There is growing evidence that oxides of complex chemistries can be formed in one step by reactive flash sintering of their elemental constituents. Here we explore the temporal relationship between ...phase transformation and sintering by combining measurements of sintering with in situ measurements of phase transformation. The experiments are carried out under current rate, where flash is induced by injecting current and increasing it at a constant rate. We show that phase transformation of powders of magnesia and α‐alumina into single‐phase magnesium aluminate spinel was completed in 45 seconds, whereas sintering to full density required 60 seconds.
A woman in her late 50s with no significant comorbidities presented with constant dull aching pain in her right arm for over a few years without any shoulder pain or restrictions in arm movement. She ...had mild symptomatic improvement in pain with non-steroidal anti-inflammatory medications. Clinically, she was found to have tenderness along the right deltoid region. Plain radiograph of the right shoulder and humerus (figure 1) showed cortical thickening, and trabecular coarsening throughout the right humerus and proximal shaft, suspicious of metastatic/metabolic disease. Blood biochemistry showed elevated alkaline phosphatase 280 U/L (45–117 U/L) with bone-specific alkaline phosphatase being 76% (14%–68%). Rest of the laboratory work-up was unremarkable with complete blood count, liver function tests and renal function tests within normal range. A radionuclide whole-body scan with 21.8 mCi technetium 99m hydroxydiphosphonate (figure 2) showed increased radiotracer activity in the right humerus consistent with Paget's disease. Patient was treated with a single dose of 5 mg intravenous zoledronic acid. At the 6-month follow-up, she continued to have dull ache in her arm. However, bone-specific alkaline phosphatase levels and whole-body scan remained stable.
We report, for the first time, the observation of an incubation time for the onset of flash sintering in experiments carried out at isothermal furnace temperatures. The incubation time varies highly ...nonlinearly with the strength of the DC field, akin to a nucleation‐like phenomenon. The setting of the maximum current at the power supply has a significant influence on the extent of densification. The hold time at these current settings has an influence on the grain size increasing it with time and the magnitude of the current setting. The experiments were carried out on 3 mol% yttria‐stabilized zirconia. In all instances the specimen temperatures during flash sintering, estimated from a previously validated blackbody radiation model remain well below the temperatures that would be required for conventional sintering of yttria‐stabilized zirconia. Taken together these observations imply a nucleation of defect avalanche as a possible mechanism for flash sintering.
Indiscriminate use of chemical fertilizers in the agricultural production systems to keep pace with the food and nutritional demand of the galloping population had an adverse impact on ecosystem ...services and environmental quality. Hence, an alternative mechanism is to be developed to enhance farm production and environmental sustainability. A nanohybrid construct like nanofertilizers (NFs) is an excellent alternative to overcome the negative impact of traditional chemical fertilizers. The NFs provide smart nutrient delivery to the plants and proves their efficacy in terms of crop productivity and environmental sustainability over bulky chemical fertilizers. Plants can absorb NFs by foliage or roots depending upon the application methods and properties of the particles. NFs enhance the biotic and abiotic stresses tolerance in plants. It reduces the production cost and mitigates the environmental footprint. Multitude benefits of the NFs open new vistas towards sustainable agriculture and climate change mitigation. Although supra-optimal doses of NFs have a detrimental effect on crop growth, soil health, and environmental outcomes. The extensive release of NFs into the environment and food chain may pose a risk to human health, hence, need careful assessment. Thus, a thorough review on the role of different NFs and their impact on crop growth, productivity, soil, and environmental quality is required, which would be helpful for the research of sustainable agriculture.
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•Nanofertilizers (NFs) are the best alternative to traditional chemical fertilizers.•Nutrients use efficiency of NFs is higher than the conventional chemical fertilizers.•NFs can increase the tolerance of plants against biotic and abiotic stresses.•Supra optimal dose of NFs had a negative impact on crops, soil, and the environment.
This is the second report on the retention of electronic conductivity in yttria‐stabilized zirconia at room temperature after cooling down from the state of flash . In the first report, the specimens ...(which were flashed in air) were quenched by in‐flash immersion into liquid nitrogen. Now we show that if the specimens are flashed in Ar in a glove box (O2 < 1 ppm), then they remain electronic conductors under nominal cooling. Indeed, the conductivity of the Ar‐flashed specimens is higher than the conductivity of LN2‐quenched samples. In both instances, their conductivity increases with flash current. In contrast, specimens flashed in air, and then air‐cooled, become insulating akin to their original condition. We propose a possible pathway for such a reaction. In addition, we report measurements of the interface resistance at the anode and the cathode by the four‐point technique. In air, the resistance at anode is higher than at the cathode, and the sum of the interface resistances is about one half of the total end‐to‐end resistance.
Reactive flash sintering is a process where off‐the‐shelf powders of elemental oxides can be simultaneously sintered and reacted to form a multicomponent oxide in a matter of seconds at low furnace ...temperatures. The fact that several cation species, each residing within their own particles, can migrate over distances of several micrometers, and mix on the atomic scale to form multicomponent oxides, so quickly, is quite remarkable. The question arises as to the rate of this solid‐state diffusion phenomenon. In this paper, we present measurements of this diffusion coefficient from live flash experiments. The results are obtained from millimeter scale bilayers of yttria‐stabilized zirconia and lanthana where the flash initiates in the zirconia layer and then migrates into the lanthana layer, forming lanthanum zirconates. The velocities of migration of the flash‐front, coupled with measurements of the length scale of the profile of zirconium and lanthanum interdiffusion, across the bilayer interface, provide an estimate of the effective diffusion coefficient. These measurements give a value for the cation diffusion to lie in the range of 2.5 × 10−10 m2 s−1 at 1380°C, with an activation energy of 200–250 kJ mol−1. In comparison, the cation diffusion coefficient in yttria‐stabilized zirconia, at 1350°C, is stated to be 1.1 × 10−20 m2 s−1 with an activation energy of ∼550 kJ mol−1. A pause for reflection.
This review addresses common questions regarding the role of surgical lung biopsy (SLB) in the diagnosis and treatment of interstitial lung disease (ILD). We specifically address when a SLB can be ...diagnostic as well as when it may be avoided; for example, when the combination of the clinical context and the imaging pattern seen on high-resolution CT (HRCT) chest scans can provide a confident diagnosis. Existing studies on the diagnostic utility as well as the complications associated with SLB are reviewed; also reviewed are the performance characteristics and reliability of HRCT scans of the chest in predicting the underlying histopathologic findings of the lung. The review is formatted in the form of answers to questions that clinicians regularly ask when considering an SLB in a patient with ILD.
•Numerically studied flow boiling in multi-parallel microchannel with inlet-outlet plenums.Three-dimensional, laminar, multi-phase, transient numerical model is developed.•Experiments are performed ...on a fourteen parallel microchannel for wide range of heat flux.•Excellent agreement between numeral and experimental results over a wide rangeVapour blocking in the channel near the outlet is primarily responsible for instabilities.•Fourteen channels demonstrate higher heat transfer coefficient compared to six channels.
A combined numerical and experimental investigation to elucidate the two-phase flow behaviour and heat transfer during subcooled boiling of water in 1 × 1 cm2 footprint area heat sinks with six, ten, and fourteen parallel microchannels is performed. A three-dimensional, laminar, multi-phase, transient numerical model is developed to simulate flow boiling in microchannels. This study is one of the first studies which reports a three-dimensional numerical simulation of flow boiling in a large area multiple parallel microchannels heat sink including the effect of inlet and outlet plenums. We show an excellent agreement in heat transfer and pressure drop data with experimental results on a heat sink with fourteen parallel microchannels over a wide range of applied heat flux spanning various boiling regimes. The results show that the vapour blocking in the channel near the outlet is primarily responsible for instabilities and oscillations in the pressure drop, the surface temperature, and the mass flux. Intensified confinement due to the decrease in the number of the channels for a constant fin width results in increased surface temperatures. Similarly, increase in the number of the channels from six to fourteen improved heat transfer significantly wherein a significant drop of 45.5 °C in surface temperature with little increase of 37% in pressure drop is observed for a mass flux of 500 kg/m2s and a heat flux of 220 W/cm2. Microchannel heat sink with fourteen channels demonstrates on an average nearly 240% higher heat transfer coefficient in comparison to the heat sink with six channels. The numerical modelling framework used in this study can be used to provide design guidelines for microchannel heat sinks.
In current-rate flash-sintering experiments the current is injected into the specimen from the very start and then increased at a constant rate, while the furnace is held at a constant temperature. ...The power supply remains under current control. The flash is induced at low current densities which reduces local heating at the electrodes. It leads to a uniform grain size across the entire gage length of the dog-bone specimen. This work pertains to 10 mol.% gadolinium-doped ceria flash sintered at current-rates ranging from 50 mA min−1 to 1000 mA min−1 at a furnace temperature of 680 °C. Full densities are obtained at a current density limit of 200 mA mm–2. Densification is shown to depend only on the instantaneous value of the current density, and not on the current-rate. The grain size, however, is shown to become finer at higher current-rates. A preliminary analysis of the “energy deficit”, that is, the estimated power input corresponding to the temperature as measured with a pyrometer, and the actual power consumption, estimates that huge concentrations of Frenkel defects may be introduced in the flash process.
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Crystalline quartz has long been identified as among the weakest of abundant crustal minerals. This weakness is particularly evident around the α–β phase inversion at 573°C, in which Si–O bonds ...undergo a displacive structural transformation from trigonal to hexagonal symmetry. Here we present data using indentation testing methodologies that highlight the precipitous extent of the transformational weakening. Although the indentations are localized over relatively small specimen contact areas, the data quantify the essential deformation and fracture properties of quartz in a predominantly (but not exclusively) compressive stress field, at temperatures and pressures pertinent to conditions in the earth's crust.
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