Thermal-Induced Transformation of Retained Austenite in the Simulated Case of a Carburized Steel

1993 ◽  
Vol 115 (1) ◽  
pp. 83-88
Author(s):  
R. W. Neu ◽  
Huseyin Sehitoglu
Keyword(s):  
Retained Austenite ◽  
Hydrostatic Stress ◽  
Volume Increase ◽  
Second Stage ◽  
Carburized Steel ◽  
Diffusion Controlled ◽  
Type Relation ◽  
Simulated Case ◽  
Kinetics Of ◽  
Diffusion Controlled Reaction

Systematic experiments were conducted on carburized 4320 steel to study thermalinduced transformation of austenite to bainite by measuring the volumetric transformation strains. Up to about 210°C, thermal-induced transformation involved a diffusion-controlled reaction and therefore was time dependent. The mechanism is similar to that described by the second stage of tempering. An Arhennius-type relation was used to model the kinetics of the reaction leading to a volume increase. A positive hydrostatic stress tended to increase the rate of transformation. The anisotropy of the transformation strains were proportional to the deviatoric stress.

Kinetic investigation of a complex curing of the guaiacol bio-based benzoxazine system

e-Polymers ◽  
2016 ◽  
Vol 16 (3) ◽  
pp. 199-206 ◽  
Author(s):  
Aleš Ručigaj ◽  
Špela Gradišar ◽  
Matjaž Krajnc
Keyword(s):  
Curing Kinetics ◽  
Second Stage ◽  
Diffusion Controlled ◽  
Polymerization Behavior ◽  
Overlapped Peaks ◽  
Friedman Method ◽  
Apparent Activation Energies ◽  
Stage 1 ◽  
Kinetics Of ◽  
And Diffusion

AbstractCuring kinetics of guaiacol based benzoxazine synthesized from guaiacol, furfurylamine and formaldehyde forming bio-based polybenzoxazine was investigated. The curing process showed complex polymerization behavior, as the exothermal signal consisted of several overlapped peaks. Differentiation and fitting of overlapped peaks was performed by Pearson VII distribution obtaining two separate exothermal signals further associated to stage 1 and stage 2. The apparent activation energies of both stages were determined to be 113.8 kJ mol-1 and 117.5 kJ mol-1, respectively, according to Kissinger. The first could be explained by benzoxazine ring-opening and electrophilic substitution, whereas the second stage corresponds to the rearrangement and diffusion-controlled step. Kinetics of each stage was studied separately. As a result, the first stage was described by Šesták-Berggren autocatalytic model, whereas the second stage appeared to follow nth order kinetics proved by the Friedman method. Application of both kinetic models demonstrated that the predicted curves fit well with the non-isothermal DSC thermograms and as such sufficiently describes the complex curing behavior of guaiacol based benzoxazine.

Kinetics of Hill-Hermans diffusion of an unstable reagent

1955 ◽  
Vol 228 (1174) ◽  
pp. 397-410
Keyword(s):  
Continuous Method ◽  
Polymer Chemistry ◽  
Reactive Site ◽  
Transient Effect ◽  
Rubber Latex ◽  
Rate Law ◽  
First Order ◽  
Diffusion Controlled ◽  
Kinetics Of ◽  
Diffusion Controlled Reaction

This work deals with a generalization of the widely applicable theory of Hill's, later developed by Hermans. It concerns the diffusion-controlled reaction of a reagent with a polymer across an interface, in the course of which the reagent is captured by an infinitely reactive site ('sink') inside the polymer. For certain applications, it becomes necessary to introduce an alternative fate which the reagent may suffer during diffusion to the sink, namely, deactivation or decomposition. The present kinetic theory of this effect is based on the method of considering the elementary jumps responsible for diffusion, while Hill and Hermans used the complementary, continuous method based on Fick's law. The present derivation of a general rate law for the conversion of the polymer is based on a pseudo lattice model. The rate law takes the form of an infinite spectrum of first-order decay terms, and is little dependent on details of the model used or on curvature of the interface. It does depend critically on a stability constant s of the reagent, which is unity for a perfectly stable and zero for a completely unstable one. In the former case the rate law reduces substantially to that of Hill and Hermans, but covers the initial transient effect as well as the steady state. As s →0, the rate law converges uniformly to that of a first-order chemisorption of a monolayer over the appropriate range. Intermediate cases (0 < s < 1) are of interest in the chemistry of rubber latex, and probably in other fields of polymer chemistry.

Simultaneous diffusion and chemical activation control of the kinetics of the binding of carbon monoxide to ferroprotoporphyrin IX in glycerol–water mixtures of high viscosity

1977 ◽  
Vol 55 (23) ◽  
pp. 3955-3960 ◽  
Author(s):  
Brian B. Hasinoff
Keyword(s):  
Diffusion Rate ◽  
Chemical Activation ◽  
High Viscosity ◽  
Diffusion Control ◽  
Glycerol Water ◽  
Diffusion Controlled ◽  
Kinetics Of ◽  
And Diffusion ◽  
Simultaneous Influence ◽  
Diffusion Controlled Reaction

The kinetics of the reaction of ferroprotoporphyrin IX with CO have been studied in mixed glycerol–water solvents of high viscosity in order that the simultaneous influence of chemical activation and diffusion control of the reaction might be observed. Analyses of curved Arrhenius plots indicated that in the low temperature high viscosity limits the reaction is largely diffusion controlled. The deviation of the second order diffusion rate constants, from that predicted by simple theory for reaction between uniformly reactive spheres of equal radii, is a factor of 0.3 to 0.9, depending upon the solvent composition. A couple of other models for diffusion controlled reaction, ascribing these deviations to changes of steric requirements, were also examined.

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