Thermodynamics Of Thermal Decomposition Research Articles

Determination of pyrolysis and combustion properties of poly(vinylidene fluoride) using comprehensive modeling: Relating heat transfer to the intumescent char's porous structure

A systematic methodology, utilizing improved experimental and numerical techniques, is used to analyze the heat transfer within an intumescent char. Thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimetry were conducted on 4–7 mg samples to determine the kinetics and thermodynamics of thermal decomposition and heats of complete combustion of gaseous pyrolyzates. Subsequently, 0.07 m diameter disk-shaped samples were pyrolyzed in the Controlled Atmosphere Pyrolysis Apparatus II to characterize the thermal transport within the decomposing solid and evolving char layer. ThermaKin2Ds was employed to analyze all the experimental data, using inverse analysis techniques, and to perform predictions. Poly(vinylidene fluoride), a widely used intumescent polymer, was investigated in this study. The model parameterization process revealed notable instabilities in the sample surface emissivity during pyrolysis. However, the resulting model can predict the experimental gasification mass loss rate with a mean error of 29%. Additionally, the physical structure of the porous char was analyzed to enable the formulation of quantitative relationships between relevant thermal transport parameters and the intumescent char's structure. A prominent linear correlation was revealed during this exercise: the product of density and thermal conductivity was directly proportional to an increasing char porosity derived from image analysis.

Comparative analysis of pyrolysis and combustion of bisphenol A polycarbonate and poly(ether ether ketone) using two-dimensional modeling: A relation between thermal transport and the physical structure of the intumescent char

A quantitative understanding of the thermal transport within a growing intumescent char layer remains largely unsolved. The development of improved techniques to analyze charring and intumescent materials is necessary to investigate the physics of heat transfer within the char. To aid in this endeavor, a systematic methodology to parameterize comprehensive pyrolysis models for charring and intumescent materials is presented. Thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimetry were conducted on 4–7 mg samples to analyze the kinetics and thermodynamics of thermal decomposition and determine heats of complete combustion of gaseous pyrolyzates. A multi-step reaction mechanism, consisting of sequential first-order reactions, was constructed to capture the physical transformations and chemical reactions observed in the milligram-scale experiments. 0.07 m diameter disk-shaped samples were gasified in the Controlled Atmosphere Pyrolysis Apparatus II to characterize the thermal transport within the condensed phase material and evolving char layer. ThermaKin2Ds was employed to interpret the experimental data using inverse analysis techniques. Bisphenol A polycarbonate and poly(ether ether ketone), widely used intumescent materials, were analyzed within this study. The resulting two-dimensional models of bisphenol A polycarbonate and poly(ether ether ketone) were capable of predicting the experimental gasification mass loss rates with a mean error of 17.8% and 16.9%, respectively. An analysis of the char pore structure was also conducted from which quantitative relationships were subsequently developed between relevant thermal transport quantities and physical descriptors of the char's physical structure. Two prominent linear correlations were discovered: the char's effective thermal conductivity increased as a function of increasing volume-weighted mean pore diameter and the product of density and thermal conductivity increased with an increasing char porosity based on image analysis. Finally, a brief sensitivity analysis of the polycarbonate and poly(ether ether ketone) burning rates was conducted to determine which key material properties were responsible for the observed differences in flammability.

A quantitative comparison of the pyrolysis and combustion behavior of plasticized and rigid poly(vinyl chloride) using two-dimensional modeling

A methodology to parameterize (or calibrate) comprehensive pyrolysis models is demonstrated on plasticized and rigid poly(vinyl chloride) specimens. Thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimetry were employed to characterize the kinetics and thermodynamics of thermal decomposition and heats of complete combustion of gaseous decomposition products. Controlled Atmosphere Pyrolysis Apparatus II gasification experiments were utilized to determine the thermal transport parameters within the undecomposed material and developing char. A numerical framework, ThermaKin2Ds, was employed to analyze and simulate all gasification experimental results. The two-dimensional (axisymmetric) models of plasticized and rigid poly(vinyl chloride) were shown to reproduce the gasification mass loss rates with mean errors of less than 19%. Idealistic, one-dimensional simulations of large burning panels in the presence of external radiant heat flux were subsequently conducted using the fully parameterized pyrolysis models. A quantitative comparison between the simulated plasticized and rigid poly(vinyl chloride) large-scale burning indicated that these materials have similar mass loss rate histories. However, significant differences become apparent when the mass fluxes of gaseous decomposition products are converted to heat release rate; the heat release rate of plasticized poly(vinyl chloride) was found to be approximately a factor of 2 greater than that of the rigid poly(vinyl chloride).

Characterization of pyrolysis and combustion of rigid poly(vinyl chloride) using two-dimensional modeling

A quantitative understanding of an intumescent material’s reaction to fire is largely an unsolved challenge in the field of fire science. To advance fire modeling, a systematic methodology to fully parameterize a comprehensive pyrolysis model for charring and intumescent materials is presented. Thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimetry were employed to characterize the kinetics and thermodynamics of thermal decomposition and heats of complete combustion of gaseous pyrolyzates. A multi-step reaction mechanism, consisting of sequential steps, was constructed to capture the physical transformations and chemical reactions observed in all milligram-scale experiments. Controlled Atmosphere Pyrolysis Apparatus II gasification experiments were conducted on 0.07 m diameter disk-shaped samples to parameterize the thermal transport within the undecomposed material and developing char layer. A recently expanded fully verified and validated numerical framework, ThermaKin2Ds, was employed to inversely model the gasification experimental results. The model accounted for spatially non-uniform swelling of the sample and associated changes in the radiant heat exposure. Rigid poly(vinyl chloride), a widely used intumescent material, was analyzed in this work. The resulting two-dimensional model was shown to reproduce the gasification experimental unexposed surface temperatures and mass loss rates with a mean error of 3.9% and 12.6%, respectively. A preliminary analysis of the char pore structure was also conducted to determine the pore size distribution and char porosity. The resulting porosity based on the density of graphite and the porosity based on image analysis (including only the pores that are greater than 1 × 10−4 m in diameter) was found to be 0.96 and 0.53, respectively.

Preparation of LiZnPO4·H2O via a novel modified method and its non-isothermal kinetics and thermodynamics of thermal decomposition

The single phase α-LiZnPO4·H2O was directly synthesized via solid-state reaction at room temperature using LiH2PO4·H2O, ZnSO4·7H2O, and Na2CO3 as raw materials. XRD analysis showed that α-LiZnPO4·H2O was a compound with orthorhombic structure. The thermal process of α-LiZnPO4·H2O experienced two steps, which involved the dehydration of one crystal water molecule at first, and then the crystallization of LiZnPO4. The DTA curve had the one endothermic peak and one exothermic peak, respectively, corresponding to dehydration of α-LiZnPO4·H2O and crystallization of LiZnPO4. Based on the iterative iso-conversional procedure, the average values of the activation energies associated with the thermal dehydration of α-LiZnPO4·H2O, was determined to be 86.59 kJ mol−1. Dehydration of the crystal water molecule of α-LiZnPO4·H2O is single-step reaction mechanism. A method of multiple rate iso-temperature was used to define the most probable mechanism g(α) of the dehydration step. The dehydration step is contracting cylinder model (g(α) = 1−(1−α)1/2) and is controlled by phase boundary reaction mechanism. The pre-exponential factor A was obtained on the basis of Ea and g(α). Besides, the thermodynamic parameters (ΔS≠, ΔH≠, and ΔG≠) of the dehydration reaction of α-LiZnPO4·H2O were determined.