Packing Density Of Materials Research Articles

Comprehensive experimental and theoretical studies on material-gap and water-gap membrane distillation using composite membranes

Experimental and theoretical studies on material-gap membrane distillation (MGMD) and water-gap membrane distillation (WGMD) are presented in this paper to demonstrate the effect of gaps filled with different materials on permeation flux. A flat-sheet composite membrane composed of an active polytetrafluoroethylene layer and a support polypropylene layer was employed in the experiments. Graphite, water, silica gel, and zeolite were used to measure the effects of these materials on permeation flux and thermal resistance. In the experiments and simulations, the size of the material and water gaps was kept constant at 5 mm. The graphite-filled MGMD permeation flux was approximately 11–22% higher than that of the WGMD at inlet feed temperatures in the range of 40–70 °C. However, the permeation flux of MGMD filled with silica gel and zeolite was 17–24% and 18–27% lower than that of WGMD, respectively. At thermal conductivities below 5 W/mK, the permeation flux of the MGMD with a material packing density of 40% was higher than that with a material packing density of 60%. The MGMD permeation flux with a material packing density of 60% was higher than that with a material packing density of 40% above a thermal conductivity of 5 W/mK. Furthermore, the MGMD permeation flux and overall thermal resistance were primarily controlled by the material gap, with materials having thermal conductivities below 30 and 20 W/mK for the bead- and pellet-type materials (i.e., packing densities of 40 and 60%), respectively.

Ball-milled biochar for efficient neutral electrosynthesis of hydrogen peroxide

Carbon-based materials are promising low-cost electrocatalysts for hydrogen peroxide (H2O2) electrosynthesis, but their widespread application are currently restricted by low activity in neutral electrolyte. Here, using peanut shell-derived biochar as an example, we show that high-performance carbon electrocatalyst can be obtained through simple mechanical milling treatment. Ball milling not only drastically increased the material packing density but also introduced rich defects and oxygen-containing functional groups, which enhanced the oxygen adsorption and two-electron oxygen reduction reaction selectivity, respectively. This renders the treated biochar increased conductivity and 4.2-fold higher H2O2-producing activity than the pristine one, as well as 87% H2O2 electrosynthesis selectivity at neutral pH. The ball-milled biochar also outperformed the commercial acetylene black and most state-of-the-art electrocatalysts in H2O2 production, and maintained stable performance during 6-h reaction. Similar enhancement effects of ball milling were also found for other types of biochars, implying a universal applicability of this method. Our work opens a new avenue towards mass production of low-cost, high-activity electrocatalysts for neutral H2O2 electrosynthesis, and offers new opportunities for waste biomass valorization.

A methodology for the effective use of materials in concrete paving block

For a long time, concrete paving blocks have been broadly utilized in different countries as a specialized problem-solving technique to provide pavement in areas where, traditional forms of construction were less robust due to several drawbacks. Low maintenance, ease of placing and evacuation and quick use after installation make it best fit for various utilizations where the conventional pavement technologies are not practical or desirable. So there emerges a dynamic enthusiasm for the concepts of the mix design process for the development of concrete paving blocks arises. This paper aims to develop an optimized mix design for concrete paver blocks for medium traffic as per relevant codes, considering quality and economy. To maximise the particle packing density of concrete, the packing density approach was used here. The method of packing density receipt maximises the concrete material packing density by selecting the perfect measure of different aggregates to fill the voids, allowing a denser and firmer structure. The higher degree of particle packing contributes to minimum voids, maximum density, and thus fewer cement and water demands, leading ideal medium traffic design.

Effects of different complexing agents on the physical properties of ZnO nanoparticles

ABSTRACTZnO nanoparticles have been synthesised via a co-precipitation method using different complexing agents. X-ray diffraction (XRD) analysis revealed that ZnO nanoparticles were composed of a single hexagonal wurtzite phase. Transmission electron microscopy (TEM) analysis indicates that the samples prepared without any complexing agent have slight agglomeration characteristics presenting a prismatic morphology and a wider size distribution from 22 to 72 nm, which provides good material packing density. However, samples synthesised using urea and glycine are similar and show spherical-like morphology. XRD and TEM analyses indicate that complexing agents also have an important role in the size of the ZnO nanoparticles, where the average particle size of 47 and 22 nm were obtained using urea and glycine, respectively.

Softening and yielding of soft glassy materials.

Solids deform and fluids flow, but soft glassy materials, such as emulsions, foams, suspensions, and pastes, exhibit an intricate mix of solid- and liquid-like behavior. While much progress has been made to understand their elastic (small strain) and flow (infinite strain) properties, such understanding is lacking for the softening and yielding phenomena that connect these asymptotic regimes. Here we present a comprehensive framework for softening and yielding of soft glassy materials, based on extensive numerical simulations of oscillatory rheological tests, and show that two distinct scenarios unfold depending on the material's packing density. For dense systems, there is a single, pressure-independent strain where the elastic modulus drops and the particle motion becomes diffusive. In contrast, for weakly jammed systems, a two-step process arises: at an intermediate softening strain, the elastic and loss moduli both drop down and then reach a new plateau value, whereas the particle motion becomes diffusive at the distinctly larger yield strain. We show that softening is associated with an extensive number of microscopic contact changes leading to a non-analytic rheological signature. Moreover, the scaling of the softening strain with pressure suggest the existence of a novel pressure scale above which softening and yielding coincide, and we verify the existence of this crossover scale numerically. Our findings thus evidence the existence of two distinct classes of soft glassy materials - jamming dominated and dense - and show how these can be distinguished by their rheological fingerprint.

Optimization and comprehensive characterization of metal hydride based hydrogen storage systems using in-situ Neutron Radiography

For the storage of hydrogen, complex metal hydrides are considered as highly promising with respect to capacity, reversibility and safety. The optimization of corresponding storage tanks demands a precise and time-resolved investigation of the hydrogen distribution in scaled-up metal hydride beds. In this study it is shown that in situ fission Neutron Radiography provides unique insights into the spatial distribution of hydrogen even for scaled-up compacts and therewith enables a direct study of hydrogen storage tanks. A technique is introduced for the precise quantification of both time-resolved data and a priori material distribution, allowing inter alia for an optimization of compacts manufacturing process. For the first time, several macroscopic fields are combined which elucidates the great potential of Neutron Imaging for investigations of metal hydrides by going further than solely ’imaging’ the system: A combination of in-situ Neutron Radiography, IR-Thermography and thermodynamic quantities can reveal the interdependency of different driving forces for a scaled-up sodium alanate pellet by means of a multi-correlation analysis. A decisive and time-resolved, complex influence of material packing density is derived. The results of this study enable a variety of new investigation possibilities that provide essential information on the optimization of future hydrogen storage tanks.

Effect of morphology on light scattering by agglomerates

Using the discrete dipole approximation (DDA), we compute light scattering from irregularly shaped particles with three different types of agglomerate morphologies. The packing density of materials in the model particles spans the range from 0.169 through 0.336. We investigate four different refractive indices m=1.313+0i, 1.6+0.0005i, 1.5+0.1i, and 1.855+0.45i, which are representative of various cosmic and terrestrial materials in the visible. In each case, we consider a wide range of size parameters that makes it possible to average the light-scattering response over particle size with a power-law size distribution. We find that despite noticeable differences in particle morphology, their light-scattering responses are remarkably similar; the difference in light scattering often does not exceed the error bars occurring in laboratory measurements of micron-sized particles. On the contrary, the impact of refractive index and size distribution on light scattering appears to be much stronger compared with the morphology of complex, agglomerate particles. This finding may simplify considerably the interpretation of photo-polarimetric observations of atmospheric aerosols, cosmic dust particles, etc., because the precise specification of target-particle shape is unnecessary for the analysis.

Modeling granular phosphor screens by Monte Carlo methods

The intrinsic phosphor properties are of significant importance for the performance of phosphor screens used in medical imaging systems. In previous analytical-theoretical and Monte Carlo studies on granular phosphor materials, values of optical properties, and light interaction cross sections were found by fitting to experimental data. These values were then employed for the assessment of phosphor screen imaging performance. However, it was found that, depending on the experimental technique and fitting methodology, the optical parameters of a specific phosphor material varied within a wide range of values, i.e., variations of light scattering with respect to light absorption coefficients were often observed for the same phosphor material. In this study, x-ray and light transport within granular phosphor materials was studied by developing a computational model using Monte Carlo methods. The model was based on the intrinsic physical characteristics of the phosphor. Input values required to feed the model can be easily obtained from tabulated data. The complex refractive index was introduced and microscopic probabilities for light interactions were produced, using Mie scattering theory. Model validation was carried out by comparing model results on x-ray and light parameters (x-ray absorption, statistical fluctuations in the x-ray to light conversion process, number of emitted light photons, output light spatial distribution) with previous published experimental data on Gd2O2S: Tb phosphor material (Kodak Min-R screen). Results showed the dependence of the modulation transfer function (MTF) on phosphor grain size and material packing density. It was predicted that granular Gd2O2S: Tb screens of high packing density and small grain size may exhibit considerably better resolution and light emission properties than the conventional Gd2O2S: Tb screens, under similar conditions (x-ray incident energy, screen thickness).

Characterization of insulating particles by dielectric spectroscopy: Case study for CaCO 3 powders

This work investigates the permittivity response of crystalline calcite powders produced by pulverizing and milling from well crystallized marble. Crystal characterization of continuous solid and powder compacts was based upon XRD. The particle size of the powders has been characterized by laser granulometry. Different packing densities of the powders were investigated i.e., unpacked, tapped, pressed to form pellets by different forces. The dielectric spectroscopy demonstrates the significance of reduced particle size and material packing density. At low frequencies, particle surface state effects dominate and the applied electrical energy is stored on the surfaces. This induces surface polarization effects that are normally considered in nanodielectric technology. As the size of the particles is reduced the surface polarization effects intensify and extend their frequency range towards the higher frequencies. In the high frequency regime (i.e., f > 100 kHz) the energy supplied by the electric field is stored in the volume of the particles. The dielectric data of the powder is determined by the packing density of the particles. A potential energy model is proposed in order to help workers to envisage the implications of surface vs. volume energy absorption process of sub-micron particle compacts when subjected to AC electric fields.

Photon attenuation, natural radioactivity content and radon exhalation rate of building materials

High concentrations of natural radionuclides in building materials can result in high dose rates indoors, from both internal and external exposure. In dose calculations, the main radionuclides of interest are 226Ra, 232Th and 40K. Usually much attention is paid to 226Ra due to 222Rn exhalation and the subsequent internal exposure. Other radionuclides of the uranium series such as 238U and 210Pb, emitting low energy photons are not usually determined and an assumption of radioactive equilibrium is made. The above assumption is seldom checked mainly because of the difficulties in the γ-spectroscopic analysis of low energy photons. For the determination of radionuclides emitting low-energy photons, in samples like building materials where intense self-absorption of the photons exists, a method for self-absorption correction has been developed. The method needs as input the linear attenuation coefficient μ for the material under analysis. This paper presents: 1. Correlations in the form μ= f( ρ, E) developed for the estimation of the linear attenuation coefficient μ (cm −1), as a function of the material packing density ρ (g cm −3) and the photon energy E (keV), for building materials as well as other materials of environmental importance. 2. Gamma-spectroscopic analysis techniques used for the determination of 238U, 226Ra, 210Pb, 232Th and 40K in environmental samples, together with the results obtained from the analysis of building materials used in Greece, and industrial by-products used for the production of building materials. Among the techniques used, one is based on the direct determination of 226Ra and 235U from the analysis of the multiplet photopeak at ∼186 keV. 3. Results from radon exhalation measurements of building materials such as cement and fly-ash and building structures conducted in the radon chambers in our Laboratory. Based on the above results, dosimetric calculations are also reported.

Methods of granular and fragmented material packing density calculation

This paper is the first in the series devoted to the problems of granular and fragmented material package density calculation. It considers the theory of the calculation of loosening for materials consisting of irregular shape particles. Two new methods for the density calculation of unlimited volume granular materials are offered. a crude method based on the empirical relation between density and the index (worked out by the author) of the uniform distribution of particles in individual fractions; the other method, a more precise one, allows for the consideration of fraction mixture quality. On this basis, problems pertaining to the calculation of granular and fragmented material package density in containers of various shapes and dimensions, to dilatancy packing or loosening of such media, blasted rock density computation and methods of overburden blasting, are discussed.