Precipitation and dissolution rate constants for cristobalite from 150 to 300°C

1995 ◽  
Vol 59 (1) ◽  
pp. 77-85 ◽  
Author(s):  
P.J.N. Renders ◽  
C.H. Gammons ◽  
H.L. Barnes
Keyword(s):  
Dissolution Rate ◽  
Rate Constants ◽  
Dissolution Rate Constants

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.

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.

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.

Time of persistence of a particle in selected state during reversible first-order conversion. Application to crystal growth and dissolution

1981 ◽  
Vol 46 (5) ◽  
pp. 1217-1221 ◽  
Author(s):  
Milan Šolc ◽  
Jiří Hostomský
Keyword(s):  
Diffusion Coefficient ◽  
Crystal Growth ◽  
Rate Constants ◽  
Probability Model ◽  
Planck Equation ◽  
One Dimensional ◽  
First Order ◽  
Approximate Form ◽  
Probability Description ◽  
Dissolution Rate Constants

The distribution of the total time of persistence of a particle in a state A was derived both in an exact and an approximate form on the basis of a probability model of the conversion A ##e B. The result was applied to the probability description of a change in size of one-dimensional crystals in a double crystallizer. The time change of the distribution of the crystal sizes can be described by the Fokker-Planck equation for diffusion with a diffusion coefficient proportional to the square of the sum of values of the growth and dissolution rate constants.

scholarly journals A multiparametric study on the dissolution of synthetic brannerite

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Hantao Lin ◽  
Stéphanie Szenknect ◽  
Adel Mesbah ◽  
Fabien Baron ◽  
Daniel Beaufort ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Amorphous State ◽  
Secondary Phase ◽  
Acid Solutions ◽  
Wet Chemistry ◽  
Dissolution Reaction ◽  
Proton Activity ◽  
Sulfuric Acid Solutions ◽  
Rate Controlling Step ◽  
Dissolution Rate Constants

AbstractBrannerite, UTi2O6 is reported to occur in various uraniferous deposits worldwide. Natural brannerite specimens are found in the amorphous state and are usually considered to be refractory to dissolution due to the formation of TiO2 passivation layer. In the present work, brannerite was synthesized by wet chemistry route, then characterized prior the development of multiparametric dissolution experiments. The evolution of U and Ti concentrations was followed in 0.1–2 mol/L H2SO4 solutions, for temperatures ranging from 25 to 80 °C, in the presence (or not) of 2.8 g/L of dissolved Fe(III). The dissolution of synthetic brannerite was congruent in the whole experimental domain. The formation of Ti-enriched secondary phase at the surface of the brannerite grains was not evidenced. The dissolution rate constants, activation energies and partial orders of the overall dissolution reaction relative to proton activity were determined in the presence (or absence) of Fe(III). The introduction of Fe(III) in sulfuric acid solutions increased the dissolution rate constant by 5 orders of magnitude and induced significant modifications of the apparent activation energy (from 71 ± 4 to 91 ± 6 kJ/mol) and of the partial order relative to proton activity (from 0.42 ± 0.09 to 0.84 ± 0.08). This study suggested that the uncongruency of the brannerite dissolution and the changes usually observed in the rate-controlling step with temperature could be linked to the loss of the crystal structure in natural samples.

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