Computational Thermodynamics and Kinetics in Materials Modelling and Simulations

Over the past two decades, Computational Thermodynamics and Kinetics have been tremendously contributed to materials modeling and simulations and the demands on quantitative conceptual design and processing of various advanced materials arisen from various industries and academic institutions involved in materials manufacturing, engineering and applications are still rapidly increasing

Numerical simulation of cyclic oxidation kinetics with automatic fitting of experimental data

This paper proposes a model, based on a Monte Carlo method, to assess cyclic oxidation tests. The numerical code fits automatically the experimental net mass change curves. Oxidation kinetics are identified as well as the relationship between spalling and local oxide thickness or time. The modelling is applied to cyclic oxidation of NiPtAl single crystals at 1150 °C in dry air

Modelling the kinetics of thermal inactivation of apple polyphenoloxidase

The enzymatic browning of fruits and vegetables caused by mechanical injury during postharvest storage or processing is initiated by the catalytic action of polyphenoloxidase (PPO). A bleaching treatment prior to processing is still considered mostly effective in inhibiting the catalytic activity of PPO, and thus controlling undesirable enzymatic browning. In this work, different mathematical routines were assessed in terms of their adequacy to describe the thermal inactivation of PPO from Golden apples over a range of temperatures from 62.5 to 72.5 ºC. The classical approach to kinetic modelling of the decay activity of apple PPO, commonly reported to follow a first-order model, employs a two-step procedure, in which the model parameters are individually obtained, by each temperature studied, using non-linear or linear regressions. Thereafter, the estimated parameters are further used to calculate their temperature dependence. Alternatively, a one-step method provides a regression fit to all experimental data sets, with the temperature dependence equation being directly built in the kinetic model. This fitting technique thus, (a) avoids the estimation of intermediate parameters and, (b) substantially increases the degrees of freedom and hence the precision of parameters’ estimates. Within this issue was further explored the logarithmic transformation of the mathematical equations used on the adequacy of the model to describe experimental data. In all cases non-weighted least-squares regression procedures were used. Both the examination and criticism of the current modelling strategies were done by assessing statistical data obtained, such as the confidence intervals of the estimates, correlation coefficients, sum of squares, and residuals normality

Markov chain aggregation and its application to rule-based modelling

Rule-based modelling allows to represent molecular interactions in a compact and natural way. The underlying molecular dynamics, by the laws of stochastic chemical kinetics, behaves as a continuous-time Markov chain. However, this Markov chain enumerates all possible reaction mixtures, rendering the analysis of the chain computationally demanding and often prohibitive in practice. We here describe how it is possible to efficiently find a smaller, aggregate chain, which preserves certain properties of the original one. Formal methods and lumpability notions are used to define algorithms for automated and efficient construction of such smaller chains (without ever constructing the original ones). We here illustrate the method on an example and we discuss the applicability of the method in the context of modelling large signalling pathways

Hydration Modeling of Calcium Sulphates

The CEMHYD3D model has been extended at the University of Twente in the last ten years [1,2]. At present the cement hydration model is extended for the use of gypsum. Although gypsum was present in the model already, the model was not suitable for high contents of gypsum and did not include the transitions between the different calcium sulphate phases (anhydrite, hemihydrate and gypsum). Besides that gypsum was seen as intermediate phase instead of a final phase. The presented model addresses these problems and has the possibility to simulate the microstructure development of gypsum, including reaction kinetics (dissolution, diffusion and precipitation) and the formation of gypsum needles. The model enables multi-time modelling which means the possibility to zoom in and out on the hydration process with respect to time. Multi-time modelling enables the user to study the hydration in more detail in both the early phase (hours) and on the long term (years). This modelling is needed, since the hydration of calcium sulphates is very short compared to that of cement

Hydration modelling of Calcium Sulphates

The CEMHYD3D model has been extended at the University of Twente in last ten years1,2. At present the cement hydration model is extended for the use of gypsum. Although gypsum was present in the model already, the model was not suitable for high contents of gypsum and did not include the transitions between the different calcium sulphate phases (anhydrite, hemihydrate and gypsum). Besides that gypsum was seen as intermediate phase instead of a\ud final phase. The presented model addresses these problems and has the possibility to simulate the microstructure development of gypsum, including reaction kinetics (dissolution, diffusion and precipitation) and the formation of gypsum needles. The model enables multi-time modelling which means the possibility to zoom in and out on the hydration process with respect to time. Multi-time modelling enables the user to study the hydration in more detail in both the early phase (hours) and on the long term (years). This modelling is needed, since the hydration of calcium sulphates is very short compared to that of cement

Influence of chemical reaction kinetics on electrokinetic remediation modelling results

A numerical model describing transport of multiple species and chemical reactions during electrokinetic treatment is presented. The transport mechanisms included in the model were electromigration and electroosmosis. The chemical reactions taken into account were water electrolysis at the electrodes, aqueous species complexation, precipitation, and dissolution. The model was applied to simulate experimental data from an acid-enhanced electrokinetic treatment of a Pb-contaminated calcareous soil. The kinetics of the main pH buffering process (i.e., calcite dissolution) was taken into account and its time-dependent behavior was described by a rate law. The influence of kinetics was evaluated by comparing the results from a set of simulations in which calcite dissolution was implemented considering thermodynamic equilibrium and another set in which the same reaction was described by the rate law. The results show that the prediction capability of the model significantly improves when the kinetic rate is taken into account.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Interaction Between Hot Carrier Aging and PBTI Degradation in nMOSFETs: Characterization, Modelling and Lifetime Prediction

Modelling of the interaction between Hot Carrier Aging (HCA) and Positive Bias Temperature Instability (PBTI) has been considered as one of the main challenges in nanoscale CMOS circuit design. Previous works were mainly based on separate HCA and PBTI instead of Interacted HCA-PBTI Degradation (IHPD). The key advance of this work is to develop a methodology that enables accurate modelling of IHPD through understanding the charging/discharging and generation kinetics of different types of defects during the interaction between HCA and PBTI. It is found that degradation during alternating HCA and PBTI stress cannot be modelled by independent HCI/PBTI. Different stress sequence, i.e. HCA-PBTI-HCA and PBTI-HCA-PBTI, lead to completely different degradation kinetics. Based on the Cyclic Anti-neutralization Model (CAM), for the first time, IHPD has been accurately modelled for both short and long channel devices. Complex degradation mechanisms and kinetics can be well explained by our model. Our results show that device lifetime can be underestimated by one decade without considering interaction

Cyclic thermogravimetry of TBC systems

The previously developed cyclic thermogravimetry analysis (CTGA) method is applied to the cyclic oxidation at 1100 °C of ZrO2–Y2O3/NiPtAl or NiCoCrAlYTa/single crystal nickel-base AM3 superalloy TBC systems. Cyclic thermogravimetry with fast heating and cooling and high accuracy in mass measurement allows to measure oxidation kinetics of the bond coating and also to detect and quantify the occurrence of the top coating cracking and spalling. The resulting data could be used later on, for time of life modelling of TBC systems

The challenges of nanostructures for theory

It is tempting to believe that modelling in nanotechnology is much the same as that for conventional solid-state physics. However, important areas of nanotechnology address different systems. The mechanics of DNA (for instance) resembles spaghetti more than silicon, the statistical physics needed is often not carrier statistics, and the role of viscosity (the low Reynolds number limit) is not always the familiar one. The idea of equilibrium may be irrelevant, as the kinetics of nonequilibrium (perhaps quasi-steady state) can be crucial. Even when the issues are limited to nanoscale structures (rather than functions), there is a complex range of ideas. Some features, like elasticity and electrostatic energies, have clear macroscopic analogies, but different questions emerge, such as the accuracy of self-organisation. Others concepts like epitaxy and templating are usually micro- or mesostructural. Some of the ideas, which emerge in modelling for the nanoscale, suggest parallels between molecular motors and recombination enhanced diffusion in semiconductors. (C) 2002 Elsevier Science B.V. All rights reserved