders of two Ti-rich compositions: near-eutectic Ti66Fe27Nb3Sn4 (at %) and off-eutectic Ti73.5Fe23Nb1.5Sn2 (at %) were explored for SLM trials. Three gas atomisation methods, namely Crucible-based Gas atomisation (CGA), Crucible-Free atomisation (CFA) and Arc-melting Atomisation (AMA) were investigated for optimising powder production. In addition to conventional techniques, a novel methodology was proposed for one-step screening of powders’ key features based on advanced image analysis of X-Ray Computed Tomography (XCT) data. The methodology generated volume-weighted particle size distributions (which were validated against conventional laser diffraction), provided accurate estimations of internal porosity and quantitatively evaluated the 3D morphology of powders. In order to create a solidification knowledge dataset and further optimise the processing of powders under high cooling rates, in-depth microstructural studies were performed on these powders sieved into different particle size ranges (experiencing different solidification rates during atomisation). Results revealed that powder particle size is clearly related to, and can possibly predict, the solidification pathway followed during gas atomisation as well as its degree of completion. The ultrafine interlamellar spacing λ (< 190 μm) of lamellar eutectics observed in powders of near-eutectic compostitions increased almost linearly with particle size and revealed solidification rates similar to those encountered during SLM/LMD processing of the same or similar compositions. Therefore, this work highlights the potential of gas atomisation as a method to study rapid solidification and Laser-AM processing. Finally, two alloys were consolidated by AM using pre-alloyed powders and characterised mechanically, i.e. LMD-built Fe82.4Ti17.6 with lamellar eutectic microstructure and SLM-built Ti73.5Fe23Nb1.5Sn2 (off-eutectic) showing a unique “composite” microstructure of α-Ti and β-Ti grains strengthened by FeTi dispersoids that partially arranged themeselves as fine lamellas. Both alloys showed high compressive yield strengths (≈ 1.8 GPa and ≈ 1.9 GPa) at room temperature, with Ti73.5Fe23Nb1.5Sn2 showing high plasticity up to 20 %. The alloy showed higher tensile yield strength and elongation at intermediate temperatures (450 °C to 600 °C) than popular (α+β) aerospace alloys, like Ti-6Al-4V built by laser-AM [4–6]. LMD-built Fe82.4Ti17.6 largely remained brittle below 500 °C, but out-performed similar induction cast [7] and sintered alloys in compressive yield strength, thus proving an impressive candidate for compression-based applications (like tools) in the intermediate temperature range.Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidenta: Mónica Campos Gómez.- Secretaria: Carmen Cepeda Jiménez.- Vocal: María San Sebastián Ormazába

Copolymer microphase separation, properties, and applications

Copolymers represent a broad, but critically important class of materials. Often having properties superior to either of its constituents, copolymers are used in virtually all industries including automotive, aerospace, coatings, packaging, and cosmetics. Certain copolymers microphase separate to form nanosized domains that improve the physical properties of the copolymer. The polymer community already has a thorough understanding of how phase separation occurs, but the commercialization of phase separating copolymers lags significantly behind academia. Many of the copolymers that exist that have been undercharacterized and underutilized. This dissertation examines two such polymers. The first, a hard polystyrene material with soft nanodomains. The second, a soft polypentenamer rubber with hard nanodomains. These copolymers have very different physical properties, and thus very different intended applications. The common thread connecting the works in this dissertation is an effort to harness microphase separation to enable new applications. The first chapter gives an overview of copolymer architectures, properties, and their applications. Special attention is given to linear diblock copolymers as well as thermoplastic elastomers as these are most relevant to Chapters II-III and IV-V respectively. Chapter II explores the use of self-assembling diblock copolymers for use as ultrafiltration membranes. In this chapter a new membrane manufacturing process is described that quickly turns dense block copolymer films into porous membranes. Chapter III expands on this work by demonstrating a novel BCP annealing method that reduces domain size variation and is roll-to-roll printing compatible. In Chapters IV and V, we shift gears from studying glassy diblock copolymers, to soft multiblock elastomers. Chapter IV explores the effect of incorporating a glassy monomer into a crosslinked elastomer in a search for a natural rubber replacement. It was found that modest glassy block incorporation could greatly increase tensile strength. Chapter V then clarifies the strengthening mechanism observed in Chapter IV by looking at the effect of the glassy monomer before chemically crosslinking the elastomer. This work showed that phase separation of the glassy domains created physical crosslinks demonstrating thermoplastic elastic behavior. Finally, in Chapter VI some general conclusions about the research are recapped and put into a broader perspective. Suggestions for future work are then provided that would further the knowledge in both of the research directions

A Probabilistic Fatigue Strength Assessment in AlSi-Cast Material by a Layer-Based Approach

An advanced lightweight design in cast aluminium alloys features complexly shaped geometries with strongly varying local casting process conditions. This affects the local microstructure in terms of porosity grade and secondary dendrite arm spacing distribution. Moreover, complex service loads imply changing local load stress vectors within these components, evoking a wide range of highly stressed volumes within different microstructural properties per load sequence. To superimpose the effects of bulk and surface fatigue strength in relation to the operating load sequence for the aluminium alloy EN AC 46200, a layer-based fatigue assessment concept is applied in this paper considering a non-homogeneous distribution of defects within the investigated samples. The bulk fatigue property is now obtained by a probabilistic evaluation of computed tomography results per investigated layer. Moreover, the effect of clustering defects of computed tomography is studied according to recommendations from the literature, leading to a significant impact in sponge-like porosity layers. The highly stressed volume fatigue model is applied to computed tomography results. The validation procedure leads to a scattering of mean fatigue life from &minus;2.6% to 12.9% for the investigated layers, inheriting strongly varying local casting process conditions