Robocasting of dense yttria-stabilized zirconia structures

Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions (<38 vol%). The sintered structures were able to retain the original morphologies with >94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability.     

Experimental determination of quantum dot size distributions, ligand packing densities, and bioconjugation using analytical ultracentrifugation

Analytical ultracentrifugation (AUC) was used to characterize the size distribution and surface chemistry of quantum dots (QDs). AUC was found to be highly sensitive to nanocrystal size, resolving nanocrystal sizes that differ by a single lattice plane. Sedimentation velocity data were used to calculate the ligand packing density at the crystal surface for different sized nanocrystals. Dihydrolipoic acid poly(ethylene glycol) was found to bind between 66 and 60% of the surface cadmium atoms for CdSe nanocrystals in the 1.54-2.59 nm radius size regime. The surface ligand chemistry was found to affect QD sedimentation, with larger ligands decreasing the sedimentation rate through an increase in particle volume and increase in frictional coefficient. Finally, AUC was used to detect and analyze protein association to QDs. Addition of bovine serum albumin (BSA) to the QD sample resulted in a reduced sedimentation rate, which may be attributed to an associated frictional drag. We calculated that one to two BSA molecules bind per QD with an associated frictional ratio of 1.2.     

Corrosion of nickel-chromium alloys, stainless steel and niobium at supercritical water oxidation conditions

Results of immersion tests of UNS N06625 (alloy 625), UNS S31609 (alloy 316 L), Ni-20Cr alloy and Nb coupons exposed to oxygenated ammoniacal sulphate solution at supercritical water oxidation (SCWO) conditions are presented. The corrosion behavior of the alloy 316 L (UNS S31603) SCWO reactor tubing is also presented under the same conditions. Immersion coupons corroded at a rate not exceeding 40 mm yr⁻¹ while the reactor tube itself corroded at a rate of between 160-1500 mm yr⁻¹, depending on which length of the reactor is considered to have corroded. Morphological and chemical analysis of the oxides present on the coupon samples suggest that iron oxides, which had initially precipitated on the corroding alloy 316 tube surface, were removed by heat flux-driven fluid mechanical action and transported through the reactor where they deposited on the coupons. Niobium was resistant to corrosion at the tested conditions.     

Novel reagents for iron and sulphur control in medium temperature leaching of sulphide concentrates

Hydrometallurgical leaching of sulphide concentrates of copper and nickel at medium temperature (150°C) produces residues that contain sulphur and iron-bearing minerals and phases. During leaching, and depending on various process parameters, iron may be precipitated as hematite, goethite, jarosite or other oxyhydroxides, which may be more or less crystalline. Hematite is the favoured iron precipitate, because it is the most environmentally stable and does not ad/absorb as much copper, nickel or other solution constituents during precipitation. However, the low solubility of iron during the medium temperature processing of sulphide ores can favour the formation of poorly crystalline, nano-scale iron oxide/oxyhydroxide phases. In some cases, these phases have been positively identified as the metastable ferrihydrite, which transforms into iron oxides such as goethite, hematite and magnetite over time. A better understanding of what may help drive this transformation during leaching would ultimately result in lower valuable metal losses and more stable leach residues. Higher acid concentrations result in increased copper extractions and favour the formation of hematite during concentrate leaching, rather than other metastable phases. Furthermore, commercially available water displacement formula ‘WD40®’ and other novel reagent(s) affect Fe precipitation and sulphur chemistry, leading to very different process outcomes such as improved extractions and larger, more easily separated, sulphur particles.     

On the Development of Thermo-Kinetic Eh-pH Diagrams

It is shown that thermo-kinetic Eh-pH diagrams can be generated through electrochemical measurements. These diagrams offer an accurate method of determining stability regions for leaching without relying on thermodynamic calculations, which may be inaccurate or for which data may be difficult to obtain. The Fe-NH₃-CO₃-H₂O system is studied here. Potentiodynamic polarization experiments were performed on an iron sample in ammoniacal solution in de-aerated condition at different temperature and pH. Polarization plots show that both active anodic dissolution and passive regions are present for pure iron in ammoniacal solution depending on the potential. The electrochemically obtained potential-pH data were used to generate the thermo-kinetic Eh-pH diagrams for the Fe-NH₃-CO₃-H₂O system.     

Damage mechanisms analysis of a multi-scale fibre reinforced cement-based composite subjected to impact and fatigue loading conditions

For several years, Laboratoire Central des Ponts et Chaussées (LCPC) has worked on the development of new cement composites in order to obtain materials sufficiently tough and ductile to be used in structures or structural elements without any other reinforcement that fibres.Then a multi-scale fibre reinforced cement-based composite (MSFRCC) has been developed and patented. It is principally characterized by a high percentage of fibres, percentage equal to 11% per m³.Three fibre dimensions are used in this composite.In the present article, a qualitative analysis of damage mechanisms of this material under impact and fatigue loadings is proposed.Concerning impact loading condition, the main conclusions are:

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Apparent fibre-matrix adherence, which increases with the loading rate, leads to an increase in material modulus of rupturel, an increase much greater than for all existing cement-based materials due to high percentage of fibres used;

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Mechanical homogenization of composite with loading rate is the result of cracks delocalization during cracking process. This delocalization results from viscous effects generated within the matrix and around the fibre-matrix interfaces.

Concerning fatigue loading condition, the main conclusions are:

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Intermediate fibre length (high percentage of meso-fibres) that is highly and positively involved in material static tensile strength, corresponds to scale of fibre that is sensitive to fatigue loading. As a matter of fact, meso-fibres become rapidly inactive and composite can no longer behave as a multi-scale reinforcement material. Material strength is then greatly affected.

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If the initial cracking state of the material before fatigue loading corresponds to a state of tensile strain that is less than or equal to 1.27 10^− 3, meso-fibres perfectly play their role with respect to relevant cracks (i.e. meso-cracks whose opening corresponds to their mechanical efficiency domain, that means less than 100 μm), material fatigue behaviour being then good (fatigue rupture after 2 millions of cycles).

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Specimens that did not break before 2 millions of cycles have better residual bending behaviour (gain of 6.5%) than reference specimens (specimens which were not previously loaded in fatigue) This result is the consequence of a morphological modification of cracks due to fatigue loading. Indeed, fatigue cycles lead to a gradual “blunting” of crack tips, cracks that subsequently become less dangerous with respect to their potential propagation.

     

From pore scale to wellbore scale: Impact of geometry on wormhole growth in carbonate acidization

Acid injection in carbonate reservoir is commonly used in the oil industry to improve, or at least recover, its productivity. The aim of this stimulation technique is to create empty channels called wormholes which, if successful, would bypass the damaged area near the wellbore. During production, wormholes become pathways for the reservoir oil to reach the well. This technique increases near-wellbore permeability, and therefore improves oil production. The interaction between the transport of acid, chemical reaction, and heterogeneities encountered at different scales, controls the unstable behaviour of wormholing and, thus, the success of the treatment. Most of the experimental and numerical studies done on this subject in the past have been limited in their observations because they only considered the dissolution process at a small scale (from pore scale to core scale). The purpose of this work is to study how the geometry of the domain can constrain wormhole competition, and influence wormholing dynamics in a core submitted to acidizing.After a short review of the literature on wormholing to see how the geometry effect could have influenced previous experiments, we study specifically the question of wormhole density. We emphasize that two mechanisms are involved in wormhole competition, with one of them being effective only at small scale. Thus we conclude that wormholing is not a full-scale independent process. We describe differences in the wormhole growth dynamics between “confined” and “unconfined” domains for different dissolution regimes. We focus on optimum conditions and their transition from “confined” to “unconfined” domain to realize that the flow rate in the dominant wormhole does not depend on geometric effects. We conclude by a comparison between 2D and 3D simulations, in both linear and radial flow, and observe changes in the wormholing process. All our results serve as a discussion about definitions of optimum conditions in the literature.     

New Raman spectrometer using a digital micromirror device and a photomultiplier tube detector for rapid on-line industrial analysis. Part I: description of the prototype and preliminary results

In this paper, a prototype of a new generation of Raman spectrometers, based on the use of a monochromator, a digital micromirror device as light modulator, and a photomultiplier tube as detector of the Raman light, is described. This spectrometer, containing no moving parts, is inexpensive, robust, and very precise. New in concept, this spectrometer makes it possible to record, in addition to classical Raman spectra, the intensity at several selected points of the spectrum and/or the total intensity in several selected intervals at the same time with great accuracy, thus giving new possibilities for analytical applications. Also, the work presented demonstrates the possibilities of this very simple prototype for rapid on-line industrial analysis, with an example of quantitative analysis of binary and ternary mixtures of xylene isomers. The precision obtained is satisfactory (errors of prediction approximately 3% in 5-6 seconds per sample).     

A better philosophy for a better psychology: Comment on Slaney and Racine (2011).

In their thought-provoking article, Slaney and Racine (2011) put forth several criticisms of the traditional view that concepts are mental representations used in the cognitive processes that underlie human higher cognitive competences (categorization, induction, etc.). Considerations of a broadly Wittgensteinian nature underlie their criticisms. In this article, I argue that the considerations advanced by Slaney and Racine do not undermine the clear account of the nature of mental states and psychological processes developed in the 1960s and 1970s and endorsed in my book Doing without Concepts (Machery, 2009). (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A predictive model based on tortuosity for pressure drop estimation in ‘slim’ and ‘fat’ foams

The use of porous structures with high external surface area represents an important breakthrough in several industrial applications. Foam structures have received an increasing scientific and industrial interest since the last decade. Knowledge of pressure drop induced by these foam structures is thus essential for successful design and operation of high performance industrial systems. In this context, an analytical investigation was conducted for the determination of the permeability and the inertial coefficient in foams. The theoretical model is based on modified cubic lattice, which allows to take into account the presence of matter at the junction of struts. The existing model developed in the literature is then modified to incorporate this geometrical approach for determining the tortuosity of the foam. Finally, the permeability and inertial coefficient analysis are performed in order to derive the pressure drop on foams. The modeling procedure is based only on physical principles and geometrical considerations with no adjustable parameters in order to reconcile the theoretical work with the experimental data of the literature. Finally, this model is validated for two marginal cases (i.e. ‘slim’ and ‘fat’ foams).