Articoli di riviste: "Kinetic of transformation"

1

Perrillat, J. P. "Kinetics of high-pressure mineral phase transformations using in situ time-resolved X-ray diffraction in the Paris-Edinburgh cell: a practical guide for data acquisition and treatment". Mineralogical Magazine 72, n. 2 (aprile 2008): 683–95. http://dx.doi.org/10.1180/minmag.2008.072.2.683.

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AbstractSynchrotron X-ray diffraction (XRD) is a powerful technique to study in situ and in real-time the structural and kinetic processes of pressure-induced phase transformations. This paper presents the experimental set-up developed at beamline ID27 of the ESRF to perform time-resolved angle dispersive XRD in the Paris-Edinburgh cell. It provides a practical guide for the acquisition of isobaric-isothermal kinetic data and the construction of transformation-time plots. The interpretation of experimental data in terms of reaction mechanisms and transformation rates is supported by an overview of the kinetic theory of solid-solid transformations, with each step of data processing illustrated by experimental results of relevance to the geosciences. Reaction kinetics may be affected by several factors such as the sample microstructure, impurities or differential stress. Further high-pressure kinetic studies should investigate the influence of such processes, in order to acquire kinetic information more akin to natural or technological processes.

2

Tone, Taiga, e Nobuyoshi Koga. "Interplay between Thermally Induced Aragonite–Calcite Transformation and Multistep Dehydration in a Seawater Spiral Shell (Euplica scripta)". Processes 11, n. 6 (29 maggio 2023): 1650. http://dx.doi.org/10.3390/pr11061650.

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While heating a seawater spiral shell (Euplica scripta), thermally induced aragonite–calcite (A–C) transformation occurred within the temperature region of multistep thermal dehydration. Here, the kinetic interplay between the A–C transformation and thermal dehydration was studied as a possible cause of the reduction in the A–C transformation temperatures. The kinetics of the A–C transformation was systematically investigated under isothermal conditions by powder X-ray diffractometry and under linear nonisothermal conditions by Fourier transform infrared spectroscopy. The thermal dehydration was characterized as a partially overlapping, three-step process by thermogravimetry–differential thermal analysis coupled with mass spectroscopy for the evolved gases. The A–C transformation occurred in the temperature range of the final part of the second dehydration step and the initial part of the third dehydration step. The kinetics of A–C transformation and thermal dehydration were characterized by contracting geometry-type models, in which the respective transformations were regulated by a constant linear advancement rate and diffusional removal of water vapor, respectively. Based on the kinetic results, the mutual interaction of those thermally induced processes is discussed as a possible cause of the reduction in the A–C transformation temperature.

3

Atabekyan, L. S., A. K. Chibisov, T. A. Svyatoslavskaya, N. L. Svyatoslavskii e V. P. Markelov. "Single- and Double-Pulse Laser Kinetic Spectroscopy of Indoline Spiropyran". Химия высоких энергий 57, n. 5 (1 settembre 2023): 349–54. http://dx.doi.org/10.31857/s0023119323050017.

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Phototransformations of 6-nitro-8-methoxy-substituted indoline spiropyran in acetonitrile have been studied by laser kinetic spectroscopy (laser photolysis) with single- and double-pulse excitation. The role of the triplet state in the kinetics of photocoloration of spiropyran has been revealed. It has been shown that photochromic transformations of spiropyran involve unstable trans-isomers (conformers) of the open merocyanine form of spiropyran. Data on the transformation kinetics of the trans-isomers are presented.

4

Chai, Zhuo. "Catalytic Asymmetric Transformations of Racemic Aziridines". Synthesis 52, n. 12 (16 marzo 2020): 1738–50. http://dx.doi.org/10.1055/s-0039-1690857.

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The catalytic asymmetric ring-opening transformations of aziridines represent an important strategy for the construction of various chiral nitrogen-containing molecular architectures. This short review covers the progress achieved in the catalytic asymmetric transformation of racemic aziridines, focusing on the catalytic strategies employed for each different type of such aziridines.1 Introduction2 Reaction of Racemic 2-Vinylaziridines3 Reaction of Racemic 2-Alkylaziridines3.1 Regiodivergent Parallel Kinetic Resolution3.2 Kinetic Resolution4 Reaction of Racemic 2-(Hetero)arylaziridines4.1 Kinetic Resolution4.2 Enantioconvergent Transformation5 Reaction of Racemic Donor–Acceptor-Type Aziridines6 Conclusion and Outlook

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Carmona, José A., Carlos Rodríguez-Franco, Rosario Fernández, Valentín Hornillos e José M. Lassaletta. "Atroposelective transformation of axially chiral (hetero)biaryls. From desymmetrization to modern resolution strategies". Chemical Society Reviews 50, n. 5 (2021): 2968–83. http://dx.doi.org/10.1039/d0cs00870b.

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Atroposelective transformations of (hetero)biaryls are classified into desymmetrization, kinetic resolution, dynamic kinetic resolution, and dynamic kinetic asymmetric transformation depending on the nature and behavior of the starting material.

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Yousfi, Oussama, Yves J. M. Bréchet, Patricia Donnadieu, Florence Robaut, Federic Charlot, Andreas Kasper e Francis Serruys. "Phase Transformations in the NiS Nickel Sulphide: Microstructure, Mechanisms and Modelling through In Situ Microscopy." Solid State Phenomena 172-174 (giugno 2011): 402–7. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.402.

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Nickel sulphide (NiS) can form inclusions in tempered glass which lead to fracture due to a phase transformation with a volume change of about 4%. A heat treatment, aiming to provoke this phase transformation, is currently used in industry to reduce this effect. In order to propose more efficient treatments, a complete study going from identification of the transformation mechanisms to the modelling of the transformation was carried out. Depending on stoichiometry and temperature, two mechanisms for the transformation (partitioned or partitionless) have been evidenced by detailed microstructural and calorimetric studies leading to a fruitful parallel with the Fe-C phase transformations which provides the basis for further modelling of the kinetics. Anin situfollow up of the transformation by optical microscopy has given information (like nucleation rate and interface migration velocity) necessary to build the kinetic models. This modelling is based on Zener and Zener-Hillert kinetics models for interface velocity and described the transformation under isothermal treatment and anisothermal conditions.

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Wang, Jun, Chen Wei, Haoxue Yang, Tong Guo, Tingting Xu e Jinshan Li. "Phase Transformation Kinetics of a FCC Al0.25CoCrFeNi High-Entropy Alloy during Isochronal Heating". Metals 8, n. 12 (3 dicembre 2018): 1015. http://dx.doi.org/10.3390/met8121015.

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The phase transformation kinetics of a face-centered-cubic (FCC) Al0.25CoCrFeNi high-entropy alloy during isochronal heating is investigated by thermal dilation experiment. The phase transformed volume fraction is determined from the thermal expansion curve, and results show that the phase transition is controlled by diffusion controlled nucleation-growth mechanism. The kinetic parameters, activation energy and kinetic exponent are determined based on Kissinger–Akahira–Sunose (KAS) and Johnson–Mehl–Avrami (JMA) method, respectively. The activation energy and kinetic exponent determined are almost constant, indicating a stable and slow speed of phase transition in the FCC Al0.25CoCrFeNi high-entropy alloy. During the main transformation process, the kinetic exponent shows that the phase transition is diffusion controlled process without nucleation during the transformation.

8

Wang, Jun, Haoxue Yang, Tong Guo, Jiaxiang Wang, William Yi Wang e Jinshan Li. "Effect of Cold Rolling on the Phase Transformation Kinetics of an Al0.5CoCrFeNi High-Entropy Alloy". Entropy 20, n. 12 (30 novembre 2018): 917. http://dx.doi.org/10.3390/e20120917.

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The solid state phase transformation kinetics of as-cast and cold rolling deformed Al0.5CoCrFeNi high-entropy alloys have been investigated by the thermal expansion method. The phase transformed volume fractions are determined from the thermal expansion curve using the lever rule method, and the deformed sample exhibits a much higher transformation rate. Two kinetic parameters, activation energy (E) and kinetic exponent (n) are determined using Kissinger– Akahira–Sunose (KAS) and Johnson–Mehl–Avrami (JMA) method, respectively. Results show that a pre-deformed sample shows a much lower activation energy and higher kinetic exponent compared with the as-cast sample, which are interpreted based on the deformation induced defects that can promote the nucleation and growth process during phase transformation.

9

Kohout, Jan. "Simple and Precise Description of the Transformation Kinetics and Final Structure of Dual Phase Steels". Materials 14, n. 7 (4 aprile 2021): 1781. http://dx.doi.org/10.3390/ma14071781.

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The kinetics of diffusion-dependent phase transformations (including austenitisation of ferrite in dual steels or ferritic nodular cast irons) is very often described by the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. This description is not complete when the conversion is only partial due to insufficient overheating, as the equilibrium fraction of ferrite transformed into austenite cannot be determined directly from the JMAK equation. Experimental kinetic curves of partial austenitisation at various temperatures can be fitted using the JMAK equation, but the equilibrium fraction of the newly formed phase for each temperature has to be calculated as a regression parameter. In addition, the temperature dependence of the kinetic exponent in the JMAK equation is quite complicated and cannot be expressed by a simple general function. On the contrary, the equation of autoinhibition used for the description of austenitisation kinetics in present work directly gives the equilibrium fraction at partial conversion. It describes transformation kinetics at various temperatures independently of whether the conversion is complete or partial. Rate constants of the equation of autoinhibition depend on temperature according to the Arrhenius equation. In addition, the equation of autoinhibition has no weakness as the JMAK equation has, which consists in questionable temperature dependence of kinetic exponent.

10

Yang, Jian, Xiang Xin Xue, Li Mei Pan, Mei Wang e Tai Qiu. "Phase-Transformation Kinetics of TiO₂ in TiO₂/(O′+β′)-Sialon Multi-Phase Ceramics". Key Engineering Materials 336-338 (aprile 2007): 2318–21. http://dx.doi.org/10.4028/www.scientific.net/kem.336-338.2318.

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TiO2/(O′+β′)-Sialon multiphase ceramics with different phase composition of TiO2 were prepared by pressureless sintering under high-purity N2 atmosphere with (O′+β′)-Sialon powder and nano TiO2 (anatase) powder as raw materials, Yb2O3 or Tb2O3 as additive. For each sample, the weight percentage of anatase in TiO2 was calculated from XRD data and the kinetics of anatase-rutile transformation was investigated, wherein the emphasis was placed on the influence of Yb2O3 and Tb2O3. The results indicate that the added Tb2O3 and Yb2O3 serve the significant function of inhibition and promotion on the phase transformation, and the effects are enhanced and attenuated with increasing additive content, respectively. For the sample without additive, the transformation process follows apparent first-order kinetic model. The addition of Yb2O3 or Tb2O3 results in completely different transformation kinetic law. For the samples with Yb2O3 added, the transformation is an apparent second-order reaction, whereas a unique kinetic model, CA=kt1/2+C, is valid for the samples containing Tb2O3. In the two cases, the effect of the additive content on the transformation can be perfectly reflected by the apparent rate constant.

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Jin, Ou, Yuanyuan Shang, Xiaohui Huang, Dorothée Vinga Szabó, Thi Thu Le, Stefan Wagner, Thomas Klassen, Christian Kübel, Claudio Pistidda e Astrid Pundt. "Transformation Kinetics of LiBH4–MgH2 for Hydrogen Storage". Molecules 27, n. 20 (18 ottobre 2022): 7005. http://dx.doi.org/10.3390/molecules27207005.

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The reactive hydride composite (RHC) LiBH4–MgH2 is regarded as one of the most promising materials for hydrogen storage. Its extensive application is so far limited by its poor dehydrogenation kinetics, due to the hampered nucleation and growth process of MgB2. Nevertheless, the poor kinetics can be improved by additives. This work studied the growth process of MgB2 with varying contents of 3TiCl3·AlCl3 as an additive, and combined kinetic measurements, X-ray diffraction (XRD), and advanced transmission electron microscopy (TEM) to develop a structural understanding. It was found that the formation of MgB2 preferentially occurs on TiB2 nanoparticles. The major reason for this is that the elastic strain energy density can be reduced to ~4.7 × 107 J/m3 by creating an interface between MgB2 and TiB2, as opposed to ~2.9 × 108 J/m3 at the original interface between MgB2 and Mg. The kinetics of the MgB2 growth was modeled by the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation, describing the kinetics better than other kinetic models. It is suggested that the MgB2 growth rate-controlling step is changed from interface- to diffusion-controlled when the nucleation center changes from Mg to TiB2. This transition is also reflected in the change of the MgB2 morphology from bar- to platelet-like. Based on our observations, we suggest that an additive content between 2.5 and 5 mol% 3TiCl3·AlCl3 results in the best enhancement of the dehydrogenation kinetics.

12

Jia, Tao, Run Ni, Hanle Wang, Jicheng Shen e Zhaodong Wang. "Investigation on the Formation of Cr-Rich Precipitates at the Interphase Boundary in Type 430 Stainless Steel Based on Austenite–Ferrite Transformation Kinetics". Metals 9, n. 10 (26 settembre 2019): 1045. http://dx.doi.org/10.3390/met9101045.

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The Cr-rich precipitates at the interphase boundary in stainless steels not only lead to the sensitization, which further induces the intergranular corrosion and intergranular stress corrosion cracking, but also significantly deteriorate the ductility and toughness. In this work, the formation of Cr-rich precipitates at the interphase boundary in type 430 stainless steel was investigated from the perspective of austenite–ferrite transformation kinetics. Cyclic heat treatment was firstly conducted to reveal the kinetic mode of transformation behavior, i.e., local equilibrium or para equilibrium. Subsequently, interrupted quenching during continuous cooling was carried out, which illustrated clearly the relevance of the formation of interphase Cr-rich precipitates to the Cr enrichment adjacent to the interphase boundary as revealed by line scanning of energy dispersive spectroscopy (EDS). Finally, this enrichment of Cr was interpreted by DICTRA simulation, which is based on the determined kinetic mode for austenite–ferrite transformation. This work has, for the first time, established the correlation between the formation of interphase Cr-rich precipitates and the austenite–ferrite transformation kinetics.

13

BOZGA, GRIGORE. "Catalytic conversion of glycerol. A review of process kinetics and catalytic reactors". Journal of Engineering Sciences and Innovation 7, n. 2 (14 giugno 2022): 175–92. http://dx.doi.org/10.56958/jesi.2022.7.2.175.

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Glycerol, the by-product of the Biodiesel manufacturing from vegetal and animal fats, is an important bio-resource, which can be transformed into a significant number of valuable products, by catalytic, enzymatic, or biological technologies. This paper presents a review of published studies on the kinetics of the main catalytic transformations of glycerol into valuable products, along with information regarding the catalytic reactors experienced or proposed for these transformations. In the kinetic description of the glycerol catalytic transformations, the most used are the rate expressions based on the Langmuir-Hinshelwood-Hougen-Watson (LHHW) theory and the empirical ones, of the power law type. The published results are evidencing that, in addition to the general technical and economic advantages, the liquid phase continuous processes of glycerol transformation are more efficient, ensuring, in many cases, a higher selectivity of the transformation and a slower deactivation of the catalyst.

14

Ilić, Dušica, Vesna Nikolić, Mihajlo Stanković, Ljubiša Nikolić, Ljiljana Stanojević, Ivana Mladenović-Ranisavljević e Andrija Šmelcerović. "Transformation of Synthetic Allicin: The Influence of Ultrasound, Microwaves, Different Solvents and Temperatures, and the Products Isolation". Scientific World Journal 2012 (2012): 1–7. http://dx.doi.org/10.1100/2012/561823.

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The transformation of the synthesized allicin, using conventional method, the influence of ultrasound and microwaves, in different organic solvents (acetonitrile, acetone, methanol, and chloroform), at various temperatures (room temperature,45∘C, and55∘C) was investigated. Allicin degradation kinetic was monitored by HPLC. Allicin transformation under the effect of microwaves is faster than transformations performed under the influence of ultrasound or by conventional method. Increase of the temperature accelerates allicin transformation. Pharmacologically active compounds of (E)-ajoene, (Z)-ajoene, 3-vinyl-4H-1,2-dithiin, 2-vinyl-4H-1,3-dithiin, and diallyl disulfide were isolated from the mixture of transformation products of allicin under the influence of microwaves in methanol at55∘C, which is according to kinetic parameters (highest values of the order of reaction and the lowest activation energy) the optimal method.

15

Uhm, Sang Ho, Joo Noh Moon, Chang Hee Lee, Ji Hyun Yoon e Bong Sang Lee. "Bainitic Transformation Model in Low Alloy Carbon Steels Considering the Effect of Reaction Constant in JMA Equation". Materials Science Forum 475-479 (gennaio 2005): 3157–60. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.3157.

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As a part of a study on modeling the microstructural evolution during the welding process, a prediction model of TTT diagram for bainite transformation was studied. This model consisted of a thermodynamic model for the bainite-start(Bs) temperature and a kinetic model for the bainite transformation. A kinetic model was empirically established for low alloy carbon steels, based on Johnson-Mehl-Avrami(JMA) equation. Reaction constants seemed not to have noticeable tendencies for temperatures and were averaged for each alloy. It was, however, found that the mean reaction constant significantly affected the reproducibility for the isothermal kinetics. Therefore, a calibration method to the kinetic parameter was proposed. From calibrations, rate constants were formulated as a function of alloying element and temperature. And TTT diagrams were calculated and compared with experiments.

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Réti, Tamás, Imre Czinege, Imre Felde, Lino Costa e Rafael Colás. "On the Temperature Rate Dependent Transformation Processes". Materials Science Forum 537-538 (febbraio 2007): 571–78. http://dx.doi.org/10.4028/www.scientific.net/msf.537-538.571.

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Kinetic models of new types are suggested which are designated primarily to predict the progress of non-isothermal transformations occurring during rapid heating and cooling in alloys. A common feature of each model outlined is that it takes into account not only the varying temperature but also the rate of temperature change on the transformation rate of the process. The two models represented by differential equations are generated by using the concept of virtual kinetic parameters, which can be determined from non-isothermal experiments only. A key property of the virtual parameter "p" involved in the transformation rate equations is that it quantitatively characterizes the temperature rate dependence of the non-isothermal reaction.

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Ludeña, E. V., R. López-Boada e R. Pino. "Approximate kinetic energy density functionals generated by local-scaling transformations". Canadian Journal of Chemistry 74, n. 6 (1 giugno 1996): 1097–105. http://dx.doi.org/10.1139/v96-123.

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Different stages in the development of density functional theory are succinctly reviewed for the purpose of tracing the origin of the local-scaling transformation version of density functional theory. Explicit kinetic energy functionals are generated within this theory. These functionals are analyzed in terms of several approximations to the local-scaling function and are applied to a few selected first-row atoms. Key words: density functional theory, kinetic energy density functionals, local-scaling transformations, explicit kinetic energy functionals, kinetic energy of first-row atoms.

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Perdahcıoğlu, Emin Semih, e Hubert J. M. Geijselaers. "Mechanical Behavior of Multi-Phase Steels Comprising Retained Austenite". Materials 15, n. 2 (10 gennaio 2022): 498. http://dx.doi.org/10.3390/ma15020498.

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The retained austenite (RA) in advanced high-strength steel (AHSS) grades, such as dual-phase (DP) steels, plays an important role on their formability. Thanks to the transformation-induced plasticity (TRIP) effect that occurs during the mechanically induced transformation of RA into martensite, additional ductility is obtained. Martensite has a higher flow stress than austenite; hence, the transformation results in an apparent hardening, which is beneficial for the stability of deformation. The stability of RA at a given temperature strongly depends on its carbon content, which, in AHSS, is not uniform but distributed. The aim of this study is to build a model that predicts the transformation as well as TRIP in a DP steel grade with RA. A physics-based kinetic model is presented that captures the transformation of retained austenite based on the thermodynamic driving force of the applied stress. A direct analytical estimate of transformation plasticity is provided, which is consistent with the kinetic model. Transformation kinetics is incorporated in a self-consistent, mean-field homogenization-based constitutive model. Finally, an indication of the effect of transformation of retained austenite on formability is given.

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Hu, Han, Gabriele Sansalone, Stephen Wroe, Paul G. McDonald, Jingmai K. O’Connor, Zhiheng Li, Xing Xu e Zhonghe Zhou. "Evolution of the vomer and its implications for cranial kinesis in Paraves". Proceedings of the National Academy of Sciences 116, n. 39 (9 settembre 2019): 19571–78. http://dx.doi.org/10.1073/pnas.1907754116.

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Most living birds exhibit cranial kinesis—movement between the rostrum and braincase—in which force is transferred through the palatal and jugal bars. The palate alone distinguishes the Paleognathae from the Neognathae, with cranial kinesis more developed in neognaths. Most previous palatal studies were based on 2D data and rarely incorporated data from stem birds despite great interest in their kinetic abilities. Here we reconstruct the vomer of the Early Cretaceous stem bird Sapeornis and the troodontid Sinovenator, taxa spanning the dinosaur–bird transition. A 3D shape analysis including these paravians and an extensive sampling of neornithines reveals their strong similarity to paleognaths and indicates that morphological differences in the vomer between paleognaths and neognaths are intimately related to their different kinetic abilities. These results suggest the skull of Mesozoic paravians lacked the kinetic abilities observed in neognaths, a conclusion also supported by our identification of an ectopterygoid in Sapeornis here. We conclude that cranial kinesis evolved relatively late, likely an innovation of the Neognathae, and is linked to the transformation of the vomer. This transformation increased palatal mobility, enabling the evolution of a diversity of kinetic mechanisms and ultimately contributing to the extraordinary evolutionary success of this clade.

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Bronnikova, S. "BASIK FOUNDATIONS OF THE FORMATION OF KINETIC ARCHITECTURE". Municipal economy of cities 3, n. 170 (24 giugno 2022): 71–76. http://dx.doi.org/10.33042/2522-1809-2022-3-170-71-76.

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The article actualizes the significance of kinetic architecture not only as the creation of a dynamic visual image of the spatial form of a building or structure, but also as a transformation, the mobility of the architectural form itself – from a kinetic facade or roof to a changing layout and volume of the building as a whole, provided by the mobility of its structural elements. Moreover, dynamic architecture is understood today as a kinematic architecture, including movement, transformation of the spatial form of the building. The purpose of the article is to reveal the basic principles of the formation of kinetic architecture in the past and present in order to determine the possibilities for further development. Summarize the trends in the expression of the plastic language of the 21st century and outline their development vectors. The historical context and the main stages in the development of kinetic architecture from the innovative ideas of the futurists to the innovative projects of our time are considered. The experience of the Soviet period and foreign experience, as well as modern trends in the development of kinetic architecture are considered. Examples of architectural objects characterized specifically by innovativeness in the materials used, developments, constructive solutions, design, engineering support are structures and structures with dynamic properties. Modern scientific and technological progress in the construction industry, the growth of material opportunities, social and cultural needs of society, led to the emergence of new ideas, concepts, projects in architectural creativity. A number of aspects (essential during the period of operation of the structure) are identified, which determine the real dynamism of the architectural form, expressed in the mechanical movement of the form itself or its individual elements (form kinetics).

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Dere, Emine Gözde, Hemant Sharma, S. Eric Offerman e Jilt Sietsma. "The Effect of NbC Precipitates and Nb in Solid-Solution on the Phase Transformation Kinetics in High-Purity Fe-C-Mn-Nb Alloys". Solid State Phenomena 172-174 (giugno 2011): 499–504. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.499.

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The precipitation of NbC in austenite is an important mechanism for improving the strength of steel because NbC-precipitates are known to decrease the ferrite grain size during the subsequent phase transformations upon cooling. The effect of the interaction between niobium (Nb) in solid solution and NbC-precipitates on the austenite-to-ferrite phase-transformation kinetics is not entirely clear. We study a high-purity Fe-C-Mn-Nb alloy cooled at different rates. Different annealing times at 850°C were applied to create different number densities and sizes of the NbC-precipitates in order to study the effect of NbC precipitation on the transformation kinetics. The alloy that is used in this study has an atomic ratio of Nb:C=1.3:1. The fraction of ferrite is measured as a function of temperature during cooling by means of dilatometry. The ferrite grain size is measured by means of optical microscopy. The results are interpreted with thermodynamic and kinetic models.

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Baram, Jonathan, Haim Weissman e Boris Rybtchinski. "Supramolecular Polymer Transformation: A Kinetic Study". Journal of Physical Chemistry B 118, n. 41 (2 ottobre 2014): 12068–73. http://dx.doi.org/10.1021/jp507945t.

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Mirzaev, D. A., K. Yu Okishev, A. A. Mirzoev e A. N. Makovetskii. "Austenite to Ferrite Transformation Kinetics in Fe-9 %Cr Alloys - I. General Kinetic Analysis". Materials Science Forum 946 (febbraio 2019): 210–14. http://dx.doi.org/10.4028/www.scientific.net/msf.946.210.

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The paper considers theoretical aspects of the kinetics of austenite → ferrite transformation in an Fe–9 %Cr alloy, a common model of diffusionless transformation. In previous studies it was shown that this transformation under isothermal conditions shows a behaviour typical for nucleation site saturation, including the change of the Avrami exponentn(determined as the slow of transformation curve on double logarithmic scale) from 4 to 1. Activation energies determined in two ways: by the ‘nose’ temperature of the normal C-curve and by the slope of the C-curve re-drawn on a reverse temperature scale are unexpectedly similar (272–315 kJ/mole) and not temperature-dependent. But the complete TTT diagrams calculated using these values determined directly from experimental data and the precise formula of Cahn’s solution of grain face nucleated transformation problem do not provide good agreement with experiment in the whole temperature range. This may mean that the theory of site saturation needs some correction.

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Secara, Natalia. "Dihydroxyfumaric Acid Transformation". Chemistry Journal of Moldova 3, n. 1 (giugno 2008): 127–28. http://dx.doi.org/10.19261/cjm.2008.03(1).06.

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This short communication presents several preliminary results obtained during kinetic investigation of dihydroxyfumaric acid decarboxylation. The reaction order towards the hydrogen ions concentration has been established, the correlation between the decarboxylation velocity and temperature has been found, the Arrhenius equation for the decarboxylation constant has been drawn.

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Wu, Zong Pei, Zhu Qing Cheng, Zhong Bo Yang, Wei Yi e Xiao Lu Xu. "Non-Isothermal Kinetics Analysis of α→β Transformation in Zirconium Alloy". Materials Science Forum 993 (maggio 2020): 344–50. http://dx.doi.org/10.4028/www.scientific.net/msf.993.344.

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Differential scanning calorimetry (DSC) was used to study non-isothermal kinetics of α→β transformation of Zr-0.5wt%Sn-0.15wt%Nb-0.5wt%Fe-0.25wt%V alloy. The DSC curves were measured from room temperature to 1030 °C at the heating rate of 15, 20, 30, 50°C /min respectively. The Flynn-Wall-Ozawa (FWO) method was used to get the activation energy (E) of α→β transformation at different conversion ratios. Then the values of activation energy obtained were modified by Ozawa iterative equation. The kinetic mechanism functions of α→β transformation were investigated by Criado-Ortega methods. The results show that the activation energy is related to conversion ratios. It means α→β transformation is not a simple one-step reaction but a complex multi-step reaction. The most probable kinetic mechanism functions are different in different temperature ranges, which are -ln(1-x) for ≤830 °C, [-ln(1-x)]1/2 for 834~848 °C, [-ln(1-x)]2/5for 850~856 °C and [-ln(1-x)]1/3 for 858~868 °C respectively.

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Kurkin, A. S. "Mathematical research of the phase transformation kinetics of alloyed steel". Industrial laboratory. Diagnostics of materials 85, n. 12 (29 dicembre 2019): 25–32. http://dx.doi.org/10.26896/1028-6861-2019-85-12-25-32.

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Regulation of the process parameters allows obtaining the desired properties of the metal. Computer simulation of technological processes with allowance for structural and phase transformations of the metal forms the basis for the proper choice of those parameters. Methods of mathematical modeling are used to study the main diffusion and diffusion-free processes of transformations in alloyed steels during heating and cooling. A comparative analysis of the kinetic equations of phase transformations including the Kolmogorov – Avrami and Austin – Rickett equations which describe in different ways the time dependence of the diffusion transformation rate and attained degree of transformation has been carried out. It is shown that the Austin – Rickett equation is equivalent to the Kolmogorov – Avrami equation with a smooth decrease of the Avrami exponent during the transformation process. The advantages of the Kolmogorov – Avrami equation in modeling the kinetics of ferrite-pearlite and bainite transformations and validity of this equation for modeling the kinetics of martensite transformations during tempering are shown. The parameters for describing the tempering process of steel 35 at different temperatures are determined. The proposed model is compared with equations based on the Hollomon – Jaffe parameter. The diagrams of martensitic transformation of alloyed steels and disadvantages of the Koistinen – Marburger equation used to describe them are analyzed. The equations of the temperature dependence of the transformation degree, similar to the Kolmogorov – Avrami and Austin – Rickett equations, are derived. The equations contain the minimum set of the parameters that can be found from published data. An iterative algorithm for determining parameters of the equations is developed, providing the minimum standard deviation of the constructed dependence from the initial experimental data. The dependence of the accuracy of approximation on the temperature of the onset of transformation is presented. The complex character of the martensitic transformation development for some steels is revealed. The advantage of using equations of the Austin – Rickett type when constructing models from a limited amount of experimental data is shown. The results obtained make it possible to extend the approaches used in modeling diffusion processes of austenite decomposition to description of the processes of formation and decomposition of martensite in alloyed steels.

27

Tang, Mingliang, Xuerun Li, Yusheng Shen e Xiaodong Shen. "Kinetic model for calcium sulfate α-hemihydrate produced hydrothermally from gypsum formed by flue gas desulfurization". Journal of Applied Crystallography 48, n. 3 (9 maggio 2015): 827–35. http://dx.doi.org/10.1107/s1600576715007141.

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Modeling of the kinetics of the synthesis process for calcium sulfate α-hemihydrate from gypsum formed by flue gas desulfurization (FGD) is important to produce high-performance products with minimal costs and production cycles under hydrothermal conditions. In this study, a model was established by horizontally translating the obtained crystal size distribution (CSD) to the CSD of the stable phase during the transformation process. A simple method was used to obtain the nucleation and growth rates. A nonlinear optimization algorithm method was employed to determine the kinetic parameters. The model can be successfully used to analyze the transformation kinetics of FGD gypsum to α-hemihydrate in an isothermal batch crystallizer. The results showed that the transformation temperature and stirring speed exhibit a significant influence on the crystal growth and nucleation rates of α-hemihydrate, thus altering the transformation time and CSD of the final products. The characteristics obtained by the proposed model can potentially be used in the production of α-hemihydrate.

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Pei, Wei, Wei Liu, Yue Zhang, Rongjian Qie e Aimin Zhao. "Study on Kinetics of Transformation in Medium Carbon Steel Bainite at Different Isothermal Temperatures". Materials 14, n. 11 (21 maggio 2021): 2721. http://dx.doi.org/10.3390/ma14112721.

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Ultra-fine carbide-free bainitic (UCFB) steel, also known as nano-bainite (NB) steel, is composed of bainitic ferrite laths with nanoscale thickness and carbon-rich film-like retained austenite located between laths. The bainite transformation kinetic model can accurately describe the bainite transformation kinetics in conventional austempering (CA) processes based on the shear mechanism combined with the dilatometer test. UCFB steels with medium and high carbon composition are designed in this work to systematically study the transformation kinetics of bainite, and the evolution of its microstructure and properties, and reveal the influence of heat treatment processes on the microstructure and properties the UCFB steels. The results show that the activation energy for BF nucleation decreases during the CA process and isothermal transformation temperature decreases. The bainite transformation is first nucleated at the grain boundaries, and then nucleated at the newly formed bainitic ferrite/austenite interface.

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Kavokin, A. A., I. H. Kazmi e B. Munir. "Computational Model of Phase Transformations in Thermo-Chemical Cathodes Using Kinetic Approach". Key Engineering Materials 510-511 (maggio 2012): 9–14. http://dx.doi.org/10.4028/www.scientific.net/kem.510-511.9.

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The paper presents the results of modeling of the processes of phases transformations occurring in cathode of plasmatron with zirconium insertion. Model describes temperature and liquid-solid phase transformation in cathode considering kinetics of transformation in accordance with a state diagram. The comparison between one-dimensional mathematical models was exploited for estimation of the kinetics coefficient. First model is based on well-known heat equation with Stefans condition on the free boundary between liquid and solid phases [. The standard analytical self-similar solution for two-phase case is applied. In the second model, for heat equation instead of Stefans conditions, differential equations of kinetics are used.

30

Mecozzi, Maria Giuseppina, C. Bos e Jilt Sietsma. "3D Cellular Automata Modelling of Solid–state Transformations Relevant in Low–alloy Steel Production". Solid State Phenomena 172-174 (giugno 2011): 1140–45. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.1140.

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A three-dimensional cellular automata (CA) model is developed for the kinetic and microstructural modelling of the relevant metallurgical mechanisms occurring in the annealing stage of low–alloy steels: recrystallisation, pearlite–to–austenite transformation and ferrite–to–austenite transformation on heating and austenite–to–ferrite transformation on cooling. In this model the austenite–to–ferrite transformation is described by a mixed–mode approach, which implies that the transformation kinetics is controlled by both the interface mobility and the diffusivity of the partitioning elements. This approach also allows incorporation of the ferrite nucleation occurring on structural defects. The developed CA algorithm, in which the transformation rules for the grain boundary and interface cells are controlled by the growth kinetics of the forming phase, allows three-dimensional systems to be treated within relatively short simulation times. The simulated microstructure reproduces quite well the microstructure observed in experimental samples. A good agreement is obtained between the experimental and simulated ferrite recrystallisation and ferrite and austenite transformation kinetics. The present approach also models the development of the carbon concentration profile in the austenite, which is, for instance, essential for subsequent martensite formation.

31

Yudin, Yu V., M. V. Maisuradze, A. A. Kuklina e P. D. Lebedev. "Application of Computer Simulation to Study the Features of the Austenite Isothermal Transformation in Steels". KnE Engineering 1, n. 1 (15 aprile 2019): 1. http://dx.doi.org/10.18502/keg.v1i1.4384.

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An algorithm was developed for the simulation of a phase transition in solid state whichmakes it possible to obtain the kinetic curves of transformation under different initialconditions (the number and arrangement of new phase nuclei, the distance betweenthe nearest nuclei). The simulation results were analyzed using the Kolmogorov-Johnson-Mehl-Avrami equation and the corresponding coefficients were determined.The correlation between the simulation results and the experimental kinetics of theaustenite isothermal transformation in alloyed steels was shown.

32

Erofeev, Vasily I. "High-informative version of nonlinear transformation of Langmuir waves to electromagnetic waves". Journal of Plasma Physics 80, n. 2 (13 dicembre 2013): 289–318. http://dx.doi.org/10.1017/s002237781300127x.

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AbstractThe concept of informativeness of nonlinear plasma physical scenario is discussed. Basic principles for heightening the informativeness of plasma kinetic models are explained. Formerhigh-informative correlation analysis of plasma kinetics(Erofeev, V. 2011High-Informative Plasma Theory, Saarbrücken: LAP) is generalized for studies of weakly turbulent plasmas that contain fields of solenoidal plasma waves apart from former potential ones. Respective machinery of plasma kinetic modeling is applied to an analysis of fusion of Langmuir waves with transformation to electromagnetic waves. It is shown that the customary version of this phenomenon (Terashima, Y. and Yajima, N. 1963Prog. Theor. Phys.30, 443; Akhiezer, I. A., Danelia, I. A. and Tsintsadze, N. L. 1964Sov. Phys. JETP19, 208; Al'tshul', L. M. and Karpman, V. I. 1965Sov. Phys. JETP20, 1043) substantially distorts the picture of merging of Langmuir waves with long wavelengths (λ ≳c/ωpe).

33

Menon, E. S. K., W. T. Reynolds e A.G.Fox. "Electron Spectroscopic Investigations of the Solute Drag Like Effect in Fe-C-Mo Alloys". Microscopy and Microanalysis 3, S2 (agosto 1997): 553–54. http://dx.doi.org/10.1017/s143192760000965x.

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The role of various alloying elements on the kinetics of austenite decomposition in steels is well documented. One of the least understood aspects is the ability of some elements like Mo to drastically reduce the kinetics of ferrite (α) growth in austenite (γ).Within specific ranges of transformation temperatures and alloy compositions, the transformation of austenite can cease entirely for extended periods of time (transformation stasis). The phenomenon is quite pronounced in Fe-C-Mo alloys and is clearly evidenced by a horizontal region in the plot of the fraction transformed vs. isothermal reaction time. Based on microstructural and kinetic evidence, the occurrence of the transformation stasis phenomenon has been ascribed to a "solute drag like effect" caused by the segregation of Mo atoms to α : γ boundaries. The proposal that interface chemistry alters the growth kinetics of ferrite is quite difficult to verify as the segregation is expected to be confined to a boundary region less than a nanometer in width.

34

Purba, Elida. "DETERMINATION OF REACTION KINETICS USING ONLINE X-RAY DIFFRACTION". Indonesian Journal of Chemistry 8, n. 3 (17 giugno 2010): 337–41. http://dx.doi.org/10.22146/ijc.21588.

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X-ray diffraction (XRD) is a powerful technique for the study of polymorphism and polymorphic phase transformations. Monitoring of phase transformation directly has been very limited to-date. The XRD system used in this study was used to determine the rate of transformation of pure glutamic acid a form to b form in a solution mediated phase. On every run starting from the pure a form, the transformation process was monitored continuously at fixed temperature, and separate experiments were performed as a function of temperature. The operating temperature was varied from 36 to 57 °C with 10% w/w solid concentration. Data were taken every 200 seconds until the transformation was completed. This paper is concerned with a study of the transformation of the alpha (a) form of L-glutamic acid (L-GA) to the beta (b) form in order to determine the kinetic reaction. The rate constant (k), activation energy (Ea) and pre-exponential factor (A) were obtained. Sensitivity tests were also carried out to examine minimum detection limit when both a and b present in the mixture. In addition, effect of particle size on XRD patterns was also determined. The results show that XRD gives useful information to observe polymorphism for pharmaceutical industry. Keywords: XRD, polymorphism, glutamic acid, reaction kinetics

35

Mihajlovic, Ivan, Nada Strbac, Zivan Zivkovic e Ilija Ilic. "Kinetics and mechanism of As2S2 oxidation". Journal of the Serbian Chemical Society 70, n. 6 (2005): 869–77. http://dx.doi.org/10.2298/jsc0506869m.

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The kinetics of realgar (As2S2) oxidation was studied under isothermal and non-isothermal conditions. The obtained values of the activation energy indicate that the process occurs in the kinetic domainwith the realgar particles being converted to As2O3 and As4O6 (g). The very fast reaction rates were limited by the chemical reaction. The kinetic equation was found to be: ?ln (1??) = 4.56 x 103 x e(?8780/T) x t. The proposed reaction mechanism and chemical transformation investigated by ICP?AES, EDXRF and thermal analysis are discussed.

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Zhang, Hengzhong, e Jillian F. Banfield. "Phase transformation of nanocrystalline anatase-to-rutile via combined interface and surface nucleation". Journal of Materials Research 15, n. 2 (febbraio 2000): 437–48. http://dx.doi.org/10.1557/jmr.2000.0067.

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The kinetics of phase transformation of nanocrystalline anatase samples was studied using x-ray diffraction at temperatures ranging from 600 to 1150 °C. Kinetic data were analyzed with an interface nucleation model and a newly proposed kinetic model for combined interface and surface nucleation. Results revealed that the activation energy of nucleation is size dependent. In anatase samples with denser particle packing, rutile nucleates primarily at interfaces between contacting anatase particles. In anatase samples with less dense particle packing, rutile nucleates at both interfaces and free surfaces of anatase particles. The predominant nucleation mode may change from interface nucleation at low temperatures to surface nucleation at intermediate temperatures and to bulk nucleation at very high temperatures. Alumina particles dispersed among the anatase particles can effectively reduce the probability of interface nucleation at all temperatures.

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Lapuzin, Alexander, Valery Subotovich, Yuriy Yudin e Svetlana Naumenko. "The Method of Determining Total Losses in the Nozzle Cascades of Turbomachines". NTU "KhPI" Bulletin: Power and heat engineering processes and equipment, n. 1-2 (8 luglio 2023): 11–17. http://dx.doi.org/10.20998/2078-774x.2023.01.02.

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To assess the level of aerodynamic efficiency of the nozzle cascades of steam and gas turbines, the method was suggested to determine the total loss coefficient instead of kinetic energy loss coefficient that takes into account both kinetic energy losses and kinematic losses. This method allows us to transform the original non-uniform spatial flow behind the cascade into an axisymmetric cylindrical flow. In the tested annular cascade with cylindrical meridional boundaries, the total loss coefficient is approximately 0.02 higher than the kinetic energy loss coefficient. By taking into account kinematic losses when performing thermal calculations for the turbines we eliminate the need for an unjustified correction of the kinetic energy loss coefficient of the nozzle cascade by 0.01–0.03, increasing thus the accuracy of calculations. To analyze the operation of individual sections of the nozzle cascade and to determine the relationship between kinetic energy losses and kinematic losses, it is advisable to use the averaging method proposed in 2021 that enables the transformation of the initial non-uniform spatial flow behind the cascade into an axisymmetric conical flow. The aerodynamic characteristics of this flow are the widely used kinetic energy loss factor and two averaged flow angles.

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Hong, Mei, Kang Wang, Yuzeng Chen e Feng Liu. "A thermo-kinetic model for martensitic transformation kinetics in low-alloy steels". Journal of Alloys and Compounds 647 (ottobre 2015): 763–67. http://dx.doi.org/10.1016/j.jallcom.2015.05.266.

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Ait Yassine, Youssef, Marwan Lakhal, Nabil Labchir, Elhassan Zantalla, Elmadani Saad e Mohamed Sannad. "Kinetic Study of the Aging and Overaging of Alloy Pb0.058%Ca0.12%Sr1.09%Sn for Battery Grids". Coatings 13, n. 9 (1 settembre 2023): 1534. http://dx.doi.org/10.3390/coatings13091534.

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In this paper, we examine the effect of a small amount of Sn, Sr and Ca on the hardening and the kinetic properties of Pb. Experimentally, we analyze the specific process from the structural hardening evolution to equilibrium of PbCaSrSn alloy occurring in two steps. In the first one, a discontinuous transformation hardening and a continuous precipitation take place. A lamellar discontinuous precipitation that occurs after aging, characterizes the second step. Theoretically, we study the aging and overaging kinetics of the alloy by using the two complimentary methods needed to calculate the apparent activation energies of the Pb0.058%Ca0.12%Sr1.09%Sn associated with the various transformations, characterizing its hardening at 20 and 80 °C. We show that activation energies of aging and overaging of Pb0.058%Ca0.12%Sr1.09%Sn alloy are 25 and 28 kJ/mole, respectively, which are four times lower than the self-diffusion energy of Pb. Moreover, the addition of Ca, Sr and Sn leads to an amplification of the maximum hardness from 5 ± 5% HV to 21 ± 5% HV and an acceleration of the transformation hardening process responsible for aging.

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Umemoto, Minoru, e Imao Tamura. "Grain size derived from transformation kinetic equations." Bulletin of the Japan Institute of Metals 24, n. 4 (1985): 262–69. http://dx.doi.org/10.2320/materia1962.24.262.

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Ghanem, Raed, Hutaf Baker, Mobeen Abu Seif, Raed A. Al-Qawasmeh, Abdl-Azizi Mataneh e Samer Ibrahim Al-Gharabli. "Photochemical Transformation of Colchicine: A Kinetic Study". Journal of Solution Chemistry 39, n. 4 (aprile 2010): 441–56. http://dx.doi.org/10.1007/s10953-010-9515-z.

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Pan, Liang, e Kun Xu. "Generalized coordinate transformation and gas-kinetic scheme". Journal of Computational Physics 287 (aprile 2015): 207–25. http://dx.doi.org/10.1016/j.jcp.2015.02.010.

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Wang, Gang, De Chang Zeng e Zhong Wu Liu. "Evaluation of Glass-Forming Ability for Metallic Melts by Phase Field Approach". Advanced Materials Research 490-495 (marzo 2012): 3129–33. http://dx.doi.org/10.4028/www.scientific.net/amr.490-495.3129.

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Evaluation of glass-forming ability (GFA) is important in the development of amorphous alloys. Based on phase field theory, the kinetic model of liquid-to-solid phase transition is build, and the time-temperature-transformation (TTT) diagram is plotted according to the phase field simulations of isothermal phase transformation kinetics for a model system. Furthermore, the critical cooling rate for glass formation is calculated on the basis of the TTT curve and is taken as the intrinsic criteria of reflecting the GFA for metallic melts.

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Ye, Qing, Gongming Qian, Lulu Liu, Fu Yang e Wei Liu. "Effect of Hydroxyapatite on the Migration of Fe(III) Ions: Kinetic, Equilibrium and Thermodynamic Study". Materials 15, n. 16 (17 agosto 2022): 5652. http://dx.doi.org/10.3390/ma15165652.

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The recycling and regeneration of Fe(III) is the key point for promoting the oxidation reaction of ore to produce acidic mine drainage (AMD). Hydroxyapatite (HAP) has excellent adsorption ability of Fe(III), which has good biocompatibility and is widely distributed in nature. In order to achieve the source treatment of AMD, the migration and transformation of Fe(III) in the presence of HAP were systematically investigated. In this study, the influence of HAP on the migration of Fe(III) was evaluated though the transformation capacity of Fe(III) by HAP. The adsorption transformation kinetic, equilibrium and thermodynamics of Fe(III) using HAP were also systematic investigated. The transformation efficiency of Fe(III) increased with the increasing initial pH value and reached 99.8% at a pH of 5 due to the hydrolysis reaction. The transformation efficiency was also up to 99% at an initial pH of 2 when the reaction temperature increased to 313 K. However, the transformation capability of Fe(III) decreases with reaction temperature. The kinetics of the adsorption of Fe(III) fitted the pseudo second order kinetic model. Experimental results were also analyzed by the Langmuir isotherm equations at room temperatures. RL separation factor for Langmuir isotherm showed that the migration of Fe(III) is successfully hindered by HAP. Various thermodynamic parameters such as enthalpy (ΔH), Gibbs free energy (ΔG) and entropy (ΔS) changes were computed, which showed that the transport lag of Fe(III) caused by HAP is spontaneous and endothermic.

45

Fultz, B. "Kinetics of short- and long-range B2 ordering in ternary alloys". Journal of Materials Research 7, n. 4 (aprile 1992): 946–54. http://dx.doi.org/10.1557/jmr.1992.0946.

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The kinetics of disorder → B2 order transformations in ternary alloys were studied in the pair approximation. The predictions of two sets of rate equations were compared, one based on an atom-atom interchange mechanism and the other based on an atom-vacancy interchange mechanism. Examples are presented to show how the evolution of order is affected by differences in interatomic potentials, differences in activation barrier heights, and effects of vacancy ordering. A wide variety of states of order are possible during the disorder → order transformation in ternary alloys, and qualitative features of the sequences of these states are discussed. The sequences of states, or “kinetic paths”, are much less intuitive than for binary alloys.

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GAONA, ALEJANDRO, e J. ANTONIO GARCÍA. "FIRST-ORDER ACTIONS AND DUALITY". International Journal of Modern Physics A 22, n. 04 (10 febbraio 2007): 851–67. http://dx.doi.org/10.1142/s0217751x07034386.

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We consider some aspects of classical S-duality transformations in first-order actions taking into account the general covariance of the Dirac algorithm and the transformation properties of the Dirac bracket. By classical S-duality transformations we mean a field redefinition that interchanges the equations of motion and its associated Bianchi identities. By working from a first-order variational principle and performing the corresponding Dirac analysis we find that the standard electromagnetic duality can be reformulated as a canonical local transformation. The reduction from this phase space to the original phase space variables coincides with the well-known result about duality as a canonical nonlocal transformation. We have also applied our ideas to the bosonic string. These dualities are not canonical transformations for the Dirac bracket and relate actions with different kinetic terms in the reduced space.

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Ma, Ya Zhu, e Feng Liu. "The Kinetic Description for Solid State Phase Transformation". Advanced Materials Research 123-125 (agosto 2010): 591–94. http://dx.doi.org/10.4028/www.scientific.net/amr.123-125.591.

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The progress of solid-state phase transformation can be subdivided into three overlapping mechanisms: nucleation, growth, and impingement. On the basis of an analytical phase transformation model, the maximum in the transformation rate of an isothermal solid-state transformation has been evaluated. Then, the mode of nucleation, growth and impingement, and the separate activation energies for nucleation and growth can be determined. Finally, application in the crystallization kinetics of amorphous alloy was described.

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Lin, Yen-Hui. "Kinetics of Cometabolic Transformation of 4-chlorophenol and Phenol Degradation by Pseudomonas putida Cells in Batch and Biofilm Reactors". Processes 9, n. 9 (15 settembre 2021): 1663. http://dx.doi.org/10.3390/pr9091663.

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The biodegradation kinetics of 4-chlorophenol (4-CP) and phenol and microbial growth of Pseudomonas putida (P. putida) cells were estimated in batch and biofilm reactors. The kinetic parameters of cells on phenol were determined using the Haldane formula. The maximum specific growth rate of P. putida on phenol, the half-saturation constant of phenol and the self-inhibition constant of phenol were 0.512 h−1, 78.38 mg/L and 228.5 mg/L, respectively. The yield growth of cells on phenol (YP) was 0.618 mg phenol/mg cell. The batch experimental results for the specific transformation rate of 4-CP by resting P. putida cells were fitted with Haldane kinetics to evaluate the maximum specific utilization rate of 4-CP, half-saturation constant of 4-CP, and self-inhibition constant of 4-CP, which were 0.246 h−1, 1.048 mg/L and 53.40 mg/L, respectively. The negative specific growth rates of cells on 4-CP obtained were fitted using a kinetic equation to investigate the true transformation capacity and first-order endogenous decay coefficient, which were 4.34 mg 4-CP/mg cell and 5.99 × 10−3 h−1, respectively. The competitive inhibition coefficients of phenol to 4-CP transformation and 4-CP to phenol degradation were 6.75 and 9.27 mg/L, respectively; therefore, phenol had a higher competitive inhibition of 4-CP transformation than the converse. The predicted model examining cometabolic transformation of 4-CP and phenol degradation showed good agreement with the experimental observations. The removal efficiencies for phenol and 4-CP were 94.56–98.45% and 96.09–98.85%, respectively, for steady-state performance.

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Dziedzic, D., K. Muszka e J. Majta. "Strain-Induced Austenitic Structure in Microalloyed Steels". Archives of Metallurgy and Materials 58, n. 3 (1 settembre 2013): 745–50. http://dx.doi.org/10.2478/amm-2013-0064.

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Abstract Austenite morphology is one of the main factors determining austenite-ferrite transformation kinetic and effectively affects the final microstructure and properties. The basic criteria for proper assessment of the austenite transformation products, theirs refinement, is the relation between the nucleation to growth rates. The main factor accelerating both, the nucleation rate of austenite during heating, and ferrite during cooling is the presence of accumulated deformation energy. The primary aim of this work is to increase our knowledge of the effects of deformation - its accumulated energy on the austenite structure and properties. Two specific steel grades were selected for the present investigation, i.e. microalloyed and IF steel, essentially different in equilibrium transformation temperatures. Obtained austenitic microstructures were analyzed, first of all as a start point for the austenite-to-ferrite transformation. Specific case of this transformation was considered i.e. Strain Induced Dynamic Transformation SIDT. The characteristic feature of the SIDT is the strong dependence of theirs kinetic on the austenite morphology, especially grain size. Thermomechanical processing, that utilize the SIDT, is one of the most effective ways to produce ultrafine-grained steel. One of the main benefits of the austenite refinement, just before the γ→α transformation, is its significant effect on the microstructure evolution during subsequent thermomechanical processing. Experimental results clearly show how direct and positive influence the austenite grain refinement has on the composition and refinement of transformation products. Presented study was focused on Strain Induced Dynamic Reverse Transformation. It is proved that this kind of transformation is very efficient way to intensify thermomechanical processing of microalloyed steels. Dynamic transformation kinetics were analyzed based upon flow curves recorded during the SIDT process. The main effect of presented research is analyze of influence of prior microstructure on dynamically formed austenite morphology

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Kumnorkaew, Theerawat, Junhe Lian, Vitoon Uthaisangsuk e Wolfgang Bleck. "Kinetic Model of Isothermal Bainitic Transformation of Low Carbon Steels under Ausforming Conditions". Alloys 1, n. 1 (13 giugno 2022): 93–115. http://dx.doi.org/10.3390/alloys1010007.

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Carbide-free bainitic steels show attractive mechanical properties but are difficult to process because of the sluggish phase transformation kinetics. A macroscopic model based on the classical nucleation theory in conjunction with the modified Koistinen–Marburger relationship is proposed in this study to simulate the kinetics of incomplete bainitic and martensitic phase transformations with and without austenite deformation. A 0.26C-1Si-1.5Mn-1Cr-1Ni-0.003B-0.03Ti steel and a 0.18C-1Si-2.5Mn-0.2Cr-0.2Ni-0.02B-0.03Ti steel were investigated with different levels of ausforming. The concept of ausforming is expected to accelerate the onset of the bainitic transformation and to enhance the thermodynamic stability of austenite by increased dislocation density. The phase transformation kinetics of both steels is quantitatively analyzed in the study by dilatometry and X-ray diffraction so that the carbon concentration in the retained austenite and bainitic ferrite, as well as their volume fractions, is determined. A critical comparison of the numerical and experimental data demonstrates that the isothermal kinetics of bainite formation and the variation of driving energy can be satisfactorily described by the developed model. This model captures the incompleteness of the bainite phase transformation and the carbon enrichment in the austenite well. A fitting parameter can be used to elucidate the initial energy barrier caused by the ausforming. An increase in austenite stability can be described by the nucleation reaction and the thermodynamic energies associated with the change of dislocation density. The proposed model provides an in-depth understanding of the effect of ausforming on the transformation kinetics under different low-carbon steels and is a potential tool for the future design of heat treatment processes and alloys.

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