A model is proposed to describe the kinetics of solute segregation to partial dislocations in solid solutions of cold-rolled
alloys. The case when half edge and half screw dislocations are present is considered. The model gives account of the kinetic
behaviour observed in a deformed Cu-19 at% Al alloy where two unknown processes could be assessed during calorimetric isothermal
experiments. The faster process corresponds to segregation to screw dissociated dislocations while the slower one corresponds
to segregation to edge dissociated dislocations. Experimental activation energies, larger for edge dislocations, are close
to that for pipe diffusion along the partials corrected by pinner binding energy terms. It is also predicted that segregation
occurs faster as the dislocation density is increased. A quantitative comparison of experimental results with model predictions
Authors:S. Li, L. Liu, H. Jiang, D. Liu, S. Chen and Z. Yang
The crystal C81H78N12O6Cd3 was synthesized and its structure was determined by single crystal X-ray diffraction method. The complex crystallizes in
the monoclinic system space group P21/n with cell parameters, a=15.959(4) , b=26.222(3) , c=25.907(6) , β=101.60(2). The non-isothermal kinetics of the crystal
was studied by use of non-isothermal TG and DTG curves. The kinetic parameters were analyzed by means of integral and differential
methods, and mechanism functions of the thermal decomposition reaction for its second step were proposed. The kinetic equation
of thermal decomposition is expressed as:
dα/dt=Aexp(-E/RT)1.5(1-α)4/3[1/(1-α)1/3-1]−1. The average values of E(kJ mol−1) and lnA/s−1 are 339.25, 43.95, respectively.
Thermogravimetric data were used to calculate the kinetics of isothermal degradation of layered tetratitanate intercalated
with n-alkyldiamines H2N(CH2)nNH2 (n=2, 3, 4, 6 or 8). The hydrous matrix showed two mass loss steps from the thermogravimetric curve, corresponding to the release
of physisorbed and lattice water molecules. For the intercalated matrices a third mass loss was observed due to the release
of organic moiety. From these values, the amine intercalated matrices can be ordered in the following sequence of thermal
stability; C4>C2>C3≅C6>C8. Kinetic studies were carried out to the release of lattice water molecules. The kinetic model that
best adjusted the experimental isothermal TG data was the diffusion mechanism controlling process.
Effects of sample mass on the kinetics of isothermal dehydration of crushed crystals of Li2SO4·H2O were investigated using conventional TG. The process was characterized by a combination of Avrami-Erofeyev and contracting
geometry models. Distribution of the fractional reaction, α, in particles within the sample assembly as well as the change
in the rate of gross diffusion of the evolved water vapour appear responsible for the sample-mass-dependent kinetic parameters
obtained for the system.
The chlorination kinetics of alkali-added (K and Li) tungsten trioxide were studied by thermogravimetry, using gaseous CCl4 as chlorinating agent. The reactivity of the modified samples was compared to the results on the chlorination of pure WO3. Similar apparent activation energies were found for the pure and alkali-added samples. However, potassium additive resulted in a strong decrease of the initial reaction rate, while surface lithium has no influence on it.
It is argued that, for the macroscopic parameters of conventional kinetic models to become meaningful, they may be and must
be expressed in terms of elementary single-barrier processes. To accomplish this means to associate some (external) extensional
measure with a single-barrier elementary act, remaining within the logic of the existing geometrical-probabilistic scheme.
A manner of doing this involving the use of Dirichlet fragmentations is suggested.
Authors:N. Binke, L. Rong, Y. Zhengquan, W. Yuan, Y. Pu, Hu Rongzu and Y. Qingsen
The kinetics of the first order autocatalytic decomposition reaction of highly nitrated nitrocellulose (HNNC, 14.14%N) was studied by using thermogravimetry (TG). The results show that the TG curve for the initial 50% of mass-loss of HNNC can be described by the first order autocatalytic equation
The precipitation process for a concentration of CoTi of super-saturated solutions of Cu-0.50 at.% Co-0.45 at.% Ti (Cu-1 at.%
CoTi) was studied through differential scanning calorimetry (DSC) and microhardness measurements. The analysis of the calorimetric
curves between the environmental temperature and 900 K shows the presence of only one exothermic reaction attributed to the
formation of CoTi particles in the matrix of copper. The energy of activation estimated by using the modified Kissinger method
came out much lower than the corresponding to the diffusion of the cobalt and titanium in copper. We may attribute this fact
to the strong contribution of the vacancies introduced by quenching.
We used the formalism of Johnson-Mehl-Avrami (JMA) to assess the kinetic parameters. The energetic and kinetic evaluations
and the molar heats of precipitation obtained from the isochor of van’t Hoff allow us to infer that the reaction corresponds
to the formation of CoTi precipitates. The isothermal kinetics of precipitation reaction could be represented satisfactory
by an overall kinetic function based in a macroscopic parameter (Vickers hardness). The kinetic parameters obtained from microhardness
model are in agreements with those obtained from DSC traces.
The kinetics of the thermal decomposition of Cu- and Co-itaconato complexes were studied using dynamic thermogravimetric techniques.
The dehydration process was found to proceed in a one-stage reaction, while the thermal decomposition of the anhydrous salts
was followed a two-stage reaction. The first stage is the decomposition of the complex to metal carbonate, whereas the second
stage is the decomposition of the formed carbonate to the oxide. Kinetic analysis of the dynamic TG curves were discussed
with reference to a composite integral method on comparison with the integral methods of Coats and Redfern and Ozawa. The
activation parameters were calculated and discussed for each decomposition step.
In 1925 a paper on kinetic analysis of data obtained with thermobalances for isothermal mass loss of some natural products
for electrical insulation was published. This is the first theoretical and experimental approach to accelerated test of electrical
insulating materials and also to kinetic analysis of thermal analysis data at isoconversional points. In succeeeding papers,
change in chemical composition and kinetics under temperature change were dealt with. A historical review of these two topics
is described in this review article, especially on the basic concept commonly induced for these two fields.