Dissolution Kinetics of a Simple Analogue Nuclear Waste Glass as a Function of Ph, Time and Temperature

1989 ◽  
Vol 176 ◽  
Author(s):  
Kevin G. Knauss ◽  
William L. Bourcier ◽  
Kevin D. McKeegan ◽  
Celia I. Merzbacher ◽  
Son N. Nguyen ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Rate Constant ◽  
Rate Constants ◽  
Dissolution Kinetics ◽  
State Theory ◽  
Alkaline Solutions ◽  
Glass Dissolution ◽  
Constant Ph ◽  
Transport Control ◽  
Dissolution Rate Constants

ABSTRACTWe have measured the dissolution rate of a simple five-component borosilicate glass (Na2O, CaO, Al2O3, B2O3, SiO2) using a flow-through system. The experiments were designed to measure the dissolution rate constant over the interval pH 1 through pH 13 at 3 temperatures (25°, 50° and 70°C). Dilute buffers were used to maintain a constant pH. Analyses of solutions and solid surfaces provided information that is used to develop a kinetic model for glass dissolution.Under all conditions we eventually observed linear dissolution kinetics. In strongly acidic solutions (pH 1 to pH 3) all components but Si were released in their stoichiometric proportions and a thick, Si-rich gel was formed. In mildly acidic to neutral solutions the gel was thinner and was both Si- and Al-rich, while the other components were released to solution in stoichiometric proportions. In mildly to strongly alkaline solutions all components were released to solution in stoichiometric proportions. By varying the flow rate at each pH we demonstrated a lack of transport control of the dissolution rate.The dissolution rates were found to be lowest at near-neutral pH and to increase at both low and high pH. A rate equation based on transition-state theory (TST) was used to calculate dissolution rate constants and reaction order with respect to pH over two pH intervals at each temperature. At 250C between pH 1 and pH 7 based on the Si release rate the log rate constant for glass dissolution (g glass/m20d) was −0.77 and the order with respect to pH was −0.48. Between pH 7 and pH 13 the log rate constant for glass dissolution was −8.1 and the order with respect to pH was +0.51. The measured simple glass dissolution rate constants compare very well with constants estimated by fitting the same TST equation to experimental results obtained for SRL-165 glass and to dissolution rate estimates made for synthetic basaltic glasses.

Magnesium fertiliser dissolution rates in pumice soils under Pinus radiata

Soil Research ◽  
2000 ◽  
Vol 38 (3) ◽  
pp. 753 ◽  
Author(s):  
A. D. Mitchell ◽  
P. Loganathan ◽  
T. W. Payn ◽  
R. W. Tillman
Keyword(s):  
Particle Size ◽  
Dissolution Rate ◽  
Pinus Radiata ◽  
Rate Constants ◽  
Elemental Sulfur ◽  
Sulfur Oxidation ◽  
Rate Of Dissolution ◽  
Cubic Model ◽  
Dissolution Rate Constants ◽  
Elemental Sulfur Oxidation

Application of Mg fertilisers has been suggested as a means of reducing the incidence of Mg deficiency of forest trees in New Zealand and Europe. The objective of this study was to determine the rates of dissolution of a range of Mg fertilisers applied to a pumice soil (Typic Udivitrand). The rate of fertiliser dissolution was little influenced by whether the fertiliser was applied directly on to the soil surface (litter removed) or on to the litter layer in a Pinus radiata plantation. Twenty-seven months since fertiliser application the mean (with and without litter) percentage of Mg dissolved was in the sequence: Epsom salts > calcined magnesite 1–2 mm > granmag (a partially acidulated and granulated calmag product) > calcined magnesite 2–4 mm > forestry grade dolomite. The specific dissolution rate constants (mg/cm2 .day of fertiliser) for the slowly soluble Mg fertilisers calculated using an elemental sulfur oxidation cubic model were 587 for calcined magnesite 1–2 mm, 426 for calcined magnesite 2–4 mm, 385 for granmag, and 18 for forestry grade dolomite. In a laboratory incubation study the elemental sulfur oxidation cubic model described the rate of dissolution of Mg fertilisers within narrow fertiliser particle size ranges. The specific fertiliser dissolution rate constants, however, increased with decreases in particle size, suggesting that the rate of dissolution depends on factors other than surface area when particle sizes varied widely. Slowly soluble, alkaline Mg fertilisers had a significant liming effect on the soil. They were more effective in increasing soil exchangeable Mg than soluble Mg salts over a long-period and therefore, they are better fertilisers for P. radiata.

Cationic Corrosion Inhibitors for Alkaliborosilicate Glass

1991 ◽  
Vol 257 ◽  
Author(s):  
H.U. Zwicky ◽  
TH. Graber ◽  
R. Grauer ◽  
R. Restani
Keyword(s):  
Dissolution Rate ◽  
Corrosion Inhibitors ◽  
Pure Water ◽  
Reaction Rates ◽  
Alkaline Solutions ◽  
Lead Silicate ◽  
Borosilicate Glasses ◽  
Glass Dissolution ◽  
Inhibiting Effect ◽  
Solid Phases

ABSTRACTThe dissolution behaviour of two alkali borosilicate glasses has been investigated at 90°C in the presence of potential corrosion inhibitors. The added materials were selected on the basis of surface chemistry considerations: Since the dissolution rate of silicate solid phases in alkaline solutions increases with growing negative surface charge, it should be expected that sorbing cations reduce the reaction rates. Due to the formation of insoluble hydroxides and silicates and to the dominance of neutral or negatively charged hydroxo complexes in the pH range of interest, the selection of potential inhibitors is very restricted.The precipitated hydroxides of Al, Zn, Cd and Pb were chosen as the solid phases. Compared with the experiments in pure water, glass dissolution is enhanced in presence of Al(OH)3 and Zn(OH)2. The concentration of the aqua ions is too low for an inhibiting effect. Sorption of silicic acid on the hydroxide accelerates the glass dissolution. Addition of PbO had a strong inhibiting effect in a 28 days experiment. At longer times an insoluble lead silicate is formed and thereby the glass dissolution rate is increased. Cd on the other hand is still effective as an inhibitor after 365 days.Based on the present results, the possibility of using glass corrosion inhibitors in a repository is considered not to be worthwhile.

Correlation between porosity and dissolution rate constants for disintegrating tablets

1980 ◽  
Vol 69 (5) ◽  
pp. 607-608 ◽  
Author(s):  
Odile Cruaud ◽  
Dominique Duchěne ◽  
Francis Puisieux ◽  
J.T. Carstensen
Keyword(s):  
Dissolution Rate ◽  
Rate Constants ◽  
Dissolution Rate Constants

The Dissolution Mechanism of Copper Weld Brazing with Cu-Based Brazing Alloys

2011 ◽  
Vol 697-698 ◽  
pp. 394-398 ◽  
Author(s):  
Yi Nan Li ◽  
Z.L. Peng ◽  
J.C. Yan
Keyword(s):  
Dissolution Rate ◽  
Rate Constants ◽  
Binary Alloys ◽  
Dissolution Mechanism ◽  
Liquid Alloys ◽  
Different Temperatures ◽  
Cu Foil ◽  
Filler Metals ◽  
Dissolution Rate Constants

In this paper, the dissolution mechanism of copper weld brazing has been researched. The thickness losses of Cu foil in contact with molten Cu-P and Cu-Ag binary alloys at different temperatures have been studied. And the dissolution rate constants in both alloys is calculated and exists following relation: kCu-P(T)=10kCu-Ag(T), which explains the special phenomenon that the dissolving amount of copper in Cu-P liquid alloys is larger than that in Cu-Ag liquid alloys by using weld brazing technology. The dissolution rate of copper in filler metals is the main reason to realize weld brazing. It can be concluded that element P is indispensable in filler metals as the function of accelerating dissolution during weld brazing.

Modelling Glass Dissolution with a Monte Carlo Technique

1995 ◽  
Vol 412 ◽  
Author(s):  
Marc Aertsens ◽  
Pierre Van Iseghem
Keyword(s):  
Monte Carlo ◽  
Dissolution Rate ◽  
Transition State Theory ◽  
Threshold Value ◽  
Simulation Method ◽  
State Theory ◽  
Monte Carlo Simulation Method ◽  
Surface Layers ◽  
Network Modifier ◽  
Glass Dissolution

AbstractWe present a Monte Carlo simulation method for modelling glass dissolution in aqueous solutions. This simulation method is consistent with transition state theory, and therefore also with the glass dissolution rate law, used for instance in the Grambow model. The simulation method allows to add dynamics (kinetics) to the existing thermodynamic models for glass dissolution. Using this method, it is possible to model non stoichiometric dissolution of the glass.Besides, we introduce a simple, first version of a model in which we use the simulation method. In this model, we approximate the glass by a lattice. We assume that the glass contains two components: a network former and a network modifier. Bonds between two network formers are assumed to be much stronger than any other bond in the system. We observe that above a threshold value for the concentration of network modifiers, the glass dissolves fast. No surface layer develops and the dissolution rate is constant (linear stoichiometric dissolution). Below this threshold, the glass is more durable and surface layers are formed. As time goes on, the thickness of the surface layers grows. The dissolution of the glass is not stoichiometric. This behaviour agrees with experimental results.

Ethylcellulose, polycaprolactone, and eudragit matrices for controlled release of piroxicam from tablets and microspheres

2012 ◽  
Vol 66 (8) ◽  
Author(s):  
Kheira Diaf ◽  
Zineb Bahri ◽  
Nafa Chafi ◽  
Lahcen Belarbi ◽  
Abderrezzak Mesli
Keyword(s):  
Controlled Release ◽  
Drug Release ◽  
Ftir Spectroscopy ◽  
Dissolution Rate ◽  
Rate Constants ◽  
Active Agent ◽  
The Matrix ◽  
Release Study ◽  
Release Model ◽  
Dissolution Rate Constants

AbstractThe present paper provides details of the preparation of polymeric tablets and microspheres based on piroxicam as a therapeutic active agent and the drug release study from these formulations. Tablets composed of ethylcellulose, Eudragit® or mixtures of Eudragit® and synthesised poly(oxepan-2-one) were prepared and tested. The effect of the matrix on the drug release at 37°C was studied. The drug-loaded microparticles were prepared using solvent evaporation microencapsulation. These systems were characterised by SEM and FTIR spectroscopy and the size and size distribution were also determined. The results demonstrated that the drug release could be modified by means of these formulations. Finally, piroxicam dissolution rate constants were calculated from Higuchi’s release model.

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