Thermal lifetime of cellulose insulation material evaluated by an activation energy based method

A rapid method, based on a logarithmic degradation model of insulation material, is proposed to reduce the test duration in lifetime assessment of cellulose paper insulating materials. This method proposes the determination of the activation energy from a non-isothermal measurement made by differential scanning calorimetry or another thermal analysis technique and an aging test at a single elevated temperature. The use of the onset temperature of the exothermal peak at ca. 300 °C is proposed for evaluation of the activation energy of degradation. For comparison, the thermal aging of Kraft cellulose paper for power transformer insulation was performed according to the general standard IEC 60216-1/2001 at three different temperatures: 155, 135 and 115 °C, and subsequently, the lifetimes at different service temperatures were estimated. The experimental data proved to have good agreement between the applied methods, the differences being <10 % in terms of the estimated lifetime across the range of service temperatures. The novel proposed method is effective in terms of both energy and manpower costs as compared to the current method: a factor of around 10 in the case of reducing the aging time, a factor of 3 for the time needed for measurements, and a factor of 10 for the reduction of power intake.     

Chemiluminescence study on the oxidation of several polyolefins—I. Thermal-induced degradation of additive-free polyolefins

Chemiluminescence (CL) has been applied to evaluate the oxidation susceptibility of various polyolefins: low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE) and isotactic polypropylene (i-PP). The intensity of CL emission in inert atmosphere could be related to the previous oxidation level. The thermal stability at 170 °C of the hydroperoxides in LDPE seems to be lower than that in LLDPE or HDPE. The kinetic parameters of the oxidation at 170 °C in oxygen, calculated from CL data, suggest the following stability order: HDPE > LLDPE > LDPEi-PP. The intensity of CL emission was related to the CH₃ content as evaluated by Fourier transform infra-red spectroscopy.     

RTL Investigation on the Radiochemical Oxidation of Polyolefins

High energy radiation causes deep modification of exposed polymers. In the irradiated polymers, the main macroscopic process is the formation of free radicals. The “cooled” electron distribution at the temperature of liquid nitrogen will develop the existence of various electron gaps with certain depths by smooth heating up to room temperature. In this paper, low density polyethylene, high density polyethylene and polypropylene were subjected to the action of gamma rays for causing structural modifications. The glow curves of quantum emission were recorded by slow heating from 106 to 286 K. The characteristic shoulders were obtained, which were ascribed to various electron traps consisting of unsaturation or carbonyl groups. For depicting the influence of molecular structures, the influence of CH₃ number/100 carbon atoms on the intensity of radiothermoluminescence (RTL) signal was studied on three types of LDPEs. A sharp decrease of maximum RTL intensity at advanced branching was pointed out. A mechanism of RTL emission is based on the present measurements.     

Copper diffusion in cable-insulating materials by chemiluminescence and DSC techniques

Journal of Thermal Analysis and Calorimetry - Chemiluminescence (CL) and differential scanning calorimetry (DSC) were applied for proving the copper ion migration processes occurring within the...     

Irradiation of Polyethylene in Presence of Several Additives as Studied by Chemiluminescence

Abstract

The protecting effect against radiation induced oxidation of poly-ethylene provided by several additives, namely pyrene, Irganox 1222 and Irganox 1010 has been investigated by mean of FTIR spectroscopy and chemiluminescence (CL) technique. Pyrene appears to be more effective and more stable to irradiation than phenolic antioxidants. Thus, about half of initial pyrene seems to remain unchanged after an exposure of the material to γ⁶⁰Co rays at 240 kGy (dose rate 1 kGy/h) in presence of air. Under the same conditions, about 90% of initial Irganox 1010 seems to be consumed as indicate a comparison of induction oxidation times of initial and irradiated material. The stabilizing effect of the residues resulted by pyrolysis at 850°C in inert atmosphere of several polymers, such as polyacrylonitrile, polyvinylchloride and methyl cellulose is discussed as well.     

Thermal oxidation of irradiated magnetic fluids and their component surfactants and dispersing oils

Magnetic fluid applications require stability under demanding conditions. Complete magnetic fluids and their component surfactants and dispersing oils were irradiated. Their subsequent thermal oxidation was characterized by chemiluminescence and DSC. Except for polyisobutylsuccinic anhydride, irradiation sensitized the components toward oxidation. The components were ranked by stability. Complete fluids were more stable than would be predicted from their components suggesting that they may be used for nuclear applications.

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Correlations between radiothermoluminescence and the catalytic properties of some active aluminas. A catalysis model

The present paper reports correlations between data obtained by the radiothermoluminescence (RTL) method and the catalytic activity of active aluminas. The correlations between the intensity of RTL signals, glow peak temperatures and activation energy obtained by RTL and the data referring to the history, catalytic activity and activation energy of the catalyzed reaction, require the use of RTL as a supplementary method in the characterization of catalysts. The results underline the role of structural defects in the catalyst (or support) on the catalysis as illustrated by the present model.     

Potentiometric investigation of the effect of the pH on the ionic transfer of some amino acids at the interface between two immiscible electrolyte solutions

The effect of the pH on the ionic transfer of glycine and beta-alanine at the interface between two immiscible electrolyte solutions (ITIES) was investigated by a simple potentiometric method. Upon addition of small amounts of solution containing the investigated amino acids, a variation of the potential drop across the interface was recorded, which was found to be pH-dependent. This behavior was explained in terms of a preferential orientation of the amino acid molecules at the ITIES, induced by the different lipoficility of the functional groups. The results enabled the measurement of this voltage variation to be used as the basis for a simple and rapid method for determining the isoelectric point of the investigated compounds. The agreement between the pH(i) values thus estimated and those reported in the literature suggests the possibility of using the method for the interpretation of processes occurring at the level of biological membranes.