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Abstract
Oxidative induction time (OIT), constant temperature stability (CTS) and isothermal crystallization are examples of isothermal time-to-event (TTE) measurements obtained using differential scanning calorimetry. In TTE experiments, a test specimen is heated/cooled at a constant rate from the setup temperature to an isothermal test temperature. Once the test temperature is achieved, a clock is started and the time to the thermal event (e.g., onset to oxidation, thermal decomposition or crystallization exotherm peak) is measured. Such TTE values may be used to rank stability of the material at the test temperature. Some portion of the reaction of interest, however, takes place during the pre-isothermal period as the test specimen approaches the test temperature. This amount of reaction is unmeasured and represents a bias in the resultant TTE value. An equation has been derived and numerically integrated to estimate this bias. This approach shows that the bias is dependent upon the activation energy of the test reaction, the heating/cooling rate used and the temperature range between the melting temperature and the test temperature. For commonly used heating rates, the bias for OIT and CTS tests is small. Further, the myth that isothermal crystallization kinetics determinations required high cooling rates is dispelled with the bias of less than 0.9 min resulting from heating rates as low as 10°C min−1. Knowledge of magnitude of this bias permits the selection of experimental conditions without the expense of high heating/cooling rate apparatus or extra cost cooling accessories.
Abstract
Biodiesel is a non-toxic biodegradable fuel that consists of alkyl esters produced from renewable sources, vegetal oils and animal fats, and low molecular mass alcohols, and it is a potential substitute for petroleum-derived diesel. Depending on the raw materials used, the amount of unsaturated fatty acids can vary in the biodiesel composition. Those substances are widely susceptible to oxidation processes, yielding polymeric compounds, which are harmful to the engines. Based on such difficulty, this work aims to evaluate the antioxidant activity of cashew nut shell liquid (cardanol), as additive for cotton biodiesel. The oxidative stability was investigated by the pressure differential scanning calorimetry (PDSC) and UV/Vis spectrophotometer techniques. The evaluated samples were: as-synthesized biodiesel — Bio T0, additivated and heated biodiesel — Bio A (800 ppm L−1 of hydrogenated cardanol, 150°C for 1 h), and a heated biodiesel — Bio B (150°C, 1 h). The oxidative induction time (OIT) analyses were carried out employing the constant volume operation mode (203 psi oxygen) at isothermal temperatures of 80, 85, 90, 100°C. The high pressure OIT (HPOIT) were: 7.6, 15.7, 22.7, 64.6, 124.0 min for Bio T0; 41.5, 77.0, 98.6, 106.6, 171.9 min for Bio A and 1.7, 8.2, 14.8, 28.3, 56.3 min for Bio B. The activation energy (E) values for oxidative processes were 150.0±1.6 (Bio T0), 583.8±1.5 (Bio A) and 140.6±0.1 kJ mol−1(Bio B). For all samples, the intensities of the band around 230 nm were proportional to the inverse of E, indicating small formation of hyper conjugated compounds. As observed, cardanol has improved approximately four times the cotton biodiesel oxidative stability, even after the heating process.
ample. OOT and OIT are crucial parameters for biodiesel because of the content of unsaturated fatty acid in the biodiesel, which make it more susceptive to the oxidation process. PDSC or the Rancimat method is usually used to measure the OIT and OOT
Biofuels”/ANP, which is the Brazilian Government Institution that controls the quality of fuels commercialized in Brazil. This Resolution establishes a minimum of 6 h for the oxidation induction time (OIT) determined by this method
sortent gagnants : Item, l’an Joseph VIc et IIII, oit grant batalhe entre Melus le duc de Galle, et Antenor le duc de Sycambre; et là fut ochis Antenor, et ses gens desconfite. 8 À partir de ce point les contours entre les deux peuples commencent à se
Mechanical ventilation (MV) is a life saving method usually applied in the Intensive Care Units (ICU) for patients in a critical condition. Today it is more and more obvious that patients treated in the ICU require not only intensive physical (medical) care, but also intensive psychological support in order to avoid severe stress and to cope with the situation. They need help to understand the aim and helpfulness of the treatment, and information about the peculiar or frightening aspects of the situation, in order to promote positive processing. In this paper we summarise an approach, called psychological support based on positive suggestions (PSBPS), where patients on MV were supported with suggestions based on the principles of hypnotic communication. We present the foci of the phases of (1) initiation, (2) maintenance and (3) weaning off from MV from a psychological point of view, along with some verbatim suggestions we used with patients during these three completely different phases of MV. The main results of a randomised prospective study testing the effectiveness of PSBPS are presented briefly.
154.2 517.9 Oxidative induction time (OIT) indicated that the as extracted oils have higher stability than the biodiesel comes from them ( Table 5 ). This occurs
final /°C b T peak DTG/°C c Δ m /% d OT onset /°C e OIT onset /min at 110 °C f
Keune, M. (1998): Youth Unemployment in Hungary and Poland. Available at: http://www.oit.org/wcmsp5/groups/public/ed_emp/documents/publication/wcms_120235.pdf Keune M
oils showed a complex multistep decomposition pattern with the first step that exhibited a quite different profile among samples [ 9 ]. In the last year two DSC methods have aroused high interest: high pressure oxidation induction time (OIT
