Residual Stresses in Alumina/Ceria-Stabilized Zirconia Composites

Measurements of the residual stresses in Al₂O₃/Ce-TZP (12 mol% CeO₂) sintered composites, containing 10, 20, and 40 vol% zirconia, obtained by neutron diffraction and by piezospectroscopy using optical fluorescence and Raman are compared. The techniques give essentially the same values for the spatial average of the hydrostatic residual stresses in the two phases despite the difference in the parameters measured in the two techniques. The measured stresses are also in accord with those predicted from a stochastic stress analysis for materials cooling from a stressfree temperature of ∼1180°C. Over the range of volume fraction investigated the hydrostatic stress in the alumina phase varies linearly with zirconia content, corresponding most closely to the upper Hashin bound.     

Digitizing Human Behavior with Wireless Sensors in Biogas 2020 Technological Business Model Innovation Challenges

Wireless Personal Communications - The ability to develop innovative Business Models (BMs) with high speed and good Return of Investment has become the cornerstone for the competitiveness of many...     

MnxCr0.3Fe0.5Co0.2Ni0.5Al0.3 high entropy alloys for magnetocaloric refrigeration near room temperature

High entropy alloys (HEAs) based on transition metals display rich magnetic characteristics,however attempts on their application in energy efficient technologies remain scarce.Here,we explore the magne-tocaloric application for a series ofMnxCr0.3 Fe0.5Co0.2Ni0.5Al0.3 (0.8 ＜ x ＜ 1.1) HEAs by integrated theoretical and experimental methods.Both theory and experiment indicate the designed HEAs have the Curie tem-perature close to room temperature and is tunable with Mn concentration.A non-monotonic evolution is observed for both the entropy change and the relative cooling power with changing Mn concentration.The underlying atomic mechanism is found to primarily emerge from the complex impact of Mn on mag-netism.Advanced magnetocaloric properties can be achieved by tuning Mn concentration in combination with controlling structural phase stability for the designed HEAs.     

Guidelines for the Integration of Autonomous UAS into the Global ATM

The growing social and economic interest in new unmanned aircraft systems (UASs) applications demands that UASs operate beyond the segregated airspace they are currently able to fly. However, UAS operations in non-segregated airspace should be regulated by aeronautical authorities before UASs can share airspace with manned aircraft. It has been a challenge for regulatory authorities to define these regulations because they do not understand the topic well. In addition, there is no consensus in the academic community regarding UAS concepts, such as taxonomy and features. This study proposes guidelines that could support UAS regulations for the future integration of autonomous UASs into the Global Air Traffic Management System (GATM). These guidelines are based on three viewpoints: the aircraft, the piloting autonomous system (PAS) and the integration of autonomous UASs into non-segregated airspace. We recommend that the UAS concept should be based on genuine aeronautical precepts, which would be directly applied, without terminology or conceptual adaptations, for the integration of these aircraft into airspace according to the GATM paradigm.     

Edge Stresses in Alumina/Zirconia Laminates

Using the technique of fluorescence piezospectroscopy, we determine the distribution of thermal residual stresses across the edges of three laminated alumina/zirconia composites. We develop a methodology for separating the measured stress state into microstresses that result from grain-to-grain thermal mismatch and macrostresses that result from lamination-induced thermal mismatch between individual plies. Comparison between the measured edge-stress distributions and those calculated based on a simple force-superposition model shows good agreement, indicating that the laminate system is well approximated as linear elastic. Given the experimental confirmation of significant edge stresses in multi-ply laminates, the possibility of failure initiating at composite edges must be considered in the design of surface-compressed laminate structures with the aim of mediating the detrimental effect of surface flaws.     

Raman Investigation of the Nitridation of Yttria-Stabilized Tetragonal Zirconia

Raman spectroscopy has been used to obtain Raman spectra of yttria-stabilized tetragonal zirconia subject to surface nitridation induced by contact with zirconium nitride. Raman spectra recorded from regions at increasing distance from the source of nitridation have been used to obtain diffusion profiles from samples treated at different times and temperatures. The coupling of X-ray diffraction data previously taken and of the Raman spectra shows that in the samples there is a two-phase region (tetragonal + cubic) near the nitrided surface and that, at larger distance inside the samples, there is only one phase (tetragonal). Fitting of the diffusive profiles in the single-phase tetragonal region with an appropriate diffusion function allows the determination of the diffusion coefficient of nitrogen in tetragonal zirconia which is expressed in terms of the preexponential factor, D ₀= (3.98 ± 0.5) × 10⁻³ cm²/s, and the activation energy, Q = 170 ± 10 kJ/mol.     

Piezospectroscopic Analysis of the Residual Stresses in the Strontium Hexaluminate/Zirconia (SrAl12O19/ZrO2) System

Samples of strontium hexaluminate (SrAl₁₂O₁₉), both pure and mixed with different amounts of ceria-stabilized zirconia (CE-TZP), have been prepared via a chemical route. The fluorescence spectrum of SrAl₁₂O₁₉ is similar to that of ruby and yttrium aluminium garnet (YAG); consequently, this similarity has been attributed to the presence of a trace impurity of Cr³⁺ ions. The most-intense fluorescence peak of SrAl₁₂O₁₉ exhibits a dependence on stress that is given by the average uniaxial piezospectroscopic coefficient ( = 1.5 cm^-1·GPa^-1). The piezospectroscopic coefficient has been used to convert to stress the fluorescence frequency shift of SrAl₁₂O₁₉ mixed with zirconia (ZrO₂). The stress, as a function of the volume fraction of ZrO₂, resides between the Hashin-Shtrikman bounds but is best reproduced by an effective medium approximation.     

Catalytic acetylation of glycerol with acetic anhydride

We studied the acetylation of glycerol with acetic anhydride using different solid acid catalysts. The results indicated that at 60 °C, zeolite Beta and K-10 Montmorillonite showed 100% selectivity to triacetin within 20 min, with a molar ratio of 4:1. Amberlyst-15 acid resin yielded 100% triacetin after 80 min, whereas niobium phosphate gave diacetin and triacetin in 53% and 47% selectivity, respectively. All catalysts were more selective to triacetin than the uncatalyzed reaction. By contrast, zeolite Beta gave poor yield of triacetin when acetic acid was used as acetylating agent. The different behavior was explained in terms of the stabilization of the acylium ion intermediate.     

Photochemical fate of carbamazepine in surface freshwaters: laboratory measures and modeling

It is shown here that carbamazepine (CBZ) would undergo direct photolysis and reaction with (?)OH as the main phototransformation pathways in surface waters. Environmental lifetimes are expected to vary from a few weeks to several months, and predictions are in good agreement with available field data. Acridine (I) and 10,11-dihydro-10,11-trans-dihydroxy-CBZ (V) are the main quantified phototransformation intermediates upon direct photolysis and (?)OH reaction, respectively. The photochemical yield of mutagenic I from CBZ is in the 3-3.5% range, and it is similar for both direct photolysis and (?)OH reaction: it would undergo limited variation with environmental conditions. In contrast, the yield of V would vary in the 4-8.5% range depending on the conditions, because V is formed from CBZ by (?)OH (9.0% yield) more effectively than upon direct photolysis (1.4% yield). Other important photointermediates, mostly formed from CBZ upon (?)OH reaction, are an aromatic-ring-dihydroxylated CBZ (VI) and N,N-bis(2-carboxyphenyl)urea (VII). Compounds VI and VII are formed by photochemistry and are not reported as human metabolites; thus, they could be used as tracers of CBZ phototransformation in surface waters. Interestingly, VI has recently been detected in river water.