Neural networks for kinetic parameters determination, signal filtering and deconvolution in thermal analysis

Feedforward neural networks have been used for kinetic parameters determination and signal filtering in differential scanning calorimetry. The proper learning function was chosen and the network topology was optimized, using an empiric procedure. The learning process was achieved using simulated thermoanalytical curves. The resilient-propagation algorithm have led to the best minimization of the error computed over all the patterns. Relative errors on the thermodynamic and kinetic parameters were evaluated and compared to those obtained with the usual thermal analysis methods (single scan methods). The errors are much lower, especially in presence of noisy signals. Then, our program was adapted to simulate thermal effects with known thermodynamic and kinetic parameters, generated electrically, using a PC computer and an electronic interface on the serial port. These thermal effects have been generated by using an inconel thread.     

A study of thermograms obtained through differential scanning calorimetry of an emulsion of a supercooled liquid

To study the breakdown of the supercooling of drops of liquids dispersed in an emulsifying medium, the heat involved at the time of the change in state has been measured by differential scanning calorimetry (DSC).In order to determine the number of drops crystallizing either as a function of temperature and of time during a continuous cooling or as a function of time at a fixed temperature, the heat generated by the thermal phenomenon itself has been determined by an analysis of the principle of DSC and the basic equations of the apparatus which has been used. The limits of the validity of the methods exposed have also been indicated.Provided that the signals obtained during either cooling or heating are correctly (and differently) delimited, it has been proved possible to measure directly the total heat of crystallization.     

Thermal oxidative destruction of complexes of heterocyclic N-oxides with Zn(II)tetra-phenylporphyrin

Thermogravimetry, differential thermal analysis and differential scanning calorimetry were applied for investigation of molecular complexes of heterocyclic N-oxide with zinc(II)tetraphenylporphyrin. The kinetic characteristics of the process of the thermal oxidative destruction for individual compounds and their molecular complexes have been calculated. The obtained results indicate that the complex formation of ZnTPhP with heteroaromatic N-oxides leads to an increase of the thermal stability both the metalloporphyrin and the ligands. It has been shown that the stability of the molecular complexes of ZnTPhP with heteroaromatic N-oxides depends on basicity of the coordinated ligand.     

Differential thermal analysis and temperature profile analysis of pyrotechnic delay systems: Slow burning mixtures of boron and potassium dichromate

The slow burning pyrotechnic reaction between boron and potassium dichromate has been studied by differential thermal analysis and temperature profile analysis. The latter technique in which the combustion process is studied directly, shows the presence of two reaction stages and validates the results from differential thermal analysis obtained under non-ignition conditions. In the first stage potassium dichromate is reduced by boron to form potassium chromate. Differential thermal analysis shows that the reaction takes place below the melting temperature of potassium dichromate and becomes much more rapid above this temperature. The second stage which occurs in the region of 1000 K involves the reaction of potassium chromate with more boron. The first stage acts as a trigger for the second and it is this latter stage which propagates the combustion.     

THERMAL DECOMPOSITION OF METAL COMPLEXES. MIXED COMPLEXES OF DIVALENT TRANSITION METALS WITH α-NITROKETONES

Abstract

The thermal behaviour of mixed complexes containing transition metals, α-nitroketones and pyridine or ethanol was investigated by thermogravimetric analysis (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The values of the activation energies and the enthalpies for the dissociation processes have been calculated in high vacuum and isothermal conditions. Comments are made on the obtained heats and correlations with structural characteristics are looked for.     

Results of a joint trial on the method of the differential thermal analysis in the temperature range from 25 to 1000°C

For settling the question to what degree standardization of differential thermal analysis (DTA) is feasible by a joint trial of different laboratories, DTA-measurements on temperature-standard-substances have been carried out. The results are comparable with those obtained on identical substances by the International Confederation for Thermal Analysis and the National Bureau of Standards. A statistic evaluation of the DTA-procedures of the individual laboratories shows that the preponderant number of laboratories is achieving data which could be considered to belong to the same basic set. As 2 common standard deviation of the procedure of differential thermal analysis in the temperature interval of 25 to 1000°C a value of 3.6 K has been ascertained.     

Crystal growth and characterization of N-hydroxyphthalimide (C8H5NO3) crystal

Single crystals of N-hydroxyphthalimide (NHPH) were obtained from saturated aqueous solutions of methanol and acetonitrile by slow cooling method. The grown crystals were bright and transparent. From the crystal structure analysis it can be inferred that the crystal belongs to monoclinic system. The grown crystals were subjected to FTIR analysis for vibrational assignments. The optical transmission spectra showed excellent transmittance from 200 to 1100nm. The thermal stability and thermal decomposition of NHPH crystal have been investigated by means of thermogravimetric analysis and differential thermal analysis.     

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.     

Glass-forming ability in the GeSbTeSe quaternary system

The glass—forming regions in the quaternary system GeSbTeSe have been obtained for quenching in air and for a constant cooling rate of 5°C min^?1. The boundaries of the glass-forming regions and the thermal behaviour of the samples have been deduced from differential thermal analysis and X-ray diffraction. The results may be compared with some limited determinations of glass-forming ability in TeSe, GeTe, GeTeSe and GeSbSe systems, allowing for the fact that in the present work the experimental parameters for preparing and quenching the melts are identical for all the compositions studied. The formation and stability of glasses is discussed in terms of the obtained glass-forming regions and the observed thermal behaviour in differential thermal analysis measurements. Potential-device quality memory and switching compositions are suggested.     

Synthesis and thermal stability of xylene-formaldehyde resins

o-,p- andm-xylene have been condensed with formaldehyde using paratoluene sulphonic acid as a catalyst and acetic acid/acetic anhydride as a solvent. The xylene-formaldehyde resins thus obtained have been characterised by IR and NMR spectra. The average molecular weight of the resin samples was determined by vapour pressure osmometry. Kinetic parameters were determined by differential thermal analysis, thermogravimetry and differential scanning calorimetry.     

Studies on selenates: II. Thermal decomposition of heavier rare-earth selenate hydrates

Thermogravimetry, differential thermal analysis and differential thermogravimetry have been used to study the decomposition of hydrated selenates of heavier rare-earths and yttrium. Based on the results obtained, mechanisms of dehydration-decomposition have been proposed. Dehydration temperatures of the hydrated selenates show a gradual decrease with order of rare-earth elements.     

New Adventures in Thermal Analysis

This paper describes recent advances in thermal analysis instrumentation which combine the high resolution imaging capabilities of the atomic force microscope with physical characterisation by thermal analysis. Images of the surface may be obtained according to the specimen's thermal conductivity and thermal expansivity differences in addition to the usual topographic relief. Localised equivalents of modulated temperature differential scanning calorimetry, thermomechanical and dynamic mechanical analysis have been developed with a spatial resolution of a few micrometres. A form of localised thermogravimetry-evolved gas analysis has also been demonstrated. The same instrument configuration can be adapted to allow IR microspectrometry at a resolution better than the optical diffraction limit. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and properties of tetragonal silver(I,III) oxide,AgO

The pure tetragonal AgO modification was obtained by ozonation of a suspension of Ag₂O or Ag in stirred water. The oxidation proceeds in two steps from Ag, with the intermediary formation of Ag₂O. An oxygen content corresponding to the formula AgO_1.15 is obtained when the bubbling of ozone is maintained for a long time. The thermal decomposition of tetragonal AgO is complex and has been studied by thermogravimetry and differential thermal analysis.     

Recommendations for reporting thermal analysis data

Recommendations for reporting of thermal analysis data relating to differential thermal analysis, differential scanning calorimetry, thermogravimetry and thermomechanical analysis were developed some two decades ago. Since that time there have been significant changes in the techniques, as well as a greater understanding of the effect of experimental variables on the results obtained from thermonalytical experiments. This paper reports on a preliminary review of the Recommendations by the Task Group established by the ICTAC Committee on Standardization to undertake their revision. Particular attention has been paid to the properties of the sample; control of the instrument variables; and the data acquisition and manipulation by computers.     

Some properties of polyethylene terephthalate-acrylic acid copolymers and ionomers

Acrylic acid has been grafted to polyethylene terephthalate (PET) by mutual irradiation, and the resulting copolymers converted to their sodium, calcium and lead salts. The electrical surface resistance of PET was reduced by grafting, the effect being most pronounced for the copolymer in the form of its sodium salt. The thermal stability of PET was studied by thermogravimetric analysis and differential thermal analysis, and activation energies were derived for the thermal decompositions; similar studies were made for the acidic and ionomeric copolymers. The stability of acidic copolymer was found to be lower than that of ungrafted PET; enhanced thermal stability was obtained only in the metallated copolymers.     

Thermal characterisation of Australian oil shales

There has been a significant research effort on the development of an oil industry based on Australian oil shales. However, to date the research has been based mainly on the processing aspects of oil shale. The thermal analyses of oil shales, while having been the subject of many studies, have been limited to some extent by instrumentation and analytical techniques. This paper reports on thermal analysis studies utilising traditional thermogravimetry/differential thermal analysis (TG/DTA) and differential scanning calorimetry (DSC). The application of modern thermal analysis techniques such as high resolution TG (HRTG) and modulated differential scanning calorimetry (MDSC) is also examined and compared to the traditional methods.     

Applicability of the du pont 900 DTA apparatus in quantitative differential thermal analysis

Some problems of quantitative differential thermal analysis have been studied by means of a Du Pont 900 DTA instrument. Applying the equation of heat transfer the features of a thermogram (base line and peak surface) may be interpreted in terms of heat of transition, specific heat and thermal conductivity. Satisfactory results are obtained for substances with thermal conductivities lower than 10^-3 cal/sec deg.     

A study of ochres from an Australian aboriginal bark painting using thermal methods

The potential of thermogravimetric analysis (TG) as a tool for the characterisation of ochre paint used in indigenous Australian bark paintings has been investigated. TG has been combined with differential scanning calorimetry (DSC) and mass spectrometry (MS) to identify and quantify the main inorganic and organic components present in the paints. The results obtained were supported by comparison with infrared spectra and XRD data obtained for the same specimens. The potential of thermal methods for the characterisation ochres has been demonstrated, with subtle differences between small samples being able to be identified.     

Thermal Studies on Chlorinated Atactic Polypropylene

Thermal behavior of chlorinated atactic polypropylene (CAPP) obtained by thermal chlorination of atactic polypropylene was evaluated by thermogravimetric analysis and differential thermal analysis (DTA). It was found that the initial decomposition temperature, integral procedural decomposition temperature, activation energy, and char yield increase with an increase in chlorine content. The thermal stability of CAPP was found to be lower in air than in nitrogen. This has been ascribed to thermooxidative degradation in air. DTA study shows that onset decomposition temperature, glass transition temperature, and polymer melting temperature increase with increasing degree of chlorination. The possible reasons for the phenomena are discussed.     

The influence of porosity of ammonium perchlorate (AP) on the thermomechanical and thermal properties of the AP/polyvinylchloride (PVC) composite propellants

The influence of porous ammonium perchlorate (P_OAP) on the thermomechanical and combustion behavior of solid rocket propellants based on polyvinylchloride binder has been investigated. Differential scanning calorimetry, differential thermogravimetry, dynamic mechanical thermal analysis, and scanning electronic microscopy measurements were used for thermomechanical and thermal decomposition properties assessment. The results obtained indicate that lower glass transitions of the propellants and catalytic effect of combustion are obtained with P_OAP.