In this study, the influence of CO.sub.2 on the rheology of silica poor and K-rich melts from highly explosive eruptions from the Colli Albani Volcanic District (Italy) (CAVD) is measured for the ...first time. The investigated melts range from foidite to tephri-phonolite to tephrite from the CAVD to a phonolite from the Vesuvius (Italy) with CO.sub.2 concentrations up to 0.50 wt%. Viscosity and calorimetric measurements are performed in the glass transition range T.sub.g between 600 and 780 °C. Although nominally anhydrous, the investigated melts contain H.sub.2O concentrations up to 0.23 wt%. The data exhibit a decrease in viscosity of approx. 10.sup.0.40 Pa s for the phonolitic composition with ~ 0.07 wt% CO.sub.2 and a T.sub.g reduced by approx. 14 °C. For the tephritic composition, T.sub.g is approx. 5 °C lower and has a viscosity reduced by 10.sup.0.25 Pa s for the sample containing ~ 0.5 wt% CO.sub.2. Calorimetric measurements of the tephri-phonolite show lowered onset of T.sub.g by approx. 6 °C for the melt with ~ 0.11 wt% CO.sub.2 and T.sub.g of the foidite appears not to be influenced by a CO.sub.2 concentration of ~ 0.37 wt% CO.sub.2. However, these tephri-phonolitic and foiditic melts foamed during calorimetric measurements preventing a reliable measurement. It would appear that most of this overall drop in viscosity is caused by the small amounts of H.sub.2O in the melts with CO.sub.2 slightly reducing the viscosity or having no effect on viscosity. Additionally, it is shown that the reduction in viscosity decreases with an increasing degree of the depolymerisation for the investigated melts. Consequently, the explosive style of the CAVD eruptions is mainly caused by crystals and bubbles which form and rise during magma storage and ascent which increases the magma viscosity whereas the CO.sub.2 in the melt slightly reduces the viscosity.
Thermal stability assessment of 4,4'-azo-bis Zhu, Jiaping; Jin, Shaohua; Cheng, Bin ...
Journal of thermal analysis and calorimetry,
04/2018, Letnik:
132, Številka:
1
Journal Article
Recenzirano
The thermal decomposition behaviors of 4,4'-azo-bis(1,2,4-triazolone) (ZTO) and its salts were investigated for the first time by using accelerating rate calorimetry. Based on the experimental ...results, the kinetic parameters of exothermic reaction of ZTO and its salts were calculated. The thermal decomposition parameters, including the initial decomposition temperature, the adiabatic temperature rise rate, were obtained from the thermal inertia factor. The adiabatic experiment revealed that ZTO and KZTO·H.sub.2O both had a relatively high initial exothermic decomposition temperature at 230.6 and 235.6 °C, respectively. The maximum self-heating rate of exothermic process of ZTO was 105.9 °C min.sup.-1 (at 248.7 °C), which meant that ZTO decomposed very fast. In addition, the reaction order, apparent activated energy (E.sub.a), and pre-exponential factor (A) were also calculated.
Heat capacity of single-crystal samples of five chalcogenides (LiInS.sub.2, LiInSe.sub.2, LiGaS.sub.2, LiGaSe.sub.2, and LiGaTe.sub.2) was measured with DSC in a temperature range from 180 to 460 K. ...The data for LiInS.sub.2 and LiInSe.sub.2 were compared with the literature data and shown to agree with the results of adiabatic calorimetry (Gmelin and Hönle in Thermochimica Acta 269: 575-590, 1995 (See CR7)) better than with other DSC data (Kühn et al. in Cryst Res Technol 22: 265-269, 1987 (See CR5)). Besides, the high-temperature fitting polynomial for C.sub.P(T) published about 30 years ago for LiInS.sub.2 is wrong. LiGaS.sub.2, LiGaSe.sub.2, and LiGaTe.sub.2 were measured for the first time.
Study of the glass stability for amorphous Se.sub.60Ge.sub.15X.sub.25 (X = Sn, As) compositions has been performed by determination and evaluation of the widely used and more recently glass stability ...(GS) criteria. Calorimetric differential thermal analysis (DTA) measurements have been used under non-isothermal conditions at different heating rates. GS criteria have been determined based on the interrelationship of the estimated characteristic temperatures from DTA curves. All GS criteria are found to be heating rate and composition dependence. Their values and behaviors indicated that the most stable composition against devitrification with As addition. The calculated criteria values based on the onset crystallization temperature T.sub.x and the maximum (peak) crystallization temperature T.sub.c exhibit a similar behavior as a function of heating rate and composition, whereas both of them have incompatible values. The relative change parameter of GS criteria as well as their heating rate and composition dependence reflects that the more suitable and sensitive GS criterion, for the studied compositions, is Saad and Poulain.sup.'s criterion K.sub.s and the less one is Lu and Liu's criterion K.sub.LL for two studied compositions.
The thermodynamic properties of the fabrication of NiTiO.sub.3 material in different reaction times are reported. The design of this material is accessible through a new efficient sol-gel methods, ...utilizing Ni(Ac).sub.2·4H.sub.2O and Ti(O.sup.iPr).sub.4 as starting materials for the formation of NiTiO.sub.3 final product through thermal decomposition. The thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques were used to analyze the reaction of Ni(Ac).sub.2·4H.sub.2O and Ti(O.sup.iPr).sub.4, which produces precursor materials at 0.5, 1, 2, 24, 48 and 72 h of reaction times, as well as the thermal stability of these precursors and the final product. The DSC data show an exothermic phenomenon of releasing large amount of energy of -1393 J/g at T.sub.Peak 655 K due to the first event of decomposition started at T.sub.Onset 607 K and finished at T.sub.Endset 663 K for the precursor materials obtained at 0.5 h of reaction, showing the presence of starting materials in this precursor. A similar exothermic behavior was observed in the sample of 1 h of reaction time and was vanished in the materials obtained at 2-72 h of reaction, indicating the influence of the time on the completion of reaction and formation of NiTiO.sub.3 crystalline phase as final product of thermal decomposition. In addition, using the information obtained from the TG/DSC, XRD and FTIR analyses, the optimum temperature for the thermal decomposition of the precursor materials to NiTiO.sub.3 with fairly high crystallinity was also determined and discussed.
Tungsten (W) doping can decrease the phase transition temperature of VO.sub.2, but underlining reasons are not clear. In this study, differential scanning calorimetry was employed to investigate the ...kinetics of the solid-solid transition in hydrothermal-synthesized W (X = 0.50, 1.09, 2.58 and 3.81 %)-doped VO.sub.2 nanoparticles. We firstly revealed the W-doping mechanism by combining the classical nucleation kinetics model with isoconversional kinetic analysis and applied them on the solid-solid transition taking place in doping. The experimentally observed large lag in the cooling stage and asymmetry effects of the decreasing temperature on insulator-metal transition and metal-insulator transition can be rationally explained. In the heating stage, W doping decreases free energy barrier (ΔG*) for homogenous nucleation and reduces geometrical factor (f(Î)) and both factors promote the transition and thus lower the phase transition temperature quickly. However, in cooling stage, the free energy barrier (ΔGhet*) for heterogeneous nucleation was much larger than that of heating stage due to lacking of proper nucleation sites. The effect of decreasing geometrical factor was accompanied with the effect of increasing free energy barrier for homogenous nucleation by doping W. Such a competition mechanism slows down the trend of reducing temperature. It is important to unravel interaction mechanisms of doped W on different VO.sub.2 phases, which is helpful to further tailor kinetic properties of VO.sub.2 phase transition.
Different proportions of polyamidoamine (PAMAM) dendrimer were blended with poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) resin in chloroform for film casting. Differential scanning calorimetry and ...scanning electron microscopy were employed to characterize the PHBV/PAMAM composite films upon stretching and tangential breaking. The results indicated that with the addition of PAMAM dendrimer, the glass transition temperature of the PHBV/PAMAM composite films became more distinct, indicating that the blends had a greater toughness than pure PHBV. The calculated crystallinity values indicated that the crystallinity of the PHBV/ PAMAM blends was lower than that of PHBV (0.09-56.18 % vs. 73.18 %, respectively). Moreover, the mechanical performance tests indicated that the addition of PAMAM dendrimer considerably increased the tangential breaking strength of PHBV from 24.08 kN/m to as high as 62.03 kN/m, whereas the tensile strength remained basically unchanged. The optimal toughening effect was observed with a PAMAM dendrimer content of 3.0 phr.
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