Diffusion theory of the thermal decomposition of diatomic molecules

A quasi-stationary solution of the Fokker—Planck equation for definite limiting conditions, describing the process of thermal decomposition of diatomic molecules in a light inert gas, has been considered. The rate of thermal dissociation of Morse oscillators has been calculated for a relatively arbitrary intermolecular interaction potential.     

Direct mass spectrometry of polymers. XIV. Thermal fragmentation processes in poly-schiff bases

The thermal fragmentation processes in poly-Schiff bases have been investigated by direct pyrolysis–mass spectrometry. The mass spectral data show that the thermal fragmentation occurring in the polymers under investigation is characterized by hydrogen transfer reactions. In the case of a totally aromatic poly-Schiff base (polymer I ), the thermal fragmentation process involves hydrogen transfer irom the methyne group with formation of fragments bearing nitrile and/or phenyl end groups. In the case of aromatic-aliphatic poly-Schiff bases (polymers II–IV ), the hydrogen transfer process occurs from the aliphatic methylene groups. The latter process involves a lower energy and therefore occurs at lower temperatures with respect to the totally aromatic polymer I , with formation of thermal fragments bearing olefin and/or imine end groups. Beside these fragments, several thermal fragmentation compounds are also evolved by multiple hydrogen transfer reactions.     

Thermal degradation of silane crosslinked unplasticized PVC

The thermal decomposition behaviour of rigid PVC, crosslinked using bis(γ-trimethoxysilylpropyl)amine as crosslinking agent has been studied. Different thermal stabilizers (tin and lead based) have been used with different crosslinking agent concentrations, and the influence of these factors on the decomposition behaviour in inert atmosphere studied. Results obtained have shown that the main effect of aminosilane is an advance of the first stage of the PVC degradation (i.e. the dehydrochlorination process). Moreover, samples with different concentrations of silane, and at different stages of their processing (i.e. after milling, pressing, crosslinking) have also been used in order to elucidate the influence of these factors on their thermal behaviour. A quantitative kinetic model has been developed and the corresponding kinetic constants have been obtained by modelling the experimental thermogravimetric data. The kinetic parameters obtained have revealed a reduction in the apparent activation energy of the hydrogen chloride loss process, which has shown to be markedly dependent on the thermal stabilizer used.     

Hydrothermal ageing of radiation cured epoxy resin-polyether sulfone blends as matrices for structural composites

The hydrothermal ageing of epoxy-thermoplastic blends, used as matrices for carbon fibre composites, cured by electron beam, has been studied. Two different thermoplastic percentages have been adopted. A suitable choice of both curing process and formulation parameters allows to carry out irradiation at mild temperature with several advantages, coming from a “non thermal” process, for both the final properties of the materials and the environment. Nevertheless the occurring of vitrification phenomena needs the use of a short thermal treatment after irradiation on the already solid materials, in order to complete the cure reactions. Radiation cured epoxy based matrices have been subjected to a thermal and moisture absorption ageing treatment and its influence on the thermal and mechanical properties has been investigated through dynamic mechanical thermal analysis and fracture toughness tests. The results have been interpreted on the basis of the different curing degree reached by the investigated systems and in the light of their morphological structures. Plasticization, thermal curing and degradation reactions occur in different extent depending on the kind of the material. In particular, for fracture properties, a better resistance to ageing is shown by the system at higher thermoplastic concentration.     

Combined kinetic analysis of thermal degradation of polymeric materials under any thermal pathway

Combined kinetic analysis has been applied for the first time to the thermal degradation of polymeric materials. The combined kinetic analysis allows the determination of the kinetic parameters from the simultaneous analysis of a set of experimental curves recorded under any thermal schedule. The method does not make any assumptions about the kinetic model or activation energy and allows analysis even when the process does not follow one of the ideal kinetic models already proposed in the literature. In the present paper the kinetics of the thermal degradation of both polytetrafluoroethylene (PTFE) and polyethylene (PE) have been analysed. It has been concluded, without previous assumptions on the kinetic model, that the thermal degradation of PTFE obeys a first order kinetic law, while the thermal degradation of PE follows a diffusion-controlled kinetic model.     

Effect of resin infiltration on fumed silica-based thermal insulations

The thermal conductivities and the strengths of fumed silica-based thermal insulations prepared by the dry process and the resin infiltration method have been studied. Infiltration of the insulation samples prepared by dry processing of mixtures, consisting of fumed silica, ceramic fiber and a SiC opacifier, was performed to strengthen their binding structure. The high temperature thermal conductivities for the insulation samples obtained by the resin infiltration method were similar to those for the samples prepared by the dry process. On the other hand, the bending strengths for the former were superior to those for the latter. However, the resin-infiltrated samples were more brittle than the samples obtained by the dry process due to the occurrence of rigid bonding between the fibers and the infiltrated resin in the porous insulations. The thermosetting resin solution infiltration method appeared to be applicable to producing a dust-free fumed silica-based thermal insulation.     

Application of heat pipe technology in thermal analysis of metals

Summary Thermal analysis has been used in foundry applications to assess the quality of the melt before casting. The high-end thermal analysis techniques such as DSC or DTA are expensive and not suitable for foundry applications. The Computer-Aided Cooling Curve Analysis (CA-CCA) method based on one thermocouple has been widely used as a batch process with poor control over heat extraction and cooling rates during solidification. A heat pipe apparatus has been developed as a thermal analysis tool. The apparatus can assess the melt quality more accurately, as well as, allow for better control of heating and cooling rates. Moreover, the solidification process can be modeled more accurately, and thus the casting parameters affecting the casting quality can be closely simulated and consequently controlled. In this paper the principles of a heat-pipe assisted thermal analysis system are highlighted. The advantages of the new system are described and the possibility of its adoption in melt assessments is discussed.     

Mechanisms of thermal decomposition in totally aromatic polyurethanes

The primary fragmentation mechanisms in the thermal decomposition of polyurethanes were studied in detail by direct pyrolysis into the mass spectrometer. The remarkable difference in the thermal stability of the two totally aromatic polyurethanes I and II (Fig. 1) reflects their different decomposition pathways. In fact, polymer I undergoes a depolycondensation process that yields diiscyanate and dialcohol as primary thermal fragments. The thermal decomposition of polymer II proceeds instead via the formation of a cyclic compound that has been isolated and characterized. In contrast, open-chain fragments are generated in the thermal decomposition of the partially aliphatic polymer III.     

稀土氨基酸配合物RE(Val)Cl3•6H2O(RE = Nd，Sm)的热分解动力学

合成了稀土氨基酸配合物晶体——三氯化缬氨酸六水合钕、钐，对合成样品进行了EDTA滴定、元素分析、红外光谱分析、热重、差热分析以及熔点测定，推测了配合物的热分解机理，采用Achar法和Coats-Redfern法研究了配合物热分解的非等温动力学过程，给出了各配合物样品失水阶段第一步反应和氨基酸骨架断裂阶段第一步反应的活化能（E）、指前因子的对数值（ln(A)）及热分解反应动力学方程式.     

TG-FTIR study of the thermal degradation of polyoxymethylene (POM)/thermoplastic polyurethane (TPU) blends

A series of blends of polyoxymethylene (POM)/thermoplastic polyesterurethane (TPU) has been obtained by mechanical processing using a double screw extruder. The thermal stability and the thermal degradation profiles of POM/TPU blends were investigated by thermogravimetric analysis (TG) coupled on-line with Fourier transform infrared spectroscopy (FTIR). It was found that incorporation of TPU into POM matrix resulted in increase of thermal stability of blends in comparison with pristine materials. The thermal degradation of TPU in inert gas atmosphere proceeds in two steps while the thermal degradation of POM is basically a one step process with a substage in a higher temperature range. The most abundant volatile products of the thermal degradation were identified; the possibly routes of their formation have been presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study on thermal behavior of thermooxidized poly(vinyl formal)

The thermal behavior of thermooxidized poly(vinyl formal) has been investigated by means of thermogravimetry, derivative thermogravimetry, and differential thermal analysis. As a result, it has been clarified (1) that thermal decomposition is composed of three weight loss processes, (2) that, when investigating the ratic of percentage of weight remaining in each process, the behavior differs for each both before and after the thermooxidizing time of 2–4 h; the second weight loss process caused by formation of crosslinking structure prevails in the initial stage of thermooxidation while the first weight loss process caused by decomposition of various types of thermooxidation products such as unsaturated bonds and crosslinking prevails as the thermooxidation proceeds, and (3) that the volume of carbonaceous residue produced as the thermooxidation advances increases about 4 times. When kinetic parameters have been evaluated by applying the Coasts and Redfern method to each weight loss process, on the other hand, it is concluded (1) that each order of reaction is first and (2) that the value of activation energy in the third process of carbonization and burning reaction is substantially lowered as the process of the thermooxidation advances.     

A Novel Thermo-Optical Measuring System for the in situ Study of Sintering Processes

A novel thermo-optical measuring system (TOM) is described, which is able to monitor simultaneously and in situ thermal and optical properties of materials during the process of sintering. These are thermal diffusivity, heat capacity, thermal conductivity, transfer of heat radiation and scattering of light. Additionally, the geometric shrinkage is recorded by a non-contact optical dilatometer. The system has been designed for an efficient optimization of time-temperature-atmosphere cycles in sintering processes. Therefore, in the construction of the TOM system transferability of process parameters to other sintering furnaces is an important requirement. Due to this, compromises have been necessary in the layout of the measuring methods. Nevertheless, a high resolution was achieved for the distinction of different sintering states. Besides dilatometry, thermal diffusivity measurement by a laser-flash technique is a promising tool for the in situ monitoring of changes in microstructure during sintering. This revised version was published online in July 2006 with corrections to the Cover Date.     

The specifics of radiation telomerization of tetrafluoroethylene in chlorinated solvents and telomer properties

Radiation telomerization of tetrafluoroethylene in butyl chloride, chloroform, and carbon tetrachloride has been investigated. The chain length of telomers and their solubility and thermal stability depend on the initial monomer concentration and telogen properties. In the case of telomerization in chloroform and carbon tetrachloride, the yield, the chain length, and the thermal stability of the telomers are significantly higher than those in butyl chloride, in which the process is less efficient but soluble telomers having a short chain length and exhibiting quite high thermal resistance are produced. The molecular structure of the telomers has been studied by IR spectroscopy.     

The thermal dissociation of diatomic molecules at high temperatures

On the basis of a solution of gas-kinetic equations describing the population of molecules (cut-off harmonic oscillators) at various oscillatory levels, the process of thermal dissociation has been analyzed. It has been shown that thermal dissociation, in addition to disturbing the Boltzmann distribution, leads to a reduction in the vibrational temperature compared with the translational one. This affects to a considerable extent the rate of thermal dissociation, and also the process of vibrational relaxation. The question of the applicability of the well-known relation of statistical thermodynamics connecting the rate constants of forward and back reactions has also been analyzed. The results obtained agree qualitatively with the experimental data.     

Mechanism of the thermal dehydrochlorination of poly(vinyl chloride) models in the liquid phase

The thermal dehydrochlorination of model compounds of PVC has been investigated in the liquid phase in an inert atmosphere. Electrophilic catalysis and the effect of various solvents on this reaction have been studied. It has been found that the electron-accepting power of the reaction medium is the decisive rate-determining factor, while the dielectric constant comes second. A mechanism of thermal dehydrochlorination has been suggested, in which a reaction between the substrate and the proton giving rise to the carbonium ion is the rate-determining step for the whole process.     

Influence of surface activation by plasma and nanoparticle adsorption on the morphology, thermal stability and combustion behavior of PET fabrics

Plasma surface activation at different process parameters (namely, power and etching time) has been combined with nanoparticle adsorption (i.e., a natural montmorillonite) in order to improve the thermal stability and flame retardancy of PET fabrics. Scanning electron microscopy coupled to elemental analysis has put in evidence a direct relationship between the distribution of nanoparticles on fibers and process parameters. The presence of the above nanoparticles affects the thermal stability of fabrics in air, as assessed by thermogravimetric analysis: a delay of the mass loss process has been observed for the treated samples.Combustion behavior has been investigated by cone calorimetry: plasma activated fabrics have shown a remarkable improvement in terms of time to ignition (up to 104%) and a slight reduction of the heat release rate (ca. 10%) as compared to neat PET.     

硫酸氢钾(KHSO4,A.R.)的低温热容和热化学性质

硫酸氢钾（ＫＨＳＯ4,Ａ．Ｒ）是一种重要的无机化工原料。在化肥工业中,它是生产复合肥硫酸铵钾（ＫＮＨ４ＳＯ４）的主要原料之一。为了找到工业上生产复合肥硫酸铵钾的最佳工艺条件,提高其产率和经济效益,并且开发其新的应用领域,迫切需要该化合物准确的热力学数据作为理论分析的依据。 硫酸氢钾的导热系数,溶解度,熔点等部分热物性数据［１－３］已有报道,但是,迄今为止,文献中未见到它的低温热容和热分解过程的详细报道。本文用精密自动绝热热量计直接测定了硫酸氢钾在７８－３７３Ｋ温区的热容,并且将实验热容值用最小二乘…     

High temperature radiation-induced reduction of no

The impact of ionising radiation on the kinetics of thermal De---NO_x process^† is discussed using the simplified mechanism. It has been found that the combined process as well as thermal De---NO_xoperates in a relatively narrow temperature window. The window to be both broader and shifted to lower temperatures in the combined process. The reduction becomes practically completed in about time τ_r = 0.1 s even at T 1100 K where the thermal reaction is slow to be used. The mechanisms and rate parameters of the combined radiation-induced De---NO_x process is illustrated.     

Heat Transfer Enhancement on the Adsorber of Adsorption Heat Pump

Three methods for improving the heat transfer of the adsorber have been developed in this paper. First, an electrically conductive polyaniline was applied for enhancing the thermal conductivity of adsorbent bed. A thermally conductive composite of polyaniline and adsorbent was prepared by chemical oxidative in situ polymerization of aniline onto the surface of adsorbent particles. A thin thermal conducting net on the surface of the adsorbent particles was grown. The experimental results indicated that the thermal conductivity of this composite could be increased to approximately 4 times that of the raw adsorbent. Second, the adsorbent bed was shaped by a compressing process. This process can reduce the thermal resistance among the adsorbent particles and the contact thermal resistance between the adsorbent bed and the heat exchanger. The thermal conductivity of the shaped adsorbent bed itself from the tests can be increased 30% when the density of the solid adsorbent bed is 1.5 times that of its original density. Furthermore, the adsorption capacity of the above treated adsorbent did not decrease obviously. Third, a proper design of adsorber has been introduced and analyzed. Further tests of this design will be conducted soon.     

Kinetics of thermal degradation and thermal oxidative degradation of poly(p-dioxanone)

The kinetics of the thermal degradation and thermal oxidative degradation of poly(p-dioxanone) (PPDO) were investigated by thermogravimetric analysis. Kissinger method, Friedman method, Flynn-Wall-Ozawa method and Coats-Redfern method have been used to determine the activation energies of PPDO degradation. The results showed that the thermal stability of PPDO in pure nitrogen is higher than that in air atmosphere. The analyses of the solid-state processes mechanism of PPDO by Coats-Redfern method and Criado et al. method showed: the thermal degradation process of PPDO goes to a mechanism involving random nucleation with one nucleus on the individual particle (F₁ mechanism); otherwise, the thermal oxidative degradation process of PPDO is corresponding to a nucleation and growth mechanism (A₂ mechanism).