α-Alumina and spinel react into single-phase high-alumina spinel in <3 seconds during flash sintering

In situ X-ray diffraction measurements at the Advanced Photon Source show that α-Al₂O₃ and MgAl₂O₄ react nearly instantaneously and completely, and nearly completely to form single-phase high-alumina spinel during voltage-to-current type of flash sintering experiments. The initial sample was constituted from powders of α-Al₂O₃, MgAl₂O₄ spinel, and cubic 8 mol% Y₂O₃-stabilized ZrO₂ (8YSZ) mixed in equal volume fractions, the spinel to alumina molar ratio being 1:1.5. Specimen temperature was measured by thermal expansion of the platinum standard. These measurements correlated well with a black-body radiation model, using appropriate values for the emissivity of the constituents. Temperatures of 1600-1736°C were reached during the flash, which promoted the formation of alumina-rich spinel. In a second set of experiments, the flash was induced in a current-rate method where the current flowing through the specimen is controlled and increased at a constant rate. In these experiments, we observed the formation of two different compositions of spinel, MgO•3Al₂O₃ and MgO•1.5Al₂O₃, which evolved into a single composition of MgO•2.5Al₂O₃ as the current continued to increase. In summary, flash sintering is an expedient way to create single-phase, alumina-rich spinel.     

Heuristic Methods for Minimum-Cost Pipeline Network Design – a Node Valency Transfer Metaheuristic

Designing low-cost network layouts is an essential step in planning linked infrastructure. For the case of capacitated trees, such as oil or gas pipeline networks, the cost is usually a function of both pipeline diameter (i.e. ability to carry flow or transferred capacity) and pipeline length. Even for the case of incompressible, steady flow, minimizing cost becomes particularly difficult as network topology itself dictates local flow material balances, rendering the optimization space non-linear. The combinatorial nature of potential trees requires the use of graph optimization heuristics to achieve good solutions in reasonable time. In this work we perform a comparison of known literature network optimization heuristics and metaheuristics for finding minimum-cost capacitated trees without Steiner nodes, and propose novel algorithms, including a metaheuristic based on transferring edges of high valency nodes. Our metaheuristic achieves performance above similar algorithms studied, especially for larger graphs, usually producing a significantly higher proportion of optimal solutions, while remaining in line with time-complexity of algorithms found in the literature. Data points for graph node positions and capacities are first randomly generated, and secondly obtained from the German emissions trading CO₂ source registry. As political will for applications and storage for hard-to-abate industry CO₂ emissions is growing, efficient network design methods become relevant for new large-scale CO₂ pipeline networks.

     

The Indianization of Colonial Medicine

ZUSAMMENFASSUNG: Anders als die weitgehend in der Geschichtsschreibung belegte psychiatrische Anstalt für Europ?er und Europ?erinnen mit ihrem englischen Leiter Owen Berkeley-Hill ist die weitaus gr??ere Institution für indische Patienten und Patientinnen im nordindischen Ranchi bisher nicht untersucht worden. Im Mittelpunkt dieses Beitrags steht die Karriere des Leiters dieser Institution, Jal E. Dhunjibhoy, zu Beginn des 20. Jahrhunderts als von der britischen Kolonialregierung eine Indianisierung der medizinischen Einrichtungen angestrebt wurde. Im Gegensatz zu bisherigen Studien über intermediaries und middles konzentriert sich dieser Aufsatz auf einen hochrangigen einheimischen Mitarbeiter. Die verbreitete Annahme zwangsl?ufiger historischer Prozesse wird dabei differenziert, eine regionale Kontextualisierung vorgenommen und die Kontinuit?t offener und versteckter Diskriminierung indischer Mediziner in Bezug auf Entlohnung, gesellschaftliche Stellung, fachliche Anerkennung, posthume Würdigung und historiographischer Berücksichtigung herausgearbeitet. Es wird verdeutlicht, in welcher Weise koloniale Akteure in bestehende gesellschaftliche Disparit?ten und soziopolitische Prozessen verstrickt waren und wie die Karriere eines leitenden Mediziners von einer Vielzahl von au?ermedizinischen Zusammenh?ngen bestimmt wurde. Gleichzeitig wird hervorgehoben, dass ihre strukturelle Positionierung als inbetweens, Kollaborateure oder Repr?sentanten einer erfolgreichen Dekolonisierung für ein nuancierteres Verst?ndnis ihrer beruflichen und pers?nlichen Identit?tsformierung nicht ausreicht.     

The Change of X‐ray Diffraction Peak Width During in situ Conventional Sintering of Nanoscale Powders

Diffraction peaks of nanoscale particles of 3 mol% yttria‐stabilized zirconia become sharper as the powder sinters. The reduction in the peak width is correlated with the increase in density. The sharpening of the peak agrees reasonably well with the remaining free surface area as the sample sinters. Therefore, high curvature of the free surface of the pores is assumed to lead to peak broadening (the grain boundaries that grow at the expense of the free surfaces of the pores do not have this curvature). The change in the grain size during sintering does not make a significant contribution to peak width.     

Untersuchungen zu Mesityldimethylhalogensilanen als Schutzgruppenreagenzien für Alkohole

Investigation on Mesityldimethylhalosilanes as Protectiv Reagents for Alcohols The use of mesityldimethylhalosilanes as protecting reagents for steroid alcohols was investigated. The resistance of the obtained silyl ethers was tested in various media. The reaction pathway of the acidic hydrolyses of the silyl ethers is explained.     

Complete Elastic Tensor for Mullite (∼2.5Al2O3·SiO2) to High Temperatures Measured from Textured Fibers

Directionally solidified mullite fibers have been grown by the laser-heated, float-zone method from starting materials with a nominal composition of 3Al₂O₃·2SiO₂. The fibers used in this study have large single-crystal regions with composition 2.5Al₂O₃·SiO₂ and (001) fiber axis orientation. The complete elastic tensor of these samples has been determined by Brillouin spectroscopy at room temperature and elevated temperatures up to 1200°C. Isotropic moduli (bulk, shear, and Young's) have been calculated using the Voigt–Reuss–Hill averaging scheme. The room-temperature values obtained are K _VRH= 173.5 ± 6.9 GPa, G _VRH= 88.0 ± 3.5 GPa, E _VRH= 225.9 ± 9.0 GPa. All moduli show gradual, linear decreases with temperature. The temperature derivatives obtained for the equivalent, isotropic moduli are d K _VRH/d T =−17.5 ± 2.5 MPa/°C, d G _VRH/d T =−8.8 ± 1.4 MPa/°C, d E _VRH/d T =−22.6 ± 2.8 MPa/°C. Substantial differences between bulk properties calculated from the single–crystal measurements in this study and the properties reported in the literature for polycrystalline sintered mullite are identified, indicating the importance of factors such as microstructure, intergranular phases, and composition to the elasticity of mullite ceramics.     

Highly Porous Geopolymers Through Templating and Surface Interactions

The natural porosity of geopolymers and the simplicity of geopolymer synthesis make them a potential candidate for the formation of highly porous ceramics. Here, the synthesis of highly porous (≈70 vol% or more) metakaolin geopolymer is demonstrated using a novel emulsion preparation with one‐pot curing and hydrophobization of the interior pores with alkylalkoxysilanes. Using mercury intrusion porosimetry, tailoring of the characteristic percolation pore size is demonstrated over a range of ≈200 nm to 10 μm. Using powder X‐ray diffraction, reactivity was shown to be decreased versus typical geopolymers, but substantial geopolymerization still occurred and the samples formed cohesive monoliths. Optional calcination under inert conditions allowed for formation of a glassy ceramic with a notable SiC phase, as well as further increasing the porosity by removing the hydrophobic pore coatings.     

Mullite (3Al2O3·2SiO2)–Aluminum Phosphate (AlPO4), Oxide, Fibrous Monolithic Composites

Mullite–AlPO₄ fibrous monolithic composites were fabricated by a co-extrusion technique using ethylene vinyl acetate (EVA) as a binder. Processing routes such as mixing formulation, extrusion sequence, binder removal cycle, pressing, and sintering procedures are described. An effort to make tougher composites was conducted by modifying the microstructures of the composites. Different kinds of monolithic composites were fabricated by changing the number of filaments, and the composition and thickness of interphase layers, and their microstructural and mechanical properties were characterized. To make the interphase more porous and to facilitate debonding and fiber pullout in the composite, graphite was added as a fugitive "space filler" into the interphase material and then removed. A fibrous monolithic composite with a sintered interphase thickness of 5–10 μm and an interphase composition of 50 vol% graphite and 50 vol% AlPO₄ had a three-point bend strength and a work of fracture of 129 ± 2 MPa and 0.86 ± 0.05 kJ/m², respectively. This corresponded to 42% of the strength but 162% of the work of fracture when compared with the values for a single-phase mullite. Two-layer, mixed 50% two-layer:50% three-layer, and three-layer fibrous monoliths were fabricated and their microstructural and mechanical properties were studied. The difference in the sintering behaviors of the two-layer and three-layer composites is described.     

使用精梳落棉生产Autocoro针织纱线

原材料成本推动Autocoro纺纱工艺发展.最近几年纱线生产成本在总成本中的份额不断地在增加.以前纱线生产成本也许占总成本的一半,目前已达75%.介绍了纺纱厂应对这种趋势的方法.