Diffusivity in Cement-Silica Fume Based Materials: Experimental and Computer Modeling Results on Mortars

2016 ◽  
Vol 711 ◽  
pp. 1098-1104
Author(s):  
Z. Bajja ◽  
W. Dridi ◽  
A. Darquennes ◽  
R. Bennacer
Keyword(s):  
Silica Fume ◽  
Diffusion Coefficients ◽  
Volume Fraction ◽  
Transport Model ◽  
Input Parameter ◽  
Tritiated Water ◽  
Effective Diffusion ◽  
Nitrogen Adsorption ◽  
Cement Matrix ◽  
Biphasic Model

Silica fume cement (SFC) based materials are largely used as a containment barrier for nuclear waste management. The safety of this storage mode depends on the knowledge of the effective diffusion coefficients of such materials. This work proposes a combination of computer models able to estimate the diffusion coefficients of SFC pastes and mortars, from a single investigation of the microstructure by nitrogen adsorption. The approach used consists firstly in manufacturing SFC mortars by varying sand volume fraction from 30 to 65% while silica fume replacement and water to binder ratio were respectively set at 10% and 0.4. Nitrogen adsorption tests were then performed and collected data on C-S-H nature are introduced into a SFC pastes hydration model. The latter provides the mineral composition which is an input parameter in the multilayer transport model that estimates the effective diffusion coefficient (De) of cement pastes. For mortars, a 3D biphasic model (sand and cement matrix) was used to compute the (De) of mortars at different inclusion volume fractions. The numerical results were approved by comparison to experimental data obtained from tritiated water (HTO) diffusion tests performed on manufactured mortars.

Bromine-Methanol Etching of Cadmium Telluride in a Rotating Disk Reactor

1990 ◽  
Vol 204 ◽  
Author(s):  
Michael B. Gentzler ◽  
Edmond I. Ko ◽  
Paul J. Sides ◽  
Paul T. Bowman
Keyword(s):  
Diffusion Coefficients ◽  
Rotation Rate ◽  
Transport Model ◽  
Effective Diffusion ◽  
Rotating Disk ◽  
One Dimensional ◽  
Effective Diffusion Coefficients ◽  
Rotating Disk Reactor ◽  
Bromine Concentration ◽  
Kinetics Of

ABSTRACTThe kinetics of the bromine-methanol etching of CdTe were studied in a rotating disk reactor as a function of temperature, bromine concentration, substrate orientation, and rotation rate. The results indicated that the etching process is mass transfer controlled from -20°C to 40°C and to a maximum rotation rate of 1200 RPM. A one-dimensional transport model was used to obtain effective diffusion coefficients for bromine in methanol. The diffusion coefficient of the etchant in methanol is given by 3.7×10-8 (T/η) cm2/s over the range of 2.5°C to 23°C.

scholarly journals The Dependency of Diffusion Coefficients and Geometric Factor on the Size of the Diffusing Molecule: Observations for Different Clay-Based Materials

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-16 ◽  
Author(s):  
Elke Jacops ◽  
Marc Aertsens ◽  
Norbert Maes ◽  
Christophe Bruggeman ◽  
Rudy Swennen ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Effective Diffusion Coefficient ◽  
Tritiated Water ◽  
Effective Diffusion ◽  
Geometric Factor ◽  
Opalinus Clay ◽  
Dissolved Gases ◽  
Exponential Relationship ◽  
Boom Clay

In order to investigate in more detail the relation between the size of diffusing molecules and their diffusion coefficients (and geometric factors), diffusion experiments with gases of different size and tritiated water (HTO) have been performed on different clayey samples (Boom Clay, Eigenbilzen Sands, Opalinus Clay, Callovo-Oxfordian Clay, and bentonite with different dry densities). We observed that, for unreactive gases in clayey materials, the effective diffusion coefficient varies with the size of the diffusing molecule and this variation can be described by an exponential or a power law function. The variation of the geometric factor can also be described by an exponential function. The observed experimental relations can be used to estimate diffusion coefficients; by measuring experimentally in clay the effective diffusion coefficient of two unreactive dissolved gases with a different size, the diffusion coefficients of other dissolved gases (with a size in between the two measured gases) can be estimated by using the fitted exponential relationship.

Research on Properties of Low Grade Cement-Based Composite Materials Modified by Silica Fume

2012 ◽  
Vol 174-177 ◽  
pp. 751-756
Author(s):  
Zi Fang Xu ◽  
Ming Xu Zhang ◽  
Jin Hua Li
Keyword(s):  
Silica Fume ◽  
Mechanical Performance ◽  
Raw Materials ◽  
Cement Matrix ◽  
Hardened Cement ◽  
Low Grade ◽  
X Ray ◽  
Matrix Microstructure ◽  
Nano Powder ◽  
Strength And Durability

In order to notably improve the mechanical properties and durability of low-grade cement-based material, superfine silica fume was used to modify the cement-based composite based on special perfomance and effects of nano powder. The mechanical performance and durability were investigated.Then the phase compositions,microstructure and morphologies of as-received cement-based composite were studied by X-ray Diffractometer、TGA-DTA and SEM. The results show that： the best formula of raw materials is 1:1:0.025:0.015, and hydration can be accelerated and increasing of hydration products is observed after modification. In the hardened cement matrix, microstructure is very compacted and C-S-H gel forms densed structure, so the structure defect is notably reduced. This means that both strength and durability of cement-based composite are notably improved by the addition of superfine silica fume.

Sulfidation Experiments in a Pressurized Thermogravimetric Analyzer With Chinese Calcined Limestones

2005 ◽  
Author(s):  
Zhanlong Song ◽  
Mingyao Zhang
Keyword(s):  
Partial Pressure ◽  
Reaction Temperature ◽  
Total Pressure ◽  
Volume Fraction ◽  
Nitrogen Adsorption ◽  
Reaction Rates ◽  
Thermogravimetric Analyzer ◽  
Morphological Studies ◽  
Shrinking Core ◽  
Structure Properties

The sulfidation experiments with two kinds of Chinese calcined limestones were performed in a pressurized thermogravimetric analyzer (PTGA). The effects of reaction temperature (700–950°C), total pressure (0–1MPa), particle size (0.055–2mm), and H2S concentration (0.1–4%) on the sorbent conversions were analyzed. Morphological studies with scanning electron microscope and energy dispersive spectroscopy (SEM-EDS) equipment were made to obtain the pictures of solid surface and of the cross-sectioned samples. Nitrogen adsorption measurements were applied to determine the pore structure properties of the particles. Experimental results show that the sulfidation rate increases with total pressure when the volume fraction of H2S is constant. However, the rate of sulfidation decreases with the increase of total pressure when the H2S partial pressure is constant. Reaction temperature affects the sulfidation greatly, and the reaction rate increases with temperature. The sulfidation is the first order with respect to H2S partial pressure. Moreover, larger particles result in lower conversions and reaction rates. The unreacted shrinking core model was applied to describe the sulfidation to determine the kinetic parameters.

Diffusion of Zinc in Two-Phase Mg-Al Alloy

2007 ◽  
Vol 263 ◽  
pp. 189-194
Author(s):  
Ivo Stloukal ◽  
Jiří Čermák
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Effective Diffusion ◽  
Residual Activity ◽  
Diffusion Path ◽  
Al Alloy ◽  
Serial Sectioning ◽  
Two Phase ◽  
Interphase Boundaries ◽  
The Mean

Coefficient of 65Zn heterodiffusion in Mg17Al12 intermetallic and in eutectic alloy Mg - 33.4 wt. % Al was measured in the temperature region 598 – 698 K using serial sectioning and residual activity methods. Diffusion coefficient of 65Zn in the intermetallic can be written as DI = 1.7 × 10-2 m2 s-1 exp (-155.0 kJ mol-1 / RT). At temperatures T ≥ 648 K, where the mean diffusion path was greater than the mean interlamellar distance in the eutectic, the effective diffusion coefficient Def = 2.7 × 10-2 m2 s-1 exp (-155.1 kJ mol-1 / RT) was evaluated. At two lower temperatures, the diffusion coefficients 65Zn in interphase boundaries were estimated: Db (623 K) = 1.6 × 10-12 m2 s-1 and Db (598 K) = 4.4 × 10-13 m2 s-1.

Transport properties of concrete-like granular materials interacted by their microstructures and particle components

2018 ◽  
Vol 32 (18) ◽  
pp. 1840011 ◽  
Author(s):  
Wenxiang Xu ◽  
Hongguang Sun ◽  
Wen Chen ◽  
Huisu Chen
Keyword(s):  
Transport Properties ◽  
Granular Materials ◽  
Soft Matter ◽  
Volume Fraction ◽  
Structural Characteristics ◽  
Effective Diffusion ◽  
Nonspherical Particles ◽  
Structure Property ◽  
Engineering Structures ◽  
Component Structure

Granular materials as typical soft matter, their transport properties play significant roles in durability and service life in relevant practical engineering structures. Physico-mechanical properties of materials are generally dependent of their microstructures including interfacial and porous characteristics. The formation of such microstructures is directly related to particle components in granular materials. Understanding the interactive mechanism of particle components, microstructures, and transport properties is a problem of great interest in materials research community. The resulting rigorous component-structure-property relations are also valuable for material design and microstructure optimization. This review article describes state-of-the-art progresses on modeling particle components, interfacial and porous configurations and incorporating these internal structural characteristics into modeling transport properties of granular materials. We mainly focus on three issues involving the simulation for geometrical components, the quantitative characterization for interfacial and porous microstructures, and the modeling strategies for diffusive behaviors of granular materials. In the first aspect, in-depth reviews are presented to realize complex morphologies of geometrical particles, to detect the overlap between adjacent nonspherical particles, and to simulate the random packings of nonspherical particles. In the second aspect, we emphasize the development progresses on the interfacial thickness and porosity distribution, the interfacial volume fraction, and the continuum percolation of soft particles representing compliant interfaces and discrete pores. In the final aspect, a literature review is also provided on modeling of transport properties on the forefront of the effective diffusion and anomalous diffusion in multiphase granular materials. Finally, some conclusions and perspectives for future studies are provided.

Analysis of the damping behavior and microstructure of cement matrix with silane-treated silica fume

2006 ◽  
Vol 21 (2) ◽  
pp. 1-5 ◽  
Author(s):  
Ou Jinping ◽  
Liu Tiejun ◽  
Li Jiahe
Keyword(s):  
Silica Fume ◽  
Cement Matrix ◽  
Damping Behavior
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