Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Magnesium aluminate (MgAl2O4) spinel (MAS) is a synthetic material with cubic crystal structure and excellent chemical, thermal, dielectric, mechanical and optical properties. These properties made MAS an indispensable material for optically transparent windows, domes and armours, and for certain refractory applications. High processing cost of dense MAS ceramics is in the main responsible for its limited usage in certain important applications despite its excellent performance in them. The volume expansion (∼8%) associated with MAS phase formation from alumina and magnesia does not allow obtaining dense MAS bodies in a single-stage reaction sintering process. Therefore, dense MAS bodies are made by following a double stage firing process, which is expensive. The existing literature suggests that the processing cost of dense MAS ceramics could be reduced to a great extent by decisive selection of starting raw materials, powder processing and densification conditions, and by understanding the under...

A review on magnesium aluminate (MgAl2O4) spinel: synthesis, processing and applications

Transparent ceramics have various potential applications such as infrared (IR) windows/domes, lamp envelopes, opto-electric components/devices, composite armors, and screens for smartphones and they can be used as host materials for solid-state lasers. Transparent ceramics were initially developed to replace single crystals because of their simple processing route, variability in composition, high yield productivity, and shape control, among other factors. Optical transparency is one of the most important properties of transparent ceramics. In order to achieve transparency, ceramics must have highly symmetric crystal structures; therefore, the majority of the transparent ceramics have cubic structures, while tetragonal and hexagonal structures have also been reported in the open literature. Moreover, the optical transparency of ceramics is determined by their purity and density; the production of high-purity ceramics requires high-purity starting materials, and the production of high-density ceramics requires sophisticated sintering techniques and optimized sintering aids. Furthermore, specific mechanical properties are required for some applications, such as window materials and composite armor. This review aims to summarize recent progress in the fabrication and application of various transparent ceramics.

Materials development and potential applications of transparent ceramics: A review

Materials for downconversion in solar cells: Perspectives and challenges

Polycrystalline Al2O3, magnesium aluminate spinel (MgAl2O4), MgO, Si3N4, and SiC were irradiated with various ions at 200-450 K, and microstructures were examined following irradiation using cross-section TEM. Amorphization was not observed in any of the irradiated oxide ceramics, despsite damage energy densities up to {similar_to}7 keV/atom (70 displacements per atom). On the other hand, SiC readily amorphized after damage levels of {similar_to}0.4 dpa at room temperature (RT). Si3N4 exhibited intermediate behavior; irradiation with Fe{sup 2+} ions at RT produced amorphization in the implanted ion region after damage levels of {similar_to}1 dpa. However, irradiated regions outside the implanted ion region did not amorphize even after damage levels > 5 dpa. The amorphous layer in the Fe-implanted region of Si3N4 did not appear if the specimen was simultaneoulsy irradiated with 1-MeV He{sup +} ions at RT. By comparison with published results, it is concluded that the implantation of certain chemical species has a pronounced effect on the amorphization threshold dose of all five materials. Intense ionizing radiation inhibits amorphization in Si3N4, but does not appear to significantly influence the amorphization of SiC.

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Influence of irradiation spectrum and implanted ions on the amorphization of ceramics

Since Clegg et al. first fabricated SiC/C multilayer composites in 1990, multilayer ceramics have received much attention because of their improved properties achieved by designing weak interfaces. The weak interface can deflect the crack propagating perpendicularly to the plane of laminates repeatedly during fracture, thus leading to extremely high work-of-fracture. In this work multilayer composites of Al2O3/LaPO4 were prepared using tape casting technique. Alumina slurry with acrylic latex binder was cast first on a polyester film, dried and then coated by LaPO4 interlayer cast on it. The coated green tapes were dried, stacked and laminated. After the removal of the binder, the green body was hot pressed in argon atmosphere at 1280 °C. A series of experiments were designed and conducted to investigate the influence of geometrical factors on mechanical properties of multilayer composites. Work-of-fracture of layered composites as high as 1100 J/m2 has been found.

Multilayer ceramic composites with high failure resistance

Fracture toughness, strength and creep of transparent ceramics at high temperature

The aim of the presented work was to study formation of magnesium aluminate spinel precursor powder during the co-precipitation of magnesium and aluminium nitrate with ammonium carbonate and its thermal transformation to spinel powder. After precipitation, the only crystalline phase is NH 4 Al(OH) 2 CO 3 ·H 2 O (ammonium dawsonite). The second one, Mg 6 Al 2 (CO 3 )(OH) 16 ·4H 2 O (hydrotalcite) appears during ageing. As found by DTA-MS and HT-XRD measurements, co-existence of both phases in very close contact results in their easier decomposition. On the base of the results obtained the scheme of phase transformations of co-precipitated precursor leading to formation of MgAl 2 O 4 is proposed.

Study of magnesium aluminate spinel formation from carbonate precursors

The aim of the work was to synthesize Y 2 O 3 , La 01 Y 19 O 3 , Nd 01 Y 19 O 3 , Nd 01 La 01 Y 18 O 3 and Nd 012 La 01 Y 178 O 3 powders using EDTA gel processes, and to examine the physicochemical properties of transparent sinters obtained from these powders A part of this goal was the determination of the influence of various dopants on the optical properties of yttria X-ray diffraction studies of the investigated powders and sinters confirmed their single-phase composition, which indicated incorporation of lanthanum and neodymium into the crystal lattice of yttria Scanning electron microscopy (SEM) combined with density measurements indicated that the studied sinters had high density An optical transparency over 50% was obtained for the Y 2 O 3 sinter in the wavelenght range of 450–1100 nm The influence of dopants on the level of transmittance was also investigated

Preparation of yttria powders co-doped with Nd3+, and La3+ using EDTA gel processes for application in transparent ceramics

The objective of the presented study was to investigate the usefulness of transparent, sintered yttrium oxide for application as optical isolators, i.e., materials with high Verdet constant. The study utilizes the magneto-optical Faraday effect. To obtain yttrium oxide sinters, a commercial Y2O3 powder was applied, with LiF added to facilitate sintering. As a result of hot-press sintering and heating, transparent, dense sinters were obtained. The structure and morphology of the powders and bulk samples and the optical properties of the latter were investigated by means of X-ray diffraction, scanning electron microscopy, visible and near-infrared reflectance spectroscopy, and a study of magneto-optical (Faraday) effects. Measurements of the Faraday effect in the wavelength range of 500–1000 nm indicate high Verdet constants for the above-described materials, which means that they can be effectively applied in laser optics.

Anna Wajler

Papers

Multilayer ceramic composites with high failure resistance

Fracture toughness, strength and creep of transparent ceramics at high temperature

Study of magnesium aluminate spinel formation from carbonate precursors

Preparation of yttria powders co-doped with Nd3+, and La3+ using EDTA gel processes for application in transparent ceramics

Transparent yttrium oxide ceramics as potential optical isolator materials