Impact of Chemical and Morphological Changes on the Phase Stability of Magnetic Materials

Permanent magnetic materials are of fundamental importance to the modern world, utilised in fields as broad as computers, cars, and MRI machines. Their importance is set to increase as the world move towards sustainable energy and away from fossil fuels. A seamless switch requires an increase in magnet production, and an improvement in performance. Rare-earth reduced permanent magnets are considered a solution to these two problems. This thesis investigates the impact of chemical and morphological changes on the phase stability of rare-earth reduced hard permanent magnets. New methodologies for investigating the position preference of atomic substitutions and dopants have been applied to the RT12 (R = Rare-Earth, T = Transition metal) phase group. This work demonstrates that substitution of the transition metal for titanium in NdFe12, SmFe12, and SmCo12, decreases the cohesive energy, and therefore increases the stability of the structure up to 8Ti at.%. Through analysis of substitution positions it is demonstrated this is tied to a structural effect, derived from a switch in the symmetry of preferential substitution positions. To gauge the manufacturing feasibility of one of these phases, computational investigations of the melting temperature of NdFe12 at various pressures were performed using a Solid Liquid coexistence methodology applied in Molecular Dynamics. Pair potentials used for this work were generated by a genetic algorithm potential fitting methodology, which has application beyond the RT12 phase group. Finally, a new methodology for understanding grain morphology is presented, which takes into consideration the shape, surfaces, and interfaces of cyrstalline grain structures. This methodology is tested on the FePt L10 structure, which is able to produce stable magnetic grains at nanometer sizes, due to it’s magnetic anisotropy of Ha = 6-10 MJ/m . This work shows that at grain sizes between 3-9nm, the morphology of the grains is dominated by surface energy, and will result in structures with {111} planes as their primary faces. This result has implications for the design of next generation hard drives.Engineering and Physical Sciences Research Council (EPSRC

Atomistic study on the pressure dependence of the melting point of NdFe12

We investigated, using molecular dynamics, how pressure affects the melting point of the recently theorised and epitaxially grown structure NdFe12. We modified Morse potentials using experimental constants and a genetic algorithm code, before running two-phase solid-liquid coexistence simulations of NdFe12 at various temperatures and pressures. The refitting of the Morse potentials allowed us to significantly improve the accuracy in predicting the melting temperature of the constituent elements

Atomistic simulations of α - Fe /Nd2Fe14B magnetic core/shell nanocomposites with enhanced energy product for high temperature permanent magnet applications

Nd 2 Fe 14 B has generated significant interest since its discovery in the 1980s due to its impressive energy density, which makes it a prime candidate for use in permanent magnet applications. Its performance is known to suffer greatly at the high temperatures required for motor applications around 450 K. Core/shell nanocomposites provide a potential route to improve material performance by combining the highly anisotropic permanent magnet with a material with high moment and high Curie temperature. We have used an atomistic spin model to investigate the magnetic properties of Nd 2 Fe 14 B with α - F e in a core/shell nanostructure. We find that at typical motor operating temperatures, increasing α - F e content reduces the coercivity of the system while enhancing the saturation magnetization. The overall effect is that an improvement in B H max is seen with increasing α - F e up to an optimal value of 70 vol. %. This property of core/shell nanostructures would make them a suitable substitute for pure Nd 2 Fe 14 B while simultaneously lowering the raw material cost of the permanent magnet component of high-performance motors

Probability distribution of substituted Titanium in RT12 (R = Nd, Sm, T = Fe, Co) structures

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordWe investigated the atomic fill site probability distributions across supercell structures of RT12-xTi (R=Nd, Sm, T=Fe, Co). We use a combined molecular dynamics and Boltzmann distribution approach to extrapolate the probability distributions for Ti substitution from lower to higher temperatures with an equilibrium condition to assess how temperature affects the predictability of the structures fill path. It was found that the Nd and Sm based Fe systems have the highest filling probability path at lower temperatures but the cohesive energy change due to Ti substitution in Sm and Nd based crystals indicates that a more stable system could be achieved with a combination Co and Fe in the transition metal site.Engineering and Physical Sciences Research Council (EPSRC)Vienna Science and Technology FundRoyal SocietyToyota Motor Corporatio

Influence of healthy sweeteners (tagatose and oligofructose) on the physicochemical characteristics of orange marmalade

This is the peer reviewed version of the following article: Rubio‐Arraez, S., Sahuquillo, S., Capella, J. V., Ortolá, M. D., & Castelló, M. L. (2015). Influence of healthy sweeteners (tagatose and oligofructose) on the physicochemical characteristics of orange marmalade. Journal of Texture Studies, 46(4), 272-280, which has been published in final form at http://dx.doi.org/10.1111/jtxs.12127. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Today's society shows a growing interest in healthy, safe and high nutritional quality food. Thus, in this paper sweet orange marmalades have been developed using healthy sweeteners (tagatose and oligofructose) in different proportions. Analyses of Brix, pH, moisture, water activity, antioxidant capacity, optical and rheological properties have been carried out, initially and after 45 days of storage. Microbiological analyses have also been performed to determine their stability. Furthermore, a sensorial assessment has been conducted to find out acceptance of these new orange marmalades by consumers. The results showed that the highest proportion of oligofructose contributed to improve the initial antioxidant capacity of marmalades. The marmalade with the same proportions of oligofructose and tagatose was more consistent and showed a further increase in the elastic component over time. All marmalades had a similar appearance, but oligofructose reduced L*. Finally, orange marmalades made with healthy sweeteners were better scored.The authors would like to thank the Serigo family for donating the raw material and the project GV/2013/029 by the GVA, Valencia, Spain.Rubio Arraez, S.; Sahuquillo Ceruelos, S.; Capella Hernández, JV.; Ortolá Ortolá, MD.; Castelló Gómez, ML. (2015). Influence of healthy sweeteners (tagatose and oligofructose) on the physicochemical characteristics of orange marmalade. Journal of Texture Studies. 46(4):272-280. https://doi.org/10.1111/jtxs.12127S27228046

Determination of mass transfer resistances of fast reactions in three-phase mechanically agitated slurry reactors

A methodology for the determination of mass transfer resistances of fast reactions in three-phase mechanically agitated slurry reactors under the reaction conditions is presented. The mass transfer resistances affect significantly the overall mass transfer rate, the design equation and consequently the scale up of the reactor. There is not established methodology to separate the mass transfer resistances under reaction conditions by changing catalyst loading and manipulating the process variables, pressure and agitation speed. This allows to avoid the use of different catalyst particles and give the chance to calculate the mass transfer resistances without caring about the type of catalyst. We calculate each mass transfer resistance under conditions which do not allow to neglect any of the resistances. It is shown that the level off of mass transfer rate which is developed in the plot of mass transfer rate against agitation speed plots is not enough to determine the limiting regime. The hydrogenation of styrene over Pd/C (5% catalyst content) is used as case study to demonstrate the methodology

Optimisation of the emulsion liquid membrane composition and demulsification for rhodium extraction

This study was aimed at designing an optimised emulsion liquid membrane (ELM) for the extraction of rhodium from precious metal refinery wastewaters. The demulsification process and the structure of the optimised ELM are reported on. Two optimised ELMs were prepared. The first one contained a 30 % solution of toluene in kerosene as diluent with the following concentrations of the ELM components: 30.000 g/L (w/v) polyisobutylene, 10.870 g/L (m/v) of trioctyl amine and 51.001 g/L (m/v) of SPAN 80. The second ELM contained the same diluent, but the concentrations of the other ELM components in it were as follows: 20.000 g/l of polyisobutylene, 10.268 g/l trioctyl amine and 50.024 g/l of SPAN 80. The stripping phase was the same in both optimised ELMs, namely a 2 M solution of HNO3. The stripping phase and the diluent solution were mixed together in ratios of 1:1 and 2:1, respectively. Two methods were used to characterise the microdroplet diameters, i.e. optical microscopy and the Zeta-sizer. For the t-test, the p-value of 0.3018 at 5 % level of significance showed that there was statistically no significant difference in the mean micro-droplet size for 1:2 ELMs containing 20 g/l and 30 g/l of polyisobutylene after 40 minutes of emulsification. The best demulsification results were obtained using the chemical demulsification with polyethylene glycol with molecular weight of 400 g/mol (PEG 400) at 50 ± 1 °C for 24 hours. However, significant carryover of toluene, trioctyl amine and polyethylene glycol into the aqueous phase was observed

Single-Phase Flow of Non-Newtonian Fluids in Porous Media

The study of flow of non-Newtonian fluids in porous media is very important and serves a wide variety of practical applications in processes such as enhanced oil recovery from underground reservoirs, filtration of polymer solutions and soil remediation through the removal of liquid pollutants. These fluids occur in diverse natural and synthetic forms and can be regarded as the rule rather than the exception. They show very complex strain and time dependent behavior and may have initial yield-stress. Their common feature is that they do not obey the simple Newtonian relation of proportionality between stress and rate of deformation. Non-Newtonian fluids are generally classified into three main categories: time-independent whose strain rate solely depends on the instantaneous stress, time-dependent whose strain rate is a function of both magnitude and duration of the applied stress and viscoelastic which shows partial elastic recovery on removal of the deforming stress and usually demonstrates both time and strain dependency. In this article the key aspects of these fluids are reviewed with particular emphasis on single-phase flow through porous media. The four main approaches for describing the flow in porous media are examined and assessed. These are: continuum models, bundle of tubes models, numerical methods and pore-scale network modeling.Comment: 94 pages, 12 figures, 1 tabl