An index to characterize gas-solid and solid-solid mixing from average volume fraction fields

A mixing index based on solid volume fraction fields is developed for gas-solid flows. Conventional mixing indices are based on particle realizations of granular mixing and are applicable to experimental data or discrete element method simulations. However, these indices cannot be used as-is for multifluid models, and an index for characterizing mixing in gas-solid flows from continuous fields is needed. The performance of the new mixing index is tested in two applications. The first is a 3D simulation of the mixing of biomass and sand in a fluidized bed reactor, and the second is a 2D simulation of binary particle segregation in a fluidized bed. The simulations are performed using OpenFOAM®. The mixing index is used to quantify gas-solid mixing using solid volume fractions and solid-solid mixing using solid fractions. The formulation of conventional mixing indices is extended to be used with solid volume fractions fields, and methods for performance improvement are presented.     

A novel strategy for fabricating zirconia implants with a trabecular biomimetic porous surface

For successful osseointegration of load-bearing implants, an improved bone–implant contact area through a trabecular porous surface resulting in minimized stress shielding effect is highly desirable. We propose a novel strategy of green net shaping a ceramic dough, combined with a reticular foam replica method and gradient coating, to fabricate biomimetic porosity in a customizable ceramic dental implant for the first time. About 85 vol% porosity and 300–600-μm pore size were evident in microCT and electron microscopy of the sintered samples, suitable for bone ingrowth. Excellent integrity at the interface along with homogeneous distribution of secondary alumina phase in zirconia matrix was achieved, despite the difference in the green state powder loading between the dough and the slurry.     

Development of spark plasma sintered conductive SiC–TiB2 composites for electrical discharge machining applications

Highly dense electrically conductive silicon carbide (SiC)–(0, 10, 20, and 30 vol%) titanium boride (TiB₂) composites with 10 vol% of Y₂O₃–AlN additives were fabricated at a relatively low temperature of 1800°C by spark plasma sintering in nitrogen atmosphere. Phase analysis of sintered composites reveals suppressed β→α phase transformation due to low sintering temperature, nitride additives, and nitrogen sintering atmosphere. With increase in TiB₂ content, hardness increased from 20.6 to 23.7 GPa and fracture toughness increased from 3.6 to 5.5 MPa m^1/2. The electrical conductivity increased to a remarkable 2.72 × 10³ (Ω cm)^–1 for SiC–30 vol% TiB₂ composites due to large amount of conductive reinforcement, additive composition, and sintering in nitrogen atmosphere. The successful electrical discharge machining illustrates potential of the sintered SiC–TiB₂ composites toward extending the application regime of conventional SiC-based ceramics.     

Characterization of Fly Ash Sources in the Synthesis of Geopolymer

Silicon - Fly ash (FA) based geopolymers are affected by the reactive nature of FA, concentration and quantity of alkali activators and the curing conditions. However, for the geopolymer...     

Molecular Sensing Using Hyperpolarized Xenon NMR Spectroscopy

Molecular imaging is the determination of the spatial location and concentration of specific molecules in a sample of interest. Sophisticated modern magnetic resonance imaging machines can collect NMR spectra from small-volume elements within a sample, enabling local chemical analysis. However, abundant water and fat signals limit detection of metabolites to near mM concentrations. Alternatively, targeted relaxation contrast agents enhance the relaxation of the strong water signal where they bind. A comparison of images with and without a contrast agent shows the target distribution, but high µM concentrations are needed. We have developed an approach that exploits the strong signals of hyperpolarized ¹²⁹Xe (an inert reporter introduced for imaging). The imaging contrast agents are composed of a biological recognition motif to localize the agent (antibodies or aptamers) and covalently tethered cryptophane cages. Xenon binds to the cryptophane and though chemical exchange saturation transfer creates contrast in a xenon image. Imaging agents can deliver many cages per target, giving detection limits in the pM concentration range. The evolution and principles of this approach are described herein.     

Erosion behavior of SiC–WC composites

Dense silicon carbide (SiC) ceramics were prepared with 0, 10, 30 or 50 wt% WC particles by hot pressing powder mixtures of SiC, WC and oxide additives at 1800 °C for 1 h under a pressure of 40 MPa in an Ar atmosphere. Effects of alumina or SiC erodent particles and the WC content on the erosion performance of sintered SiC–WC composites were assessed. Microstructures of the sintered composites consisted of WC particles distributed in the equi-axed grain structure of SiC. Fracture surfaces showed a mixed mode of fracture, with a large extent of transgranular fracture observed in SiC ceramics prepared with 30 wt% WC. Crack bridging by WC enhanced toughening of the SiC ceramics. A maximum fracture toughness of 6.7 MPa*m^1/2 was observed for the SiC ceramics with 50 wt% WC, whereas a high hardness of 26 GPa was obtained for the SiC ceramics with 30 wt% WC. When eroded at normal incidence, two orders of magnitude less erosion occurred when SiC–WC composites were eroded by alumina particles than that eroded by SiC particles. The erosion rate of the composites increased with increasing angle of SiC particle impingement from 30° to 90°, and decreased with WC reinforcement up to 30 wt%. A minimum erosion wear rate of 6.6 mm³/kg was obtained for SiC–30 wt% WC composites. Effects of mechanical properties and microstructure on erosion of the sintered SiC–WC composites are discussed, and the dominant wear mechanisms are also elucidated.     

Evolution of particle metrics in a buoyant aerosol cloud from explosive releases

Abstract

The detonation of high explosive (HE) material generates a cloud containing a high concentration of detonation products in the form of aerosol particles and gases. Modeling and simulation of aerosol metrics in an explosive cloud is a complex problem as it involves various processes such as chemical reaction, nucleation, volume expansion, and coagulation. Several models have been developed to study the atmospheric dispersion of these detonation products, but very few or no model is available to study the evolution of aerosol metrics at the early stage. In this work, we present a numerical model to simulate the temporal evolution of aerosol metrics in an expanding cloud by coupling transient thermodynamic properties with important microphysical processes. To illustrate the application, the numerical model is applied to a typical HE, and the aerosol particle properties such as size distribution, number concentration, and average size are estimated from the numerical results. These results will provide the essential input conditions for atmospheric dispersion models to estimate the atmospheric concentration and deposition of aerosol particles.

Copyright © 2020 American Association for Aerosol Research     

Transport and solvent sensing characteristics of styrene butadiene rubber nanocomposites containing imidazolium ionic liquid modified carbon nanotubes

Obtaining strong interfacial interaction between filler and polymer matrix is very crucial for the fabrication of polymer nanocomposites with superior performance. Present study is aimed to fabricate high performance styrene butadiene rubber (SBR) nanocomposites with imidazolium type ionic liquid modified multiwalled carbon nanotube (MWCNT). Ionic liquid facilitates the dispersion of MWCNT in rubber matrix and it is obvious from transmission electron microscopy images. Diffusion of toluene through SBR nanocomposite membranes has been investigated as a function of surface modified MWCNT (f-MWCNT) content to analyze the chain dynamics and filler-polymer interactions. O₂ gas barrier effect of nanocomposites with special reference to the filler loading is explored. The substantial improvement in the barrier effect in presence of filler interpreted on the grounds of a theoretical model describing permeability of heterogeneous systems. Finally solvent sensing characteristics of prepared nanocomposites are also analyzed and it is observed that prepared nanocomposites can be used as a flexible solvent sensor.     

Quality characteristics of biscuits prepared from finger millet seed coat based composite flour

Finger millet seed coat is an edible material and contains good proportion of dietary fibre, minerals and phytochemicals. The seed coat matter (SCM) forms a by-product of millet milling, malting and decortication industries and can be utilised as composite flour in biscuit preparation. The SCM from native, malted and hydrothermally treated millet contained 9.5–12% protein, 2.6–3.7% fat and 40–48% dietary fibre, besides 3–5% polyphenols and 700–860 mg/100 g of calcium. The biscuits prepared using the composite flour were of crisp texture and exhibited breaking strength of 1480–1690 g compared to control biscuits (1560 g). The biscuits were of mild grey colour (ΔE = 40–50) and exhibited higher protein, dietary fibre and calcium contents. The sensory evaluation of the biscuits indicated that 10% of SCM from native and hydrothermally processed millet and 20% from malted millet could be used in composite biscuit flour.