There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400042527

Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants

Controlled self-organization of nanoparticles can lead to new materials. The colloidal crystallization of non-spherical nanocrystals is a reaction channel in many crystallization reactions. With additives, self-organization can be stopped at an intermediary step-a mesocrystal-in which the primary units can still be identified. Mesocrystals were observed for various systems as kinetically metastable species or as intermediates in a crystallization reaction leading to single crystals with typical defects and inclusions. The control forces and mechanism of mesocrystal formation are largely unknown, but several mesocrystal properties are known. Mesocrystals are exiting examples of nonclassical crystallization, which does not proceed through ion-by-ion attachment, but by a modular nanobuilding-block route. This path makes crystallization more independent of ion products or molecular solubility, it occurs without pH or osmotic pressure changes, and opens new strategies for crystal morphogenesis.

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Mesocrystals: Inorganic superstructures made by highly parallel crystallization and controlled alignment

Supersaturated reverse micelles and microemulsions containing either AOT (sodium bis(2-ethylhexylsulfosuccinate)), C12EO4 (poly(oxyethylene-4-dodecyl ether)), or DDAB (didodecyldimethylammonium bromide) surfactants have been used as organized reaction microenvironments for barium sulfate precipitation. Nanoclusters of amorphous barium sulfate, 2−4 nm in size, were formed in association with BaNaAOT reverse micelles. In contrast, highly elongated filaments of crystalline barium sulfate, with lengths up to 100 μm and aspect ratios of 1000, were formed in BaNaAOT microemulsions. The individual filaments were single crystals of barite elongated predominantly along the [010] axis and in some instances consisted of coaligned nanofilaments, 20−50 nm in width. Similar reactions in C12EO4 reverse micelles and microemulsions afforded barite nanocrystals, 5−7 nm in dimension and tabular-shaped barite crystals, up to 400 nm in size, respectively. Rhombic crystals of barite, approximatety 200 nm in size, were deposite...

Synthesis of Barium Sulfate Nanoparticles and Nanofilaments in Reverse Micelles and Microemulsions

The chemical construction of organized architectures is an important aspect of innovative materials synthesis. Bicontinuous water-filled microemulsions can be used as preorganized systems for the fabrication of crystalline calcium phosphate materials with extended reticulated microstructures. These macroporous materials are formed by mineralization reactions located within the interconnecting water channels of the bicontinuous network. The resulting materials represent replicas of the microemulsion architecture, but the pore sizes are incommensurate, suggesting that secondary modifications in the bicontinuous microstructure occur during crystal growth. Synthetic macroporous calcium phosphates could have uses in biomaterial implants.

https://science.sciencemag.org/content/sci/264/5165/1576.full.pdf

Crystal Tectonics: Construction of Reticulated Calcium Phosphate Frameworks in Bicontinuous Reverse Microemulsions

BaSO4 fibres with morphological complexity were formed in aqueous solution with polyacrylate and partially monophosphonated poly(ethyleneoxide)-block-poly(methacrylic acid) additives by a simple precipitation reaction. For polyacrylate, formation of the fibrous deposits was strongly dependent on the level of supersaturation (S) and Ba2+:polymer molar ratio (R). At S=60 to 80, and R=3 to 14, highly anisotropic crystalline fibres consisting of bundles of BaSO4 nanofilaments were formed after several weeks, although the yield was low. The nanofilaments were also organized into cone-shaped aggregates at S=80, and at lower R values these formed higher-order structures that consisted of multiple cone-on-cone assemblies with remarkable self-similarity. Increasing the supersaturation produced ovoid or cross-shaped dendritic particles for the range of molar ratios studied. In contrast, BaSO4 crystallisation in the presence of a partially phosphonated block copolymer gave a high yield of BaSO4 fibres up to 100 μm in length, and consisting of co-aligned bundles of 30 nm-diameter defect-free single-crystal nanofilaments with a uniform growth tip. A model for the defect-free growth of BaSO4 nanofilaments in aqueous polymer solutions based on amorphous precursor particles, vectorially directing forces and van der Waals attraction is proposed.

/pdf/formation-of-baso4-fibres-with-morphological-complexity-in-55xhjvl9ws.pdf

Formation of BaSO4 Fibres with Morphological Complexity in Aqueous Polymer Solutions

Xenophyophores are a group of giant deep sea protists characterized by intracellular barium sulphate (BaSO4) crystals. X-ray diffraction, electron diffraction and electron microscopy studies have been performed on barium sulphate crystals from three xenophyophore species (Aschemonella ramuliformis, Reticulammina labyrinthica, Galatheammina lamina) obtained at bathyal and abyssal depths in the north-eastern Atlantic. Two populations of crystals were observed. The first were tablets, similar to 2 mu m in length and rhombic or hexagonal in outline. In both cases, the tabular face was of index (100). The second population consisted of much smaller particles (< 0.5 mu m) of poor crystallinity. A comparison of the larger xenophyophore crystals with synthetically grown crystals indicated that the former probably grew at low supersaturation (S < 25) in solutions of low to moderate ionic strength (I < 1.0 M). Some preliminary observations of the cellular organisation of A. ramuliformis are reported. The protoplasm is multinucleate and characterized by what seems to be a system of extracellular lacunae formed by invaginations of the cell wall. Similar features have been observed in the deep sea foraminiferan Rhizammina algaeformis. Possible origins of the BaSO4 crystals and the taxonomic relationship between xenophyophores and certain foraminiferans are discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002531540003856X

The crystallography and possible origin of barium sulphate in deep sea rhizopod protists (Xenophyophorea)

Phosphate is added to drinking water in the UK to minimise the release of lead from lead water pipes. The phosphate encourages the formation of insoluble lead apatites on the walls of the pipe. Hydroxylpyromorphite Pb5(PO4)3OH is the lead apatite that is most often used to model lead levels in tap water; however, its presence has not been confirmed. Our aims were to identify the lead pipe apatite and synthesise it. The synthetic mineral would then be used in future solubility studies to produce better predictions of lead levels in tap water. XRD and FTIR were used to characterise the minerals on a range of lead pipes. Pyromorphite and hydroxylpyromorphite were absent and instead a range of mixed calcium lead apatites were present. For every five lead ions in the general formula Pb5(PO4)3X between one and two ions were replaced with calcium and there was evidence of substitution of by either or . Calcium lead apatites with similar unit cell dimensions to those found on lead water pipes were then synthesised. The calcium : lead ratio in these reaction mixtures was in excess of 500 : 1 and the resulting crystals were shown by TEM to be nanosized rods and flakes. The synthetic apatites that most closely resembled the unit cell dimensions of the apatites on lead water pipes were shown to be Pb3.4Ca1.3(PO4)3Cl0.03OH0.97, Pb3.6Ca1.2(PO4)3Cl0.07OH0.93, and Pb3.6Ca1.2(PO4)3Cl0.27OH0.73.

/pdf/the-identification-and-synthesis-of-lead-apatite-minerals-2hpfnkm0vo.pdf

Jeremy D. Hopwood

Papers

Synthesis of Barium Sulfate Nanoparticles and Nanofilaments in Reverse Micelles and Microemulsions

Crystal Tectonics: Construction of Reticulated Calcium Phosphate Frameworks in Bicontinuous Reverse Microemulsions

Formation of BaSO4 Fibres with Morphological Complexity in Aqueous Polymer Solutions

The crystallography and possible origin of barium sulphate in deep sea rhizopod protists (Xenophyophorea)

The Identification and Synthesis of Lead Apatite Minerals Formed in Lead Water Pipes