The use of thermal and spectroscopic methods to study chemically modified materials

The application of thermal and spectroscopic techniques in the characterisation of chemically modified materials is illustrated with several examples: ethylene vinyl acetate (EVA) copolymers which had been hydrolysed under alkaline conditions, amosite asbestos fibres which had been reacted with alkyldimethylchlorosilanes, and a polymeric composite material which had been affected by moisture.The authors acknowledge the following for assistance in the project: Rhona MacBeth, Conservator, Courtauld Institute of Art and presently at the Boston Museum of Fine Arts, for the TMA measurements, conditioning of composite samples, and useful discussions. PL-Thermal Sciences (John Gearing for the DETA measurements on EVA). PL-Thermal Sciences (Epsom Laboratories) for the use of Dynamic Mechanical Thermal Analysis equipment.     

The complementary use of radioanalytical methods and trace analysis methods for the characterisation of environmental IAEA reference materials

The IAEA laboratories have access to both nuclear analytical methods and conventional instrumental methods for trace analysis for the characterisation of its environmental and biological reference materials. A technical concept integrating the homogeneity data, the recommended test portion mass and the uncertainty on the trace element concentrations is explored using a combination of INAA, XRF, ICP-MS, ICP-AES, and AAS. The above approach is illustrated by selected examples of reference materials currently under evaluation for their trace element content. They include some or all of the following elements Al, As, Br, Ca, Cd, Co, Cr, Cs, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, Pb, Rb, Se, Sr, Th, U, Zn in environmental biomonitor organisms (lichen, algae) and air dust filters.     

The use of inverse gas chromatography to study surface thermal oxidation of polypropylene

Thermo-oxidative effects on the surface energy of polypropylene were measured by inverse gas chromatography as a function of exposure time and temperature. Unaltered polypropylene had a surface energy of 33 mJ/m². Oxidized polypropylene, after exposure to air at temperatures of 100 °C and 110 °C, had a range of maximum surface energies from 38 to 41 mJ/m². Comparisons between FTIR carbonyl peak growth and the surface energy showed that both methods detect oxidation, though the increase in surface energy is detected before the carbonyl peak growth is noticeable. The work of adhesion predicted by the surface free energies obtained in this work between a coated calcium carbonate and polypropylene changes by 10% due to the oxidation of the polymer at 110 °C.     

The use of radioanalytical techniques to study intermediate energy,relativistic, and ultra-relativistic nuclear collisions

The use of radioanalytical techniques to study heavy ion induced nuclear reactions offers some distinct advantages over conventional physical techniques. Among these are (a) unit Z and A resultion in detecting the reaction products (b) high sensitivity for low probability events (c) lack of low energy thresholds or cutoffs in measuring reactcion product energy spectcra (d) economical use of accelerator time and (e) simple, portable experimental apparatus allowing broad survey measurements of reaction mechanisms at a variety of nuclear particle accelerators. We describe examples of these advantages from our research in nuclear chemistry.     

A thermal study of some lanthanide trifluoromethyl sulfonates

Lanthanide trifluoromethyl sulfonates, M(SO₃CF₃)₃ · 9H₂O, have been prepared and characterized by analysis, optical properties and thermal behaviour. Dehydration proceeded in two steps for the lanthanum, cerium, praseodymium and neodymium salts and in three steps for other members of the lanthanide series. Thermal decomposition to lanthanide fluoride, carbonyl fluoride and sulfur dioxide occurred at temperatures greater than 400°C. This decomposition has been shown to be a two step process.     

A radioanalytical study of the chromate conversion coating formed on aluminium

Phosphate/chromate and accelerated chromate coatings were produced on commercially available aluminium. The Cr, P and Fe components of the conversion coatings were determined by radioactive tracer technique. The tracer technique was combined with ion-exchange and film-sectioning methods to determine the chromium (III)/total chromium ratio in the accelerated chromate coating. It was found that during the acidic dissolution of the conversion coating the chromium (III)/total chromium ratio may suffer changes. The filmforming components in the metal/bath interface are supersaturated and deposited onto the aluminium. The identified components of the accelerated chromate coatings are Cr/OH/₃, Cr/OH/CrO₄ and Cr₄[Fe/CN/₆]₃ and the chromium (III)/total chromium ratio was found to be cca. 2/3.     

A thermal analysis study of the oxidation of brown coal chars

The combustion of brown coal chars, obtained at different pyrolysis temperatures, have been investigated using TG, DTG and DTA thermal analysis methods. The burning profiles and the kinetic parameters derived from TG and DTA data show that all the chars are less reactive than the parent coal. The higher temperature chars have lower overall reactivity. From the corresponding infrared spectra, the chars obtained at 800 °C and 1000 °C appear to have graphitic structures.

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Zusammenfassung Mittels TG-, DTG- und DTA-Methoden wurde die Verbrennung von unter verschiedenen Pyrolysetemperaturen erhaltenen Braunkohlenschwelkoksen untersucht. Das Verbrennungsprofil und die kinetischen Parameter, erhalten aus TG und DTG, zeigen, daß die Schwelkokse eine geringere Aktivität haben, als die ursprüngliche Braunkohle. Die Schwelkokse höherer Temperatur besitzen eine niedrigere resultierende Aktivität. Aufgrund der entsprechenden IR-Spektren besitzen die bei 800 °C und 1000 °C erhaltenen Schwelkokse eine Graphitstruktur.

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Application of emanation and surface labelling methods in the study of thermal processes

The emanation method and the method of surface labelling have been applied to study thermal processes. Using these methods, processes which are not connected with thermal effects can be analysed. In certain cases, for example in the study of poorly crystalline, or amorphous phases, these methods are even more sensitive than thermographic and X-ray techniques. The method of surface labelling is advantageous in cases when it is impossible to activate the samples by the parent isotope of the gas during the process of their preparation. This work was performed during the author's study leave to Moscow State University, Department of Radiochemistry.     

A radioanalytical technique to study the behavior of organic toxicants applied to a study of the photodegradation of 2,3,7,8-tetrachlorodibenzo-p-dioxin

A general method for tritium labeling of organic compounds by the use of thermal activation of tritium is described. It allows obtaining uniformly tritium-labeled organic compounds with high specific activity (up to 50 Ci/mmol) which permits tracing the majority of the biodegradation products of compounds studied. More than 40 compounds were labeled using this simple, rapid and inexpensive method. Separation of the biodegradation products is performed by thin layer chromatography. Quantification is performed by direct measurement of the radioactivity by liquid scintillation counting after transfer of the layer from TLC plates into scintillation vials, or by densitometry of autoradiographs. The technique is useful for a wide range of organic compounds, including ones with unknown structure, and can be applied to various in vivo and in vitro studies.     

A survey of methods for the detection of thermal oxidation in high-density polyethylene pipes

Seven methods for the detection of thermal oxidation of the inner wall surface of high-density polyethylene (HDPE) pipes are presented. The methods presented include infrared spectroscopy, polarized light microscopy, differential scanning calorimetry, scanning electron microscopy, gloss measurements and uniaxial creep tests. These tests have been developed on the basis of earlier reported data for a large number of PE pipes. The tests are compared with each other and with the internal pressurizing test with respect to reliability of results, the time taken to determine whether or not a pipe is oxidized, the experimental difficulties, costs, etc.     

Application of instrumental radioanalytical techniques to nuclear waste testing and characterization

This paper describes the validation of a multi-technique analytical methodology that uses inductively coupled plasma-mass spectrometry, α-spectrometry, and γ-spectrometry for the routine analysis of samples containing transuranic radionuclides. This methodology is capable of the determination of concentrations of both²³⁸Pu and²⁴¹Pu in the presence of²³⁸U and²⁴¹Am without the need for chemical separations. The relative merits of these three techniques were evaluated as they are applied in a nuclear waste material and spent nuclear fuel testing program by analytical (1) standards and (2) solutions prepared from the dissolution of glasses doped with²³⁷Np,²³⁹Pu, and²⁴¹Am. The uncertainty associated with technique was within ±4% for standards and ±10% for doped nuclear waste glasses. The methodology was then used to analyze three fully radioactive waste glasses.     

Hydroperoxide build-up in the thermal oxidation of polypropylene - A kinetic study

The thermal oxidation of unstabilised polypropylene (PP) was studied at 80 °C under various oxygen pressures: 0.02, 0.5 and 5.0 MPa, and, under 5.0 MPa oxygen pressure at various temperatures: 60, 80, 100 and 120 °C. Hydroperoxides were titrated using a chemical titration method and modulated DSC (taking an enthalpy of −325 kJ mol⁻¹). Starting from a previous kinetic analysis of carbonyl growth in same exposure conditions, we have tried to simulate experimental results by a model based on the classical mechanistic scheme in which initiation results from POOH (mainly bimolecular) decomposition. The model, which takes into account substrate consumption and does not rely on usual simplifying assumptions (steady state for radicals, long kinetic chains, interrelations between termination rate constants), generates kinetic curves with the same shape as experimental ones and predicts well the effect of O₂ pressure and temperature on hydroperoxide and carbonyl concentrations.     

On the use of platinized and activated titanium anodes in some electrodeposition processes

Substitution of classical lead anodes containing 6–8% of antimony, 4–6% of tin or 0.75–1.00% of silver in the zinc electrowinning and hard chromium plating bath with platinized and activated titanium anodes is discussed in this paper. Depending on the type of electrochemical processes, the main effects of this substitution are as follows: smaller electrical energy consumption, better current efficiency, increased cell capacity, smaller electrode gap, higher purity of the deposit and savings in manpower and chemicals. Ti/Pt, Ti/Pt-IrO₂, Ti/RuO₂, Ti/Pt-IrO₂-MnO₂, Ti/Pt-IrO₂-PbO₂, Ti/Pt-IrO₂-RuO₂, Ti/MnO₂, Ti/RuO₂-MnO₂ and Ti/PbO₂ coated titanium anodes have been tested in synthetic as well as in industrial electrolytes. At working current densities some activated titanium anodes showed lower overpotential than the lead anode. These electrodes have continued to perform in this way during a one-year test in synthetic and industrial electrolytes so far. No signs of corrosion of the electrodes have been noticed during the test. Received: 31 January 1997 / Accepted: 28 May 1997     

Application of various population methods to some oxygenated compounds

The charge on oxygen for a series of compounds was obtained using Mulliken population, natural population analysis (NPA), integrated projected electron population (IPP) analysis, and Bader's topological density analysis, “integrated Bader populations” (IBP). The orbital-based methods (Mulliken and NPA) predict oxygen charges of about –0.6 whereas the spatial-based methods (IPP and IBP) predict charges of about – 1.2 to – 1.3. The differences are ascribed primarily to the nuclear-centered basis sets used in the orbital methods that minimize local atomic polarization effects. Accordingly, such population analyses should be used for electronic structure considerations only with due circumspection. The IPP method as an approximation to IBP shows gross similarities; small but significant differences vary in a nonsystematic manner and IPP values must also be used with care.     

The use of thermal analysis to study thermal processing effects on polypropylene

The thermal stability of a polypropylene copolymer has been examined at several stages during the processing of the material into its final product in order to obtain information on the influence of processing steps such as grinding and thermal heating on the expected lifetime of the material. Mass loss kinetics in an inert atmosphere were able to detect differences in thermal stability, but oxidative differential scanning calorimetry studies proved to be a more sensitive techiique. A comparative study of a specially prepared series of samples revealed the importance of additives on measured thermal stability and indicated that both mechanical and thermal processing can cause reduction in measured thermal stability.     

A study of the oxidation of titanium hydride powder by measurements of its electrical resistance

The oxidation of titanium hydride powder by air oxygen and the influence of oxidation conditions on the degree of oxidation of hydride particles, specific gas content in the powder, and kinetics of its thermal decomposition were studied. The resistometry method was used to determine the effective activation energy of oxidation of titanium hydride by air oxygen. The content of the surface nonconducting phase formed by titanium oxide and oxohydride films under various oxidation conditions was estimated.     

Role of titanium oxidation states in polymerization activity of Ziegler-Natta catalyst: A density functional study

The role of titanium oxidation states in olefin polymerization activity for Ziegler-Natta (ZN) catalyst has been investigated using density functional calculations at B3LYP/LANL2DZ as well as extended LANL2DZ basis that includes diffuse and polarization functions for C, H and Cl. Using the simple [TiCl₂CH₃]ⁿ (n = +1, 0, −1) model catalyst systems, we could rationalize some of the well-known experimental facts with varying Ti oxidation states (+4, +3, +2) in the real ZN systems. Firstly, irrespective of Ti oxidation states, the activation barriers (E_act) for ethylene and syn propylene insertion in Ti-CH₃ bond are comparable in accordance with experimental and modeling studies. Secondly, it was observed that Ti(IV) catalyst has the lowest E_act which progressively increase in the order Ti(IV) < Ti(III) < Ti(II) high spin < Ti(II) low spin catalysts in line with experimental and several modeling results. The effect of solvation on olefin insertion barriers are seen more prominent in case of Ti(IV) systems compared to other oxidation states.