Due to the presence of efflorescences and improper microclimate conditions for conservation, pink-pigmented areas were reported in two historic monuments in Northern and Central part of Romania. The ...aims of the present study were to find the nature of pink pigments observed on the pictorial layer, original and infilling mortar, to investigate the presence of carotenoids both on mural paintings and in the isolated halophilic bacterial strains and to preliminary characterize and identify the producing strains. Their role in the aesthetical biodeterioration of historic monuments was also pointed out. Obtained Raman spectra of the pink pigments extracted both from the isolated bacterial cultures (molecularly identified as mostly related to Halobacillus hunanensis and Halobacillus naozhouensis) and from the mural painting samples contain diagnostic bands of carotenoids. These results were confirmed by FTIR spectroscopy. The strong Raman signal of bacterial carotenoids detected on mural painting indicated their potential use as biomarker molecules in the evaluation of contamination and state of conservation of mural paintings and lithic monuments. Our results contribute to opening a new direction in cultural heritage restoration to assess the conservation status on the basis of interdisciplinary research, starting with spectroscopic methods (Raman, FTIR) and confirmed by microbiological analysis.
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.
This paper presents the investigation work on different polymeric materials used as insulation materials of conductors in a multicore instrumentation cable. Among differently colored materials, only ...the white one presented cracks after a few years of use. Isothermal and non-isothermal DSC measurements were performed on initial (non-used) and aged (in service used or laboratory aged) materials as well as on raw materials in order to characterize their stability and the ageing state after storage, use in service or laboratory ageing. As shown by the oxidation induction time values, a pronounced antioxidant loss occurred for all materials during storage or service; plus a strong effect of the ambient light on stability was observed for the white insulation material. Around 3% of filler, consisting mainly of TiO
2 particles (as revealed by SEM-XRF elemental analysis), was found in the white material. The higher degradability of the white material can be related to both the photocatalytic effect of the TiO
2 particles and rapid loss of stabilizers.
A chemiluminescence study on thermal degradation of some polyethylenes (LDPE, LLDPE, HDPE, UHMWPE) on seven metal trays in the presence of triazines as stabilisers was carried out. The kinetic ...effects of metals (Al, Zn, Ti, Mo, Mn, Fe and Cu) were assessed at 200 °C by the calculation of oxidation induction period, half-oxidation time, maximum oxidation time and rate in the propagation stage. Different sequences of catalytic effect provided by the studied metals in LDPE and HDPE are reported. A characteristic copper index for each metal was also calculated. Some considerations on the thermal stability of polyethylenes in intimate contact with metal surfaces are presented.
The thermal degradation of some polyethylenes (one type of high density PE and two of low-density) was studied by isothermal chemiluminescence. Each polymer was stabilized by one of four phenolic ...additives:
p-
t-butylphenol (considered as reference), 2,4,6-tri-
t-butylphenol,
p-
t-butylcalix4arene, and
p-
t-butylcalix6arene. Six kinetic parameters of thermal oxidation (induction period, maximum oxidation rate, half-period of ageing, maximum CL intensity, maximum degradation time, and activation energy) along with relative activity and stability were calculated. Protection efficiency of additives was evaluated by relative activity and relative stability indexes. Considerations of a stabilization mechanism involving calixarenes are presented.
Polyacrylonitrile (PAN) and some copolymers of acrylonitrile with divinylbenzene (AN-DVB) were investigated by the characterization of their thermal and radiation stabilities. The contribution of DVB ...to the thermal stability of PAN by the modification in the amount of unsaturated hydrocarbon between 6 and 20% was revealed by the evaluation of oxidation induction periods and required activation energies. The exposure of these materials to the action of γ-radiation points out the higher stability of copolymers (AN-DVB) in comparison to the relative stability of PAN.
RTL study of structural modifications in irradiated PTFE Jipa, S.; Zaharescu, T.; Setnescu, R. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
12/2007, Letnik:
265, Številka:
1
Journal Article
Recenzirano
The exposure of polytetrafluorethylene to the action of high energy radiation is examined by radiation thermoluminescence. The radiolysis causes the formation of various traps, which correspond to ...four maxima in the glow curve of PTFE. The activation energy of molecular motion is discussed. The modification of emission intensity at a large dose range is evaluated for three glow maxima that appear at 139, 173 and 205
K. The RTL emission is correlated with different types of oxygenated products that are formed during the radiolysis of PTFE. Changes in other properties like molecular mass, density, crystallinity are investigated for emphasizing the radiodegradation in this matrix. The mechanism of RTL emission is explained by the recombination of thermalized electrons with positive intermediates.
The stabilization effect of various carbon materials:
C60fullerene, three adducts with levopimaric acid, two sorts of carbon black and nanocarbon on HDPE, LDPE and LLDPE have been studied by ...chemiluminescence at 180, 190 and 200 °C. Kinetic parameters: oxidation induction time, rate of oxidation and activation energy were determined. On the basis of these results some considerations on oxidation prevention mechanism are revealed.
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