scholarly journals On the use of the Jander equation in cement hydration modelling

2016 ◽  
Vol 1 ◽  
pp. 62 ◽  
Author(s):  
John Lloyd Provis
Keyword(s):  
Cement Hydration ◽  
Particle Surface ◽  
Surface Curvature ◽  
Diffusion Control ◽  
Dimensional Changes ◽  
Degree Of Reaction ◽  
Solid Reactant ◽  
Kinetics Of Dissolution ◽  
Kinetics Of ◽  
Selection Of

The equation of Jander [W. Jander, Z. Anorg. Allg. Chem. (1927) 163: 1-30] is often used to describe the kinetics of dissolution of solid cement grains, as a component of mathematical descriptions of the broader cement hydration process. The Jander equation can be presented as kt/R2 =[1-(1-α) (1/3) ]2 where k is a constant, t is time, R is the initial radius of a solid reactant particle, and α is the fractional degree of reaction. This equation is attractive for its simplicity and apparently straightforward derivation. However, the derivation of the Jander equation involves an approximation related to neglect of particle surface curvature which means that it is strictly not correct for anything beyond a very small extent of reaction. This is well documented in the broader literature, but this information has not been effectively propagated to the field of cement science, which means that researchers are continuing to base models on this erroneous equation. It is recommended that if the assumptions of diffusion control and unchanging overall particle size which lead to the selection of the Jander equation are to be retained, it is preferable to instead use the Ginstling-Brounshtein equation [A.M. Ginstling, B.I. Brounshtein, J. Appl. Chem. USSR (1950) 23: 1327-1338], which does correctly account for particle surface curvature without significant extra mathematical complication. Otherwise, it is possible (and likely desirable) to move to more advanced descriptions of particle-fluid reactions to account for factors such as dimensional changes during reaction, and the possibility of rate controlling influences other than diffusion.

Elaboration and Characterization of the Properties of Refractory Cr Base Alloys

2010 ◽  
Vol 72 ◽  
pp. 46-52 ◽  
Author(s):  
Laurent Royer ◽  
Stéphane Mathieu ◽  
Christophe Liebaut ◽  
Pierre Steinmetz
Keyword(s):  
Mechanical Properties ◽  
Melting Point ◽  
Molten Glass ◽  
Energy Production ◽  
Creep Properties ◽  
Refractory Alloys ◽  
Industrial Use ◽  
Kinetics Of ◽  
Selection Of

For energy production and also for the glass industry, finding new refractory alloys which could permit to increase the process temperatures to 1200°C or more is a permanent challenge. Chromium base alloys can be good candidates, considering the melting point of Cr itself, and also its low corrosion rate in molten glass. Two families of alloys have been studied for this purpose, Cr-Mo-W and Cr-Ta-X alloys (X= Mo, Si..). A finer selection of compositions has been done, to optimize their chemical and mechanical properties. Kinetics of HT oxidation by air, of corrosion by molten glass and also creep properties of several alloys have been measured up to 1250°C. The results obtained with the best alloys (Cr-Ta base) give positive indications as regards the possibility of their industrial use.

scholarly journals Role of antigen, CD8, and cytotoxic T lymphocyte (CTL) avidity in high dose antigen induction of apoptosis of effector CTL.

1996 ◽  
Vol 184 (2) ◽  
pp. 485-492 ◽  
Author(s):  
M A Alexander-Miller ◽  
G R Leggatt ◽  
A Sarin ◽  
J A Berzofsky
Keyword(s):  
T Lymphocytes ◽  
Cytotoxic T Lymphocyte ◽  
Target Cells ◽  
High Dose ◽  
High Avidity ◽  
Apoptotic Pathway ◽  
Peptide Antigen ◽  
Kinetics Of ◽  
Selection Of

Experimental data suggest that negative selection of thymocytes can occur as a result of supraoptimal antigenic stimulation. It is unknown, however, whether such mechanisms are at work in mature CD8+ T lymphocytes. Here, we show that CD8+ effector cytotoxic T lymphocytes (CTL) are susceptible to proliferative inhibition by high dose peptide antigen, leading to apoptotic death mediated by TNF-alpha release. Such inhibition is not reflected in the cytolytic potential of the CTL, since concentrations of antigen that are inhibitory for proliferation promote efficient lysis of target cells. Thus, although CTL have committed to the apoptotic pathway, the kinetics of this process are such that CTL function can occur before death of the CTL. The concentration of antigen required for inhibition is a function of the CTL avidity, in that concentrations of antigen capable of completely inhibiting high avidity CTL maximally stimulate low avidity CTL. Importantly, the inhibition can be detected in both activated and resting CTL. Blocking studies demonstrate that the CD8 molecule contributes significantly to the inhibitory signal as the addition of anti-CD8 antibody restores the proliferative response. Thus, our data support the model that mature CD8+ CTL can accommodate an activation signal of restricted intensity, which, if surpassed, results in deletion of that cell.

Phosphorus removal by apatite in horizontal flow constructed wetlands for small communities: pilot and full-scale evidence

2011 ◽  
Vol 63 (8) ◽  
pp. 1629-1637 ◽  
Author(s):  
N. Harouiya ◽  
S. Martin Rue ◽  
S. Prost-Boucle ◽  
A. Liénar ◽  
D. Esser ◽  
...  
Keyword(s):  
Constructed Wetlands ◽  
Particle Surface ◽  
Full Scale ◽  
Retention Capacity ◽  
Small Communities ◽  
Lab Experiments ◽  
Apatite Mineral ◽  
Kinetics Of ◽  
P Removal

Phosphorus (P) removals in constructed wetlands (CWs) have received particular attention in recent decades by using specific materials which promote adsorption/precipitation mechanisms. Recent studies have shown interest in using apatite materials to promote P precipitation onto the particle surface. As previous trials were mainly done by lab experiments, this present study aims to evaluate the real potential of apatites to remove P from wastewater in pilot units and a full-scale plant over a 2 year period. P retention kinetics of two qualities of apatites are presented and discussed. In this work apatite appears to have high retention capacity (>80% of P removal) and is still an interesting way for P removal in CWs for limiting the risk of eutrophication downstream of small communities. Nevertheless, the apatite quality appears to be of great importance for a reliable and long term P removal. The use of materials with low content of apatite mineral (40–50%) seems to be not economically relevant.

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