Effect of Second-Phase Doping on Laser Deposited Al2O3 Ceramics

Direct fabrication of engineering ceramic components by additive manufacturing (AM) is a relatively new method for producing complex mechanical structures. This study investigates how a second-phase doping may affect Al2O3 ceramic parts deposited by AM with a laser engineered net shaping (LENS) system. In this study, ZrO2 and Y2O3 powders are respectively doped into Al2O3 powders at the eutectic ratio as second-phases to improve the quality of a deposited part. The deposited Al2O3, Al2O3/ZrO2 and Al2O3/YAG (yttrium aluminum garnet) parts are examined for their micro-structures and micro-hardness, as well as defects. The results show that doping of ZrO2 or Y2O3 as a second-phase performs a significant role in suppressing cracks and in refining grains of the laser deposited parts. The micro-hardness investigation reveals that the second-phase doping does not result in much hardness reduction in Al2O3 and the two eutectic ceramics are both harder than 1500 Hv. The study concludes that the second-phase doping is good for improving laser deposited ceramic parts.Mechanical Engineerin

Surface Properties of SiCp/Al Composite by Powder-Mixed EDM

AbstractThis paper uses a kind of moderate volume fraction (40%) of SiC particle reinforced Al matrix composites (SiCp/Al) to research how the surface properties are affected in conventional EDM (EDM) and powder-mixed EDM (PMEDM). By means of environment scanning electron microscope (ESEM) and HIT friction and wear tester, surface micro-topography, elements and wear resistance were analyzed. Experiments and researches indicate that compared with EDM, the surface properties machined by using PMEDM are improved greatly. The PMEDM surface roughness decreases about 31.5%; corrosion resistance is better too; and wear resistance is twice of EDM. Powder-mixed EDM has promising applications in metal matrix composites machining field

Acute effects of ambient nitrogen oxides and interactions with temperature on cardiovascular mortality in Shenzhen, China

Background: Though inconsistent, acute effects of ambient nitrogen oxides on cardiovascular mortality have been reported. Whereas, interactive roles of temperature on their relationships and joint effects of different indicators of nitrogen oxides were less studied. This study aimed to extrapolate the independent roles of ambient nitrogen oxides and temperature interactions on cardiovascular mortality.Methods: Data on mortality, air pollutants, and meteorological factors in Shenzhen from 2013 to 2019 were collected. Three indicators including nitric oxide (NO), nitrogen dioxide (NO2), and nitrogen oxides (NOX) were studied. Adjusted generalized additive models (GAMs) were applied to analyse their associations with cardiovascular mortality in different groups.Results: The average daily concentrations of NO, NO2, and NOX were 11.7 mu g/m(3), 30.7 mu g/m(3), and 53.2 mu g/m(3), respectively. Significant associations were shown with each indicator. Cumulative effects of nitrogen oxides were more obvious than distributed lag effects. Males, population under 65 years old, and population with stroke related condition were more susceptible to nitrogen oxides. Adverse effects of nitrogen oxides were more significant at low temperature. Impacts of NO2 on cardiovascular mortality, and NO on stroke mortality were the most robust in the multi-pollutant models, whereas variations were shown in the other relationships.Conclusions: Low levels of nitrogen oxides showed acute and adverse impacts and the interactive roles of temperature on cardiovascular mortality. Cumulative effects were most significant and joint effects of nitrogen oxides required more attention. Population under 65 years old and population with stroke-related health condition were susceptible, especially days at lower temperature

Ultra-sharp asymmetric Fano-like resonance spectrum on Si photonic platform

In this paper, we report the generation of an ultra-sharp asymmetric resonance spectrum through Fano-like interference. This generation is accomplished by weakly coupling a high-quality factor (Q factor) Fabry–Pérot (FP) cavity and a low-Q factor FP cavity through evanescent waves. The high-Q FP cavity is formed by Sagnac loop mirrors, whilst the low-Q one is built by partially transmitting Sagnac loop reflectors. The working principle has been analytically established and numerically modelled by using temporal coupled-mode-theory (CMT), and verified using a prototype device fabricated on the 340 nm silicon-on-insulator (SOI) platform, patterned by deep ultraviolet (DUV) lithography. Pronounced asymmetric resonances with slopes up to 0.77 dB/pm have been successfully measured, which, to the best of our knowledge, is higher than the results reported in state-of-the-art devices in on-chip integrated Si photonic studies. The established theoretical analysis method can provide excellent design guidelines for devices with Fano-like resonances. The design principle can be applied to ultra-sensitive sensing, ultra-high extinction ratio switching, and more applications

Compression Behavior of Biodegradable Thermoplastic Plasticizer-Containing Composites

Thermoplastic starch-based composites generate worldwide interest as they are based on green raw materials and undergo complete degradation. The composites were first fabricated from starch and sisal fibers as the major materials via the forming process. The effect of starches with different contents of single- and multicomponent plasticizers on the cushioning properties of the composites was studied. An increase in plasticizer contents within a certain range is shown to enhance materials resistance to pressure and its cushioning performance. With the multicomponent plasticizer content of 15%, the resistance to pressure for four types of composites prepared at different weight ratios of formamide and urea were of the order of 2:1>1:1>1:2, and that of the four types of composites fabricated at different weight ratios of glycerol and ethylene glycol were of the order of 1:2>2:1>1:1. Multicomponent plasticizer-containing starch-based composites are shown to be irregular elastomers and the stress-strain relation to be first defined by a hyperbolic tangent curve function and then by the tangent one.Композиты на основе термопластичного крахмала оказались в центре внимания как отечественных, так и зарубежных ученых, так как они основаны на экологичном сырье и полностью разлагаются. Такие композиты получали формовкой с использованием крахмала и сизалевых волокон в качестве основных материалов. Изучено влияние термопластичного крахмала с различной долей простых и составных пластификаторов на амортизационные свойства композитов. Экспериментальные результаты показали, что в определенных пределах с увеличением содержания пластификаторов повышаются сопротивление материала давлению и его амортизационные характеристики. При содержании составного пластификатора 15% сопротивление давлению четырех типов композитов, полученных с использованием различных массовых соотношений фомамида и мочевины, изменяется в ряду 2:1>1:1>1:2, а с использованием различных массовых соотношений глицерина и этиленгликоля в последовательности 1:2>2:1>1:1. Композиты на основе крахмала, содержащие составной пластификатор, являются нерегулярными эластомерами, и зависимость между напряжением и деформацией описывается в первую очередь функцией гиперболической тангенсоиды и во вторую очередь функцией тангенсоиды.Композити на основі термопластичного крохмалю виявилися в центрі уваги як вітчизняних, так і зарубіжних вчених, так як вони засновані на екологічної сировині і повністю розкладаються. Такі композити отримували формуванням з використанням крохмалю і сизалевих волокон в якості основних матеріалів. Вивчено вплив термопластичного крохмалю з різною часткою простих і складових пластифікаторів на амортизаційні властивості композитів. Експериментальні результати показали, що в певних межах зі збільшенням вмісту пластифікаторів підвищуються опір матеріалу тиску і його амортизаційні властивості. При утриманні складеного пластифікатора 15% опір тиску чотирьох типів композитів, отриманих з використанням різних масових співвідношень фомаміда і сечовини, змінюється в ряду 2: 1> 1: 1> 1: 2, а з використанням різних масових співвідношень гліцерину і етиленгліколю - в послідовності 1 : 2> 2: 1> 1: 1. Композити на основі крохмалю, які містять складовою пластифікатор, є нерегулярними еластомерами, і залежність між напруженням і деформацією описується в першу чергу функцією гіперболічної тангенсоіди і в другу чергу функцією тангенсоіди

Geochronological and geochemical constraints on Late Cryogenian to Early Ediacaran magmatic rocks on the northern Tarim Craton:implications for tectonic setting and affinity with Gondwana

The Tarim Craton provides a geologic record of both the fragmentation of the Rodinian supercontinent and the subsequent assembly of Gondwana. However, the timing and interactions of these radically different tectonic processes remain contested. A critical part of this debate revolves around the Late Cryogenian-Ediacaran igneous rocks along the Craton’s northern margin, specifically, whether they record super-plume related Rodinian breakup or Gondwanan orogeny. To address this issue, we present zircon U-Pb-Hf isotopic data and whole rock geochemistry from Late Cryogenian to Early Ediacaran granitoids of the northern Tarim Craton. U-Pb zircon ages reveal three magmatic periods along the northern Tarim margin: ca. 660–640 Ma, 635–625 Ma and 620–600 Ma, associated with small scale felsic and mafic magmas. These granitoids have an A2-type affinity and are enriched in alkalines, but are depleted in Nb, Ta, Sr, P and Ti. Elemental data and generally negative εHf(t) values (−13.96 to 1.65) suggest that they were mainly derived from partial melting of enriched, subduction-modified lithospheric mantle triggered by upwelling of the asthenospheric mantle along the active continental margin of northern Tarim. We suggest that the Tarim Craton travelled as an isolated plate for much of the Late Neoproterozoic, near the outer part of Rodinia and subsequently Gondwana. During this time it was affected by localized and periodic subduction-related intrusion and eruption. However, within the samples of this study, there is no U-Pb-Hf isotopic and whole-rock geochemical evidence to support either super-plume-related rifting (i.e. Rodinian breakup) or Pan-African orogeny (i.e. Gondwanan assembly).</p

Development of a metal-free black phosphorus/graphitic carbon nitride heterostructure for visible-light-driven degradation of indomethacin

The development of affordable and efficient technologies for the removal of pharmaceuticals and personal care products (PPCPs) from water has recently been the subject of extensive attention. In this study, a black phosphorus/graphitic carbon nitride (BP-g-C3N4) heterostructure is fabricated as an extremely active metal-free photocatalyst via a newly-developed exfoliation strategy. The BP-g-C3N4 shows an 11 times better decomposition rate of a representative PPCPs-type pollutant, indomethacin (IDM), compared to the widely used P25 TiO2 under real-sunlight illumination. Also, its visible-light activity is even better than that of the best photocatalysts previously developed, but only consumes 1/10-1/4 of the catalyst. The results show that BP performs a cocatalyst-like behavior to catalyze the generation of reactive oxygen species, thus speeding up the decomposition of IDM. In addition, the BP-g-C3N4 photocatalyst also exhibits excellent IDM removal efficiency in authentic water matrices (tap water, surface water, and secondarily treated sewage effluent). Large-scale application demonstration under natural sunlight further reveals the practicality of BP-g-C3N4 for real-world water treatment operations. Our work will open up new possibilities in the development of purely metal-free photocatalysts for "green" environmental remediation applications. (C) 2021 Elsevier B.V. All rights reserved.Environmental Biolog