Primary products and processes in the γ-radiolysis of 2-methyltetrahydrofuran

1965 ◽  
Vol 285 (1402) ◽  
pp. 319-338 ◽  
Keyword(s):  
Glassy Phase ◽  
Kcal Mole ◽  
Radical Species ◽  
Molecule Reaction ◽  
Positive Ions ◽  
Primary Products ◽  
Diffusion Controlled ◽  
Thermal Bleaching ◽  
The Matrix ◽  
Kinetics Of

From a study of the u. v., visible, near i. r. and e. s. r. spectra induced by γ -irradiation at 77°K in glassy MTHF and in glassy MTHF containing various additives and from a study of controlled temperature increases on these spectra, the following conclusions are drawn. (1) The primary products of the radiolysis are electrons ( e - ) and positive ions ( MTHF + ) which undergo a rapid ion-molecule reaction to give O CH 3 radicals ( R ⋅). (2) e - can either be trapped in the glassy MTHF matrix or can be captured by either napththalene, ferric chloride, carbon tetrachloride, nitrous oxide or trans -stilbene if these substances are present. (3) The e - T are bleachable by light or heat and disappear independently of the radicals R⋅ without either augmentation of R⋅ or the production of any new radical species. (4) e - T and R⋅ disappear thermally and independently by second-order reactions, the rate constants being K e - + e - (M -1 S -1 ) = 10 12⋅4±1⋅1 exp ─ [0⋅85 ± 0⋅10 kcal/mole/ R ( T ─ 75)] and K R˙ + R˙ (M -1 S -1 ) = 10 13⋅3±1⋅4 exp ─ [1⋅20 ± 0⋅15 kcal/mole/ R ( T ─ 75)]. These rate expressions suggest that both reactions are diffusion controlled at low temperatures in the glassy phase. (5) The kinetics of the thermal bleaching of e - T indicate that the electrons migrate distances of about 150 Å from their parent positive ions before being trapped in the matrix. (6) The effect of FeCl 3 in reducing the formation of e - T at 77°K and its lack of effect on the thermal bleaching of e - T suggests that the reaction e - + FeCl 3 → FeCl 2 + Cl - only occurs before the electron is thermalized.

Effect of Excess PbO on the Kinetics of the Growth of PMNT Polycrystals by Templated Grain Growth Method

2005 ◽  
Vol 475-479 ◽  
pp. 1137-1140
Author(s):  
Lili Zhao ◽  
Feng Gao ◽  
Wei Min Wang ◽  
Chang Sheng Tian
Keyword(s):  
Grain Growth ◽  
Templated Grain Growth ◽  
Experimental Conditions ◽  
Precipitation Mechanism ◽  
Oriented Structure ◽  
Diffusion Controlled ◽  
The Matrix ◽  
Growth Method ◽  
Final Composition ◽  
Kinetics Of

The oriented 0.67Pb (Mg1/3Nb2/3)O3-0.33PbTiO3 (PMNT) polycrystals were prepared by the conventional ceramic technique and the templated grain growth method adding excess PbO in the matrix. Kinetics of the development of oriented structure was investigated systemically. In the presence of PbO liquid phase, the oriented PMNT polycrystals mainly grow by the dissolution-precipitation mechanism. The diffusion is determined by the sintering temperature and the PbO-excess content in the matrix. The thickness of oriented PMNT polycrystals displays a t1/3 dependence, which is characteristic of diffusion-controlled growth. For the thicker oriented structure, 20% excess PbO in the PMNT matrix and 1150oC for 10h are the proper experimental conditions. Moreover, the addition of PbO in the matrix hardly affects the final composition of ceramic matrix.

Improving the Diffusion Controlled Cementation of Cadmium Ions Using Reciprocating Fixed Bed of Zinc Rings

2011 ◽  
Vol 312-315 ◽  
pp. 694-699 ◽  
Author(s):  
A.H. El-Shazly ◽  
Ashraf A. Mubarak ◽  
Hesham S. Bamufleh
Keyword(s):  
Arrhenius Equation ◽  
Fixed Bed ◽  
Effect Of Temperature ◽  
Vibration Velocity ◽  
Kcal Mole ◽  
Cadmium Ions ◽  
Bed Height ◽  
Diffusion Controlled ◽  
Ring Diameter ◽  
Kinetics Of

The aim of the present work is to investigate the effect of pulsation on improving the rate of the diffusion controlled cementation of cadmium ions using reciprocating fixed bed of zinc rings. The kinetics of the cementation reaction was investigated under different conditions of initial concentration of cadmium ions, frequency and amplitude of oscillation (vibration velocity), zinc ring diameter, bed diameter, bed height and temperature. The effect of temperature was found to fit the Arrhenius equation with an activation energy of 7.58 kcal/mole which confirms the diffusion controlled nature of the reaction. A dimensionless correlation in the form of Sh = 6.9 Re0.45 Sc0.33 (Bd/Bh)0.89 was deduced. The industrial application of the obtained results was discussed.

Pore growth kinetics in heat-treated glass-like carbons

1986 ◽  
Vol 1 (6) ◽  
pp. 832-835 ◽  
Author(s):  
Jalil Lachter ◽  
Leo G. Henry ◽  
Robert H. Bragg ◽  
Stephen Spooner
Keyword(s):  
Growth Kinetics ◽  
Matrix Material ◽  
Radius Of Gyration ◽  
Void Size ◽  
Kcal Mole ◽  
X Ray ◽  
X Ray Scattering ◽  
Heat Treated ◽  
The Matrix ◽  
Kinetics Of

The kinetics of changes in void size during annealing of glass-like carbons in the temperature range 1000°−2800 °C for times up to 150 h were studied using small-angle x-ray scattering determinations of the radius of gyration Rg. The results show that Rg ranged from 9 Å at 1000°C to about 24 Å at 2800 °C. A pore coarsening analysis and a superimposition kinetic analysis applied to Rg gave activation energies of 76 ± 4 kcal/mole and 74 ± 9 kcal/mole, respectively, which are associated with migration of vacancies within graphitic layers in the matrix material.

The Reaction Kinetics of Liquid 60/40 Sn/Pb Solder With Copper and Nickel: A High Temperature X-Ray Diffraction Study

1984 ◽  
Vol 40 ◽  
Author(s):  
Patrick W. Dehaven
Keyword(s):  
High Temperature ◽  
Reaction Kinetics ◽  
X Ray Diffraction ◽  
Kcal Mole ◽  
Nickel Metal ◽  
X Ray ◽  
Diffusion Controlled ◽  
Solder Reaction ◽  
Kinetics Of

AbstractWith proper sample preparation, high temperature x-ray diffraction can be used to study in-situ the reactions occurring at a solder/metal interface. We have applied this technique to an investigation of the reaction kinetics between copper and nickel metal and 60/40 Sn/Pb solder. The copper and nickel are shown to follow similar pathways, each having a complex reaction profile that involves an initial “hold” of little reactivity, followed by a two-step diffusion controlled reaction. Activation energies were obtained from Arrhenius-type plots, and result in values of 6.8 kcal/mole for the nickel/solder reaction, and 13 kcal/mole for the copper/solder reaction. These results are compared with those obtained by previous investigators, and discussed in terms of the growth of the different intermetallic phases.

scholarly journals On a numerical model for diffusion-controlled growth and dissolution of spherical precipitates

1998 ◽  
Vol 4 (2) ◽  
pp. 115-133 ◽  
Author(s):  
R. Van Keer ◽  
J. Kacur
Keyword(s):  
Numerical Model ◽  
Fick’S Law ◽  
Fick's Law ◽  
Diffusion Limited ◽  
Diffusion Controlled ◽  
The Matrix ◽  
Space Discretization ◽  
Element Technique ◽  
Domain Transformation ◽  
Kinetics Of

This paper deals with a numerical model for the kinetics of some diffusion-limited phase transformations. For the growth and dissolution processes in 3D we consider a single spherical precipitate at a constant and uniform concentration, centered in afinitespherical cell of a matrix, at the boundary of which there is no mass transfer, see also Asthana and Pabi [1] and Caers [2].The governing equations are the diffusion equation (2nd Fick's law) for the concentration of dissolved element in the matrix, with a known value at the precipitate-matrix interface, and the flux balans (1st Fick's law) at this interface. The numerical method, outlined for this free boundary value problem (FBP), is based upon a fixed domain transformation and a suitably adapted nonconforming finite element technique for the space discretization. The algorithm can be implemented on a PC. By numerous experiments the method is shown to give accurate numerical results.

High-resolution observations of metastable γ’ precipitation in Al-15at.%Ag

1996 ◽  
Vol 54 ◽  
pp. 1004-1005
Author(s):  
N. V. Larcher ◽  
I. G. Solorzano
Keyword(s):  
Discontinuous Precipitation ◽  
Equilibrium Phase ◽  
Quantitative Description ◽  
Present Contribution ◽  
Α Phase ◽  
The Matrix ◽  
Aging Sequence ◽  
Matrix Precipitation ◽  
Considerable Detail ◽  
Kinetics Of

It is currently well established that, for an Al-Ag alloy quenched from the α phase and aged within the metastable solvus, the aging sequence is: supersaturated α → GP zones → γ’ → γ (Ag2Al). While GP zones and plate-shaped γ’ are metastable phases, continuously distributed in the matrix, formation of the equilibrium phase γ takes place at grain boundaries by discontinuous precipitation (DP). The crystal structure of both γ’ and γ is hep with the following orientation relationship with respect to the fee α matrix: {0001}γ′,γ // {111}α, <1120>γ′,γ, // <110>α.The mechanisms and kinetics of continuous matrix precipitation (CMP) in dilute Al-Ag alloys have been studied in considerable detail. The quantitative description of DP kinetics, however, has received less attention. The present contribution reports the microstructural evolution resulting from aging an Al-Ag alloy with Ag content higher than those previously reported in the literature, focusing the observations of γ' plate-shaped metastable precipitates.

Influence of Formulation Variables and Processing Techniques on Drug Release from Carbopol-971 based Matrix Tablets of Cinnarizine and Nimodipine.

2010 ◽  
Vol 2 (1) ◽  
Author(s):  
Singh K. ◽  
Pandit K. ◽  
Mishra N.
Keyword(s):  
Drug Release ◽  
Release Rate ◽  
Polymer Concentration ◽  
Matrix Tablets ◽  
Wet Granulation ◽  
Weight Variation ◽  
Diffusion Controlled ◽  
The Matrix ◽  
Processing Techniques ◽  
Formulation Variables

The matrix tablets of cinnarizine and nimodipine were prepared with varying ratio of Carbopol- 971P and co-excipients of varying hydrophilicity (i.e. dicalcium phosphate and spray dried lactose) by direct compression and wet granulation using alcoholic mucilage. The prepared tablets were evaluated for weight variation, hardness and friability. The influence of concentration of the matrix forming material and co-excipients on the release rate of the drug was studied. The release rate of Cinnarizine (more soluble drug) from tablets followed diffusion controlled mechanism whereas for nimodipine (less soluble drug), the drug release followed case-II or super case- II transport mechanism based on Korsmeyer- Peppas equation. The results indicated that the drug release from matrix tablets was increases with increase in hydrophilicity of drug and co-excipients. The release of drug also increased with thermal treatment and decreasing polymer concentration.

Kinetics of the Thermal Disappearance of Radicals Formed During the Radiolysis of Aspartic Acid

2009 ◽  
Vol 59 (12) ◽  
Author(s):  
Mihai Contineanu ◽  
iulia Contineanu ◽  
Ana Neacsu ◽  
Stefan Perisanu
Keyword(s):  
Thermal Resistance ◽  
Aspartic Acid ◽  
Room Temperature ◽  
Esr Spectra ◽  
Complex Mechanism ◽  
Radical Species ◽  
Mechanisms Of Formation ◽  
Kinetics Of

The radiolysis of the isomers L-, D- and DL- of the aspartic acid, in solid polycrystalline state, was investigated at room temperature. The analysis of their ESR spectra indicated the formation of at least two radicalic entities. The radical, identified as R3, resulting from the deamination of the acid, exhibits the highest concentration and thermal resistance. Possible mechanisms of formation of three radical species are suggested, based also on literature data. The kinetics of the disappearance of radical R3 indicated a complex mechanism. Three possible variants were suggested for this mechanism.

scholarly journals Synthesis and Polymerization Kinetics of Rigid Tricyanate Ester

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1686
Author(s):  
Andrey Galukhin ◽  
Roman Nosov ◽  
Ilya Nikolaev ◽  
Elena Melnikova ◽  
Daut Islamov ◽  
...  
Keyword(s):  
Kinetic Analysis ◽  
Single Step ◽  
Polymerization Kinetics ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
Diffusion Controlled ◽  
Polymerization Product ◽  
The One ◽  
Kinetics Of

A new rigid tricyanate ester consisting of seven conjugated aromatic units is synthesized, and its structure is confirmed by X-ray analysis. This ester undergoes thermally stimulated polymerization in a liquid state. Conventional and temperature-modulated differential scanning calorimetry techniques are employed to study the polymerization kinetics. A transition of polymerization from a kinetic- to a diffusion-controlled regime is detected. Kinetic analysis is performed by combining isoconversional and model-based computations. It demonstrates that polymerization in the kinetically controlled regime of the present monomer can be described as a quasi-single-step, auto-catalytic, process. The diffusion contribution is parameterized by the Fournier model. Kinetic analysis is complemented by characterization of thermal properties of the corresponding polymerization product by means of thermogravimetric and thermomechanical analyses. Overall, the obtained experimental results are consistent with our hypothesis about the relation between the rigidity and functionality of the cyanate ester monomer, on the one hand, and its reactivity and glass transition temperature of the corresponding polymer, on the other hand.

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