查看更多>>摘要：A reinterpreted analysis method of the Ozawa model is presented for the non-isothermal kinetics of the nucleation and growth processes of polymer spherulites. The Ozawa model is based on the Avrami model which is valid for an isotropic crystallization with randomly dispersed nuclei and with growth rate dependent only on temperature. The crystallinity phi for the non-isothermal kinetics is expressed using a term of the form (beta(T)/beta(i))(n) with the applied scan rates of cooling beta(i) (i = 1 N) and a function beta(T) dependent only on the temperature T. The reinterpretation involves writing this term as (beta(half)(T)/beta(i))(n)ln(2), where beta(half)(T) is regarded as an inverse function of T-half(beta), i.e., the temperature T-half of phi = 1/2 at a fixed scan rate beta. The temperature-dependent beta(half)(T) is given by the fitting curve of T-half measured at the various scan rates beta(i). The original Ozawa plot shows phi as a function of a finite number of data points beta(i) (i = 1 N) at a certain fixed temperature T. The reinterpreted Ozawa plot is a continuous curve of phi as a function of the T-dependent beta(half)(T) at a fixed scan rate beta, and can be utilized for a more reliable determination of the Ozawa index n. Moreover, beta(half) (T) can be replaced by beta(peak)(T), which is an inverse function of the peak temperature T-peak at a fixed scan rate beta. The applicability of the reinterpreted Ozawa model was examined experimentally for the spherulitic crystallization of poly(vinylidene fluoride) and by numerical calculations.
查看更多>>摘要：CuO/ZIF-8 hybrid structure was obtained by adding the PVP-modified foliaceous CuO microstructures during the preparation of ZIF-8 polygon particles as a promising candidate for promoting the thermolysis process of NC. Thermoanalysis and pyrolysis kinetics based on the DSC and TG/DTG data revealed that the CuO/ZIF-8-NC decomposition had a weightlessness rate of 77.81%, heat release of 2882.5 J.g(-1), the exothermic peak temperature of 471.25 K, and activation energy of 172.2 +/- 16.0 kJ.mol(-1), indicating that CuO/ZIF-8 has better catalytic activity than CuO and ZIF-8. The reconstructed nth-order kinetic models for NC/catalysis complexes were obtained using a modified fitting algorithm based on the results of isoconversional kinetic analysis, indicating that CuO/ZIF-8, CuO, and ZIF-8 had different catalytic effects on the thermolysis pathways of NC. This study suggests that CuO/ZIF-8 composite may have prospective application as a high potential and unique catalyst for accelerating NC pyrolysis.
查看更多>>摘要：This work investigates the degradation kinetics and the pyrolysis behavior of Poly (vinyl chloride) (PVC) and its mixture with ZnO using thermogravimetric analysis under an inert atmosphere. The investigation was carried out due to the increased interest in the co-thermal treatment of the hazardous waste electric arc furnace dust (EAFD) which contains significant quantities of ZnO with PVC. The degradation of pure PVC was characterized by three main decomposition stages: PVC de-hydrochlorination (two overlapped stages) and subsequent polyene thermal cracking, while ZnO-PVC mixture (ZPVC) demonstrated four decomposition/volatilization stages. The Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Friedman models were utilized for the extraction of the kinetic parameters. The average activation energy for pure PVC de-hydrochlorination was calculated to be 119.8 +/- 12.4 kJ/mol, which changed to 110.6 +/- 11.2 kJ/mol when a stoichiometric quantity of ZnO was added to it. The suggested mechanism for the ZPVC de-hydrochlorination starts by chlorine abstraction on ZnO at temperatures well-below 272 degrees C with an activation energy comparable to that of pure PVC de-hydrochlorination (115.8 kJ/mol). The chlorination of ZnO then yields zinc oxy/hydroxide chloride phases (Zn2OCl2 center dot 2H(2)O/beta-Zn (OH)Cl) by the reaction between ZnCl2, ZnO and emitted H2O. These phases then decompose at approximately 222 degrees C into ZnCl2, ZnO, and H2O with a relatively low energy barrier of 102.2 kJ/mol. Formed ZnCl2 then lowers the activation energy for the polyene thermal cracking of PVC from 218.4 +/- 17.7 (PVC) to 87.3 +/- 9.7 kJ/mol (ZPVC) due to the physical contribution of volatilization to the overall mass loss.
查看更多>>摘要：Physical stability as well as isothermal and non-isothermal cold-crystallization of quench-cooled drug carbamazepine (CBZ) was studied using powder X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FT-IR). Three phase transitions on heating were reported: glass softening (similar to 329 K), cold-crystallization (similar to 389 K) and melting (similar to 463 K). XRD results and evaluation of DSC data using Adam-Gibbs model extended to the glassy state revealed, that the amorphous sample of CBZ remains physically stable for 8 h at room temperature (i.e. about 30 K below glass transition temperature). Isothermal XRD measurements showed that amorphous CBZ is prone to rapid nucleation even about 50 K below the glass transition, but crystal growth is considerably slowed down in such conditions. Fragility parameter m was calculated and quench-cooled CBZ was identified as moderately fragile glass. FT-IR measurements coupled with moving-window two-dimensional correlation spectroscopy proved that changes in vibrational dynamics accompanied all phase transitions. Considerable strengthening of hydrogen bonding was observed during cold crystallization.
Mert, Hatice HandeKekevi, BurcuMert, Emine HilalMert, Mehmet Selcuk...
9页
查看更多>>摘要：beta-myrcene based foam / n-tetradecane composite phase change materials (PCMs) were prepared for cold thermal energy storage systems. beta-myrcene based foams were synthesized as PCM support material, while n-tetradecane was selected as organic phase change cold storage material due to its appropriate phase change temperature and high heat storage capacity for supplying temperature requirements of the food refrigeration, storage and transportation systems. The polymer foams were prepared in presence of different nanoclay particles by using beta-myrcene as bio-based monomer and ethylene glycol dimethacrylate as crosslinker. The form-stable composite PCMs were obtained via impregnation of n-tetradecane into the porous frameworks in one-step. Based on the results, the highest latent heat was measured as 82.14 J/g for form-stable composite PCM, which has framework with higher cavity diameters besides to higher surface area, while the melting and crystallization temperatures determined as 4.37 degrees C and 1.73 degrees C.
查看更多>>摘要：Forward and reverse transformation temperatures of shape memory alloys are significantly affected by their thermal and processing history. Controlling these temperatures is of great importance when designing materials displaying shape memory effect. In this direction, the present work shows the influence of particle size and heat treatments on thermodynamic properties of a gas-atomized Cu-Al-Ni-Mn shape memory alloy. Commercially pure elements were used in the gas atomization process and differential scanning calorimetry was used to measure As, Af (austenitic start and final transformation temperatures), Ms, Mf (martensitic start and final transformation temperatures), transformation temperature hysteresis and chemical/non-chemical energies involved in the martensitic-austenitic transformation. The influence of quenched-in defects and annealing was also studied. Results show a correlation between particle size and transformation energies, which can be attributed to atomic ordering in the austenitic phase upon cooling, after the solidification process. This is further confirmed by the increase in the reverse and forward transformation temperatures after thermal cycling and annealing.
查看更多>>摘要：Anhydrous CrCl3 center dot epsilon H2O exhibited, under helium stream (6 L h-1, 5 K min(-1)), several transformations between room temperature and (1175 +/- 2) K. The compound loses the physisorbed water molecules between (300 +/- 2) K and (400 +/- 2) K and the hydration degree (e) was determined by thermogravimetry to be 0.14. However, using mass spectrometry, we were able to detect the transformation of CrCl3(cr) into CrCl3(g) at T = (776.00 +/- 0.01) K. In this context, Delta H-sub (776 K) value was estimated using some literature data and the Clausius-Clapeyron relation to be (245.20 +/- 0.01) kJ mol(-1). This value was corrected at (298.15 +/- 0.01) K and (0.105 +/- 0.01) MPa, resulting in (254.93 +/- 0.01) kJ mol(-1). Our thermodynamic calculations revealed that CrCl3(g) is decomposed into CrCl2(cr) and Cl-2(g) within two distinct temperature ranges: (776 +/- 2) to (860 +/- 2) K and (950 +/- 2) K to (1050 +/- 2) K. Between (860 +/- 2) and (950 +/- 2) K, the evaporation of CrCl2(cr) in the form of CrCl4(g) takes place due to the presence of Cl-2(g). However, at higher temperatures (T > 1050 K), residual CrCl2(cr) is evaporated and a final mass loss of 94 % is obtained.
查看更多>>摘要：Thermal decomposition of hydrous volcanic glass occurs through the release of different water species under overlapping processes over wide temperature range. Its investigation is of practical interest since it constitutes integral processing part towards its valorization as source for the production of high-quality porous material for various applications. The study presents investigation of thermal decomposition of hydrous rhyolite through the non-isothermal solid-state kinetics approach. Rhyolite decomposition occurs through three partially overlapping processes, where loosely held and chemically bound water, as well as hydroxyl release at different temperature regions and through different mechanisms. The separation of overlapped thermal curves was done through peak deconvolution method using Frazier-Suzuki equation. Subsequently, the isoconversional (model-free) Friedman, generalized master-plots and Kissinger methods were applied for the determination of apparent activation energy (E-a), reaction model (f(a)) and pre-exponential factor (A) for each individual reaction step considered. Using the kinetic triplet values of each process, the kinetic rate equations were combined allowing precise simulation of the dehydration and dihydroxylation processes. A comparison of model results with thermogravimetric (TG) data, as well as data from the literature, showed the satisfactory accuracy of the model in the simulation of the process and the successful prediction of each water type fraction, during the process evolution. Spectroscopy techniques in UV-VIS and NIR (near infra-red) spectral ranges were applied to raw rhyolite and sample with different water content allowed calculation of color coordinates and its correlation with dehydration and dehydroxylation degrees, and also identification of water species.
查看更多>>摘要：To boost the fire safety of epoxy resin (EP) at lower loading, FeCu-montmorillonite (FeCu-MMT) is synthesized, which is modified by hexadecyl trimethyl ammonium bromide (CTAB) and Fe polycations for preparing multiply modified FeCu-MMT (mm-FeCu-MMT). EP/mm-FeCu-MMT and EP/mm-FeCu-MMT/DOPO nanocomposites are prepared by incorporating mm-FeCu-MMT and 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO) into EP matrix. The XRD results indicate that EP nanocomposites are intercalated-exfoliated structure. EP/4wt% DOPO composites pass UL-94 V-1 level and EP/1 wt% mm-FeCu-MMT/3 wt% DOPO nanocomposites pass V-0 level. The cone calorimeter data further confirmed that mm-FeCu-MMT can obviously improving flame retardancy of EP nanocomposites due to the synergistic effect of mm-FeCu-MMT and DOPO. Importantly, the mechanical performances of EP nanocomposites have not been damaged based on the synergism between mmFeCu-MMT and DOPO.
NSTL
Elsevier