Kinetics Of Heat Treatment Research Articles

Modeling of Thermal Conductivity in a Medium with Phase Transition with a Moving Boundary of Phase Change

This work is devoted to the theoretical study of the effect of the phase interface motion on thermal conductivity in a liquid-solid nonlinear medium with a phase transition. The problem under consideration deals with the Stefan problems. Its most significant feature is the jump in the phase properties at separation of their moving boundaries. The objective was achieved by solving the following tasks: the construction of the process mathematical model based on its cell representation and with the use of the Markov chain theory mathematical apparatus, performing numerical experiments with the developed model, demonstrating its operability and the possibility to achieve the set goal. The most significant scientific results were as follows. First was an algorithm for the construction of a cell mathematical model of nonlinear thermal conductivity in a phase transitions medium with a moving phase interface for domains of a canonical shape (plane wall, cylinder, ball). Second, the results of the numerical experiments, showing that the jump of properties affected greatly the kinetics of the process. The significance of the results obtained consisted in the development of a simple but informative mathematical model of the media heat treatment kinetics with phase transformations, available for a direct use in the engineering practice. The proposed algorithm for constructing the model can be effectively used in prediction the open water pipes freezing in cold regions, in modeling the heat treatment of metals, in choosing the freezing modes of food products for a long-term storage, and other thermo-physical processes.

Thermal and Mechanical Activation of Sericite for Recovery of Potash Values

Sericite sample having potash (K2O) content ~ 9% was evaluated as a source of potash. The mineralogical studies revealed the fine grain structure of sericite containing muscovite, orthoclase, and phlogopite as the major potash bearing phases. The feed sample directly leached in different lixiviants yielded low potash dissolution values. Planetary ball milling was carried out to liberate the potash values from silicate matrix. It was observed that the K-bearing phases were quite stable, with milling action of about 8 h yielded ~ 30% values. The heat treatment of sericite with NaOH resulted in ~ 90% K-dissolution at optimum conditions (60% flux, 600 °C, 30 min) with the formation of sodium silicate and kalsilite. Mechanical activation had a positive effect on heat treatment kinetics as temperature decreased from 600 to 250 °C with ~ 100% potash recovery. CaCl2 and Na2CO3 were also evaluated as flux and based on a comparison of process variables and yield, NaOH was found to be the best flux.

Heat treatment kinetics using three-stage approach for sustainable wood material production

The purpose of this study is to develop a numerical tool to predict the mass loss of a wood board during heat treatment as a marker of the process advancement. Mass loss dynamics during the wood heat treatment is experimentally obtained using a specially conceived equipment. The investigation method is applied on large scale wood samples whose radial and transvers dimensions are close to the boards used in industry. A two-step reaction mechanism is adopted to describe the behavior of wood thermodegradation. Model parameters are obtained by fitting the experimental data according to a new approach developed in this study for their optimal determination. The originality of the implemented modelling strategy is the establishment of a three-stage approach based on the analysis of wood thermal sensitivity depending on the treatment temperature range. Model equations are solved numerically by the commercial package Matlab® software. A good agreement is achieved between the numerical predictions and the experimental data. The developed model and established kinetics can be used for heat treatment process and reactor design in industry to produce wood materials for their applications.

Overall Kinetics of Heat Treatment of Municipal Solid Waste

A mathematical model of the overall kinetics of heat treatment of municipal solid waste was developed. The model considers the main initial substances and products of the reaction of municipal solid waste treatment at high temperatures (1300–1500°C) in a tubular flow reactor.

Strengthening mechanisms and deformation behavior of cryomilled Al–Cu–Mg–Ag alloy

In the last decade, the commercially available heat-treatable aluminum alloy (AA) 2139 (Al–Cu–Mg–Ag) has generated interest within the aerospace and defense communities because of its high strength and damage tolerance as compared to those of other AA 2XXX alloys. In this work we investigate the possibility of enhancing the performance of AA 2139 via a nanostructuring approach involving the consolidation of cryomilled powders. For comparison purposes, two types of feedstock powders (cryomilled and unmilled, gas-atomized powder), were consolidated via dual mode dynamic forging. Our results show that, following heat treatment (HT), the strength of the cryomilled material increases in the range of ∼25% to ∼200% relative to that of the unmilled counterparts, depending on specific processing parameters. We present microstructural data, including grain size and precipitate chemistry, to provide insight into the underlying strengthening mechanisms. Vickers microhardess tests are used to evaluate peak heat treatments, and tensile testing is performed to characterize mechanical behavior. The kinetics of precipitation, strengthening mechanisms and deformation behavior are discussed. It is proposed that the combination of elemental segregation with the presence of oxides along grain boundaries, both facilitated by enhanced diffusion paths, are responsible for the observed change in HT kinetics in the cryomilled material.

Poplar wood heat treatment: effect of air ventilation rate and initial moisture content on reaction kinetics, physical and mechanical properties

The kinetics of heat treatment as well as its effect on some physical and mechanical properties of poplar wood (Populus alba L.) were analysed in this research. Kinetic tests were performed at different treatment temperatures and two different air ventilation settings [low and high air exchange rate (AER) with the exterior]. The treatment kinetics was studied, starting from the oven-dry condition, according to the mass loss during time. The time–temperature equivalency was checked, the mass loss versus time formalised through a master curve. The analysis clearly showed how the heat treatment at low and high AER presents different degradation kinetics even if similar activation energy values were found. Some physical and mechanical properties of wood after treatments up to a mass loss of 7 and 10 % starting from oven-dry or standard environmental conditions state were also studied. All of the treated samples showed statistically significant differences compared to the untreated one. The treatments performed at 7 or 10 % of dry mass loss showed homogeneous behaviour. The same tendency was observed for the treatments starting at oven-dry or standard environmental conditions with the exception of Young’s modulus, which resulted in smaller reductions in wet starting condition when compared to dry samples.