Kinetic investigation of the carbothermal reduction of an Iranian clay

The kinetics of the carbothermal reduction of clay under argon atmosphere has been investigated by the X-ray diffraction method. The clay-carbon (excess) mixture was formed into 2 cm diameter disks of different thicknesses. Experimental data evidences the significant effect of sample thickness on the reaction rate at 1400 °C. Decreasing thickness promotes mullite dissociation and formation of SiC and alumina powders. Mathematical modeling of the reaction system showed the gas diffusion in the Knudsen regime through the pellet to be the rate controlling step. Diffusivity of CO and reacted core tortuosity factor have been calculated.     

Removal of aqueous Fe2+ using MnO2–clinoptilolite in a batch slurry reactor: Catalyst synthesis,characterization and modeling of catalytic behavior

An Iranian clinoptilolite has been modified with MnO₂ for the catalytic removal of Fe²⁺ cations from water in a batch slurry reactor. The modified zeolite was subjected to FESEM, XRD, WDX, XRF and specific surface area analysis. A correlation for the intrinsic catalytic reaction rate incorporating both Fe²⁺ and dissolved oxygen concentration as a function of reaction temperature has been presented. The effect of the modified zeolite aggregate particle size on the iron removal kinetics has been investigated. It was shown that for particles larger than 150 μm, diffusion through the mesopores of the zeolite aggregate is rate controlling. The effective diffusion coefficient through the particles at RT has been calculated as 2.3 × 10^?6 cm² s^?1. It is shown that liquid phase molecular diffusion within the mesopores is the dominating mass transfer mechanism.     

Reconciliation between experimental and Monte Carlo-based simulation of the pore size distribution in mesoporous silicon

It is demonstrated for the first time that mesoporous PS structures obtained by the electrochemical etching of p(+)(100) oriented silicon wafers might assume the peculiarity of invariance of the first peak positions in their pore size distribution curves, albeit for current densities far from the electropolishing region and at constant electrolyte composition. A new Monte Carlo-based simulation model is presented that predicts reasonably the pore size distribution of the PS layers and the observed invariance of peak position with respect to changes in current density. The main highlight of the new model is the introduction of a 'light avalanche breakdown' process in a mathematical fashion. The model is also able to predict an absolute value of 4.23?? for the smallest pore created experimentally. It is discussed that the latter value has an exact physical meaning: it corresponds with great accuracy to the width of a void created on the surface due to the exclusion of one Si atom.     

Mass Transfer Mechanisms in the Fixed‐Bed Ion‐exchange Process for Dilute Colloidal Silica Manufacture

The ion exchange behavior of the H⁺ form C‐100 Purolite resin for the production of colloidal silica from dilute sodium silicate solutions has been investigated. The exchange isotherm has been found to be almost irreversible. The effective resin diffusion coefficient has been found to be 2.84 × 10^–10 m² s^–1 using a shrinking core model for the batch uptake experiments. Fixed bed experiments for different column heights and feed flow rates were performed. Numerical solution of the governing equations showed that the process is initially controlled by film diffusion and consequently by resin diffusion. Axial dispersion had to be taken into account. A simple power law correlation has been determined that relates the fluid Peclet number to the Reynolds number. It is presumed that some sort of resin ‘deactivation’ due to intraparticle microgel formation is responsible for the sluggish end part of the breakthrough curves.     

Effect of electric arc and ladle furnace slags on the strength and swelling behavior of cement-stabilized expansive clay

Bulletin of Engineering Geology and the Environment - The current research evaluated the effect of expansive clay stabilization using a combination of cement (0, 2, 5, 8%) with electric arc furnace...     

Strength Properties of Hexametaphosphate Treated Soils

The present technical note focuses on the potential application of sodium hexametaphosphate (HMP) in geo-environmental engineering. HMP may have many applications in geotechnical and geo-environmental engineering such as: improvement and stabilization of tailing dams, rehabilitation of old landfills, construction of new clay liners, containment and permeable barriers, etc. In this technical note, it is observed that the strength of silty-clayey sand containing a high concentration of metals (like tailings) is increased by mixing of HMP. On the other hand the strength of the kaolinite clay that may be used during the construction of a liner has been reduced by mixing with HMP. In order to study the influence of HMP, soil mixtures with various amount of HMP are prepared to conduct unconfined compression tests. The strength of the HMP-treated kaolinite specimens is always less than the kaolinite specimens for four weeks. HMP has decreased the strength of silty sand during the first days. However, the cations in the soil (specially Ca and Fe) may lead to precipitation and sorption mechanism to govern and, therefore, the strength increases noticeably up to 740%.     

Taguchi design of experiments approach to the manufacture of one-step alumina microfilter/membrane supports by the centrifugal casting technique

The Taguchi design of experiments method was implemented for the optimization of the manufacture of sintered one-step alumina microfilter/membrane supports by the centrifugal casting technique for the first time. A 10 wt.% alumina aqueous slip containing Tiron (0.001 g/g alumina) as dispersant and PVA as binder were used. Acceleration (3 levels), slip volume (3 levels), binder content (3 levels) and pH (2 levels) were selected as controlling parameters (saturated L-9 array). The use of three different target functions has been discussed: (1) the product of top-layer surface porosity times the reciprocal of top-layer surface pore diameter; (2) the product of permeability times thickness; and (3) membrane curvature. It is deduced that the first target function is the most appropriate as far as the membrane characteristics of the sintered compact are concerned. Using this target function a distinct optimum configuration for the controlling parameter levels could be obtained.     

New Insights of the Glycine-Nitrate Process For the Synthesis of Nano-Crystalline 8YSZ

Nano-crystalline 8YSZ was synthesized by the glycine-nitrate process in a muffle furnace using zirconyl nitrate and yttrium nitrate as sources of oxidants. The effect of changing the elemental stoichiometric coefficient over a wide range (0.756–1.605) on the product characteristics (crystallite size, percent unreacted, surface area) has been investigated. It is demonstrated that the combustion reaction proceeds most efficiently in the fuel-lean region. A novel and simple mathematical model is presented that allows to evaluate the thickness of the sheet-like particles of the foamy final product based on BET data. The calculated thickness values are in good agreement with the experimental data. For the first time, the effect of using ammonium nitrate as a combustion aid for the stoichiometric precursor composition has been studied. The optimum amount of combustion aid addition has been determined.     

A novel microfluidic high-throughput resistive pulse sensing device for cells analysis

Microfluidic impedance-based devices offer a simple method for counting and sizing particles and cells in fields of biomedical research and clinical diagnosis. In this work, we present design, fabrication and operational characteristics of a novel high throughput original MEMS-based Coulter counter. This microfluidic device possesses two sub channels including two pairs of coplanar Au/Cr electrodes in each channels which allows double detection of the particles simultaneously and increases the throughput. The present design provides minimizing the cross talk and obviating the need for hydrodynamic focusing of the sample particles by adjusting Y shape insulation obstacle in direction of flow. Moreover, reducing coincidence events and removing electrode polarization effect were purposed by applying optimum sizes for electrodes considering the ease of fabrication and low costs. The reliability of the novel device was evaluated for polystyrene particles and cancer cells in conductive solutions. Results, which were recorded as relative resistance pulses across four sensing zones, illustrate the capability of the double-channel proposed device in detecting, counting and sizing 10 and 20 µm polystyrene particles. The superiority of present design was proved by relative counting error of below 3 and 11% for the 10 µm and 20 µm particles, respectively and a throughput of hundreds particles per second. Aiming at demonstrating the functionality of the proposed device in the biomedical area, counting of SP2/0 cells was performed. The measured counting outputs for cells in the size range of 5.63–17.6 µm were validated with results of hemocytometer cell counter, with relative error less than 7%.

     

Use of nano-silica carriers for the fabrication of Li2o/MgO catalyst nano-particles on the surface of alpha-alumina supports

A novel method for the production of detached ceramic oxide catalyst nano-particles on ceramic supports is presented. By the addition of a W/O micro-emulsion of colloidal silica to a W/O micro-emulsion of lithium and magnesium nitrate salts, a micro-emulsion of silica aggregates containing detached groups of the ceramic parent salts is prepared. The solid support (porous alpha-alumina) is put into contact with the latter and, after proper heat treatment, nano-sized particles of Li₂O/MgO ceramic oxides are formed on separate islands of silica in a detached fashion. The obtained composite shows significant activity for the oxidative coupling of the methane reaction.