In recent years, a variably high amount of uranium (U) and radon (Rn) were found in the water and airof the Kiirunavaara mine in Kiruna, northern Sweden. The Swedish Agency for Marine and WaterManagement (Havs och vattenmyndigheten) has maximum limits for “special polluting substances” inwater that is released to natural recipients (HVMFS 2019:25), therefore, the mining company LKAB,owner and operator of the Kiirunavaara mine, decided to conduct a study to investigate the issueregarding these findings, triggering this master thesis.From LKAB’s geochemical database, 25 samples were selected, prepared and studied throughpetrographic microscopy. Fourteen samples went through more than 70h of EPMA and BSE imageanalysis and 5 of them went through MLA. All methods were performed either in Uppsala’s Universitylaboratories or in Kiruna, at LKAB´s research facility in Malmberget. The ultimate goal of this projectwas to determine the primary metal source of uranium that could cause future problems in the watertreatment processes and leakages to recipients.In order to aboard this study in Kiirunavaara, where no previous uranium related study was everconducted, the main objectives were divided into identifying the main mineral carrier(s) of uranium thatcould be the source for these U anomalies, the characterization of the rock types and mineralassemblages associated with U-bearing minerals, and last, to try to propose preliminary implications forU solubility and distribution in the rock mass and mine water. This study found uraninite, thorite and anunknown species bearing uranium in some of the samples, both hanging and foot wall, all related tohydrothermal alterations and anhydrite. The water circulation throughout the rock mass of the minecould have been the trigger and transporter of these elements that were causing the anomalies in the firstplace.

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Silicon oxynitride (SiON) films for applications of optical waveguide devices deposited using plasma-enhanced chemical vapor deposition were investigated. The SiON films were deposited on 4¡¨ silicon wafers based on the reaction of N2O/SiH4 precursors. The refractive indices of the films were adjusted by varying the partial pressure of SiH4 in the precursors. In addition, films prepared at conventional flow (~1500 sccm) and low flow (~1000 sccm) conditions were compared. We found that the nitrogen content of the films grown at low flow conditions can be significantly reduced resulting in a reduction of absorption around 1500 nm. Therefore SiON films grown at low flow conditions would be more suitable for optical waveguide fabrication. Finally, with the aid of the beam propagation method (BPM) software, a single-mode optical waveguide based on the proposed technology was designed and fabricated. The propagation loss was 0.79dB/cm for TE polarization, and 0.73db/cm for T

Uranium-10wt% zirconium (U-10Zr) alloy nuclear fuels have been used for decades and new variations are under consideration ranging from U-5Zr to U-50Zr. As a precursor to understanding the fission gas behavior in U-Zr alloys using ion implantation, a basic study on the U-Zr metallurgy was completed using EPMA, DSC, XRD, Optical microscopy, and TEM with a focus on solid state phase transformations in alloys containing 2, 5, 10, 20, 30, and 50wt% zirconium. Alloys were cast by crucible melting using high temperature furnace under argon atmosphere in yttrium oxide crucibles and various thermal profiles were used to study phase transformations in these alloys. Using TEM, XRD, and DSC data, it was ascertained that athermal-ω, along with martensitic α1, formed in all alloys quenched from γ phase. XRD could detect the presence of athermal-ω only in U-20, 30 and 50wt%Zr alloys. BSE images for as-cast alloys of 2, 5, 10, 20, and 30wt%Zr had lamellar microstructure with lamellae rich in zirconium. All alloy samples clearly showed a heating transformation pertaining to δ → γ in DSC data while XRD could only confirm the presence of δ phase in U-20, 30, and 50wt%Zr alloys. An explanation is offered for the absence of δ phase peaks in uranium-rich alloys based on its formation mechanism. Alloy samples of U-2, 5, and 10wt%Zr were step-cooled from γ phase by annealing in the (α + δ) phase field before cooling to room temperature revealed broad peaks for δ phase indicating incomplete collapse of {111}γ planes. Both as cast and γ- quenched alloys were annealed at 600degreeC, in the (α + δ) phase field for 1, 3, 7, and 30 days. Microstructures of the samples in both cases contained uranium-rich matrix and zirconium-rich precipitates and WDS analyses were consistent with their being α-U and δ phase respectively. However, XRD data for annealed alloys never showed peaks for δ phase even though it’s area fraction was within the detection limits. Moreover, the peaks which were present in U-20wt%Zr vanished after annealing for 7 days. Based on the data obtained, it is suggested that it is more appropriate to consider the presence of metastable diffusional-ω instead of a stable δ in the as-cast alloys and that it is not stable at 600degreeC.

Decorative, polychrome ceramics from Corinth, Greece, produced during the 8th-6th centuries B.C.E. are luxury goods that were widely traded throughout Greece and the Mediterranean. The decorated ceramics were produced in a variety of shapes, including aryballos, alabastron, and olpe. They were decorated with slip-glazes in distinctive white, black, red, yellow, and purple colors, and in a variety of surface finishes, matte, semi-matte and glossy. Artisans in Corinthian workshops experimented to change the colors of the slips by varying the type and amount of iron-rich raw materials. They also varied the composition of the clay used as a binder and the amount of flux used as a sintering aid to promote glass formation. This research reconstructs the technology used by the Corinthian craftsmen to produce the Archaic polychrome ceramics, and shows how these technologies differed from the production of better known, more prestigious Athenian black-figure and red-figure ceramics. Through microstructural examination of archaeological samples and replication experiments, this thesis proposes that the purple iron oxide pigment is the result of acid treatment and oxidation of iron metal. The firing temperature range of the Corinthian polychrome ceramics was determined experimentally to be 925-1025° C, which is higher than previously reported and similar to that reported for Corinthian transport amphoras. The firing range is higher by 50-150° C than the Athenian black-figure and red-figure ceramics. Samples of Corinthian polychrome and Athenian black-figure ceramics from the Marie Farnsworth collection at the University of Arizona were tested and compared to Corinthian clay collections. Analytical techniques included Fourier-transform infrared spectroscopy (FTIR), scanning-electron microscopy with energy-dispersive spectroscopy (SEM-EDS), micro-Raman spectroscopy, and wavelength-dispersive electron microprobe (EPMA with BSE-SEM).

L’émergence des bactéries photosynthétiques oxygéniques (BPO), ou cyanobactéries, est probablement l’évènement le plus important de l’histoire de la Terre, depuis l’apparition de la vie elle-même. Par la libération d’O2 dans l’environnement, les BPO ont conduit à l’oxygénation de notre planète, jusqu’alors anoxique, et au développement de la vie complexe. Cependant, cette évolution n’est toujours pas datée. Dans cette étude, j’ai cherché à identifier des signatures chimiques spécifiques aux BPO, in situ à l’échelle du μm, dans des tapis microbien fossiles datant de 3,45 à 1,88 Ga, recouvrant ainsi une période allant de la Terre anoxique à la Terre oxygénée après le « Great Oxidation Event » (GOE). Nous avons utilisé la microscopie optique, la spectroscopie Raman, le MEB/EDX, l’EPMA, la μ-XRF à rayonnement synchrotron (SR-XRF), et des analyses isotopiques. Une nouvelle méthode de quantification élémentaire pour SR-XRF, ainsi qu’une nouvelle méthodologie de préparation d’échantillons ont été developpés. Les résultats obtenus par EPMA et μ-XRF montrent que, dans certains contextes de déposition, un enrichissement en lanthanides (par exemple La, Sm, Gd) de cellules fossiles, et un enrichissement en Cu de pyrites diagénétiques formées en association avec des BPO, pourraient représenter des signatures chimiques spécifiques aux BPO. Suite à ces résultats, je propose que les BPO ont évolué entre 3,33 et 2,98 Ga. Je propose que les techniques élémentaires telles que l’EPMA et la μ-XRF sont les techniques les plus appropriées pour trouver des signatures chimiques spécifiques aux BPO et contraindre leur émergence dans le temps. / The evolution of oxygenic photosynthetic bacteria (OPB) is probably the most important biological event of Earth’s history since the emergence of life itself. The release of their by-product O2 in the environment, which was globally anoxic, fundamentally changed the face of the Earth and led to the development of complex life. However, the specific timing of this evolutionary step remains unclear. This study is based on the search for in situ chemical signatures of OPB at the microbial (μm) scale, within fossilized microbial photosynthetic mats in Archean and Paleoproterozoic sediments dated between 3.45 Ga and 1.88 Ga, i.e. spanning the anoxic Earth to the aftermath of the GOE. We used optical microscopy, Raman spectroscopy, SEM/EDS, EPMA, synchrotron radiation μ-XRF, and isotope analytical techniques. The μXRF results were improved by the use of a new sample preparation method and a new quantification method, both developed during this study.Results obtained by EPMA and μXRF show that, under certain depositional contexts, enrichment in lanthanides (such as Sm, La and Gd) in individual OPB cells, as well as a Cu enrichment in diagenetic pyrites formed in association with OPB, may represent chemical signatures of OPB. I propose that OPB evolved sometime between 3.33 Ga and 2.98 Ga. Also, I argue that elemental techniques such as EPMA and μ-XRF are the most suitable techniques to find chemical signatures of OPB and constrain the timing of their emergence.

O grande magmatismo intracontinental ocorrido a 133 Ma na Bacia do Paraná foi desenvolvido por um sistema fissural no qual a interação da Pluma Tristão da Cunha na base da litosfera (com ou sem contaminação crustal) gerou derrames, diques e sills no Brasil, nos Estados do RS, SC, PR, SP, MT, MS e GO, e em parte do Paraguai, Argentina e Uruguai. Na Formação Serra Geral, representativa deste intenso magmatismo, foram coletadas amostras de sills (RS, PR, SP e GO) cristalizados entre os sedimentos Paleozóicos pré-vulcânicos da Bacia do Paraná. Já haviam sido realizados diversos estudos geoquímicos a partir da década de 80 com objetivo de identificar as variações químicas de diques, derrames e sills da Formação Serra Geral. No entanto, a utilização de novas técnicas analíticas (EPMA e LA-ICP-MS), utilizadas no presente estudo, proporcionaram o entendimento das variações químicas de forma pontual em minerais ígneos. A geoquímica dos sills estudados caracteriza-os como sub-alcalinos toleíticos continentais que variam de basaltos a andesitos basáltico. Assim, podendo ser divididos em dois grupos químicos: sills do Rio Grande do Sul (baixo TiO2 < 2 wt.%, com concentrações inferiores de P2O5, Nb, Sr, Zr, Zn, Y e Pb e concentrações superiores de Rb, Th, U, e Cs) e sills do Paraná, São Paulo e Goiás (alto TiO2 >2 wt.%, de geoquímica oposta). Petrograficamente, os sills do RS possuem granulação mais fina, ocorrência restrita de cobre nativo e distribuição modal elevada para plagioclásios cálcicos, quando comparados ao sills do PR, SP e GO. A determinação geoquímica por micro-análise em plagioclásios e clinopiroxênios demonstra que as variações químicas identificadas em rocha total são relatas as modificações químicas ocorridas nestes minerais. Variações do coeficiente de partição (KD) de elementos traços compatíveis em diversas zonas de cristais de plagioclásio e clinopiroxênio possuem correlação na substituição dos elementos Ca, Na, Al, Fe e Mg nos sistemas NaAlSi3O8-CaAl2Si2O8 e Mg2Si2O6-CaMgSi2O6-CaFeSi2O6- Fe2Si2O6, respectivamente. Coeficientes de partição de cristais de plagioclásio e clinopiroxênio agora são determinados em diferentes porções de núcleo, intermédio e borda aprimorando o conhecimento da variação do KD até então determinado como um único valor apenas para o cristal. / The large intracontinental magmatism occurred at 133 Ma in the Paraná Basin was developed by a fissure system in which the interaction of Tristan da Cunha plume at the base of the lithosphere (with or without crustal contamination) caused lava flows, dikes and sills in the RS, SC, PR, SP, MT, MS and GO and part of Paraguay, Argentina and Uruguay. In the Serra Geral Formation, representative of intense magmatism, sills crystallized samples were collected (RS, PR, SP and GO) between the Paleozoic prevolcanic sediments of Paraná basin. Several geochemical studies have been carried out since the 80's in order to identify the chemical variations of dikes, sills and lava flows of the Serra Geral Formation. However, the use of new analytical techniques (EPMA and LA-ICP-MS) provided the study of chemical variations in a timely manner in igneous minerals. The geochemistry of the sills studied characterized them as sub-alkaline continental tholeiitic basalts ranging from the basalt to basaltic andesites. Divided into two chemical groups: sills of Rio Grande do Sul (low TiO2 <2 wt.%, With lower concentrations of P2O5, Nb, Sr, Zr, Zn, Y and Pb and higher concentrations of Rb, Th, U, and Cs) and sills of Parana, Sao Paulo and Goiás (high TiO2> 2 wt.%, geochemical opposite). Petrographically the sills of the RS have finer grain, restricted occurrence of native copper and modal higher to calcic plagioclase, compared to the sills of the PR, SP and GO. Geochemical determination by micro-analysis in plagioclases and clinopyroxenes show that the chemical variations identified in whole rock we describe the chemical changes occurring in these minerals. Variations of the partition coefficient (KD) of compatible trace elements in various parts of crystals of plagioclase and clinopyroxene were correlated in the replacement of Ca, Na, Al, Fe and Mg systems NaAlSi3O8-CaAl2Si2O8 and Mg2Si2O6-CaMgSi2O6-CaFeSi2O6-Fe2Si2O6, respectively. Partition coefficients of crystals of plagioclase and clinopyroxene are now determined in different portions of core, intermediate and rim enhance knowledge of the variation of KD previously determined as a single value only to the crystal.

O grande magmatismo intracontinental ocorrido a 133 Ma na Bacia do Paraná foi desenvolvido por um sistema fissural no qual a interação da Pluma Tristão da Cunha na base da litosfera (com ou sem contaminação crustal) gerou derrames, diques e sills no Brasil, nos Estados do RS, SC, PR, SP, MT, MS e GO, e em parte do Paraguai, Argentina e Uruguai. Na Formação Serra Geral, representativa deste intenso magmatismo, foram coletadas amostras de sills (RS, PR, SP e GO) cristalizados entre os sedimentos Paleozóicos pré-vulcânicos da Bacia do Paraná. Já haviam sido realizados diversos estudos geoquímicos a partir da década de 80 com objetivo de identificar as variações químicas de diques, derrames e sills da Formação Serra Geral. No entanto, a utilização de novas técnicas analíticas (EPMA e LA-ICP-MS), utilizadas no presente estudo, proporcionaram o entendimento das variações químicas de forma pontual em minerais ígneos. A geoquímica dos sills estudados caracteriza-os como sub-alcalinos toleíticos continentais que variam de basaltos a andesitos basáltico. Assim, podendo ser divididos em dois grupos químicos: sills do Rio Grande do Sul (baixo TiO2 < 2 wt.%, com concentrações inferiores de P2O5, Nb, Sr, Zr, Zn, Y e Pb e concentrações superiores de Rb, Th, U, e Cs) e sills do Paraná, São Paulo e Goiás (alto TiO2 >2 wt.%, de geoquímica oposta). Petrograficamente, os sills do RS possuem granulação mais fina, ocorrência restrita de cobre nativo e distribuição modal elevada para plagioclásios cálcicos, quando comparados ao sills do PR, SP e GO. A determinação geoquímica por micro-análise em plagioclásios e clinopiroxênios demonstra que as variações químicas identificadas em rocha total são relatas as modificações químicas ocorridas nestes minerais. Variações do coeficiente de partição (KD) de elementos traços compatíveis em diversas zonas de cristais de plagioclásio e clinopiroxênio possuem correlação na substituição dos elementos Ca, Na, Al, Fe e Mg nos sistemas NaAlSi3O8-CaAl2Si2O8 e Mg2Si2O6-CaMgSi2O6-CaFeSi2O6- Fe2Si2O6, respectivamente. Coeficientes de partição de cristais de plagioclásio e clinopiroxênio agora são determinados em diferentes porções de núcleo, intermédio e borda aprimorando o conhecimento da variação do KD até então determinado como um único valor apenas para o cristal. / The large intracontinental magmatism occurred at 133 Ma in the Paraná Basin was developed by a fissure system in which the interaction of Tristan da Cunha plume at the base of the lithosphere (with or without crustal contamination) caused lava flows, dikes and sills in the RS, SC, PR, SP, MT, MS and GO and part of Paraguay, Argentina and Uruguay. In the Serra Geral Formation, representative of intense magmatism, sills crystallized samples were collected (RS, PR, SP and GO) between the Paleozoic prevolcanic sediments of Paraná basin. Several geochemical studies have been carried out since the 80's in order to identify the chemical variations of dikes, sills and lava flows of the Serra Geral Formation. However, the use of new analytical techniques (EPMA and LA-ICP-MS) provided the study of chemical variations in a timely manner in igneous minerals. The geochemistry of the sills studied characterized them as sub-alkaline continental tholeiitic basalts ranging from the basalt to basaltic andesites. Divided into two chemical groups: sills of Rio Grande do Sul (low TiO2 <2 wt.%, With lower concentrations of P2O5, Nb, Sr, Zr, Zn, Y and Pb and higher concentrations of Rb, Th, U, and Cs) and sills of Parana, Sao Paulo and Goiás (high TiO2> 2 wt.%, geochemical opposite). Petrographically the sills of the RS have finer grain, restricted occurrence of native copper and modal higher to calcic plagioclase, compared to the sills of the PR, SP and GO. Geochemical determination by micro-analysis in plagioclases and clinopyroxenes show that the chemical variations identified in whole rock we describe the chemical changes occurring in these minerals. Variations of the partition coefficient (KD) of compatible trace elements in various parts of crystals of plagioclase and clinopyroxene were correlated in the replacement of Ca, Na, Al, Fe and Mg systems NaAlSi3O8-CaAl2Si2O8 and Mg2Si2O6-CaMgSi2O6-CaFeSi2O6-Fe2Si2O6, respectively. Partition coefficients of crystals of plagioclase and clinopyroxene are now determined in different portions of core, intermediate and rim enhance knowledge of the variation of KD previously determined as a single value only to the crystal.

O grande magmatismo intracontinental ocorrido a 133 Ma na Bacia do Paraná foi desenvolvido por um sistema fissural no qual a interação da Pluma Tristão da Cunha na base da litosfera (com ou sem contaminação crustal) gerou derrames, diques e sills no Brasil, nos Estados do RS, SC, PR, SP, MT, MS e GO, e em parte do Paraguai, Argentina e Uruguai. Na Formação Serra Geral, representativa deste intenso magmatismo, foram coletadas amostras de sills (RS, PR, SP e GO) cristalizados entre os sedimentos Paleozóicos pré-vulcânicos da Bacia do Paraná. Já haviam sido realizados diversos estudos geoquímicos a partir da década de 80 com objetivo de identificar as variações químicas de diques, derrames e sills da Formação Serra Geral. No entanto, a utilização de novas técnicas analíticas (EPMA e LA-ICP-MS), utilizadas no presente estudo, proporcionaram o entendimento das variações químicas de forma pontual em minerais ígneos. A geoquímica dos sills estudados caracteriza-os como sub-alcalinos toleíticos continentais que variam de basaltos a andesitos basáltico. Assim, podendo ser divididos em dois grupos químicos: sills do Rio Grande do Sul (baixo TiO2 < 2 wt.%, com concentrações inferiores de P2O5, Nb, Sr, Zr, Zn, Y e Pb e concentrações superiores de Rb, Th, U, e Cs) e sills do Paraná, São Paulo e Goiás (alto TiO2 >2 wt.%, de geoquímica oposta). Petrograficamente, os sills do RS possuem granulação mais fina, ocorrência restrita de cobre nativo e distribuição modal elevada para plagioclásios cálcicos, quando comparados ao sills do PR, SP e GO. A determinação geoquímica por micro-análise em plagioclásios e clinopiroxênios demonstra que as variações químicas identificadas em rocha total são relatas as modificações químicas ocorridas nestes minerais. Variações do coeficiente de partição (KD) de elementos traços compatíveis em diversas zonas de cristais de plagioclásio e clinopiroxênio possuem correlação na substituição dos elementos Ca, Na, Al, Fe e Mg nos sistemas NaAlSi3O8-CaAl2Si2O8 e Mg2Si2O6-CaMgSi2O6-CaFeSi2O6- Fe2Si2O6, respectivamente. Coeficientes de partição de cristais de plagioclásio e clinopiroxênio agora são determinados em diferentes porções de núcleo, intermédio e borda aprimorando o conhecimento da variação do KD até então determinado como um único valor apenas para o cristal. / The large intracontinental magmatism occurred at 133 Ma in the Paraná Basin was developed by a fissure system in which the interaction of Tristan da Cunha plume at the base of the lithosphere (with or without crustal contamination) caused lava flows, dikes and sills in the RS, SC, PR, SP, MT, MS and GO and part of Paraguay, Argentina and Uruguay. In the Serra Geral Formation, representative of intense magmatism, sills crystallized samples were collected (RS, PR, SP and GO) between the Paleozoic prevolcanic sediments of Paraná basin. Several geochemical studies have been carried out since the 80's in order to identify the chemical variations of dikes, sills and lava flows of the Serra Geral Formation. However, the use of new analytical techniques (EPMA and LA-ICP-MS) provided the study of chemical variations in a timely manner in igneous minerals. The geochemistry of the sills studied characterized them as sub-alkaline continental tholeiitic basalts ranging from the basalt to basaltic andesites. Divided into two chemical groups: sills of Rio Grande do Sul (low TiO2 <2 wt.%, With lower concentrations of P2O5, Nb, Sr, Zr, Zn, Y and Pb and higher concentrations of Rb, Th, U, and Cs) and sills of Parana, Sao Paulo and Goiás (high TiO2> 2 wt.%, geochemical opposite). Petrographically the sills of the RS have finer grain, restricted occurrence of native copper and modal higher to calcic plagioclase, compared to the sills of the PR, SP and GO. Geochemical determination by micro-analysis in plagioclases and clinopyroxenes show that the chemical variations identified in whole rock we describe the chemical changes occurring in these minerals. Variations of the partition coefficient (KD) of compatible trace elements in various parts of crystals of plagioclase and clinopyroxene were correlated in the replacement of Ca, Na, Al, Fe and Mg systems NaAlSi3O8-CaAl2Si2O8 and Mg2Si2O6-CaMgSi2O6-CaFeSi2O6-Fe2Si2O6, respectively. Partition coefficients of crystals of plagioclase and clinopyroxene are now determined in different portions of core, intermediate and rim enhance knowledge of the variation of KD previously determined as a single value only to the crystal.

The object of the present investigation has been to relate the mechanical properties of a high strength Mg-Y-Gd alloy to alloy composition, extrusion parameters and microstructure. Three alloys with various Y: Gd ratios, of similar total solute content (at %) to Elektron 675, have been investigated in this study:9122: Mg – 6.5 wt % Y – 7.6 wt % Gd – 0.4 wt % Zr 9123: Mg – 8.2 wt % Y – 4.8 wt % Gd – 0.4 wt % Zr9124: Mg – 2.6 wt % Y – 13.1 wt % Gd – 0.4 wt % ZrThe three alloys were extruded at 425 and 475 °C with extrusion ratio 17: 1 to give two samples from each alloy, group a and b. Alloy 9122 was also extruded at 460 and 500 °C with extrusion ratio 10: 1 to give another two samples c and d. The as-cast microstructure of the three alloys comprised equiaxed α-magnesium grains and regions of eutectic decorating some grain boundaries formed during solidification of the ingot. Variation of extrusion parameters has resulted in a dispersion of different volume fractions of second phase particles in different groups of samples. The chemistry of second phase particles was determined by in-situ bulk energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD); magnesium yttrium was identified for near-equiaxed particles and yttrium hydride was proposed as a possible identification for cuboids. The composition of these compounds varied with variation of Y: Gd in the three alloys. Variation of extrusion ratio and extrusion temperature had a clear effect on the evolution of the extruded microstructure and the development of crystallographic texture as characterized by optical microscopy, electron backscattered diffraction (EBSD) and inverse pole figures. The microstructure of the extruded samples was refined during extrusion through dynamic recrystallization (DRX). Samples of groups a, b and c exhibited a microstructure in which bands of fine, equiaxed grains in association with stringers of second phase particles (running along the extrusion direction) were formed between bands of coarse, equiaxed grains. Sample d contained only small volume fraction of second phase particles; only a few alternating bands were formed and considerable grain growth occurred. A random texture was developed during extrusion in samples of groups a, b and c; a wide spread of orientations accompanied by a (new) previously unreported texture component in which basal poles of some grains are aligned nearly parallel to the extrusion direction was developed. The new texture component was weak in sample c and entirely suppressed in sample d. The asymmetry in tensile and compressive yield stress commonly associated with magnesium extrusions was nearly eliminated in samples of group a and b. The new basal texture component was likely to be a result of nucleation of DRX on sites rotating into this orientation. This is proposed to be a result of deformation in those regions in grains was accomodated by basal, prismatic and pyramidal slip. The grains nucleated in this orientation appear to have developed a form of preferred growth which led to strengthening of this new component following solution treatment. The effect of varying solute content (Y & Gd) and different ageing temperatures 150, 200, 250 and 300 °C (T5 & T6) on the ageing response and precipitation reaction were investigated using hardness measurements and transmission electron microscopy (TEM). Alloy 9122 showed the highest ageing response of the three alloys at 150, 200 and 250 °C (T5 & T6); specimens aged in the T5 gave higher hardness than the T6 treatment, a contribution of fine grain size. The three alloys did not respond to ageing at 300 °C. The precipitation reactions that occurred in alloy 9122 (at under, peak and overageing) and alloys 9123 and 9124 (at peak ageing) at 250 °C have been characterized. The precipitation sequence observed in sample 9122a can be described as: . The microstructure of peak aged specimens of alloys 9122 and 9124 were similar; both contained a homogeneous dispersion of precipitates and some metastable precipitates. Alloy 9123 contained only a homogeneous dispersion of precipitates and remnants of precipitates and no precipitates. The enhanced thermal stability of and phases are most likely responsible for the superior elevated temperature properties of Elektron 675. The effect of varying solute content (Y & Gd) and extrusion parameters on the mechanical properties were determined using tensile testing. Alloys 9122 and 9124 exhibited higher 0.2 % proof stress and UTS than alloy 9123 and alloy 9122 was the hardest alloy. Alloy 9122 exhibited the worst ductiliy (T5 and T6) among 9123 and 9124, and this was attributed to the higher volume fraction of second phase particles. The ductility of samples a, b and c in the as-extruded & T5 conditions, particularly in the transverse direction, was limited by stringers of second phase particles, whereas ductility and failure in sample d was governed by grain size and texture. The ductility and failure of all samples aged in the T6 treatment, irrespective of the extrusion history, was controlled by texture and grain size rather than stringers of second phase particles.